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Multi-simultaneous Absorption and Adsorption Processes for Biogas Purification using Ca(OH)2 Solution and Activated Clinoptilolite Zeolite/Chitosan Composites

This study examined the effects of acid/base activation and chitosan coating on clinoptilolite zeolite as an adsorbent for biogas purification from palm oil mill effluent (POME) using simultaneous absorption–adsorption methods. The effects of chitosan concentration in the clinoptilolite zeolite/chitosan (ZAC) composites were studied to determine the best type of adsorbent for purifying biogas to obtain the highest methane (CH4) concentration: the biogas produced from POME via an anaerobic digestion process had a CH4 concentration of 87% and a carbon dioxide (CO2) concentration of 13%. In this study, the Ca(OH)2 solution was used for the absorption process, and the ZAC composite was used as the adsorbent in the adsorption process. To enhance the adsorption efficiency of the adsorbent when purifying biogas, clinoptilolite zeolite (ZA) was activated using strong acid (HCl) and base (NaOH) in various concentrations (ranging from 1–3 M), calcination at 450°C for 2 h, and coating with chitosan concentrations (ranging from 0.25–1 v/v%). The ZA was coated with chitosan to increase its adsorption efficiency, as chitosan contains high levels of amine and hydroxyl groups that interact with CO2 impurities and form carbamic acid, ultimately producing carbamate salt. The composition of biogas before and after treatment was analyzed using gas chromatography. Overall, the final content of the biogas after the purification process with absorption using the Ca(OH)2 solution and adsorption in a fixed-bed column using the ZAC2-0.5 composite was 0.42% CO2 and 99.58% CH4. The purified biogas had a very high methane gas content; thus, this study’s findings suggest that purified biogas can be used as a clean energy source for wider industrial applications.