Pervaporation separation of water/ethanol mixtures through polysaccharide membranes. V. The relationships between the permselectivity of chitosan salt membrane and its solid state structure

Abstract

AbstractThe separation of water/alcohol mixtures through chitosan salt membranes was investigated. When neutralized by sulfuric acid, the separation factor increased to over 1000, but neutralized by hydrochloric acid, it was at most 50. The difference was mainly explained not only by the contraction of the “hole” due to the conformation change of chitosan molecule but also by the mobility of chitosan molecule which would correspond to the fluctuation of the “hole” size. The conformation change and the mobility of chitosan molecule were meaśured using CP/MAS 13C‐NMR. The spin–lattice relaxation time reflects the mobility of chitosan molecule. The results of the spin–lattice relaxation time obtained from NMR indicated that the mobility of chitosan sulfate was not affected much by the neutralization degree, but the mobility of the hydrochloride was markedly affected. The difference of the selectivity in these membranes could be explained by these results.