Simulations help integrate membranes into process streams.

The annual commercial growth of membrane technology has been in the 12% to 15% range in recent years. However, most uses for the technology have involved seawater desalination and medical applications.

In the food industry, membranes have potential for yielding products of high value. Developing effective simulation software for separation processes will increase the number of applications for membranes. With this in mind, German scientists have been developing new processes that can separate valuable substances from product and process streams. They've also been using simulations to integrate membranes into processing streams.

Efficient simulation models can lead to the development of new processes. Using membranes to produce high-value products is one thing. In addition, the application of efficient simulations that are based on the interactions in real systems can improve the quality and the effectiveness of membrane processes.

The Germans have developed and optimized two different processes. These include the integration of pervaporation in a membrane-hybrid process and a membrane extraction technique that uses a hollow-fiber membrane module, in a process called perstraction, to separate flavors from a fermentation broth. The investigators have written a mathematical model that would allow you to use membranes in wastewater treatment. The model takes into account physicochemical parameters and coupling effects.

Pervaporation is a process in which a liquid stream containing two or more components comes in contact with one side of a nonporous polymeric membrane while a vacuum or gas purge is applied to the other side. The components in the liquid stream sorb into the membrane, permeate through the membrane and evaporate into the vapor phase. The vapor, referred to as the permeate, is condensed.

Because different species in the feed mixture have different affinities for the membrane and different diffusion rates through the membrane, a component at low concentration in the feed can be highly enriched in the permeate. The permeate composition may differ widely from that of the vapor evolved after a free vapor-liquid equilibrium process. Concentration factors can range to more than 1,000, depending on the compounds, the membrane and process conditions.

Pervaporation and perstraction can separate flavor compounds from aqueous-organic solutions, such as a fermentation broth or fruit extracts. Pervaporation can be used for the in situ separation of a product in order to increase the time and rate of the fermentation process, as well as to avoid product inhibition. Undertaking an extraction with hollow-fiber membrane modules makes possible a faster separation of flavors than conventional extraction processes.

Further information. Birgit Ditgens, Department of Food Technology, University of Bonn, Roemerstrasse 164, Bonn, D-53117, Germany; phone: [phone]; fax: [phone]; email: [e-mail].