A MEMBRANE that lets hydrogen atoms pass through while blocking larger
molecules could pave the way for an efficient heat-recycling system. This would
shift waste heat to where it is needed in industrial plants.
Researchers at Japan鈥檚 Agency of Industrial Science and Technology say that
waste industrial heat can be used to break methanol down into hydrogen and
carbon monoxide, and that it can then be recombined elsewhere to generate
heat.
鈥淭his is a very efficient method of recovering low heat,鈥� says Tetso Yazawa,
head of the agency鈥檚 advanced glass section. 鈥淯ntil now it has been difficult to
achieve because of the high temperature鈥攁round 300 掳C鈥攔equired
to break down methanol.鈥� But Yazawa says that by 鈥渟iphoning off鈥� hydrogen so the
reaction does not reach equilibrium, his method breaks down methanol at
temperatures between 150掳 C and 200 掳C. He points out that 200 掳C is
the point below which heat generated by factories is generally considered to be
not worth recovering. Above this temperature, other recovery methods are
used.
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The membrane is formed from a hollow tube made of bonded alumina and silica
with walls just 0.1 micrometres thick, which is inserted into a vessel
containing silica vapour. Silica is deposited on the surface, blocking up the
larger pores in the membrane. Most of the remaining gaps are so small that only
hydrogen can pass through. Hot methanol vapour passing through the tube breaks
down, using a silicon-doped nickel catalyst, to form carbon monoxide and
hydrogen, which passes through the membrane 60 times as fast as other
molecules.
Waste heat is used to heat the methanol. The hydrogen and carbon monoxide can
be sent by separate pipelines to an area where heat is required, where they can
be made to recombine to release energy and re-form methanol. This can be
returned to complete the cycle.