Carbon molecular sieve membranes containing a group 13 metal and method to make them
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).
1. A method of making a carbon molecular sieve membrane comprising,
(i) providing a precursor polymer without any sulfur, wherein the precursor polymer is a polyimide copolymer comprising 3,5-diaminobenzoic acid (DABA);
(ii) incorporating a group 13 metal into the precursor polymer to form a group 13 metal bearing precursor polymer,
(iii) heating said group 13 metal bearing precursor polymer to a final pyrolysis temperature and non-oxidizing atmosphere sufficient to form the carbon molecular sieve membrane containing the group 13 metal; and
(iv) cooling the carbon molecular sieve membrane to room temperature.
2. The method of claim 1 , wherein the incorporating of the group 13 metal is by ionic bonding of the group 13 metal to one or more moieties present in the precursor polymer.
3. The method of claim 2 , wherein the incorporating of the group 13 metal is by adding the group 13 metal during synthesis of the polyimide or by infusing the group 13 metal dissolved in a solvent into the polyimide.
4. The method of claim 3 , wherein the incorporating of the group 13 metal is by ionic bonding of the group 13 metal with the diaminobenzoic acid (DABA) moieties of a copolymer of hexafluoroisopropylidene diphthalic anhydride (6FDA),2,4,6-trimethyl-1,3-phenylenediamine (DAM) and the diaminobenzoic acid (DABA).