Preparation And Characterization Of Cellulose Acetate Butyrate Thin Film Composite Forward Osmosis Membranes

The forward osmosis technology realizes the separation process without external pressure.It is currently the most advanced desalination and water purification technology in the world.The thin film composite membrane?TFC?with high water flux and salt rejection rate has received extensive attention.In the application process of the CAB thin film composite forward osmosis membranes,the permeation flux of the membrane is generally far below the theoretical value,and one of the important factors influencing the membrane performance can not achieve the desired effect is the porous support base membrane layer.The thickness,surface morphology,flow path tortuosity and hydrophilicity of the porous support layer affect the mass transfer resistance,polarization concentration polarization,and contamination resistance of the forward osmosis process.Therefore,the preparation of a support layer with excellent properties and structure is a matter of urgency for the development of the efficient performance of CAB thin film composite forward osmosis membranes.In this paper,cellulose acetate butyrate?CAB?was used as membrane material.CAB substrate membranes were prepared by Nonsolvent Induce Phase Separation and Nonsolvent thermally-induced phase separation.The effects of various membrane conditions on the structure and properties of substrate membranes were investigated.M-phenylenediamine?MPD?and trimesoyl chloride?TMC?were the active monomers.The CAB thin film composite forward osmosis membrane was prepared by interfacial polymerization on the surface of the support membrane.The effect of the support membrane on the structure and properties of the CAB thin film composite forward osmosis membranes was investigated.Finally,the best CAB thin film composite forward osmosis membranes prepared by the two methods were tested for forward osmosis contamination.The fouling mechanisms of the two osmosis composite membranes were studied,and the antifouling performance of the membranes was compared.The main findings are as follows:?1?Cellulose acetate butyrate?CAB?was used as the membrane material,formamide as an additive,N,N-dimethylacetamide?DMAc?,acetone,and 1,4-dioxane as solvents,substrate membranes were prepared by non-solvent phase formation method.With m-phenylenediamine and trimesoyl chloride as active monomers,composite forward osmosis membranes were obtained by interfacial polymerization on the surface of the CAB substrate membranes?the support layer?.The results showed that the support layer prepared in the mixed solvent had better structure and performance than that prepared in single solvent.The performance of the CAB thin film composite forward osmosis membranes prepared by interfacial polymerization on the substrate membrane is affected by the support layer.The CAB substrate membranes were prepared using a mixed solvent of N,N-dimethylacetamide?DMAc?and 1,4-dioxane(m_DMAc/m _1,4-dioxane=58:10)and a coagulant bath temperature of 20°C.The pore structure of the prepared CAB substrate membrane was dense on the surface and sponge-like on the inside.The water flux reached 843 L·m^-2·h^-1 and the retention rate of bovine serum albumin?BSA?was 97%.For the forward osmosis composite membranes prepared by interfacial polymerization,the membrane structure parameter S value of the membrane structure parameter is small,the positive water flux reaches 67.4 L·m^-2·h^-1,and specific salt flux?salt reverse flux/water flux?is 0.076 g/L,with excellent forward osmosis performance.?2?CAB was used as the membrane material,caprolactam?CPL?as the diluent,the substrate membranes were prepared by Nonsolvent thermally-induced phase separation.A layer of polyamide was polymerized on the surface of the substrate membrane,and the thin film composite forward osmosis membrane was obtained.The results showed that the surface pore size of the substrate membrane became smaller and the number of finger holes in the subcortical layer became smaller as the concentration of membrane polymer increased.The water flux decreased.The higher the coagulation bath temperature,the larger the pore size of the base membrane.When the coagulation bath temperature was 60°C,the substrate membrane was dense near the top-surface,and sublayer was a large cavity structure,and the sublayer to the subsurface was a through-cell honeycomb structure.16%CAB,84%CPL,and the coagulation bath temperature was 60?were the best substrate membrane preparation conditions.The CAB thin film composite forward osmosis membranes prepared by this method has the best performance,and its forward osmosis performance test results show that the water flux reaches 53.9 L·m^-2·h^-11 and?b?and specific salt flux what the reverse salt flux ratio water flux is 0.08 g/L.The RO performance test result is R value.It reaches 96%.Concentration polarization effect was further explored,flow rate and concentration of the draw solution were changed in the FO test,and it was found that the test flow rate was increased,the external concentration of the membrane surface polarization effect was reduced,the membrane water flux increased,and specific salt flux decreased.The higher the concentration of the draw solution,the higher the osmotic pressure.As the water flux increases,specific salt flux also increases,and the influence of the concentration-diffusion polarization on the membrane increases.When 1mol/L NaCl was used as the draw solution,the CAB thin film composite forward osmosis membranes had higher water flux and lower specific salt flux.?3?The CAB thin film composite forward osmosis membranes which prepared by the two methods were subjected to fouling test.Sodium alginate and BSA were used as foulants.The anti-pollution mechanism of the CAB thin film composite forward osmosis membranes with two structures and the influence of the membrane performances were studied.The results show that f the CAB thin film composite forward osmosis membranes with large pore size of the support layer cannot be cleaned by simple physical cleaning.The flux recovery rate of the CAB thin film composite forward osmosis membranes prepared by nonsolvent thermally-induced phase separation is higher than that prepared by the non-solvent induced phase separation method,and the honeycomb pore structure is easier to clean.