Permeate, membrane technology

Sugano, H. Artifidal membrane technologies to assess transfer and permeation of drugs in drug discovery. In ADME/Tox Approaches, Tests, B.,... 

Both of the current commercial pervaporation processes concentrate on the separation of VOCs from contaminated water. This separation is relatively easy, because organic solvents and water have very different polarities and exhibit distinct membrane permeation properties. No commercial pervaporation systems have yet been developed for the separation of organic/organic mixtures. However, current membrane technology makes pervaporation for these applications possible, and the process is being actively developed by a number of companies. The first pilot-plant results for an organic-organic application, the separation of methanol from methyl tert-butyl ether/isobutene mixtures, was reported by Separex in 1988 [14,15], This is a particularly favorable application... 

My introduction to membranes was as a graduate student in 1963. At that time membrane permeation was a sub-study of materials science. What is now called membrane technology did not exist, nor did any large industrial applications of membranes. Since then, sales of membranes and membrane equipment have increased more than 100-fold and several tens of millions of square meters of membrane are produced each year—a membrane industry has been created. 

Figure 8.18 Flow schemes ofthe separation train of a 50-million gallon/y bioethanol plant. Current technology is illustrated in (a). Pervaporation membranes can be used to replace the molecular-sieve drier of the plant (b) or vapor-permeation membranes can be used to replace the rectifier column and molecular-sieve units (c).

Sulfur dioxide is a common pollutant found in coal-fired facilities. Various membrane permeation schemes have been proposed but few are competitive with wet scrubbing. More recently, however, bipolar membrane technology (q.v.) has been successfully used to recycle the scrubbing effluent and convert the sulfur into sulfuric acid. 

Membrane technology is also offered by other licensors an example is the Polysep Membrane System of UOP [970], In addition to the systems based on hollow fibers, membrane modules have been developed in which the membrane is in the form of a sheet wrapped around a perforated center tube using spacers to separate the layers. The raw gas flows in axial direction in the high pressure spacer and the permeate is withdrawn in the low pressure spacer. Such a module, for example, is marketed under the name Separex [971], [972],... 

Over the course of development of the membrane technology, RO module designs, as shown in Figure 8.4, evolved. They are tubular, plate-and-frame, spiral wound, and hollow hne-hber modules. In the tubular design, the membrane is lined inside the tube which is made of ordinary tubular material. Water is allowed to pass through the inside of the tube under excess pressure causing the water to permeate through the membrane and to collect at the outside of the tube as the product or permeate. The portion of the influent that did not permeate becomes concentrated. This is called the concentrate or the reject. 

Besides some measures of separation efficiency such as the separation factor and extent of separation defined above, some quantity indicative of the throughput rate of a membrane system is needed to compliment the permselectivity of the membrane. It is quite common and practical in the membrane technology to use a phenomenological expression to relate the permeate flux (Ja in the unit of cm (STP)/s-cm7) of a given gas (A) through the membrane to the driving force, the transmembrane pressure difference (Ap) as follows ... 

Recent research efforts brought about new and exciting developments in membrane technology, some with direct implications for the membrane filtration of beer. For example, Stopka et al. [21] reported flux enhancement in the microfiltration of a beer yeast suspension when using a ceramic membrane with a helically stamped surface. A relatively simple modification of the ceramic membrane surface resulted in modified hydrodynamic conditions and disturbance of the fouling layer. As compared with a regular, smooth ceramic membrane of the same nominal pore size, the stamped membrane leads to higher flux and lower power consumption per unit volume of permeate at the same velocity of the feed. 

The drastic reduction of the permeate flux to only a fraction of the theoretical capacity of the membrane is rather common in pressure-driven membrane processes, but it is more pronounced for beer as compared to other fluid foods such as milk, wine, or fruit juices. This explains the earlier introduction of membrane technology at a commercial scale in those industries as compared to the beer industry. 

Both retentate and permeate from membrane separation techniques have become important starting materials in producing novel products and ingredients from milk of unique functional properties and organoleptic quality. Henning et al. [7] enumerated the current and new applications of membrane technologies in the dairy industry, which include... 

Carbon dioxide is the major compound of greenhouse gases the emission of which should be reduced. Membrane technology is one of the most promising methods for this purpose since it may be able to recover CO2 at elevated temperatures without losing sensible heat [1-4]. In this study, Y-type zeolite membranes were developed, and their C02-selective permeation was evaluated. 

Sugano, H. (2007) Artificial membrane technologies to assess transfer and permeation of drugs in drug discovery, in ADME/ToxApproaches, Vol. 5 (eds B. Testa and H. van de Waterbeemd), in Comprehensive Medicinal Chemistry, 2nd edn (series eds J.BTaylor and D.J. Triggle), Elsevier, Oxford. 

Du Pont does not currently market Permasep permeators for gas separations. They did, however, in the B-1 Permasep permeator, introduce the first commercial, hollow fiber permeator for gas separations. This permeator employed hollow fibers of polyethylene terephthalate as the membrane. Later, permeators having aramid hollow fiber membranes were field tested for hydrogen separations. Du Pont is presently actively engaged in research for the development of membrane technology for a wide variety of applications. 

---