Preparation And Characterization Of Thermo-sensitive Draw Solution And High Flux Forward Osmosis Support Layer

Forward osmosis (FO) is a process in which the osmotic pressure differential of two sides of the semi-permeable membrane acts as driving force, and it is operated under low hydraulic pressure or zero hydraulic pressure. Forward osmosis process is a green process for separation and purification while it is low energy consumption and low cost. Currently, FO process has been applied in desalination, water treatment, food processing, pharmaceutical industry, power generation et al. Thus, high performance forward osmosis membrane and draw solution should be developed and improved to meet the requirement. In this paper, thermo-sensitive polyelectrolyte draw solutions were prepared and their forward osmosis properties were characterized. And then high flux forward osmosis support layers were developed and their formation mechanism was studied.A series of polyelectrolytes were evaluated as draw solutions for the forward osmosis process. Such polyelectrolytes were synthesized by copolymerization of N-isopropylacrylamide with different amounts of sodium acrylate. These polyelectrolytes were thermo-sensitive and water soluble. Hot ultrafiltration (HUF) operated at45℃and2bar was used as a low-energy method to recover the water from the polyelectrolyte draw solutions. The results showed that4-P solution worked best among nine polyelectrolyte solutions in the forward osmosis process and HUF process, and its FO water flux was0.347L·m-2·h-1(LMH) while the feed solution was pure water and its water recovery fraction was65.2%.A convenient and pragmatic method was developed to prepare high flux forward osmosis support layer by blending20wt.%charged polymer (sulfonated poly (phenylene oxide)) and80wt.%neutral polymer (commercialized ultrafiltration membrane materials:cellulose acetate, polyethersulfone and poly (vinylidene fluoride)). The blend membranes performed excellent ultrafiltration performance. The pure water flux of CA-SPPO was3times as much as those of CA membrane, which increased from462LMH to1432LMH. The pure flux of PES-SPPO was76times as much as PES membrane, which increased froml9LMH to1460LMH. And the pure flux of PVDF-SPPO was30times as much as PVDF membrane, which increased from79LMH to2386LMH. Their rejection rates slightly decreased. After blending with SPPO, the membranes became highly porous, possess good hydrophilicity, and charged gradient was formed across the blend membranes, that facilitated the formation of high flux blend membrane. These blend membranes with high porosity and good hydrophilicity are excellent support layer for forward osmosis membrane.