A B S T R A C TPyrolysis chars from wastes were investigated as sorbents for H 2 S removal from syngas. The H 2 S removal tests were performed at ambient temperature in various dry gas matrices (N 2 , Air, Syngas) to study the effect of the gas composition on the adsorption efficiency. Two chars were produced by the pyrolysis of: used wood pallets (UWP), and a 50/50% mixture of food waste (FW) and coagulation-flocculation sludge (CFS). The chars were functionalized by low-cost processes without chemicals: gas phase oxygenation and steam activation. Activated chars were the most efficient materials due to their large specific surface area, alkaline pH, basic O-containing groups and structural defects in graphene-like sheets. Raman analysis evidenced that inherent mineral species (especially Ca and Fe) increased the H 2 S removal efficiency by promoting the formation of metal sulfide and metal sulphate species at the char surface. Mesopores lower than 70 Å were revealed to be important adsorption sites. Under dry Syngas matrix, the chars remained efficient and selective toward H 2 S removal despite the presence of CO 2 , while O 2 in the Air matrix decreased their removal capacity due to the formation of sulfur acid species. The most efficient material was the steam activated char from FW/CFS, with a removal capacity of 65 mg H2S .g −1 under dry syngas. This char was proved to be completely regenerated with a thermal treatment under N 2 at 750°C. This study demonstrated that activated chars from food waste and sludge could be used as eco-friendly, affordable, and selective materials for syngas desulfurization even under dry atmosphere.

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International audienceSyngas from thermochemical conversion of waste or biomass is a renewable energy carrier that may contain pollutants – such as tar – that should be removed before further syngas utilisation. Chars have proved to be promising catalysts for tar cracking, but the influence of the physico-chemical properties on their reactivity is still unclear. This work aimed to better understand the structure and the composition of the mineral species of pyrolysis char, as well as their catalytic role in tar cracking. For this purpose, a characterisation of the minerals has been performed at bulk, surface (studied at micro and nano-scale) and crystallite scale. Pyrolysis chars were produced from wastes generated on cruise ships – namely used wood pallets (UWP), food waste (FW) and coagulation flocculation sludge (CFS) – having different mineral amount and content. Ethylbenzene was used as surrogate of light aromatic hydrocarbons in a tar cracking process. The results showed that ethylbenzene was converted into lighter gases meaning that the chars were efficient for this. Ethylbenzene conversion at 650 °C was found to be significantly higher with the char from a mixture of sludge and food waste (c.FW/CFS) compared to that of wood-based char (c.UWP): 71 wt.% against 45 wt.%, respectively. The combination of multi-scale and complementary techniques has highlighted that the higher catalytic activity of this char was mainly attributed to the mineral content. Well dispersed mineral particles with various morphologies and natures were observed on the surface of c.FW/CFS using Scanning and Transmission Electron Microscopy (SEM and TEM). Especially, Ca, Al and P were the main mineral species identified using XRFS and SEM. These mineral species in form of oxides and hydroxyapatite were considered to be the main active mineral components for tar cracking. Oxides were identified using EDX-analysis. XRD analysis highlighted the presence of crystalised particles of hydroxyapatite (Ca5(PO4)3(OH)), while Raman spectroscopy revealed that these particles were embedded in the carbon matrix

This paper aims at studying the catalytic activity of waste-derived chars for the reforming of a tar compound (ethylbenzene), and to identify the relationships between the modification process, the physicochemical properties and their resulting catalytic behaviour. Two chars were produced by pyrolysis: (1) used wood pallets (UWP), and (2) a mixture of food waste (FW) and coagulation-flocculation sludge (CFS) from wastewater treatment plant. Two chemical-free modification processes were separately applied to the pyrolysis chars: a gas phase oxygenation at 280°C, or a steam activation at 850°C. At 650°C, the ethylbenzene conversion due to thermal cracking was significantly increased by the catalytic activity of the chars (from 37.2 up to 85.8%). Ethylbenzene was decomposed into six molecules: hydrogen, carbon dioxide, ethylene, benzene, styrene, and toluene. Cracking, oxidative dehydrogenation, and hydrogenolysis reactions were involved in the decomposition mechanism of ethylbenzene. The catalytic efficiency of the char was also discussed based on the energy transferred from tar to syngas during tar cracking reactions. The characterization, performed with SEM, XRD, Raman, XRF, BET and TPD-μGC, evidenced that the presence of mineral species in the metallic form strongly increased the syngas production and quality by catalysing aromatic-ring opening reactions and Boudouard reaction. The oxidation of mineral species, occurring during the oxygenation process, decreased the char efficiency, while rising S BET increased the syngas production for UWP-based chars. This study demonstrated that waste-based chars were efficient catalysts to convert the lost energy contained in tar into useful syngas, thus increasing simultaneously the syngas yield and quality.

, et al.. Separation of particles from syngas at high-temperatures with an electrostatic precipitator. Separation and Purification Technology, Elsevier, 2012, 92, pp.181 -190. 10 The study, which is submit to you, was supported by the French National Agency and it is incorporated in the EPURGAZ project (ANR-06-BIOE-O05). The aim of this project was to study the different existing possible way to clean syngas from biomass gasification at high temperatures (> 500°C). This project was realized in partnership with the French Institute of Petrol (IFP -Lyon), the French Atomic Energy Commission (CEA -Grenoble), Air Liquid (Loges en Josas) and the Savoie University.This study shown the possibility to use an electrostatic precipitator at temperatures above 500°C to remove the particles contained in syngas from biomass gasification. Indeed, the filtration efficiency obtained during the filtration tests conducted at the CEA site in Grenoble, FRANCE, were greater than 95%.I submit you only 2 reviewers because I did not find an others :  The possibility of removing the particles from syngas at high temperature with an electrostatic precipitator (>500°C) was studied. Syngas filtration tests conducted directly downstream of a gasifier. Two filtration tests were realized : the first at a temperature of 510°C and the second at 680°C. For each filtration tests, an average mass filtration efficiency greater than 95% was obtained. Grenoble Cedex 9, FRANCE Abstract-The synthesis gas stemming from biomass gasification contains particles (ashes, soot, etc.), which, if not removed, can induce severe operational damage. The problem is more serious if syngas must be used for chemical synthesis as in the Fischer-Tropsch catalyst reaction or the water-gas shift. The particles contained in syngas can reduce or inhibit the catalyst effect. Moreover, for energy reasons, it is also necessary to develop a filtration process at as high a temperature as possible. To address this issue, a study to show the possibility of removing the particles from syngas with an electrostatic precipitator at high temperature (500-1000°C) and pressure (0.1-1 MPa) was conducted. Syngas filtration tests conducted directly downstream of a gasifier demonstrated the feasibility of implementing an electrostatic precipitator to clean syngas at temperatures above 500°C.

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• Waste-derived char was used as catalyst for tar cracking at different temperatures. • Chars from food waste and sludge are more efficient than wood-based chars. • Char deactivation was due to coke deposition and minerals melting/sintering. • Deactivation mechanism depends on the physicochemical properties of the chars.

This study aims at understanding the structural changes occurring in the carbonaceous matrix of wood-based chars during their thermal conversion. Although chars are routinely characterized by porosity measurements or scanning electron microscopy, the composition and structure of the carbonaceous matrix is often not investigated. Here, advanced characterization using X-ray synchrotron microtomography, transmission electron microscopy, Raman spectroscopy and X-ray diffraction provided a precise description of the char properties, allowing for an accurate discussion of their catalytic properties. Two chars were produced by slow pyrolysis of wood waste (400 and 700°C) and a third one was fabricated by activation under steam at 850°C of the char obtained at 700°C. The results show that the pyrolysis temperature and the activation performed did not affect the macrostructure of the chars and that the pores were interconnected at the macroscopic scale. However, at 700°C, the micro-and nanostructures were modified: short-range organized graphene fringes were observed. The activated char showed a homogeneous microstructure similar to that of its precursor. Besides, the ratio of graphene-like structures, the local organization of graphene sheets, and the imperfections in graphene-like sheets were clearly improved by the post-treatment. To our knowledge, this is the first time that such an approach, combining various tools, is applied for the study of pyrolysis chars.