Equilibrium and heat of water vapor adsorption on the surface of natural lignocellulose materials

Abstract

Water vapor is to be separated from industrial gaseous streams at reduced costs. Natural lignocellulose materials have demonstrated a high water adsorption capacity and great potential in industrial gas dehydration, specifically natural gas dehydration. In this work, flax shives, a representative of abundant lignocellulose materials generated as by-products of agriculture industry, was chosen as a model to investigate their water adsorption. The focus of this work is on analyzing the surface morphology and the chemistry of the material, and investigating the effects of key parameters on the equilibrium, isotherms, surface affinity, and heat of water adsorption. The results showed that total operating pressure had the most significant effect on the equilibrium, followed by the temperature. The shape of water adsorption isotherm was changed from type III to type I as the total operating pressure was decreased and temperature was increased. The Anderson, Toth, and multi-site Langmuir models successfully described the isotherms obtained at various operating conditions. The modeling results were further used to determine the standard heat of adsorption, isosteric heat, heat of individual sites, and excess heat of liquefaction that the second and subsequent adsorbed layers released. In addition, the material surface was characterized by FE-SEM and FTIR, and the water transport through the material’s structure was visualized using optical microscopy images and video. These findings contributed to the fundamental science of water adsorption and natural lignocellulose materials and provided information for the design of drying processes based on adsorption and related interface sciences.