Biomass decomposition (HTU process) - determination of the reaction pathways under subcritical conditions

HTU is a hydrothermal conversion of biomass into an organic crude oil (biocrude). During this process the oxygen content of the organic material is reduced from about 40% to 10-15%.

The removed oxygen ends up in CO2 and water. It may be expected that primary reactions in this process involve the hydrolysis of polysaccharides into saccharides. The latter might then be converted into furan derivatives, which on their turn could be converted into a variety of other products. Previous studies in the laboratory of TU Delft surprisingly showed that almost no CO2 is formed during hydrothermal reactions of several simple model compounds, including furan derivatives, glucose, cellobiose and cyclodextrins. It can be concluded that either decarboxylation reactions take place prior to the complete hydrolysis or that factors as the chemical composition of the feedstock and the ultra-structure of cell wands play a role in the decarboxylation reactions. Insight into the major pathways is essential for the development of a kinetic model for the HTU process.

The complexity of the phenomena involved, however, will not allow the description of the process by some simple kinetic equations. Therefore, it will be probably more useful to develop a model with a series of semi-empirical equations that describe the chemical characteristics of the resulting biocrude as a function of parameters regarding the composition of the feedstock and the reaction conditions.