Fundamental study on oxidation properties at elevated pressure of typical renewable synthetic liquid fuels through low-temperature CO2 electroreduction

Abstract

Using renewable energy to convert CO2 into liquid fuels is a game changing technology that makes transportation and industrial fuels independent of fossil energy. Electrochemical reduction of CO2 is such an example. Liquid fuels produced through this route can be potential candidates for internal combustion engine in the future. However, organic acids such as acetic acid and formic acid will be formed during this process inevitably. To understand oxidation properties of these renewable synthetic fuels, a newly developed variable pressure laminar flow reactor has been used for experimental investigations, and methanol experiments have been performed to validate the reliability of this platform. Pure ethanol and binary fuel experiments have been carried out at 700–1000 K, 10 bar and Φ = 0.25. Several kinetic models obtained from literature has been validated against experimental data and further used for kinetic analysis. Through comparison of experimental results, formation rates of intermediates such as hydrogen, carbon monoxide, methane and acetaldehyde at lower temperature setpoints are larger in pure ethanol experiments than that in binary fuel. This is because acetic acid consumes reactive radicals and then produce less reactive methyl radical, which directly competes with H-abstraction reactions of ethanol. Furthermore, the H-abstraction reaction products of acetic acid will consume methyl radical, this chain-terminating reaction in addition to the consumption of reactive radicals reduce the low-temperature reactivity of the whole system. At higher temperature, stable species formed by acetic acid will be consumed, which makes the concentration of four aforementioned intermediates higher in binary fuel experiments at intermediate to high temperature region. Present work will be conductive to understanding direct usage of renewable synthetic liquid fuels in engine. Further investigation of synthetic fuels can be proceeded based on results of present work.