Ugo Pelay

Catherine Azzaro-Pantel

Yilin Fan

Lingai Luo
email: lingai.luo@univ-nantes.fr

Life Cycle Assessment of Thermochemical Energy Storage Integration Concepts for a Concentrating Solar Power Plant

Keywords: Concentrating Solar Power (CSP), Life Cycle Assessment (LCA), Thermal Energy Storage (TES), Thermochemical, Environmental impact, Midpoint categories

This paper presents an original life cycle assessment (LCA) of a concentrating solar power (CSP) plant with thermochemical energy storage (TCES). The studied CSP plant is a hypothetic solar tower plant with a Rankine power cycle, and the TCES material used is calcium hydroxide. Based on three proposed TCES integration concepts, detailed sizing and the associated emission inventory are performed for four main groups that constitute the CSP plant, including the solar field, the solar tower, the storage system and the power cycle. Various midpoint impact categories are evaluated using the IMPACT 2002+ method embedded in the SimaPro 7.3 software. A sensitivity analysis is performed to identify the most influencing elements of the CSP plant on the environmental impacts. LCA results show that the CSP plant with different TCES integration alternatives has comparable global warming potential (~11 kg CO2.eq/MWh) and energy payback time (~4 months). The additional environmental burden due to the addition of the TCES system is relatively small (about 30%). The use of calcium hydroxide for the TCES has noticeable midpoint impacts on the respiratory inorganics, the terrestrial ecotoxicity and the mineral extraction. Solar field group (heliostat mirrors) is generally the most sensitive and environmental impacting factor of the CSP installation. The Turbine integration concept has the smallest environmental impacts among the three concepts proposed.

Novelty & significance

The present study seeks to fill the research gap by providing, for the first time, an LCA of the CSP plant with TCES integration. The contributions of this paper are important because it will expand the limited literature and provide additional information on the environmental impacts of CSP plants with TES, especially with TCES. The results obtained may be used to assist in the decision-making process in evaluating and selecting appropriate TES technologies and integration concepts for future CSP plants from the life cycle point of view.

Introduction

The global energy demand and the energy-related CO2 emission are estimated to increase by 30% and 15%, respectively, between 2017 and 2040 [1]. Clean energy technologies using renewable energy sources have experienced remarkable growth in recent years to meet the growing energy needs, to reduce the air pollution and to limit the global warming. As one of the typical low-carbon technologies, the Concentrating Solar Power (CSP) is expected to play a more and more important role for an "electrifying future", owing to its relatively high efficiency, low operating cost and good scale-up potential [START_REF] Del Río | An overview of drivers and barriers to concentrated solar power in the European Union[END_REF]. The total installed capacity of CSP globally was around 5.5 GW at the end of the year 2018, increased by a factor of 4.2 compared to that in 2010 [START_REF] Irena | Renewable Power Generation Costs in 2018[END_REF]. The global weighted average levelized cost of energy (LCOE) of CSP in 2018 was 0.185 USD/kWh, 26% lower than in 2017 and 46% lower than in 2010 [START_REF] Irena | Renewable Power Generation Costs in 2018[END_REF].

CSP technology, when equipped with thermal energy storage (TES) systems, could allow for the shifted electricity production to the periods when it is most needed or valuable. The option of lowcost TES can thus improve the adaptability and dispatchability of the CSP plants, which is considered as central to its cost-effectiveness and competitiveness. TES systems seem indispensable for the future more powerful CSP plants still under construction or planned all over the world [START_REF]Renewables 2018, Global Status Report (GSR)[END_REF][START_REF] Pelay | Thermal energy storage systems for concentrated solar power plants[END_REF].

The vast majority of TES systems in CSP plants are based on sensible heat storage (mostly molten salts), for their reliability, low cost and a large amount of feedback obtained [START_REF] Pelay | Thermal energy storage systems for concentrated solar power plants[END_REF][START_REF] Pelay | Technical data for concentrated solar power plants in operation, under construction and in project[END_REF]. However, their low energy density results in significantly increased equipment sizes for high storage capacities, making them less competitive for large-scale powerful CSP plants. Latent heat-based TES technology using Phase Change Materials (PCMs) is also proposed for their higher storage capacity compared to sensible heat technology and almost constant charging or discharging temperature [START_REF] Chirino | Generalized diagrams of energy storage efficiency for latent heat thermal storage system in concentrated solar power plant[END_REF]. Nevertheless, additional enhancement measures are usually needed to augment their limited thermal conductivity.

Over the last decade, growing interests have been focused on the thermochemical energy storage (TCES) technology which is mainly based on reversible endothermic/exothermic chemical reactions involving a large amount of reaction heat. The TCES technology using suitable materials could have the highest energy storage density, thus seems very promising in future CSP plants [START_REF] Pelay | Thermal energy storage systems for concentrated solar power plants[END_REF]. Abundant literature is available on the selection, development and properties characterization of various TCES material candidates, as reviewed in the works [START_REF] Dizaji | A review of material screening in pure and mixed-metal oxide thermochemical energy storage (TCES) systems for concentrated solar power (CSP) applications[END_REF][START_REF] Liu | Review on concentrating solar power plants and new developments in high temperature thermal energy storage technologies[END_REF]. The latest advances are made on the enhancement of mass transfer during combination and also the enhancement of heat transfer during decomposition [START_REF] Aydin | The latest advancements on thermochemical heat storage systems[END_REF]. Many researchers worked on the design and test of proper TCES reactors as described in the work [START_REF] Zsembinszki | Review of reactors with potential use in thermochemical energy storage in concentrated solar power plants[END_REF]. Recently, great efforts have also been devoted to the integration issue, which is the appropriate coupling of the TCES system with the power generating cycle of the CSP plant [START_REF] Cabeza | Thermochemical energy storage by consecutive reactions for higher efficient concentrated solar power plants (CSP): Proof of concept[END_REF][START_REF] Ortiz | Power cycles integration in concentrated solar power plants with energy storage based on calcium looping[END_REF].

Meanwhile, the environmental impacts of CSP plants as well as their associated TES systems need to be estimated, for the purpose of comparing different power production technologies and design alternatives. Hence the Life Cycle Assessment (LCA) has been introduced, which is recognized as a holistic and standard method for quantifying environmental impacts of a product or a process from "the cradle to the grave", allowing comparisons in a standardized way [START_REF] Salvador | Life cycle assessment of electricity from biogas: A systematic literature review[END_REF][START_REF]Life cycle greenhouse gas emissions from concentrating solar power[END_REF]. This method provides a structured analysis of inputs and outputs covering the whole life-cycle within a generic environmental evaluation framework [START_REF] Tukker | Life cycle assessment as a tool in environmental impact assessment[END_REF]. A great number of LCA studies on the environmental profiles of CSP plants have been reported in the last decade, as has been synthesized in a recent state-of-the art review by Lamnatou and Chemisana [START_REF] Lamnatou | Concentrating solar systems: Life Cycle Assessment (LCA) and environmental issues[END_REF]. CSP plants (together with low-cost TES) generally present Global Warming Potential (GWP) of less than 40 g CO2eq/kWh and Energy Payback Time (EPBT) less than 1 year [START_REF] Lamnatou | Concentrating solar systems: Life Cycle Assessment (LCA) and environmental issues[END_REF], indicating significantly reduced environmental impacts compared to conventional power plants based on fossil sources [START_REF] Kharecha | Options for near-term phaseout of CO2Emissions from coal use in the united states[END_REF][START_REF] Klein | Multi-criteria decision analysis of concentrated solar power with thermal energy storage and dry cooling[END_REF].

Relatively fewer LCA works in the literature include or focus on the TES materials/systems for CSP plants. In terms of TES materials, it has been reported that the environmental impacts could be reduced by switching from synthetic molten salts to mined salts [START_REF] Burkhardt | Life cycle assessment of a parabolic trough concentrating solar power plant and the impacts of key design alternatives[END_REF][START_REF] Whitaker | Life cycle assessment of a power tower concentrating solar plant and the impacts of key design alternatives[END_REF], to recycled industrial ceramics [START_REF] Lalau | Comparative LCA between current and alternative waste-based TES for CSP[END_REF] or to concrete [START_REF] Laing | Economic analysis and Life Cycle Assessment of concrete thermal energy storage for parabolic trough power plants[END_REF]. AISI 347H seems better than INCONEL 617 for being used as the containment material for molten salts [START_REF] Mayo | Comparative environmental assessment of two materials suited to central tower CSP technology[END_REF]. In terms of integration concept, commonly used two-tank (molten salt) sensible TES concept is recommended to be substituted by single-tank thermocline concept [START_REF] Burkhardt | Life cycle assessment of a parabolic trough concentrating solar power plant and the impacts of key design alternatives[END_REF][START_REF] Whitaker | Life cycle assessment of a power tower concentrating solar plant and the impacts of key design alternatives[END_REF] or by passive concept (a tubular heat exchanger integrated into storage (concrete) materials [START_REF] Laing | Economic analysis and Life Cycle Assessment of concrete thermal energy storage for parabolic trough power plants[END_REF]. Few LCA studies involve the latent TES, with the notable exception of [START_REF] Oró | Comparative life cycle assessment of thermal energy storage systems for solar power plants[END_REF]. In their study, three TES systems have been compared including (i) molten salts sensible system (two-tank);

(ii) concrete sensible system (passive tubular exchanger) and (iii) PCM latent system (passive finnedpipes module). LCA results show that the molten salt system presents the highest global environmental impacts followed by the PCM system, and the concrete system is the most environmental friendly. Nevertheless, the ranking may be different for different scenarios [START_REF] Oró | Comparative life cycle assessment of thermal energy storage systems for solar power plants[END_REF].

The above literature survey highlights that more investigations about the TES on the environmental profile of the whole CSP plant are needed, as concluded in [START_REF] Lamnatou | Concentrating solar systems: Life Cycle Assessment (LCA) and environmental issues[END_REF]. Moreover, there is a need for the adoption of midpoint and endpoint approaches (e.g., IMPACT 2002+) as useful supplement for some frequently-used indicators such as GWP, embodied energy and EPBT [START_REF] Lamnatou | Concentrating solar systems: Life Cycle Assessment (LCA) and environmental issues[END_REF].

Further investigation is particularly needed for the TCES technology which seems pretty promising, but also the most complicated one with a large variety of TCES materials, reactor designs and integration concepts proposed. Nevertheless, to the best of the authors' knowledge, no LCA study involving TCES systems in CSP plants has been reported in the open literature.

Previously a conceptual study on the coupling of the TCES system with the Rankine cycle of a hypothetic solar power tower (SPT) plant has been reported [START_REF] Pelay | Integration of a thermochemical energy storage system in a Rankine cycle driven by concentrating solar power: Energy and exergy analyses[END_REF]. Based on the three proposed integration concepts, the present study seeks to fill the research gap by providing, for the first time, an LCA of the CSP plant with TCES integration. The main objectives of this paper are then threefold:

(1) to compare the environmental performance of three proposed TCES integration alternatives for the SPT plant; (2) to provide more information for CSP systems based on various midpoints categories by adopting the IMPACT 2002+ method; and (3) to evaluate and compare the environmental impacts of four main groups constituting the CSP plant (e.g., solar field, solar tower, TES unit and power cycle), so as to identify the most influencing and sensitive factors. This paper will then contribute to expand the limited literature and to provide additional insights on the environmental impacts of CSP plants with TES, especially with TCES. The results obtained may be used to assist in the decision-making process in evaluating and selecting appropriate TES technologies and integration concepts for future CSP plants from the life cycle point of view.

Reference SPT plant and TCES integration concepts

This section recapitulates the reference SPT plant (without TES) as well as the three integration concepts. Note that for each concept, the components of the whole installation are divided into four groups [START_REF] Oró | Comparative life cycle assessment of thermal energy storage systems for solar power plants[END_REF], including the Rankine group (power cycle), the TCES group, the solar field group (heliostats, concentrators) and the solar tower group, as marked by different colors in Fig. 1. The reason for this categorization is to evaluate their separate environmental impacts and to make a proper comparison. The reaction couple is CaO/Ca(OH)2, which is found to be a pertinent TCES material for high-temperature use [START_REF] Pelay | Thermal energy storage systems for concentrated solar power plants[END_REF], including good reversibility, atmospheric operating pressure, low material cost, environment-friendly and abundant experimental feedback.

Reference SPT plant without TES (Ref. Case)

The reference case studied is a 100 MWel SPT plant (schematically shown in Fig. A1 of the supplemental material). The solar field group is comprised of heliostats while the solar tower group is mainly composed of the tower and the central solar receiver at the top. The conventional regenerative Rankine cycle includes a steam generator, a turbine, a condenser, an open feedwater heater and pumps. The TES group is not included in this reference SPT plant.

Thermal integration (Thermal Int.)

The Thermal Int. concept is shown in Fig. 1(a). The additional TCES group includes a TCES reactor, a water reservoir, a second condenser and two heat exchangers. During the charging stage (endothermic reaction), Ca(OH)2 salts in the TCES reactor are decomposed into CaO and water vapor at 500 °C (1 bar). The water vapor is partially condensed in the heat exchanger 1 to preheat the working fluid of the power circuit, then completely condensed in the condenser 2 and stored as the saturated liquid (100 °C, 1 bar) in the separate water reservoir. During the discharging stage, the liquid water in the reservoir is firstly heated up and vaporized by the steam extracted from the turbine of the principal Rankine circuit via the heat exchanger 2. The saturated vapor (100 °C, 1 bar) enters then into the TCES reactor and reacts with the CaO reactive salts for heat release. The TCES reactor serves as the steam generator to run the power cycle steadily. The power circuit and the TCES group are thermally coupled with each other but without direct mass contact or exchange.

Mass integration (Mass Int.)

The Mass Int. concept is shown in Fig. 1(b). Compared to the Ref. Case, a TCES group is added including a TCES reactor, a second condenser, a throttle valve, a third pump and two heat exchangers.

Different from the Thermal Int. concept, the Rankine power cycle and the TCES circuit are coupled and share the same working fluid with mass exchange. The water vapor generated in the TCES reactor during the charging stage is stored as saturated water (41 °C, 0.008 MPa) in the common water reservoir. During the discharging stage, the stored liquid water is pressurized by pump 3 and then evaporated into saturated vapor (100 °C, 0.1 MPa) by high temperature extracted steam via the heat exchanger 2. The exothermic reaction between the saturated vapor and the CaO salts in the TCES reactor provides needed heat to run the Rankine cycle.

Turbine integration (Turbine Int.)

The Turbine Int. concept is schematically shown in Fig. 1(c). The TCES group is composed of a TCES reactor, a second turbine, a second condenser, a third pump, a water reservoir and a heat exchanger. During the charging stage, high temperature water vapor (500 °C, 1 bar) from the TCES reactor passes through the turbine 2 to valorize a part of its thermal energy as power production. It will finally be stored as sub-saturated water (41.5 °C, 0.1 MPa) in a water reservoir. The discharging stage is the same as that of the Thermal Int.

Methodology

LCA is a standardized, mature, systems-oriented analytical tool assessing potential impacts of products or services using a life cycle perspective [START_REF] Kim | Life cycle assessment for a solar energy system based on reuse components for developing countries[END_REF]. LCA involves the definition of goal and scope, inventory analysis, impact assessment and interpretation, following the general guidelines described in ISO 14040 (Principles and Framework) and ISO14044 (Requirements and Guidelines).

Method and indicators

Different LCA methods and environmental indicators have been used for CSP plants, as summarized in [START_REF] Lamnatou | Concentrating solar systems: Life Cycle Assessment (LCA) and environmental issues[END_REF]. This study is based on the IMPACT (IMPact Assessment of Chemical Toxics) 2002+ embedded in the SimaPro 7.3 software. IMPACT 2002+ is actually an adapted impact assessment method by proposing a feasible implementation of a combined midpoint/damage approach linking the environmental evaluation results of the inventory flow list via 15 midpoint categories (e.g., global warming potential, human toxicity, respiratory inorganics, non-renewable energy used, etc.), which can then be regrouped into four damage categories (human health, ecosystem quality, climate change, resources) [START_REF] Jolliet | IMPACT 2002+: A new life cycle impact assessment methodology[END_REF]. In fact, the midpoint/damage approach performs environmental impact assessment of a process at relatively early stages in the cause-effect chain (midpoint categories) and as far back as possible in the cause-effect chain (damages categories) [START_REF] Perez-Gallardo | Ecodesign of photovoltaic grid-connected systems[END_REF].

Compared to the assessment performed with "endpoint" methods, the midpoint methods lead to more accurate results [START_REF] Welz | Environmental impacts of lighting technologies -Life cycle assessment and sensitivity analysis[END_REF]. All midpoint scores expressed in different units (of a reference substance) can be normalized into "eco-point", by introducing some weighting factors. This normalized score (ecopoint) permits then an easy comparison of different midpoint categories. Specifically for power plants, the GWP (kg CO2.eq/MWh) and the EPBT will be discussed in more detail, the latter refers to the time required to recover primary energy consumption throughout its life cycle by its own energy production, defined as: 𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸 = Total primary energy required throughout the life cycle Annual primary energy generated

(1)

Functional unit and assessment boundary

The functional unit quantifies the performance requirements of the CSP plant, providing a reference for all the design alternatives (TCES integration concepts). This LCA study is based on a constant production rate of 100 MWel of the principal Rankine cycle and a 25 year-lifetime.

The assessment boundary is shown in Fig. 2. The extraction and processing of materials are taken into account. Regarding CSP plant maintenance during its operation, only the mirror cleaning of the heliostats is considered. Transport is taken into account as if the materials had been transported to the Switzerland, close to the France where the hypothetical CSP plant is located. Note that the dismantling and the disposal of the CSP plant were not addressed due to the lack of industrial feedbacks, rendering this study a "cradle-to-gate" approach.

Sizing and emissions inventory

Conventional components libraries (e.g. Ecoinvent, LCA Food DK, USA Input Output Database) are not adequate for the power plant with such a high production rate. The proper sizing and estimation of the materials used for every individual component are thereby necessary. Note that the component selection and sizing are based on the results of energy analysis reported in [START_REF] Pelay | Integration of a thermochemical energy storage system in a Rankine cycle driven by concentrating solar power: Energy and exergy analyses[END_REF].

Solar field

The solar field is composed of heliostats reflecting and focusing solar rays on the high temperature solar receiver. Its sizing depends on the needed energy to run the Rankine cycle (QSG,C) and to charge the TCES reactor (QR,C) as well as the Direct Normal Irradiance (DNI) of the plant site.

𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻 𝐻𝐻𝑠𝑠𝑠𝑠𝑠𝑠𝐻𝐻𝑠𝑠𝐻𝐻 𝐻𝐻𝑠𝑠𝐻𝐻𝐻𝐻 = 𝑄𝑄 𝑆𝑆𝑆𝑆,𝐶𝐶 +𝑄𝑄 𝑅𝑅,𝐶𝐶 𝐷𝐷𝐷𝐷𝐷𝐷 (2)
Supposing an average DNI of 700 W.m -2 (for Themis power plant located in the eastern Pyrenees, France), the estimated mirror surface area (Sm) is 388930 m 2 for the reference case, 920228 m 2 for the Thermal Int. concept, 943001 m 2 for the Mass Int. concept and 842918 m 2 for the Turbine Int. concept, respectively.

Heliostats are mainly composed of metal and mirrors. Their emissions are due to materials extraction, transformation, shaping and maintenance. Heliostat maintenance by mirrors washing plays an important role because the mirror reflectivity decreases when it is getting dirty. The washing frequency depends on the environment condition and economic policy. Generally, a cleanout every two weeks is economically advantageous [START_REF] Bradshaw | Final Test and Evaluation Results from the Solar Two Project[END_REF]. In addition, the water must be demineralized to prevent the fouling and transported by trucks to be sprayed on the mirrors.

Several studies have been performed on the LCA of heliostats [START_REF] Heath | Life Cycle Environmental Impacts Resulting from the Manufacture of the Heliostat Field for a Reference Power Tower Design in the United States[END_REF][START_REF] Kuenlin | Life cycle assessment and environomic optimization of concentrating solar thermal power plants[END_REF]. Supposing that the heliostats used in this conceptual study are similar to those of Gemasolar (mirror of 120 m²) [START_REF] Kuenlin | Life cycle assessment and environomic optimization of concentrating solar thermal power plants[END_REF] and that the washing frequency is the same (every two weeks during 25 years), identical emissions per square meter seem to be reasonable. Table 1 lists the emission inventory for 1 m² of heliostat.

Solar tower & receiver

The height of the solar tower has been sized following the quick sizing rules determined by [START_REF] Falcone | A handbook for solar central receiver design[END_REF].

Heliostats density (dH) is defined as the ratio of the mirrors surface to the ground surface, generally varying between 0.2 and 0.25. The height of the solar tower (TH) could then be determined as a function of the mirror surface areas (Sm), following Eq. 3 [START_REF] Falcone | A handbook for solar central receiver design[END_REF].

𝐸𝐸𝐻𝐻 = � 4×𝑆𝑆 𝑚𝑚 80.4375×𝜋𝜋×𝑑𝑑 𝐻𝐻 (m) (3)
The TH=195 m [START_REF]Concentrating solar power projects[END_REF]). Hence, a height of 250 m has been chosen for the SPT plant in this study.

The emissions of the solar tower are due to the materials extraction, transformation and shaping.

No exchanges are considered to occur between the solar receiver and the outside during the life of the plant. Based on the estimation of Kuelin et al. [START_REF] Kuenlin | Life cycle assessment and environomic optimization of concentrating solar thermal power plants[END_REF], a proportional rule has been adopted to determine the emissions of the current hypothetical solar tower, as listed in Table 2.

Rankine power cycle

Similar components are involved in the Rankine cycle group of the three TCES integration concepts as well as the reference plant. However, their power and operational conditions vary. Hence, each component has to be selected and sized based on its critical operation point, e.g., the one that requires the largest volume and the transfer surface area. The sizing of various heat exchangers (including evaporators and condensers) is based on the shell-and-tube concept [START_REF] Kuppan | Heat Exchanger Design Handbook[END_REF]. Carbon steel, cheaper and less polluting than stainless steel, was chosen whenever possible. Pumps and turbines were sized based on the reference [START_REF] Pei | Gas Turbine Technical Data[END_REF]. Additional assumptions as follows were made for the estimation: (i) concrete supports were neglected; (ii) water and steam pipes connecting components were neglected; and (iii) water contained in the Rankine cycle was neglected. The sensitivity of these assumptions will be evaluated later to show whether they will have a significant impact.

The mass amount required for various Rankine power cycle components is gathered in Table A1 of the supplemental material. The emissions are due to the materials extraction and transformation.

No exchange is considered to occur between the Rankine cycle group and the outside during the life of the plant. Table 3 lists the Rankine cycle emissions for different integration concepts.

TCES group

The TCES reactor as the major component of the TCES group is designed based on the concept of a plate-type heat exchanger composed of CaO, expanded natural graphite (ENG) and stainless steel. The mass of reactive salts (mCaO) is following the energy analysis, with 20% overestimation of the masses needed. The mass of ENG is supposed to represent about 10% of the mass of CaO. The total volume of the composites (Vcomp) can be calculated by Eq. ( 4):

𝑉𝑉 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = (1-𝜏𝜏).𝑐𝑐 𝐶𝐶𝐶𝐶𝐶𝐶 𝜏𝜏×𝜌𝜌 � 𝐸𝐸𝐸𝐸𝑆𝑆 (4)
𝜏𝜏 = 𝑚𝑚 𝐶𝐶𝐶𝐶𝐶𝐶 𝑚𝑚 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 � (5)
Where 𝜌𝜌 � 𝐸𝐸𝐷𝐷𝐸𝐸 (kg•m -3 ) is the bulk density of ENG. By fixing the dimensions of composite plate (6 m in length, 1 m in width and 3 mm in thickness), it is then possible to determine the number of composite plates (ncomp), which equals to the number of stainless steel heat exchanger plates (nHEP).

𝑛𝑛 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = 𝑛𝑛 𝐻𝐻𝐸𝐸𝐻𝐻 = 𝑉𝑉 𝐶𝐶𝐶𝐶𝑚𝑚𝐶𝐶 𝑙𝑙 𝑐𝑐𝐶𝐶𝑚𝑚𝐶𝐶 ×𝑤𝑤 𝑐𝑐𝐶𝐶𝑚𝑚𝐶𝐶 ×𝑡𝑡 𝑐𝑐𝐶𝐶𝑚𝑚𝐶𝐶 (6)
Assuming that the envelope, the diffusers and the internal connections account for 10% of the total mass of the plate-type heat exchanger (mHEP), the required total mass of stainless steel is:

𝑚𝑚 𝐻𝐻𝐸𝐸𝐻𝐻 = 𝑛𝑛 𝐻𝐻𝐸𝐸𝐻𝐻 × (𝐻𝐻 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 × 𝑤𝑤 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 × 𝐻𝐻 𝐻𝐻𝐸𝐸𝐻𝐻 ) × 𝜌𝜌 𝑠𝑠𝑠𝑠 × (1 + 10%) (7)
Where tHEP and ρss are the thickness of each heat exchanger plate (2 mm) and the density of the stainless steel (7.8×10 3 kg•m -3 ), respectively. The sizing and mass estimation of other components of the TCES group (e.g., heat exchangers, turbine, pump, etc.) follow the same procedure as presented for the Rankine power cycle. The mass required for various components of the TCES group is listed in Table A2 of the supplemental material.

The emissions of the TCES components are due to the materials extraction and transformation.

No exchange is considered to occur between the thermal storage and the outside during the lifetime of the CSP plant. Table 4 lists the TCES group emissions for different integration concepts.

Results and discussion

Comparison of the TCES integration concepts: normalized midpoint impacts

Figure 3 shows a comparison on various normalized midpoint categories for different TCES integration concepts in the SPT plant. It can be observed that among various midpoint categories, the SPT plant (with or without TCES) has significant impact on respiratory inorganics, global warming and non-renewable energy; noticeable impact on carcinogens, non-carcinogens and terrestrial ecotoxicity and negligible impact on the rest categories. The normalized midpoint impacts of three TCES integration concepts are close in each category.

Among them, the Turbine Int. has the least impact followed by the Thermal Int. and the Mass Int.

This ranking is in accordance with the results of energy and exergy analyses presented in [START_REF] Pelay | Integration of a thermochemical energy storage system in a Rankine cycle driven by concentrating solar power: Energy and exergy analyses[END_REF]. The Ref. Case without TCES shows smaller environmental impacts than other concepts with TCES, particularly in the respiratory inorganics category. The absence of TCES materials (e.g., calcium hydroxide) and a smaller solar field (heliostat mirrors) may explain this difference.

Comparison of the components share: midpoint impact

Figure 4 shows the contribution of the four groups for the 15 midpoint impact categories. The three integration concepts has similar contribution for each midpoint category. The slight difference is due to the use and the sizing of relevant components for different SPT plant concepts. While the combined contribution of the solar field and the TCES groups to the total midpoint impact is dominant in each category, the impacts of solar tower and Rankine power cycle groups are negligible. For the respiratory inorganics, the terrestrial ecotoxicity and the mineral extraction, the impacts from TCES group are dominant due to the involvement of CaO/Ca(OH)2. For the rest 12 categories, the solar field group is the most impacting factor.

GWP and EPBT

Figure 5 shows a comparison on the GWP (kg CO2.eq/MWh) for different TCES integration concepts, as well as the contribution of each components' group. The solar field group is the most impacting factor (≈75 %) on GWP, followed by the TCES group. The solar tower and the Rankine power cycle groups represent a negligible contribution (≈3 %). Regarding the TCES integration concepts, the Turbine Int. has the lowest GWP impact (10.64 kg CO2.eq/MWh), followed by the Thermal Int. (11.27 kg CO2.eq/MWh) and the Mass Int. (11.59 kg CO2.eq/MWh). This difference is mainly due to the different sizes of the solar field. Compared to the Ref. Case without storage (8.39 kg CO2.eq/MWh), the GWP increase due to the TCES integration is about 6%. This moderate increase can be attributed to the higher daily power production rate owing to the TCES integration. Table 5 lists the EPBT for the CSP plant with different TCES integration concepts; the Ref. Case is also included for comparison. Among the three concepts with TCES integration, the Turbine Int.

has the shortest EPBT (120 days) followed by the Thermal Int. (127 days) and the Mass Int. (130 days). The EPBT for the Ref. Case without storage is about 90 days, 30 days shorter than that for Turbine Int. For all these cases, the ratio of EPBT to a 25 years lifetime is really small (<1.5%). The choice of a wet instead of a dry cooling condenser may decrease the GWP from 28 kg CO2.eq /MWh to 24 kg CO2.eq/MWh [START_REF] Burkhardt | Life cycle assessment of a parabolic trough concentrating solar power plant and the impacts of key design alternatives[END_REF]. The use of mined salts as the HTF instead of synthetic salts can reduce the GWP by 38% (24 kgCO2.eq/MWh against 39 kgCO2.eq/MWh) [START_REF] Burkhardt | Life cycle assessment of a parabolic trough concentrating solar power plant and the impacts of key design alternatives[END_REF]. This part has been neglected in the current study. Furthermore, the choice of TES materials strongly influences the GWP value [START_REF] Nahhas | Life cycle assessment of air-rock packed bed storage system and its comparison with other available storage technologies for concentrating solar power plants[END_REF]: a Thermocline/Mullite system leads to 17 kg CO2.eq/MWh vs. 2 kg CO2.eq/MWh for a Thermocline/basalt system. In the current case, the use of CaO/Ca(OH)2 as the storage material reduces the impacts on GWP compared to other storage materials such as liquid salts or ceramics.

Finally, a natural gas backup system can increase the GWP impact by about 10% [START_REF] Whitaker | Life cycle assessment of a power tower concentrating solar plant and the impacts of key design alternatives[END_REF]. The absence of a backup system in the TCES integration concepts contributes to a lower environmental impact. In future studies, these simplified factors may have to be considered to render a more detailed analysis.

Sensitivity analysis

The sensitivity analysis aims at evaluating the possible variation of the concerned indicators (e.g., GWP, non-renewable energy) when some parameters are varied from their designed values.

This kind of analysis is useful since some parameters and quantities are estimated with assumptions and approximations at the design stage. The most influencing factors identified have then to be determined with the greatest precision so as to minimize the uncertainties of the LCA. In contrast for less influencing parameters, the estimation could be more or less approximate.

The sensitivity analysis performed in this study is mono parametric "one-at-a-time" approach.

Each input value xi is individually modified around a relative variation Δxi/xi. The value of the impact Ij for xi enables to calculate the variation ΔIj and the relative impact variation ΔIj/Ij. The sensitivity indicator (S) is defined as the ratio of the relative variation of the output quantity to the input value:

𝑆𝑆 = Δ𝐷𝐷 𝑗𝑗 /𝐷𝐷 𝑗𝑗 Δ𝑥𝑥 𝑖𝑖 /𝑥𝑥 𝑖𝑖 (8)
A relative variation (Δxi/xi) of 20 % was applied individually to each component in this study. It may be observed from Fig. 6 that the solar field group is the most sensitive group of the CSP installation. A small variation in its sizing or in its emissions inventory will result in a significant uncertainty in the calculation of the overall environmental impacts. The TCES group, less sensitive than the solar field, remains as the element that should be carefully designed and sized (especially for the TCES reactor). The solar tower and the Rankine power cycle groups are relatively insensitive elements. Some approximate values of their masses may not affect much the results of the LCA.

Conclusion and perspectives

This paper presents an original comparative study of the environmental impacts of a CSP plant with the TCES integration. The LCA is performed using the IMPACT2002+ method. Based on the analysis results obtained, the following main conclusions could be reached:

• The SPT plant with different TCES integration alternatives has the same level of GWP (~11 kg CO2.eq/MWh) and EPBT (~4 months). Compared to the reference plant without storage (8.5 kg CO2.eq/MWh; 3 months), the additional environmental impact due to the TCES system is relatively small (~30%). This is mainly because of more than 65% higher daily power production rate owing to the TCES integration (higher dispatchability).

• The use of CaO/Ca(OH)2 in the TCES system results in noticeable influences on the respiratory inorganics, the terrestrial ecotoxicity and the mineral extraction categories.

• Solar field group (heliostat mirrors) is generally the most sensitive and environmental impacting group of the CSP installation while the solar tower and the Rankine power cycle groups are relatively insensitive and less impacting elements.

• Among the three integration concepts proposed, the Turbine Int. has the smallest environmental impacts followed by the Thermal Int. and then the Mass Int.

The main limitations of this study are as follows.

• The results obtained pertain to the specific hypothetical TCES integration concepts in the SPT plant employed here, since no such plant is actually in operation. The sizing and mass estimation may not be so precise.

• The definition of the assessment boundary are simplified (e.g., round-the-clock operation all through the year, neglecting site improvement activities, HTFs, foundations and disposal phase, etc.). Some environmental impacts may have been underestimated.

Additional LCA research is thus necessary to confirm the results and tendency reported here, by adopting more realistic estimations and precise sizing of the components based on real operational experiences and feedback. In parallel, the dynamic simulation of the whole installation under real conditions is the ongoing work, providing updated data for alternative energy production scenarios.

Finally, multi-objective optimization under energetic, economic and environmental considerations for multiple criteria decision making is the future direction.

Figure 1 .

 1 Figure 1. Schematic view of the CSP with TCES integration. (a) Thermal Int. concept; (b) Mass Int. concept; (c) Turbine Int. concept. Adapted from [26].

Figure 2 .

 2 Figure 2. Definition of the assessment boundary.

Sm=1052480 m 2 ;

 2 estimated solar tower height is thus (240-270 m) for the Thermal Int., (244-273 m) for the Mass Int., (231-258 m) for the Turbine Int. and (157-175 m) for the Ref. Case, respectively. The height has the same order of magnitude as those of existing solar plants having comparable heliostats surface areas (e.g., Atacama-1 (Chile): Sm=1484000 m 2 ; TH=243 m; Ashalim Plot B (Israel): TH=250 m; Crescent Dunes Solar Energy Project (United-States): Sm=1197148 m 2 ;

Figure 3 .

 3 Figure 3. Comparison on normalized midpoint impacts for different TCES integration concepts.

Figure 4 .

 4 Figure 4. Proportion of midpoint impacts from different component groups. (a) Thermal Int.; (b) Mass Int.; (c) Turbine Int.

Figure 5 .

 5 Figure 5. Global warming potential for different TCES integration concepts.

Figure 6 .

 6 Figure 6. Sensitivity analysis results. (a) GWP; (b) Non-renewable energy

Table 1 . Emissions inventory for 1 m 2 of heliostat [33]. Quantity Library Name Heliostat

 1

	Mirror	10 kg	Ecoinvent Flat glass coated, RER
	Steel structure	35.22 kg Ecoinvent Reinforcing steel, RER
	Steel structure building	35.22 kg Ecoinvent Steel product manufacturing, RER
	Concrete foundations	0.026 m 3 Ecoinvent Concrete, sole plate and foundation, CH
	Concrete foundations building 0.026 m 3 Ecoinvent Excavation, hydraulic digger, RER
	Maintenance
	Demineralized water	550.31 kg Ecoinvent Water, deionized, CH

Table 2 . List of the solar tower & receiver emissions for the CSP plant in this study.

 2

		Quantity	Library	Name
	Stainless steel structure	10696 kg Ecoinvent Chromium steel 18/8, RER
	Stainless steel structure	10696 kg Ecoinvent Chromium steel product manufact.,
	manufacturing		RER
	Cold pipes	6714 kg	Ecoinvent Reinforcing steel, RER
	Cold pipes manufacturing	6714 kg	Ecoinvent Steel product manufact., RER

Table 3 . Rankine power cycle emissions inventory.

 3

	Material	Library	Name	Thermal	Mass	Turbine	Ref.
				Int.	Int.	Int.	Case

Table 4 . TCES group emission inventory.

 4

	Material	Library	Name	Thermal	Mass	Turbine	Ref.
				Int.	Int.	Int.	Case
	Stainless	Ecoinvent	Chromium steel	11643100 11844100 11944100	0
	steel (kg)		18/8, at plant/RER S
	Carbon steel	Ecoinvent Steel, low-alloyed, at	685000	685000	267000	0
	(kg)		plant/RER U
	ENG (kg)	Ecoinvent	Graphite, at	1235700	1289000	1289000	0
			plant/RER U
	Ca(OH)2	Ecoinvent	Lime, hydrated,	14697000 15327000 15327000	0
	(kg)		packed, at plant/CH
			U

Table 5 . Energy payback time (EPBT) for different TCES integration concepts.

 5 EPBT≈1 year[START_REF] Lamnatou | Concentrating solar systems: Life Cycle Assessment (LCA) and environmental issues[END_REF]). Besides various simplifications made for the assessment boundary (i.e., excluding the impacts of site improvement activities, foundations and piping accessories), several design choices can further explain the lower GWP and EPBT values.

		Thermal Int. Mass Int. Turbine Int. Ref. Case
	EPBT (days)	127	130	120	90
	Ratio to a 25 years lifetime (%)	1.39	1.42	1.31	0.99
	Comparison with other CSP LCA studies
	Compared to other LCA results reported in the literature, the values of GWP (about 11 kg
	CO2.eq/MWh) and EPBT (about 4 months) obtained in this study are within the same order of
	magnitude as those obtained for different electricity production technologies [38] and for CSP plants
	(GWP<40 kgCO2.eq/MWh;

Acknowledgement

This work is supported by the French ANR within the project In-STORES (ANR-12-SEED-0008).

Literature Citation


W Jbali

W Selmi

L Jouffret

R Marzouki

M F Zid

Synthesis, crystal structure, spectroscopic study and Hirshfeld surface analysis of [Ni(C6H8N2)3]Cl2.2(H2O) (1)

Keywords: Nickel (II) organic-inorganic materials, Crystal structure, Hirshfeld surface, XRD, Hydrogen bonds

The title compound, [Ni(C6H8N2)3]Cl2.2(H2O), was synthesized by slow evaporation method at room temperature. The structural study by X-ray diffraction indicate that this compound crystallize in the triclinic system, P-1 space group with a=10.222(2) Å, b=10.757(2) Å, c=11.441(3) Å, α=114.30(4)°, β=99.43(3)° and γ=93.01(3)°. The structure is formed by the cation [Ni(C6H8N2)3] 2+ , tow chloride anions and two molecules water of crystallization. The nickel (II) atom is coordinated to six nitrogen donors from three neutral 2-AMP ligands, adopting a slightly distorted octahedral geometry. The crystal structure is stabilized by strong hydrogen bonds of N-H…Cl, O-H…Cl, C-H…Cl and π-π interactions to obtained three-dimensional network. The newly prepared compound was characterized by XRD, Infrared, UV-Vis spectroscopy and Hirshfeld surface (3D-HS) analysis. Vibrational analysis of the compound was realized by infrared spectroscopy. The optical properties of the crystal were studied using optical absorption UVvisible spectroscopy which confirmed the semiconducting properties by revealing a direct optical band. Hirshfeld Surface projections and Fingerprint plots were elucidated the relative contribution of the H…Cl, C…H, C…C, C...N, H…O intermolecular contacts in the crystal.

Introduction

Crystal engineering in recent years is the most area of research developed, which study the new solids materials establish by the intermolecular attractions with specific structural topology design and applications [START_REF] Nangia | Supramolecular chemistry and crystal engineering[END_REF].The surge in the field of supramolecular chemistry is due to the several capacities which offered in the fields of biological and materials sciences. The easy manipulation of their assemblage process and prospective applications has been involved tremendous attention to supramolecular systems for many years, not only in the field of chemistry but also physics, materials and biological sciences, making this field a true interdisciplinary domain of research [START_REF] Pradeep | Coordination and supramolecular aspects of the metal complexes of chiral Nsalicyl-β-amino alcohol Schiff base ligands: Towards understanding the roles of weak interactions in their catalytic reactions[END_REF].

Complexation of transition metals with 2-(aminomethyl)pyridine (2-AMP) in aqueous solutions has been extensively studied [START_REF] Yang | Structural insights into the coordination and selective extraction of copper(II) by tertiary amine ligands derived from 2-aminomethylpyridine[END_REF]. As a ligand the tow amino-methyl-pyridines can function as bridging as well as chelating [START_REF] Sunkari | Chain of dimers to assembly of trimers: temperature and ligand influenced formation of novel supramolecular assemblies of Cu(II) with isomeric (aminomethyl) pyridines and azide[END_REF]. Recently much more attention has been paid to the study of complexes formed by 2-aminopyridine with metal ions which have good magnetic properties, biological activity, and structural diversity. These complexes can serve as pro-drugs such as antitumor, antibacterial and anticancer agents [START_REF] Abbas | Preparation, Diagnosis, Biological Activity, and Theoretical Studies of Some Mixed Drug Complexes[END_REF]. The bi-functional organic amine 2-aminomethylpyridine include a pyridine ring and an aliphatic amine group is an excellent choice as an organicinorganic synthesis model. It is used in large-scale industrial applications [START_REF] Dan | Low-Temperature Heat Capacities and Standard Molar Enthalpy of Formation of Dichloro Bis(2-aminopyridine) Zinc (II), ZnCl2(C5H6N2)2[END_REF], it is also used for analytical chemistry and medical detection [START_REF] Okamato | High-sensitivity detection and postsource decay of 2-aminopyridine-derivatized oligosaccharides with matrix-assisted laser desorption/ionization mass spectrometry[END_REF]. In addition, some metal-pyridine coordination compounds have been explored for the design of novel nonlinear optical materials [START_REF] Bella | Zinc(II) as a Versatile Template for Efficient Dipolar and Octupolar Second-Order Nonlinear Optical Molecular Materials[END_REF].

In our paper, we report the synthesis of new coordination compound of nickel(II) with 2-AMP.

The structure [Ni(C6H8N2)3]Cl2.2(H2O) was determined by X-ray diffraction, identified by IR spectroscopy and the Tauc plot method was also applied to determine the optical band gap from UV-Vis diffuse reflectance spectroscopy. The intermolecular contacts in the crystal were investigated by Hirshfeld surface (3D-HS) analysis.

Experimental

Materials and measurements

All reagents and solvents were obtained from commercial sources and used without further purification, 2-(aminomethyl)pyridine (2-AMP) was obtained from Aldrich chemical. To gain more information on the crystal structure, a vibrational study was undertaken. The absorption spectroscopy FT-IR was measured in the 500-4000 cm -1 range, by KBr pellet technique on a Bruker FT-IR spectrophotometer. The UV-visible spectrum of title compound was measured with Ellice SLe164 Double BEAM at room temperature in the range from 200 to 800 nm. The sample was measured with the PANalytical Empyrean powder diffractometer equipped with a focusing mirror and a PIXCel3D detector.

Synthesis of [Ni(C6H8N2)3]Cl2.2H2O

The coordination compound [Ni(C6H8N2)3]Cl2.2H2O was prepared by mixing nickel(II) chloride hexahydrate (NiCl2.6H2O) (0.237g) and 2-amino-methylpyridine (C6H8N2) (1.049 g/mL) (purity 99 %) in water. The resulting solution was well stirred than kept at room temperature. After three weeks, pink-violet crystals were formed. The slow evaporation allows the obtention of very highquality crystals of [Ni(C6H8N2)3]Cl2.2H2O. A single crystal suitable for X-ray diffraction analysis was selected and studied. The elemental analysis for [Ni(C6H8N2)3]Cl2.2H2O is : %C=44.12 , %H=5.76 , %N=17.15 , %Cl=14.47 , %O=6.53, %Ni=11.98.

Crystallographic studies

A crystal of size (0.56x0.490.28 mm 3 ) was selected for the structural analysis diffraction data which collected at 298 K with Enraf-Nonius CAD4 automatic four-circle equipped with graphite monochromator using Mo Kα radiation (λ = 0.71073 Å) [START_REF] Sun | Z)-5-(4-Fluoro-benzyl--idene)-1,3-thia-zolidine-2,4dione. Enraf Nonius[END_REF].

The hydrogen atoms bonded to the carbon atoms of the aromatic ring were placed by geometric calculation, C-H = 0.93 Å, N-H = 0.85 Å. At this stage, an absorption correction by psi-scan [START_REF] North | A semi-empirical method of absorption correction[END_REF] was performed (Tmin= 0.882, Tmax= 1.000). In addition, the refinement of the anisotropic parameters leads to confidence factors of the order of R(F 2 ) = 4% and wR(F 2 ) = 11.2%.

The results of the crystallographic data, the data collection conditions and the refinement of the [Ni(C6H8N2)3]Cl2.2H2O structure are presented in Table 1.

The graphical illustrations of the structure were made using the CIF file, using the Diamond 3.0 program [START_REF] Brandenburg | Version 3.2e, Crystal Impact GbR[END_REF].

CIF file having complete information about the structure of dichlorotris(2aminomethylpyridine)nickel(II) dihydrate, was deposited in the Cambridge Crystallographic Data Center (1896844). The file is freely available upon request from the following web site: http://www.ccdc.cam.ac.uk/data_request/cif.

Hirshfeld surface analysis

Analysis of intermolecular interactions via Hirshfeld Surface-based tools is a major advance in enabling supramolecular chemist to clarify the intermolecular interactions and to understand the role of the organic base in structural propagation. The Hirshfeld surfaces [START_REF] Parkin | Comparing entire crystal structures: structural genetic fingerprinting[END_REF] and their relative 2D fingerprint plots [START_REF] Spackman | Fingerprinting intermolecular interactions in molecular crystals[END_REF] were drawn using CrystalExplorer 3.1 [START_REF] Wang | Three New Compounds Derived from Nitrofurantoin: X-Ray Structures and Hirshfeld Surface Analyses[END_REF]. The quantifying and decoding of the intermolecular contacts in the crystal packing are visualized using dnorm (normalized contact distance) and 2D fingerprint plots were di (inside) and de (outside) represent the distances to the Hirshfeld surface from the nuclei, with respect to the relative van der Waals radii. The dnorm values were mapped into the Hirshfeld surface using a red; white, blue color scheme as follows: closer contacts and the negative dnorm value represents the red regions; contacts around the van der Waals separation represents the white areas , the longer contacts and the positive dnorm value represents the blue regions.

[ -x+1, -y+1, -z+1 ], ii [ x, y+1, z ], iii [ -x+1, -y, -z+1 ], iv [ -x+2, -y, -z+1 ], v [ -x+2, -y+1, -z+1 ], vi [ -x+1, -y+1, -z+2 ], vii [ x, y-1, z ], viii [ -x+1, -y, -z+1 ].
As it shown clearly from Fig. 5, the two neighboring anti-parallel organic cations are linked together through the aromatic-aromatic interactions with

The experimental XRPD pattern

The XRPD pattern of the compound have been analyzed to confirm the homogeneity of the synthesized material and the result was correlated with the powder pattern obtained from the single crystal XRD data simulation Fig. 6. The experimental XRPD pattern corroborate well with the corresponding powder pattern simulated from single crystal data and prove the purity phase of the bulk product. Phase purity was further confirmed by comparing the unit cell parameter obtained from single crystal XRD data and the same calculated from XRPD data.

Hirshfeld surface calculations

In addition to the structural investigation of the title compound, the Hirshfeld Surfaces has been illustrated. The 3D-HS surface of the studied complex is showed in Fig. 7. The volume of contact surface is equal to 552.14 Å 3 , with a contact area of 450.87 Å 2 . The two-dimensional fingerprint plots (2D-FP) showing the distinct kinds of intermolecular contacts are represented in Figure 8. The 2D-FP of Cl…H/H…Cl (21.1%) (Fig. 8a) and the O…H/H…O contacts have contributed in the 2D-FP with a minor percentage equal to 7.4% (Fig. 8b). The C…H/H…C (14.8%) (Fig. 8c) contact appear as a symmetric spike form which confirms the presences of π-π interactions equal to 3.930 Å. As well, the H…H contacts appear in the middle of the scattered points in the 2D-FP with 54.9% of the total surface (Fig. 8d). This higher percentage of contribution is due to the higher proportion of hydrogen in the aromatic Ligand and the easy interactions between hydrogens atoms of the aminomethylpyridine of one molecule with the neighboring molecule. The results discussed above have the most significant contribution to the total Hirshfeld surface, but the analysis shows the existence of other weak intermolecular contacts which contributes to the vander vals interactions.

3.4.Spectroscopy IR

Infrared Spectroscopy technique was used to identify the functional groups of the crystal structure.

3.5.Optical properties

The optical properties were studied by measuring the diffuse reflectance. The UV-vis spectrum is realized on solid-state sample at room temperature (Fig. 11). The absorption spectrum of dichlorotris(2-aminomethylpyridine)nickel(II) dihydrate is consist by two bands. The strongest band appear in the 200-300 nm region, is primarily due to ligand to ligand charge transfer (LLCT) attributed to transition states of 2-AMP, the absorption band observed at 268 nm describe the small contribution from metal to ligand charge transfer (MLCT) [START_REF] Amamou | Crystal structure, vibrational and magnetic properties of the monohydrated cobalt (II) complex with 1-(4-Nitrophenyl)-1Himidazolium cation, (C9H8N3O2)2CoCl4.H2O[END_REF], whereas the reported values in literature are in the range of 200-400 nm which attributed to ligand to ligand charge transfer (LLCT) with a small contribution from metal to ligand charge transfer (MLCT) [START_REF] Sunkari | Chain of dimers to assembly of trimers: temperature and ligand influenced formation of novel supramolecular assemblies of Cu(II) with isomeric (aminomethyl) pyridines and azide[END_REF]. In addition, a weak band appear in the 500-800 nm region which can be attributed to the d-d transitions of metal transition [START_REF] Sunkari | Chain of dimers to assembly of trimers: temperature and ligand influenced formation of novel supramolecular assemblies of Cu(II) with isomeric (aminomethyl) pyridines and azide[END_REF]. The band gap energy determination depends on a linear part of the spectrum. This region of high absorption corresponds to the fundamental absorption (l < 300 nm), resulting from the inter band electronic transition. The gap energy can be defined as difference of energy between the lowest conduction band free of electrons and the highest valence band maximum filled with electrons that is related to the electric conductivity of the materials [START_REF] Hashim | Studying the influence of cobalt chloride on the optical properties of poly (vinyl alcohol) films[END_REF]. Using the Kubelka-Munk (K-M) [START_REF] Pradeep | Coordination and supramolecular aspects of the metal complexes of chiral Nsalicyl-β-amino alcohol Schiff base ligands: Towards understanding the roles of weak interactions in their catalytic reactions[END_REF] model and the Tauc methods (3) the band gap energy (Eg) of the compound can be determined.

The K-M method is expressed by the equation ( 2) [START_REF] Kubelka | Ion exchange recovery of palladium (II) from nitrate weak acidic solutions Tech[END_REF][START_REF] Hassen | Crystal structure, spectroscopic study, photoluminescent properties and DFT calculations of the 2-guanidinobenzimidazolium dichloride and dibromide monohydrate salts[END_REF][START_REF] Moussa | Structural study, vibrational and optical properties, Hirshfeld surface analysis and DFT investigation of a novel organic cation hexachloridostannate(IV), (C5H8N3)2[END_REF]: n: a constant that takes different values depending on the type of electronic transition, for an indirect allowed transition n is equal to 2, (plotted as (F(R) hυ) 1/2 versus E and n is equal to 1/2 for a direct allowed transition (plotted as (F(R) hυ) 2 versus E. The K-M method can be used as a standard model to determine the optical gap for organic-inorganic semiconductors [START_REF] Selmi | A comparative structural, spectroscopic, optical and photoluminescence studies by DFT of Fe(II) difluoro(oxalato)borate complex[END_REF].

𝐹(𝑅 𝑑 ) = (1-𝑅) 2 2𝑅 𝑑 , 𝐹 (
The Eg value was obtained by extrapolating the slope to (F(R) hυ) 𝑛 equal to zero. The direct and indirect transitions (Fig. 12) for the compound show a band gap values equal to 1.30 and 1.64 eV, respectively. As reported in the literature [START_REF] Mott | Electronic process in non-crystalline materials[END_REF], the lower optical band gap of the material is incredibly significant in applications of electronic and optoelectronic devices.

Conclusion

In summary, a novel coordination complex [Ni(C6H8N2)3]Cl2.2(H2O) formed by nickel with the 2aminopyridine ligand has been successfully synthesized at room temperature by slow evaporation.

This compound belongs to the triclinic system with the P-1 space group and characterized through

3. Results and discussion 3 . 1 .Fig. 1 .

 311 Fig. 1. The asymmetric unit of [Ni(C6H8N2)3]Cl2.2H2O.

Fig. 2 .

 2 Fig. 2. N-H…Cl interactions in the (001) plane in the structure of [Ni(C6H8N2)3]Cl2.2H2O.

Fig. 3 .Fig. 4 .

 34 Fig. 3. O-H…Cl; N-H…O interactions in the (100) plane in the structure of [Ni(C6H8N2)3]Cl2.2H2O.

3 .

 3 930Å distance between two pyridine rings and piled each other by turns in face to face. The two adjacent cationic dimers [Ni(C6H8N2)3] 2+ , ensure the cohesion of the crystal structure in the sub-network by the π-π interactions between the aromatic rings.

Fig. 5 .

 5 Fig. 5. The cycle stacking interaction.

Fig. 6 .

 6 Fig. 6. Experimental and calculated diffractograms of [Ni(C6H8N2)3]Cl2.2H2O.

Fig. 7 .

 7 Fig. 7. 3D Hirshfeld surface mapped over dnorm for visualizing the molecular interactions of the studied complex. The surface is shown as transparent to allow visualization of the orientation and conformation of the functional groups.

Fig. 8 .Fig. 9 .

 89 Fig. 8. 2D Fingerprint plots of the studied complex resolved into Cl…H/H…Cl (a), C…H/H…C (b), H…H (c), and O…H/H…O (d) contacts showing the percentages participations to the total Hirshfeld surface area.

  The infrared absorption spectrum of [Ni(C6H8N2)3]Cl2.2(H2O) is shown in Fig.10. In the IR spectrum intense absorption band of water-crystallization molecule is observed between 3420 and 3640 cm -1 . The typical stretching vibrations of NH2, NH, and CH2 are located between 2900 and 3300 cm -1 . The asymmetric and symmetric stretching mode of NH2 are found as very weak bands located respectively at 3326 and 3208 cm -1 . The elongation modes ʋ(C=C), ʋ(C=N), ʋ(C-C) and ʋ(C-N) of the organic unit are observed in the region of 1610-1171 cm -1 . The bands at 1290, 980, 880, 730,500 and 465 cm -1 are related to the vibration in the plane and out of the plane of elongation of C=N-C, C=C-C and C-C=N. The bands detected at 1303 and 1241 cm -1 in the infrared spectrum are attributed to the stretching modes of the C-NH2 bonds. The Ni-N stretching vibration is found at 620 cm -1 . These assigned absorption bands in the infrared spectrum of nickel complex are in agreement with previous complexes in the literature[START_REF] Yang | Structural insights into the coordination and selective extraction of copper(II) by tertiary amine ligands derived from 2-aminomethylpyridine[END_REF][START_REF] Sunkari | Chain of dimers to assembly of trimers: temperature and ligand influenced formation of novel supramolecular assemblies of Cu(II) with isomeric (aminomethyl) pyridines and azide[END_REF].

Fig. 10 .

 10 Fig. 10. Infrared spectrum of the [Ni(C6H8N2)3]Cl2.2(H2O) complex.

Fig. 11 .

 11 Fig. 11. Diffusion reflectance spectrum of dichlorotris(2-aminomethylpyridine)nickel(II) dihydrate at room temperature.

  reflectance of light a: absorption coefficient of light S: diffusion coefficient of light According the theory of Tauc and Abeles the optical band gap was determined using relation (3) (𝛼ℎ𝜐) 𝑥 = 𝐴(ℎ𝜐 -𝐸 𝑔 ) 𝑛 (3) α: absorption coefficient hυ: energy of the incident photon h: Planck's constant (J.s), υ: light frequency (s -1 ) A: absorption constant Eg: optical gap energy (eV)

Fig. 12 .

 12 Fig. 12. Tauc Plots of (F(R) hυ) 1/2 versus E (a) and (F(R) hυ) 2 versus E (b) of dichlorotris(2aminomethylpyridine)nickel(II) dihydrate.

  single-crystal X-ray diffraction, IR and UV-Vis diffuse reflectance spectroscopy. The crystal structure of dichlorotris(2-aminomethylpyridine)nickel(II) dihydrate is stabilized by N-H…Cl, O-H…Cl and N-H…O hydrogen bonds. Moreover, 2-amino-methlpyridine shows a π-π interaction adding extra stability to the three-dimensional architecture. Vibrational study has been carried out to identify the functional groups present in the crystal and the gap energy values equal to 1.30 and

Table 1 .

 1 Crystallographic and structure refinement data of [Ni(C6H8N2)3]Cl2.2H2O

	Crystal data

Table 3

 3

	D-H	d(D-H)	d(H..A)	<DHA	d(D..A)	A
	C7-H2	0.926	2.816	167.45	3.725	Cl2
	C7-H4 i	0.992	2.837	167.54	3.811	Cl2
	N5-H5	0.907	2.428	154.04	3.267	Cl2
	C14-H6	0.942	2.662	122.69	3.268	N1
	N5-H8 i	0.852	2.538	169.67	3.380	Cl1
	C8-H12 ii	1.004	2.853	151.16	3.763	Cl2
	N6-H13 iii	0.859	2.760	154.95	3.557	Cl2
	N6-H14	0.900	2.292	167.79	3.135	Ow1
	C15-H15 iv	0.942	2.559	139.36	3.485	Ow1
	C12-H16 v	1.024	2.756	119.17	3.595	Cl1
	C5-H17 vi	0.924	2.627	121.97	3.214	Ow2
	N4-H19	0..883	2.748	153.03	3.557	Cl1
	Ow1-H23	0.760	2.481	166.13	3.224	Cl2
	Ow1-H24 vii	0.886	2.437	166.37	3.304	Cl1
	N4-H26 viii	0.893	2.427	172.17	3.315	Cl2
	Ow2-H28	0.846	2.373	156.83	3.168	Cl2
	Symmetry codes : i

. Specified hydrogen bonds (Å) and angle (°) of [Ni(C6H8N2)3]Cl2.2H2O

Acknowledgment:

The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through General Research Project under grant number (G.R.P-235-41).

1.64 eV confirmed that this compound can be classified as semiconductor which can be used in electronic and optoelectronic applications.


MD Bastien Herlin
email: bastien.herlin@aphp.fr

MD Claude Adam

MD, PhD Marie-Odile Habert

MD Bertrand Mathon

MD Stéphane Clemenceau

MD, PhD Vincent Navarro

MD, PhD Sophie Dupont

Temporal pole epilepsy surgery -Sparing the hippocampus

Temporal pole epilepsy (TPE) is a poorly known and difficult to individualize subtype of temporal lobe epilepsy. Consequently, in drug-resistant TPE, there is still a debate on the need for a large surgical removal of the temporal pole and mesial temporal structures or a limited resection of the temporal pole. We reviewed all patients who underwent presurgical evaluation for drug-resistant epilepsy over a 17-year period, and report here 19 patients with proven drug-resistant temporal pole epilepsy who underwent a selective temporal pole resection with respect of mesial structures. Most (15) TPE patients exhibited seizures resembling mesio-temporal seizures, whereas the others exhibited nocturnal hyperkinetic seizures or an association of both seizure types. MRI revealed a temporal pole lesion in 58% of patients. Long-term postoperative outcome after a conservative surgery was excellent: 63% of patients were seizure-free (ILAE 1) at one-year post-surgery and 78% at 5 years.

These results show that TPE has no specific electroclinical features but is a distinct type of temporal lobe epilepsy allowing a conservative surgery. Respecting the mesio-temporal structures is a valid surgical approach for drug-resistant temporal pole epilepsy.

Introduction:

The involvement of the temporal pole has already been substantiated in mesial temporal lobe epilepsy (MTLE), as assessed by intracranial recording of MTLE patients showing early propagation of the epileptic discharge arising from the hippocampus to the temporal pole [START_REF] Abel | The role of the temporal pole in temporal lobe seizure networks: an intracranial electrode investigation[END_REF] , MRI temporal pole blurring frequently associated with hippocampal sclerosis (HS) 2 , and temporal pole hypometabolism frequently found in FDG-PET of MTLE patients with HS [START_REF] Fountas | Temporal pole proton preoperative magnetic resonance spectroscopy in patients undergoing surgery for mesial temporal sclerosis[END_REF] .

Nevertheless, little is known about seizures that arise directly from the temporal pole. Many questions remain: are temporal pole seizures clinically distinct from MTL seizures? Are there any specific symptoms related to an epileptic discharge located in the temporal pole, or are symptoms due to secondary involvement of adjacent structures? If a surgery is considered for drug-resistant temporal pole epilepsy (TPE), what kind of resection should be proposed: anterior temporal resection involving the temporal pole, amygdala and hippocampus, or focal resection restricted to the temporal pole? 7 To address these questions, we aimed to better characterize the electroclinical profiles of TPE patients and to demonstrate that TPE is a distinct subtype of TLE allowing a conservative surgical approach sparing the hippocampus. We therefore examined long-term postsurgical outcome of patients with drug-resistant TPE who underwent selective temporal pole resection.

Methods:

We selected all patients with drug-resistant TPE who underwent selective temporal pole resection between 2000 and 2017 at the Pitié-Salpêtrière Hospital (Paris, France) Epileptology Unit.

All patients underwent a standardized presurgical evaluation including a long-term video-EEG monitoring, a dedicated structural MRI and a neuropsychological assessment. All patients underwent the same imaging protocol on a 1.5T or 3T MRI depending on the year, including 3mm-thick coronal fluid-attenuated inversion recovery (FLAIR) and T2-weighted sequences, 3mm-thick axial T2 and T2* sequences, and volumetric pulse sequences (3DT1) reformatted in axial, sagittal and coronal planes.

If necessary, further examinations were performed to delineate the epileptogenic focus including FDG-PET, interictal-ictal SPECT, and intracranial EEG recording (sEEG).

All surgeries were done at the Pitié-Salpêtrière Hospital Neurosurgery Department. For the surgery, the patient is positioned supine, with the shoulder elevated, and the head turned about 75° contralaterally while being extended to make the zygomatic arch the highest point of the operative field. Scalp incision is a small curvilinear shape that starts at the superior border of the zygomatic arch just in front of the tragus, extends to the superior temporal line and anteriorly to the hairline. The temporalis muscle is incised via a curvilinear incision and retracted anteriorly. Two burr holes are placed on each side of the sphenoid wing. A small temporal craniotomy is fashioned to expose the superior and middle temporal gyri, and the sylvian fissure. The sphenoid wing is flattened with a rongeur to allow adequate exposure to the anterior part of the temporal pole. The dura is opened in a semicircular fashion and reflected over the temporalis muscle. Using an ultrasonic aspirator, a cortectomy is made about 3 cm from the temporal tip in the dominant hemisphere and 4 cm from the temporal tip in a non-dominant hemisphere. Identifying the temporal horn of the ventricle marked the medial extent of the resection. Intraoperative MRI or electrophysiology were not used.

Epilepsy surgery outcome was assessed using ILAE classification at 1, 3 and 5 years after surgery.

All the patients gave their informed consent to the use and publication of data related to their epilepsy at the time of video-EEG.

Results:

Clinical characteristics

Nineteen patients (15 males, 4 females) were identified. Demographic and clinical data are summarized in table 1. In most cases, TPE started during childhood (median age at first seizure: 13 years ± 8) and median age at surgery was 25 years ± 10. Preoperative average seizure frequency was 37 per month (min 1/month, max 150/month). All patients had antiepileptic drug polytherapy, ranging from 2 to 4 antiepileptic drugs (mean: 2.5 drugs).

Patients with TPE experienced different seizure types. 15 patients had seizures resembling mesio-temporal seizure, starting with rising epigastric sensation, déjà-vu, or feeling of fear, followed by loss of awareness and gestural or swallowing automatisms. Two patients had nocturnal hyperkinetic seizures and two patients had both diurnal MTLE-type seizures and nocturnal hyperkinetic seizures. 8 of 19 patients also had focal seizures evolving to bilateral tonic-clonic seizures.

Neuropsychological assessment was normal in 7 patients. 8 patients had episodic memory impairment compatible with the lateralization of their epilepsy (visual memory deficiency for patient with right-sided TPE, verbal memory deficiency for patient with left-sided TPE), and 4 patients had both visual and verbal episodic memory impairment. 8 patients also exhibited signs of frontal dysfunction (attention impairment, dysexecutive syndrome).

Imaging and electrophysiological characteristics

Brain MRI was performed at 1.5T in 2 patients and 3T in 17 patients. It showed a temporal pole lesion in 11 of 19 patients (Table 1).

Ten patients, including the 8 patients with normal MRI, had an FDG-PET. It showed a unilateral temporopolar hypometabolism in all patients, associated with an ipsilateral mesiotemporal hypometabolism in 3 patients and an orbitofrontal hypometabolism in 4 patients.

Ten patients had an interictal-ictal SPECT. It showed a predominant temporopolar hyperperfusion in 3 patients, and a more diffuse hyperperfusion pattern (ipsilateral temporopolar, mesiotemporal and orbitofrontal hyperperfusion) in 7 patients.

Examples of imaging finding are shown in figure 1.

Seven of 8 patients with a normal MRI had intracranial EEG recording, assessing that the seizure onset zone was located in the temporal pole. Clinical and electrophysiological data are summarized in Table 2. For all patients, the epileptic discharge spread to the ipsilateral hippocampus and amygdala during the first seconds after seizure onset. For two patients, it secondarily spread to the ipsilateral orbitofrontal cortex. Symptoms associated with an epileptic discharge strictly located to the temporal pole were indistinguishable from MTLE symptoms. Electrical stimulations on temporal pole electrodes (n=5 patients) elicited the same MTLE symptoms in three patients. Spreading to the ipsilateral hippocampus was associated with loss of awareness, while spreading to the orbitofrontal cortex was associated with motor manifestations.

Surgery outcome

Histopathological findings were consistent with imaging findings for the 11 MRI-positive patients. For the 8 MRI-negative patients, histopathological analyses showed slight cytoarchitectural alterations (neuronal heterotopia or non-specific gliosis) in 6 patients and no anomalies in 2.

Surgery outcome was assessed using ILAE classification at 1, 3 and 5 years after surgery (Figure 2). At 1 year after surgery, 12 patients (63%) were seizure-free (ILAE 1) and 2 patients (11%) had only auras with no other seizure (ILAE 2). The 5 remaining patients had at least 4 seizures per year with a 50% reduction of their baseline seizure frequency (ILAE 4).

Several patients had further improvement between the first and the third year after surgery. Therefore, at 3 years after surgery, 15 patients (79%) were classified ILAE 1, and only 2 were still ILAE 4.

At 5 years after surgery, one patient was lost during follow-up (he was ILAE 1 at 1 and 3 years). For the 18 remaining patients, 14 patients (78%) were classified as ILAE 1. Their antiepileptic medications were gradually decreased: at 5 years, 9 patients were on antiepileptic drug monotherapy and treatment was discontinued in 5 patients.

All patients had a neuropsychological assessment 1 year after surgery. It showed identical results in comparison with the pre-operative neuropsychological assessment in 13 patients, slight worsening of episodic memory in 4 patients (verbal episodic memory worsening after left TPE surgery in 3 patients, and visual episodic memory worsening after right TPE surgery in one patient), and improvement of executive functions in 2 patients.

Discussion:

Our study pointed two major findings: TPE has no specific electroclinical feature, and a conservative resection sparing the hippocampus is a viable surgical approach for drugresistant TPE.

Electroclinical features

Some previous studies reported that most TPE patients exhibited nocturnal hyperkinetic seizures [START_REF] Mai | Sleep-related hyperkinetic seizures: always a frontal onset?[END_REF]7,[START_REF] Vaugier | Neural networks underlying hyperkinetic seizures of "temporal lobe" origin[END_REF][START_REF] Wagner | Memory outcome after hippocampus sparing resections in the temporal lobe[END_REF] . In our study, nocturnal hyperkinetic seizures was found in 4 of 19 patients, i.e. 21%, which is higher than usually found in TLE (6% in Staack's cohort 7 ). Most of our patients had focal seizures with impaired awareness mimicking MTLE seizures. The only distinctive features of TPE compared with MTLE were the higher seizures frequency (37/month in TPE, vs 6/month in our MTLE cohort [START_REF] Mathon | Predictive factors of long-term outcomes of surgery for mesial temporal lobe epilepsy associated with hippocampal sclerosis[END_REF] ), and the absence of febrile seizure during childhood ( 0/19 TPE patients). TPE may thus mimic either MTLE or frontal lobe epilepsy, certainly depending of the preferential spreading of the epileptic discharge. A fast spreading to the ipsilateral mesio-temporal structures was found in all patients who underwent sEEG, which was associated with MTLE symptoms, and the nocturnal hyperkinetic seizures might be related to the spread to the frontal lobe. TPE is a rare subtype of temporal lobe epilepsy, accounting for only a small number of TLE patients: over the same period, in our centre, 308 patients had a surgery for drug-resistant MTLE [START_REF] Mai | Sleep-related hyperkinetic seizures: always a frontal onset?[END_REF] , including 214 associated with hippocampal sclerosis and 94 associated with other etiology (focal cortical dysplasia, DNET…). However, TPE is hard to identify and individualize.

In our cohort, MRI-negative TPE patients underwent sEEG with implantation scheme sampling the mesial temporal structure (hippocampus and amygdala), enabling us to assess that the seizures indeed started from the temporal pole and secondarily spread to the mesial temporal structure. On the other side, some MRI-negative patients might have been falsely identified as MTLE instead of TPE if we missed a temporal pole onset during sEEG due to an insufficient sampling of the temporal pole.

Surgical approach and postoperative outcome

Our study is the first one reporting postoperative outcome of patients with drug-resistant TPE after a conservative surgery sparing the mesial temporal structures. In the only other cohort of patients with temporal pole epilepsy, Wang et al [START_REF] Wang | Hypermotor seizures in patients with temporal pole lesions[END_REF] reported 8 patients who underwent a surgery, 6 of which had anterior temporal lobectomy including amygdalohippocampectomy, and only 2 had a conservative surgery.

The excellent surgical outcome in our cohort (79% patients ILAE I at 3 year after surgery and 78% at 5 years) is similar to the best results of MTLE surgery. In a 2015 Cochrane metaanalysis [START_REF] West | Surgery for epilepsy[END_REF] , 69% of patients were Engel class I (which approximately correspond to ILAE 1 and 2) at 1 year after temporal lobe surgery, and 74% in case of hippocampal sclerosis. In our previously published cohort of MTLE patients [START_REF] Mai | Sleep-related hyperkinetic seizures: always a frontal onset?[END_REF] , seizure outcome after surgery was classified Engel I in 83.7% patients at 8.7 years.

For the two patients classified ILAE 4 at 5 years, a missed mesiotemporal onset of the seizure might be considered, but they had both benefited from presurgical sEEG, sampling temporal pole, hippocampus and amygdala, that did assess an onset in the temporal pole. Another hypothesis might be a second epileptogenic focus not recorded during sEEG. The patients were proposed a second presurgical evaluation, but they declined it.

Temporal lobe resections sparing the hippocampus have a cognitive benefit compared with resections including the hippocampus, such as a benefit in verbal learning performance in resections within the dominant hemisphere [START_REF] Wagner | Memory outcome after hippocampus sparing resections in the temporal lobe[END_REF] , but they can still be associated with a decline in memory performances. Wagner et al [START_REF] Wagner | Effects of hippocampus-sparing resections in the temporal lobe: Hippocampal atrophy is associated with a decline in memory performance[END_REF] demonstrated that any resection within the temporal lobe might lead to a secondary hippocampal atrophy, and thus a memory decline. This could explain the slight worsening of episodic memory seen in 4 of our patients at one year post-surgery. Nevertheless, as the majority of our patients (13/19) did not show any neuropsychological worsening after surgery, we recommend to spare the hippocampus in temporal pole epilepsy.

Limitation of the study

The main limitation of our study is the lack of a comparative group. In our centre, we favoured the most conservative surgical approach, therefore no TPE patient underwent anterior temporal resection including the mesial structures.

Conclusion

TPE is a specific epileptic syndrome with electroclinical features resembling MTLE, except for a higher seizure frequency and the absence of febrile seizure during childhood. TPE must be differentiated from MTLE, and may require intracranial EEG in the absence of MRI lesion.

TPE is accessible to a conservative resective surgery, sparing the mesial temporal structures, with a good surgical outcome both in terms of seizure freedom and memory outcome.

Tables and figures:

Table 1

Figure 1 .Figure 2 .

 12 Figure 1. Example of preoperative assessment in an MRI-negative patient. A: FDG-PET

  . Summary of patient demographic, clinical and paraclinical data

	Gender	M : 15 / F : 4
		Febrile seizure during childhood: 0/19
		Prematurity: 2/19 (10.5 %)
	Epilepsy risk factor
		Familial history of epilepsy: 0/19
		Cranial trauma: 0/19
	Age at 1 st seizure: median (minimum-maximum), years	13 (3-33)
	Age at surgery: median (minimum-maximum), years	25 (17-50)
	Seizure frequency: median (minimum-maximum)	37/month (5/month -10/day)
	Epilepsy lateralisation	Left: 11 (58 %) / Right: 8 (42 %)
		Normal MRI: 8 /Temporal pole lesions: 11
		Cystic lesion: 3
	MRI findings	Cortical dysplasia: 3
		Tumoral lesion: 4
		Cerebral cavernous malformation: 1
		Homolateral temporal spikes: 19/19 (100 %)
	Interictal scalp EEG findings	Contralateral temporal spikes: 4/19 (21 %)
		Homolateral frontal spikes: 3/19 (16 %)
		Focal cortical dysplasia: 3
		DNET: 3
		Ganglioglioma: 2
		Dermoid cyst: 1
	Histopathology	Ependymal cyst: 1
		Arachnoïd cyst: 1
		Neuronal heterotopia: 2
		Gliosis: 4
		No anomaly: 2

Table 2 .

 2 Clinical and electrophysiological data during seizures and electrical stimulations for the 7 TPE patients who underwent sEEG.

	Patients	Seizure onset	Early spreading (1 to 10	Late spreading	Electrical stimulation
			seconds after seizure	(more than 10
			onset)	seconds after
				seizure onset)
	Patient 1	Anterior	Ipsilateral hippocampus	No late	Temporal pole
		temporopolar fast		spreading	stimulation: feeling of
		discharge			fear or joy
	Histology: heterotopia neuronal	No symptom	awareness fear, followed by loss of Feeling of anxiety and	NA	fear or joy stimulation: feeling of Hippocampus
	Patient 2	Mesial	Ipsilateral amygdala,	Ipsilateral	Temporal pole
		temporopolar fast	hippocampus, and mesial	orbitofrontal	stimulation: not
		discharge	temporo-basal cortex	cortex	practiced (technical
	Histology: gliosis	Gustatory hallucination,	Loss of awareness	Contralateral arm dystonia,	issue) Hippocampus
		memory recall		contralateral	stimulation: triggers an
				tonic head	amygdalo-hippocampal
				deviation	rhythmic discharge,
					associated with
					paleness and aphasia
	Patient 3	Basal	Ipsilateral hippocampus	Ipsilateral	Temporal pole
		temporopolar and		fronto-insular	stimulation: triggers a
		anterior		areas	focal seizure with the
	Histology:	temporopolar fast			same electrical pattern
	neuronal	discharge			and the same
	heterotopia	Tachycardia, feeling of	Loss of awareness	Shout, bilateral upper limbs	symptoms than spontaneous seizure
		« adrenaline		hyperkinetic	Hippocampus
		rush »		movements	stimulation: triggers an
					asymptomatic
					temporopolar fast
					discharge
	Patient 4	Anterior	Ipsilateral hippocampus,	No late	Not done
		temporopolar	then contralateral	spreading
		onset with fast	hippocampus
	Histology:	involvement
	no anomaly	(200ms) of
		ipsilateral
		temporo-basal
		cortex and

This work received support from the "Investissements d'avenir" program ANR-10-IAIHU-06, and from the Fondation Assistance Publique Hôpitaux de Paris (EPIRES -Marie Laure PLV Merchandising).