Effects of bio‐syngas CO2 concentration on water‐gas shift and side reactions with Fe‐Cr based catalyst

Summary To increase the hydrogen (H2) concentration in bio‐syngas containing carbon dioxide(CO2), water‐gas shift reaction (WGSR) is widely used. In this study, the effects of CO2 concentration on the WGSR and unwanted side reactions were investigated by varying the operating parameters, such as the steam/carbon monoxide (CO) ratio, reaction temperature, and the gas‐hourly space velocity (GHSV). Based on the obtained results, CO conversion and H2 yield decreased with increasing CO2 concentration, especially when the steam/CO ratio was lower than 3. This implies that to minimize the negative effect of CO2 on WGSR, the steam/CO ratio should be 3 or higher. For any CO2 concentration, the highest CO conversion and H2 yield were obtained at a reaction temperature of 400°C. Therefore, the temperature should be precisely controlled at 400°C. As GHSV decreased, the CO conversion approached equilibrium with any CO2 concentration; however, the H2 yield remained unchanged. The results of this study exhibited that CO conversion and yield of H2 decreased when the CO2 concentration of bio‐syngas was increased. The operating parameters were thus analyzed to minimize the negative effects of CO2. Results confirmed that a lower gas‐hourly space velocity, a reaction temperature of 400°C, and a steam/CO ratio of 3 or higher are needed to achieve this.