Study On Change Of Structure Characteristics Of Membrane In Ultrafiltration Process Of Protein

In order to further understand membrane fouling mechanism of various proteinsystem during ultrafiltration, This article choose the bovine serum albumin (BSA) andlysozyme (LYS) and their binary mixture as a typical protein, with different molecularweight cut ultrafiltration membrane ultrafiltration process was tested. According todifferent systems of proteins of membrane fouling during UF process, takingmembrane as a factors, investigating: membrane hydrophobictiy, surface roughness,average pore diameter and pore diameter distribution, membrane pore fractal dimension,porosity, membrane pore density changes in the protein ultrafiltration process.Combining membrane characteristic parameters change with the change of membraneflux decline and rejection rate to analytic process protein ultrafiltration membranefouling mechanism.Main conclusions are as follows:(1) The flux change of protein ultrafiltration process of PES-30k could be dividedinto: the initial stage (0~60minutes) and the later stage (60~120min), the initialstage of the flux decline rapidly, later stage tend to stability. While the flux changeof protein ultrafiltration process of PES-50k presents three stages: initial stage(0~5min), medium stage (5~60min) and last stage (60~120min). Initial flux declinedramatically. a slow flux decline during a transition stage; stable flux in the laststage.(2)The PES-50k fouling rate is faster than PES-30k in the initial stage, due to thebigger molecular weight could lead to carrying more contaminants on the surfaceof the membrane.The three proteins system caused by membrane fouling: LYS>LYS+BSA> BSA. (3) The PES-30k and PES-50k new membrane have a similar surface roughnessand membrane hydrophobictiy. The membrane hydrophobictiy increases with thefiltering time, and the biggest increase appeared in the first stage, which indicatethat with the initial adsorption of membrane protein had a great influence onmembrane flux. Membrane surface roughness increases with the increase offiltering time of protein, the biggest increase also appeared in the first stage. Differfrom BSA,LYS and LYS+BSA systems appear aggregates in the medium and laststage of membrane fouling test. Meanwhile the LYS,LYS+BSA fouled membranesuffered greater flux decline than BSA-fouled membrane, indicating theseaggregate can aggravate membrane fouling rate.(4) The structural parameter change of membrane shows that: with the UF processof PES-30k, BSA could form cake layer on membrane surface at the early foulingstage, then cake layer compaction continuously, can prevent pollutants fromentering the membrane pores. In the initial filtration of LYS, LYS+BSA mainlyprobably LYS could block the membrane pore entrance and this occur in thesepores which is small. Later gradually formed cake layer. And for PES-50k,membrane pore diameter reduce continuously with the whole UF process. LYS,LYS+BSA fouled membrane suffered the largest reduction of membrane porediameter in the first stage. It shows that pore narrowing is a major mechanism ofmembrane fouling in this stage. However, BSA fouled membrane shows biggestdrop in the transition stage.(5) For PES-30k UF membrane, membrane pore blocking is the mainly foulingmechanism of LYS, LYS+BSA fouled membrane at the initial stage. Cakefiltration is the main mechanism of LYS, LYS+BSA fouled membrane at the lastfouling stage. While the cake filtration is the main mechanism of BSA fouledmembrane with the whole period. For PES-50k, the initial filtration stage ofLYS-fouled membrane was controlled by pore constriction, while pore blockingand pore constriction were the mainly fouling mechanism of the transition stage.Pore blocking was the mainly fouling mechanism of BSA in the initial foulingstage, the transition stage was controlled by pore constriction. Cake filtration wasthe main fouling mechanism of LYS and BSA in the last filtration. The membrane fouling of binary mixtures LYS+BSA appeared to be dominated by LYS.(6) Membrane rejection rate could be influenced by different fouling mechanism,the formation of the cake layer can increase the membrane rejection. For thebigger distribution of membrane pore diameter, and which small pore have highproportion, pore blocking could lead to lower rejection rate thus bad for separation.And when the pore distribution is large, which big pore have high proportion, poreblocking could lead to higher rejection rate thus good for separation...