Alkylamine functionalized metal-organic frameworks for composite gas separations
Functionalized metal-organic framework adsorbents with ligands containing basic nitrogen groups such as alkylamines and alkyldiamines appended to the metal centers and method of isolating carbon dioxide from a stream of combined gases and carbon dioxide partial pressures below approximately 1 and 1000 mbar. The adsorption material has an isosteric heat of carbon dioxide adsorption of greater than −60 kJ/mol at zero coverage using a dual-site Langmuir model.
1. A porous organic framework (MOF) adsorbent for gas separations, comprising:
(a) a porous metal-organic framework of M 2 (dobpdc) where M is selected from the group of metals consisting of Mg, Ca, Mn, Cr, Fe, Co, Ni, Cu and Zn, the framework having coordinatively unsaturated metal centers; and
(b) a plurality of ligands disposed within pores of the metal-organic framework to produce a functionalized framework, said ligands having a ligand bridge with at least one first functional group capable of adsorbing a gas and at least one second functional group coupled to at least one metal center of said metal-organic framework;
(c) wherein contact of the functionalized framework with a volume of gases produces a stepped adsorption isotherm; and
(d) wherein gas adsorption properties before and after each step cannot be modeled as a continuous Langmuir function.
2. The adsorbent of claim 1 , wherein said bridge of said ligand comprises a molecule selected from the group consisting of a linear alkane, a branched alkane, a linear alkene and a branched alkene.
3. The adsorbent of claim 1 :
wherein said first functional group of said ligand has a reactive atom that contains at least one lone pair of electrons selected from the group consisting of nitrogen, sulfur, and phosphorous; and
wherein said ligand is reversibly bonded through a nitrogen, sulfur, or phosphorous atom to open metal sites of the framework.
4. The adsorbent of claim 1 , wherein said first functional group of said ligand comprises:
an oxygen containing group selected from the group consisting of alcohols, ethers, and alkoxides;
wherein the ligand is reversibly bonded through an oxygen atom to open metal sites of the framework.
5. The adsorbent of claim 1 , wherein said first functional group of said ligand is selected from the group consisting of carbenes, alkenes, and alkynes.
6. The adsorbent of claim 1 , wherein said second functional group of said ligand is selected from the group consisting of a primary alkylamine, a secondary alkylamine, and a tertiary alkylamine.
7. The adsorbent of claim 1 , wherein said second functional group of said ligand is selected from the group consisting of a primary imine and a secondary imine.
8. The adsorbent of claim 1 , wherein said second functional group of said ligand is selected from the group consisting of a Tetraethylenepentamine and a Diethylenetriamine.
9. The adsorbent of claim 1 , wherein said second functional group of said ligand is selected from the group consisting of Tris(2-aminoethyl)amine and Tris[2(methylamino)ethyl]amine.
10. The adsorbent of claim 1 , wherein said ligand comprises N,N′-dimethylethylenediamine (mmen).
11. The adsorbent of claim 1 , wherein the metal-organic framework comprises open metal sites and ligand occupied metal sites.
12. A porous organic framework (MOF) adsorbent for carbon dioxide gas separations, comprising:
(a) a porous metal-organic framework of M 2 (dobpdc) where M is selected from the group of metals consisting of Mg, Ca, Mn, Cr, Fe, Co, Ni, Cu and Zn, the framework having coordinatively unsaturated metal centers; and
(b) a plurality of ligands disposed within pores of the metal-organic framework, coupled to at least one metal center of said metal-organic framework, to produce a functionalized framework, said ligands comprising at least two functional groups separated by a ligand bridge, each functional group having at least one reactive atom of nitrogen that contains one or more lone pairs of electrons;
(c) wherein contact of the functionalized framework with a volume of gases produces a stepped adsorption isotherm; and
(d) wherein gas adsorption properties before and after each step cannot be modeled as a continuous Langmuir function.
13. The adsorbent of claim 12 , wherein said functional group of said ligand is selected from the group consisting of a primary alkylamine, a secondary alkylamine, and a tertiary alkylamine.
14. The adsorbent of claim 12 , wherein said functional group of said ligand is selected from the group consisting of a primary imine and a secondary imine.
15. The adsorbent of claim 12 , wherein said functional group of said ligand is selected from the group consisting of a Tetraethylenepentamine and a Diethylenetriamine.
16. The adsorbent of claim 12 , wherein said functional group of said ligand is selected from the group consisting of Tris(2-aminoethyl)amine and Tris[2(methylamino)ethyl]amine.
17. The adsorbent of claim 12 , wherein said ligand comprises N,N′-dimethylethylenediamine (mmen).
18. The adsorbent of claim 12 , wherein the metal-organic framework comprises open metal sites and ligand occupied metal sites.