Dehydration of alcohols has attracted a great deal of attention owing to its wide application in several medical, pharmaceutical and chemical industries. High separation efficiency, low energy consumption, simplicity and minimum contamination are the main characteristics making pervaporation (PV) a promising method in the area of alcohol dehydration to provide extremely pure alcohols. Due to their high selectivity and processability, polymers are the main materials for PV membranes. Poly(vinyl alcohol) (PVA) is the most commonly used polymer because of its desired hydrophilicity, flexibility, good film-forming ability and low cost. However, excessive swelling is the main challenge in fabrication of PVA membranes for dehydration application,to overcome this disadvantage, various attempts have been made to modify PVA membranes for separation of water and alcohols. In this paper, various modifications and developments performed to improve the PV performance of PVA-based membranes for separation of water and alcohols are reviewed.

Acetic acid was separated from a dilute mixture using a commercial polyvinyl alcohol (PVA) membrane. Intrinsic separation characteristics of the membrane were studied as a function of temperature. The degree of membrane swelling decreased marginally with increase in feed temperature. At 25oC the maximum degree of swelling was found out to be 46. 3%, which reduced to 39. 5% at 65oC. Although the pervaporation flux increased with increasing temperature of the liquid feed mixture, the separation factor decreased. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters for water permeation were estimated. Diffusion and partition coefficient for water and acid were found to increase with temperature, but the diffusion coefficient of water was substantially higher than that of acetic acid at a constant feed concentration. The membrane used in the present study could tolerate highly concentrated corrosive acetic acid, thus may be useful for dehydration of other organics.

In this work, performance of composite membranes was investigated for desalination of Kashan city’s water via pervaporation process. PEBA/PAN/PE, PEBA/PSF/PE and PEBA+NaX/PSF/PE composite membranes that used, was synthesized via a phase inversion route. For all experiments under 45◦, salt rejection was too high and equals to 99.9% that this quantity dropped by increasing the temperature that cause membrane swelling in high temperatures. Water contact angle and water take-up were measured to evaluate the hydrophilicity of the membrane. Also the effect of operating conditions including feed temperature and permeate pressure on permeability and selectivity is discussed. A permeate flux of 4.93 kg/m2h with salt rejection of 99.9% could be achieved at a feed temperature of 50oC and a vacuum of 0.04 bar. Apparent diffusion coefficients of water at various permeate pressure and feed temperature are calculated. The most effective parameter was feed temperature.

Nanopore silicalite type membranes were prepared on the outer surface of a porous-mullite tube by in situ liquid phase hydrothermal synthesis. The hydrothermal crystallization was carried out under an autogenously pressure, at a static condition and temperature of 180 ° C with tetrapropylammonium bromide (TPABr) as a template agent. The molar composition of the starting gel of silicalite zeolite membrane was: Na2O/SiO2=0. 287-0. 450, H2O/SiO2 = 8-15, TPABr/SiO2 = 0. 01-0. 04. The zeolites calcinations were carried out in air at 530° C, to burn off the template (TPABr) within the zeolites. X-ray diffraction (XRD) patterns of the membranes consisted of peaks corresponding to the support and zeolite. The crystal species were characterized by XRD, and morphology of the supports subjected to crystallization was characterized by scanning electron microscopy (SEM). Performance of silicalite nanoporous membranes was studied for separation of water-unsymmetrical dimethylhydrazine (UDMH) mixtures using pervaporation (PV). Finally, a comprehensive steady state model was developed for the pervaporation of a water-UDMH mixture by COMSOL Multiphysics software version 5. 2. The developed model was strongly capable of predicting the effect of various dimensional factors on concentration and velocity distribution within the membrane module. The best silicalite zeolite membranes had a water flux of 3. 34 kg/m2. h at 27 ° C. The best PV selectivity for silicalite membranes obtained was 53.

Membrane‐based pervaporation (PV) has attracted much attention in the dehydration of organic solvents. Permeate pressure and feed flow rate are two important parameters, which affect membrane performance in pervaporation. The effects of these two parameters on the performance of a commercial poly (vinyl alcohol) membrane in the dehydration of benzene have been investigated in this work. The experiments have been carried out at a constant temperature of 60oC, and pressure and feed flow rate range from 1 to 20 mmHg and from 200 to 1200 ml/min respectively. The results indicate that variations in vacuum, especially in permeate pressures of less than 10 mmHg, greatly affect flux and selectivity so that water flux and separation factor increase from 0.98 to 2.63 (gr/hm2) and from 160 to 310 respectively by decreasing permeate pressure from 10 to 1 mmHg. Furthermore, increasing flow rate improves membrane performance only at rates of below 1000 ml/min, and no changes are observed at higher feed flow rates.