Sorption of water and volatile organic compounds using kitosan based membranes

Pervaporation and adsorption are the most commonly used methods for the separation of organic liquid mixtures and the removal of water from organic solvents. The preparation of hybrid composite membranes by combining the high hydrophilicity, good forming ability and easy modification properties of chitosan, a natural polymer, with the thermal stability and large surface areas of inorganic fillers, provides great advantages in pervaporation and adsorption. In this study, homogeneous chitosan and chitosan-bentonite hybrid composite membranes with different chitosan:bentonite ratios (2:1, 1:1 and 1:2) were prepared by solution-casting method using two chitosans having deacetylation degrees of 82 and 87, and commercial sodium bentonite sample. SEM-EDX and FTIR analyzes of the prepared membranes were performed, and the physical and chemical structures was elucidated. Mechanical properties of the membranes such as swelling degree at different temperatures (30-50 °C), water vapor sorption, water vapor transmittance and permeability were determined. Experimental studies of water sorption, organic solvent (methanol, ethanol and isopropyl alcohol) sorption and sorption of water from organic solvent-water mixtures (dehydration) at different temperatures (30-50 °C) were carried out for the determination of the membranes performance. As a result of the evaluation of SEM-EDX and FTIR analysis data, it was determined that dense hybrid composite membranes with chitosan and bentonite properties were successfully obtained. It was observed that the degree of swelling of the homogeneous chitosan membranes was higher than the composite membranes and the degree of swelling decreased as the bentonite ratio in the composites increased. However, it was determined that the sorption rate and permeability values did not change much with the increase of the bentonite ratio in the composite membranes. It was observed that the sorption capacities of pure ethanol, methanol and isopropyl alcohol in homogeneous chitosan and chitosan-bentonite hybrid composite membranes at different temperatures (30, 40 and 50 °C) increased in order of methanol>ethanol>isopropyl alcohol. It was concluded that the sorption process in all membranes for all three components is physical adsorption and the maximum sorption can be achieved around 40 °C. Alcohol sorption capacities increased with the increase of bentonite content in the membranes. It was determined that the sorption capacity of alcohol-water mixtures in the prepared membranes decreased with the increase of the alcohol composition in the mixture. However, with the increase of the bentonite ratio in the composite membrane, an increase in the sorption capacity was observed in general.