Abstract:
A carbon molecular sieve (CMS) membrane having improved separation characteristics for separating olefins from their corresponding paraffins is comprised of carbon with at most trace amounts of sulfur and a transition metal, wherein the transition metal is one or more of a group 4-10 and 12 transition metal. The CMS membrane may be made by pyrolyzing a precursor polymer devoid of sulfur in which the precursor polymer has had a transition metal incorporated into it. The pyrolyzing for the precursor having the transition metal incorporated into it is performed in a nonoxidizing atmosphere and at a heating rate and temperature such that the metal has a valence greater than zero (i.e., not metal bonded) to a valence desirably closer to its maximum valence.
Abstract:
A carbon molecular sieve (CMS) membrane having improved separation characteristics for separating olefins from their corresponding paraffins is comprised of carbon with at most trace amounts of sulfur and a group 13 metal. The CMS membrane may be made by pyrolyzing a precursor polymer devoid of sulfur in which the precursor polymer has had a group 13 metal incorporated into it, wherein the metal is in a reduced state. The pyrolyzing for the precursor having the group 13 metal incorporated into it is performed in a nonoxidizing atmosphere and at a heating rate and temperature such that the metal in a reduced state (e.g., covalently bonded to carbon or nitrogen or in the metal state).
Abstract:
A polyimide separation membrane is comprised of a polyimide, a halogen compound (e.g., halogenated aromatic epoxide) that is soluble in the polyimide and a hydrocarbon having 2 to 5 carbons (e.g., ethane, ethylene, propane or propylene). The gas separation membrane has improved selectivity for small gas molecules such as hydrogen compared to polyimide membrane not containing the halogen compound or hydrocarbon. The polyimide separation membrane may be made by shaping a dope solution comprised of a polyimide, a halogen containing compound that is soluble in the polyimide, removing the solvent and then exposing the untreated polyimide membrane to a treating atmosphere comprising a hydrocarbon having 2 to 5 carbons for a sufficient time to form the polyimide membrane.
Abstract:
A novel microporous carbon molecular sieve may be used as the basis for carbon adsorbent pellets that have discrete areas of carbonized binder and of carbonized precursor, macropores having an average pore diameter greater than or equal to 1 micrometer and a total macroporosity of at least 30 percent, both as measured by mercury porosimetry, and micropores that are capable of selectively admitting a C2-C3 alkene and excluding a C2-C3 alkane, and a total microporosity ranging from 10 percent to 30 percent. The pellets may be prepared by pyrolyzing a pellet structure comprising a carbon forming, non-melting binder and a non-porous gel type sulfonated polystyrene precursor at a temperature ranging from 500° C. to 1000° C., under an inert atmosphere and other conditions suitable to form the described pellets. The pellets are particularly useful in pressure swing and temperature swing adsorption processes to separate C2-C3 alkane/alkene mixtures.
Abstract:
A carbon molecular sieve (CMS) membrane having improved separation characteristics for separating olefins from their corresponding paraffins is comprised of carbon with at most trace amounts of sulfur and a group 13 metal. The CMS membrane may be made by pyrolyzing a precursor polymer devoid of sulfur in which the precursor polymer has had a group 13 metal incorporated into it, wherein the metal is in a reduced state. The pyrolyzing for the precursor having the group 13 metal incorporated into it is performed in a nonoxidizing atmosphere and at a heating rate and temperature such that the metal in a reduced state (e.g., covalently bonded to carbon or nitrogen or in the metal state).
Abstract:
The invention is an improved method of making an improved carbon molecular sieve (CMS) membrane in which a precursor polymer (e.g., polyimide) is pyrolyzed at a pyrolysis temperature to form a CMS membrane that is cooled to ambient temperature (about 40° C. or 30° C. to about 20° C.). The CMS membrane is then reheated to a reheating temperature of at least 250° C. to 400° C. to form the improved CMS membrane. The CMS have a novel microstructure as determined by Raman spectroscopy. The improved CMS membranes have shown an improved combination of selectivity and permeance as well as stability for separating light hydrocarbon gas molecules such as C1 to C6 hydrocarbon gases (e.g., methane, ethane, propane, ethylene, propylene, butane, butylene).
Abstract:
An asymmetric hollow fiber (CMS) carbon molecular sieve is made by providing a dope solution comprised of a polvimide and a solvent, at a temperature greater than 250° C. that is less than the storage modulus at a temperature of 250° C., but no more than ten times less as measured using dynamic mechanical thermal analysis from 250° C. to a temperature where the polyimide carbonizes. The polvimide is shaped into a hollow polvimide fiber, the solvent removed and the polyimide hollow fiber is heated to pyroiyze the polvimide and form the asymmetric hollow carbon molecular sieve. The asymmetric hollow fiber carbon molecular sieve has a wall that is defined by an inner surface and outer surface of said fiber and the wall has an inner porous support region extending from the inner surface to an outer raicroporous separation region that extends from the inner porous support region to the outer surface. Surprisingly, when the polyimide has the particular storage modulus characteristics, the method allows for the hollow fiber CMS to be made without any pre-treatmenis or additives to inhibit stractural collapse of the inner microporous region.
Abstract:
The invention is an improved method of making a carbon molecular sieve (CMS) membrane in which a precursor polymer is pyrolyzed to form a carbon molecular sieve membrane that is then exposed to a conditioning atmosphere comprised of a target permeate gas molecule such as ethylene when the membrane is desired to separate it from a light hydrocarbon gas stream. The exposure to the ethylene desirably occurs prior to the CMS permeance and selectivity combination substantially changing (e.g., within 5 days) of cooling from the pyrolyzing temperature. The CMS membranes have shown an improved combination of selectivity and permeance as well as stability and are useful to separate gases in gas streams such methane from natural gas, oxygen from air and ethylene or propylene from light hydrocarbon streams.
Abstract:
The invention is an improved method of making a carbon molecular sieve (CMS) membrane in which a polyimide precursor polymer is pyrolyzed to form a carbon molecular sieve membrane by heating, in a furnace, said polyimide precursor polymer to a final pyrolysis temperature of 600 C to 700 C at a pyrolysis heating rate of 3 to 7 C/minute from 400 C to the final pyrolysis temperature, the final pyrolysis temperature being held for a pyrolysis time of at most 60 minutes in a non-oxidizing atmosphere. In a particular embodiment, the cooling rate from the pyrolysis temperature is accelerated by methods to remove heat. The CMS membranes have shown an improved combination of selectivity and permeance as well as being particularly suitable to separate gases in gas streams such methane from natural gas, oxygen from air and ethylene or propylene from light hydrocarbon streams.
Abstract:
A method of making a hollow fiber carbon molecular sieve is comprised of heating a hollow polymer fiber to a carbonization temperature in an atmosphere that is non-oxidizing to form a hollow fiber carbon molecular sieve, wherein during at least a portion of the heating a tensile force is applied to the hollow polymer fiber. The method may improve the separation of gases similar in size such a propylene from propane.