| 摘要 |
In a process for purifying H2 by condensing out CH4 impurity, the f.p. of the CH4 is depressed by at least 1.5 DEG K, preferably 3-5 DEG K, by the presence of C2H6, C2H4, C3H8 or mixtures thereof and the impure H2 is cooled below the f.p. of pure CH4 (90.7 DEG K) but above the depressed f.p. under a superatmospheric pressure (10-50 atm.) such that more hydrocarbon is condensed out and substantially pure H2 is separated from the condensate. The feed gas may be refiner or reformer off-gas containing H2O, C1-C5 alkanes and possibly C2H4, in which case the water and the butanes, pentanes and preferably propane are removed in one or more preliminary drying and condensation steps. Preferred components for depressing the f.p. of CH4 are ethane, in amount 2-33 molar per cent of total CH4 plus C2H6 content, or ethylene, in amount 5-13%. These hydrocarbons may be added to the H2/CH4 mixture when it is initially free of other hydrocarbons. N2, CO or other impurities boiling below the f.p. of the hydrocarbon mixture will not be separated by the process of the invention but their presence does not affect the removal of CH4. The cooled uncondensed gas and condensate are used to cool incoming gas by indirect heat exchange in one or more stages, the condensate being expanded to a lower pressure (about 1 atm. abs) before the final heat exchange and to which may be added thereafter pure or impure H2 in amount 2-4%. A closed N2 refrigeration cycle is used for cooling, and additional cooling is provided by expansion of the purified H2 with performance of external work and indirect heat exchange with the impure H2.
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