Comparison of Water Scrubbing and Propylene Carbonate Absorption for Biogas Upgrading Process

Abstract

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.

Development of Ionic Liquids Tethered to Coconut Shell Activated Carbon for Biogas Upgrading in a Packed Bed

“…To estimate the isosteric heat of adsorption, a series of biogas upgrading experiments was conducted in the packed bed at different temperatures and pressures. The isosteric heat of adsorption of the adsorbents was calculated according to Equation (2). [69] The isosteric heats of adsorption were calculated by plotting lnP against 1/T at a constant adsorption capacity under different pressures.…”

“…T in , T out , F in , F out , P in , and P out refer to the temperature, flow rate, and pressure of the inlet and outlet of the packed bed, respectively, and R is the universal gas constant. C 0 is the initial concentration of CO 2 [vol %] and C t is the real-time concentration of CO 2 during the adsorption [vol %]. CO 2 ad is the amount of CO 2 captured by the adsorbents, and biogas ad is the total amount of adsorbed biogas.…”

“…[1] The presence of CO 2 reduces the calorific value significantly. [2] Biogas upgrading to high-quality fuels is of growing importance. After the removal of CO 2 and other impurities, the final biomethane, which contains~97 % CH 4 and less than 3 % CO 2 , can be used as an alternative fuel for vehicles.…”

“…[2] Biogas upgrading to high-quality fuels is of growing importance. After the removal of CO 2 and other impurities, the final biomethane, which contains~97 % CH 4 and less than 3 % CO 2 , can be used as an alternative fuel for vehicles. [3,4] The physical and chemical adsorption of CO 2 can be achieved using solvents, cryogenic processes, membranes, and solid adsorbents.…”

“…For comparison, the raw coconut shell AC was also examined in biogas upgrading. The raw material has a saturated CO 2 …”