Study On Preparation And Performance Of Pervaporation Membranes For Separating Xylene Isomers

The pervaporation is an effective separation process for azetopic or similar mixtures.In this paper,PVA membranes containingβ-cyclodextrin (β-CD)and polyacrylic acid/hydrotalcite(PAA/HT)organic-inorganic hybrid membranes have been prepared for separation of xylene isomers,respectively. The interactions between membranes and xylene isomers have been investigated.And pervaporation performance has been discussed by dissolution-diffusion mechanism.1.PVA membranes containingβ-CDWith the presence of cross linker ethylene glycol diglycidyl ether(EGDE), theβ-CD polymer of branching chain extension(β-CD/EGDE)and the crosslinked copolymer(β-CD/EGDE/PVA)were prepared,and then the blend membrane(B-β-CD/EGDE/PVA)and copolymerized membrane(C-β-CD/ EGDE/PVA)were formed,respectively.The structures of the two kinds of polymers were characterized by FTIR,and the results showed that the structure of cavity ofβ-CD existed.The results of swelling behavior showed that the S_eqorder of blend membranes in different xylene isomers was OX＞PX＞MX which is the same with the order of complex formation constant(K)of forming host-guest complexes,while the S_eqorder of copolymerized membranes was OX＞MX＞PX which is coincident to the polarity order of xylenes.The result meant that the complex formation constant K and the polarity of xylenes were the two main factors in the swelling behavior.The results of desorption behavior demonstrated that xylene isomers in the membranes can be desorbed completely.In binary xylene isomers mixture,the pervaporation performance of PVA membranes containingβ-CD was much better than that of PVA membrane.It verified that introducingβ-CD into the membrane could improve the separation of xylene isomers.The effects of the EGDE content and feed concentration on the pervaporation performance of blend and copolymerized membranes were investigated.In the PX/MX mixture,with X_p increasing from 10 wt%to 40 wt%,the separation factorα_m/pincreased from 0.798 to 2.04 and the flux decreased from 32.7 to 24.1 g m^-2h^-1.The results of pervaporation performance were explained by dissolution-diffusion mechanism successfully. In PX/MX/OX ternary isomers mixture,the pervaporation performance was similar with that of PX/MX or PX/OX mixture,besides the permeation flux changed a little with increasing X_p.2.Polyacrylic acid/hydrotalcite(PAA/HT)organic-inorganic hybrid membranesPAA/HT hybrid materials were synthesized via inverse polymerization by intercalating PAA into modified HT.The FTIR and XRD proved that the intercalation was successful and modified HT was completely exfoliated after polymerization.The effects of the HT content in the hybrid membranes and feed concentration on the pervaporation performance of hybrid membranes were investigated.The permeation flux increased gradually and the separation factorα_m/pfirst increased then decreased with the increment of HT content.In the PX/MX mixture with 10 wt%PX concentration,when the HT content reached 2 wt%,the separation factorα_m/p,was 1.412 and the flux achieved 49.82 g m^-2 h^-1.The permeation flux increased and the separation factor decreased gradually with increasing X_p.The results of pervaporation performance were explained from the structures of hybrid membranes.The pervaporation performance of the hybrid membranes was superior to pure PAA membrane.It verified that introducing HT into the PAA membrane can improve the separation of xylene isomers.