To supplement the demands of petroleum fuels and chemicals using existing infrastructure of engines, pipeline and fuel delivery, it is logical to target producing compatible hydrocarbons from biomass resources. Bio-oil produced from biomass fast pyrolysis technology can be converted into hydrocarbons. However, this conversion process remains a major challenge due to the instability of bio-oil, making it challenging to store, transport and convert into useful fuels and chemicals. In addition, high oxygen content in bio-oil makes it very unstable. Oxygen must be removed and additional hydrogen must be added to maximize hydrocarbon production.
Traditional bio-oil upgrading usually involves extensive hydrotreating, which is energy intensive and costly. Hence, Dr. Ajay Kumar, Associate Professor of Biosystems and Agricultural Engineering (BAE), Oklahoma State University (OSU), collaborated with another OSU Professor, Dr. Allen Apblett from Chemistry, to demonstrate proof-of-concept of a novel natural Gas and Biomass to Liquids (GBTL) technology that will synergistically use biomass (e.g. switchgrass and eastern red cedar) and methane to produce liquid hydrocarbons that are compatible with existing infrastructure. Kumar’s research team used a synergistic reaction system consisting of activation of methane and deoxygenation of pyrolysis-derived volatiles with metal-loaded HZSM-5 catalysts.
“We found that methane significantly improved the yield and selectivity for the formation of aromatic hydrocarbons in the bio-oil obtained from catalytic pyrolysis of biomass,” Kumar said. “Methane did not show effective improvement in the yield of aromatic hydrocarbons from cellulose and hemicellulose in the presence of molybdenum modified HZSM-5 catalysts, but significantly improved the aromatic hydrocarbons from lignin,” Kumar added.
Torrefaction pretreatment on switchgrass did not increase the aromatic hydrocarbon yield. “Torrefaction infavorably altered the biomass composition by reducing cellulose content while increasing lignin content. The aromatic hydrocarbon yield decreased as the torrefaction temperature increased from 230 to 270 oC,” Kumar said.
This project shows that direct co-conversion of biomass and methane with an appropriately designed catalyst leads to significant improvements in hydrocarbon yields. Kumar said, “the direct conversion of biomass pyrolysis volatiles and methane in a catalytic reactor is a unique approach that makes it possible to produce hydrocarbon fuels more efficiently than traditional pyrolysis-based refinery processes.”
Demonstration of the proof-of-concept through optimization and analysis of economic feasibility is underway. Dr. Kumar collaborated with two other OSU Professors from the Department of Agricultural Economics, Drs. Francis Epplin and Phil Kenkel, for this part of the study. Funding of this project was provided by the U.S. Department of Agriculture-National Institute of Food and Agriculture (USDA-NIFA) through the South Central Sun Grant Program.