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Virtuous cycle

作者:俞习铄    发布时间:2019-03-08 05:10:16    

By Peter Hadfield in Tokyo 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’s 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. “This is a very efficient method of recovering low heat,” says Tetso Yazawa, head of the agency’s advanced glass section. “Until now it has been difficult to achieve because of the high temperature—around 300 °C—required to break down methanol.” But Yazawa says that by “siphoning off” hydrogen so the reaction does not reach equilibrium, his method breaks down methanol at temperatures between 150° C and 200 °C. He points out that 200 °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. 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,

 

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