Lecture+15.++Spinning+Cone+and+RO - UNIVERSITY OF...

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UNIVERSITY OF CALIFORNIA Department of Viticulture and Enology VEN 135 WINE TECHNOLOGY AND WINERY SYSTEMS 16. REVERSE OSMOSIS AND SPINNING CONE These are two special technologies that have commercial applications in the wine industry. The first is a "molecular" filter, or more correctly a "molecular and ionic" filter that has applications in the depletion of acetic acid and ethanol from wines. The second is a vacuum still in which a central rotating device develops a very thin liquid film in which heat and mass transfer are greatly enhanced. Its most useful application is the reduction of ethanol from wines at moderate temperatures. REVERSE OSMOSIS Osmosis (Figure 15.1a) is the physical phenomenon by which water will pass across a membrane into a solution high in salt (ie low in water). This occurs in plants for the uptake of water in roots while excluding ions and in the opening and closing of stomata in leaves. The driving force is the difference in osmotic pressure between the water and the salt solution Reverse osmosis (Figure 15.1b) is when pressure is applied to a salt solution and it pushes the water in the reverse direction, from high salt strength to low. For this to occur, the pressure must exceed the "osmotic pressure” of the solution and the membrane must be capable of handling this pressure. Reverse osmosis membranes (Figure 15.2) are synthetic polymers which have very small pore, typically the size of small molecules and they also have surface charge layers which effectively repel all ions, anions and cations. The pore size is usually expressed in terms of molecular weight cut-off (MWCO) and typical RO membrane for wine applications would have about 75 % rejection at 100 Dalton and partial rejection at smaller molecular sizes. Permeable membrane OSMOSIS REVERSE OSMOSIS Permeable membrane Figure 15.1. Osmosis and reverse osmosis. In normal osmosis (a), water will move across a permeable membrane to the higher solute concentration side in order to “even out” the solute concentration through
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Lecture+15.++Spinning+Cone+and+RO - UNIVERSITY OF...

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