Gas separation by adsorbent membranes

Reference Number: N 04-02

Inventors: Rao, Madhukar B.; Sircar, Shivaji; Golden, Timothy C.

Owner: NISTAC

USPTO Link: 5104425

Invention Summary

The invention is a composite semipermeable membrane comprising porous adsorptive material supported by a porous substrate, a series of methods for making the membrane, and a process for the separation of a multicomponent fluid mixture containing one or more primary components and one or more secondary components comprising bringing the fluid mixture into contact with a first surface of the composite semipermeable membrane, wherein a significant portion of at least one of the primary components is selectively adsorbed within the pores in the adsorptive material and permeates through the pores by surface flow in an adsorbed fluid phase to produce a first fluid product enriched in at least one of the primary components at a second surface of the membrane, and withdrawing the remaining fluid mixture from contact with the first surface of the membrane to yield a second fluid product enriched in the secondary components.

A method for making a layered composite semipermeable membrane for the separation of a multicomponent fluid mixture containing one or more primary components and one or more secondary components comprises the steps of: (a) coating a surface of a porous substrate with a layer of a precursor material; (b) heating the resulting coated porous substrate in an inert atmosphere to a temperature sufficient to convert the precursor material into a layer of porous adsorptive material; and (c) cooling the resulting composite membrane to ambient temperature; wherein the porous adsorptive material can selectively adsorb a significant portion of at least one of the primary components and has a pore size distribution such that at least 10% of the pores have diameters larger than the largest of the molecular diameters of the primary and secondary components. Precursor materials can include polymeric materials which are carbonized by heating in an inert atmosphere to form a layer of porous activated carbon on the surface of the substrate or inorganic materials which are dried and crystallized to form a layer of porous inorganic adsorbent material on the surface of the substrate. The porous adsorptive material forms a layer up to about 20 microns thick.

A method is also disclosed for making a densified composite semipermeable membrane for the separation of a multicomponent fluid mixture containing one or more primary components and one or more secondary components comprising the steps of: (a) introducing a precursor into the pores of a porous substrate; (b) heating the porous substrate containing the precursor under conditions sufficient to convert the precursor to porous adsorptive material within the pores; and (c) cooling the resulting composite membrane to ambient temperature; wherein the porous adsorptive material can selectively adsorb a significant portion of at least one of the primary components and has a pore size distribution such that at least 10% of the pores have diameters larger than the largest of the molecular diameters of the primary and secondary components. The porous adsorptive material can be activated carbon formed by the carbonization of polymeric materials or by the deposition of carbon by vapor phase cracking of gaseous hydrocarbons followed by activation in an oxidizing atmosphere.

A method is also disclosed for making a densified composite semipermeable membrane for the separation of a multicomponent fluid mixture containing one or more primary components and one or more secondary components comprising the steps of: (a) introducing a suspension of porous adsorptive particles in a liquid into the pores of a porous substrate; (b) heating the porous substrate containing the suspension of adsorptive porous particles to a temperature sufficient to evaporate the liquid whereby the particles are deposited within the pores; and (c) cooling the resulting membrane to ambient temperature; wherein the porous adsorptive particles can selectively adsorb a significant portion of at least one of the primary components and have a pore size distribution such that at least 10% of the pores have diameters larger than the largest of the molecular diameters of the primary and secondary components.