THERMOOSMOSIS AND TRANSPORTED ENTROPY OF WATER ACROSS HYDROCARBONSULFONIC ACID-TYPE CATION-EXCHANGE MEMBRANES

Solvent transport across hydrocarbonsulfonic acid-type cation-exchange membranes was measured for aqueous electrolyte solutions under a temp erature difference and an osmotic pressure difference. The hydrocarbon sulfonic acid-type cation-exchange membranes, Aciplex(R) K-181, Aciple x(R) K-182, and Neosepta(R) C66-5T with the H+, Li+, Na+, K+, NH4+, CH 3NH3+, (CH3)(2)NH2+, (CH3)(3)NH+, (CH3N+, (C2H5N+, (n-C3H7N+, and (n-C 4H9N+ forms were used. The direction of thermoosmosis across the membr anes with the H+ and the Na+ forms was from the cold side to the hot s ide, as observed for various anion-exchange membranes. However, the di rection was from the hot side to the cold side for the membranes with ammonium and the alkylated ammonium ion forms, except for Neosepta(R) C66-5T with the (CH3N+, (C2H5N+, and (n-C3H7N+ forms. This is why the entropy of the water in the membranes will increase with increasing th e number of hydrogens combining with the nitrogen of the alkylated amm onium counterions, because they are exchangeable with the hydrogens of water molecules in the membranes. Thermoosmosis across the membranes with the (n-C3H7N+ and the (n-C4H9N+ forms will also occur toward the cold side, because the hydrophobic interaction between the hydrophobic alkyl groups of the counterions and the membrane matrix is very stron g and the membranes act as a hydrophobic polyethylene membrane.