Conversion of CO2 by reverse water gas shift (RWGS) reaction using a hydrogen oxyflame

Abstract

Climate change concerns demand for drastic measures to mitigate greenhouse gas (GHG) emissions from fossil resources particularly those of CO2. Effective conversion of CO2 into syngas (a mixture of CO and H2) via reverse water gas shift (RWGS) reaction requires high temperatures (> 900 °C) to overcome thermodynamic limitations. Challenges may arise in commercial catalytic reactors in achieving close to equilibrium efficiencies due to physical barriers such as maximum catalyst operating temperature and associated operating costs. Herein, a simple and novel approach is presented to produce syngas from CO2 via RWGS reaction using a high temperature hydrogen oxyflame. Test results from a tubular laboratory reactor show that a CO2 conversion of up to 75 % is achievable in a single pass with a gas residence time of < 0.03 s. Lower than equilibrium CO2 conversions are observed due to non-adiabatic temperatures in the reactor. Heat integration and reactor insulation at industrial scale would help in a closer to equilibrium performance. Systematic analysis of reactor performance supported by empirical modelling revealed that there is an optimum economical point where hydrogen consumption can be minimized (< 1.0 mol H2/mol CO2). A trade-off must be made to identify an optimum operating point depending on required syngas quality. Relatively small effect of reactor wall material (within 10 % in CO2 conversion) may indicate an enhancing effect of hydrogen oxyflame as the main contributor to the reactor performance.