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.

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.

• 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 article investigates the gasification of Solid Recovered Fuels (SRFs). To better understand the influence of SRF composition on gasification efficiency and syngas quality, two industrial SRFs having different compositions were studied. A detailed SRF characterization was performed (elemental analysis; ash composition; LHV; fraction of biomass, non-biomass, and inert materials) to precisely describe the chemical complexity of such materials. The gasification tests were performed at pilot-scale in a bubbling fluidized bed using air as gasifying agent, and olivine as bed material. The separate contribution of gasification temperature (T=750-900°C) and equivalence ratio (ER=0.21-0.35) on the gasification efficiency was investigated by sequentially varying these two parameters. Gasification tests revealed that the LHV of the syngas and the cold gas efficiency decreased by 45-50% and by 20-30%, respectively, with rising equivalence ratio. These evolutions were attributed to syngas oxidation reactions which promoted the formation of CO2. Indeed, mass balances calculation revealed that the part of carbon atoms in syngas in the form of CO2 rises from 43 to 54% for SRF1, and from 35 to 50% for SRF2. High plastic content in SRF2 was responsible for the formation of stable light hydrocarbons (CH4, C2H4 and C6H6) from the decomposition of the plastic polymer chains, and to lower amount of H2 compared to syngas from biomass-rich SRF1. The carbon conversion decreased by 8% with rising ER from 0.21 to 0.30 for SRF2, as a result of plastics-biomass interactions promoting secondary reactions and leading to char formation. For both SRFs, rising temperature significantly improved the gasification efficiency whatever the SRF composition, and decreased the CO2 concentration. These evolutions were attributed to the promotion of several reactions, such as gasification, steam and dry reforming, Boudouard reaction, and Reverse Water-Gas Shift reaction.

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.

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The influence of the gasification temperature and Equivalence Ratio (ER) on the behavior of an industrial low-grade Solid Recovered Fuel (SRF) was investigated in an air bubbling fluidized bed. The studied SRF exhibits an intermediate composition between biomass-rich SRF and plastic-rich SRF. Its Lower Heating Value (14 MJ/kg) is low since its ash content is very high (35 wt.%). But surprisingly, the Cold Gas Efficiency and the Carbon Conversion were relatively high with this type of low-grade SRF. As a result, the syngas produced is quite rich (LHV > 8 MJ/m 3 STP) and it may be valorized in gas engines. H2S, HCl, HCN and NH3 in the syngas were analyzed. These results confirm that inorganic gases are an important issue for the valorization of SRF as fuel in gasification processes, even if significant parts of S, N and Cl are not converted into inorganic gases.