Yangzheng Lin

Synthesis of Polyimides Containing Fluorine and Their Pervaporation Performances to Aromatic/Aliphatic Hydrocarbon Mixtures

Two kinds of polyimides containing fluorine were synthesized based on dianhydride of 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and diamines including 2,2‐bis[4‐(4‐aminophenoxy)phenyl] hexafluoropropane (BDAF) and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane (BAPP) using solution condensation and following chemical imidization. The structures of 6FDA‐BDAF and 6FDA‐BAPP were characterized by FT‐IR, NMR, and XRD. Their glass transition temperatures characterized by DSC were in the range of 235–251°C, and the initial decomposition temperatures determined by TGA were over 540°C. The membranes of polyimide thus obtained were employed in pervaporation separation of aromatic/aliphatic mixtures. 6FDA‐BDAF membranes obtained better separation performances than 6FDA‐BAPP and had a flux of 0.66 kg · µm/m2 · h and separation factor of 6.49 for toluene/n‐heptane (20/80 wt.%) at 80°C. The effects of the fluorine group on polyimides properties and separation performances were investigated.

ULTRAFILTRATION MEMBRANE FORMATION OF PES-C, PES AND PPESK POLYMERS WITH DIFFERENT SOLVENTS *

Ultrafiltration membranes were prepared using phenolphthalein polyarylethersulfone (PES-C), polyethersulfone (PES) and poly(phthalazinone ether sulfone ketone) (PPESK) as polymers and NMP, DMAc, DMF and DMSO as solvents by immersion precipitation via phase inversion. Experimental data of thermodynamic properties of the polymer solutions and kinetic process of membrane formation were reported. For polymer solutions with good solvents, the sequence of the viscous flow activation energy (Eη) was coincident with that of the viscosity (η), without depending on the dissolving power of the solvents (characterized by intrinsic viscosity ([η])). The cloud point of the dilute polymer solutions was related to [η] of the polymer and gave a strong influence on the gelation rate in membrane formation process. The pure water flux (J) and the bovine serum albumin (BSA) rejection (R) of PES-C, PES and PPESK membranes were measured, the pure water flux (J) of membranes significantly depended on the gelation rate. The open porosity (OP) and the maximum pore size of membrane surface were calculated, and the relationship between membrane performance and membrane pore structure was discussed.

Preparation and Pervaporation Performances of PEA‐based Polyurethaneurea and Polyurethaneimide Membranes to Benzene/Cyclohexane Mixture

Pervaporation is promising in the separation of benzene/cyclohexane mixture for the petrochemical industry. Two kinds of pervaporation membrane materials, including PEA‐based polyurethaneurea (PUU) and polyurethaneimide (PUI), were successfully synthesized from the same soft segment of poly(ethylene adipate)diol (PEA) and different hard segments via a two‐step method. The hard segment of PUU was prepared from toluene diisocyanate (TDI) and 4,4′‐diaminodiphenyl methane (MDA), while that of PUI was from 4,4′‐methylene‐bis(phenylisocyanate) (MDI) and pyromellitic dianhydride (PMDA). The structures and properties of PUU and PUI were characterized by means of FT‐IR, DSC and TGA. During the pervaporation experiment, the PUI membranes had a flux of 12.13 kg µm m−2 h−1 and separation factor of 8.25, while the PUU membranes had a flux of 26.35 kg µm m−2 h−1 and separation factor of 6.29 for 50 wt% benzene in the benzene/cyclohexane mixture at 40°C. The effects of the structures of hard segments on pervaporation performances were discussed. The investigation of the relationship in molecular structure and PV performances will be helpful for the choice and design of membrane materials in the separation of benzene/cyclohexane mixture.

SEPARATION OF PROPANE FROM PROPANE/NITROGEN MIXTURES USING PDMS COMPOSITE MEMBRANES BY VAPOUR PERMEATION *

This study deals with polydimethylsiloxane (PDMS)/polyvinylidene fluoride (PVDF) composite membranes for propane separation from propane/nitrogen mixtures, which is relevant to the recovery of propane in petroleum and chemical industry. The surface and cross-section morphology of PDMS/PVDF composite membranes was observed by scanning electron microscope (SEM). The surface morphology of PDMS/PVDF composite membranes is very dense. There are three layers, the thin dense top layer, finger-like porous middle layer and sponge-like under layer in the cross-section SEM image of PDMS/PVDF composite membranes. The effects of the types of cross-linking agents and pressure on the membrane permselectivity were investigated. The permeability of nitrogen was independent of feed pressure. However, the permeability of propane increased with the pressure increasing for all membranes. The membrane cured by a tri-functional crosslinker with attached vinyl groups had better performance than the tetra-functional one, in both ...

PERVAPORATION SEPARATION FOR TOLUENE/ n-HEPTANE MIXTURE BY POLYIMIDE MEMBRANES CONTAINING FLUORINE *

Five kinds of polyimides were synthesized using five dianhydrides (including 2,2-bis[4-(3,4-dicarboxyphenoxy)-phenyl] propane dianhydride (BPADA), 3,3′,4,4′-diphenylsulfone-tetracarboxylic dianhydride (DSDA), 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA), 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA), and 4,4′-oxydiphthlic dianhydride (ODPA)) and 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane (BDAF) via the two-step method that included polyaddition to form the polyamic acid and subsequent chemical imidization at ambient temperature. The structures of polyimides were characterized by FTIR and NMR. The thermal properties were characterized by DSC and TGA. All five kinds of polyimides showed good thermal properties and solubility in organic solvents such as DMF, DMAc, NMP and THF at room temperature. The pervaporation (PV) experiments of polyimides for toluene/n-heptane mixture were carried out, and all the polyimides showed selective permeation towards toluene. The fluxes of 6FDA-BDAF, DSDA-BDAF, HQDPA-BDAF and ODPA-BDAF at 80°C were 1.08, 0.96, 1.77 and 0.10 kg·μm/(m2·h), and the separation factors were 5.44, 1.64, 1.28 and 11.44, respectively. The increasing feed temperature resulted in higher flux and lower separation factor of the 6FDA-BDAF membrane.