Hydrothermal liquefaction of wood using a modified multistage shrinking-core model

Wood liquefaction in hot compressed water is modeled using the hydrolysis of Cellulose, Hemicellulose, and Lignin. These three components are reacted under catalyst-free subcritical conditions in a temperature range from 553 K to 640 K, and the heating rate ranges from 2 K/min to 6 K/min. Using a simplified reaction scheme, water-soluble products1 (WSP), Biocrude, char, and gas are generated through intermediates with each wood component. A modified multistage shrinking core model is employed to simulate biomass particle degradation. The reaction and kinetic regime of the hydrothermal liquefaction2 (HTL) process are treated separately for each wood component. Although the lack of initial fast reaction kinetic data limits the development of more accurate models, computed results displayed a generous fit to data from the literature. At 593 K for a 2 K/min heating rate and particle size of 0.08 mm, biocrude shows the maximum yield of 26.87% for wood liquefaction. Although lower heating rates show fast initial lignin hydrolysis, for longer residence times, and close to the critical point, yield outputs show similar yields. Meanwhile, char and gas yields of cellulose model show maximums of 55 wt% and 25 wt% respectively at 640 K with a 2 K/min heating rate. Nevertheless, char yield values become very similar at 640 K for different heating rates for the cellulose hydrolysis model. Both cellulose and lignin hydrolysis models show better hydrolysis with smaller particle sizes. Besides, lignin decomposition shows more dependence on the particle size, where it decomposes much faster with 0.08 mm particle and slower than Cellulose with the 1 mm particle.