Chetna Mohabeer

Luis Reyès

Lokmane Abdelouahed

Stéphane Marcotte

Bechara Taouk
email: bechara.taouk@insa-rouen.fr

Luis Reyes

Investigating catalytic de-oxygenation of cellulose, xylan and lignin bio-oils using HZSM-5 and Fe-HZSM-5

Keywords: Pyrolysis, woody biomass components, catalytic de-oxygenation, de-oxygenation schemes 1

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Introduction

The aromatic compounds benzene, toluene and xylenes are often grouped together as BTX [START_REF]Energy and Environmental Profile of the U[END_REF]. They are bulk chemicals which are vital for the petrochemical industry, namely for transportation fuels.

However, these aromatics have a negative environmental impact given that they are produced from fossil resources in an energy intensive process. It is thus important to find sustainable options to produce BTX. One such option is using biomass as feedstock in a process such as catalytic pyrolysis, using catalysts to de-oxygenate the produced oil. It should be noted that biomass comprises of three major components: cellulose, hemicellulose and lignin. Investigating the catalytic pyrolysis of the latter components can help in better comprehending how this process works.

Zhou et al. [START_REF] Zhou | Catalytic pyrolysis of cellulose with zeolites[END_REF] have studied the catalytic pyrolysis of cellulose with different zeolites in a TG-FTIR setup from 30 to 800 °C under a 30 mL/min N2 flow. They have found that HZSM-5 was the most efficient catalyst in terms of de-oxygenation degree as it improved the conversion of oxygenated families like esters, aldehydes and acids into aromatics. About the same observations were made by Lei et al. [START_REF] Lei | Catalytic Fast Pyrolysis of Cellulose by Integrating Dispersed Nickel Catalyst with HZSM-5 Zeolite[END_REF], who used a Py-GC/MS setup with temperatures ranging from 150 to 700 °C. Guo et al. [START_REF] Guo | Catalytic pyrolysis of xylan-based hemicellulose over zeolites[END_REF] investigated the catalytic pyrolysis of xylan-based hemicellulose in a TG-FTIR setup from 30 to 350 °C under 30 mL/min N2 using different zeolites (HZSM-5, H-β and USY). They found that all of the zeolites had a significant effect on the de-oxygenation of xylan, and that HZSM-5, along with having good de-oxygenation efficiency, suppressed the formation of char residues. Zhu et al. [START_REF] Zhu | Fast and catalytic pyrolysis of xylan: Effects of temperature and M/HZSM-5 (M = Fe, Zn) catalysts on pyrolytic products[END_REF], on their part, performed experiments in a pyroprobe with temperatures between 350 and 900 °C. They found that metal-modified HZSM-5 (Fe and Zn) was even more efficient than the parent zeolite concerning de-oxygenation activity. Lignin de-oxygenation was examined by Zhan et al. [START_REF] Zhan | Py-GC/MS study of lignin pyrolysis and effect of catalysts on product distribution[END_REF] in a µ-pyrolysis reactor using an array of catalysts (HZSM-5, MCM-41, TiO2, ZrO2 and Mg(Al)O) at 400, 500 and 600 °C using He as carrier gas. They found that HZSM-5 was the most efficient catalyst in forming aromatics; the highest yield obtained was at 600°C, the highest temperature they used. Now, concerning the pyrolytic conversion schemes of chemical families involved in catalytic pyrolysis, several studies tackling one or arbitrary compounds have indeed been reported in literature [START_REF] Danuthai | Conversion of methylesters to hydrocarbons over an H-ZSM5 zeolite catalyst[END_REF]- [START_REF] Zhang | Catalytic Deoxygenation of Bio-Oil Model Compounds over Acid-Base Bifunctional Catalysts[END_REF].

To report on some of the relevant data previously published in literature, Gayubo et al. [START_REF] Gayubo | Transformation of Oxygenate Components of Biomass Pyrolysis Oil on a HZSM-5 Zeolite. I. Alcohols and Phenols[END_REF] investigated on the pyrolytic conversion of alcohols and phenols using HZSM-5. They found that the dehydration process gave rise to propene from alcohols, which later produced hydrocarbons. They also noted a very low conversion rate of phenols. Guaiacols were found to form aromatics by decarboxylation, along with a carbonaceous material deposited within the catalyst matrix. In another study [START_REF] Gayubo | Transformation of Oxygenate Components of Biomass Pyrolysis Oil on a HZSM-5 Zeolite. II. Aldehydes, Ketones, and Acids[END_REF], it was observed that aldehydes converted to C6+ olefins, albeit with a low conversion rate; ketones produced alkenes via dehydration followed by decarboxylation and decarbonylation; acids and esters, having the same reactivities, gave rise to ketones, which later decomposed as mentioned above. Finally, they found that levoglucosan formed furans, which degraded further to give aromatics, olefins, CO, CO2, water and coke.

However, to the best of our knowledge, no study undertook detailed analysis of the pyrolytic products of the three woody biomass components in a single setup, under the same operating conditions. This study aims to shed some light on the mechanisms of BTX production from the catalytic pyrolysis of cellulose, hemicellulose and lignin so as to better understand their provenance. This can help in optimising their production from the catalytic pyrolysis of biomass. This study is a direct follow-up of previous research led by our group on the same raw materials [START_REF] Mohabeer | Comparative analysis of pyrolytic liquid products of beech wood, flax shives and woody biomass components[END_REF].

2.

Experimental section

Materials used and elemental analyses

The bio-polymers were utilised in their pure form: microcrystalline cellulose having a density of 1.5

g/cm 3 at 20 °C was purchased from Merck (Ref. 1.02330.0500-500G) while xylan, which was used as proxy for hemicellulose as the latter is not commercialised in its original form, was of corn stover origin. Xylan was bought from Tokyo Chemical Company Co. Ltd. (Ref. X0078-100G). Finally, the lignin used was "alkali lignin" or "Kraft lignin" obtained from Sigma-Aldrich (Ref. 471003-100G). This type of lignin might not completely represent the behaviour of native lignin in biomass, but, it was chosen based on its frequent use in literature [START_REF] Choi | Fast pyrolysis of Kraft lignin-Vapor cracking over various fixed-bed catalysts[END_REF]- [START_REF] Zhou | A novel method for kinetics analysis of pyrolysis of hemicellulose, cellulose, and lignin in TGA and macro-TGA[END_REF] so as to acquire some information about the products of pyrolysis and de-oxygenation of native lignin. Tables 1 and2 show the ultimate and the proximate analyses of all raw materials used in this study. The total C, H and N were measured on samples using a CHN elemental analyser Flash 2000 (Thermofisher Scientific) while the proximate analysis was conducted by using TGA experiments, based on Garcia et al. [START_REF] García | Catalytic cracking of bio-oils improved by the formation of mesopores by means of Y zeolite desilication[END_REF]. A detailed mineral analysis was conducted on the biomass components samples used for this study. The complete results can be found in the supplementary materials (Table A-1). The catalyst [hydrophobic HZSM-5 catalyst in its proton form (H + )] was acquired from ACS materials in the form of pellets. The SiO2/Al2O3 ratio was 38, the specific surface area about 250 g/m 2 and the pore size about 5 Å. The catalyst was triturated and sieved between 1.0 and 1.4 mm. The apparent porosity of this catalyst was calculated by a method described in the supplementary materials and was found to be 0.61. The dried catalyst was introduced in a tubular furnace to be calcined at a temperature of 550 °C during 4 hours [START_REF] Aho | Catalytic upgrading of woody biomass derived pyrolysis vapours over iron modified zeolites in a dual-fluidized bed reactor[END_REF] at atmospheric pressure, with a heating rate of 2 °C/min.

Fe-HZSM-5

The previously mentioned catalyst, HZSM-5, was used as a support for synthesis by impregnation of Fe-HZSM-5. An iron nitrate salt, ferric (III) nitrate 9-hydrate (Fe(NO3)3.9H2O), was purchased from PanReac AppliChem. For each 10 g of HZSM-5, 4.04 g of the iron nitrate salt were diluted in 100 mL of deionized water [START_REF] Aho | Catalytic upgrading of woody biomass derived pyrolysis vapours over iron modified zeolites in a dual-fluidized bed reactor[END_REF]. The catalyst was impregnated by the ferric solution, agitated and heated at 80 °C for 10 minutes. The catalyst was then dried overnight in an oven at a temperature of 105 °C. The dried catalyst then underwent the same calcination programme described previously. The apparent porosity was 0.61 for Fe-HZSM-5.

Catalyst characterisation methods

2.2.2.1 Specific surface area and pore size distribution BET surface area was measured by nitrogen adsorption at -196 °C in a Quanta Sorb Junior apparatus (Ankerschmidt). Before analysis, the samples were degassed for 30 min at 200 °C. Each measurement was repeated three times and an average value was taken.

Nitrogen adsorption-desorption isotherms were obtained on a Micromeritics TRISTAR 3000 analyser at -196 °C over a wide relative pressure range from 0.01 to 0.995. The samples were degassed under vacuum for several hours before nitrogen adsorption measurements. The pore diameter and the pore size distribution were determined by the Barret-Joyner-Halenda (BJH) method using the adsorption branch of isotherms.

Surface acidity

The acidity of the catalysts was measured by infrared spectroscopy of adsorbed pyridine. It has been demonstrated in literature that pyridine is the probe molecule of choice to examine the acidity of zeolites as used in biomass pyrolysis applications [START_REF] Deka | Acidity in zeolites and their characterization by different spectroscopic methods[END_REF]. To investigate the nature of acid sites and bonding of sulphate ions on the surface of catalysts, FT-IR (Spectrum BX, Perkin-Elmer) spectra were obtained in the range of 600-4000 cm -1 . The samples for acidity measurement were prepared in powder form, then saturated with small amount of pyridine, and degassed at 100 °C for one hour.

The FTIR spectra in absorbance mode after the pyridine treatment were subtracted with those of the untreated catalysts to obtain the peaks only due to pyridine-acid interactions [START_REF] Topaloǧlu Yazıcı | Determining the surface acidic properties of solid catalysts by amine titration using Hammett indicators and FTIR-pyridine adsorption methods[END_REF].

Pyrolysis experimental and analytical setup

Pyrolysis setup

The pyrolysis runs were done in a semi-continuous experimental set up. It comprised of a quartz reactor with a special configuration, as illustrated by "spoon" could be inserted at the reactor inlet and the other end was connected to a condenser and a flask, placed inside a cold bath to recover the bio-oils formed from the condensation of pyrolytic vapours. The flask was connected to a sampling bag, in which the non-condensable gases were collected to be later analysed. A flowmeter, placed near the mouth of the reactor, allowed the regulation of the flow of nitrogen, used as carrier gas. The cold bath and the refrigerant were both kept at a constant temperature of -10 °C.

The pyrolysis experiments were conducted at temperature of 500 °C using a flow rate of 500 mL/min of nitrogen for each raw material used. About 3 g of raw materials were placed onto the spoon, which was kept near the mouth of the reactor. For the experiments comprising the catalysts, a catalyst-to-biomass ratio of 4:1 was used. The vapour residence time through the catalyst bed was calculated to be about 3 s. After the reaction, the non-condensable gases were recovered in the sampling bag and the setup was finally left to cool so as to permit the collection of the solid char. The oil was recovered by using acetone with 99.98% purity, with a known added amount of nonane, used as internal standard.

Pyrolytic products analysis methods

GC-MS analysis

The liquid product analysis methods have previously been detailed in Mohabeer et al. [START_REF] Mohabeer | Comparative analysis of pyrolytic liquid products of beech wood, flax shives and woody biomass components[END_REF]. The analysis of the recovered bio-oil was performed using a gas chromatograph-mass spectrometer instrument GC-MS (Varian 3900 -Saturn 2100T). The analysed components were identified with

Varian WS (WorskStation) and NIST 2002 software by comparing the mass spectrum obtained to mass spectra from the NIST library. Kovats retention indices of the identified peaks were then calculated and compared to reference values for confirmation of their identity.

GC-FID analysis

Once the identity of the peaks was confirmed, a flame ionisation detector (FID), GC-FID Scion 456-GC Bruker instrument, was used to quantify the components. The compounds obtained were then grouped into chemical "families", each having the same main functional group.

GC analysis of non-condensable products

The analysis of the non-condensable gases was performed with a gas chromatograph instrument from Perkin Elmer, Clarus 580, equipped with two detectors, a FID and a thermal conductivity detector (TCD). The instrument also comprised of a Shincarbon St 100 120 column, a methaniser and a hydrogen generator. The oven was regulated from 100-200 °C. The carrier gas was argon. The TCD was used to determine the components such as H2 and N2. The FID detected the carbonated components, except for CO and CO2, which were detected with the help of the methaniser.

Karl Fischer (KF) titration method

Volumetric KF titrations were performed with a Metrohm 870 KF TitrinoPlus apparatus. An aqualine sodium tartrate solution was used as titrating agent, along with Hydranal Composite 5 and Hydranal Methanol Rapid as working media. The sample weight used was in the range of 0.17-0.20 g.

Results

Catalyst characterisation

The values obtained for the specific surface area of the catalysts used were 286 m 2 /g for HZSM-5 and 221 m 2 /g for Fe-HZSM-5. It can be seen that the BET surface area decreased after the iron modification, but remained relatively high. As for the pore size distribution, from the isotherms, it was seen that HZSM-5, along with the modified version, exhibited mostly microporous structures. It was also seen that while the microporous volume did not change significantly for both catalysts (0.15 cm 3 /g), the pore specific volume did incur a change: 0.41 cm 3 /g for HZSM-5 and 0.25 cm 3 /g for Fe-HZSM-5, pointing that some pores were occupied by Fe ions.

Infrared is the most powerful technique for the study of zeolite acidity [START_REF] Topaloǧlu Yazıcı | Determining the surface acidic properties of solid catalysts by amine titration using Hammett indicators and FTIR-pyridine adsorption methods[END_REF]. Zeolites are known to possess two kinds of acidities. Firstly, for zeolites in the H-form, the hydroxyl groups linking Si and Al atoms are said to have strong Brønsted acid properties. Then, Lewis acid sites are usually associated with extra-framework Al and O species [START_REF] Ward | Thermal decomposition of ammonium Y zeolite[END_REF]. The stepwise desorption of the two catalysts used was performed at 100, 150, 200, 300 and 400 °C. Figure 2 shows the spectra obtained at 150 and 400 °C.

The figure for HZSM-5 clearly demonstrates the presence of bands at 1436 and 1580 cm -1 , characteristic of Brønsted acid sites, as well as bands at 1482 and 1596 cm -1 , representing Lewis acid sites [START_REF] Stevens | In situ infrared study of pyridine adsorption/desorption dynamics over sulfated zirconia and Pt-promoted sulfated zirconia[END_REF]. The principal effect of the iron modification can be observed as a decrease in the acid bands. However, only the bands at 1482 and 1596 cm -1 were completely removed, providing evidence that Lewis acid sites were occupied by Fe.

Effect of catalyst use on pyrolytic product distributions

The pyrolysis of the three biomass components at 500°C with and without any catalytic treatment yielded different product distributions. It should be noted that values exceeding 95 % were obtained for all mass balances conducted, and all were brought to 100 %. The results obtained have been illustrated in Figure 3, from which it can clearly be seen that the most significant amount of bio-oil came from the pyrolysis of xylan and cellulose, with79 wt. % and 77 wt. %, respectively. The largest quantity of non-condensable gases was produced by cellulose pyrolysis (about 12 wt. %), while that of lignin yielded more char than any other component, approximately 57 wt. %. Now, even though xylan seemed to give rise to more liquid than the other two biomass components, it should be noted that cellulose is present in a higher fraction in biomass; hence, it can be said that cellulose contributed most in liquid and gas production. These experiments provided the product distribution of the pyrolysis of the three biomass components as conducted in a semi-batch reactor, under the same operational conditions; and this provided the base of our study.

The use of catalysts had a significant impact on the product distribution of the biomass components.

Concerning cellulose and xylan, the use of the zeolites increased gas production, while impeding that of bio-oil. Also, as can be seen from Figure 4, the oxygen content of the bio-oils (oxygen present in humidity notwithstanding) was quite impacted by the use of the catalysts. This result seems to indicate that certain oxygenated compounds present in the pyrolytic vapours were de-oxygenated in the presence of the catalysts to form more gaseous (CO, CO2 and H2) and water molecules. The only exception was the lignin bio-oil, where the difference in oxygen content was insignificant. This may be explained by the fact that the major part of lignin (57 wt. %) remained unconverted, and so, no important change was observed. Also, a table listing the water content of the different bio-oils can be found in the supplementary materials (Table A-2). It could be seen that HZSM-5 tended to favour the formation of water, and hence, the dehydration reaction, for all the biomass components as compared to the iron-modified catalyst.

Effect of catalyst use on bio-oil and non-condensable gas composition

The percentages of the different chemical families present in the bio-oils recovered and those of the various components present in the non-condensable gases are listed in Tables 3 and4. It is clearly shown by the results obtained that without any catalytic treatment, the major part of carboxylic acids present in the bio-oils came from xylan and lignin (24.68 mol. % and 14.01 mol. %, respectively)

while the bio-oil from cellulose mainly comprised of carbohydrates (42.84 mol. %). Concerning the effect of catalyst use on the oxygen content of the bio-oil, Figure 4 showed that Fe-HZSM-5 and HZSM-5 had about the same efficiency in terms of de-oxygenation; the use of both catalysts reduced the oxygen content of cellulose and xylan quite significantly. An interesting point is that even though the same catalysts were used with respect to the three biomass components, not the same families were impacted. For instance, de-oxygenation efficiency notwithstanding, in the case of cellulose pyrolysis, the use of both catalysts resulted in reducing the carbohydrates percentage. On the other hand, for xylan, the use of the catalysts brought down the carboxylic acids percentage. The same phenomenon was noted with lignin, where the catalyst activity affected the phenols percentage. This observation led to the conclusion that a "competition" existed within the chemical families present; the catalysts mainly targeted the group present in a higher percentage in the bio-oil.

To better compare the different results obtained when utilising the catalysts, the conversion and production rates of the different chemical families in the bio-oils, and those of the non-condensable gas components were used as reference. The calculations done to obtain these values have been presented in the supplementary materials. These values have been tabulated in Tables 5 and6. Also, Now, Mullen and Boateng [START_REF] Mullen | Production of Aromatic Hydrocarbons via Catalytic Pyrolysis of Biomass over Fe-Modified HZSM-5 Zeolites[END_REF] presented the possibility that phenol formation was inhibited by the addition of Fe on an HZSM-5 support; this statement can be confirmed by our observations. From Tables 5 and6, it can be observed that HZSM-5 had a more pronounced selectivity towards phenol production as compared to Fe-HZSM-5 (HZSM-5: +109 % for cellulose and +185 % for xylan vs. Fe-HZSM-5: +29 % for cellulose and +34 % for xylan). Another observation that was noted was that the addition of Fe suppressed the formation of aromatics; HZSM-5 had a higher production rate than its iron-modification when it came to aromatics (122 % more for cellulose and 119 % more for xylan).

Effect of catalyst on products of cellulose pyrolysis

If the results obtained for cellulose are examined, it can be seen that there was a complete reduction of carbohydrates with both HZSM-5 (-100 %) and Fe-HZSM-5 (-100 %). However, it could be seen that the use of HZSM-5 resulted in a high production of aromatics (+257 %), but also some oxygenated chemical families like furans and phenols; meanwhile, the use of Fe-HZSM-5 did lead to the formation of phenols and furans, but, the percentages produced were much lower, while the aromatics formation was less significant (+61 %). This difference is explained when the conversion rates of the gaseous components are analysed: the production rates of H2 and CO2 were noticeably higher with Fe-HZSM-5 than with HZSM-5. These observations can prompt the supposition that the use of Fe-HZSM-5 favoured the production of gas molecules over other oxygenated liquid components and water molecules.

Effect of catalyst on products of xylan pyrolysis

There were a few noticeable differences between the data obtained for the pyrolysis of xylan without and with catalytic treatment and those for cellulose. These differences are logical and can be explained by the different structures of cellulose and xylan [START_REF] Patwardhan | Understanding the product distribution from biomass fast pyrolysis[END_REF]. An important observation is that while almost carbohydrates were converted by the use of catalysts for cellulose, for xylan, the carboxylic acid group was the one targeted by the catalysts. Almost complete reduction was achieved by using both catalysts (-95 % with HZSM-5 and -100 % with Fe-HZSM-5). Now, the difference in product distribution when utilising the two catalysts could be seen in the products formed by the catalytic activity: for HZSM-5, the end product was mainly phenols and aromatics, with a less significant formation of gas molecules like CO and C2H4, while for the iron-modified catalyst, only an important production of the gas molecules H2, CO, CO2 and C2H4 was observed, strengthening the previously-drawn observation about the catalytic activity of Fe-HZSM-5, and contradicting the findings of Zhu et al. [START_REF] Zhu | Fast and catalytic pyrolysis of xylan: Effects of temperature and M/HZSM-5 (M = Fe, Zn) catalysts on pyrolytic products[END_REF].

Effect of catalyst on products of lignin pyrolysis

The behaviour of lignin was completely different from those of cellulose and xylan. Again, this observation can be explained by the differences in the structures of the three biomass components [START_REF] Patwardhan | Understanding the product distribution from biomass fast pyrolysis[END_REF]. However, in this case, there was absolutely no correlation in the catalytic behaviour. Phenols were found to be the major family present in the lignin bio-oil and they were indeed impacted by the use of the catalysts (-52 % for HZSM-5 and -100 % for Fe-HZSM-5); it should be noted nonetheless that a very low liquid yield was obtained from lignin (57 wt. % was recovered as solid residue). What could be observed from this part was that at an operating temperature of 500 °C, lignin pyrolysis with catalytic treatment did not contribute in the liquid fraction. It should however not be forgotten that the extraction method used to separate lignin from a biomass, the interactive forces that exist between the three biomass components when they are intertwined and the presence of minerals influence greatly the behaviour of the said lignin. Hence, the native lignin might present a different behaviour.

Further discussion

Concerning the evolution of non-condensable gas molecules, an interesting observation was made pertaining to the CO and CO2 emitted with the use of the catalysts. The gas percentages have been illustrated in Figure 6. However, the percentages themselves can be misleading for, from Table 6, it can be seen that while the use of HZSM-5 did boost the production of CO for all three biomass components (+185 %, +366 % and +20 % for cellulose, xylan and lignin, respectively), that of Fe-HZSM-5 privileged the production of CO2 (+208 %, +304 % and +28 % for cellulose, xylan and lignin, respectively). From these observations, it can be inferred that the use of HZSM-5 privileged the decarbonylation route over decarboxylation one, while the opposite can be said for Fe-HZSM-5.

Comparing the different production and conversion rates investigated during the course of the study enabled the proposal of the conversion schemes for different chemical families. The proposals put forward are illustrated in this part. "Model molecules", that is, the most abundant molecule present in each family, were taken to represent each chemical group; a detailed list of these molecules can be found in the supplementary materials (Table A-3). Conversion schemes have only been proposed

for the major chemical families in each bio-oil sample from three biomass components.

In the case of cellulose, the major family were carbohydrates and the main compound found was levoglucosan. The conversion schemes obtained when using HZSM-5 and its iron-modification have been illustrated in Figure 7 (a) and (b). From the latter figures, it can be seen that the common molecule formed following the activities of both catalysts is a furan. This observation is coherent in the light of studies led by Mullen and Boateng [START_REF] Mullen | Production of Aromatic Hydrocarbons via Catalytic Pyrolysis of Biomass over Fe-Modified HZSM-5 Zeolites[END_REF]: levoglucosan underwent dehydration to form furans, then through decarboxylation to produce aromatics, olefins, CO, CO2, water and coke.

However, from our results, it was apparent that decarbonylation, not decarboxylation, was predominant in the HZSM-5 activity (formation of CO), while decarboxylation was predominant in that of Fe-HZSM-5 (production of CO2). Another difference noted was the production of hydrogen gas; the utilisation of the iron-modified zeolite seemed to enhance significantly the production of hydrogen in the non-condensable gases.

In the same manner as above, the schemes for the conversion reactions of carboxylic acids with HZSM-5 and Fe-HZSM-5 have been shown in Figure 8 (a) and (b). From the results obtained, it can be inferred by the processes of dehydration, decarbonylation and decarboxylation did take place (formation of water, CO and CO2). However, Gayubo et al. [START_REF] Gayubo | Transformation of Oxygenate Components of Biomass Pyrolysis Oil on a HZSM-5 Zeolite. II. Aldehydes, Ketones, and Acids[END_REF] have stipulated that acids underwent catalytic de-oxygenation to produce ketones first, which further degraded into alkenes. Our observations did not corroborate this statement as our results showed that along with alkenes (C3H6), other products like unoxygenated aromatics, phenols and other light gases were also formed.

This alternate observation can be explained by the difference in vapour residence time; Gayubo et al.

[28] having used a residence time shorter than the one used in this study. Hence, no intermediate products (ketones, in this case) were seen during our experiments.

Finally, the transformation scheme for the conversion of the major constituents of lignin (phenols) has been presented in Figure 9 (a) and (b). However, it should be noted that the lignin fraction did not completely degrade under the reaction conditions; as mentioned earlier, it would take a larger range of temperatures to completely decompose lignin. Also, this transformation scheme should be taken as a tentative one as the catalytic behaviour of the lignin chosen for this study might not be completely representative of native lignin. From Figure 9, it can be seen that the difference between the two catalysts was the same as in the previous instances (transformation schemes for cellulose and xylan); HZSM-5 favoured decarbonylation and formation of guaiacols while the iron-modified HZSM-5 gave rise to decarboxylation.

Conclusion

This study aimed at presenting a detailed analysis of the liquid and gaseous pyrolytic products of the three principal components of biomass (cellulose, hemicellulose and lignin) using two different catalysts (HZSM-5 and its iron-modification, Fe-HZSM-5) in the same experimental setup and under the same operating conditions. The goal was to be able to present transformation schemes for the catalytic de-oxygenation of the biomass components and thus determine the provenance of aromatic compounds in the liquid product so as to get a better idea of the composition of bio-oil to be used as a bio-fuel. It was firstly found that a "competition" arose due to the presence of a catalyst; rather than one single chemical family being targeted, the family which was present in majority was the one converted by the catalyst. Secondly, it was found that HZSM-5 tended to privilege the decarbonylation route (production of CO), whilst Fe-HZSM-5 favoured the decarboxylation one (production of CO2) for the same feed. It was also seen that cellulose contributed most in terms of liquid and gas molecules, while lignin gave rise to mostly solid particles. Finally, from the transformation schemes, it was seen that even though both catalysts boosted the aromatics production, HZSM-5 produced more aromatics than its iron-modification. It was also observed that HZSM-5 formed more phenols, and hence, more coke, than Fe-HZSM-5.

Figure captions

Figure 1 .

 1 The total length was 1050 mm. The reactor included two zones: a pyrolysis zone ( = φ 56 mm and L = 760 mm) and a catalysis zone ( = φ 26 mm and L = 290 mm). Both zones were placed horizontally in a tubular furnace. A stainless steel

Figure 5

 5 Figure5illustrates the evolution of the percentages of the major chemical families for each bio-oil

Figure 1 :Figure 2 : 5 Figure 3 :Figure 4 :Figure 5 :

 125345 Figure 1: Layout of pyrolysis reactor

Figure 6 :

 6 Figure 6: Evolution of percentages (vol. %) of major non-condensable gas components with and

Figure 7 : 5 Figure 8 : 5 Figure 9 :

 75859 Figure 7: Conversion scheme of the major chemical family in cellulose with (a) HZSM-5 and (b) Fe-

Table 1 : Ultimate analysis of the different biomass components Biomass/Biomass Component used Elemental analysis (wt. %)

 1

		Carbon	Hydrogen	Nitrogen	Oxygen
	Cellulose	41.74	6.08	<0.01	52.18
	Xylan	41.47	6.48	<0.01	52.05
	Lignin	57.04	4.76	<0.01	38.21

Table 2 : Proximate analysis of different biomass components based on TGA experiments (wt. %) Moisture content Volatile matter Fixed carbon Ash

 2

	Cellulose	4.61	91.87	3.51	<0.01
	Hemicellulose	4.66	76.80	18.31	0.23
	Lignin	11.28	60.38	22.31	6.03
	2.2 Catalysts preparation and characterisation
	2.2.1 Catalysts preparation
	2.2.1.1 HZSM-5

Table 3 : Composition (mol. %) of chemical families present in bio-oils

 3

	Chemical
	groups in
	bio-oil

Table 4 : Composition (vol. %) of components present in non-condensable gases

 4

	Non-
	condensable
	gases
	components

Table 5 : Conversion and production rates of chemical families present in bio-oils Chemical families Conversion rate (-%) and production rate (+%)

 5

		Cellulose +	Cellulose +	Xylan +	Xylan + Fe-	Lignin +	Lignin + Fe-
		HZSM-5	Fe-HZSM-5	HZSM-5	HZSM-5	HZSM-5	HZSM-5
	Carboxylic
		-100	-90	-95	-100	-100	-100
	acids
	Alkanes	-43	-100	-100	-100	-3	-9
	Aromatics	+257	+61	+130	+5	-100	-100
	Alcohols	+69	-61	-80	-88	No change	No change

Table 6 : Conversion and production rates of non-condensable gas components Non- condensable gases components Conversion rate (-%) and production rate (+%)

 6

		Cellulose +	Cellulose +	Xylan +	Xylan + Fe-	Lignin +	Lignin + Fe-
		HZSM-5	Fe-HZSM-5	HZSM-5	HZSM-5	HZSM-5	HZSM-5
	H2	+114	+3261	+103	+4364	+1	-39
	CO	+185	+121	+366	+340	+20	-2
	CO2	+75	+208	+106	+304	-2	+28
	CH4	+90	+110	+66	+170	+9	+93
	C2H2	No change	No change	No change	No change	No change	No change
	C2H4	+508	+439	+1494	+1644	+191	+160
	C2H6	+48	+28	+46	+75	-75	-74
	C3H4	-100	-100	-84	-89	No change	No change
	C3H6	+495	+406	Production Production Production	No change
	C3H8	-100	-100	No change	No change	Production	No change

  2 , CH 4 , C 2 H 4 , C 3 H 6 + coke 2 H 4 O 2 (Carboxylic acids) + CO, C 2 H 4 , C 3 H 6 , H 2 O + coke

	(a)
			C 11 H 10 (Aromatics)	+ CO, C 2 H 4 , H 2 O + coke
			C 8 H 10 O 3 (Guaiacols)
	(a)
			C 7 H 8 O (Phenols)
	C 6 H 6 O
	(Phenols)
	(b)	(b)	H 2 , CO, CO 2 , CH 4 , C 2 H 4 , C 3 H 6 , + coke CO 2 , CH 4 , C 2 H 4 + coke

C 6 H 8 O (Furans) C 6 H 6 O (Furans) C 7 H 8 O (Phenols) C

Acknowledgements

This project has been funded with the support from the European Union with the European Regional Development Fund (ERDF) and the Regional Council of Normandie.


Gérôme Calvès
email: gerome.calves@get.omp.eu

Ysabel Calderon

Vincent Roso

Cédric Bonnel

Martin Roddaz

Stéphane Brusset

Patrice Baby

Peter D Clift

; Cédric Bonnel

Past Amazon Basin fluvial systems, insight into the Cenozoic sequences using seismic geomorphology (Marañón Basin, Peru)

Keywords: Seismic geomorphology, fluvial systems, meanders, channels sinuosity, Amazon Basin, Cenozoic

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Paleogeomorphology and drainage organization of fluvial settings has long been of great interest for resource/energy, life habitat, earth cycle research (e.g. [START_REF] Martin | Paleogeomorphology and its application to exploration for oil and gas (with examples from western Canada)[END_REF][START_REF] Southwood | Habitat, the templet for ecological strategies[END_REF][START_REF] Fisher | Functional ecomorphology: Feedbacks between form and function in fluvial landscape ecosystems[END_REF] due to the architectural complexity of these types of natural reservoirs and environments. Observations from present-day earth surface fluvial systems are commonly used to inform subsurface interpretation of fluvial-system seismic geomorphology [START_REF] Posamentier | Depositional elements associated with a basin floor channel-levee system: case study from the Gulf of Mexico[END_REF].

Limited publications document ancient river deposits in the subsurface, most of which were deposited in marine-to-fluvial or lacustrine-to-fluvial transition zone settings (e.g. [START_REF] Weber | The Use of 3-D Seismic in Reservoir Geological Modelling[END_REF][START_REF] Hardage | 3-D seismic stratal-surface concepts applied to the interpretation of a fluvial channel system deposited in a high-accomodation environment[END_REF][START_REF] Posamentier | Lowstand alluvial bypass systems: incised vs. unincised[END_REF][START_REF] Miall | Architecture and sequence stratigraphy of Pleistocene fluvial systems in the Malay Basin, based on seismic time-slice analysis[END_REF][START_REF] Sarzalejo | Stratigraphy and lithologic heterogeneity in the Mannville Group (southeast Saskatchewan) defined by integrating 3-D seismic and log data[END_REF][START_REF] Ethridge | Fluvial seismic geomorphology: a view from the surface[END_REF][START_REF] Wood | Quantitative seismic geomorphology of Pliocene and Miocene fluvial systems in the northern Gulf of Mexico, USA[END_REF][START_REF] Zeng | Seismic imaging for seismic geomorphology beyond the seabed: potentials and challenges[END_REF][START_REF] Maynard | From bars to valleys: the sedimentology and seismic geomorphology of fluvial to estuarine incised-valley fills of the Grand Rapids Formation (Lower Cretaceous), Iron River Field, Alberta Canada[END_REF][START_REF] Reijenstein | Seismic geomorphology and highresolution seismic stratigraphy of inner-shelf fluvial, estuarine, deltaic, and marine sequences, Gulf of Thailand[END_REF][START_REF] Hubbard | Seismic geomorphology and sedimentology of a tidally influenced river deposit, Lower Cretaceous Athabasca oil sands, Alberta, Canada[END_REF][START_REF] Wang | Seismic geomorphology of a channel reservoir in lower Minghuazhen Formation, Laizhouwan subbasin[END_REF][START_REF] Qi'an | A seismic geomorphology study of the fluvial and lacustrine-delta facies of the Cretaceous Quantou-Nenjiang Formations in Songliao Basin, China[END_REF][START_REF] Zhuo | Contrasting fluvial styles across the mid-Pleistocene climate transition in the northern shelf of the South China Sea: Evidence from 3D seismic data[END_REF][START_REF] El-Mowafy | Quantitative seismic geomorphology of the middle Frio fluvial systems, south Texas, United States[END_REF][START_REF] Alqahtani | Controls On the Geometry and Evolution of Humid-Tropical Fluvial Systems: Insights From 3D Seismic Geomorphological Analysis of the Malay Basin, Sunda Shelf, Southeast Asia[END_REF].

Despite this effort to address some of the most studied objects in the rock record, rivers and their deposits continue to be problematic to earth scientists [START_REF] Miall | Fluvial Depositional Systems[END_REF]. "Big rivers" are the main arteries that deliver the water and sediment from both orogenic and non-orogenic areas of continents to the world's oceans [START_REF] Potter | Significance and Origin of Big Rivers[END_REF][START_REF] Miall | How do we identify big rivers? And how big is big?[END_REF][START_REF] Ashworth | How do big rivers come to be different?[END_REF][START_REF] Lewin | Defining large river channel patterns: Alluvial exchange and plurality[END_REF]. Reconstructing big rivers from ancient deposits is especially challenging due to difficulties in measuring/identifying (and scaling) the architectural elements composing past big rivers. Such deposits are often beyond the scale of conventional outcrops. However, 3D seismic offers the spatial extent to capture the full scale of these elements [START_REF] Bridge | Interpreting the Dimensions of Ancient Fluvial Channel Bars, Channels, and Channel Belts from Wireline-Logs and Cores[END_REF] and enables characterization of many ancient rivers whose scale may rival the 'big rivers' of the modern world, such as the Amazon River.

The Amazon River (Figure 1A) ranks number one in terms of global mass transfer from the continents to the oceans (Figure 1B). Indeed, the Amazon River supplies about 20% of the water [START_REF] Callède | Evolution du débit de l'Amazone à Óbidos de 1903 à 1999/Evolution of the River Amazon's discharge at Óbidos from 1903 to 1999[END_REF], ~10% of the dissolved load [START_REF] Gaillardet | Chemical and physical denudation in the Amazon River Basin[END_REF] and ~3% of the suspended load [START_REF] Milliman | Geomorphic/tectonic control of sediment discharge to the ocean: the importance of small mountainous rivers[END_REF] to the world's oceans. These numbers for transport are only surpassed by the sediment yield in the rivers of south and south-east Asia such as the Huanghe or the Ganges-Brahmaputra (Figure 1B). The present day Amazon Basin is covered by dense tropical vegetation partly protected by nature reserves and is drained by major rivers (Figure 1C). The detailed architecture of the river and its floodplain can be revealed by modern airborne data acquisition, such as Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) (Figure 1C). Satellite imagery allows clear discrimination of the two primary elements of this system: the river loaded by suspended fine sediments and the lateral floodplain covered by vegetation.

Recent studies of the outer continental shelf and uppermost Amazon deep-sea fan sediments suggest that the Amazon River initiated as a transcontinental river between 11.8 and 8.7 Ma [START_REF] Figueiredo | Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin[END_REF][START_REF] Gorini | Late Neogene sequence stratigraphic evolution of the Foz do Amazonas Basin, Brazil[END_REF][START_REF] Hoorn | The Amazon at sea: Onset and stages of the Amazon River from a marine record, with special reference to Neogene plant turnover in the drainage basin[END_REF]van Soelen et al., 2017), and reached its present shape and size during the late Pliocene [START_REF] Figueiredo | Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin[END_REF]. Before the Amazon River transected South America the Middle Miocene environment of the study area was characterized by a long-lived mega-wetland, the Pebas system [START_REF] Wesselingh | On the origin of Amazonian landscapes and biodiversity: a synthesis[END_REF][START_REF] Hoorn | Amazonia through time: Andean uplift, climate change, landscape evolution, and biodiversity[END_REF]. Before the Neogene, the drainage of the Amazon River is postulated to have been to the North with a probable river mouth in the Maracaibo Lake [START_REF] Roddaz | Cenozoic Sedimentary Evolution of the Amazonian Foreland Basin System[END_REF][START_REF] Hurtado | Cretaceous-early Paleocene drainage shift of Amazonian rivers driven by Equatorial Atlantic Ocean opening and Andean uplift as deduced from the provenance of northern Peruvian sedimentary rocks (Huallaga basin)[END_REF].

The stratigraphy of the Marañón Basin is characterized by two sequences related to the pre-Andean series that consists of Paleozoic-Mesozoic deposits and the Andean series that corresponds to Cenozoïc marine to continental foreland successions (e.g. [START_REF] Hermoza | The Huallaga foreland basin evolution: Thrust propagation in a deltaic environment, northern Peruvian Andes[END_REF][START_REF] Roddaz | Cenozoic Sedimentary Evolution of the Amazonian Foreland Basin System[END_REF][START_REF] Baby | Thick-skinned tectonics in the Oriente foreland basin of Ecuador[END_REF][START_REF] Calvès | Mass balance of cenozoic andes-amazon source to sink system-marañón basin, Peru[END_REF][START_REF] Hurtado | Cretaceous-early Paleocene drainage shift of Amazonian rivers driven by Equatorial Atlantic Ocean opening and Andean uplift as deduced from the provenance of northern Peruvian sedimentary rocks (Huallaga basin)[END_REF]. Stratigraphic analysis of the continental and fluvial record of the foreland succession (e.g.: [START_REF] Latrubesse | The Late Miocene paleogeography of the Amazon Basin and the evolution of the Amazon River system[END_REF] has improved over the past decades with documentation of marine incursion in a globally continental sequence [START_REF] Westaway | Late Cenozoic sedimentary sequences in Acre state, southwestern Amazonia: Fluvial or tidal? Deductions from the IGCP 449 fieldtrip[END_REF][START_REF] Wesselingh | On the origin of Amazonian landscapes and biodiversity: a synthesis[END_REF][START_REF] Hoorn | Amazonia through time: Andean uplift, climate change, landscape evolution, and biodiversity[END_REF][START_REF] Roddaz | Cenozoic Sedimentary Evolution of the Amazonian Foreland Basin System[END_REF]Rebata et al., 2016;Jallamillo et al., 2017). In contrast, the structural control on sedimentation and river location in this context has received limited attention [START_REF] Dumont | Morphostructural provinces and neotectonics in the Amazonian lowlands of Peru[END_REF][START_REF] Räsänen | Recent and ancient fluvial deposition systems in the Amazonian foreland basin, Peru[END_REF][START_REF] Roddaz | Cenozoic Sedimentary Evolution of the Amazonian Foreland Basin System[END_REF][START_REF] Gross | Late Miocene sedimentary environments in south-western Amazonia (Solim?es Formation; Brazil)[END_REF][START_REF] Kröhling | Analysis of the Quaternary climatic and tectonic forcing along some different tectonic settings of South America[END_REF].

The objective of our study is to document the detailed structure of the paleo-fluvial Amazonian system using 3D seismic geomorphology techniques and compare these images to the present day surface drainage geometry of the Amazon Basin in order to discuss the evolution and the preservation of large-scale river deposits in continental drainage areas.

MATERIALS AND METHODS

To document the evolution of the present day and paleo-landscape of the Marañón Basin in the Amazon drainage, we have used two data sets. The main data set is 3D multi-channel, post-stack, time-migrated reflection seismic. These data have been acquired over the past decades over oil and gas fields in the Marañón Basin in Peru (Figure 2). The seismic data displayed in this study are zero phase, and follow the Society of Exploration Geophysicist normal polarity, i.e. black peaks indicating an increase in acoustic impedance. The areal extent of the 3D cube is from 90 km² to 190 km². The 3D grid is subdivided into in-line and cross-line directions, spaced at 30 m.

The sampling rate is 4 ms two-way travel time (TWT). In the shallow subsurface the frequency range is 10-70 Hz, with a dominant frequency in the 20-50 Hz range.

Borehole information has been used to constrain the stratigraphy over this area in conjunction with standard seismic stratigraphic principles. The seismic data have been interpreted using various techniques (horizon picking, stratal slicing) and various seismic attributes [START_REF] Taner | Application of amplitude, frequency, and other attributes to stratigraphic and hydrocarbon determination: In[END_REF][START_REF] Taner | Complex seismic trace analysis[END_REF][START_REF] Taner | A 30 Ma history of the Amazon River inferred from terrigenous sediments and organic matter on the Ceará Rise[END_REF] such as amplitude, phase, sweetness [START_REF] Hart | Channel detection in 3-D seismic data using sweetness[END_REF] or thin-bed indicators have been extracted and used to enhance interpretation (Figure 3). To screen the data and allow the reader to scroll through the volume, we have extracted seismic amplitude on stratal horizons, and compiled them to produce an animated movie (supplementary data; movie: Hor_slice_Amp.mpg and metadata). A seismic facies chart has been established based on the geometries and acoustic properties observed and quantified on vertical sections and horizontal displays within the 3D volumes. The seismic facies (SF) identified are summarized in Figure 4.

We interpret the morphologic elements found in the 3D data and compare these to morphologies observed in present day river systems [START_REF] Posamentier | Seismic stratigraphy into the next millennium; a focus on 3D seismic data[END_REF]. To accomplish the later, we utilized our second primary data set, satellite images and digital elevation models (DEMs) from the present day surface of the Amazonian Basin. We have used public satellite images and airborne radar (https://uavsar.jpl.nasa.gov), as well as digital elevation models from the NASA Shuttle Radar Topography Mission (SRTM) (https://www2.jpl.nasa.gov/srtm/). Geomorphological features such as channels (Figure 5) have been quantified following the scheme developed by previous workers on quantitative seismic geomorphology of fluvial features (e.g. [START_REF] Miall | Architecture and sequence stratigraphy of Pleistocene fluvial systems in the Malay Basin, based on seismic time-slice analysis[END_REF][START_REF] Wood | Quantitative seismic geomorphology of Pliocene and Miocene fluvial systems in the northern Gulf of Mexico, USA[END_REF][START_REF] Ethridge | Fluvial seismic geomorphology: a view from the surface[END_REF]. Measurements are summarized in Table 1. Parameters of alluvial channels and classification are sourced from [START_REF] Schumm | Patterns of Alluvial Rivers[END_REF]. Paleocurrent flow direction of the fluvial features (trunk rivers, channel, and meander) has been determined following the methods of [START_REF] Miall | Basin-Mapping Methods[END_REF].

RESULTS

Seismic stratigraphy of the Marañón Basin

The Marañón Basin is a foredeep depozone of the Northern Amazonian foreland basin located between the Andes to the West and the Brazilian and Guyanan shields on its eastern flank (Figure 2). Part of its eastern side is constituted by the Iquitos forebulge [START_REF] Roddaz | Forebulge dynamics and environmental control in Western Amazonia. The case study of the Arch of Iquitos (Peru)[END_REF] (Figure 2A). We have focused our study on the Cenozoic infill of this basin (Figure 2B), which comprises a thick pile (>3500 m) of clastic sedimentary rocks sourced from the Andes and the South American Cratons. Above the Casablanca-Yahuarango Formation (Cretaceous to lower Paleogene, Figure 2C), the overlying Pozo Shale and Pozo Sandstone [START_REF] Hermoza | The Huallaga foreland basin evolution: Thrust propagation in a deltaic environment, northern Peruvian Andes[END_REF] marks the initiation of an overall aggrading fluvial sequence (Chambira, Pebas, Marañón and Corrientes Formations). The seismic images associated to this sequence are characterized by regional >100 km continuous to discontinuous reflections (Figure 2B). At the field scale (less than 10 km), these stratal amplitudes show slight vertical discontinuities (<10-20 ms TWT).

These are marked by bright amplitude and high sweetness compared to background values (Figures 3A and 3B). These discontinuous reflections are marked on their edge by phase changes (Figure 3C) and tuning effects marked by the thin-bed detector attribute (Figure 3D).

Below we describe the observations made based on calibrated 3D seismic reflection images. We further interpret these observations in the context of the morphologies that characterize the sedimentary section and summarize its evolution during the Cenozoic.

Seismic geomorphology of the Paleo-Amazon drainage system

The main seismic facies observed in the studied interval are summarized in Figure 4. Features observed in vertical seismic section are associated with their plan view observed on horizon amplitude extraction. Discrimination of facies in this fluvial environment cannot be solved only on 2D vertical seismic display. The conformable and parallel seismic reflection makes the plan view and amplitude information essential in recognizing sedimentary features interpreted as channel and streams. Eight SFs have been identified (Figure 4). Seismic facies SF1 to SF5 are interpreted to represent fluvial meandering features, each with various degrees of sinuosity and channel widths that flowed without cross-cutting relationship, whereas seismic facies SF6 is interpreted to reflect deposits from similar types of channels but exhibiting crosscutting relationships. Seismic facies SF7 is interpreted to represent an anastomosing fluvial network.

Seismic facies SF1-SF7 occur within a background facies of channel-free material, that is herein interpreted as floodplain overbank sediment (SF8). The peak frequency of these seismic facies ranges from 15 to 45 Hz. The velocity range of the section based on sonic measurement is ~1850 m/s in the shallower section and up to 3800 m/s in the deepest part of the investigated section (over 2.5 sTWT). These velocity values enable bed thickness to be estimated (1/4 wavelength; e.g. [START_REF] Sheriff | Vertical and Lateral Seismic Resolution and Attenuation: Part 7[END_REF]) at ~40 m for the higher frequency in the upper section and ~250 m for the lower frequency in lower section. Channels and related parameters have been quantified in plan view following the parameters defined in Figure 5. Channel-widths range from 40 to >650 m (Figure 4). The larger channels show sedimentological features interpreted as channel bars, meander cut-offs and lateral migration of meanders of various sinuosities. The channels can be ranked in three categories based upon their width, following the classification of [START_REF] Gibling | Width and Thickness of Fluvial Channel Bodies and Valley Fills in the Geological Record: A Literature Compilation and Classification[END_REF]. This is as follows: narrow to medium 10s of meters width for individual channels, >100 m wide medium scale composite channels, and >1000 m -wide fluvial systems. Seismic geomorphologic analysis of eight sequential decomposition RGB blended stratal horizon slices provides a temporal history from youngest to oldest stratigraphic levels (Figure 3A; Horizons 8 through 1) and as shown in Figure 6. The seismic facies are interpreted with three main types of fine grained sediment (mostly shale and silt) associated with splay and other flood plains sediments, as well as two coarse grained lithologies (mostly sand to gravels) associated with channel fills and channel belts.

The oldest horizon within the Marañón Formation, Horizon 8 (pink, Figures 3A and6A), displays a main channel running in a WNW-ESE trend that is connected to narrow, sparselyspaced linear to low sinuosity streams. The underlying horizon, Horizon 7, is interpreted to be the Pebas Formation and shows a denser network of parallel medium-to-wide channels associated with rare meandering narrow channels (red, Figure 6B). Horizon 6 shows the transition from Pebas to Chambira Formations and is marked by the interconnection of medium-to-wide channels with N-S to W-E orientations (orange, Figure 6C). Horizon 5, the top of the Chambira Formation (yellow, Figure 6D) shows well developed densely developed interval of high sinuosity, medium width meandering channels. The upper Chambira Formation, Horizon 4 (light green, Figure 6E) shows a greater frequency of wide channels without any characteristic orientation. The channels in this interval show intricate meandering architecture. The transition from upper to lower Chambira Formation at Horizon 3 shows sinuous channels with a potentially anastomosing organization (deep green, Figure 6F). The next underlying interval shown on Horizon 2 is interpreted as the lower Chambira Formation, and shows isolated NNE-SSW oriented, wide meandering belts with high sinuosity meander scars (light blue, Figure 6G). Finally, the oldest Horizon 1, is representative of the Pozo Formation that is characterized by a set of sinuous parallel W-E channels with narrow to medium in width (marine blue, Figure 6H).

Quantification of channels and fluvial features properties

Quantification of the channel width (n = 420) from the studied seismic horizons interpreted from the Pozo to the Marañón Formations allows a frequency analysis to be conducted and illustrated by the histogram (Figure 7). The median channel width is 121 m (σ = 107 m). Minimum channel width is 29 m and the maximum value is 641 m (Figure 7A). Based on fluvial channel classifications [START_REF] Gibling | Width and Thickness of Fluvial Channel Bodies and Valley Fills in the Geological Record: A Literature Compilation and Classification[END_REF] The sinuosity of meandering channels has been quantified (n = 84; Figures 5 and8) on plan view.

The median sinuosity is 1.4 (σ = 0.47) with a minimum value of 1 and a maximum value of 2.9. About 40% of the measured channels have a sinuosity lower than 1.4. Based on the classification scheme of [START_REF] Schumm | Patterns of Alluvial Rivers[END_REF] for channel sinuosity and load, the measured channels can be divided as follows: with bedload (29.8%) and a sinuosity lower than 1.3, related to a mixed load (53.6%) and a sinuosity higher than 1.3 but and lower than 2, and to suspended load (16.7%) with a sinuosity higher than 2 (Figure 8).

Temporal evolution and dynamics of Paleo-Amazon drainage system

The Cenozoic evolution of the fluvial architecture of the basin fill is summarized through three parameters (channel width, channel belt width and sinuosity) and measurements of paleocurrent directions (Figure 9). Channel width evolves up-sectionwith apparent increasing size from the Pozo Formation (horizon H1, Figure 9A) to the Chambira Formation (Horizon H2, Figure 9A).

Within the Chambira Formation, the upper member shows an increase in channel width with peaks up to 400 m between Horizons H3 and H4, and up to >600 m width between horizons H4 and H6 (Figure 9A). The upper units of the Chambira Formation show a decrease in channel width that increase again slightly in the upper part of the section, between the Pebas and Marañón Formations (horizons H6 to H8; Figure 9A). The channel belt width increases in association with the type of facies and fluvial patterns, especially with the occurrence of high sinuosity streams (Figures 9B andC). The channel belt width is narrow (~2 km) in the Pozo Formation (H1) while it increase during the emplacement of the Chambira Formation (up to 7.2 km). Then, it decreases in the upper part of the Chambira Formation (horizons H5-H6) and in the Pebas Formation (H7), and finally increase slightly in the Marañón Formation (above H8, Figure 9B). This evolution is highlighted by the sinuosity parameter (Figure 9C). In the same area, the observed modern sinuosity is around 2 where there is the transition from mixed to bed load types [START_REF] Schumm | Patterns of Alluvial Rivers[END_REF].

The Pozo Formation fluvial deposits are characterized by sinuosity over 2 and is associated with suspended load transport (horizon H1; Figure 9C). The sinuosity of the Chambira Formation shows a lower member (horizons H2 to H4; Figure 9C) with values associated with low to moderate values (bed load and mixed load) and occasional high values (suspended load). The Upper Member of the Chambira Formation (horizons H5 to H6; Figure 9C) shows low values of sinuosity (mainly bed load). The Pebas and Marañón Formations (horizons H7 to H8; Figure 9C)

show mainly low values with some rare high values of sinuosity. The evolution of paleocurrents follows a two steps evolution with NE and SE flowing streams during sedimentation of the Pozo Formation. A wide, south-directed flow was observed during deposition of the Chambira Formation, while a more SE-ward direction of flow was noted for the Pebas and Marañón Formations (Figure 9D). This sequence of aggrading stacked streams and rivers contains three main fluvial features, including: straight, meandering and anastomosing channels (Figure 4 and supplementary data; movie: Hor_slice_Amp.mpg and metadata).

Present day proximal Amazon drainage and rivers

The present day surface of the Amazon Basin is characterized by a W to E oriented drainage (Figure 1A) with rivers that are both controlled by and incising into topographical structures (Figure 10A) related to the recent evolution of the South American Plate and the Andean mountain range (e.g.: [START_REF] Räsänen | Fluvial Perturbance in the Western Amazon Basin: Regulation by Long-Term Sub-Andean Tectonics[END_REF][START_REF] Räsänen | Evolution of the Western Amazon Lowland Relief: impact of Andean foreland dynamics[END_REF][START_REF] Räsänen | Recent and ancient fluvial deposition systems in the Amazonian foreland basin, Peru[END_REF][START_REF] Roddaz | Forebulge dynamics and environmental control in Western Amazonia. The case study of the Arch of Iquitos (Peru)[END_REF][START_REF] Shephard | Miocene drainage reversal of the Amazon River driven by plate-mantle interaction[END_REF][START_REF] Latrubesse | Large rivers, megafans and other Quaternary avulsive fluvial systems: A potential "who's who" in the geological record[END_REF][START_REF] Stokes | Ongoing River Capture in the Amazon[END_REF]. The Marañón Basin sits at the confluence of two main river networks, one originating from the Napo-Pastaza Fan to the northwest (Figure 10A; [START_REF] Bernal | Late Glacial and Holocene avulsions of the Rio Pastaza Megafan (Ecuador--Peru): frequency and controlling factors[END_REF] and a second from the Fitzcarrald Arch to the southwest [START_REF] Espurt | How does the Nazca Ridge subduction influence the modern Amazonian foreland basin?[END_REF].

These two drainages combine at the town of Iquitos to form the Rio Solimões that run to the Amazon River mouth and from there into the Atlantic Ocean. An SRTM digital elevation model has been extracted to document the shape and size of the rivers and drainage from the Andes to Iquitos (Figure 10B to 10E). The NW-SE present river located above the seismic cube is the Rio Pataza (Figure 6 and supplementary data movie). We have seen that since the Cenozoic the river network and types evolved in two major steps recorded by the Pozo, Chambira, Pebas and Marañón Formations. Downstream the rivers are able to incise the edge of the older watershed, related with the recent rise of the Iquitos Arch along a NW-SE axis (Figure 10C). An incision is presently filled by highly sinuous meanders and streams that are controlled by kilometer wide lows (Figure 10C). Laterally the Pastaza-Corrientes transition band (Figure 10A) with its low land and flood plains shows rivers that are isolated with more linear streams and lower sinuosity (Figure 10D). Finally, after the connection of the Rio Tigre, Marañón and Ucayali, a wide to very large river flows to the NE with large point bar and cut off (Figure 10E). All these present day settings represent the large diversity of rivers and streams along this proximal part of the Amazon Basin.

DISCUSSION

Comparing present day and past morphologies of rivers using different images sources

We have documented the seismic geomorphology of the sedimentary infill of part of the Marañón Basin and the present day fluvial network of the western Amazon Basin. The areal cover and vertical penetration of the subsurface data allows channels associated to a paleo-river network to be recognized. Characterization of the vertical resolution of a channel in subsurface imaging is a difficult task, whereas the lateral extend is easier to achieve. In contrast, measurements of lateral extent based on downhole wireline logs is challenging [START_REF] Bridge | Interpreting the Dimensions of Ancient Fluvial Channel Bars, Channels, and Channel Belts from Wireline-Logs and Cores[END_REF] but thickness is easy to quantify (e.g.; [START_REF] Gibling | Width and Thickness of Fluvial Channel Bodies and Valley Fills in the Geological Record: A Literature Compilation and Classification[END_REF]). Here we discuss the sizes, shape recognition and potential risk when using analogues and various sources of data displayed in plan view analysis, i.e. the comparison of relative resolution (Figure 11). From a high resolution UAVSAR image, a Landsat image or a stratal seismic horizon we can try to understand the predictive nature of the observations. From a giant meander in the Rio Ucayali, a reference 5x5 km box allows a river and its internal structures such as meanders, bars, oxbow lakes or a portion of them to be framed regardless of where the box is located (Figure 11A). Using a set of Landsat images (Figure 11B), we can characterize the shape of various rivers even for the widest meanders, oxbow lakes and bars. However, the lateral continuity of the channel laterally cannot be described. In contrast, the 3D images of the channels derived from the seismic reflection data allow a mixed perspective with a lower resolution (Figure 11C). A 5x5 km box applied to a given 3D stratal horizon allows the definition of the channel and its content, especially when using spectral decomposition and color blend display [START_REF] Partyka | Interpretational applications of spectral decomposition in reservoir characterization[END_REF]. Targeting channels and their net infill is the goal of natural resources exploration if such work is to define good quality reservoirs. Comparison of the ancient geologic reservoir and its present day analogues can help to assist with reservoir properties prediction [START_REF] Alexander | A discussion on the use of analogues for reservoir geology[END_REF][START_REF] Clift | Grain-size Variability within a Mega-scale Point Bar System[END_REF]. The fluvial sedimentary environment is a challenge because the shape of a river can be associated with various locations on the erosional-depositional profile and upstream controls [START_REF] Schumm | River Variability and Complexity[END_REF].

Persistent fluvial landscape

The fluvial features described above characterize most of the Cenozoic infill of the Marañón Basin and the present day surface of the Amazon Basin. Our study outlines the preservation of fluvial geomorphic elements in the rock record, as observed in modern sedimentary basins (Weissman et al., 2015). The difficulty in establishing long-term quantified rates of sedimentation and related supply from mountain ranges could be solved using the fluvial features observed in the subsurface. The morphology of the present day Amazon Basin and its meandering rivers and floodplain are driven by the sediment supply [START_REF] Constantine | Sediment supply as a driver of river meandering and floodplain evolution in the Amazon Basin[END_REF]. Thus, investigation of calibrated fluvial features could allow the paleo-sediment supply of the Cenozoic Andes to the Amazon Basin to be quantified.

The role of deep solid-earth structure on the vertical movements of the Earth's surface and the processes related to drainage/fluvial dynamics at continental scale has been investigated (e.g., [START_REF] Flament | Influence of subduction history on South American topography[END_REF][START_REF] Rodríguez Tribaldos | Spatial and temporal uplift history of South America from calibrated drainage analysis[END_REF]. Limitation of the models mean that the earlier history of the Amazon Basin cannot be solved in this way. The Late Eocene to Early Oligocene times are predicted to represent periods of low incision rates over the entire Amazon catchment [START_REF] Rodríguez Tribaldos | Spatial and temporal uplift history of South America from calibrated drainage analysis[END_REF]. Incision rates increased in the Early Miocene in those areas west of the Guyana and Brazilian Cratons. The incision rate near the Cordillera only increased at 11 Ma. Our observations of the early dynamics of incision and deposition of fluvial system in the proximal part of the Amazon Basin near the Cordillera are in agreement with this timing of uplift. Fluvial systems of continental drainage have existed since the transition from the Pozo to the Chambira Formations, i.e., at least since the Oligocene.

CONCLUSIONS

Modern techniques of seismic imaging and geomorphology have allowed the sedimentological evolution of the Marañón Basin in Peru to be reconstructed. We document the fluvial history of the Amazon Basin at the scale of the Cenozoic for the first time. This sequence of an aggradational stack of streams and rivers contains three main fluvial features, including straight, meandering and anastomosing channels. The size and shape of the channels observed are comparable with present day observations from DEMs or satellite images of Amazon Basin drainage and its river network. This study represents a first step toward a methodology for regional exploration of the fluvial record through the use of modern seismic geomorphology techniques in the Amazon Basin. Yet far from answering all the points raised by other studies of fluvial geomorphology, further detailed mapping of the Cenozoic sedimentary basins of the Amazon Basin is needed (e.g. Solimões, Amazonas). These work must stretch from the source to the sink if it is to depict the sediment routing systems [START_REF] Allen | Sediment Routing Systems: The Fate of Sediment from Source to Sink[END_REF], from the foothills of the Andes Mountains to the Amazon mouth and its slope margin deep-water fan. Specific aspects that need to be developed and tested included: (1) integration of borehole resistivity imagery to constrain paleoflow of stream and rivers, (2) quantitative geomorphology and stream flow orientation, (3) combining tracer techniques of sediments to define the sources of sediments.

Update of the paleogeographic map for this specific period of geological time will allow better constraints on the evolution of the South American plate that is relatively inaccessible to field study compared to other continents. Acquisition of vertical 'transitional' subsurface data ranging from the surface to the youngest resolved seismic reflection image in subsurface could allow a full and continuous analysis of the evolution of this giant sedimentary basin. McCarney-Castle and the regional editor Victor Ramos, are thanked for their support and constructive comments. of the channels and its infill. The colored triangles are selected horizons displayed in Figure 6.

Série (ConocoPhillips

TABLES

FIGURES CAPTIONS

Location of the seismic line is located in Figure 2A and in Figure 6. [START_REF] Schumm | Patterns of Alluvial Rivers[END_REF].

The cutoffs used to differentiate the type of channels based on sinuosity are 1.3 and 2.

  36% of the measured population is classified as being narrow channel. The others are associated to the medium channel group, that have at least of 100 m width. No individual channel features measured in the study area are wider than 641 m. The median channel belt widith (n = 83) is 3598 m (σ = 1295 m), with a minimum measured width of 994 m and a maximum of 7187 m (Figure 7B).

  ) and C. Kirkham (University of Oxford) for help during the manuscript revision. An earlier reviewed version of this work has benefited from valuables review performed by L. Wood (Colorado School of Mines), Y. Sun (Chevron), and J. Bhattacharya (University of Houston). Tiago Alves (Cardiff University), an anonymous reviewer, the managing editor Kerry

Figure 1 :

 1 Figure 1: A. Amazon Basin drainage outline over SRTM digital elevation model and HydroSHEDS river network (EO, NASA). B. Major world rivers yield (drainage area >10 3 km²)

Figure 2 :

 2 Figure 2: (A) Example of the Marañón Basin Cenozoic infill from the (B) seismic line that

Figure 3 :

 3 Figure 3: (A) Seismic reflection amplitude and stratigraphy of the Marañón Basin Cenozoic infill.

Figure 4 :

 4 Figure 4: Quantitative geomorphologic measures along a horizon slice with sweetness attribute

Figure 5 :

 5 Figure 5: Seismic facies observed and interpreted in the Marañón Basin within the Cenozoic

Figure 6 :

 6 Figure 6: Evolution of the fluvial patterns observed and interpreted on colored blended spectral

Figure 7 :

 7 Figure 7: Statistical analysis of quantified fluvial channel width from the Cenozoic record of the

Figure 8 :

 8 Figure 8: Statistical analysis of sinuosity from quantified meanders of the Cenozoic record of the

Figure 9 :

 9 Figure 9: Stratigraphic evolution of channels width, belt width, sinuosity and paleocurrents from

Figure 10 :

 10 Figure 10: (A) Present day surface of the western part of the Amazon Basin. Inset of fluvial

Figure 11 :

 11 Figure 11: Comparative fluvial views from detailed (A) UAVSAR over the Rio Ucayali, (B)

Table 1 :

 1 Channels morphometry from Marañón Basin Cenozoic infill, Peru

	Horizon number	Seismic	Formation	Depth	Channel Width	Channel length on one	Meander
		Stratigraphy	name			wavelength (La)	wavelength
				min	max
				s (TWT)	(m)	(m)	(m)

ACKNOWLEDGEMENTS

GC would like to thank PeruPetro for allowing this work being published. Financial support from Institut-Carnot IsiFor (Agence National de la Recherche) is appreciated. Thanks to IHS-Kingdom, dGB Earth Sciences OpendTect and GeoTeric, for their academic software donations and support. Palaeocurrent diagram were produced using freeware Rose 2.1.0 (Todd Thompson Software). Many thanks to A. Hartley (University of Aberdeen) and S. Leleu (ENSEGID -IPBordeaux) for earlier discussion and perspectives on fluvial sedimentary systems. Thanks to C.


Charbel Habchi

Akram Ghanem

Thierry Lemenand

Dominique Della Valle

Hassan Peerhossaini
email: hassan.peerhossaini@univ-paris-diderot.fr

Mixing Performance in Split-And-Recombine Milli-Static Mixers -a Numerical Analysis

Keywords: mixing enhancement, CFD study, static mixer, creeping flow, baker's transform

Very low Reynolds number laminar flow in Split-And-Recombine (SAR) static mixers is numerically investigated by using a finite volume method. In these configurations, advective chaotic flow structures are created by the passive control of the flow, mimicking the baker's transformation, through a series of flow splitting, rotations, and re-combinations that generate intertwined lamellar structures. This process leads to extra surface creation, which ultimately intensifies mass transfer. The main aim of this study is firstly to demonstrate the interest of this technique for enhancing mixing, while keeping pressure drops moderate, and secondly to optimize this type of geometry. For the latter stake, two different SARs, namely SAR1 (Gray's configuration) and SAR2 (Chen's configuration), are compared in terms of distributive and dispersive mixing and energy expenditures evaluated by the pressure drop. The enhancement

Introduction

Laminar mixing is important for many engineering applications where turbulence cannot be used or generated. This is a common issue in pharmaceutical, cosmetic, and biological applications where highly viscous and fragile fluids are frequently used. In this case, mixing should be enhanced at very low Reynolds numbers without utilizing vortex generators or turbulence promoters. Compactness of mixers in laminar regime is also of great importance [START_REF] Neerincx | Compact Mixing Using Multiple Splitting, Stretching, and Recombining Flows[END_REF] since the mixing time, i.e. the time required for achieving a certain degree of homogeneity, is usually larger than that in turbulent flow regimes. This challenge has led to the development and optimization of the so-called "Split And Recombine" (SAR) static mixers [START_REF] Gray | Novel interconnection technologies for integrated microfluidic systems[END_REF][START_REF] Chen | Topologic mixing on a microfluidic chip[END_REF][START_REF] Jarrahi | Heat transfer enhancement in split and recombine flow configurations: A numerical and experimental study[END_REF][START_REF] Hirata | Development of Channel Mixers Utilising 180° Fluid Rotation Combined with Split and Recombination[END_REF]. SAR mixer consists of a network of divided and then recombined channels in which several fluids are introduced separately and mixed by a multilamination process. This SAR topology performs a series of baker's transforms on the concentration profile [START_REF] Carriere | On a three-dimensional implementation of the baker's transformation[END_REF]. The flow stream-tubes are split out, rotated in opposite directions and then recombined, folding over the concentration profile and doubling the transvers gradient.

Successive vertical separation and horizontal reuniting of fluid streams increase the number of laminates with each stage; hence the contact-surface area between the two fluids is exponentially increased, resulting in faster mixing [START_REF] Ghanem | Static mixers: Mechanisms, applications, and characterization methods -A review[END_REF][START_REF] Hossain | Mixing analysis in a three-dimensional serpentine split-andrecombine micromixer[END_REF]. Recent investigations [START_REF] Carriere | On a three-dimensional implementation of the baker's transformation[END_REF][START_REF] Ghanem | Optimized chaotic heat exchanger configurations for process industry: A numerical study[END_REF][START_REF] Creyssels | Laminar heat transfer in the "MLLM" static mixer[END_REF] revealed the chaotic nature of the SAR flow and under favorable conditions, the maximum value of Lyapunov exponent of ln 2 was recorded in the SAR static mixer designed by Gray et al. [START_REF] Gray | Novel interconnection technologies for integrated microfluidic systems[END_REF]. SAR mixers can be classified in two types: the planar or 2D mixers, and the 3D configurations. Ansari and Kim [START_REF] Ansari | Mixing performance of unbalanced split and recombine micomixers with circular and rhombic sub-channels[END_REF] investigated numerically the mixing process in unbalanced splits and cross-collisions planar circular and rhombic micro-channels for Reynolds numbers ranging from 1 to 80. They showed that the lowest mixing performance is observed in the balanced collision configurations whereas the highest mixing index was obtained in the circular micro-channels in which Dean roll-cells are generated at Reynolds numbers higher than 10. Chen et al. [START_REF] Chen | Optimal designs of staggered dean vortex micromixers[END_REF] studied the mixing process in staggered planar Dean vortex micromixers for Reynolds numbers ranging from 0.5 to 50. It was found that for Reynolds numbers lower than 5, diffusion is dominant over advective transport, while for Reynolds numbers higher than 10 mixing is governed by Dean roll-cells.

Anxionnaz-Minvielle et al. [START_REF] Anxionnaz-Minvielle | Implementation of 'chaotic' advection for viscous fluids in heat exchanger/reactors[END_REF] studied experimentally heat transfer in three different configurations of 3D SAR static mixers and compared their efficiency to planar corrugated channels. It was found that the energy efficiency of SAR mixers increases compared to that of 2D corrugated channels with increasing viscosities, especially for Reynolds numbers lower than 50. Ghanem et al. [START_REF] Ghanem | Optimized chaotic heat exchanger configurations for process industry: A numerical study[END_REF][START_REF] Ghanem | Transport phenomena in passively manipulated chaotic flows: Split-and-recombine reactors[END_REF] used both numerical and experimental techniques to study the mass and heat transfer in different milli-3D SAR flow configurations for different flow regimes.

Comparison of the relative mixing efficiency and the energy consumption among the different flow configurations showed that the mixer proposed by Gray et al. [START_REF] Jarrahi | Heat transfer enhancement in split and recombine flow configurations: A numerical and experimental study[END_REF] is more efficient in the laminar and moderately turbulent flow regimes, for Reynolds numbers ranging from 40 to 5000 [START_REF] Ghanem | Optimized chaotic heat exchanger configurations for process industry: A numerical study[END_REF][START_REF] Ghanem | Transport phenomena in passively manipulated chaotic flows: Split-and-recombine reactors[END_REF]. From the heat transfer point of view, the SAR configuration proposed by Chen and Meiners [START_REF] Chen | Topologic mixing on a microfluidic chip[END_REF] shows an advantage over the other configurations for creeping and deeply laminar flows, with Reynolds numbers between 10 -4 and 10 [START_REF] Ghanem | Optimized chaotic heat exchanger configurations for process industry: A numerical study[END_REF][START_REF] Ghanem | Transport phenomena in passively manipulated chaotic flows: Split-and-recombine reactors[END_REF].

In the present paper, numerical simulations are conducted to analyze passive scalar mixing in different 3D SAR flow configurations for a very low Reynolds number value of 10 -3 , based on the inlet mean flow velocity. This low Reynolds number allows to highlight the baker's transforms occurring in SAR configurations and to exhibit its effects on mixing versus the increase in the pressure drop. This analysis allows establishing a hierarchy of mixers based and their mixing efficiency and opens into an optimization process.

The paper is organized as follows: section 2 is devoted to problem description and numerical model used, the results are discussed in section 3, and finally the concluding remarks are given in section 4.

Problem description

Governing equations

For an incompressible, steady, Newtonian fluid, the flow is governed by the continuity (Eq.

(1)) and Navier-Stokes (Eq. ( 2)) equations:

∇ • = 0 (1)
• ∇ = - ∇ + ∇ (2)
where u is the velocity vector, and are respectively the density and kinematic viscosity of the working fluid, and p is the pressure.

The mixing process is analyzed by tracking a passive scalar C that will allow computing the variance destruction downstream and to characterize mixing. The mass balance should be treated in a pure convective transport to quantify the kinematic mixing. Actually, CFD simulations generate a numerical diffusion that depends on the numerical scheme, the solver, and mostly the meshing. In order to obviate numerical diffusion, we have introduced a physical diffusion coefficient , which indeed damps the pure SAR mixing effect (but remains identical in all systems for the global mixing comparison), and could be closer to the eventual experimental results. The mass transfer equation is hence given in Eq. ( 3):

∇ • = α∇ (3)

Numerical method

The computational fluid dynamics (CFD) code ANSYS Fluent 15 [START_REF]Fluent, Academic Research[END_REF] is used for the present simulations. It is based on an Eulerian approach to compute Navier-Stokes equations through cell-centered finite volume discretization. The flow and scalar equations are solved sequentially with double precision. Third order MUSCL scheme is used for spatial discretization of the linear momentum and mass transfer equations. Diffusion terms are central-difference and second-order accurate. Pressure-velocity coupling is achieved by the SIMPLE algorithm proposed by Patankar [START_REF] Patankar | Numerical Heat Transfer and Fluid Flow[END_REF].

Flow configurations and operating conditions

Numerical simulations are performed for four different flow configurations summarized in Table 1: Plain straight channel, 3D-Flow, SAR1 and SAR2 geometries. All configurations have the same flow cross-sectional area. The number of units per mixer is chosen so that all configurations lead to the same residence time (defined by the reactive volume over the flow rate ratio). For each configuration, pre-and post-conditioners are added to attenuate the entrance and exit effects on the results and to obtain a fully developed flow at the inlet of the mixer elements.

Plain channel 3D-Flow SAR1 [START_REF] Gray | Novel interconnection technologies for integrated microfluidic systems[END_REF] SAR2 [START_REF] Chen | Topologic mixing on a microfluidic chip[END_REF] Cross section (mm 2 ) No-slip boundary conditions are prescribed on all wall boundaries. A uniform velocity profile with average velocity equal to 3.33 cm/s is imposed at the inlet of the pre-conditioner.

The scalar field at the inlet cross-section is divided into two equal parts, left and right, with = 0 and !"# = 1. At the outlet, streamwise gradients of all the variables are set to zero.

The working fluid properties and operating conditions are shown in Table 2. The Reynolds number Re, is calculated based on the hydraulic diameter of the duct cross-section and the inlet mean flow velocity. The viscosity µ of the working fluid is chosen to match that of viscous fluid products encountered in industrial applications where SAR devices are usually used for creeping flows [START_REF] Thakur | Static Mixers in the Process Industries-A Review[END_REF]. Numerical simulations are carried out in isothermal conditions, with a low mass diffusivity coefficient (high Péclet number) so that diffusion cannot dominate over advective mixing. In Table 2, %& is the Péclet number representing the ratio between advective and diffusive transport rates. As noticed, the advective transport is dominant over diffusion since the diffusivity coefficient is very small. Scaled residual values of 10 -8 are set as a convergence criterion for the solution of momentum and passive scalar equations.

Mesh

Since in the SAR configurations mixing elements are repeated, a series of numerical simulations were conducted for a single element in SAR1 configuration with different mesh densities in order to determine the appropriate final mesh to be used in the study. The mesh sensitivity analysis is done according to the procedure proposed by Celik et al. [START_REF] Celik | Procedure for Estimation and Reporting of Uncertainty Due to Discretization in CFD Applications[END_REF]; five different mesh densities were considered as shown in Table 3. The grid size ratio is the grid size of mesh ' + 1 divided by that of mesh '; it is recommended to be at least equal to 1.3 [START_REF] Celik | Procedure for Estimation and Reporting of Uncertainty Due to Discretization in CFD Applications[END_REF]. For all cases the mesh is structured in cubical cells to reduce numerical diffusion. The criteria for the mesh sensitivity are the pressure drop, i.e. the pressure difference between the inlet and outlet of the SAR geometry, and the normalized standard deviation of the computed scalar value which is used to quantify mixing in the different geometries in this paper:

( ( ) = * ++++ -̅ -) ++++ -) +++ (4)
where ̅ ) corresponds to the average scalar concentration at a given cross section computed in plain duct flow.

Table 3 represents the mesh sensitivity analysis performed on one element in the SAR1 configuration. As shown in this table, the value of GCI on (/( ) is 0.33% and it is 0.48% for Δ for the finer mesh (mesh number 5). The GCI is similar to discretization error and could be used as error bar when presenting the results. Finally, the finer mesh 5 is adopted for all geometries.

Mesh

Results and discussion

Flow structure

The flow streamlines through the last element in the three different geometries are shown in For a better quantitative comparison of the distributive mixing effects [START_REF] Soman | Effects of internal geometry modifications on the dispersive and distributive mixing in static mixers[END_REF][START_REF] Park | Strategies for evaluating distributive mixing of multimodal Lagrangian particles with novel bimodal bin count variance[END_REF], the coefficient of variation of the particle locations is computed using the radius as the characteristic length:

;< = ( =̅ (5)
where =̅ is the average radius and ( the standard deviation obtained as follows:

( = >? = ! -=̅ @ -1 A !BC (6)
Figure 4 compares the coefficient of variation of the distributive mixing among all the geometries studied in this work. The plain pipe represents the lowest distributive mixing performance with a ;< almost equal to zero. The 3D-Flow configuration comes second with a very low ;< , which is consistent with the Poincaré section shown in Figure 3 (b). The SAR2 geometry shows the highest performance with ;< around 0.347 compared to 0.299 in the SAR1 configuration, showing around 17% relative increase compared to that of the SAR1. In the next section the mixing performance is studied by the analysis of passive scalar mixing in the studied geometries.

Figure 4: Distributive mixing analysis using the coefficient of variation of the particle location as characteristic distance.

Scalar mixing

Pure kinematic mixing produced by the baker's transform leads to the formation of parallel fluid layers with varying properties following the initial (inlet-section) state of segregation [START_REF] Carriere | On a three-dimensional implementation of the baker's transformation[END_REF].

However, using finite volume method results in numerical diffusion due to the interpolation and discretization schemes adopted [START_REF] Hossain | Mixing analysis in a three-dimensional serpentine split-andrecombine micromixer[END_REF]. To further reduce the numerical diffusion, in addition to the mesh sensitivity analysis, we use higher order discretization schemes. Therefore a 3 rd order MUSCL scheme was adopted for the convective terms in the Navier-Stokes equations.

Scalar mixing is studied by dividing the inlet-section of each configuration into two parts as shown in Figure 5 where, the left part corresponds to an arbitrary scalar value equal to 0 and the right part corresponds to a scalar value at the exit-plane of the first five elements of the 3D-Flow and the two SAR configurations. In spite of the low fluid diffusivity, with the low velocity and relatively large contact time intervals, small diffusion occurs at the interface between different scalar layers producing rather intertwined lamellar structures. Yet the signature of the SAR mechanism can be clearly detected and the arrangement of scalar strata following the theoretical predictions of the baker's transform is visible, though accompanied by the distortion caused by in the interfacial area. The exponential fitting after the 3 rd element shows that the decay in (/ ( ) for the SAR2 is almost 2.4 times greater than that in SAR1. At the inlet-section of the 5 th element in SAR2 geometry, the deviation from the mean becomes inferior to 1%, a value largely acceptable for a wide range of process engineering applications, while the deviation is equal to 27% in the SAR1 configuration at the same location.

(

Pressure losses and friction factors

Figure 7 (a) represents the normalized pressure drop between the inlet and the outlet of each mixing element in the three configurations, where ∆p 0 corresponds to the pressure drop in the plain duct flow. The seemingly surprising result from this figure is that the pressure drop in the 3D-Flow configuration is larger than that in the SAR configurations and that the relative pressure drop in the latter case is lower than 1. This implies that the pressure losses across the SAR mixing elements are smaller than those in the straight plain duct with the same inlet mean flow velocity. However, the reason behind this behavior is that in the SAR configurations, the flow is divided into two channels of the same cross section, so that the flow rate is divided by 2 in each channel, inducing lower pressure drop as it can be observed from the streamlines colored by the mean flow velocity in Figure 2. Therefore, to account for this issue, it is preferable to compare the friction factors that can scale out the flow rate issue.

The Fanning friction coefficient is obtained from the pressure drop across the mixer inlet and outlet via the following relation:

D = Δ E # 2F G H (7)
where G H is the mean flow velocity.

In the straight plain pipe and 3D-Flow configurations, G H is simply the mean flow velocity, which is uniform throughout the entire mixer length. However, in the SAR configurations, the calculation of the friction coefficient should be weighted by the corresponding flow velocity. In SAR1 configuration, 10% of the flow volume corresponds to a mean flow velocity G H while 90% corresponds to the half of the mean flow velocity G H /2 . In SAR2, the volume corresponding to G H is 13% while that corresponding to G H /2 is 87%. Let us denote I the fraction of the volume corresponding to G H /2; the friction coefficient would be calculated using the following expression:

D JKL = Δ E # 2F G H 1 -I + Δ E # 2F M G H 2 N I (8)
which leads to the following equation:

D JKL = Δ E # 2F G H 1 + 3I (9)
The normalized friction coefficients are shown in Figure 7 (b) where f 0 corresponds to the fiction coefficient of the plain duct flow. The friction ratios are greater than 1, since the losses in straight duct are always the lowest. Moreover, the friction in the 3D-Flow configuration is smaller than in the SAR configurations due to smaller number of bends. The increase in the friction losses in the 3D-Flow relative to the straight duct is about 11%, while it is larger in the SAR cases: SAR1 has an increase of about 65% and SAR2 has an increase of about 68%, which quite similar although slightly higher than SAR1 configuration.

For equal pumping power:

< Q ) Δ ) = < Q Δp ( 11
)
where < Q is the volumetric flow rate.

Substituting Δp by an expression in terms of D and substituting < Q by an expression in terms of Reynolds number R&, it follows that:

R& R& ) = S D D ) T U C V (12)
Thus at constant pumping power, the relative mixing efficiency becomes:

O = S ( ) -( ( ) T S D D ) T U C V (13)
Figure 8 represents the variation of the relative mixing efficiency versus the residence length for the three different configurations. The SAR2 geometry has higher relative mixing efficiency than SAR1 and 3D-Flow configurations. In the 3D-Flow, the efficiency increases very slowly to reach a maximum value of about 22% at the mixer exit since the mixing in this configuration is almost entirely due to molecular diffusion. In the SAR configurations, the efficiency increases rapidly to reach a plateau after about 300 mm from the inlet. The maximum efficiency in SAR1 and SAR2 geometries is almost the same; it is around 83%. However, mixing increases faster in the SAR2 compared to SAR1. The governing momentum and passive scalar conservation equations are solved using a Eulerian approach and a finite volume method with the SIMPLE algorithm for pressure-velocity coupling.

As the flow is deeply laminar and the fluid is highly viscous, the 3D-Flow configuration shows little mixing enhancement with respect to plain pipe flow and generates a higher pressure drop. The flux recombination mixers however, show an interesting rapid decrease in scalar concentration gradients. In SAR2 configuration, for example, the normalized scalar concentration standard deviation from the mean attains values as low as 1% as early as at the inlet of the fifth element. At the same location, those for SAR1 geometry are calculated at 27%. Indeed, SAR2 mixer shows superior mixing performance compared to the other configurations.

The Poincaré sections, produced by releasing inert particles at the inlet and following their paths through the mixer outlet, show the capacity of SAR configurations to generate chaotic-type behavior in laminar flow. Particles remain grouped in plain pipe and 3D-flow while they get dispersed and visit several locations in the cross-section of the SAR configurations, especially in SAR2 mixer, confirming the conclusions based on scalar standard deviation values.

To properly evaluate the interest of these devices in process industry, energy expenditures behind the mixing enhancement are evaluated in terms of pressure drop. For similar inlet Reynolds number, SAR mixers generate lower pressure drops than 3D-Flow and the plain channel due to the fact that the fluid flows in the majority of their volume with half of the inlet velocity due to splitting, thus decreasing head losses. To account for this point, the normalized non-dimensional longitudinal Fanning friction coefficient is calculated and compared: 3D-Flow shows values 11% increase compared to the plain channel; the increase in SAR1 and SAR2 mixers being 65% and 68% respectively.

Mixing performance and energy consumption are simultaneously evaluated in the relative mixing efficiency parameter which gives the relative increase in mixing quality with respect to a plain square channel at constant pumping power. While the maximum efficiency in 3D-Flow remains limited to 22%, SAR1 and SAR2 configurations show values as high as 83% with the SAR2 mixer finally manifesting the fastest mixing rates, dissipating concentration gradients with minimal residence time and moderate pressure drops.

In this context, the numerical simulations offer a powerful design and optimization tool giving insight to the optimal number of elements as a compromise between product quality and energy expenditures.

Figure 1 :

 1 Figure 1: Isometric view of one element from each flow configuration: (a) 3D-Flow configuration, (b) SAR1 (Gray configuration [2]), and (c) SAR2 (Chen configuration [3])

Figure 2 .Figure 2 : 3 . 2 Figure 3 .Figure 3 :

 223233 Figure 2. In the 3D-Flow configuration (Figure2 (a)), the streamlines are simply twisted periodically while circulating in the successive bends. Since the flow inertial forces are small relative to the viscous forces, there is no generation of hydrodynamic instability or vortices and thus the only irreversible mixing mechanism present is the molecular diffusion. In the SAR2 configuration (Figure2 (c)), the streamlines are evenly split into two perpendicular directions, then rotated by 90° two times before they are recombined. This process is repeated two times in each element. Here also there are no vortices or instabilities due to high fluid viscosity. However,

Figure 5 :

 5 Figure 5: Scalar mixing at the outlet-section of each of the first five elements for (a) the 3D-Flow, (b) the Gray (SAR1), and (c) the Chen (SAR2) configurations.

Figure 6 :

 6 Figure 6: Normalized scalar standard deviation (a) at the outlet of each element and (b) versus the residence length for the three configurations: 3D-Flow, SAR1, and SAR2

Figure 7 : 20 3. 5

 7205 Figure 7: (a) Normalized pressure drop and (b) normalized Fanning friction coefficient for the three configurations: 3D-Flow, SAR1, and SAR2

Figure 8 : 4 Conclusions

 84 Figure 8: Relative mixing efficiency versus the residence length in the three configurations: 3D-Flow, SAR1, and SAR2

Table 1 :

 1 Characteristics of the flow configurationsThe first flow configuration, plain channel, is a plain straight duct of square cross section.

		3 3	3 3	3 3	3 3
	Number of elements	-	18	13	10
	Element developed length (mm)	-	39	54	69
	Total developed length (mm)	700	702	702	690
	Pre-conditioner length (mm)	-	30	30	30
	Post-conditioner length (mm)	-	30	30	30
	The 3D-Flow configuration consists of a continuous duct flow with alternate bends at right
	angles. The two SAR configurations are referred as SAR1 and SAR2. Basic elements of the 3D-

Table 2 :

 2 Working fluid properties and operating conditions

Table 3 :

 3 Mesh sensitivity analysis performed on one element in the SAR1 geometry

	number	1	2	3	4	5
	Cell number	1.07 10 0 7.09 10 0 5.67 10 4 1.15 10 5 2.25 10 5
	Grid size (mm)	0.363	0.193	0.097	0.076	0.061
	Grid size ratio		1.9	2.0	1.3	1.3
	(/( )	0.7683	0.8373	0.9227	0.9344	0.9351
	6 7 8 (%)			13.17	1.57	0.33
	Δ (bar)	1.632	1.749	1.806	1.969	1.971
	6 7 9: (%)			4.49	10.35	0.48

Acknowledgments C. Habchi and T. Lemenand would like to thank the PHC CEDRE program and the Research Commission of Angers University for the grants allowing researcher exchange between France and Lebanon. The authors dedicate this work to their dear colleague Philippe Carrière, senior scientist in the CNRS, deceased in February 2015. Among many other contributions, he has introduced us to the art of the baker's transform, in the framework of the Energy Program 2006 AC PR1-2-22.