Hydrophilic chitosan-modified polybenzoimidazole membranes for pervaporation dehydration of isopropanol aqueous solutions

Surface-modification of polybenzoimidazole (PBI) membrane with chitosan chains has been performed using 4-isocyanato-4′-(3,3′-dimethyl-2,4-dioxo-azetidino)diphenylmethane (IDD) as a coupling agent to build up chemical linkages between the PBI membrane surface and chitosan chains. Incorporation of chitosan chains to PBI membrane surface increases its surface hydrophilicity and enhances its performance of pervaporation dehydration on isopropanol aqueous solutions. The surface chemical structure of the chitosan-modified PBI membrane (PBI-CS) has been characterized with attenuated total reflectance Fourier transform infrared and X-ray photoelectron spectroscopies. The scanning electron micrographs of PBI-CS indicate the surface reaction between PBI and IDD might take place at the top surface of the PBI matrix in a thickness of about 2 μm as the PBI membrane is swollen with the used solvent. PBI-CS is effective for pervaporation dehydration on isopropanol aqueous solutions in a wide concentration range from 30 to 90 wt%. The chitosan layer increases the dissolution rate of water into the PBI-CS membrane so as to simultaneously increase the water permeability and selectivity of the membrane. PBI-CS shows high pervaporation separation indexes which are about 3.9-fold of the value measured with the neat PBI membrane.