Hydrophobic Modification Of Polysulfone Membrane And Application In Vacuum Membrane Distillation

Membrane distillation is a new separation technology, the vapor molecules goes through the thermal insulator porous hydrophobic membrane under the common driving force-heat and pressure difference of the two sides of the membrane. Therefore, the rejection rate of the non-volatile solution can reach 100% theoretically.The main research contents of this paper are the hydrophobic modification of hydrophilic polysulfone membrane with chemical methods and using the modified membranes in the vacuum membrane distillation process and membrane fouling research.In the hydrophobic modification experiments, the γ-aminopropyltriethoxysilane-amino silicone oil emulsion and tetraethylorthosilicate-trimethylchlorosilane were used in the polysulfone membrane hydrophobic modification. Different modification conditions were researched on the influence of the hydrophobic properties of the modified PSF membrane. The hydrophobicity of the modified PSF membrane was improved which the maximum contact angle of modified PSF membrane treated with amino silicone oil emulsion and trimethylchlorosilane reached 116° and 135° respectively.In the vacuum membrane distillation process, the effect of feed solution concentration, flow rate, feed temperature and the vacuum pressure on the membrane flux and the salt rejection rate were researched repectively. Results show that the maximum membrane flux of the trimethylchlorosilane and amino silicone oil emulsion modified PSF membrane was 10.45 kg/(m2·h) and 9.71 kg/(m2 · h) respectively in the conditions of 4% NaCl concentration, 80℃ feed liquid temperature,4 mL/s feed liquid flow rate and 0.095MPa vacuum pressure. The desalination results were well with the salt rejection rate exceeding 99.2%.In the membrane fouling experiments, two reasons may mainly be included in the reducing membrane flux, one is due to the accumulation of sodium chloride particles on the membrane surface which may block up the membrane pores, the other is that high temperature may make the modified polysulfone plate membrane shrink and deformation, both of these could cause the membrane flux decline with decrease of the membrane pore size and porosity.The lmol/L HC1 solution was used to wash the fouled PSF membrane and there was certain degree of recovery membrane flux through the flux recovery experiments. As for the PSF membrane modified with ASOE, the recovery rate of membrane flux is about 96.9%, 94.9% and 85.9% for the third times cleaning. As for the PSF membrane modified with TMSC1, the recovery rate of membrane flux is about 95.4% and 94.8% for cheaning twice respectively. Therefore, the membrane flux is reduced with the increase of running and cleaning times.