- Email: [email protected]
Dewatering of organics by pervaporation with silica membranes
Separation and Purification Technology 22-23 (2001) 361– 366 www.elsevier.com/locate/seppur
Dewatering of organics by pervaporation with silica membranes H.M. van Veen *, Y.C. van Delft, C.W.R. Engelen, P.P.A.C. Pex Department of Energy Efficiency,Netherlands Energy Research Foundation, ECN, Westerduinweg 3, 1755 ZG Petten, The Netherlands
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 100°C, even up to 300°C. 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 80°C for polymeric membranes and about 100 m2 for silica membranes at the same temperature to only a few square meters for silica membranes at 200°C. 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. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Pervaporation; Dewatering; Silica; Ceramic; Membrane
1. Introduction * Corresponding author. Tel.: +31-224-564606; fax: + 31224-563615. E-mail address: [email protected] (H.M. van Veen).
Chemical feedstocks, solvents and products of (chemical) reactions in the liquid phase are very often a complex mixture of organic components
1383-5866/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 3 - 5 8 6 6 ( 0 0 ) 0 0 1 1 9 - 2
362
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366
and in many cases water. These mixtures are difficult to separate. The separation is mostly performed by various distillation techniques sometimes combined with the use of entrainers which are hazardous to the environment. Distillation is a very energy intensive process mainly due to the need to evaporate liquid for generating reflux in addition to the liquid taken off at the column head as top product. This disadvantage becomes most pronounced in the separation of close boiling mixtures, where the reflux stream is far larger than the tops product stream and in the separation of azeotropes where multiple distillation steps are required. Pervaporation is the selective evaporation of one component of a liquid stream by a membrane, which is in direct contact with the liquid mixture. Because of this, a much more energy efficient process can be obtained. Even difficult separation of azeotropic mixtures can be performed in one step. Thus, the (partial) replacement of distillation by pervaporation or the combination of pervaporation and reaction in one unit operation will have important benefits, with respect to energy consumption, yield, product quality and size of down-stream process equipment. Polymeric membranes are commercially being used as pervaporation membranes. A major drawback of these membranes is their limited solvent and temperature stability. This means that for several 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. A new microporous membrane based on hydrophilic silica for the dewatering of organic solvents has been developed by ECN. 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. In contrast to the polymeric membranes the ECN silica membranes can be used above 100°C, even up to 300°C. Furthermore this membrane is stable in all solvents tested.
2. Silica membrane development and performance
2.1. Membrane manufacturing The support system for the silica membrane consists of 4 layers and is basically made in the following way. The a-alumina macroporous support tubes which are used as structural carrier for the actual membrane are made by ceramic paste extrusion followed by a sintering procedure. The standard diameter of the support tube is ID/OD =8/14 mm whereas the tubes can be manufactured in a length up to 1 m. Before the final membrane layers can be applied two intermediate layers are applied to the support. These layers accommodate predominantly the surface roughness and pore size in order to obtain a nearly defect free support system for the pervaporation membrane layer. The intermediate layer is coated onto the support tube by means of a filmcoat technique using an a-alumina colloidal suspension. After drying a sintering step is involved ensuring consolidation. The so called ‘gamma’ layer is applied onto the second intermediate layer by slipcoating of a boehmite sol. After drying and during a heat treatment this boehmite will transform to gamma-alumina. The silica membrane, which is the final separation layer, is made by means of sol-gel processing. A silicon alkoxide is hydrolysed from which a polymeric inorganic silica sol is obtained. This sol is coated onto the support followed by drying and calcination. All layers are applied on the outside of the tube. The final structure of the membrane can be seen in Fig. 1. The thickness of the silica membrane as measured with SEM is in the range 150 –200 nm. From gas permeancy measurements using several gasses with different kinetic diameters, the pore size has been estimated to be about 0.4 nm. The silica membrane layer is currently calcined at 400°C which limits the operating temperature to 350°C. Due to the very hydrophilic nature of the silica and the small pores this membrane can be used for dehydration. Details on the membrane preparation can be found in [1,2].
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366
363
2.2. Per6aporation results The silica membranes have been used for long term testing in the dewatering of isopropylalcohol. The feed contained approximately 4.5 wt.% water, 95.5 wt.% IPA and some heavy hydrocarbons, which are present in the process mixture used. Polymeric membranes for pervaporation are not stable in (exactly) the same mixture as used here for long term testing of the silica membranes, amongst others due to the presence of these heavies [3,4]. The process has been operated at 80°C and 25 mbar pressure at the permeate side, with a
Fig. 2. Dewatering of 95.5 wt.% IPA, 80°C, 25 mbar.
total time on stream of 73 days, see Fig. 2. In this figure the process selectivity is defined as: XH2O Xi perm process selectivity= XH2O Xi feed In which,
XH20 XH20
Fig. 1. SEM micrograph of a high selective silica membrane.
Xi,
perm
Xi,
feed
= waterconcentration in the permeate (wt.%) = waterconcentration in the feed (wt.%) = concentration other/organic component in the permeate (wt.%) = concentration other/organic component in the feed (wt.%)
After an initial decrease of both the water and IPA flux, both fluxes stabilise and a process selectivity of about 1100 is obtained. This means that the permeate contains 98.1 wt.% water. The change of fluxes is probably due to a rearrangement of the hydroxyl groups on the pore surface of the silica membrane. No deterioration of the membrane has been found. The dehydration of ethanol has been used to study the influence of temperature on the membrane performance. In Fig. 3 it can be seen that 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: the selectivity increases significantly with temperature. This means that
364
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366
Fig. 3. Dehydration of 96 wt.% EtOH vs. temperature.
the membrane surface area needed for silica membranes can be decreased by applying higher feed temperatures. Experimentally supported model calculations (for the model used, see [5]) show that at high temperatures the required membrane area for a case study (batchwise dewatering of 30 000 l/day 95% ethanol to 99,9% ethanol) decreases strongly from about 1000 m2 at 80°C for commercially available polymeric membranes and about 100 m2 for silica membranes at the same temperature to only a few square meters for silica membranes at 200°C, see Fig. 4. Thus, due to the outstanding performance at high temperatures the higher price of the ceramic membranes is no longer a drawback. Measurements at higher temperatures are being performed and show that the silica membranes can operate up to temperatures of 240°C without problems. Detailed results will be reported in future.
Fig. 4. Membrane area needed for polymeric and silica membranes as a function of temperature.
Fig. 5. Water fluxes for several available membranes as a function of the feed temperature [6].
In Fig. 5 an overview of the performance of several available pervaporation membranes is given as a function of the feed temperature. It can be seen that in general inorganic membranes have much higher fluxes than polymeric pervaporation membranes. Compared to zeolite A membranes the silica membrane had a flux which was somewhat lower than these membranes, however, due to changes in the production of the silica membrane, fluxes are now comparable to the zeolite A membranes. A very important advantage of the silica membranes compared to the zeolite A membranes is the better stability in acid environments. However, in several dewatering applications a feed stream with an extreme acidity or alkaline solutions e.g. for cleaning are used. For these applications even more stable membranes, by using other types of ceramics, are under development. The microporous silica membranes have been tested in a wide variety of organic solvents, see Table 1. In almost all cases high fluxes and high selectivities are obtained. Even the dewatering of very low water concentrations is possible. For example in the dewatering of 0.24% water in dichloorethaan almost 99% water in the permeate is obtained with a waterflux of almost 1 kg/m2h at 70°C. In general dewatering of such low concentrations is not possible with polymeric membranes as these membranes need a certain minimum water concentration. The silica membranes have shown to have a stable performance in the wide variety of solvents tested.
a
Measurements by partners of ECN.
THF
6 8 10 10 11
10 2 5 5 5
Acetone Ethyl Acetate DMF
Feed permeate pressure (mbar) 6 5 25 10 10 8 10 10 10
Water concentration (%)
3.6 4.5 Isopropylalcohol 4.5 n-Butanol 5 1,2-dichlorethanea 0.24 Triethyleenglycol 9 Ethyleen diamine 30 Acetonitrila 10 Methylethylketone 2.5
Ethanol
Organic component
Table 1 Dewatering results of silica membranes for several organic solventsa
50 70 75 100 60
70 71 80 75 70 80 75 70 66
Feed temperature (°C)
752 2936 189 1007 5819
1485 1220 1855 4500 964 184 28 2630 2280
Waterflux (g/m2h)
78.8 95.9 56.1 84.8 87.9
92.8 94.2 98.1 97 98.9 99.5 99.7 96.4 97.7
Wt.% water in permeate
33 1118 24 102 147
350 208 1150 600 39645 2054 210 100 1458
Process selectivity
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366 365
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H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366
In all tests described above tubular silica membranes with a length of 10 – 40 cm have been used. These membranes have been cut out of 1 meter tubes, which are made in batches of 20 tubes at a time. The membranes used are selected at random and all measurements have been performed in duplo.
tion for energy and environment (NOVEM) for financially supporting part of the work described here. We would like to thank Stefan Sommer of the IVT-RWTH in Aachen for performing the measurements on ACN dehydration and Ine Bos and Wridzer Bakker of Akzo Nobel in Arnhem for the 1,2 –DCE measurements.
3. Conclusions
References
Ceramic pervaporation membranes have much higher fluxes and selectivities than commercially available polymeric membranes. This means that the higher prices of these membranes is no limiting factor any more for commercial use. The manufacturing process of the silica membranes is relatively easy upscalable. The performance of the silica membranes is comparable to commercially available zeolite A membranes. Due to the better stability and the development of even more stable ceramic membranes the range of applications for these membranes is much wider. The silica membranes have shown good performances in the dewatering of solvents like methylethylketone, DMF, THF and ethylacetate.
[1] B.C. Bonekamp, Preparation of asymmetric ceramic membrane supports by dipcoating, in: A.J. Burggraaf, L. Cot (Eds.), Fundamentals of Inorganic Membrane Science and Technology, vol. 4, Elsevier, Amsterdam, 1996 Chapter 6. [2] B.C. Bonekamp, P.P.A.C. Pex, Suspensions and Sol Processing for the Manufacturing of High Performance Ceramic Pervaporation and Gas Separation Membranes, to be published in Industrial Ceramics, 2000. [3] G.W. Meindersma, Membrane Experiences from the Petrochemical Industry, presentation at the Membrane Technology information day, Antwerp, Belgium 1996. [4] G.W. Meindersma, M. Kuczynski, Implementing membrane technology in the process industry: problems and opportunities, J. Membr. Sci. 113 (1996) 285. [5] M. Mulder; Basic principles of Membrane Technology-second edition, Kluwer Academic Publishers, 1998. [6] (a) Brochure GFT-Carbone Lorraine, Applications of Pervaporation Processes, 1995. (b) K. Okamoto, H. Kita, Membrane for liquid mixture separation, European Patent Application 1995, no. 659 469 A2. (c) S.A.I. Barri, G.J. Bratton, T. de V. Naylor, Membranes, European Patent Application 1992, no. 481 660 A1.
Acknowledgements We gratefully acknowledge the Dutch organisa-
.
Dewatering of organics by pervaporation with silica membranes H.M. van Veen *, Y.C. van Delft, C.W.R. Engelen, P.P.A.C. Pex Department of Energy Efficiency,Netherlands Energy Research Foundation, ECN, Westerduinweg 3, 1755 ZG Petten, The Netherlands
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 100°C, even up to 300°C. 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 80°C for polymeric membranes and about 100 m2 for silica membranes at the same temperature to only a few square meters for silica membranes at 200°C. 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. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Pervaporation; Dewatering; Silica; Ceramic; Membrane
1. Introduction * Corresponding author. Tel.: +31-224-564606; fax: + 31224-563615. E-mail address: [email protected] (H.M. van Veen).
Chemical feedstocks, solvents and products of (chemical) reactions in the liquid phase are very often a complex mixture of organic components
1383-5866/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 3 - 5 8 6 6 ( 0 0 ) 0 0 1 1 9 - 2
362
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366
and in many cases water. These mixtures are difficult to separate. The separation is mostly performed by various distillation techniques sometimes combined with the use of entrainers which are hazardous to the environment. Distillation is a very energy intensive process mainly due to the need to evaporate liquid for generating reflux in addition to the liquid taken off at the column head as top product. This disadvantage becomes most pronounced in the separation of close boiling mixtures, where the reflux stream is far larger than the tops product stream and in the separation of azeotropes where multiple distillation steps are required. Pervaporation is the selective evaporation of one component of a liquid stream by a membrane, which is in direct contact with the liquid mixture. Because of this, a much more energy efficient process can be obtained. Even difficult separation of azeotropic mixtures can be performed in one step. Thus, the (partial) replacement of distillation by pervaporation or the combination of pervaporation and reaction in one unit operation will have important benefits, with respect to energy consumption, yield, product quality and size of down-stream process equipment. Polymeric membranes are commercially being used as pervaporation membranes. A major drawback of these membranes is their limited solvent and temperature stability. This means that for several 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. A new microporous membrane based on hydrophilic silica for the dewatering of organic solvents has been developed by ECN. 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. In contrast to the polymeric membranes the ECN silica membranes can be used above 100°C, even up to 300°C. Furthermore this membrane is stable in all solvents tested.
2. Silica membrane development and performance
2.1. Membrane manufacturing The support system for the silica membrane consists of 4 layers and is basically made in the following way. The a-alumina macroporous support tubes which are used as structural carrier for the actual membrane are made by ceramic paste extrusion followed by a sintering procedure. The standard diameter of the support tube is ID/OD =8/14 mm whereas the tubes can be manufactured in a length up to 1 m. Before the final membrane layers can be applied two intermediate layers are applied to the support. These layers accommodate predominantly the surface roughness and pore size in order to obtain a nearly defect free support system for the pervaporation membrane layer. The intermediate layer is coated onto the support tube by means of a filmcoat technique using an a-alumina colloidal suspension. After drying a sintering step is involved ensuring consolidation. The so called ‘gamma’ layer is applied onto the second intermediate layer by slipcoating of a boehmite sol. After drying and during a heat treatment this boehmite will transform to gamma-alumina. The silica membrane, which is the final separation layer, is made by means of sol-gel processing. A silicon alkoxide is hydrolysed from which a polymeric inorganic silica sol is obtained. This sol is coated onto the support followed by drying and calcination. All layers are applied on the outside of the tube. The final structure of the membrane can be seen in Fig. 1. The thickness of the silica membrane as measured with SEM is in the range 150 –200 nm. From gas permeancy measurements using several gasses with different kinetic diameters, the pore size has been estimated to be about 0.4 nm. The silica membrane layer is currently calcined at 400°C which limits the operating temperature to 350°C. Due to the very hydrophilic nature of the silica and the small pores this membrane can be used for dehydration. Details on the membrane preparation can be found in [1,2].
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366
363
2.2. Per6aporation results The silica membranes have been used for long term testing in the dewatering of isopropylalcohol. The feed contained approximately 4.5 wt.% water, 95.5 wt.% IPA and some heavy hydrocarbons, which are present in the process mixture used. Polymeric membranes for pervaporation are not stable in (exactly) the same mixture as used here for long term testing of the silica membranes, amongst others due to the presence of these heavies [3,4]. The process has been operated at 80°C and 25 mbar pressure at the permeate side, with a
Fig. 2. Dewatering of 95.5 wt.% IPA, 80°C, 25 mbar.
total time on stream of 73 days, see Fig. 2. In this figure the process selectivity is defined as: XH2O Xi perm process selectivity= XH2O Xi feed In which,
XH20 XH20
Fig. 1. SEM micrograph of a high selective silica membrane.
Xi,
perm
Xi,
feed
= waterconcentration in the permeate (wt.%) = waterconcentration in the feed (wt.%) = concentration other/organic component in the permeate (wt.%) = concentration other/organic component in the feed (wt.%)
After an initial decrease of both the water and IPA flux, both fluxes stabilise and a process selectivity of about 1100 is obtained. This means that the permeate contains 98.1 wt.% water. The change of fluxes is probably due to a rearrangement of the hydroxyl groups on the pore surface of the silica membrane. No deterioration of the membrane has been found. The dehydration of ethanol has been used to study the influence of temperature on the membrane performance. In Fig. 3 it can be seen that 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: the selectivity increases significantly with temperature. This means that
364
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366
Fig. 3. Dehydration of 96 wt.% EtOH vs. temperature.
the membrane surface area needed for silica membranes can be decreased by applying higher feed temperatures. Experimentally supported model calculations (for the model used, see [5]) show that at high temperatures the required membrane area for a case study (batchwise dewatering of 30 000 l/day 95% ethanol to 99,9% ethanol) decreases strongly from about 1000 m2 at 80°C for commercially available polymeric membranes and about 100 m2 for silica membranes at the same temperature to only a few square meters for silica membranes at 200°C, see Fig. 4. Thus, due to the outstanding performance at high temperatures the higher price of the ceramic membranes is no longer a drawback. Measurements at higher temperatures are being performed and show that the silica membranes can operate up to temperatures of 240°C without problems. Detailed results will be reported in future.
Fig. 4. Membrane area needed for polymeric and silica membranes as a function of temperature.
Fig. 5. Water fluxes for several available membranes as a function of the feed temperature [6].
In Fig. 5 an overview of the performance of several available pervaporation membranes is given as a function of the feed temperature. It can be seen that in general inorganic membranes have much higher fluxes than polymeric pervaporation membranes. Compared to zeolite A membranes the silica membrane had a flux which was somewhat lower than these membranes, however, due to changes in the production of the silica membrane, fluxes are now comparable to the zeolite A membranes. A very important advantage of the silica membranes compared to the zeolite A membranes is the better stability in acid environments. However, in several dewatering applications a feed stream with an extreme acidity or alkaline solutions e.g. for cleaning are used. For these applications even more stable membranes, by using other types of ceramics, are under development. The microporous silica membranes have been tested in a wide variety of organic solvents, see Table 1. In almost all cases high fluxes and high selectivities are obtained. Even the dewatering of very low water concentrations is possible. For example in the dewatering of 0.24% water in dichloorethaan almost 99% water in the permeate is obtained with a waterflux of almost 1 kg/m2h at 70°C. In general dewatering of such low concentrations is not possible with polymeric membranes as these membranes need a certain minimum water concentration. The silica membranes have shown to have a stable performance in the wide variety of solvents tested.
a
Measurements by partners of ECN.
THF
6 8 10 10 11
10 2 5 5 5
Acetone Ethyl Acetate DMF
Feed permeate pressure (mbar) 6 5 25 10 10 8 10 10 10
Water concentration (%)
3.6 4.5 Isopropylalcohol 4.5 n-Butanol 5 1,2-dichlorethanea 0.24 Triethyleenglycol 9 Ethyleen diamine 30 Acetonitrila 10 Methylethylketone 2.5
Ethanol
Organic component
Table 1 Dewatering results of silica membranes for several organic solventsa
50 70 75 100 60
70 71 80 75 70 80 75 70 66
Feed temperature (°C)
752 2936 189 1007 5819
1485 1220 1855 4500 964 184 28 2630 2280
Waterflux (g/m2h)
78.8 95.9 56.1 84.8 87.9
92.8 94.2 98.1 97 98.9 99.5 99.7 96.4 97.7
Wt.% water in permeate
33 1118 24 102 147
350 208 1150 600 39645 2054 210 100 1458
Process selectivity
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366 365
366
H.M. 6an Veen et al. / Separation/Purification Technology 22-23 (2001) 361–366
In all tests described above tubular silica membranes with a length of 10 – 40 cm have been used. These membranes have been cut out of 1 meter tubes, which are made in batches of 20 tubes at a time. The membranes used are selected at random and all measurements have been performed in duplo.
tion for energy and environment (NOVEM) for financially supporting part of the work described here. We would like to thank Stefan Sommer of the IVT-RWTH in Aachen for performing the measurements on ACN dehydration and Ine Bos and Wridzer Bakker of Akzo Nobel in Arnhem for the 1,2 –DCE measurements.
3. Conclusions
References
Ceramic pervaporation membranes have much higher fluxes and selectivities than commercially available polymeric membranes. This means that the higher prices of these membranes is no limiting factor any more for commercial use. The manufacturing process of the silica membranes is relatively easy upscalable. The performance of the silica membranes is comparable to commercially available zeolite A membranes. Due to the better stability and the development of even more stable ceramic membranes the range of applications for these membranes is much wider. The silica membranes have shown good performances in the dewatering of solvents like methylethylketone, DMF, THF and ethylacetate.
[1] B.C. Bonekamp, Preparation of asymmetric ceramic membrane supports by dipcoating, in: A.J. Burggraaf, L. Cot (Eds.), Fundamentals of Inorganic Membrane Science and Technology, vol. 4, Elsevier, Amsterdam, 1996 Chapter 6. [2] B.C. Bonekamp, P.P.A.C. Pex, Suspensions and Sol Processing for the Manufacturing of High Performance Ceramic Pervaporation and Gas Separation Membranes, to be published in Industrial Ceramics, 2000. [3] G.W. Meindersma, Membrane Experiences from the Petrochemical Industry, presentation at the Membrane Technology information day, Antwerp, Belgium 1996. [4] G.W. Meindersma, M. Kuczynski, Implementing membrane technology in the process industry: problems and opportunities, J. Membr. Sci. 113 (1996) 285. [5] M. Mulder; Basic principles of Membrane Technology-second edition, Kluwer Academic Publishers, 1998. [6] (a) Brochure GFT-Carbone Lorraine, Applications of Pervaporation Processes, 1995. (b) K. Okamoto, H. Kita, Membrane for liquid mixture separation, European Patent Application 1995, no. 659 469 A2. (c) S.A.I. Barri, G.J. Bratton, T. de V. Naylor, Membranes, European Patent Application 1992, no. 481 660 A1.
Acknowledgements We gratefully acknowledge the Dutch organisa-
.