Biogas separation using a membrane gas separator: Focus on CO2 upgrading without CH4 loss

Abstract

The CO2 in biogas could be utilized as a resource for industrial or agricultural application, even though it was treated as impurity in many previous studies for biogas upgrading. In this study, biogas was upgraded in terms of recovering highly concentrated CO2 without incurring CH4 loss. Tests under various conditions were conducted to enhance CO2 concentration and recovery efficiency. First, the effects of temperature and pressure on CO2 upgrading were investigated. 40°C and 7bar being selected as the optimal conditions that were then applied for further experiments. Separation tests under varying CO2 and CH4 compositions in a synthetic biogas were performed. The CO2 concentration in the permeate gas was upgraded to a maximum of 70.1%, 77.3% and 83.1% at feed gas compositions of 30%, 35%, and 40% CO2, respectively. Next, when applying a triple-stage separation configuration, a simultaneous improvement in both the CO2 concentration and CH4 loss were observed. These results indicate that an increase in CO2 concentration caused a reduction of CH4 loss. Finally, at biogas plant, CO2 was concentrated at 95.6% with 0.57% CH4 loss, which could be utilized in area to want the carbon source such as industrial and agricultural field.