Membrane processes for effective methanol synthesis in the forest based biorefinery
Abstract: 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.
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