Pervaporation acetic acid/water mixture

Keywords Membranes Selectivity Separations Transport processes Pervaporation Acetic acid-water mixtures Poly(vinyl alcohol) membranes Graft copolymerization... 

Another recent work presents the possibility to use a membrane made by PVA-g-acrylonitrile (AN) to separate acetic acid/water mixtures by pervaporation [70], The best separation factor (14.6) has been obtained by using PVA-g-AN (52 %) membrane, at 30°C, 90 % acetic acid in the feed. The permeation rate was 0.09 kg m"2h 1. 

Separation of acetic acid-water mixtures through acrylonitrile grafted poly(vinyl alcohol) membranes by pervaporation... 

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). 

Aminabhavi and Naik [37] obtained similar results in the pervaporation of acetic acid-water mixtures by using PVA membranes. They reported that for 20 wt.% acetic acid solutions separation factor stayed constant at 35 and 45 °C although permeation rate increased with temperature. 

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],... 

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

R.Y.M. Huang, A. Moreira, R. Notarfonzo, X.F. Xu, Pervaporation separation of acetic acid-water mixtures using modified membranes. Part I. Blended poly(acrylic acid) (PAA)-nylon 6 membranes, J. Appl. Polym. Sci. 35 (1988) 1191-1200. 

R.Y.M. Huang, C.K. Yeom, Pervaporation separaion of aqueous mixtures using crosslinked poly(vinyl alcohol) membranes. Part III. Permeation of acetic acid-water mixtures, J. Membr. Sci. 58 (1991) 33-47. 

S.Y. Lu, C.P. Chiu, FLY. Fluang, Pervaporation of acetic acid/water mixtures through silicate filled polydimethylsiloxane membranes, J. Membr. Sci. 176 (2002) 159-167. 

A good example of separation on the basis of affinity is the separation of alcohol/ water mixtures using a hydrophobic, silicalite membrane. Pervaporation of an ethanol/ water mixture through such a membrane resulted the removal of the alcohol from the mixture [16]. The separation selectivities achieved are between 10 and 60, depending on temperature and the alcohol content in the feed. In this way azeotropes can be broken. The reason for this is that the principle of separation, namely, differences in adsorptive behavior, is different from separation based on vapor pressure differences, used in distillation. Another example of such a separation is the pervaporation of an acetic acid/water mixture through a silicalite membrane, resulting in the removal of acetic acid [17]. 

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]... 

Sano T, Ejiri S, Yamada K, Kawakami Y, and Yanagishita H. Separation of acetic acid-water mixtures by pervaporation through sihcalite membrane. J Memhr Sci 1997 123 225-233. 

Van Baelen, D. Van der Bmggen, B. Van den Dungen, K. Degreve, J. and C. Vandecasteele, 2005, Pervaporation of water-alcohol mixtures and acetic acid-water mixtures. Chemical Engineering Science, 60, 1583-1590. 

Kuila SB, Ray SK. 2013. Sorption and permeation of acetic acid-water mixtures by pervaporation using copolymer membrane. Poly. Eng. Sci. 53(5) 1073-1084. doi 10.1002/ pen.23352. 

The economic feasibility of mordenite membranes for pervaporation of acetic acid/water mixtures has been also studied by the researchers of Mitsubishi [209]. The membrane performance in pervaporation was measured in a feed mixture of water (50 wt.%)/AAc (50 wt.%) to be 10.9 kg m /h for permeate flux and to be 0.77 x 10" mol mV(s Pa) for water permeance with separation factor of 500 at 130°C. 

Ishida, M., Tasaka, Y. and Aseada, M. 2005. A study on vapor permeation and pervaporation of acetic acid/water mixtures by porous silica membranes, 38(11) ... 

Lai, J.Y., Yin, YL. and Lee, K.R. 1995. Chemically modified poly(4-methyl-l-pentene) membrane for pervaporation separation of acetic acid-water mixtures. 27(8) ... 

Pervaporation was next carried out to test the selectivity of polyaniline membranes toward acetic acid-water mixtures. Different feed ratios of acetic acid and water were pervaporated through both undoped and doped polyaniline, as shown in Fig. 33.18, where the feed water content is plotted versus the permeant water content. For comparison the vapor-liquid equilibrium curve for acetic acid-water [78] is plotted just above the line of no separation. From Fig. 33.18 it is clear that undoped polyaniline has a small preference for permeating water over acetic acid at essentially any composition. However, this small preference at an average water permeability of about 0.5 g mm/(m--h) is too low to have any utility. More interesting is fully HCl-doped polyaniline, which permeates water over acetic acid in a much more selective fashion. In fact, even with a mixture of 859f acetic acid-15% water, at least 93 wt % of the permeant was water. It should be pointed out that when undoped membranes are used in the presence of acids, they will partially dope the polyaniline, the extent depending on the pH of the acid used. However, when a... 

Fig. 33.18 Pervaporation of acetic acid-water mixtures through doped and undoped polyaniline membranes. All polyaniline experiments were carried out at room temperature. The vapor-liquid equilibrium curve is plotted based on data points from Ref. 78 at 110-115.3°C and 760 mm Hg.

Acrylonitrile based membranes were also used in acetic acid-water separation. Lee and Oh [11] copolymerized 4-vinylpyridine with acrylonitrile in order to prepare a membrane for the dehydration of water-acetic acid mixture by pervaporation. Yoshikava et al. [25] reported that membranes prepared from poly (acrylic acid-co-acrylonitrile)... 

The catalytic esterification of ethanol and acetic acid to ethyl acetate and water has been taken as a representative example to emphasize the potential advantages of the application of membrane technology compared with conventional distillation [48], see Fig. 13.6. From the McCabe-Thiele diagram for the separation of ethanol-water mixtures it follows that pervaporation can reach high water selectivities at the azeotropic point in contrast to the distillation process. Considering the economic evaluation of membrane-assisted esterifications compared with the conventional distillation technique, a decrease of 75% in energy input and 50% lower investment and operation costs can be calculated. The characteristics of the membrane and the module design mainly determine the investment costs of membrane processes, whereas the operational costs are influenced by the hfetime of the membranes. 

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. 

Y.M. Lee, B.K. Oh, Pervaporation of water—acetic acid mixture through poly(4-vinylpyridine-co-acrylonitrile) membrane, J. Membr. Sci. 85 (1993) 13-20. 

T.Q. Nguyen, A. Essamri, R. Clement, J. Nell, Synthesis of membranes for the dehydration of water—acetic acid mixture by pervaporation. Part 1. Polymer material selection, Makromol. Chem. 188... 

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. 

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]. 

Yeom CK and Lee KH. Pervaporation separation of water-acetic acid mixtures through poly(vinyl alcohol) membranes crosslinked with glutaraldehyde. J. Memb. Sci. 1996 109(2) 257-265. 

Li G, Kikuchi E, and Matsukata M. A study on the pervaporation of water-acetic acid mixtures through ZSM-5 zeolite membranes. J Membr Sci 2003 218 185-194. 

The pervaporation of water/acetic acid mixtures was also evaluated with ZSM-5 membranes by the Matsukata group [181] the initial values of the separation factors in a 50 wt.% acetic acid aqueous solution were around 10-20, due to the preferential adsorption of acetic acid that decreased the amount of water adsorbed. In order to inaease the amount of water adsorbed, a surface modification that consisted of an alkali treatment with NaOH was carried out. After the treatment, the water flux and separation factor increased maikedly, reaching values up to 381 and 0.783 kg/(m h), respectively. 

NaA/polyelectrolyte multilayer-pervaporation membrane showing a greater stability under acidic conditions in comparison with a pure zeolite A membrane and maintaining a high selectivity for water over alcohols. For the same purpose, Kita et al. [181-183] proposed a zeolite T membrane, prepared by ex situ crystallization, for the per-vaporation-aided or vapor-permeation-aided esterification of acetic acid with ethanol. This membrane has a higher acid resistance and can be directly immersed in the liquid-phase reaction mixture. The conversions achieved exceed the equilibrium limit and reached to almost 100% after a stabilization period of 8 h. 

Li G, Kikuchi E, Matsukata M. Separation of water-acetic acid mixtures by pervaporation using a thin mordenite membrane. Sep PurifTechnol 2003 32 199-206. 

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