Effects Of Additives And Substrates On The Performance Of Cellulose Triacetate Forward Osmosis Membranes

Forward osmosis membrane process is a novel membrane process that using osmotic pressure difference as driving force. It has advantages of low energy cost, high water recovery, environment friendly, low membrane fouling and easy to implement. Because of these advantages forward osmosis is widely used in water treatment, food processing, drug releasing, electric power generation and emergency bag.Through forward osmosis membrane process has so many advantages, it has not been applied in a large scale because of a lower water flux than anticipated in theory. The phenomenon is caused by the concentration polarization. A high flux forward osmosis membrane is expected to be prepared by using cellulose triacetate as membrane material through phase inversion and additives complex formulation in this study. First the effects of various substrates such as nonwoven, nonwoven 40# and mesh 300 on cellulose triacetate forward osmosis membrane separation performance are investigated and the results are explained. It turns out that under our condition using glass as substrate has optimum performance.For seeking monomers for additives complex formulation, various kinds of additives are investigated such as acetic acid, zinc chloride, lactic acid, maleic acid, polyvinyl pyrrolidone, polyethylene glycol and methanol. The mechanism is explained and acetic acid, zinc chloride, lactic acid and maleic acid are chosen as monomers for additives complex formulation among the additives. Furthermore, the optimum concentrations of acetic acid, zinc chloride, lactic acid and maleic acid are confirmed and they are 10 wt%,8.75 wt%,7 wt% and 5.25 wt%. The surface property and morphology of the membrane are characterized.After that additives complex formulation is investigated and acetic acid plus lactic acid, acetic acid plus maleic acid, zinc chloride plus lactic acid and zinc chloride plus maleic acid are used as complex additives. The mechanism is explained and the optimum variety and concentration of complex additive are confirmed. They are acetic acid 7.5 wt% plus lactic acid 5.25 wt%. Under this condition the membrane exhibits rejection of 95.55% and the corresponding water flux of 7.16 L/(m2·h).Finally the effects of operational parameters such as draw solution concentration and membrane orientation on forward osmosis membrane separation performance are investigated and the results are explained. It turns out that using an active layer facing feed solution membrane orientation and a 4 mol/L glucose draw solution concentration has a better performance.