Characteristics of oat hull based biosorbent for natural gas dehydration in a PSA process

Abstract

Temperature swing adsorption is currently one of the methods used for the dehydration of natural gas; however, several operating problems including high operating cost, pollution, low selectivity, and the thermal degradation of adsorbents need to be addressed. In this work, pressure swing adsorption was investigated for the dehydration of natural gas using a cost effective biosorbent. Oat hulls, a byproduct from the agricultural industry, were used as a representative of lignocellulose materials for the first time to develop the biosorbent for the pressure swing adsorption process. The morphology, surface functional groups, and thermal stability of the biosorbent were investigated by FE-SEM, XPS and TGA. The effects of the key operating parameters including temperature, pressure, gas flow rate, feed concentration, and biosorbent particle size on the process were analyzed by a full factorial experimental design. The results demonstrated a higher water adsorption capacity at room temperature and a higher selectivity towards methane than those of commercial adsorbents. Furthermore, the biosorbent showed a stable performance after being used for fifty adsorption-desorption cycles. Though the biosorbent was regenerated at room temperature, the TGA results showed that biosorbent was stable at temperatures up to 210 °C. Additionally, the analysis of adsorption and desorption rates revealed that a cyclic adsorption-desorption process is possible. Adsorption equilibrium and kinetics were investigated, and the experimental equilibrium data was analyzed by the Anderson, and Toth isotherm models, and kinetic data by the Thomas model. The monolayer adsorption capacity, surface affinity and mass transfer coefficients were determined. The results indicate that this high-performance and environmental friendly process has potential for natural gas dehydration industry.