Younes Chhiti

Sylvain Salvador

Jean-Michel Commandr

Franc -Ois Broust

Carole Couhert

Wood Bio-Oil Noncatalytic Gasification: Influence of Temperature, Dilution by an Alcohol and Ash Content

Biomass gasification is gaining attention as a route for biomass energy production. When large scale units are considered, bio-oil shows lots of advantages compared to solid biomass such as high energy volume density and easy handling and storing. Syngas (H 2 and CO) can be produced from bio-oil by two gasification processes, also called reforming processes: catalytic reforming at medium temperature and noncatalytic reforming at high temperature. In the literature, most of the works focus on the catalytic reforming and mainly concern the aqueous fraction of bio-oil or model compounds. Only very few works can be found on the noncatalytic reforming of crude bio-oil. The objectives of this work were to perform experimentally the injection and gasification of nondiluted bio-oil in a lab-scale High Temperature Entrained Flow Reactor (HT-EFR) and to determine the syngas composition and yield. The influence of temperature on the gasification process has been investigated over a wide range from 1000 to 1400 °C. Hydrogen yield increases with temperature via steam reforming of CH 4 and C 2 H 2 and with water gas shift reaction. A thermodynamic equilibrium calculation was conducted. It shows that equilibrium is reached within several seconds at the temperature of 1400 °C. After that, experiments of gasification were realized at 1400 °C with pure ethanol and with ethanol added bio-oil and in order to study the impact of dilution on the syngas yield. The influence of ash on the gasification process has also been evaluated. The ash seems to cause a decrease in the total amount of gas produced.

Introduction

The process of obtaining energy from conventional sources causes atmospheric pollution, resulting in problems like global warming, acid rain, etc. The development of nonconventional sources like wind, sunlight, water, biomass, etc., is inevitable. Syngas (H 2 and CO) production from renewable sources such as lignocellulosic biomass can reduce the emissions of SO 2 and NO x remarkably; the CO 2 neutral energy supply can also be achieved. 1 Biomass gasification process is one of the main routes to produce either syngas, dedicated to second generation biofuels synthesis, or hydrogen. However, lignocellulosic biomass is a resource with variable composition, wide geographical dispersion, and low energy density. These are important drawbacks when large-scale bioenergy production units are considered. In order to minimize the impact of transport, an alternative to the direct upgrading of biomass consists of preconditioning it on decentralized sites before transportation to a centralized bioenergy production unit.

Fast pyrolysis is a thermal decomposition process operated in the absence of oxygen with the aim to convert biomass into liquid products (bio-oil) together with noncondensable gases and solid char as byproduct. For a few years, fast pyrolysis is being considered as a promising route for preconditioning biomass into bio-oil as liquid intermediate biofuel before its transport to a gasification unit. Indeed, bio-oil has much higher volume energy density than that of solid biomass and could be easily stored and transported from decentralized production sites to a large-scale processing unit. A lot of works on fast pyrolysis have been reported within the last years. 2,3 The essential features to obtain high yields of bio-oil (up to 75 wt % on dry basis) are a moderate pyrolysis temperature (500 °C), high heating rates (10 3 -10 5 °C/s), short vapor residence times (<2 s), and rapid quenching of the pyrolysis vapors. A number of pyrolysis reactors have been developed, including bubbling or circulating fluid bed, rotating cone, vacuum pyrolysis reactor, ablative reactor, and twin screw reactor. [4][5][6] Since 1990, demonstration and precommercial units have been developed within EU and North-America.

A lot of works have also been dedicated to bio-oil characterization, upgrading, and utilization. Bio-oil is very different compared to petroleum fuels. It is necessary to develop *To whom correspondence should be addressed. Telephone: þ33(5)63493241. E-mail: ychhiti@mines-albi.fr.

(1) Sharma.; Bakhshi, N. N. Catalytic upgrading of biomass-derived oils to transportation fuels and chemicals. Can. J. Chem. Eng. 1991, 69, 1071-1081.

(2) Meier, D.; Faix, O. State of the art of applied fast pyrolysis of lignocellulosic materialsa review. Bioresour. Technol. 1999, 68, 71-7.

(3) Mohan, D.; Pittman, C. U.; Steele, P. H. Pyrolysis of wood/ biomass for bio-oil: a critical review. Energy Fuel 2006, 20, 848-89.

(4) Bridgwater, A. V.; Peacocke, G. V. C. Fast pyrolysis processes for biomass. Renewable Sustainable Energy Rev. 2000, 4, 1-73.

(5) Bridgwater, A. V.; Czernik, S.; Piskorz, J. An overview of fast pyrolysis technology. In Progress in thermochemical biomass conversion; Bridgwater, A. V., Ed.; Blackwell: Oxford, 2001; pp 977-97.

(6) Bridgwater, A. V.; Maniatis, K. The production of biofuels by the thermochemical processing of biomass. In Molecular to global photosynthesis; Archer, M. D., Barber, J., Eds.; IC Press: London, 2004; pp 521-612.

new technologies for their successful utilization, which requires adequate understanding of their overall fuel properties. 7 However, the behavior of these bio-oils within the gasification reactor also called reforming reactor has been hardly studied so far in the literature, and the improvement of the scientific knowledge is necessary to the emergence of this route. A number of experimental studies devoted to bio-oil combustion brought some knowledge about the behavior of a single droplet when heated and submitted to a reactive atmosphere.

Calabria and Alessio carried out lots of studies on the combustion behaviors of fiber-suspended single bio-oil droplets. The droplet size varied between 300 and 1100 μm and the furnace temperature changed in the range of 400-1200 °C. The droplets were observed to undergo initial heating, swelling, and microexplosion before ignition. During this stage, the temperature-time curves showed two zones with constant temperatures (100 and 450 °C), which corresponded to the evaporation of light volatiles and the thermal cracking of unstable components, respectively. The droplets were ignited at around 600 °C. The combustion of the droplets started with an enveloping blue flame. Then, the flame developed a yellow tail with its size increasing, which indicated the formation of soot. After that, the flame shrank and extinguished, and the remaining solid carbonaceous residues burned leading to the formation of ash. [8][9][10] Various pathways can be used for the production of hydrogen and hydrogen-rich gases from biomass: anaerobic digestion, fermentation, metabolic processing, high pressure supercritical conversion, gasification, and pyrolysis. 11-13 Among them gasification appear to be the most feasible. The combination of fast pyrolysis of biomass followed by transportation in large units for steam reforming has attracted considerable attention of the research community, as one of the most promising viable methods for hydrogen production.

In air/steam gasification process the essential steps are pyrolysis, partial oxidation, cracking of tar, solid carbon residue gasification, reforming (steam and/or dry), and water gas shift to yield syngas, water, carbon dioxide, and unwanted products like tars, methane, and carbon. 14 As a summary, a schematic representation of air/steam gasification of single droplet of bio-oil is proposed in Figure 1.

1. 1. Steam Reforming of Bio-Oil. The steam reforming of the bio-oil can be simplified as the steam reforming of an

oxygenated organic compounds (C n H m O k ) following C n H m O k þ ðn-kÞH 2 O T nCO þ ðn þ m=2-kÞH 2 ð1Þ
During the past decade, catalytic steam reforming of biooil components has been widely studied, focusing on acetic acid as one of the most representative compounds.

Production of hydrogen from catalytic steam reforming of bio-oil was extensively investigated by NREL. 15,16 Czernik et al. obtained hydrogen in a fluidized bed reactor from the carbohydrate derived fraction of wood bio-oil with a yield of about 80% of theoretical maximum. 17 The catalytic steam reforming of the bio-oil or the model oxygenates (e.g., ethanol, acetic acid) has been widely explored via various catalysts, e.g., Ni-based catalysts, 18 Mg-doped catalysts, 19 and noble metal-loaded catalysts. [20][21][22] A lower steam-to-carbon ratio (S/C) and a lower reforming temperature are essential from the viewpoint of economy. Noble metals (Pt, Ru, Rh) are more effective than the Ni-based catalysts and less carbon depositing. Such catalysts are not common in real applications because of their high cost. Catalytic steam reforming of bio-oil is a costly process and presents several disadvantages such as carbon deposit and the deactivation of catalysts due to coke or oligomer deposition even in the presence of an excess of steam (S/C > 5). 20,23 For these reasons, there is an interest in developing noncatalytic gasification of bio-oil, which is the propose of this work.

Only very few works can be found on the noncatalytic reforming of whole bio-oil. Bimbela et al. studied catalytic and noncatalytic steam reforming of acetol (bio-oil model compound) in fixed bed at low temperature (550-750 °C) in order to highlight the specific role of the catalyst in this process. 24 The same study is carried out by Guus van Rossum et al. concerning catalytic and noncatalytic gasification of bio-oil in a fluidized bed over a wide temperature range (523-914 °C). 25 Marda et al. has developed a system for the volatilization and conversion of a bio-oil mixed with methanol to syngas via noncatalytic partial oxidation (NPOX) using an ultrasonic nozzle to feed the mixture. The effects of (7) Oasmaa, A.; Czernik, S. Fuel oil quality of biomass pyrolysis oilsstate of the art for the ender users. Energy Fuel 1999, 13, 914-21.

(8) Calabria, R.; Chiariello, F.; Massoli, P. Combustion fundamentals of pyrolysis oil based fuels. Exp. Therm. Fluid Sci. 2007, 31, 413-20.

(9) Allessio, J. D.; Lazzaro, M.; Massoli, P.; Moccia, V. In Thermooptical investigation of burning biomass pyrolysis oil droplets. Twentyseventh symposium (international) on combustion. The Combustion Institute: Pittsburgh, 1998; pp 1915-22.

(10) Calabria, R.; Allessio, J. D.; Lazzaro, M.; Massoli, P.; Moccia, V. Bio-fuel oil. Upgrading by hot filtration and novel physical methods. The first process step is a fast pyrolysis at atmospheric pressure, which produces large condensate, that was mixed to a slurries. The slurries are pumped into a slagging entrained flow gasifier and are atomized and converted to syngas at high operating temperatures and pressures. 28 The present study is focused on the noncatalytic steam reforming in the absence of O 2 of whole wood bio-oil in a High Temperature Entrained Flow Reactor (HT-EFR). The objectives of this work are to determine the syngas yield and composition as a function of temperature and to carry in parallel a thermodynamic equilibrium calculation to determine the temperature at which the thermodynamic equilib-rium is reached. Moreover, the impact of bio-oil alcoholdilution on the syngas yield has been investigated. Finally the influence of ash on the reforming process has also been evaluated.

Materials and Methods

2.1. Description of Experimental Device. The steam reforming experiments of bio-oils were carried out in a laboratory scale HT-EFR. It consists in a vertical tubular reactor electrically heated by a total 18 kW three-zones electrical furnace and is able to reach 1600 °C in a 1 m long isothermal reaction zone, as illustrated in Figure 2. The atmosphere gas is generated by feeding the controlled flows of water and nitrogen in a 2 kW electrical steam generator. This atmosphere gas is then preheated to 900 °C using a 2.5 kW electrical battery of heating elements before reaching the isothermal reaction zone. The HT-EFR was initially set up to achieve high heating-rate gasification of solid biomass and was equipped for the present work with a specially designed bio-oil pulverization feeder, with the aim to obtain a very constant mass flow rate spray. 29 The feeder consists of a 1 m long and 14 mm o.d. probe cooled with water at 50 °C. At its extremity a stainless steel The oil is fed with a syringe which is pushed automatically. The expected mass flow rate of 0.3 g/min was too low for direct pulverization. Therefore, a 3.5 NL/min N 2 flow rate was used to entrain oil in the feeding probe and to ensure a thin spray of the oil. The spray of droplets is dispersed on the section of a 75 mm i.d. alumina reactor swept by 16 NL/min of an atmosphere gas containing 10 vol. % of steam in N 2 . The steam to fuel mass ratio (fuel includes inherent water in bio-oil) was S/F = 4.5, which is equivalent to steam to carbon molar ratio of S/C = 8.3.

Steam reforming takes place along the reactor during a controlled vapor residence time, which was about 3 s. The gas residence time is calculated as ratio of the reaction zone to the average gas velocity in the reactor. At 1760 mm downstream of the injection point, gases and solid residue were sampled by a hot-oil cooled probe. Gas and solid residue were separated using a settling box and a filter, both heated to avoid water condensation. The water and potential remaining tars were first condensed in a heat exchanger, and noncondensable gases were forwarded to a microchromatograph analyzer (μGC) to quantify H 2 , CO, CO 2 , CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , C 3 H 8 , and C 6 H 6 .

Gases were also analyzed by other analyzers that allowed to check the absence of O 2 , to confirm the analysis, and to control continuously gas production during the gasification: a Fourier Transform InfraRed (FTIR) analyzer, a Non-Dispersive InfraRed (NDIR) analyzer coupled with a paramagnetic analyzer for O 2 , and a Thermal Conductivity Detector (TCD) to quantify H 2 .

2.2. Feedstock. The feedstock used for all experiments is a bio-oil produced by fast pyrolysis of hardwood on an industrial-scale fluidized bed unit (provided indirectly through CIRAD, France). Its physicochemical properties have been measured (see Table 1). The water content of the bio-oil measured by Karl Fischer method (ASTM E203) is around 26 wt % which is in agreement with the average values reported in the literature. It can be noticed that the solid particles content is rather high (2.34 wt %), while the ash content remains low (around 0.06 wt %). This confirms that the solid particles mainly consist of high-carbon content char particles. These particles were entrained by the gas stream to the bio-oils condensers. Ultimate analysis and LHV of the bio-oil are very similar to those of wood. The LHV is measured according to the NF M 07-030 standard, which is technically equivalent to the ASTM D240 standard.

From the ultimate analysis, the chemical formula of the bio-oil can be established as CH 1.18 O 0.48 .0.4H 2 O.

The bio-oil was stored in a refrigerator. Before experiments, it was heated and filtered on a 30 μm sieve to eliminate larger solid particles; this represented less than 0.01%wt.

Results and Discussion

3.1. Effect of Temperature. The first objective was to study the influence of temperature -over a wide range -on the syngas yield and composition.

Generally the gas mixture formed from catalytic reforming of bio-oil is composed of hydrogen, carbon monoxide and dioxide, methane, acetylene, unconverted steam, coke (carbon), and soot. Figure 3

CO þ H 2 O T CO 2 þ H 2 ð3Þ
The water gas shift reaction can also explain the increase of carbon dioxide and the decrease of carbon monoxide between 1000 and 1200 °C. Above 1200 °C, carbon monoxide slightly increases. This may be explained by steam gasification of the solid carbon residue resulting from the pyrolysis of oil droplets to yield carbon monoxide and hydrogen following the reaction

C þ H 2 O T CO þ H 2 ð4Þ
and potentially following the Boudouard reaction which would explain the slight decrease of CO

2 C þ CO 2 f 2CO ð5Þ
It was observed that as the temperature increases the amount of collected solid decreases significantly above 1000 °C. The process allows achieving very high heating rate estimated at 2000 °C 3 s -1 . 30 In these conditions, the char yield measured is very low: < 1 wt %. At 1400 °C more than the 99.9% the bio-oil is converted to gas.

3.2. Equilibrium Calculation. The thermodynamic equilibrium calculation is independent of reactor to predict the yield of final products, based on the minimization of the Gibbs free energy of the system. It was conducted here using Fact-Sage software 5.4. to establish whether the syngas was closed or not to equilibrium at the different temperatures. Operating temperature varied from 1000 to 1400 °C; pressure was fixed at 1 atm. The software is not presented in detail in this paper; details of the thermodynamic calculation could be found in FactSage Web site. 31 The results of prediction are presented in Figure 4, expressed in g of gas produced per g of crude bio-oil injected. As the temperature increases from 1000 to 1400 °C the calculated equilibrium yield of H 2 remains approximately constant at 0,11 g/g, while the yield of CO increases from 0.3 at 1000 °C to 0.45 g/g at 1400 °C. The CO 2 yield decrease from 1.1 g/g at 1000 °C down to 0.9 at 1400 °C.

At 1000 °C the calculation yields are far away from the experimental results. The deviation from equilibrium at lower temperatures is also reported by Sakaguchi et al. 18 At 1200 °C the thermodynamic equilibrium begins to establish. The calculation nevertheless does not retrieve the presence of CH 4 and C 2 H 2 . At 1400 °C the experimental yields are very closed to the equilibrium calculation yields: 0.11 and 0.12 respectively for H 2 , 0.45 and 0.45 respectively for CO, and 0.86 and 0.88 respectively for CO 2 . It can be concluded that at this temperature the equilibrium is reached.

It is also interesting to compare the obtained experimental yields at 1400 °C to theoretical yields corresponding with complete gasification of oil that would follow

CH 1:18 O 0:48 :0:4H 2 O þ 1:12H 2 O f CO 2 þ 2:11H 2 ð6Þ
The maximum stoichiometric H 2 yield for this oil would be 0.150 g per 1 g crude bio-oil, while a value of 0.126 g was obtained experimentally. This shows that in our experimental conditions and at 1400 °C steam reforming of bio-oil lead to a production of H 2 with a yield of about 84% of theoretical maximum.

3.3. Effect of Dilution by a Solvent. Most of the published works of steam reforming concern the aqueous fraction of bio-oil, model compounds, or a mixture of bio-oil/solvent. This choice is essentially linked to injection problems of the very viscous bio-oil. The injection of a mixture bio-oil/solvent is a classical way to facilitate nebulization of crude bio-oil and to avoid injection plugging. It was therefore decided in this work to study the gasification of alcohol added bio-oil in order to evaluate the impact of dilution on the syngas yield. Bio-oil and ethanol were simply mixed and agitated in a container. The two components appear to be miscible; no segregation was observed even after storage. Figure 5 shows the gas yields of steam reforming of crude bio-oil, 75/25% bio-oil/ethanol mixture, 50/50% bio-oil/ethanol mixture, and pure ethanol at 1400 °C. We can notice that the hydrogen and carbon monoxide yield increases when we increase the fraction of ethanol in crude bio-oil, while CO 2 remains more or less constant, CH 4 and C 2 H 4 were not present in the produced gas at 1400 °C.

Considering the yield of pure ethanol and crude bio-oil, we can observe that the H 2 and CO yields seem to follow an additivity law: theoretical yields as calculated from an additivity law fit with experimental yields of gasification products. Some dispersion can be observed concerning CO yields. Nevertheless, the difference between experimental results and calculated values remain smaller than experimental error bars. This validates an additivity law. The fact that an additivity law is observed cannot be interpreted as a noninteraction between bio-oil and the solvent along the primary pyrolysis step, but rather by the fact that at high temperature and closed to equilibrium conditions the composition of the gas tends toward a sum of the gas that would be produced from bio-oil and solvent separately. This result essentially allows to trace a crude bio-oil behavior if it is diluted in a solvent.

3.4. Effect of Ash. Ash is known for their catalytic effect during thermo-chemical conversion of biomass, as previously approved the works done on solid biomass. They indicated that biomass ash acted catalytically and specifically in tar steam reforming; it lowered the temperature of steam reforming reactions during gasification. [START_REF] Skoulou | Effect of biomass leaching on H 2 production, ash and tar behavior during high temperature steam gasification (HTSG) process[END_REF][START_REF] Masek | Examination of catalytic roles of inherent metallic species in steam reforming of nascent volatiles from the rapid pyrolysis of brown coal[END_REF] The aim of this part was to evaluate the potential influence of the presence of mineral matter on yields of final products from bio-oil gasification. Crude bio-oil containing 0.057% of minerals and crude bio-oil with 3% of ash were prepared to highlight effect of minerals in gasification process. The added ash is prepared by burning crushed beech wood (particle size of 300-400 μm) in a furnace equipped with 3 drawers at 600 °C. The choice of this temperature is designed to perform a , mild . heat treatment in order to preserve the initial properties of minerals present in the biomass, as in the case of the production of bio-oil by pyrolysis. The wood is distributed in the drawers on a thin layer of 1.5 cm thickness to ensure good heat transfer and air diffusion. Air was fed to the reactor at low flow rate, 30 NL/h, to avoid ignition and high temperature rapid combustion of wood.

The analysis of the elements most cited in literature was performed in the prepared ash. Silica, especially, is an important element that reacts easily with alkali metals and creates fusion and deposition problems during combustion and gasification. 34 Calcium is present in considerable amount in ash, while potassium is at lower amounts quite volatile at high temperature. Trace elements Fe, Ni, and Al, are known to get involved in various steam reforming reactions during gasification. [START_REF] Masek | Examination of catalytic roles of inherent metallic species in steam reforming of nascent volatiles from the rapid pyrolysis of brown coal[END_REF]35 The ash components were quantified by ICP, presented in Table 2. It can be noticed that Ca, K, Mg, and Mn are present in high concentration. Other minority elements such as Co, Cr, Cu, Fe, Pb, Si, Zn, and Cd are present in much lower concentration.

The gasification temperature of 1200 °C was chosen, because as demonstrated before at this temperature the equilibrium is not reached. Error bars were established by repeating each test 2 or 3 times. Figure 6 shows the obtained gas yields from ''crude bio-oil" and ''crude bio-oil þ3% beech ash". Surprisingly one can notice a clear decrease in the yields of all gas species when the amount of ash is increased. The results are expressed in g of gas produced per g of ash free crude bio-oil injected. Among them, the H 2 yield decreases from 0.094 to 0.067 g/g. CO and CO 2 yields decreased significantly: from 0.38 to 0.20 g/g and from 0.84 to 0.67 g/g, respectively. An explanation could be that added minerals favor polymerization reactions. These reactions lead to the formation of larger quantity of carbonaceous solid residue that is not gasified, causing a decrease in the amount of produced gas, especially CO and CO 2 .

At the high gasification temperature, volatilization of alkalies probably played a negative role on ash catalytic effect. The fact that ash did not favor gas formation at the temperature of 1200 °C could also be explained by the work of Masek et al. [START_REF] Masek | Examination of catalytic roles of inherent metallic species in steam reforming of nascent volatiles from the rapid pyrolysis of brown coal[END_REF] who pointed out ash deactivation at 950 °C. Such a high temperature was shown to accelerate iron sintering leading to a loss of Fe dispersion. [START_REF] Skoulou | Effect of biomass leaching on H 2 production, ash and tar behavior during high temperature steam gasification (HTSG) process[END_REF]

Conclusions

Whole bio-oil was successfully steam reformed in a labscale High Temperature Entrained Flow Reactor. The reaction temperature has a significant influence on the process. An increase in the reaction temperature implies higher hydrogen yield and higher solid carbon conversion. A thermodynamic equilibrium calculation showed that equilibrium is reached at 1400 °C but not at 1300 °C and below for residence times of about 3 s.

The gasification of mixtures bio-oil/alcohol showed that the yields of gas follow an additivity law based on the yields of solvent and of bio-oil.

When adding ash to bio-oil, it has been observed a strong decrease in gas yield, while an increase was expected as in the case of catalytic process. Ash may favor polymerization reactions, causing a decrease in the yield of gas. The volatilization of alkalies and the iron sintering at high gasification temperature may have also played a negative role on ash catalytic effect.

Experiments conducted in a high-temperature entrained flow gasifier showed the capability of this technology to obtain high gaseous product yield using noncatalytic steam gasification. This work was performed without O 2 as first simplified approach. Prior to up scaling, experiments in the presence of O 2 will be required.

Acknowledgment. The authors gratefully acknowledge the financial support from EnerBio Program of Fondation Tuck France and express their gratitude to Mr. Bernard AUDUC technician in Ecole des Mines d'Albi-Carmaux for his technical assistance and contribution to device design and operation.

  both temperature (from 625 to 850 °C) and added oxygen (effective O/C ratio from 0.7 to 1.6) on the yields of CO and H 2 have been explored. They obtained hydrogen yield of about 75% of theoretical maximum. 26 Panigrahi et al. gasified biomass-derived oil (BDO) to syngas and gaseous fuels at 800 °C. They obtained syngas (H 2 þ CO) yield ranging from 75 to 80 mol %. 27 Henrich et al. gasified lignocellulosic biomass.

Figure 1 .

 1 Figure 1. Schematic representation of air steam gasification of bio-oil droplet.

Figure 2 .

 2 Figure 2. Schematic view of the entrained flow reactor of Ecole des Mines d'Albi.

  presents the mole fraction of the gaseous products from this work (in dry basis and without N 2 ) as a function of temperature in the range 1000 to 1400 °C. Error bars were established by repeating each test 2 or 3 times. The species C 2 H 4 , C 2 H 6 , C 3 H 8 , and C 6 H 6 are not detected by chromatograph. Whatever the operating temperature between 1000 and 1300 °C, bio-oil is mainly decomposed to H 2 , CO, CO 2 , CH 4 , and C 2 H 2 . Above 1300 °C C 2 H 2 disappears, while CH 4 disappears above 1400 °C. As the temperature rises, the fraction of H 2 increases monotonically at the expense of carbon monoxide, methane, and acetylene. Above 1300 °C the hydrogen content remains almost stable. At 1400 °C hydrogen mole fraction reaches the maximum value of 64 mol % of the syngas.The reactions that may explain the increase of hydrogen with temperature are -The steam reforming of CH 4 and C 2 H 2 into H 2 and CO ð2Þ -The water gas shift reaction

Figure 3 .

 3 Figure 3. Composition of the produced syngas (dry basis and without N 2 ) -effect of temperature, at S/F = 4.5.

Figure 5 .

 5 Figure 5. Yield of H 2 , CO, and CO 2 during gasification at 1400 °C and S/F = 4.5 of crude bio-oil with different dilutions (CH 4 and C 2 H 4 were not present in the produced gas at 1400 °C).

Figure 4 .

 4 Figure 4. Gas yield from bio-oil reforming at 1000, 1200, and 1400 °C, S/F = 4.5.

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Table 1 .

 1 Ultimate Analysis and Several Characteristics of Bio-Oil Derived from Hardwood Fast Pyrolysis

		ultimate analysis (wt %)
	C	H	O	N	H 2 O (wt %)	ash (wt %)	solids (wt %)	LHV (MJ/kg)	kinematic viscosity at 20 °C (mm 2 3 s -1 )
	42.9	7.1	50.58	<0.10	26.0	0.057	2.34	14.5	103

Table 2 .

 2 Composition of Ashes (from Combustion of Wood) [wt %, Dry Ashes] Figure 6. Yield of gas species during gasification of crude bio-oil and crude bio-oil with 3% of ash at 1200 °C and S/F = 4.5-effect of ash on product yield. (34) Arvelakis, S.; Koukios, E. G. Physicochemical upgrading of agroresidues as feedstocks for energy production via thermochemical conversion methods. Biomass Bioenergy 2002, 22, 331-8. (35) Zhang, R.; Wang, Y.; Robert, C. Brown Steam reforming of tar compounds over Ni/olivine catalysts doped with CeO2. Energy Convers. Manage. 2007, 48, 68-77.

	Ca	K	Mn	Mg	P	Ni	Na	Al
	11.67	3.80	1.74	1.54	1.01	0.25	0.24	0.10


Ilir Hysi
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André Vincentelli

Francis Juthier

Lotfi Benhamed

Carlo Banfi

Natacha Rousse

Jean-Marc Frapier

Fabien Doguet

Alain Prat

Alain Wurtz

Cardiac surgery and repair of pectus deformities: When and how? ☆

Keywords:

Objectives: There is currently a lack of recommendations about patients with pectus deformities requiring cardiac surgery. This study reports the results of our surgical strategy on this issue. Methods: Eleven patients, from three centers treated over a 9-year period were included in this study. Pectus deformities were operated with a modified Ravitch procedure. In the case of pectus excavatum repair and concomitant cardiac surgery, subperichondrial resection of abnormal rib cartilages was always performed before the sternotomy and an easily removable retrosternal metallic strut was inserted at the end of the procedure ensuring anterior chest wall stability. During follow-up patients had to estimate their current appearance with a numeric scale ranging from 0 to 100. Results: Mean age was 27 ± 9.4 years. Pectus excavatum was present in 8 patients and pectus arcuatum in 3. There were 6 Marfan syndrome patients. Nine patients had concomitant surgery and, 2 underwent pectus repair after a history of cardiac surgery. There was no operative mortality. In the case of concomitant surgery, heart exposure through median sternotomy was facilitated by abnormal rib cartilage resection. Median follow-up was 54 months (range 16.7-119.7). Mean cosmetic result evaluated by the patients was 97.3 (±2.5). Conclusions: In adults, concomitant scheduled surgery is reliable and offers excellent long-term cosmetic results. Moreover, it allows a better thoracic exposition with no added perioperative risk. The modified Ravitch technique seems more adequate in these patients as it can be used in all types of pectus deformities.

Introduction

Anterior chest wall deformities are not uncommon. They consist of pectus excavatum (PEx), the most frequent form of chest deformities, and by protrusion deformities such as pectus arcuatum or carinatum. Pectus deformities are usually isolated and patients are referred for scheduled surgical correction. However, some patients present with coexisting pectus deformities and congenital or acquired cardiac disease requiring surgical correction. Traditionally, the combined approach has been avoided due to the bleeding risk or other major complications such as infection or sternal dehiscence [START_REF] Shamberger | Anterior chest wall deformities and congenital heart disease[END_REF]. Growing evidences recently appear to both feasibility and reliability of the simultaneous surgical correction, especially in patients with connective tissue disorders such as Marfan or Ehlers-Danlos syndromes [START_REF] Rousse | Staged repair of pectus excavatum during an aortic valve-sparing operation[END_REF][START_REF] Sacco Casamassima | Modified Nuss procedure in concurrent repair of pectus excavatum and open heart surgery[END_REF][START_REF] Schmidt | Pectus excavatum and cardiac surgery: simultaneous correction advocated[END_REF]. However important questions remain unanswered, notably: (i) on the effect of age; (ii) safety of concomitant surgery; and (iii) choice of procedure, Ravitch, Nuss or other techniques.

Materials and methods

Population

This was a retrospective study of 11 patients from 3 centers (Lille, Montpellier, Rouen) who have received treatment over a 9-year period (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014). Of these patients, 2 have been previously reported [START_REF] Rousse | Staged repair of pectus excavatum during an aortic valve-sparing operation[END_REF]. Nine patients underwent concomitant surgery and 2 patients with a medical history of cardiac surgery underwent a delayed pectus repair. Transthoracic echocardiograms were performed in all patients, specifically looking for patent foramen ovale in the cases of PEx. Patients' clinical and biological data were collected from medical charts. The study was approved by the Institutional Review Board of the French Society of Thoracic and Cardio-Vascular Surgery (CERC-SFCTCV-2014-3-1-18-21-28-HyIl) and patients' consents were orally obtained.

Surgical technique

The pectus repair was performed by using a simplified open procedure based on the subperichondrial resection of abnormal rib cartilages and optional transverse osteotomy across the anterior table of the upper sternum, as previously described [START_REF] Wurtz | Simplified open repair for anterior chest wall deformities. Analysis of results in 205 patients[END_REF]. Depending on the morphology of pectus deformity, resection was performed at the level of the second/ third, to the seventh paired rib cartilages for PEx correction, and second to fourth/fifth for pectus arcuatum.

In the case of concomitant surgery, patients were monitored in the operating room as in all routine cardiac surgical procedures. Patients with PEx, were operated with a sequential technique as described elsewhere [START_REF] Rousse | Staged repair of pectus excavatum during an aortic valve-sparing operation[END_REF]. Briefly, after a vertical presternal incision and minimal detachment of the pectoralis major and rectus abdominis muscles, the subperichondrial resection of the lower paired rib cartilages was performed. Sternotomy and cardiac procedure with cardiopulmonary bypass, according to surgeon's preferences, were then carried out. Last, after heparin reversal and sternum closure with six to eight simple wires, PEx repair was achieved by additional resection of the upper second and third cartilages, sternal osteotomy if needed and placement of a substernal metallic strut (Medicalex, Bagneux, France). The latter was positioned at the level of the sixth perichondrial sheaths and anterior to the ribs laterally and secured to the sternum with an absorbable suture [START_REF] Rousse | Staged repair of pectus excavatum during an aortic valve-sparing operation[END_REF]. In the case of pectus arcuatum, the pectus repair was performed immediately after the achievement of the cardiac procedure, without insertion of a metallic strut. Surgical chest tubes were placed in the pericardium, mediastinum and presternal space. Antibiotic coverage was administered as usually in cardiac surgery, without any modification due to the presence of the metallic strut.

Postoperative management

After the surgical procedure, patients were monitored in intensive care units (ICU) for at least 48 h. Total amount of fluid drainage within the first 24 h was assessed.

Follow-up

Follow-up was complete. The metallic strut was routinely removed under outpatient local anesthesia procedure, 5-9 months after the initial operation. The most recent clinical data were collected by telephone interviews. Patients were asked to estimate their current cosmetic appearance with a numeric scale ranging from 0 (the lowest) to 100 (the highest).

Results

Patient demographics

Mean age of our cohort was 27 (±9.4) years and were mostly male (N = 9 or 81.8%). Pectus excavatum and arcuatum were present in 8 (72.7%) and 3 (27.3%) patients, respectively. In patients with PEx and pectus arcuatum, the mean Haller index was 5.06 (± 1.73) and 2.5 (± 0.8), respectively (Table 1). Nine patients (81.8%) underwent concomitant surgery, and 2 patients with a history of cardiac surgery (atrial septal defect in patient 3 and transposition of the great vessels in patient 7) underwent a delayed pectus repair (pectus arcuatum and PEx, respectively). Table 1 summarizes surgical details for all patients of our cohort. Five patients [START_REF] Sacco Casamassima | Modified Nuss procedure in concurrent repair of pectus excavatum and open heart surgery[END_REF][START_REF] Hasegawa | Simultaneous repair of pectus excavatum and congenital heart disease over the past 30 years[END_REF][START_REF] Jones | Staged approach to combined repair of pectus excavatum and lesions of the heart[END_REF][START_REF] Humphreys | Pectus excavatum. Late results with and without operation[END_REF][START_REF] Haller | Concomitant mitral valve replacement and re-re-repair of severe pectus deformity correction in a patient with Marfan syndrome[END_REF], had a previous sternotomy, due to a history of cardiac surgery during childhood or infancy. Patient 8 presented with 4 previous sternotomies. He had two recurrent ventricular septal defect closure, and pulmonary and aortic stenosis correction. Routine preoperative transthoracic echocardiograms showed a patent foramen ovale in 2 patients (7 and 9). There were 6 (54.5%) Marfan patients requiring an aortic root surgery and 2 of them (patients 2 and 10) underwent an additional aortic arch replacement.

Operative characteristics and postoperative outcomes

In patients who underwent concomitant surgery, mean cross-clamp, CPB and pectus operative times were 109.9 (±55.4) min, 183.4 (±87.2) min and 167 (±29.9) min respectively. After sternal closure with wires, partial sternal transversal osteotomy was carried out in 5 patients. Total amount of fluid drainage in the first 24 h was 736 (±354) ml. Average length of ICU and hospital stays were 6.1 (±8.8) days and 19.3 (±14.1) days, respectively. In both patients (3 and 7) who underwent a delayed pectus repair operative times were 117 and 120 min, total amount of fluid drainage in the first 24 h was 100 and 150 ml and they were discharged on days 4 and 8, respectively.

For the whole cohort, there was no operative mortality and overall morbidity was of 63.6% (n = 7). In these patients morbidity details were as follows: 3 lymphatic subcutaneous effusions, 3 unilateral lung infections and 1 stroke with complete recovery. In all our patients, we did not observe any injury of the internal thoracic arteries and sternal healing occurred as usually after cardiac surgery within six to ten weeks after the procedure. When a metallic strut was inserted, median removal delay was 6.2 months (range 5.5-8.9). Median follow-up was of 54 months (range 16.7-119.7) and mean cosmetic result of the pectus repair, evaluated by the patients, was 97.3 (±2.5).

Discussion

Cardiac surgery indication in patients suffering from pectus deformities is infrequent [START_REF] Shamberger | Anterior chest wall deformities and congenital heart disease[END_REF]. Indication and timing of concomitant surgery remain to be defined. Some authors advocate simultaneous repair [START_REF] Schmidt | Pectus excavatum and cardiac surgery: simultaneous correction advocated[END_REF][START_REF] Hasegawa | Simultaneous repair of pectus excavatum and congenital heart disease over the past 30 years[END_REF], while others debate the blanket application of this strategy, because of concerns about potential major complications such as bleeding, prolonged operation times, postoperative instability of the chest wall and infection due to the metallic bar [START_REF] Shamberger | Anterior chest wall deformities and congenital heart disease[END_REF][START_REF] Jones | Staged approach to combined repair of pectus excavatum and lesions of the heart[END_REF]. Pectus excavatum when diagnosed during the first year or during the childhood has respectively a 50% or 15% rate of deformity disappearance or improvement as shown by Humphreys and Jaretzki [START_REF] Humphreys | Pectus excavatum. Late results with and without operation[END_REF]. In addition, early surgical chest wall repair bears the increased risk of latter recurrence [START_REF] Haller | Concomitant mitral valve replacement and re-re-repair of severe pectus deformity correction in a patient with Marfan syndrome[END_REF] or occasionally restrictive chest wall deformity [START_REF] Jaroszewski | Operative management of acquired thoracic dystrophy in adults after open pectus excavatum repair[END_REF]. Last, the current orthopedic treatments are very efficient in this patients' population [START_REF] Wurtz | Simplified open repair for anterior chest wall deformities. Analysis of results in 205 patients[END_REF]. On the basis of the above, we believe that concomitant surgery in infants and children may be better avoided and, if needed, pectus repair be delayed until the end of the second growth spurt.

In young patients with full body growth as well as adults with pectus deformities and congenital or acquired cardiomyopathies, the surgical strategy may differ. In this case no spontaneous improvement is expected [START_REF] Humphreys | Pectus excavatum. Late results with and without operation[END_REF] and concomitant cardiac surgery and pectus repair may be recommended. Concomitant surgery requires optimal operative exposure during cardiac procedure without any added bleeding risk. An optimal chest-wall stabilization in the postoperative period is also mandatory, usually by means of a device that enables eventual urgent postoperative reentry and cardiac resuscitation maneuvers [START_REF] Rousse | Staged repair of pectus excavatum during an aortic valve-sparing operation[END_REF]. Several authors have followed this approach with good postoperative results in coronary artery bypass grafting [START_REF] Pevni | Combined repair of pectus excavatum and coronary artery bypass grafting[END_REF], aortic root surgery [START_REF] Javangula | Combined severe pectus excavatum correction and aortic root replacement in Marfan's syndrome[END_REF] and acute type A aortic dissection [START_REF] Schwill | An alternative surgical approach for the combined treatment of pectus excavatum and acute aortic dissection type-A in Marfan syndrome[END_REF]. In addition, concomitant pectus repair may be recommended as it improves cardiovascular function by facilitating heart filling [START_REF] Neviere | Pectus excavatum repair improves respiratory pump efficacy and cardiovascular function at exercise[END_REF] and potentially improves postoperative outcome.

Our results support that the modified sequential Ravitch approach [2] is reliable and is not associated with major morbidity. Our Ravitchtype repair allowed treatment of all types of chest wall deformities with acceptable degrees of postoperative bleeding due to careful preservation of the pericondrial sheets, which protects the intercostal and internal thoracic arteries from damage. Moreover, the subperichondrial excision of the costal cartilages decreased the traction forces on the sternum resulting in a low postoperative risk of sternal dehiscence.

With respect to the surgical strategy, different techniques have been suggested for the PEx correction. Hasegawa and colleagues [START_REF] Hasegawa | Simultaneous repair of pectus excavatum and congenital heart disease over the past 30 years[END_REF] proposed an initial subperichondrial resection of the deformed costal cartilages followed by section of the deformed sternum in 2-3 points and then fixation of the sternum in elevated position using two Kirschner wires and a bridge external traction. They concluded that this technique permitted satisfactory simultaneous treatment of congenital heart disease and PEx deformities. However, as the Kirschner wires may present frequent displacements and the external traction seriously limits patient's recovery in the postoperative period, this technique may be inadequate for concomitant surgery. Subsequently, Okamura and colleagues [START_REF] Okamura | Simultaneous repair of pectus excavatum and congenital heart defect in adults by using the convex bar[END_REF] proposed the use of convex Nuss bars in concomitant surgery. Since, others have expressed the potential interest of the Nuss technique in this indication [START_REF] Sacco Casamassima | Modified Nuss procedure in concurrent repair of pectus excavatum and open heart surgery[END_REF][START_REF] Zoeller | Cardiopulmonary resuscitation in patients with a Nuss bar-a case report and review of the literature[END_REF]. However, the Nuss repair raises several issues. First, the curved bar used for chest wall stabilization impedes effective external cardiac compression during an eventual postoperative external cardiac massage [START_REF] Okay | Simultaneous open-heart surgery and pectus deformity correction[END_REF] or prompt reentry. Second, the Nuss procedure presents, in the setting of concomitant surgery via a mid sternotomy, a risk of sternal dehiscence from the pushing forces of the elastic bar to the anterior chest wall [START_REF] Bouchard | Catastrophic cardiac injuries encountered during the minimally invasive repair of pectus excavatum[END_REF]. Third, Bouchard and colleagues [START_REF] Bouchard | Catastrophic cardiac injuries encountered during the minimally invasive repair of pectus excavatum[END_REF] have shown that postoperative pericardial effusions following the Nuss procedure could lead to dense adhesions between the curved bar, the pericardium and the underlying heart, thus, increasing the risk of heart injury during the bar removal. Fourth, a history of cardiac surgery also strongly contraindicates the Nuss, because of pericardial/ myocardial adhesions the bar placement or removal is becoming a high risk procedure [START_REF] Haecker | Near-fatal bleeding after transmyocardial ventricle lesion during removal of the pectus bar after the Nuss procedure[END_REF]. It has also been shown that the Nuss bar negatively affects the blood flow in the internal thoracic arteries with almost 45% of the patients having artery obstruction or severe reduced blood flow in the postoperative period, and 67% after Nuss bar removal [START_REF] Yüksel | Do Nuss bars compromise the blood flow of the internal mammary arteries? Interact[END_REF][START_REF] Külcü | Patency of the internal mammary arteries after removal of the Nuss bar: an initial report[END_REF]. Since the internal thoracic arteries are widely used for coronary bypass grafting, these findings raise an issue for the surgical treatment of coronary disease. Finally, in elderly patients with acquired cardiomyopathies and pectus deformities the chest wall may be very rigid and might contraindicate the Nuss procedure.

For all the reasons above-mentioned the Nuss procedure may be unsuitable for concomitant or delayed cardiac surgery and pectus repair. A synthetic algorithm of our operative strategy is proposed in Fig. 1.

In conclusion, concomitant surgery is contraindicated before adolescence because pectus deformity may spontaneously disappear or recur after early sternal surgery. Alternatively, concomitant surgery is a reliable strategy in adolescents and adults, offering excellent longterm results. With respect to the pectus repair technique, the modified Ravitch technique may be more adequate as it can be used in all types of deformities and in concomitant surgery. It also provides optimal operative exposure during cardiac procedure, and allows easy postoperative reentry and resuscitation maneuvers if needed.

Fig. 1. Algorithm of our surgical strategy for concomitant cardiomyopathy and pectus deformity.

Table 1

 1 Demographics, clinical and operative characteristics.

	Patient no.	Age	Sex	Pectus	Haller	Marfan	Previous cardiotomy	Concomitant	Cardiac	Follow-up after pectus repair
				deformity	index			surgery	procedure	(months)
	1	14	F	PEx	7.1	+	-	+	T David	119
	2	37	M	PEx	5.9	+	-	+	T David + Arch	98
	3	22	M	PA	2.6	-	ASD	-	-	59
	4	23	M	PEx	2.9	-	-	+	Cor triatriatum	55
	5	29	M	PA	2.4	-	TOF	+	RVOTR	55
	6	24	M	PEx	2.9	-	TOF	+	RVOTR	54
	7	17	M	PEx	5.4	+	Transposition of great vessels	-	-	53
	8	36	M	PA	2.5	-	4	+	Bentall	46
	9	28	F	PEx	3.7	+	-	+	T David	43
	10	48	M	PEx	6.8	+	-	+	T David + Arch	32
	11	35	M	PEx	3.4	+	-	+	T David	16

M: Male; F: female; PEx: pectus excavatum; PA: pectus arcuatum; ASD: atrial septal defect; TOF: Tetralogy of Fallot; RVOTR: right ventricle outflow tract reconstruction.

Conflict of interest

The authors report no relationships that could be construed as a conflict of interest.