(821a) Overall Decomposition Pathways of Lignin Related Compounds in Sub- and Supercritical Water

Hydrothermal gasification of biomass is a promising technology for high moisture content compounds. Although lignin can be gasified under hydrothermal conditions, char formation is significantly enhanced under supercritical conditions. This is a major complication since char formation is undesirable and gaseous pathway is favored. Moreover, lignin compounds are found to inhibit the overall gasification of biomass under sub- and supercritical conditions. Our previous studies have established the mechanisms, overall decomposition pathways, and elucidation of the kinetics parameters for lignin decomposition in sub- and supercritical water. To elucidate the primary pathways of gaseous formation in comparison to char from phenolic and aromatic groups in lignin constituent, it is important to study monomeric model compounds such as guaiacol, phenol, and benzene. Therefore, the mechanisms, overall decomposition pathways, and kinetics parameters for these three model compounds were determined in similar manner. From these studies, there are several common reaction pathways from these four compounds, therefore, this study aims to compare these kinetic parameters and give a complete view of the main reactions in the overall decomposition pathways of lignin under sub- and supercritical conditions. Thus, hydrothermal gasification of lignin, guaiacol, phenol, benzene was conducted at temperatures of 300–450 °C at pressure of 25 MPa using a continuous flow apparatus designed to instantly heat the system to the desired temperature. The residence time used in this study are in the range of 0.5–100 s with the aim to determine the initial reaction pathways when the compound was mixed with water. The yield of char, gaseous products, phenolic, aromatic compounds, and other water-soluble products (TOC) were determined. Based on our kinetics elucidations, we discovered the reaction rate constants, k from the Arrhenius plot of the common reaction pathways between this four compounds are consistent with one another and should be able to accurately represent the reaction parameters on its own.