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Title:
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Dewatering of organics by pervaporation with silica membranes
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Author(s):
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Published by:
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Publication date:
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ECN
Energy Efficiency in Industry
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1-10-2001
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ECN report number:
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Document type:
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ECN-RX--01-066
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Article (scientific)
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Number of pages:
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15
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Published in: Separation and Purification Technology (Elsevier), , 2001, Vol.22-23, p.361-366.
Abstract:
A major drawback of polymeric membranes for pervaporation is their limited solvent and temperature stability. This means that for several potential applications the membrane lifetime in combination with a relatively low performance is the limiting factor for introducing them into the market. More stable membranes are therefore needed.ECN has developed a new tubular microporous membrane based on hydrophilic silica for the dewatering of organic solvents. The membranes can be made on a large scale, with lengths of up to 1 meter and have a pore size of about 0.4 nm. The performance of these ceramic membranes for the dewatering of several organic streams has been tested as a function of feed temperature, feed flow, feed concentration, permeate pressure and time-on-stream. Under the same conditions the silica membranes give much higher fluxes and selectivities than commercially available dewatering membranes made of polyvinylalcohol. Up to periods of several weeks the performance of the silica membranes remains constant. In contrast to the polymeric membranes the ECN silica membranes can be used above 100oC, even up to 300oC. Due to an increase in driving force, the water flux in dewatering by pervaporation increases exponentially with the temperature whereas the organics flux remains small. This means that the membrane surface area needed for silica membranes can be decreased even further due to the use at higher temperatures. Experiments learn that at high temperatures the required membrane area for a case study (dewatering of 30,000 l/day 95% ethanol to 99,9% ethanol) decreases strongly from about 1000 m2 at 80oC for polymeric membranes and about 100 m2 for silica membranes at the same temperature to only a few square meters for silica membranes at 200oC. Thus, due to the outstanding performance at high temperatures the higher price of the ceramic membranes is no longer a drawback. Furthermore the acid stability of the membrane is much better than zeolite A pervaporation membranes. The results of the dewatering of several organic solvents are shown as examples of the dewatering capability of the silica membranes.
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