Evaluation of ZIF-7 media for biogas upgrading into vehicular fuel quality standard by pressure swing adsorption through experiment and dynamic simulation under non-isothermal conditions

Abstract

Biomethane (bioCH4) has gained increasing attention as a potential alternative to traditional fossil fuels due to its environmentally friendly and sustainable nature. An evaluation was carried out to determine the suitability of ZIF-7 as an adsorbent for capturing CO2 from a biogas mixture in pressure swing adsorption (PSA) under non-isothermal conditions. ZIF-7 was prepared and characterized using various analytical techniques such as SEM, BET, FTIR, XRD, TGA, particle size distribution, and TPD. Subsequently, a numerical model was created to effectively illustrate the dynamic behavior of the ZIF-7 adsorbent during methane enrichment. The development of the model took into account the characterization outcomes of ZIF-7, as well as the geometry of the adsorption bed, which was adjusted using the extended Langmuir model to consider multicomponent adsorption. Aspen Adsorption platform was utilized to perform a dynamic simulation, which was then corroborated against experimental breakthrough data of CH4 and CO2 loading over ZIF-7. The experiment and simulation results of biogas upgrading performed under comparable PSA operating conditions and bed dimensions to ensure consistency. Following this, the model was utilized to analyze the impact of specific parameters such as CH4 concentration, bed pressure, and outside wall temperature on the purity of the biomethane. The CCD and desirability property into Design of Experts platform were applied to analyze and optimize the interaction effects of the studied factors on the separation performance. According to the findings indicate that the PSA system and ZIF-media were capable of producing high-grade bioCH4 to meet the quality standard of a vehicle fuel with the most stringent emission regulation. The purity and recovery of the bioCH4 after the optimization from Aspen simulation were 99.96% and 96.5% at optimum conditions of 28 °C outside wall temperature, 2 bar adsorption pressure, and 60% initial CH4 content in the biogas feed stream with feed flowrate 55 mL/min.