The infinite dilute activity coefficients and diffusion coefficients of water, methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol in cross-linked polyvinyl alcohol (PVA) were measured in the temperature range of (363.15 to 413.15) K by inverse gas chromatography. The cross-linked PVA was obtained by dissolving PVA, cross-linking agent, and catalyst in water and characterized by FTIR spectra. The van Deemter equation was used to obtain diffusion coefficients of solvents from the variation of chromatographic peak under the different flow rates of carrier gas. The interdependence on the infinite dilute diffusion coefficient and temperature follows the Arrhenius equation. Pre-exponential factor and activation energy are obtained from the Arrhenius equation.

Four kinds of different structures of homogeneous polyimide (PI) membranes were prepared by two kinds of dianhydrides and two kinds of diamines. A set of dynamical sorption/desorption equipment on-line was used to determine the sorption/desorption behaviors of steam in polyimide membranes. The diffusion of steam in PI membranes was studied under different temperatures. The diffusion coefficients and anomalous diffusion factors were calculated. The relation between diffusion coefficients of steam and the repeat unit molar free volume of PI was found from the diffusion coefficients. It can be concluded that the diffusion coefficients of steam in PI membranes increase with temperature increasing and the diffusion coefficients of steam in PI increase with the repeat unit molar free volume of PI growing.

Low-temperature plasma techniques have widely been used to modify surface properties of polymer membranes. The NF membranes were prepared from PAN UF membrane by Ar low-temperature plasma treatment and subsequent grafting of the monomer styrene in vapor phase. FTIR-ATR spectroscopy, DSC analysis and contact angle measurement were used to characterize the chemical and physical changes of PAN membranes modified by plasma-induced graft polymerization in vapor phase. FTIR spectra and DSC analysis revealed that hydrophobic monomer, styrene, was successfully grafted onto PAN UF membrane surface. DSC analysis also indicated that the average pore size decreased and the pore size distribution was narrowed with increasing graft time. The contact angle measurement results showed that the hydrophobicity of the grafted membrane was significantly increased. The filtration performances including permeation flux (J) and rejection (R) were determined with a mixture containing dewaxed oil (M-w approximate to 450 g/mol) and dewaxing solvent (toluene and methyl ethyl ketone) in the range of temperature. For the feed composition of 83.94 wt.% dewaxed solvent, the solvent in permeate solution was 98.42 wt.%, and the rejection of lube oil was up to 90.2%, which implied that these PAN membranes may be potentially used to recover the dewaxing solvent from the dewaxed lube oil. (c) 2006 Elsevier B.V. All rights reserved.

膜分离技术是当代化工领域的高新技术.由于它是解决人类面临的能源、资源、环境等重大问题的新技术,所以近30多年来取得了极为迅速的发展,已经在海水、苦咸水淡化,饮用水净化,超纯水制备,电站锅炉补给水的供应,气体净化以及石油化工、医药、冶金、食品轻工、生物产品的分离、提纯和浓缩等方面发挥了巨大的作用.正因为如此,世界各国,特别是发达国家不惜投巨资设立研究基金,以期在该领域占据领先地位.

In order to control surface performances of polyacrylonitrile(PAN) membrane,low temperature plasma-induced graft modifications was used to prepare hydrophilic membranes.By argon(Ar) treating and subsequent grafting reaction,a hydrophilic monomer,NVP,was introduced onto PAN membrane.The effectiveness of modification and the chemical changes at the modified surface was studied under different plasma operating variables and graft reaction conditions such as plasma power,treatment time,monomer temperature and reaction time.The structure and chemical composition at the PAN membrane surface were characterized by reflection FTIR,X-ray photoelectron spectroscopy(XPS),and DSC.It was revealed that NVP monomers were successfully grafted onto PAN membranes.The water permeabilities of the PAN membranes modified in different graft condition,such as reaction time,reaction temperature were measured.The flux and retention of the modified PAN membranes were determined with a mixed salt(0.03 mol/L MgSO_4+0.02 mol/L NaCl)/water system.

The infinite dilute activity and diffusion coefficients of solvents in poly(vinyl alcohol) and cross-linked poly(vinyl alcohol) are determined by using inverse gas chromatography technique with a packed column. Experimental results for water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, and 3-methyl-1-butanol in poly(vinyl alcohol); for water, methanol, and ethanol in cross-linked poly(vinyl alcohol) at different temperatures are presented. The van Deemter equation is used to obtain diffusion coefficients of solvents from the variation of chromatographic peak under the different flow rates of carrier gas. The interdependence on the infinite dilute diffusion coefficient and temperature follows Arrhenius equation well. Diffusion constant and activation energy are obtained from the Arrhenius equation.

The transport of penetrants in polymeric membranes is assumed to be a process of mixing of penetrant and polymer molecules, in which a creep strain is induced concurrently. Based on the assumption and combined with the mass conservation equation and phenomenological diffusive flux expression, a new transport model of penetrant in polymeric membrane is established, in which the total change of excess Gibbs free energy is considered as a sum of three parts calculated by the modified Scatchard–Hildebrand model, Flory–Huggins theory and linear viscoelastic theory, respectively. The partial difference equations in the model are solved by implicit finite difference method of Crank–Nicolson form, and the model parameters are optimized by simplex algorithm. The model is used to calculate various diffusions (Fickian diffusion, and non-Fickian diffusion) of ethanol in polyphthalazine ether sulfone (PPES), and polyphthalazine ether sulfone ketone (PPESK) membranes at 293.15, 298.15, and 303.15 K. The calculated results are in agreement with the experimental data and the maximal relative deviation is no more than 10.54% and the average relative deviation is 4.35%.

The nanofiltration processes for purifying fructo-ligosaccharides were simulated successfully based on extended pore model and different operation modes. Base on previous reports, the methods for calculating solution properties of fructo-oligosaccharides, including density, osmotic pressure, viscosity and diffusion coefficient, were obtained in terms of the structure comparability between oligosaccharides and small molecular sugars. Three technical indices for purifying fructo-oligosaccharides, including yield, dilute water consumption and normalized operation time, were chosen as the optimization goal. Then, the initial feed concentration, system temperature, operation pressure and dilute ratio were optimized by the results of process simulation. All these optimized results provided dependable data to the industrial design for fructo-oligosaccharides purification.

In order to control surface pore sizes of polyacrylonitrile (PAN) ultrafiltration membranes and their distribution, the present work concerns the graft-modification of membranes by Ar low-temperature plasma. Some typical plasma irradiation conditions such as plasma power of 30–40 W, irradiation time of 60 s and pressure of 15–20 Pa were experimentally selected by our previous experiments. N-vinylpyrrolidone (NVP) monomers mixed in water were grafted onto the PAN membrane surface in this investigation. The effectiveness of grafting was systemically studied under different graft reaction conditions, such as concentration of monomer, reaction time and reaction temperature. The chemical changes at the modified surface were characterized by reflection FTIR, X-ray photoelectron spectroscopy (XPS). The permeation of the prepared nanofiltration membranes were studied using pure water. Water flux significantly declines with increase in both graft reaction time and temperature of grafting medium. In the low concentration range studied, NVP monomer concentration did not have strong effect on flux. At 2 MPa and 30°C filtration conditions, the grafted membrane has a retention of 83.5% salts for a mixed salt aqueous solution (0.03 MMgSO4+0.02 MNaCl).