1-Cyclohexylpiperidine as a thermolytic draw solute for osmotically driven membrane processes

• CHP–H2CO3 is a high osmotic pressure thermolytic draw solute. • CHP–H2CO3 solutions produce relatively high forward osmosis water fluxes. • Low grade heat should be sufficient to degas CHP–H2CO3 solutions. • CHP–H2CO3 solutions display good material/membrane compatibility. • Water flux and reverse draw solute flux of CHP–H2CO 3 occur by different mechanisms.

1-Cyclohexylpiperidine (CHP) displays osmotic pressures (N500 atm) and flux performance comparable to the previously reported N,Ndimethylcyclohexylamine with greatly improved material compatibility and degassing performance. The combination of CHP draw solution and polyamide TFC membrane displayed long term stability. Reverse draw solute flux was found to be independent of draw solute concentration while water flux varied proportionally with draw solute concentration suggesting that Js could be minimized without impacting Jw. The initial degassing studies suggest that 70 °C should be sufficient to degas CHP at ambient pressure with the use of lower temperatures possible given reduced pressures. These results are very promising and address all of the major challenges in developing an integrated SPS-FO process as identified in our initial SPS-FO study [11]. A forthcoming techno-economic process model of SPS-FO is also favorable [44]. The aggregate of this work suggests further research into developing a SPS-FO process is warranted. Nomenclature Am membrane area C solution concentration CHP 1-cyclohexylpiperidine CTA cellulose triacetate DMCHA N,N-dimethylcyclohexylamine FO forward osmosis FO mode active layer towards feed solution Js reverse solute flux 70 °C DMCHA 80 °C DMCHA 95 °C DMCHA Osmolality (Osm/Kg) 2.5 70 °C CHP 80 °C CHP 1.5 0.5 1,000 1,200 1,400 1,600 1,800 2,000 Time (min) Fig. 7. 1-Cyclohexylpiperidinium bicarbonate polar to non-polar transition driven by a circulation through a high surface area heat exchanger at 70 °C.