Preparation Of Chitosan Membranes And Pervaporation Of Ethanol Aqueous Solution

In this dissertation, membranes was preparaed withchitosanCS as main membrane material, glutaraldehyde ( GA ) , tetraethoxysilane ( TEOS ) as cross-linkers, HCl as catalyst. Composite membranes were prepared via interfacial adhesive methed. The composition and structural properties of the membranes were extensively investigated by FT-IR, XRD, TGA , DSC and XPS. The relationships among membrane material, membrane structure and separation performance were discussed.Cross-linked chitosanCS membranes were prepared by in-situ hydrolysis and condensation of tetraethoxysilane (TEOS) within chitosan aqueous solution for pervaporation dehydration of aqueous ethanol solution. The characterization results showed that the introduction of TEOS improved the hydrophilicity and restricted chain mobility of the membranes by formation of cross-linked structure. The remarkable decrease in the degree of swelling was observed with increasing TEOS mass ratio in the membranes and was attributed to the formation of hydrogen and covalent bonds within the membrane matrix. The effect of TEOS mass ratio on the pervaporation of aqueous ethanol solution was investigated. The relationship between the structure of CS-TEOS membranes and their separation characteristics was tentatively discussed. CS-TEOS membranes showed lower swelling degree and improved selectivity for aqueous ethanol solution. Comparing with chitosan control membrane CS-TEOS membrane with 6wt.% TEOS mass ratio exhibited a remarkably improved pervaporation performance with separation factor 460 and flux 281g/m2 h under the identical experimental condition. at 80℃for 90wt.% ethanol aqueous solution.Cross-linked quaternized chitosan membranes were prepared by glutaraldehyde(GA) as cross-linker with various cross-linking densities. The composition and structural properties of the membranes were extensively investigated by FT-IR, XRD, TGA and DSC. The characterization results showed that quaternized chitosan had high hydrophilicity and chain mobility of membranes by formation of cross-linked structure. The remarkable decrease in the degree of swelling was observed with increasing GA content in membranes and was attributed to the formation of covalent bonds in the membrane matrix. The effect of TEOS content on the pervaporation of water/ethanol mixtures was investigated. The membranes with fixed molar ratio 3.9 (GA to molar ratio of 100 repeated unit q-CS) and exhibited the highest permselectivity of 754 with a permeation flux of 756g/m2 h at 80℃for 90wt.% ethanol aqueous solution.Cross-linked CS thin composite membranes were fabricated via interfacial adhesive technique, The results indicated that dispersion of the interfacial adhesive dopamine in the support layer intensified the interface interaction between the cross-linked CS layer and support layer. A homogeneous, defect-free thin film of cross-linked CS on the support layer produced due to a strong interaction between the thin cross-linked CS layer and the support layer. The cross-linked CS separating layer with an approximate thinkness of 4~5μm was formed through dip-coating process. The membranes with fixed mass ratio 3.3 (GA to 100 molar ratio of repeated unit CS) and exhibited the highest permselectivity of 269 with a permeation flux of 1149g/m2 h at 80℃for 90wt.% ethanol aqueous solution. The structural stability of the composite membrane is satisfactory.