Effect Of Downstream Pressure Research Articles

Efficient recovery of high‐purity aniline from aqueous solutions using pervaporation‐fractional condensation system

Selective recovery of valuable minor component with high‐purity form from dilute aqueous solution is an interesting issue in the area of organophilic pervaporation. High‐purity aniline was recovered with a high production rate from dilute aqueous solution by a pervaporation‐fractional condensation (PVFC) coupling system. The effects of downstream pressure and temperature (the first condenser) on the performance of PVFC system were investigated based on experimental measurements and Aspen simulations. Sorption and desorption experiments demonstrated that the sorption selectivity of poly(ether block amide) (PEBA‐2533) membrane to aniline was extremely high, indicating excellent pervaporation performance for aniline/water solutions. The perfect integration of high‐performance PEBA‐2533 membrane with the fractional condensation process yielded high production rate of 1222.5 g/(m2 h) as well as high recovery efficiency (86.5%) for recovering high‐purity aniline in the first condenser when feed concentration and temperature were 1 wt % and 80°C, respectively. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4445–4455, 2015

Membrane vacuum stripping process for volatile organics removal from water using an asymmetric PVDF (polyvinylidene fluoride) hollow fiber membrane module

The vacuum membrane stripping process (VMS) for removing a VOC (trichloroethylene) from water was studied in a polyvinylidene fluoride (PVDF) hollow fiber membrane module containing 187 fibers with a length of 0.59 m. The porous PVDF asymmetric hollow fiber used was prepared by the wet phase inversion technique. The feed solution containing trichloroethylene (TCE) was passed through the lumen of the PVDF hollow fiber. Vapors of TCE and water were transported through the pores of the membrane into the shell side maintained at a sub-atmospheric pressure, and condensed in cold traps. The effects of down-stream pressure, solution temperature, feed concentration, and feed flow rate on TCE removal, TCE permeation flux, water permeation flux and TCE concentration of the permeated solution, as well as the mass transfer coefficient were investigated. The down stream pressure and solution temperature were identified as the major factors to control VOC removal and TCE concentration in the permeate stream. A small amount of the permeated solution with higher TCE concentration was obtained at the temperature of 50°C and pressure of 80 mmHg when about 90% TCE was removed from the water.

Organophilic pervaporation: an engineering science analysis of component transport and the classification of behaviour with reference to the effect of permeate pressure

An extended mass transfer model for pervaporation that includes upstream, membrane and downstream resistances is presented. Included is a factor that can account for the potentially adverse change in the partition coefficient with low activity. Concentration-independent membrane diffusion coefficients have been assumed and so the model is mainly restricted to organophilic pervaporation. The desorption factor can be important for the permeation of less volatile organics. It is shown that the separation factor for pervaporation is influenced by the product of four terms: vapour–liquid equilibrium separation factor ( α VLE), intrinsic membrane properties ( E ∗ mem ), effectiveness of the module ( ε bl ) and the operating conditions (including feed concentration and permeate pressure). A quadratic expression relating inter alia the composition of each phase, membrane resistance and saturated vapour pressure was obtained. The effect of downstream pressure on partial fluxes and separation factor was investigated and a comparison between pervaporation and gas separation is included. Pervaporation experimental data was also used to test the derived model and found to be in good agreement. Simple dimensionless terms E and y ∗ i were derived to characterise the transport performance at various permeate pressures. The E number is a ratio of the organic flux per unit of driving force to water flux per unit of driving force determined at ultimate vacuum. y ∗ i is the permeate mole fraction of the organic at ultimate vacuum. Using E–y ∗ i coordinates a useful diagram, similar to Geldart's powder classification for fluidisation, was developed for the characterisation of the behaviour of pervaporation systems. The effect of various factors, including temperature, feed concentration and boundary layer resistance, was investigated and general rules for predicting the change of behaviour developed.

Effects of downstream pressure on pervaporation performance for dilute alcohol solution using porous hydrophobic membranes.

In the present study, we investigated the relationship between pervaporation separation properties of dilute ethanol solutions and the separation conditions, especially downstream pressure using porous hydrophobic membranes

Polyvinyl Alcohol γ-Ray Grafted Nylon 4 Membrane for Pervaporation and Evapomeation

Abstract Nylon 4, which possesses high mechanical strength and good affinity for water, can be considered as a liquid separation membrane. To improve the hydrophilicity of a Nylon 4 membrane for pervaporation and evapomeation processes, and to overcome the hydrolysis of polyvinyl alcohol (PVA), this study attempts to prepare a PVA-g-Nylon 4 membrane by γ-ray irradiation grafting of vinyl acetate (VAc) onto Nylon 4 membrane, followed by hydrolysis treatment. The effects of down-stream pressure, irradiation dose, VAc monomer concentration, degree of grafting, feed composition, and size of alcohols on the separation of water–alcohol mixtures were studied. The surface properties of the prepared membrane were characterized by FTIR, ESCA, and a contact angle meter. A separation factor of 13.8 and a permeation rate of 0.352 kg/m2·h can be obtained for a PVA-g-Nylon 4 membrane with a degree of grafting of 21.2% for a 90-wt% ethanol feed concentration. Compared to the pervaporation process, the evapomeation proces...

Plasma deposition of vinyl acetate onto Nylon-4 membrane for pervaporation and evapomeation separation of aqueous alcohol mixtures

Pervaporation and evapomeation separations of water-alcohol mixtures through a modified Nylon-4 membrane - coated with plasma deposited, hydrolyzed vinyl acetate (VAc) - (PVA-p-N4), were investigated. The effects of downstream pressure, plasma deposition conditions, feed composition, feed temperature, and size of the alcohols on the performance of the PVA-p-N4 membranes were studied. The separation factor and the permeation rate of this PVA-p-N4 membrane are both higher than those of the unmodified Nylon-4 membrane for pervaporation of aqueous ethanol solutions. A separation factor of 13.5 and a 420 g/m 2-hr permeation rate can be obtained. Compared with pervaporation, evapomeation effectively increases the separation factor for the water-alcohol mixtures, while the permeation rate is decreased.

Studies on the state of permeant in the membrane and its effect on pervaporation phenomena

AbstractPervaporation experiments of pure water and 2‐propanol through poly‐dimethylsiloxane membranes were carried out in order to study the effect of the interaction between permeant and membrane material on pervaporation phenomena. From the effect of downstream pressure on the pervaporation rate, the saturation vapor pressure of water in the membrane was determined to be 2.799 × 103 Pa (21.0 mmHg), which is the same as the literature value, whereas that of 2‐propanol in the membrane was estimated to be 5.865 × 103 Pa (44.0 mm Hg), which is 8.53 × 102 Pa (6.4 mmHg) higher than that of pure 2‐propanol. In the differential scanning calorimetry analyses of permeants in the membrane, it was evident that the state of 2‐propanol in the polydimethylsiloxane membrane was different from that of bulk 2‐propanol. On the other hand, the state of water in the membrane was assigned to that of bulk water. Throughout the present study, it was observed that the interaction between permeant and membrane material plays an important role in determining pervaporation phenomena.

Permeation equations developed for prediction of membrane performance in pervaporation, vapor permeation and reverse osmosis based on the solution-diffusion model.

General permeation equations based on the solution-diffusion model were proposed for pervaporation (PV), vapor permeation (VP) and reverse osmosis (RO) on two different assumptions about the pressure gradient inside a membrane: a flat gradient (case 1) and a linear gradient (case 2). With these equations the permeation properties in PV, RO and VP can be estimated once the transport parameter of a membrane is known.The effect of upstream pressure on selectivity and flux in RO and PV was estimated by sample calculations for water- and ethanol-selective membranes in ethanol–water system. Flux and selectivity in RO is smaller and, reaching that in PV at infinite pressure. This ultimate value is different in cases 1 and 2, and in the latter the molar volume ratio of the permeants becomes important. The effect of downstream pressure in PV was also estimated and compared with the case of vacuum-enhanced membrane distillation (MD) with a porous membrane. With increasing pressure the separation factor approaches that of vapor–liquid equilibrium in both PV and MD. With decreasing pressure that in MD is governed by the ratio of diffusion coefficients inside the membrane. Since the Knudsen diffusion coefficient of water is larger than that of ethanol, the separation factor decreases in ethanol–water separation with decreasing downstream pressure. This was verified by experiment, using PTFE membranes.