Hitachi Zosen Corp. (Hitz; Tokyo, Japan) is commercializing a new membrane for a hybrid-distillation system (HDS) that is especially suitable for dehydrating ethanol and isopropanol. The HDS can produce 99.7 vol.% ethanol from ethanol-water mixtures with 10 vol.% H2O at a dehydration rate of 50 kg/m2/h/atm (at 130°C), which is more than two times higher than conventional ceramicmembrane processes, says the firm.
The membrane element consists of a porous alumina tube that is closed at one end. A thin zeolite film is synthesized onto
the tube, and the pore size is precisely controlled by proprietary technology to be around 10Å, which enables the element to act as a molecular sieve for the two alcohols. In the HDS, the mixture is fed to the outside of the tubes and the dehydrated water is removed from the inner side of the tubes.
The membrane is able to dehydrate ethanol- water mixtures with less than 30-wt.% water and, when combined with distillation, covers a wider range of mixtures. Hitz estimates that HDS can save up to 30% of the energy required to dehydrate ethanol, and the required installation space for the membrane unit is about half that needed for a pressure-swing-absorption unit.
Hitz has demonstrated the technology in a test plant with the capacity to produce 30 kL/d of ethanol, and plans to expand the production capacity (for the membranes) to 750,000 m.t./yr this year. The firm has also designed an HDS for producing 99.7 vol.% ethanol from a 10 vol.% ethanol feed, with a capacity of 50-million gal/yr.
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