Application of Reaction Additives to Suppress Degradation Reactions in a Hydrothermal Pretreatment in a Wheat Straw Biorefinery

Abstract

For the development of biorefineries and the production of bio-based products, lignocellulosic biomass constitutes the largest source of renewable organic feedstock. The fractionation of its main components (hemicellulose, cellulose and lignin) is a promising approach for the production of platform chemicals. At the Institute of Thermal Separation Processes (TVT) at the Hamburg University of Technology (TUHH), a second-generation biorefinery approach is being investigated and Liquid Hot Water (LHW) pretreatment is conducting in a batch screening reactor. LHW pretreatment can remove up to 80% of the hemicellulose and enhances the enzymatic digestibility of the material. Nevertheless, sugar degradations to furfural and others is unwanted and to be avoided. Application of citrate and acetate pH-buffers as reaction additives to suppress degradation reactions was studied. Different buffer concentrations were tested in a range of 0.005 M to 0.05 M. Highest buffer concentrations had an undesirable effect in hemicellulose yield and citrate buffers resulted to be noneffective to minimize furfural yield. As a consequence, they are not useful to reduce xylose degradation. Acetate pH-buffer was used with two different pH: 4 and 5. Unfortunately, the use of pH 4 buffer did not have a positive effect on the reduction of degradation reactions. However, it was found that pH 5 buffers can be used to reduce furfural yield (but not selectivity) and to keep the pH more basic after the LHW pretreatment in order to make suitable the consecutive enzymatic hydrolysis for the production of glucose and a highly pure solid lignin.