| Membrane technology used in solvent recovery in oils processing has many advantages over the traditional ways. It does not involve a phase transition so that it can substantially reduce energy consumption. The key of such technology is to select a suitable material with excellent performance and can stand organic solvent with long stability.In this paper, poly(dimethylsiloxane)(PDMS) was selected as nanofiltration(NF) membrane material based on the physi-, chemical properties of soybean oil and hexane molecules. The NF membranes prepared in this work were employed in the recovery of hexane from soybean oil/hexane miscellas (1:3, w/w). And various methods, such as cross-linking, zeolite filling, single-wall carbon nanotubes filling and incorporation of fluorine-contained groupes, were used to improve the separation performance and the solvent resistance of PDMS membranes.Cross-linked polydimethylsiloxane/polyvinylidene fluoride (PDMS/PVDF) NF membranes were prepared. The different function composition of the PDMS/PVDF nanofiltration membranes were characterized by reflection Fourier transform infrared (FTIR) spectroscopy. The surface and section of PDMS/PVDF composite membranes were investigated by scanning electron microscope (SEM). The influences of cross-linking temperature, the thickness of PDMS layer, different solvents used in the casting membrane solution, and feed pressure on the separation performance were investigated. The results indicated that with the increase of cross-linking temperature, cross-linking degree increase, which lead to the rise of density and caused smaller available free volume of polymer matrix for diffusion, so flux dropped and oil retention increased. As the thickness of membrane increased, the flux showed a remarkable decrease, which was due to the increase in mass transport resistance; the oil retention exhibited a little increase. At the same time, the different organic solvent also has certain influence on separation performance. For the membrane with best performance, an oil retention of 92.76% and permeation flux of 2.99 kg/(m2·h) was observed under a feed pressure of 2.1 MPa.By incorporating single-wall carbon nanotubes (SWNTs) into PDMS, SWNTs filled PDMS/PVDF nanofiltration membranes were prepared. The influences of filling content and thermal pre-treatment of SWNTs on the separation performance were studied. Results indicated that after thermal purify treatment, the separation performances of the SWNTs filling composite membranes were greatly improved. An oil retention of 96.91% and permeation flux of 4.09 kg/(m2-h) was observed under 1.8 MPa.Zeolite with Si/Al ratio of 300 was used to fill PDMS/PVDF nanofiltration membranes. It was found that the filling of Zeolite into PDMS/PVDF membranes can improve the separation performance in both selectivity and permeation flux. When the content of zeolite is 30%, an oil retention of 93.21% and permeation flux of 3.88 kg/(m2·h) was observed under 2.4MPa.For the good solvent resistance, cross-linked fluorinated silicone rubber/polyvinylidene fluoride nanofiltration membranes were also prepared in this paper. It was also found that this kind of membrane has a long-term stability in organic solvent while still keep good separation performance. The separation performances changed little within one and half months. This membrane material has a broad industrial applied future. |
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