Cooperative chemical adsorption of acid gases in functionalized metal-organic frameworks
A system and method for acid gas separations using porous frameworks of metal atoms coordinatively bound to polytopic linkers that are functionalized with basic nitrogen ligands that expose nitrogen atoms to the pore volumes forming adsorption sites. Adjacent basic nitrogen ligands on the metal-organic framework can form an ammonium from one ligand and a carbamate from the other. The formation of one ammonium carbamate pair influences the formation of ammonium carbamate on adjacent adsorption sites. Adsorption of acid gas at the adsorption sites form covalently linked aggregates of more than one ammonium carbamate ion pair. The acid gas adsorption isotherm can be tuned to match the step position with the partial pressure of acid gas in the gas mixture stream through manipulation of the metal-ligand bond strength by selection of the ligand, metal and polytopic linker materials.
1. A cooperative chemical adsorption method for acid gas separations, the method comprising:
(a) providing a porous metal-organic framework, wherein the metal-organic framework comprises metal-ligand bonds;
(b) functionalizing pore surfaces with a plurality of ligands selected from the group of primary and secondary imines, said ligands producing two adjacent imines that define adjacent adsorption sites; and
(c) adsorbing acid gas molecules with said adjacent amine adsorption sites;
(d) wherein a plurality of imines adsorb acid gas at the same time and form covalently linked aggregates of more than one ammonium carbamate ion pair;
(e) wherein the aggregates spatially extend along the pore surface in at least one dimension; and
(f) wherein a gaseous stream depleted in acid gas and a solid-phase composition enriched in acid gas is produced.
2. The method of claim 1 , further comprising matching a step position of a produced isotherm to a partial pressure of an acid gas for removal by changing the metal-ligand bond strength.
3. A cooperative chemical adsorption method for acid gas separations, the method comprising:
(a) providing a porous metal-organic framework of metal atoms bound to 4,4′-dioxidobiphenyl-3,3′-dicarboxylate metal polytopic organic linkers;
(b) functionalizing pore surfaces with a plurality of ligands of N,N′-dimethylethylenediamine, said ligands producing two adjacent amines that define adjacent adsorption sites; and
(c) adsorbing acid gas molecules with said adjacent amine adsorption sites;
(d) wherein a plurality of amines adsorb acid gas at the same time and form covalently linked aggregates of more than one ammonium carbamate ion pair;
(e) wherein the aggregates spatially extend along the pore surface in at least one dimension; and
(f) wherein a gaseous stream depleted in acid gas and a solid-phase composition enriched in acid gas is produced.