CO2-Mediated catalytic pyrolysis of rice straw for syngas production and power generation

Abstract

As emissions of anthropogenic CO2 from the use of fossil fuels become more severe, the renewable energy production has received considerable interests. In this study, CO2 was used as a raw material to produce energy as a form of syngas (H2/CO) as a precautious measure for mitigating the atmospheric CO2 levels. Rice straw pyrolysis was conducted under various N2/CO2 purge gas environments. The present study experimentally proved that CO2 expedited gas phase homogeneous reactions between volatile organic compounds (VOCs), evolved from rice straw pyrolysis. These CO2 functionalities led to the conversion CO2/rice straw into CO at ≥ 480°C. To accelerate reaction kinetics of syngas formation, additional thermal energy (500 or 700°C) was applied through multi-stage pyrolysis setups. In addition, SiO2 supported Co (Co/SiO2) catalyst was further accelerate reaction kinetics of CO (3 times) and H2 (6 times) in reference to non-catalytic pyrolysis at 500°C. The synergistic effects of Co/SiO2 catalyst and CO2 feedstock resulted in substantial formations of H2 and CO at ≤ 480°C. To analyze the potential capability of rice straw fuels, their power generation performances were evaluated through a simple gas turbine cycle. When the constant amount of air was assumed to be supplied to a combustion chamber, different amounts of fuel feedstocks were required for their complete combustions. In this condition, the resulting power generations of rice straw fuels (maximum 138 MJ s−1 from catalytic pyrolysis under 100% CO2) were up to 1.9 times higher than the power generations from natural gas references (74 and 82 MJ s−1). These results suggest that a renewable power generation platform could be constructed with a valorization of greenhouse gas (CO2) and biomass waste (rice straw) through pyrolysis process at mild temperature.