Comparison of water scrubbing and propylene carbonate absorption for biogas upgrading process

Biogas upgrading using a physical absorbent is a simple and efficient technology with low energy requirements for regeneration. Owing to the good performance of carbon dioxide removal, propylene carbonate absorption is widely utilized in the purification of natural gas and synthesis gas. In this work, the feasibility of biogas upgrading with propylene carbonate as the absorbent was studied by the comparative tests of water scrubbing and propylene carbonate absorption. The influence factors of absorption gas/liquid ratio, air stripping gas/liquid ratio and hydrogen sulfide content in the feed gas were investigated. The capacity of biogas treated by propylene carbonate was 4-5 times of that by water. The propylene carbonate absorption showed better tolerance to the existence of hydrogen sulfide. When the concentration of hydrogen sulfide in the feed gas increased to 4000 ppm, the methane content in the product gas decreased by 5.09% with water as the absorbent, while it decreased only 1.68% in the propylene carbonate absorption test. The results showed that the propylene carbonate absorption had high efficiency and an obvious advantage of energy conservation when applied for biogas upgrading. The drawbacks of low methane recovery and high solvent loss could be avoided through flash evaporation and solvent recovery.