Bing-Bing Li

Poly (dimethylsiloxane)-poly (tetrafluoroethylene)/poly (vinylidenefluoride) (PDMS-PTFE/PVDF) hollow fiber composite membrane for pervaporation of chloroform from aqueous solution

A novel PDMS-PTFE/PVDF hollow fiber composite membrane using PTFE-PDMS as the top active layer and PVDF hollow fiber as the support layer was prepared for the pervaporation of chloroform from water. Sorption and diffusion behaviors of chloroform and water in PDMS-PTFE membranes, which had different PTFE content, were investigated. The results showed that with increasing PTFE content from 0 wt% to 40 wt%, chloroform/water ideal separation factor first increased and then decreased, and permeabilities of both chloroform and water increased. For the 30% PTFE-PDMS membrane, when feed temperature ranged from 40 °C to 60 °C, permeabilities of both chloroform and water increased, but ideal separation factor for chloroform/water first increased and then decreased. Effects of operating conditions, such as feed flow rate, active layer thickness, feed concentration and feed temperature, on PV performances of the 30% PDMS-PTFE/PVDF hollow fiber membrane for the pervaporation of chloroform-water mixtures were studied. Examination showed that concentration polarization on the membrane surface occurred when feed flow rate was less than 3,000 mL/min. With the increase in active layer thickness from 13.8 to 78.0 μm, chloroform flux and water flux dropped from 21 to 13 g·h−1·m−2 and from 93 to 22 g·h−1·m−2, respectively, but the separation factor increased from 1494 to 3949. With an increase of feed concentration from 55 to 850 ppm, chloroform flux increased linearly but water flux remained constant, and separation factor decreased. With an increase of the feed temperature from 40 to 60 °C, both flux and separation factor increased, the variation of permeation flux followed the Arrhenius relationship, and the activation energy values were 21.65 and 9.6 KJ/mol for water and chloroform, respectively.

Preparation and characterization of poly(dimethylsiloxane)- polytetrafluoroethylene (PDMS-PTFE) composite membrane for pervaporation of chloroform from aqueous solution

Hydrophobic polydimethylsiloxane — polytetrafluoroethylene (PDMS-PTFE) flat-sheet membranes for pervaporation (PV) of chloroform from aqueous solution were successfully fabricated by solution casting method. The structures and the performance of the membranes was characterized by X-ray diffraction (XRD), scanning electron microscope combined with energy dispersive X-ray spectroscopy (SEM-EDXS), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and the tests of contact angle and mechanical properties. The adding of PTFE particles (<4 μm) in the PDMS matrix enhanced the crystallinity, hydrophobicity, mechanical strength and thermal stability of the membranes. The examinations showed that the PTFE filled PDMS membranes exhibited striking advantages in flux and separation factor as compared with unfilled PDMS membranes. All the filled PDMS membranes with different PTFE content showed excellent PV properties for the separation of chloroform from water. When the content of the PTFE additive in PDMS composite membrane was 30 wt%, membrane performance was the best at feed temperature 50 °C and permeate-side vacuum 0.101MPa. For the 30% PTFE-PDMS membrane, with the increase of the feed temperature from 30 to 60 °C, the total, water and chloroform fluxes as well as the separation factor increased, the apparent activation energy (ΔEa) of total, chloroform and water were 21.08, 66.65 and 11.49 KJ/mol, respectively, with an increase of chloroform concentration in the feed from 50 to 950 ppm, total, water and chloroform fluxes increased but the separation factor decreased.