ECN publication
Reduction of energy comsumption in the process industry by pervaporation with inorganic membranes : techno-economical feasibility study
Published by: Publication date:
ECN Energy Efficiency in Industry 1-7-2001
ECN report number: Document type:
ECN-C--01-073 ECN publication
Number of pages: Full text:
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The aim of the project was to study the possible reduction of energy consumption in the process industry by using inorganic pervaporation membranes. This was done by evaluating the technical and economic feasibility of these membranes for dewatering, thus enhancing a quicker implementation of the membranes and membrane technology. The microporous silica and silicalite membranes should replace energy intensive distillation processes for the separation of liquid mixtures. The project focussed on four process cases: i) ether production, ii) extraction of aromatics from gasoline, iii) ester production and iv) dewatering of solvents. These processes are representative for a large group of applications in different fields of industry. The project consisted of four main activities:1) membrane manufacturing 2) module design, development and optimisation 3) membrane and process testing on laboratory and bench scale 4) process calculations, optimisation and evaluation by flowsheeting. Microporous silica membranes can be produced on a large scale and have shown to be able to separate effectively water from various organics by means of pervaporation. A new type of silica membrane has been used in the project to separate methanol from MTBE and toluene and ethanol from ETBE. The stability of the membranes in acid environments is good but should be improved further to enlarge the field of applications. Modules based on tubular ceramic membranes with a silica top layer have been made on lab scale (1-tube) and on bench scale: 7 tubes with a diameter of 14 mm and a length of 40 cm. Detailed designs of a full-scale (5 m2) module and a design of a 50 m2 module have been made. The modules can be used up to 300oC and 25 bar pressure. The total price is governed by the module price and not by the membranes, assembly or sealing. From the techno-economic evaluation studies several conclusions have been drawn for the different processes. For the separation of methanol from MTBE pervaporation can not compete with catalytic distillation as membrane selectivities are too low, costs are too high and the conventional process is more energy efficient than the hybrid (combination of distillation and pervaporation) flowsheet. Reduction of benzene in gasoline via pervaporation is not possible thus far, because of the very simple and cheap base case and low membrane performance. Membrane pervaporation to separate EtOH from ETBE in the ether production process leads to about 30% lower costs for ETBE. The reduction in energy consumption for the whole process is between respectively 21 % and 37% when simple distillation or catalytic distillation is replaced by membrane pervaporation. Dehydration of the ethanol recycle by pervaporation increases the catalyst life time, leads to less by-products and a better water wash operation. In Europe 19 PJ/year can be saved when esterification processes are assisted by pervaporation in stead of distillation. The production costs for esters by an esterification process based upon pervaporation are 30% lower than in using the distillation process. The use of pervaporation membranes for dewatering in esterification reactions furthermore results in a much better product quality, compared to normal distillation and to an increased reactor efficiency. The energy use is only 16% of the total energy use in the conventional distillation process. The dewatering of isopropanol (IPA) by a hybrid distillation inorganic pervaporation membrane process is about 40% cheaper than the conventional distillation case and requires up to 70% less energy than the distillation process. The energy savings in Europe for IPA production could be up to 2 PJ/year. When IPA recycle streams are included, the energy savings in Europe could be as high as 10 PJ/year. Following the results of the project the technology of producing microporous silica membranes for dewatering has been licensed to Sulzer Chemtech, world-wide leader of polymeric membranes and membrane systems for pervaporation. Sulzer will produce and sell the membranes, membrane modules and technology on a commercial basis.

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