Water desalination using thermally responsive hydrogels

Jochen Gutmann, University of Duisburg-Essen, Essen, Germany
Wael Ali, University of Duisburg-Essen, Essen, Germany
Karlheinz Graf, HS-Niederrhein, Krefeld, Germany
Mathias Ulbricht, University of Duisburg-Essen, Essen, Germany

Developing low cost technologies for water purification and seawater desalination is of strategic importance in meeting the current and future needs for water. In our study we explore the feasibility to use copolymer hydrogels incorporating temperature-sensitive and polyelectrolyte units to desalinate salt water by means of reversible thermally induced absorption-desorption. [1] The influence of the chemical topology on the swelling/ deskilling behaviour for such hydrogels was investigated by tailor-made network structures.

To this end, a series of chemically cross-linked polymeric hydrogels were synthesized via free radical-initiated copolymerization of sodium acrylate (SA) with different structural types of the thermoresponsive comonomer Nisopropylacrylamide. The performance of the hydrogels in terms of swelling and deskilling was measured as a function of salt concentration. While the water recovery rate for all hydrogels was roughly the same, pronounced differences in the swelling ratio were found. Sorption kinetics showing non-Fickian and relaxationcoentrolled types of diffusion were evaluated for each hydrogel. Overall, the salt content of a 2 g/L KCl "brine" solution could be reduced by as much as 20%.

[1] H. S. Bloch, U.S. Pat, 3,234,125 (1966).
[2] R. E. Anderson, G. D. Jones, U.S. Pat, 3,438,893 (1969).
[3] F. J. Glavis, D. H. Clemens, U.S. Pat, 3,753,898 (1973).
[4] E. A. Blair, U.S. Pat, 5,354,835 (1994).
[5] Ali, W. ; Gebert, B.; Hennecke, T.; Graf, K; Ubrich, M.; Gutmann, J.S.; ACS Applied Materials & Interfaces, 2015 7 (29), 15696-15706

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