Pervaporation module

Alternatively, a sequence of pervaporation steps can be used to remove the reaction water (Figure 4.10). The reaction solution is pumped through a first fixed-bed reactor and afterwards a pervaporation module is used to remove the water at 80 °C. The solution is subsequently cooled to 60 °C and passed through a second reactor unit. After the next pervaporation step the water content is lowered to 0.2 wt%. By this process, isopropyl myristate is produced from myristyric acid. This and other esters of isopropyl alcohol are used in soaps, skin creams, lubricants and greases [43],... 

Figure 4.10 Pervaporation synthesis of isopropyl palmitate from palmitic acid applying a sequence of fixed-bed reactors and pervaporation modules...

Tubular loop reactors, 25 710 Tubular membrane modules, 25 821 Tubular pervaporation modules,... 

M. Kondo, M. Komori, H. Kita and K. Okamoto, Tubular-type Pervaporation Module with Zeolite NaA Membrane, J. Membr. Sci. 133, 133 (1997). 

A flow scheme for an integrated distillation-pervaporation plant operating on a 5 % ethanol feed from a fermentation mash is shown in Figure 9.10. The distillation column produces an ethanol stream containing 80-90 % ethanol, which is fed to the pervaporation system. To maximize the vapor pressure difference and the pressure ratio across the membrane, the pervaporation module usually... 

For treating water containing VOCs with separation factors of more than 500, for which concentration polarization is a serious problem, feed-and-bleed systems similar to those described in the chapter on ultrafiltration can be used. For small feed volumes a batch process as illustrated in Figure 9.16 is more suitable. In a batch system, feed solution is accumulated in a surge tank. A portion of this solution is then transferred to the feed tank and circulated at high velocity through the pervaporation modules until the VOC concentration reaches the desired level. At this time, the treated water is removed from the feed tank, the tank is loaded with a new batch of untreated solution, and the cycle is repeated. 

Pervaporation modules have been basically adapted from the module designs already used in other applications, such as RO, NF, and UF. However, the major difference is that in the latter case the applications mainly pertain to treatment of predominantly aqueous solutions. Therefore, the glues, gaskets, etc. to be used do not require any special consideration except... 

Cao B and Henson MA. Modeling of spiral wound pervaporation modules with application to the separation of styrene/ethylbenzene mixtures. J Membr Sci 2002 197 117-146. 

Kondo M, Komori M, Kita H, and Okamoto K. Tubular-type pervaporation module with zeolite NaA membrane. J Membr Sci 1997 133 133-141. 

Analytical pervaporation is the process by which volatile substances in a heated donor phase evaporate and diffuse through a porous hydrophobic membrane, the vapour condensing on the surface of a cool acceptor fluid on the other side of the membrane. Surface tension forces withhold the fluids from the pores and prevent direct contact between them. A temperature difference that results in a vapour pressure difference across the membrane provides a strong driving force for the separation, which also occurs in the absence of a temperature gradient. Evaporation will occur at the sample surface if the vapour pressure exceeds that at the acceptor surface. One important feature of pervaporation modules used for analytical purposes is the air gap between the donor phase and the hydrophobic membrane, which avoids any contact between them and reduces the problems associated with fouling of the membrane. 

Fig. 4.17. (A) Parts of a conventional pervaporation module (a) acceptor chamber (b) membrane support (c) spacer (d) donor-sample chamber (e) aluminium supports (f) and (g) rods for screwing and aligning the module, respectively (h) connectors (i) screws. (Reproduced with permission of Wiley Sons.) (B) Most significant parts of a hexagonal pervaporation module (j) membrane. (Reproduced with permission of Elsevier.)...

Fig. 4.18. Continuous iscrete approach to implementing analytical pervaporation of solid samples. The dotted line corresponds to a potential derivatization reaction of the pervaporated species and the dashed lines represent the continuous manifold used for automatic insertion of liquid samples. P peristaltic pump, AS acceptor stream, IV injection valve, SV switching valve for changing between continuous and discrete insertion of sample into the pervaporator, R reagent, DS donor-sample stream, S sample, RC reaction coil, PM pervaporation module, M membrane, D detector, W waste.

Fig. 4.19. Simplified scheme of a hydrodynamic manifold for evaluation of pervaporation efficiency. Note that, when a derivatization reaction is required prior to or after analyte separation, one or more additional channels for the reagent solution(s) must be included in the donor and acceptor stream, respectively. AIV auxiliary injection valve, MIV main injection valve, PM pervaporation module, m membrane, a merging point, D detector, W waste, AUX auxiliary channel containing acceptor solution, S sample, AS acceptor solution, DS donor solution. (Reproduced with permission of Wiley Sons.)...

The flow was stopped again and the signal corresponding to the urea concentration in the sample was recorded as before. During measurements, the pervaporation module was kept in a thermostatted water bath at the required temperature [173],... 

Consolidation of this technique as an effective, widespread analytical tool is bound to rely on future, sequential developments such as the following (a) the gathering of sufficient research experience to compile a cookbook of methods where potential users can search for solutions to specific problems and (b) the commercialization of inexpensive pervaporation modules meeting the requirements of a variety of samples and analytes. The development of such methods and theoretical studies should turn pervaporation into a useful tool for routine environmental, clinical, food and industrial analyses. 

For the model validation and the analysis of the heat integration in the hybrid pervaporation distillation process, a laboratory plant has been built at the TU -Berlin and prepared for the connection with the distillation column (see fig. 3). With this plant experiments with a flat PVA-based (Polyvinylalcohol from GKSS) hydrophilic membrane have been done. A heat exchanger has been built within the pervaporation module. The temperature in the heat exchanger has been necessary to avoid the temperature drop between feed and retentate streams in the pervaporation process. In the process a 2-Propanol/ Water mixture has been separated. The concentration of 2-Propanol in the feed is between 80 and 90 % in weight and the temperature range in the experiments was between 70 and 90°C. The feed flow is turbulent and the system fully insulated to avoid heat looses. The pressure in the permeate side has been kept at 30 mbar and the feed pressure at 1.5 bar. 

The increase in the permeate flux has an important influence into the process, making possible, either the reduction of the necessary membrane area (for a desired product purity), or the increase of the product purity (if the membrane area is kept constant). No need of external heat exchangers between two pervaporation modules is required, and... 

Fig. 13 High flux pervaporation module for silica membrane. (View this art in color at www.dekker.com.)...

A typical pervaporation set-up is depicted in Fig. 3.6-13. The liquid feed is re-circu-lated continuously between the feed reservoir (1) and the pervaporation module (2). 

A pervaporation module designed for analytical purposes, Figure 1, consists of the following parts ... 

Figure 1 Parts of a pervaporation module (A) acceptor chamber (B) membrane support (C) spacer (D) donor chamber (E) aluminum supports (F) and (G) rods for screwing and aligning the module, respectively (H) connectors (I) screws. (Reprinted with permission from De Mattos et al. (1995) Pervaporation an integrated. Talanta, 42 757 Elsevier.)...

The use of long waste tubing in the lower part of the pervaporation module can also improve the... 

The versatility of the design of an analytical pervaporation module, attributable to its changeable donor volume and the air gap present above the sample, has enabled its use with liquid, solid, and semisolid samples. Table 1 summarizes the applications of analytical pervaporation and the main fields in which it has been used. The manifold used and the way in which the sample is introduced in the system vary depending on whether it is liquid or solid. The main difference between the treatment of liquid and solid samples is the fact that with liquids the whole pervaporation process, from sample introduction to delivery of the results can be fully automated, while some operator s intervention is needed when dealing with solids. 

The feasibility of an integrated photocatalysis-pervaporation process can be preliminarily evaluated by taking into account some characteristics of photocatalysis. In the typical appHcations of photocatalysis, the reagents, which are termed substrates in the common terminology of photocatalysis (Braslavsky et al., 2011), should be present in low concentrations in order to ensure the economy of the process. Therefore the system is not as chemically aggressive for the membrane, particularly if the pervaporation modules are kept in separate equipments. In this way, the membrane is not exposed to the radiation or to the photoactivated radicals, which are present only close to the surface of the photocatalyst, as long as it is illuminated, since the lifetime... 

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