Vapor permeation systems

Adding a pervaporation/vapor permeation system to a pinched distillation can give the following benefits ... 

Schucker, R.C. 2001. Membrane pervaporation and vapor permeation system. US 6273937. 

The most common membrane systems are driven by pressure. The essence of a pressure-driven membrane process is to selectively permeate one or more species through the membrane. The stream retained at the high pressure side is called the retentate while that transported to the low pressure side is denoted by the permeate (Fig. 11.1). Pressure-driven membrane systems include microfiltration, ultrafiltration, reverse osmosis, pervaporation and gas/vapor permeation. Table ll.l summarizes the main features and applications of these systems. 

On-line pervaporation, 18 518 On-line probes, for fermentation, 11 39 On-line vapor permeation, 18 518 On/off feedback controllers, 20 691 Onstream analyzers, 20 682 On-tank leak detection systems, 24 311 Onyx thermal printing process, 19 321 Oocytes, retroviral infection of, 12 457 Oolitic limestone, 15 28 Opacification, colorants for ceramics, 7 344-345... 

This test is conducted on containers heat-sealed with foil laminate therefore, only the properties of the container are evaluated. The level of protection from water vapor permeation provided by a packaging system marketed with a heat-sealed foil laminate inner seal (up to the time the inner seal is removed) is expected to be approximately the same as that determined by this test. The acceptance criteria are those established in USP <671>. 

This test measures the water vapor permeation of a singleunit or unit-dose container closure system and establishes acceptance criteria for five standards (Class A-E containers). 

This test is intended for drugs being dispensed on prescription, but it has also been applied to the drug product manufacturer s container closure system. If the container closure system has an inner seal, it should be removed before testing. The results from this study reflect the contributions to water vapor permeation through the container and through the seal between the container and the closure. 

Gas Dehydration. It has been found that water vapor permeates cellulose acetate membranes at a rate approximately 500 times that of methane (Ref. 2). This exceptionally high selectivity for water vapor make cellulose acetate membrane systems attractive for dehydration of hydrocarbon gas streams to pipeline specifications on either a pure gas stream or while simultaneously removing contaminating acid gases. For these applications the small size, low weight and low maintenance of the SEPAREX system is particularly advantageous for offshore installations. 

B. Will, R.N. Lichtenthaler, Comparison of the separation of mixtures by vapor permeation and pervaporation using PVA composite membranes. Part I. Binary alcohol—water systems, J. Membr. Sci. 68 (1992) 119-125. 

T. Kataoka, T. Tsuro, S.-I. Nakao and S. Kimura, Membrane Transport Properties of Pervaporation and Vapor Permeation in an Ethanol-Water System Using Polyacrylonitrile and Cellulose Acetate Membranes, J. Chem. Eng. Jpn 24, 326 (1991). 

An alternative carrier-gas system uses a condensable gas, such as steam, as the carrier sweep fluid. One variant of this system is illustrated in Figure 9.7(d). Low-grade steam is often available at low cost, and, if the permeate is immiscible with the condensed carrier, water, it can be recovered by decantation. The condensed water will contain some dissolved organic and can be recycled to the evaporator and then to the permeate side of the module. This operating mode is limited to water-immiscible permeates and to feed streams for which contamination of the feed liquid by water vapor permeating from the sweep gas is not a problem. This idea has been discovered, rediscovered, and patented a number of times, but never used commercially [37,38], If the permeate is soluble in the condensable... 

FIGURE 25 Medium-scale (30,000 liters/day) ethanol dehydration system by vapor permeation (Lurgi GmbH). 

The ability of a container closure system to protect against moisture can be ascertained by performing the USP (661) water vapor permeation test. The USP sets limits on the amount of moisture that can penetrate based upon the size and composition of the plastic components [HDPE, LDPE, or polyethylene terephthal-ate (PET)]. 

It should also be noted that the symbol Ki is utilized for the mol fraction ratio y, /x, in comparing the permeate composition to the reject or raffinate composition, as will be developed in Example 19.4. This is the usual symbolism as used in phase equilibria, say that of the X-value or equilibrium vaporization ratio for correlating the behavior of vapor/liquid systems—and, ideally, reflects Raoult s law. The foregoing illustrates the general problem... 

Indeed, in many cases the membrane system cannot be used directly and often pretreatment is necessary to facilitate the membrane process. Pretreatment is important and necessary in micro-, ultra-, and nanofiltration, while it is not that important for pervaporation (PV), vapor permeation (VP), or gas separation for which feed streams are usually much cleaner and do not contain many impurities. The cost of pretreatments can contribute appreciably to the overall costs. However, due to the intrinsic... 

As the membrane-based absorption process is usually efficient if the VQC concentration in the feed is ranging between 300 and 100 ppmv, whereas the membrane-based vapor permeation process is more effective at higher VQC concentrations, Poddar and Sirkar [34] studied the potentialities of a hybrid system where the two processes are coupled. The vapor permeation... 

Acetone Does not azeotrope with water, but when distilled, a large reflux is required to get a half dry product. Pervaporation is ideal for final dehydration or for debottlenecking existing distillation systems. Very often pervaporation and vapor permeation plants are designed for operation with various solvents or with solvent mixtures. 

A choice of batch or continuous pervaporation systems, or continuous vapor permeation depending on the duty. 

Existing entrainer distillation systems can also be effectively debottlenecked using pervaporation/vapor permeation (Fig. 15). Normally, the rectification column will be operating to give a product as close to the azeotrope as possible, running with a high reflux. 

According to a recent conference given by Prof. Kita [162], the classical synthesis method currently used by Mitsui allows to produce about 250 zeolite membranes per day. Both the LTA and T types (Na K) membranes are now commercial and more than 80 pervaporation and vapor permeation plants are operating in Japan for the dehydration of organic liquids [163]. A typical pervaporation system, similar to the one described in [8], is shown in Fig. 11. One of the most recent applications concerns the production of fuel ethanol from cellulosic biomass by a vapour permeation/ pervaporation combined process. The required heat is only 1 200 kcal per liter of product, i.e. half of that of the classical process. Mitsui has recently installed a bio-ethanol pilot plant based on tubular LTA membranes in Brazil (3 000 liters/day) and a plant with 30 000 liters/day has been erected in India. The operating temperature is 130 °C, the feed is 93 % ethanol, the permeate is water and the membrane selectivity is 10 000. 

However, the use of PU finishes on automotive metal on assembly lines will not come about unless or until the toxicity problem is overcome. Urethane coating producers are active in the development of new PU systems—some involving proprietary blocking agents—to tackle this problem. Their efforts should show some success by 1985. Positive influences here include the growing use of base coat/clear coat systems clear PU topcoats are under active consideration. In addition, vapor permeation curing (VPC) is under investigation. Here, acrylic/urethane topcoats are cured rapidly under ambient conditions in an amine catalyst atmosphere. 

Since the pioneering work of Tehennepe et al. [152] in 1987, many efforts have been made filling the polymeric matrix with zeolites in order to improve their stability. There are several companies that offer pervaporation organic membranes and composite membranes such as Sulzer Chemtech [153]. Commercial pervaporation and vapor permeation installations utilize polymeric membranes, like PVA (Sulzer Chemtech), polyimide (Vaperma), per-fiuoropolymers (MTR and Compact Membrane Systems), and polyelectrolytes (GKSS) or ceramic membranes, like zeolite A (Mitsui, Mitsubishi, Inocermic) and silica... 

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