Energy-efficient carbon dioxide removal in biogas with hydrogen recycling electrochemical system

Abstract

Biogas has attracted much attention as modern society gradually emphasizes carbon neutrality on the fossil-based energy system. To balance energy production from renewables with total energy demand, biogas should be upgraded to RNG (Renewable Natural Gas) in order to make use of all the energy system benefits of natural gas. Removing carbon dioxide in raw biogas with low energy-intensive technology has been one of the vital aspects of biogas utilization. This study explores the usefulness of the electrochemical approach in biogas upgrading and evaluates how effective the system is in terms of CH4 recovery and energy demand. By combining fuel cell and electrolysis cell, CO2 was dissolved in the cathode, and produced H2 from the cathode was recycled to the anode where the H2 oxidation reaction significantly reduces the total cell potential. The study adopted a comparative experimental design with a water electrolysis system to evaluate the system's performance. In this regard, the contribution factor of overall cell potential reduction was analyzed from the Electrochemical Impedance Spectroscopy (EIS) response. Consequently, electrochemical methanation achieved 99.67 ± 0.58% purity. Also, substituting anodic reaction from O2 evolution to H2 oxidation resulted in approximately 65% of overall cell potential reduction. What is striking about this result is that 93.7% of the anodic overpotential in water electrolysis was eradicated in H2 recycling system.