Membrane separation techniques

Hafez A, Khedr M, Gadallah H (2007) Wastewater treatment and water reuse of food processing industries. Part II Techno-economic study of a membrane separation technique. Desalination 214 261-272... 

Recent scattered reports on use of immobilized bioreactors [38,197,302,303], membrane separation techniques [271] provide initial results and possible ways to employ these techniques to achieve product separation however, the limitations posed by each of these such as reduced rates due to immobilization, or limited yield using membranes are issues which have not been completely addressed. 

Alcohol is a clean energy source that can be produced by the fermentation of biomass. However, it needs to be highly concentrated. In general, aqueous alcohol solutions are concentrated by distillation, but an azeotrope (96.5 wt% ethanol) prevents further separated by distillation. Pervaporation, a membrane separation technique, can be used for separation of these azeotropes pervaporation is a promising membrane technique for the separation of organic liquid mixtures such as azeotropic mixtures [34] or close-boiling point mixtures. 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

Evapomeation is a new membrane-separation technique for liquids mixtures, which eliminates some disadvantages of the pervaporation technique such as the decreasing of membrane permselectivity, due to its swelling by the direct contact with the feed solution. In evapomeation technique the membrane is not in direct contact with the feed solution, only with the solution s vapors. In this way the swelling of the membrane could be suppressed and consequently, the permeation rates in evapomeation are smaller than those in pervaporation, but the separation factor is greater [83],... 

There is increasing interest in the use of specific sensor or biosensor detection systems with the FIA technique (Galensa, 1998). Tsafack et al. (2000) described an electrochemiluminescence-based fibre optic biosensor for choline with flow-injection analysis and Su et al. (1998) reported a flow-injection determination of sulphite in wines and fruit juices using a bulk acoustic wave impedance sensor coupled to a membrane separation technique. Prodromidis et al. (1997) also coupled a biosensor with an FIA system for analysis of citric acid in juices, fruits and sports beverages and Okawa et al. (1998) reported a procedure for the simultaneous determination of ascorbic acid and glucose in soft drinks with an electrochemical filter/biosensor FIA system. 

Since fermentation takes place in a dilute aqueous solution, the reaction continues until the alcohol concentration approaches about 14%. At higher concentrations, the process becomes self-inhibitory. By-products from starch fermentation to ethanol can include higher-molecular-weight alcohols, glycerine, and ethers. Usually no more than 10% starch is converted to these compounds. Atmospheric distillation, vacuum distillation, and membrane separation techniques can be used to recover ethanol from the final fermented product. The distillate bottoms, called stillage, are recovered as a by-product for animal feed. A biomass fermentation flow diagram is provided in FIGURE 12-2. 

Figure 19.1 gives an overview of some of the most common membrane separation techniques, their application range and their denotation. It should be pointed out that the terminology for membrane separation processes is partly traditional. The kind of membrane-solute interactions and the respective mass-transport phenomena can therefore not necessarily be derived from the designation of the membrane separation, and should always be evaluated for the individual application envisaged. 

Membrane separation techniques, which are used mainly in industrial processes, include dialysis, electrodialysis, reverse osmosis, ultrafiltration,... 

Bdnisch, M.P., Tolkach, A., and Kulozik, U. (2006). Inactivation of an indigenous transglutaminase inhibitor in milk serum by means of UEIT-treatment and membrane separation techniques. Int. Dairy J. 16 (6) 669-678. 

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... 

Tolkach, A. and Kulozik, U., Fractionation of whey proteins and caseinomacropeptide by means of enzymatic cressbnking and membrane separation techniques, J. Food Eng., 67, 13, 2005. 

Nanofiltration is a rapidly advancing membrane separation technique for concentration/separation of important fine chemicals as well as treatment of effluents in pharmaceutical industry due to its unique charge-based repulsion property [5]. Nanofiltration, also termed as loose reverse osmosis, is capable of solving a wide variety of separation problems associated with bulk drug industry. It is a pressure-driven membrane process and indicates a specific domain of membrane technology that hes between ultrafiltration and reverse osmosis [6]. The process uses a membrane that selectively restricts flow of solutes while permitting flow of the solvent. It is closely related to reverse osmosis and is called loose RO as the pores in NF are more open than those in RO and compounds with molecular weight 150-300 Da are rejected. NF is a kinetic process and not equilibrium driven [7]. 

Supported Liquid Membrane Separation Technique—THE Principle... 

A survey of membrane separation techniques and the applied external driving forces is given in Fig. 1, in which the mean pore diameter of the membranes and the particle size are compared with the respective separation process. 

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