CO₂ Removal from Biogas as Product of Waste-Water-Treatments

Abstract

In order to satisfy the future energy demands, the development of alternative sources of energy is currently object of interest. Among all the possibilities, biogas is a renewable methane-based fuel obtainable by anaerobic digestion of different types of raw materials, including waste-waters. This gas product contains relevant amounts of methane (CH₄), carbon dioxide (CO₂) with traces of other compounds and, to be used, it needs to be purified from the components responsible of a decreasing in the combustion efficiency. On the upgrading process, the CO₂ removal is necessary to respect the Wobbe Index specification and it can be realized by various technologies in different devices. Among all the current techniques, CO₂-absorption into physical or chemical solvents in packed towers is commonly applied, but the use of gas-liquid membrane contactors represents an innovative alternative. In particular the second ones are characterized by various operational advantages, such as independent gas/liquid control, optimal load of the absorbent, no entrainment, flooding or foaming and modular and very compact devices. In this work a polypropylene hollow fiber membrane contactor was used to investigate the CO₂-absorption from a model gas mixture into aqueous solutions of monoethanolamine (MEA), piperazine (PZ), methyildiethanolamine (MDEA) and their mixtures. The effect of reagent type and concentration was studied as well as the influence of temperature and gas composition. Experimental results show the high reactivity of MEA and PZ, capable of increasing the absorption rate in MDEA-based solvents, characterized by large loading capacity and easiness of regeneration.