Presented by Dr. Xinying Wang - Chemical Engineer, Illinois Sustainable Technology Center, Prairie Research Institute, University of Illinois at Urbana-Champaign
September 12, 2013
Forward osmosis (FO) for dewatering/desalination applications has received increasing interest due to its potential use of low grade thermal energy, ability to operate at low pressure, and reduced tendency to foul. Developments in FO are primarily focused on two areas: (a) expanding the availability of draw solutions that generate high osmotic pressure; are easily separated from water using physical and/or chemical means; are non-corrosive, nontoxic, and chemically stable; exhibit near neutral pH; and are inexpensive and (b) developing membranes that exhibit high flux and suitable salt rejection under FO conditions. In this presentation we focus on the challenges of draw solution utilization and regeneration.
In this presentation, we will talk about a forward osmosis desalination process that employs a temperature-reversible polymer to recycle the draw solute. In our work, a high concentration MgSO4 solution is used as draw solution. After forward osmosis, the diluted draw solution is mixed with a thermally-reversible polymer, poly (propyleneoxide) -co-poly (ethyleneoxide). This polymer extracts water from the diluted draw solution and the whole solution forms two phases, a polymer-water phase and a concentrated MgSO4 solution phase (bottom). The bottom MgSO4 solution phase is recycled back to the forward osmosis module, while the polymer-water phase is heated above the polymer's cloudy point (60°C) to recycle the polymer and to produce clean water. Experimental details on the process will be presented.