Membrane processes for effective methanol synthesis in the forest based biorefinery

A new promising way to produce synthesis gas from biomass is by black liquor gasification. In commencing forest based biorefineries, bio fuels such as methanol may be produced from the synthesis gas. However, biorefineries will produce relatively small quantities of bio fuels compared to traditional oil refineries producing fossil fuels. This calls for development of more efficient processes to reduce the production costs for production of bio fuels in small scale. Such processes could be membrane based. I the present work, ZSM-5 membrane reactors and ZSM-5 membrane modules, are explored and compared to traditional methanol synthesis processes. This is done through mathematical modelling. As basis for the calculations, a forest based biorefinery with a production of 70 000 tonne methanol per year was used. For a stoichiometric feed, the one- pass COx-conversion for a traditional methanol process is about 26 % per pass, which requires a recirculation loop with the associated disadvantages. The zeolite research group at Luleå University of Technology has prepared ZSM-5 membranes and evaluated their performance at atmospheric pressure and room temperature. By assuming that the same membrane performance could be obtained at industrial conditions for methanol syntheis, it was shown by mathematical modeling that a ZSM-5 membrane reactor with a membrane area of 400 m2 could potentially reach 97% COx- conversion per pass, while a ZSM-5 membrane module process with the same membrane area could potentially reach 81% conversion per pass for a stoichiometric feed. As a result of the high conversion per pass for the membrane processes, one-pass design with the associated advantages is possible for these processes. A membrane module based system is preferable over a membrane reactor of practical reasons. However, similar performance to the membrane processes can of course be achieved with a one pass process comprised of a series of methanol reactors, reactor effluent heat exchangers, coolers and condensers.Validerat; 20101217 (root