Utilization of CO2 in thermochemical conversion of biomass for enhanced product properties: A review

Abstract

CO2 is the primary greenhouse gas emitted through human activities. CO2 emissions from burning fossil fuels increased by approximately 2.7 percent in 2018, after global emissions of 35.8 Gt in 2017. Thus, finding energy and cost-effective methods to use the CO2 generated from industries for productive purposes is crucial, abating CO2 emissions while producing economic benefits. This paper aims to comprehensively review the effects of CO2 on syngas, biochar and bio-oil from gasification and pyrolysis processes. It was found that the utilization of CO2 during gasification and pyrolysis provides both control over syngas H2/CO ratio and biochar with enhanced properties for high value applications. Furthermore, it was determined that co-gasification under CO2 atmosphere can enhance synergistic effects. Results also showed that the presence of CO2 can increase the hydrocarbon concentration of bio-oil due to the different reactions that can occur between biomass and CO2 compared to biomass and N2. The use of CO2 as a feedstock also reduces the net CO2 emissions and therefore provides environmental benefits. However, the utilization of CO2 during biomass gasification and pyrolysis currently has some limitations, including the endothermic nature of gasification reactions, resulting in large energy and compressed CO2 inputs, which can be expensive. It is recommended that comprehensive studies to address the current limitations of the utilization of CO2 in biomass gasification and pyrolysis processes be conducted. Promoting the use of CO2 is integral to global CO2 emission reduction, aiding in efforts to achieve CO2 emission regulations outlined by the Paris Agreement (PA).