Separation Of Cyclopentadiene/Methylcyclopentadiene Mixtures With Polyimide Pervaporation Membrane

Pervaporation(PV) has advantages of high efficiency, convenient operating, low energyconsumptions, less pollution compared with conventional separation processes such asdistillation, adsorption, and extraction, and thus it’s especially suitable for the separation ofazeotropic or near-boil mixtures. Cyclopentadiene (CPD)/methylcyclopentadiene (MCPD)has became one important area among the separation of C5mixtures recently. Increasingenergy crisis provides an opportunity to impulse PV and makes it a most promising separationtechnology.Homogeneous polyimide (PI) membranes were prepared by pyromellitic dianhydride(PMDA),4,4’-(4,4’-Isopropylidenediphenoxy) bis(phthalic anhydride)(BPADA) and4,4’-diaminodiphenyl (ODA). PI membranes were investigated for PV separation of CPD/MCPD binary systems and the membrane swelling characteristies. The results show that themembrane display good selectivity and high PV performance for CPD in the CPD/MCPDbinary systems. Polymers with low chain packing density and weak chain mobility have highswelling ratio.PI was synthesized based on the PMDA, BPADA and ODA in DMAC by the lowtemperature solution-chemical imidization co-polymerization method. The bisphenol PI wasreadily soluble in the polar solvents such as NMP, DMAC, and DMF, butpolypyromelliticimide wasn’t.Asymmetric PI membranes were prepared by phase-inversion method and using a novelBPADA-ODA condensation Polymer as the membrane material. The effects of preparationprocess conditions such as evaporation time, on the structure of asymmetric PI membraneswere investigated. The PV properties of the asymmetric PI membranes were characterized bythe use of CPD/MCPD mixture. After the investigation of the relationship between PV properties and preparation process conditions, the suitable preparation process of theasymmetric membrane was as the following: the suitable PI membrane is prepared under thecondition of concentration of polyimide being18％,the content of the additive of acetonebeing15%,the evaporation time being60s, the coagulation bath being water, and the thicknessbeing150μm.Asymmetric PI membranes were used to separate the mixture of CPD and MCPD by PV.The influence of operation pressure difference, feed flow rate was studied thoroughly. Theseparation factor(α) was2.1and the flux(J) was1003g/m2·h for CPD/MCPD at XCPDof19.14%.After continuous PV, Asymmetric PI membranes show good stability.