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Two series of six wet torrefaction tests were performed using a pressurized batch reactor in order to upgrade almond-tree pruning (a largely available agricultural waste in Mediterranean areas) as a fuel. The assayed maximum temperatures were in the range of 175–300 °C, held for either 10 or 60 min. Raw almond-tree pruning and wet-torrefied solid products were systematically characterized through a wide range of analytical procedures, such as bulk density, particle size, structural and elemental composition, ash content, heating values, moisture uptake, FTIR spectra and SEM micrographs. The effects of temperature and time on the wet torrefaction process of almond-tree pruning were simultaneously evaluated through the severity factor. Higher temperatures and longer holding times brought the fuel properties of wet-torrefied solid products closer to those of sub-bituminous coal. The most severe operating conditions (i.e., 300 °C held for 60 min, or a severity factor equal to 7.68) allowed achieving an energy densification ratio of 1.67. However, the optimal processing conditions in terms of energy yield, which were found at a severity factor of 5.78, led to 57.1 wt% solid yields, with a higher heating value of 24.0 MJ/kg and an energy densification ratio of 1.36.

This paper aims to study the compositions, energetic properties, combustion behaviours and pyrolysis kinetics of six tropical hardwoods species from which significant amounts of industrial lignocellulosic wastes are generated in West African countries. The composition of the biomass was studied by determining their percentages of biopolymers (cellulose, hemicelluloses and lignin) and applying FTIR analysis, proximate analysis and ultimate analysis. From the experimental data of the higher calorific value, equations based on the ultimate analysis have been selected since they allow estimating the parameter with a low Average Absolute Error (less than 5%). As regards the behaviour in combustion based in the comprehensive combustibility index (S), the best result was reached by Aucoumea klaineana (S = 3.50 × 10–6 min−2 °C−3), while the worst values were obtained by Alstonia boonei (S = 1.46 × 10–6 min−2 °C−3) and Pterocarpus soyauxii (S = 1.78 × 10–6 min−2 °C−3) which are, in addition, the biomasses with higher ash content. By the same token, Testulea gabonensis and Pterocarpus soyauxii were the species with the highest capacity to produce biochar through pyrolysis. With the mathematical modeling of pyrolysis, maximum activation energies were determined for cellulose (201.3–215.4 kJ/mol), intermediates for hemicellulose plus extractives (191.6–214.9 kJ/mol) and minimum for lignin (63.0–77.0 kJ/mol).

Endocarps of the olive fruit were subjected to short-time hydrothermal carbonization (SHTC) to study the effect of temperature and holding time on the properties of hydrochars. In general, the incr...

The effect of the H2SO4 concentration in the hydrolysis of sunflower-stalk waste, at 95oC and using a liquid/solid relation of 20, was studied. In a later stage, the hydrolysates were fermented at different temperatures with the aim of ethanol and xylitol production. A total conversion of the hemicellulose at the acid concentration of 0.5 mol/L was achieved; whereas an acid concentration of 2.5 mol/L was needed to reach the maximum value in the conversion of the cellulose fraction. The analysis of the hydrolysis kinetics has enabled to determine the apparent reaction order, which was 1.3. The hydrolysates from hydrolysis process with H2SO4 0.5 mol/L, once detoxified, were fermented at pH 5.5, temperatures 30, 40, and 50oC with the yeast Hansenula polymorpha (ATCC 34438), resulting in a sequential uptake of sugars. In relation to ethanol and xylitol yields, the best results were observed at 50°C ( YE/sO = 0.11 g/g; YXy/sO = 0.12 g/g). Instantaneous xylitol yields were higher than in ethanol, at the three temperatures essayed. Different phenolic compounds were analyzed in the hydrolysates; hydroxytyrosol was the most abundant (3.79 mg/L). The recovery of these compounds entails the elimination of inhibitors in the fermentation process and the production of high value-added antioxidant products.

The effect of the H(2)SO(4) concentration in the hydrolysis of sunflower‐stalk waste, at 95ºC and using a liquid/solid relation of 20, was studied. In a later stage, the hydrolysates were fermented at different temperatures with the aim of ethanol and xylitol production. A total conversion of the hemicellulose at the acid concentration of 0.5 mol/L was achieved; whereas an acid concentration of 2.5 mol/L was needed to reach the maximum value in the conversion of the cellulose fraction. The analysis of the hydrolysis kinetics has enabled to determine the apparent reaction order, which was 1.3. The hydrolysates from hydrolysis process with H(2)SO(4) 0.5 mol/L, once detoxified, were fermented at pH 5.5, temperatures 30, 40, and 50ºC with the yeast Hansenula polymorpha (ATCC 34438), resulting in a sequential uptake of sugars. In relation to ethanol and xylitol yields, the best results were observed at 50°C ([Formula: see text] = 0.11 g/g; [Formula: see text] = 0.12 g/g). Instantaneous xylitol yields were higher than in ethanol, at the three temperatures essayed. Different phenolic compounds were analyzed in the hydrolysates; hydroxytyrosol was the most abundant (3.79 mg/L). The recovery of these compounds entails the elimination of inhibitors in the fermentation process and the production of high value‐added antioxidant products.