The Investigation of Dimethylaminoethanol (DMAE) as a CO2-Responsive Draw Solute for Forward Osmosis

Abstract

Water scarcity and the limited amount of freshwater resources available worldwide is driving the need for more sustainable water treatment methods. The reverse osmosis (RO) process is a common desalination method, but is energy intensive due to the high external pressure requirements of the system. Thus, low-energy alternatives are needed. Forward osmosis (FO) is a membrane-based process which does not need external pressure to drive the system, but instead uses a high osmotic pressure solution, the draw solute, to drive the process. Therefore, the FO process has the potential to be superior than RO through reduced energy requirements. Currently, the performance of the FO process is largely dictated by the draw solute. The search for an ideal draw solute is critical in making FO more techno-economically viable. In this thesis, first, non-stimuli responsive draw solutes were tested for their FO performance. An FO custom-built bench-scale setup was used to investigate the draw solutes NaCl, MgSO4, polyethyleneimine (PEI) and poly(acrylic acid) sodium salt (PAA-Na) in terms of water flux. The performance of the draw solutes was compared and it was found that 2 M NaCl solution generated high initial and average flux values of 28.1 L m-2 h-1 (LMH) and 14.5, respectively. The flux values of these conventional draw solutes were also successfully compared to literature to validate the FO system. Next, a CO2-responsive draw solute, dimethylaminoethanol (DMAE), was explored. The best performing draw solute was the protonated 40 wt% DMAE solution which generated the highest initial flux of 47.1 LMH and average flux of 13.6 LMH. This draw solute was then tested against a model seawater feed yielding an initial flux of 12.6 LMH and an average flux of 8.3 LMH. DMAE successfully showed good promise as a draw solute for FO in this research as a proof-of-concept study. However, future work will be needed to further evaluate and optimize DMAE for FO.