Sugar separation using liquid membranes

Sugar Separation Using Liquid Membranes and Boronic Acid Carriers... 

Di Luccio M, Smith BD, Kida T, Borges CP, and Alves TLM. Separation of fructose from a mixture of sugars using supported liquid membranes. J. Membr. Sci. 2000 174 217-224. 

OMD offers major advantages in comparison with the conventional thermal concentration techniques. The low temperature employed can help avoid chemical or enzymatic reactions associated with heat treatment [85] and prevent degradation of flavor, color, and loss of volatile aroma [38]. The low-operating pressure (atmospheric pressure) results in low investment costs, low risks of fouling, and low limits on compactive strength of the membrane. Since the separation is based on vapor-liquid equilibrium, only volatile compounds which can permeate the membrane and the nonvolatile solutes such as ions, sugars, macromolecules, cells, and colloids are totally retained in the feed. These factors make OMD an attractive alternative to traditional thermal routes currently used for concentration of liquid foods or aqueous solutions of thermally labile pharmaceutical products and biologicals [86]. 

Ultrafiltration (UF) is another membrane separation method used to purify liquids. UF is commonly used for recovery of proteins and in food and pharmaceutical applications. It is useful for separating permanent emulsions since the oil droplets will not pass through the membrane. UF is used for the removal of fine colloidal particles, and for recovery of dyes from wastewater. In many applications such as whey processing UF and RO are used in series. The valuable proteins are recovered by UF, and permeate from the UF system is sent to the RO system. The remaining sugars and salts are concentrated in the RO system by removing water. The concentrated permeate can then be fermented to produce ethanol, lactic acid or other products. 

The application of ultrafiltration membranes, which are currently all of a polymeric nature, is more widespread because it is possible to separate smaller molecules such as sugars from larger molecules such as proteins. The main attraction for ultrafiltering cheese milk is the increased yield that results from the incorporation of whey protein into the cheese. In a traditional process these proteins remain in the waste liquid whey. The waste stream from a membrane unit still contains lactose (milk sugar) and this can be used for alcohol production, as an animal feed or as a feed to an anaerobic digester which will produce methane. The technology is being applied to both hard and soft cheese examples includes Cheddar and Camembert. 

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