To investigate the influencing mechanisms of calcium and magnesium on the solid products of biomass torrefaction, cellulose was selected as the feedstock in this article. The experiments were conducted in the holding temperature range of 200 °C to 300 °C under the atmosphere of nitrogen. Based on the impregnation methods (chlorides, hydroxides, and acetates of Ca and Mg), the results showed that the solid product yield of torrefacted cellulose impregnated with calcium or magnesium salts was lower than that of raw cellulose torrefaction at 200 °C to 275 °C. However, at 300 °C, the solid product yield of impregnated cellulose torrefaction was higher. During torrefaction, the CaCl2 had a stronger effect than other calcium salts. The Mg(CH3COO)2 had less of an effect than other magnesium salts. The crystallinity of the torrefied cellulose with impregnated calcium or magnesium salts was considerably reduced from 51.1% (raw cellulose) to 7.7% (addition of CaCl2), 34.8% (addition of Ca(OH)2), 28.6% (addition of Ca(CH3COO)2), 9.2% (addition of MgCl2), 13.6% (addition of Mg(OH)2), and 12.0% (addition of Mg(CH3COO)2). The results of the thermal gravimetric analysis showed that the impregnated calcium or magnesium salts dramatically reduced the activation energy of the torrefaction.

To investigate the influencing mechanism of potassium on solid products of biomass torrefaction, peanut shell, a typical agricultural waste in China, was selected as the feedstock and the experiments were carried out in the holding temperature range of 200 ~ 300°C, and in the atmosphere of nitrogen. Based on the water-leaching and impregnation (K₂CO₃, KCl and K₂SO₄; impregnation concentration: 0.5%K, 1%K and 2%K) methods, the results showed that the solid product yield of WLPS (water leached peanut shell) torrefaction was higher than that of RPS (raw peanut shell) torrefaction at 200 ~ 300°C. And all these three potassium salts (K₂CO₃, KCl, and K₂SO₄) inhibited solid product yields of torrefaction. Potassium existing in RPS was not beneficial for upgrading the organic content during the torrefaction process. The carboxylate was the key intermediate during the biomass torrefaction conversion process. Besides, the activation energy of WLPS (106.28 kJ·mol⁻¹) was higher than that of RPS (83.34 kJ·mol⁻¹) during the torrefaction. The impregnated potassium salts reduced the activation energy of WLPS torrefaction process. However, the activation energy of potassium salt impregnated WLPS torrefaction was still higher than that of RPS.

Acetaldehyde is a key intermediate to explore the biomass gasification process in supercritical water. To investigate the effects of potassium carbonate on acetaldehyde gasification in supercritical water at different temperatures (500 ~ 600 °C), pressures (22.5 ~ 27 MPa), residence time (6 ~ 12 s) and K₂CO₃ concentrations (0 ~ 2 wt.%), the experiments using the continuous reactor and the kinetics analysis using the lumped kinetic model were carried out, respectively. The experimental results showed that the operating parameters affected the yields of gaseous products during the acetaldehyde gasification in supercritical water, which were on the order of temperature>residence time>pressure. Effects of K₂CO₃ on the gaseous products were highly related to the temperatures. At the high temperature of 550 ~ 600 °C, K₂CO₃ significantly promoted the gasification efficiency and yields of H₂, CO₂, CH₄, and C₃H₆, while reduced the yield of CO. At the low temperature of 500 ~ 525 °C, K₂CO₃ obviously inhibited the yields of H₂ and CH₄. Besides, with the increasing pressures from 22.5 MPa to 27 MPa, the effects of K₂CO₃ kept in the similar level. In addition, with the increasing residence time from 6 s to 12 s, the increased K₂CO₃ concentrations improved acetaldehyde gasification. The lumped kinetic results indicated that the effects of K₂CO₃ on main gaseous products were explained by promoting the direct decompositions of acetaldehyde/intermediates and methanation reaction (CO+3H₂→CH₄+H₂O), while inhibiting the water gas reverse reaction (CO+H₂O←CO₂+H₂). Moreover, with the increasing K₂CO₃ concentration, the value of k_total generally improved. Higher K₂CO₃ concentration facilitated the acetaldehyde decomposition in supercritical water.

The optimal preparation conditions for cellulose/diatomite composite adsorbents (CDAs) were determined to be a diatomite concentration of 40 wt%, a holding temperature of 700 °C, and a holding time of 30 min. Meanwhile, the yield of CDAs was 70.6%, and the methylene blue (MB) adsorption value was 191.8 mg/g. The specific surface area, total pore volume, and average pore size of the CDAs were 489 m2/g, 0.372 cm3/g, and 3.04 nm, respectively. It was inferred that the diatomite was cross-linked with the cellulose carbon to form some micropores. Greater MB initial concentrations and pH values improved the adsorption on the CDAs. The MB adsorption behavior of the CDAs was described very well by the pseudo-second-order model. The isotherm models showed relatively high adsorption of MB.