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The goal of this study is to assess the release of contaminants during the oxygen/steam gasification of two waste-derived fuels using three different bed materials. The solid recovered fuels (SRFs) were tested at 850 °C in a bench-scale fluidized-bed reactor with sand, dolomite, and olivine as bed materials. The effects of the experimental conditions were assessed based on the gasification performance (product yields, carbon conversion, etc.) and the presence of tar, including polycyclic aromatic hydrocarbons (PAHs) and minor contaminants (HCl, H2S, HCN, and NH3) in the producer gas. The results show higher gas yields with the use of catalysts, particularly dolomite, and a lower catalytic activity of olivine toward tar abatement. The presence of contaminant precursors (Cl, S, and N) together with the concentration of metals from both catalysts and waste fuel ashes appear to influence the evolution of contaminants. In general, dolomite is more efficient than olivine in reducing tar compounds and most minor contaminants but NH3, whereas olivine mainly exhibits the ability to reduce light PAHs and nitrogenous compounds (HCN and NH3) in the producer gas.

Almond shells are agricultural residues with a high content of xylan that are produced abundantly in some regions with a Mediterranean climate. We have studied the production of xylo-oligosaccharides from almond shells by autohydrolysis at 150−190 °C. The yield, composition, and molar mass distribution of the xylo-oligosaccharides were dependent on temperature and time:  the maximum yield of xylo-oligosaccharides increased from 42% at 150 °C and 300 min to 63% at 190 °C and 19 min, while their anhydroarabinose-to-anhydroxylose and acetyl-to-anhydroxylose mass ratios were 0.039 and 0.076 at 150 °C and 0.129 and 0.125 at 190 °C, respectively. Experimental data was used to fit the parameters of a kinetic model for xylan autohydrolysis, which describes the yields of the different reaction products and accounts for the changes in the chemical composition of xylan and xylo-oligosaccharides. The recovery of the xylo-oligosaccharides by spray drying was also evaluated. Spray drying of the autohydrolysis liquor obtained at 179 °C and 23 min gave a yield of nonvolatile products of 29.4 g/(100 g of dry almond shells). The composition of this product was 58.3% xylo-oligosaccharides, 2.4% xylose, 1.5% arabinose, 0.78% glucose, 0.27% HMF, 16% Klason-type lignin, 4.8% ash, and 14.9% nonidentified products, which probably included organic extractives and protein present in almond shells, and products formed by the degradation of carbohydrates.

Xylose-based oligosaccharides produced from xylan-rich hemicelluloses (xylo-oligomers) are carbohydrates with potential food and pharmaceutical uses. Autohydrolysis of lignocellulosic biomass is an efficient way to produce xylo-oligomers in a reasonable yield and a wide variety of compositions (anhydroarabinose/anhydroxylose and acetyl/anhydroxylose mass ratios). In this work, we develop a kinetic model for the autohydrolysis of xylan in lignocellulosic biomass that describes the yields of the different reaction products and explains the changes in the chemical composition of the xylo-oligomers due to reaction temperature and time. This model assumes that xylan is made up of three monomers (xylose, arabinose, and acetic acid) and that there are two xylan fractions with different compositions and reactivities toward hydrolysis. Both fractions are hydrolyzed to xylo-oligomers, which are hydrolyzed to xylose, arabinose, and acetic acid. Finally, monosaccharides dehydrate to furfural and degradation products. The model is validated with experimental data obtained for the autohydrolysis of corncobs in a batch reactor system at temperatures from 150 to 190 °C. The amount and composition of each xylan fraction, as well as the activation energies and frequency factors for all the reactions, are calculated from the experimental data. This model provides a satisfactory interpretation of the experimental data.

Vegetable oils and fats are a renewable resource derived from biomass that can contribute to reduce the net emission of CO2 into the atmosphere if used to produce hydrogen for fuel-cell-based energy systems. In this paper, we present the results of the steam reforming of several vegetable oils with three different nickel-based commercial catalysts (ICI 46-1, ICI 46-4, and UCI G90C) and two research catalysts (UdeS and HT). The experiments were performed in an isothermal fixed-bed tubular reactor at steam-to-carbon (S/C) ratios of 9, 6, and 3 and temperatures between 500 and 630 °C. High space velocities of 0.76−1.90 molcarbon/(gcat h) were used so that conversions of the feed would be incomplete. Hydrogen productions were from 0.3 to 7.5 molH2/(gNi h) depending on the operating conditions. The HT catalyst, which was prepared from a hydrotalcite-like precursor, seems promising for steam reforming vegetable oils because of its very high activity per gram of catalyst. Results for the steam reforming of sunflower, rapeseed, corn, and soybean oils at the same catalyst temperature and S/C ratio show that oil conversion to gases and hydrogen yields do not depend on the type of vegetable oil. This indicates that the process might be suitable for producing hydrogen from residual oils and fats from food processing, for which process economics are more favorable.

Autohydrolysis and dilute-acid hydrolysis were used as pretreatment methods to enhance the enzymatic digestibility of cellulose in two different lignocellulosic substrates, a softwood mixture and an agricultural residue of almond shells. The changes in the chemical composition of the softwood mixture during dilute-acid pretreatment were studied, and the results were grouped by using a severity parameter, KROH, which was derived from the kinetics of hemicellulose solubilization. The average degree of polymerization of the cellulose retained in the pretreated substrate, DPv, was investigated and its trend compared with that of almond shells. Cellulose DPv decreased for both the substrates from a value of 700 for the untreated lignocellulosic to around 200, which corresponds to the leveling-off degree of polymerization, as there is no significant variation in DPv when severity increases. Glucose yields after enzymatic saccharification of the pretreated substrates turned out to be higher for almond shells than for the softwood mixture, which had a very low susceptibility to enzymatic hydrolysis throughout the spectrum of experimental conditions investigated. At KROH = 15 000, the glucose yield for the softwood mixture is 44% of the potential fraction present in the pretreated pulp, while for almond shells the maximum yield surpasses 97% for KROH = 3. The different behavior between these lignocellulosic species is not caused by different degrees of cellulose depolymerization nor by the removal of different amounts of carbohydrates during pretreatments in equivalent conditions.