Advanced upgrading of extracted water phase bio-oil via esterification by ZSM-5 catalysis

摘要

Biomass is one of important renewable energy sources. It can be used to produce carbon-based liquid fuels through biochemical and thermochemical methods. Pyrolysis is a thermal chemical method that converts biomass to high energy fuels called bio-oilswhich are expected to replace the transportation fuel. However, the bio-oil from biomass pyrolysis is an intermediate and cannot be directly used as a fuel as it contains large oxygen content and organic acids. Various organics with quite different oxygen-containing functional groups mixing together lead to the high instability of bio-oils. Esterification can extend the carbon chain length and stabilize the oxygen-containing compounds. Commonly, esterification process takes place on homogenous mineralacids such as sulfuric acid and hydrochloric acid, leading to a difficulty in separation, which may cause ion pollution in bio-oils. Efforts have been put on using solid acids as catalysts to achieve a better separation and recovery from bio-oil esterification, such as using ion-exchange resins, metal oxides, silica-supported sulfonic acids and zeolites. Zeolites are well-developed industrial acid catalysts and have been used in the bio-oil upgrading process, which helps cracking the oxygen functional groups to produce hydrocarbons. However, catalyst coking was identified in literature as a major issue using zeolite for bio-oil upgrading. This study developed a liquid-liquid extraction process to remove coking precursors followed by an esterification upgrading focusing on acids, aldehyde and furfurals transformations. Catalyst recovery and recycling were conducted to evaluate the catalysis efficiency. Pyrolysis bio-oil from Douglas fir pellet was used as feedstock. ZSM 5 was modified and used as catalysts. Temperature was set as a factor with five levels ranging from 60 to 135 °C with reaction time from 1 to 8 hours. The results showed that 89% of high conversion rate was obtained from the feedstock via ZSM-5 catalysts in a fixed feedstock to methanol ratio analyzed by HPLC and GC/MS.