(607f) Separation of Urea from Water Solution Using Sulfonated Poly (styrene-isobutylene-styrene) Membranes with Counter-Ion Substitution

Water is of vital importance for space exploration. Currently, the International Space Station (ISS) uses a vacuum distillation system for the purification of water from urine; however, this method requires high energy and includes numerous mechanical components, so lower energy alternatives need to be considered. The objective of this work is to test the transport properties of urea throughout polymeric membranes based on sulfonated poly(styrene-isobutylene-styrene) (S-SIBS). The polymer was sulfonated using a sulfonation agent made from sulfuric acid; this functionalization gives the polymer the ability to form hydrophilic ionic nanochannels. The membranes were obtained by membrane casting technique to let the chemical domains thermodynamically self-assemble. The nanochannels of the membranes were chemically modified by the substitution of 12 different counter-ions; by submerging the membranes for 24 h in a 1 M solution of the counter-ion salt. The membranes were characterized by water uptake and swelling tests, FTIR, and TGA. The percentage of sulfonation was quantified by elemental analysis obtained at 66.48%. The presence of the sulfonic groups was verified by FTIR with the appearance of four additional bands (1151, 1124, 1034, 1007 cm^-1), representative of the stretching vibrations associated with the sulfonate group. Finally, the urea permeability of the membranes was estimated using the time-lag method in a free diffusion cell. The change in concentration during diffusion was monitored using FTIR; by the implementation of a calibration curve relating the intensity of a small peak nearby the range of 1150 to 1170 cm^-1 associated with bonds, with urea concentration from 0.1 to 1 M. So far, we have found that there is a relationship between the oxidation state of the counter-ions and the water adsorption capacity of the membranes, affecting the transport properties. The incorporation of counter-ion substitution decreases urea transport. The urea permeabilities range from 1.42x10^-4 to 6.93x10^-6 for unsubstituted and Fe (III) substituted membrane respectively. Some of these membranes are outstanding candidates for the permselective separation of urea from water.