Equilibria of lignocellulose biosorbents for gas dehydration

Gas dehydration is a critical process in petro-chemical industries. High energy consumption and costs associated with the current industrial dehydration processes lead to an incentive to develop alternative solutions. Recently, it was demonstrated that dehydration of natural gas was successfully done using the oat hull based biosorbent. However, in-depth analysis of equilibrium of water adsorption by the biosorbent is essential to be further done to elucidate the adsorption characteristics. In this work, water vapor adsorption data was analyzed using various isotherm models in order to obtain key equilibrium parameters such as surface affinity, monolayer adsorption capacity, adsorption heat and the lateral interactions between the adsorbates at various temperatures and pressures, and the effect of these operating conditions on the equilibrium parameters were investigated. The system showed multilayer adsorption behavior at 24 degrees C and 300 kPa (type III isotherm), while ideal Langmuir behavior (type I isotherm) was seen at higher temperatures (35-50 degrees C). Redhead isotherms were considered as multilayer adsorption models, while Langmuir, Toth, and Fowler-Guggenhein models were used to fit the rest of the experimental data. Site energy distribution was also determined using the density functional theory. In addition, the isosteric heat of adsorption was determined using various models, and as a function of surface heterogeneity and surface loading. Finally, the specific surface area available for water vapor adsorption were determined. These findings can be very useful for the design and control of the pressure swing adsorption systems, and provide insights on the adsorption mechanisms of lignocellulose biosorbents in dehydration processes.