Study On Preparation/Characterization Of PES Membrane And Purification Of Lactose By Ultrafiltration

This dissertation was carried out based on the domestic or overseas research work about preparation and application of polyethersulfone（PES） membrane,as well as membrane separation technique for dilute lactose treatment.Firstly,the effects of PES,poly（vinylpyrrolidone） or Dimethylacetamide（DMAc） content, the temperature of coagulation bath,as well as the pre-evaporation time on the structure and properties of membrane were investigated,for the purpose of preparing a better separation membrane with uniform pores and stable performance,as well as high flux and retention.Secondly,the membrane-casting conditions were optimized based on Data Processing System（DPS）,and the PES ultrafiltration membrane with the Molecular Weight Cut-off of 20000 for PEG was obtained.Thirdly,the composition of dilute lactose solution,the structure of lactose and the method for measuring lactose content were studied by UV, Fourier Transform Infrared Spectroscopy（FTIR） and Different Scanning Calorimetry（DSC）,which provided a reference to improve membrane separation of lactose and protein.Finally,the influences of the properties of lactose feed and ultrafiltration parameters on the retention of protein and the yield of lactose were studied.The main research work is described as follows:（1）The effects of PES or polyvinyl pyrrolidone content on the structure and performance of PES membrane were investigated.As the PES concentration varied from 12%to 22%,the tensile strength of membrane increased obviously, while,the porosity decreased due to the densification of membrane structure in a high concentration,thus,the retention level for bovine scrum albumin increased and the pure water flux decreased.With the increase of PVP content,the viscosity of casting membrane solution gradually increased,and the tensile strength decreased.However,the addition of PVP remarkably improved the hydrophilicity of PES membrane.It was found the pure water flux increased first and then decreased with the PVP content（from 1%to 9%）.The maximal flux was 508.33L/（m²·h） when PVP content was 5%.At this point,the retention level for bovine serum albumin was mimimal,being 66.3%.（2） The effects of membrane-casting conditions on the structure and performance of PES membrane were discussed.As pre-evaporation time increased,the water flux first decreased and then it increased as the pre-evaporation time was over 90s,The retention level for albumin bovine first increased and then decreased,and a maximal value was 60.6%occurred at 50s. The porosity remained almost unchanged.When the coagulation bath concentration varied from 10%to 20%,the water flux decreased,but when the coagulation bath temperature increased,the retention level for albumin bovine increased,the flux increased,and the retention level for albumin bovine decreased.（3） Based on the uniform experimental design method and mechanism,DPS was used to optimize the main elements that influenced membrane preparation by L-S phase translation.The regression equations of corelations between water flux/ rejection to PEG 10000 and the related membrane prapartion conditions were established by DPS software,and then the simulation values of related membrane praparation conditions were determined.In other words,on the basis of model equations,the effects of PES concentration,additive concentration, DMAc content in the coagulation,and pre-evaporation time upon the flux and retention were investigated by simulation analysis.The result showed good agreement with experiment,indicating that this method was effective for the calucation of vluve for membrane preparation control.The optimal conditions were confirmed by the retention equation,as follows:PES concentration 22w%, additives concentration 5.1057w%,evaporation time 120s,and the DMAc content in coagulation 23.75%.Thus,PES membranes with average pore radius 12.1nm and maximal radius 25.4nm were prepared based on previous optimized conditions.The flux of pure water was 339.85 L/（m²·h·MPa）,and the rejection to PEG20000 was 89.7%. （4） The physicochemical properties of lactose were characterized by UV,FTIR and DSC.The rough lactose included 91.68%lactose,1.8%protein,and other constituents.And there was 0.67%glycoprotein,in which sugar and peptide were bonded by N-linkage.The DSC data showed a strong endothermal peak appeared at 150℃and another endothermal peak appeared at about 219℃.The former represented the dehydration ofα-lactose monohydrate,and the latter represented the decomposition ofα-lactose monohydrate.The bands of 876cm^-1, 899cm^-1 and 916cm^-1 appeared in FTIR spectrum,which were a typical absorption ofα-lactose monohydrate.The calibration curve of lactose was established by picric acid colorimetric method using ultraviolet spectrum at 520nm.The corresponding equation was y（g/L）=-0.05607+10.95571x,the related coefficient R=0.99813.（5） The effects of feed temperature and concentration,ultrafiltration pressure and time on the retention of protein,flux,and yield of lactose were studied.The optimal process conditions were obtained:the ultrafiltration pressure of 0.3MPa, feed temperature of 50-60℃,lactose concentration of 100-150g/L,operation time of 45-60min.With the increase of ultrafiltration time,the rejection of protein increased,but the flux and yield of lactose drastically decreased.The flux was reduced to half the original value after 1h.However,70%of the flux could be recovered easily by rinsing the membrane in 0.5%NaOH solution for 20min.This study may serve as experimental foundation to further research on the control of membrane structure and performance,and effective application of ultrafiltration membrane in lactose purification.