Pervaporation separation

Fig. 41. The pervaporation separation of acetone—water mixtures achieved with a water-selective poly(vinyl alcohol) (PVA) membrane and with an acetone-selective siUcone mbber membrane. The PVA membrane is best suited to removing small amounts of water from a concentrated acetone solution, whereas the siUcone mbber membrane is best suited to removing small amounts of acetone from a dilute acetone stream (89).

The pervaporation separation of water-phenol mixtures was carried out using poly(vinyl alcohol) (PVA) cross-linked membranes with low molecular weight poly(aciylic acid) (PAA), at 30, 40, and 50 °C. They have used pervaporation because the separation rate is higher (for liquid organic mixtures) in pervaporation than in reverse osmosis. 

Hybrid membranes composed of poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS), synthetised via hydrolysis and a co-condensation reaction for the pervaporation separation of water-isopropanol mixtures has also been reported [32], These hybrid membranes show a significant improvement in the membrane performance for water-isopropanol mixture separation. The separation factor increased drastically upon increasing the crosslinking (TEOS) density due to a reduction of free volume and increased chain stiffness. However, the separation factor decreased drastically when PVA was crosslinked with the highest amount of TEOS (mass ratio of TEOS to PVA is 2 1). The highest separation selectivity is found to be 900 for PVA TEOS (1.5 1 w/w) at 30°C. For all membranes, the selectivity decreased drastically up to 20 mass % of water in the feed and then remained almost constant beyond 20 mass %, signifying that the separation selectivity is much influenced at lower composition of water in the feed. 

The PVA/PAAm IPN membranes were found to have pervaporation separation factors ranging from 45 to 4100 and permeation rates of about 0.06-0.1 kg m 2 h 1, for 95 % ethanol aqueous solution, at 75 °C [46], For a concentration of 10 wt% ethanol, the permeation rates were as large as 9 kg m 2 h 1 and the separation factors were about 20 [46],... 

Ghen, X., Yang, H., Gu, Z., and Shao, Z. (2001) Preparation and characterization of HY zeolite-filled chitosan membranes for pervaporation separation. /. Appl. 

Kittur, A.A., Kariduraganavar, M.Y., Kulkarni, S.S., and Aralaguppi, M.I. (2005) Preparation of zeolite-incorporated poly(dimethyl siloxane) membranes for the pervaporation separation of isopropyl alcohol/water mixmres. /. Appl. Poly. Sci., 96 (4), 1377-1387. 

Pervaporation is a membrane separation process where the liquid feed mixture is in contact with the membrane in the upstream under atmospheric pressure and permeate is removed from the downstream as vapor by vacuum or a swept inert gas. Most of the research efforts of the pervaporation have concentrated on the separation of alcohol-water system [1-20] but the separation of acetic acid-water mixtures has received relatively little attention [21-34]. Acetic acid is an important basic chemical in the industry ranking among the top 20 organic intermediates. Because of the small differences in the volatility s of water and acetic acid in dilute aqueous solutions, azeotropic distillation is used instead of normal binary distillation so that the process is an energy intensive process. From this point of view, the pervaporation separation of acetic acid-water mixtures can be one of the alternate processes for saving energy. 

The permeation and separation characteristics of PVA-g-AN membranes toward acetic acid-water mixtures were expressed as permeation rate (flux) (0, separation factor (a) and pervaporation separation index (PSI). 

Pervaporation separation index (PSI), which is a measure of the separation ability of a membrane was defined by Huang and Yeom [7] and expressed as the product of separation factor and permeation rate. 

Aptel et al. [40] observed a reduction of separation factor as a function of decreasing membrane thickness for grafted polytetrafluoroethylene films using a water/dioxane mixture. They have shown in a different study [41] that transport rate is inversely proportional to thicknes in the pervaporation separation of water through poly(tetra fluoroethylene)-poly(4-vinylpyridine) membranes. 

Similar results were obtained in the pervaporation separation of acetic acid-water mixtures using blended polyacrylic acid-nylon 6 membranes [22], poly(4-vinylpyridine-co-aciylonitrile) membranes [11] and in the permeation and separation of aqueous alcohol solutions through PVA-AN-HEMA latex membranes [5],... 

Fig. 7. Change of pervaporation separation index with feed composition (T = 30 °C).

Comparison of the performance of the membranes based on pva for the pervaporation separation of acetic acid-water mixtures... 

Additionally in pervaporation separation follows the solution-diffusion mechanism. Therefore the molecular size of the permeating molecules becomes very important to characterize the permeation behavior [43], It is known that acetic acid has larger molecular size (0.40 nm) than water molecules (0.28 nm). As the amount of acetic acid increases in the feed mixture it becomes difficult for acetic acid molecules to diffuse through the less swollen membrane, so separation factor increases at high acid concentrations. 

Pervaporation separation index values were calculated using Eq. (3) and presented in Fig. 7. As it is reflected from... 

Y.F. Xu, R.Y.M. Huang, Pervaporation separation of ethanol-water mixtures using ionically crosslinked blended poly(acrylic acid) (PAA)-nylon 6 membranes, J. Appl. Polym. Sci. 36 (1988) 1121— 1128. 

R.Y. Huang, C.K. Yeom, Pervaporation separation of aqueous mixtures using crosslinked poly(vinyl alcohol) (PVA). Part II. Permeation of ethanol-water mixtures, J. Membr. Sci. 51 (1990) 273-292. 

S.Y. Nam, H.J. Chun, Y.M. Lee, Pervaporation separation of water-isopropanol mixtures using carboxymethylated poly(vinyl alcohol) composite membranes, J. Appl. Polym. Sci. 72 (1999) 241— 249. 

J.W. Rhim, C.K. Yeom, S.W. Kim, Modification of poly (vinyl alcohol) membranes using sulfur-succinic acid and its application to pervaporation separation of water/alcohol mixtures, J. Appl. Polym. 

U.S. Toti, M.Y. Kariduraganavar, K.S. Soppimath, T.M. Aminabhavi, Sorption, diffusion and pervaporation separation of water/acetic acid mixtures through the blend membranes of sodium alginate and guar gum-g-poly(acrylamide), J. Appl. Polym. Sci. 83 (2002) 259-272. 

Figure 9.3 The pervaporation process shown in Figure 9.1 can be described by the thermodynamically equivalent process illustrated here. In this model the total pervaporation separation /9pervap is made up of an evaporation step followed by a membrane permeation step [18]...

Figure 9.3 illustrates the concept of permeation from a saturated vapor phase in equilibrium with the feed liquid as a tool to obtain Equation (9.5). A number of workers have experimentally compared vapor permeation and pervaporation separations and have sometimes shown that permeation from the... 

The relationship between the three separation factors, /3pe ap, /3evap and /3mem, is illustrated in Figure 9.4. This type of plot was introduced by Shelden and Thompson [20] to illustrate the effect of permeate pressure on pervaporation separation... 

Figure 9.5 Pervaporation separation of acetone-water mixtures achieved with a water-selective membrane poly(vinyl alcohol) (PVA), and an acetone-selective membrane (silicone rubber) [21]. Reprinted from Hollein et al. [21], p. 1051 by courtesy of Marcel Dekker, Inc.

Table 9.2 Typical silicone rubber membrane module pervaporation separation factors (VOC removal from water)...

Figure 9.14 Pervaporation separation factor, /9pervap> as a function of the VOC evaporation separation factor, /3evaP- Data obtained with laboratory-scale spiral-wound modules containing a composite silicone rubber membrane and in laboratory cells with thick membranes...

S. Matsui and D.R. Paul, Pervaporation Separation of Aromatic/Aliphatic Hydrocarbons by a Series of Ionically Crosslinked Poly(n-alkyl acrylate) Membranes, J. Membr. Sci. 213, 67 (2003). 

As an example of hybridization of zeolites with cellulose derivatives, self-supporting zeolite membranes with a sponge-like architecture and zeolite microtubes were prepared by using CA filter membranes as a template [154]. The hierarchical structure with sub-nanometer- to micrometer-sized pores is a characteristic of great promise for a wide range of applications such as catalysis, adsorption, and separation. There was also an attempt to prepare alginate membranes incorporated with zeolites, e.g., for pervaporation separation of water/acetic acid mixtures [155]. 

The pervaporation separation factor, f3pen,ap, simply equals the product of the evaporation (distillation)... 

Alginate hydrogel membranes, crosslinked with EIX2, can be used in the pervaporation separation of ethanol-water mixtures. ... 

The pervaporation separation index (PSI) indicates the overall productivity of PV membrane ... 

Separation of water-acetic acid poly(vinyl alcohol) membranes cross-linked with mixtures glutaraldehyde Aroma compound separation, pharmaceutical and flavor-perfume industry Pervaporative separation of acetic acid-water mixtures was performed over a range of 70-90 wt% acetic acid in the feed at temperatures varying from 35°C to 50°C [110]... 

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