Performance Evaluation of 1-Cyclohexylpiperidine as a Draw Solute for Forward Osmosis Water Separation and CO₂...

Membrane-based technologies, such as forward osmosis (FO), offer the advantage of treating water through a spontaneous process that requires minimal energy input while achieving favorable water permeability and selectivity. However, the FO process still has some challenges that need to be solved or improved to become entirely feasible. The main impediment for this technology is the recovery of the draw solute used to generate the osmotic potential in the process. In this paper, we discuss the use of a switchable polarity solvent, 1-cyclohexylpiperidine (CHP), as a draw solute that responds to external stimuli. Specifically, the miscibility of CHP can be switched by the presence of carbon dioxide (CO₂) and is reversible by applying heat. Thus, in this study, the hydrophobic CHP is first converted to the hydrophilic ammonium salt (CHPH⁺), and its capability as a draw solution (DS) is thoroughly evaluated against the typical osmotic agent, sodium chloride (NaCl). Our results show that the water permeability across the thin film composite membrane increases by 69% when CHPH⁺ is used as the DS. Also, the water permeability when using different feed solutions: aqueous solutions of (a) urea and (b) NaCl were evaluated. In both cases, the CHPH⁺ generates water fluxes in the range of 65 ± 4 LMH and 69 ± 2 LMH, respectively. We then separate the diluted DS by applying 75 °C to the solution to recover the pure CHP and water. The results of this work provide a proof-of-concept of a CHP wastewater and desalination method via an FO process.