The removal and capture of CO2 from biogas by vacuum pressure swing process using silica gel

In this study, silica gel was employed as adsorbent in a vacuum pressure swing adsorption process for the removal and capture of CO2 from biogas. Adsorption isotherms of CH4 and CO2 on silica gel were measured experimentally, meanwhile a series of breakthrough experiments were also performed on a fixed bed packed with silica gel. In order to design experiments of VPSA process more reasonable, Central Composite Design Methodology was employed to implement the design of experiments, while Response Surface Methodology was used to analyze experimental results. Experimental results showed that the biogas simulated by 55% CH4 balanced with CO2 could be concentrated to an enriched CH4 stream with CH4 purity higher than 98%, after most of the CO2 had been depleted from feed gas by VPSA process. Moreover, dynamic and transient behaviors, such as temperature profiles and concentration profiles in adsorption bed, were revealed by numerical modeling. A good consistency between experimental data and simulation results was observed. Furthermore, an industrial scale dual pressure swing adsorption unit was designed and evaluated by numerical simulation to achieve the goal of CH4 enrichment and CO2 capture simultaneously. Simulation results indicated that the simulated biogas could be separated to an enriched CH4 stream at 98.01% CH4 purity and 97.31% CH4 recovery, as well as a concentrated CO2 stream at 96.74% CO2 purity and 97.58% CO2 recovery.