Preparation and properties of a weak acid ion exchange polyacrylonitrile (PAN) nanofiber membrane

Autor: Jian-min Lin, 林兼民
Rok vydání: 2012
Druh dokumentu: 學位論文 ; thesis
Popis: 100
Ion exchange membranes are commonly used in separation and purification systems. However, micropore blockage within its resin structure can easily lead to a reduction in the effectiveness of purification, with regeneration response rate dropping as a result. The resin itself is vulnerable to extrusion pressure and damage. To tackle this problem, we adopted the concept of membrane separation. By combining electrospinning techniques with rapid alkaline hydrolysis, we successfully prepared a weak acid ion exchange nanofiber membrane. The membranous material was made of nonwoven polyethyleneterephthalate (PET) spunbond fabric for the intermediate substrate. The upper and lower layers were made of polyacrylonitrile (PAN) nanofiber membranes. Using a heat pressing technique, the PAN-PET-PAN (AEA) layers were combined into an asymmetrical membrane structure. NaOH was applied to quickly alkaline hydrolyze -C ≡ N bond to the PAN nanofiber surface, converting it into -COOH carboxyl group. In this manner, we succeeded in preparing a weak acid ion exchange nanofiber membrane (AEA-COOH). SEM observation showed that the diameter of the electrospun PAN nanofiber distribution was uniform, falling between 200-250nm. After the heat pressing, the 3D reticular structure of the membrane increased in density and the pore distribution became more concentrated. Organic solvent residue analysis proves no significant dimethylacetamide release from electrospun polyacrylonitrile nanofibers. Various conditions in the alkaline hydrolysis process, such as temperature (25-85 ℃), concentration (1-3N), and time (0-40min), were simultaneously tested in order to get a better understanding of the density of the PAN nanofiber surface -COOH group. To understand the characteristics of the AEA-COOH membrane, we used the commercially available product SartobindR ion exchange membrane as the standard of comparison. Results of the experiments showed that the base weight and thickness AEA-COOH were 33% and 64%, relative to SartobindR C membrane. The surface area (6.1768 m2/g) was 7 times larger, and its pore rate (84.4%) was higher than SartobindR C membrane (73.4%). AEA-COOH membrane pyrolysis temperature (320 ℃) was far higher than that of SartobindR C of 115 ℃, indicating high thermal stability. Finally, we use commercial SartobindR ion-exchange membranes as the comparison standard. Results show that AEA-COOH membranes in a pH 9 environment can adsorb approximately 105 mg of lysozyme, which is twice that of SartobindR C and SartobindR S membranes. The lysozyme was directly purified from the chicken egg white using Millipore stirred cell reactor equipped with AEA-COOH membranes. Despite a protein recovery of only 22.3 %, the purified lysozyme had an activity recovery as high as 80.5 % with a 73.6-fold purification. SDS-PAGE (sodium dodecyl sulfate - polyacrylamide gel electrophoresis) confirms the purified lysozyme product. This study thereby verified that lysozyme protein can be isolated and purified directly from chicken egg whites using AEA-COOH membranes. Comparisons between the lysozyme adsorption density and rates of different ion exchange membranes, confirmed that PAN nanofiber, formed by weak acid ion exchange membrane, was lighter, thinner, faster, and possessed higher adsorption efficiency and adsorption concentration, than SartobindR membrane. This PAN nanofiber could enhance the overall adsorption efficiency of purification processes.
Databáze: Networked Digital Library of Theses & Dissertations
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