Hydrogen recovery by adsorbent membranes
Reference Number: N 04-02
Inventors: Rao, Madhukar B.; Sircar, Shivaji
The invention is method for the recovery of hydrogen from a gaseous feed mixture comprising hydrogen and one or more hydrocarbons, in which the hydrocarbons are more strongly adsorbed on an adsorbent material than hydrogen. The method comprises passing the feed mixture into a separator containing a composite semipermeable membrane consisting essentially of microporous adsorbent material supported by a porous substrate, in which the membrane has a feed side and a permeate side, and withdrawing from the separator a nonpermeate product stream enriched in hydrogen. Portions of the hydrocarbons are selectively adsorbed by the microporous adsorbent material and diffuse from the feed side to the permeate side of the membrane as an adsorbed fluid phase. Contacting of the gaseous feed mixture with the membrane and permeation of components through the membrane occur in the absence of chemical reaction. A permeate comprising these hydrocarbons is withdrawn from the permeate side of the membrane.
The key feature of the invention is passing a sweep gas across the permeate side of the membrane and withdrawing from the separator a sweep gas/permeate effluent stream, wherein the sweep gas comprises one or more of the same hydrocarbons present in the feed mixture. The use of the sweep gas enhances permeation of the hydrocarbons from the hydrogen-hydrocarbon gas mixture through the adsorptive membrane.
The one or more hydrocarbons in the feed mixture include methane, ethane, ethylene, propane, propylene, butane, isobutane, butylene, isobutylene, and mixtures thereof; the sweep gas comprises one or more of these same hydrocarbons. In one embodiment, the sweep gas is methane or natural gas. Alternatively, the sweep gas contains hydrogen and may contain in addition one or more of the hydrocarbons listed above.