Compatibility study of nanofiltration and reverse osmosis membranes with 1-cyclohexylpiperidenium bicarbonate solutions

Any forward osmosis (FO) based water treatment process using a thermolytic draw solute requires a method to remove/recycle low concentrations of residual draw solute contained in the product water. For switchable polarity solvent forward osmosis (SPS FO) this means the removal of residual tertiary amines from the product water. This study explores membrane filtration of 1-cyclohexylpiperidenium bicarbonate (CHP-H2CO3) draw solute under conditions relevant to the SPS FO process. Fourteen commercially available nanofiltration (NF) and reverse osmosis (RO) membranes were screened. Several NF membranes displayed good chemical compatibility at CHP-H2CO3 concentrations of 2.5 wt% or higher while maintaining fair selectivity, with flux normalized rejection of similar to 80-99% and flux normalized net driving pressure of 80-400 psi for the normalized flux of 20 LMH. Most sea water and brackish water RO membranes tested showed flux normalized rejection of above 98% and flux normalized net driving pressure of 300-900 psi. A two-pass NF/tap(')water (TW) RO system is proposed as an effective low-pressure method to remove residual CHP-H2CO3 from water.