GB2437063A

GB2437063A - A process for oxide gas capture

Info

Publication number: GB2437063A
Application number: GB0607175A
Authority: GB
Inventors: Kjell Ove Kongshaug; Richard Hamilton Heyn; Fjellvaag Helmer; Richard Blom
Original assignee: Universitetet i Oslo
Current assignee: Universitetet i Oslo
Priority date: 2006-04-10
Filing date: 2006-04-10
Publication date: 2007-10-17
Also published as: GB0607175D0; WO2007128994A1

Abstract

The invention provides a process for oxide gas capture which process comprises contacting a gas comprising an oxide with a metal-organic framework wherein a metal-coordinating organic component carries a non-metal-coordinating electron pair donor group, and optionally releasing captured gas from said metal-organic framework by raising temperature and/or reducing pressure. The gas comprising an oxide is a carbon-dioxide containing and the non-metal-coordinating electron pair donor group is an amine group. In particular the process is used in exhaust gas treatment of a hydrocarbon fuelled engine.

Description

Compounds The invention relates to the use of metal-organic frameworks

as oxide gas adsorbents, in particular as carbon dioxide adsorbents.

Carbon dioxide is a by-product of many processes, not least hydrocarbon combustion, which is undesirable to release into the atmosphere. Accordingly processes for carbon dioxide capture have been developed. At present the standard techniques for carbon dioxide capture involve the use of aqueous solutions of amino-alcohols with carbon dioxide-containing gas being passed through such solutions and the captured carbon dioxide subsequently being released by increasing the temperature of the solution. Such "temperature swing" processes have high energy requirements and cause loss, possibly into the environment, of the expensive and toxic amino-alcohols. There is thus a continuing need for improved and alternative carbon dioxide capturing agents and processes.

We have now found that metal-organic frameworks (MOFs) having electron pair donor functions on the organic component which are uncoordinated to the metal component are particularly effective as carbon dioxide capturing agents and can be used in pressure-swing (rather than just temperature-swing) carbon dioxide capture and release.

Thus viewed from one aspect the invention provides a process for oxide gas capture which process comprises contacting a gas comprising an oxide with a metal-organic framework wherein a metal-coordinating organic component carries a non-metal-coordinating electron pair donor group, and optionally releasing captured oxide gas from said metal-organic framework by raising temperature and/or reducing pressure.

Viewed from a yet still further aspect the invention provides an oxide gas capture apparatus comprising a conduit containing a metal-organic framework wherein a metal-coordinating organic component carries a non-metal-coordinating electron pair donor group.

Metal-organic frameworks (MOF5) are a category of materials in which metal atoms or metal atom containing clusters are linked into a three-dimensional framework by bi-or polyfunctional organic groups. MOFs have been described for example in many publications of Yaghi et al of the University of Michigan, US, e.g. in US-A- 20040225134.

Other publications by Yaghi et al relating to MOFs, and which are incorporated herein by reference, include US Patents Nos 5648508, 6624318, 6893564, 6929679 and 6930193 and published US Patent Applications Nos 2003 0004364, 2003 0078311, 2003 0148165, 2003 0222023, 2004 0249189, 2004 0265670, 2005 0004404, 2005 0124819, 2005 0154222, and 2005 0192175.

US-A-20040225134, the contents of which are incorporated by reference, discloses the preparation of one MOF, MOF-177, which has been proposed for use in carbon dioxide capture. MOF-177 has zinc containing clusters linked together by 4,4' ,4"-benzene-l,3,5-triyl-tri-benzoic acid, i.e. a trifunctional compound having three metal-coordinating carboxyl groups but not containing any non-metal-coordinating electron pair donor functional groups.

In the MOFs of the invention, the electron pair donor group typically has the electron pair located on a heteroatom, e.g. an amino, thiol or hydroxy group, preferably an amino group. The electron pair donor group is typically not a group capable of chelating a metal, i.e. of coordinating a metal via two or more atoms of the group. The electron pair carrying atom is not part of a delocalized electron system.

The electron pair carrying atom is desirably separated by at least two atoms from the metal-coordinating groups (e.g. from the carbon of a carboxyl group). It is especially preferred that the organic component should carry more than one electron pair donor group, e.g. 2-6 such groups, and it is also preferred that such groups be close to each other, e.g. separated by no more than 4 backbone atoms, more preferably by no more than 2 backbone atoms.

In the organic component of the MOF, the spacing of the metal-coordinating groups (eg carboxyl groups) is preferably unaffected by rotational motion within the component, eg as in terephthalic acid or the tri-benzoic acid-benzene of MOF-177.

The organic and metal components of the MOF5 of the invention may otherwise be components typical of known MOFs, e.g. as described in US-A-20040225l34.

Introduction of electron pair donor groups onto such organic components is chemically straightforward and many electron pair donor group carrying organic compounds suitable for MOF production are available commercially or known from the literature.

Typically the metal of the MOF will be selected from Group 1 through 16 metals, e.g. Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Rn, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga. In, Ti, Si, Ge, Sn, Pb, As, Sb and Bi. Preferably it is Al, Zn or Ni, especially Ni and Al. The metal may form part of a MnXm cluster where M is the metal and X is a Group 14 to 17 atom, e.g. 0, N or 5, especially 0, m is 1 to 10 and n is a number selected to balance the charge of the cluster.

The organic component is preferably a polycarboxylate, especially a material containing at least one cyclic group which may be aromatic or non-aromatic.

The metal component in the MOF will typically be coordinated by at least one non-linking ligand (i.e. one which does not form part of the backbone of the MOF), e.g. sulphate, nitrate, halide, phosphate etc. The gas treated in the process of the invention is one containing or consisting of a gaseous oxide, e.g. a sulphur, nitrogen or carbon oxide, in particular carbon dioxide. Typically this may be a gas resulting from combustion (e.g. of hydrocarbons), natural gas or the product of a shift reactor (i.e. reactors used in production of hydrogen from methane).

The apparatus of the invention will typically comprise a conduit filled or lined with the MOF.

However the MOF, optionally with a binder or diluent may itself be formed into a gas absorbent structure, e.g. a brick or perforated brick and such structures, which may be used in or to construct conduits, form a further aspect of the present invention. The process of the invention will typically comprise passing the gas from which the oxide gas is to be extracted through such a conduit in a gas uptake phase and ceasing such gas flow and raising the temperature in the conduit and/or reducing the pressure in the conduit to release the adsorbed oxide gas. Typically the apparatus will contain at least two such conduits with gas flow divertible into either so that one may operate in adsorption mode while the other is operating in desorption mode. (The term adsorption as used herein to refer to oxide gas uptake by the MOF should be considered to cover any form of gas sorption) Alternatively gas oxide-saturated MOF elements may be replaced by fresh MOF elements and sent to a remote location for oxide gas desorption (e.g. where the MOF elements are in an exhaust gas system of a hydrocarbon-fuelled vehicle).

Gas release from the MOF may be achieved by temperature increase -however the MOF is preferably not exposed to temperatures above 500CC, more preferably not to temperatures above 400 C. More preferably however gas release is achieved by reducing the ambient pressure at the MOF, e.g. by 1 to 100 bar, more preferably 10 to bar.

Embodiments of the invention will now be described further with reference to the following non-limiting Examples and the accompanying drawings, in which: Figure 1 shows powder X-ray diffraction patterns for the MOF5 of Examples 1 and 2; Figure 2 shows powder X-ray diffraction patterns for the MOFs of Examples 3 and 4; Figure 3 shows thermogravimetric traces for the MOFs of

Examples 1 and 2;

Figure 4 shows thermogravimetric traces for the MOF5 of

Examples 3 and 4;

Figure 5 shows CO2 adsorption-disorption isotherms, measured at 25 C, for the MOFs of Examples 1 and 2; and Figure 6 shows CO2 adsorption-disorption isotherms, measured at 25 C, for the MOF5 of Examples 3 and 4.

Example 1 (Comparative) tJSO-l-A1 0.36g of A1C136H20, 0.17g of terephthalic acid, l.58g of ethanol and 9.08g of diethylformamide were mixed and transferred to a teflon-lined steel autoclave. The autoclave was heated at 110 C for 24 hours, and then it was quenched to room temperature. The product was collected by filtration and washed with dimethylformamide. The product was dried at ambient temperature overnight.

Example 2

USO-1-Al-A 0.36g of A1C136H20, 0.149 of 2-aminoterephthaliC acid, l.58g of ethanol and 9.08g of diethylformamide were mixed and transferred to a teflon-lined steel autoclave.

The autoclave was heated at 110 C for 24 hours, and then it was quenched to room temperature. The product was collected by filtration and washed with dimethylformamide. The product was dried at ambient temperature overnight.

Example 3 (Comparative) USO-2-Ni 0.49g of Ni(NO)3 6H20, 0.28g of terephthalic acid, 0.14g l,4-diazabicyclo[2.2.2]oCtafle and 18.88g of dimethylforinamide were mixed and transferred to a teflon-lined steel autoclave. The autoclave was heated at 110 C for 24 hours, and then it was quenched to room temperature. The product was collected by filtration and washed with dimethylformamide. The product was dried at ambient temperature.

Example 4

USO-2-Ni-A 0.29g of Ni(NO)36H20, 0,189 of 2-aminoterephthalic acid, 0.28g 1,4-diazabicyclo[2.2.2]Octafle and 18.88g of dimethylformamide were mixed and transferred to a teflon-lined steel autoclave. The autoclave was heated at 110 C for 24 hours, and then it was quenched to room temperature. The product was collected by filtration and washed with dimethylformamide. The product was dried at ambient temperature overnight.

Example 5

X-Ray Diffraction Powder X-ray diffraction patterns were recorded for the MOFs of Examples 1 to 4 using radiation of wavelength 1.5406 A. These are shown in Figures 1 and 2.

Indexation of the powder patterns indicated very similar unit cells for the compounds of Examples 1 and 2, and furthermore the cells are similar to that of two compounds based on Al and Cr published in the literature (C. Serre, F. Millange, C. Thouvenot, M. Nogues, G. Marsolier, D. Louer, G. Ferey, J. Am. Chem. Soc. 2002, 124, 13519) . The structure of the amine functionalized material (tJSO-l-A1-A) shows disorder in the placement of the amine groups.

On basis of the powder X-ray data the unit cell of the compounds of Examples 3 and 4 were determined, and the two cells were similar indicating isostructurality between the two compounds. Furthermore the unit cells of the two compounds were similar to that of a Zn compound published recently in literature (D.N. Dybtsev, H. Chun, K. Kim, Angew. Chem. mt. Ed. 2004, 43, 5033), so it can be assumed that the two compounds are isostructural with this compound. The crystal structure of the Zn compound shows a 3D metal-organic framework (MOF) structure containing a 3D channel system with channel sizes of about 0.8x0.8nm2. As for the compound of Example 2, the structure of the amine functionalized material (USO-2-Ni-A) of Example 4 shows disorder in the placement of the amine groups.

Example 6

Thermogravimetric Analysis About 20mg of USO-A-A1 and USa-i-Al-A were separately heated to 700 C at a rate of 5 C/mm. Both compounds show a continuous weight loss starting at room temperature and ending at about 300 C resulting from the solvent removal (Figure 3) . The second weight loss is representing the decomposition of the structures. The specific surface areas were measured by multipoint BET analyses using nitrogen as probe gas at 77K on a Quantachrome Autosorb-l instrument. After de-solvating the materials at 300 C under reduced pressure the specific surface areas were measured to: USO-l-Al:1300m2/g and USa-i-Al-A: 980m2/g. The results are shown in Figure 3.

About 20mg of USO-2-Ni and USO-2-Ni-A were separately heated to 700 C at a rate of 5 C/mm. The two compounds show the first weight loss in the range 200 to 250 C consistent with the removal of the solvent molecules (Figure 4). After the first weight loss, both compounds show a plateau in their TGA curves indicating the presence of porous compounds. The second weight loss is then due to decomposition of the frameworks. High temperature powder X-ray diffraction data for both compounds indicate that the structural integrity of the compounds are maintained after the first weight loss, and this is further supported by the measurements of high internal BET surface areas for the two compounds when they were desolvated under reduced pressure at 200 C: USO-2-Ni-A: l529m2/g and USO-2-Ni: 1910m2/g.

(Specific surface areas were measured by multipoint BET analyses using nitrogen as probe gas at 77K on a Quantachrome Autosorb-l instrument)

Example 7

CO2 Adsorption-DesOrptiOn Isotherms CO2 isotherms were measured at 25 C by keeping the compounds of Examples 1 and 2 in a thermostated water bath using a Quantachrome Autosorb-l instrument. The CO2 adsorption-desorptiOfl isotherms measured at 25 C on USO- 1-Al and USO-l-Al-A show a CO2 adsorption capacity of about 10 and 12 weight percent, respectively, for the two compounds at 1 atmosphere partial pressure of carbon dioxide (Figure 5). The amine functionalized material (USO-l-Al-A) showing significantly higher CO2 adsorption capacity than the unfunctionalized material despite the fact that the functionalized material has a lower specific surface area. The results are shown in Figure 5.

CO2 isotherms were measured at 25 C by keeping the compounds of Examples 3 and 4 in a thermostated water bath using a Quantachrome Autosorb-l instrument. The CO2 adsorption-desorption isotherms measured at 25 C on USO- 2-Ni and USO-2-Ni-A show a CO2 adsorption capacity of about 10 and 14 weight percent, respectively, for the two compounds (Figure 6) at 1 atmosphere partial pressure of carbon dioxide. As with the compounds of Examples 1 and 2, the amine functionalized material (TJSO-2-Ni-A) shows significantly higher CO2 adsorption capacity than the unfunctionalized material despite the fact that the functionalized material has a lower specific surface area. The results are shown in Figure 6. $ I

Claims

Claims: 1. A process for oxide gas capture which process comprises

contacting a gas comprising an oxide with a metal-organic framework wherein a metal-coordinating organic component carries a non-metal-coordinating electron pair donor group, and optionally releasing captured gas from said metal-organic framework by raising temperature and/or reducing pressure.

2. A process as claimed in claim 1 wherein said gas comprising an oxide is a carbon dioxide-containing gas.

3. A process as claimed in either of claims 1 and 2 wherein said group is an amine group.

4. An oxide gas capture apparatus comprising a conduit containing a metal-organic framework wherein a metal- coordinating organic component carries a non-metal-coordinating electron pair donor group.

5. An apparatus as claimed in claim 4 wherein said group is an amine group.

6. An apparatus as claimed in either of claims 4 and 5 being an exhaust gas treatment apparatus for a hydrocarbon-fuelled engine.