Patent Application
20120070353
The present invention relates to a process for separating off at least one acidic gas from a gas mixture in the presence of metal-organic frameworks and also such frameworks as such.
Separating off acidic gases from gas mixtures is a known task. This can be carried out, for example, by absorption, in which the gas mixture passes through a liquid which takes up the undesirable components in the mixture so that a purifying effect is achieved. This process is generally referred to as a gas scrub. Suitable liquids are likewise known from the prior art. In the case of acidic gases, amines are particularly suitable for binding these. Such a process which is carried out using amines is therefore referred to as an amine scrub.
Apart from the absorption of acidic gases such as carbon dioxide, sulfur oxides or nitrogen oxides in liquids, adsorption on solids is also possible. Here, for example, zeolites, activated carbons or the like have been found to be suitable. A new class of substances, namely metal-organic frameworks, are attracting particular attention here.
Their suitability for the adsorption of gases such as carbon dioxide is likewise known. Especially for the removal of carbon dioxide, metal-organic frameworks have already been described in the literature, and may also have amine-functionalized ligands.
WO-A 2008/061958 and WO-A 2008/129051 describe, for example, the separation of CO2 from gas mixtures.
G. Férey, Chem. Soc. Rev., 2008, 37, 191; B. Arstad, H. Fjellvåg, K. O. Kongshaug, O. Swang, R. Blom, Adsorption, 2008, 14, 755 and P. L. Llewellyn, S. Bourrelly, C. Serre, Y. Filinchuk and G. Férey, Angew. Chem., 2006, 118, 7915, also refer to metal-organic frameworks.
Despite the methods known in the prior art, there continues to be a need for alternative processes using alternative adsorbents for separating off acidic gases from gas mixtures.
It is therefore an object of the present invention to provide such processes and adsorbents.
The object is achieved by a process for separating off at least one acidic gas from a gas mixture comprising at least one acidic gas, which comprises the step
The object is also achieved by a porous metal-organic framework according to the invention comprising at least one at least bidentate organic compound coordinated to at least one metal ion, where the porous metal-organic framework is impregnated with an amine suitable for a gas scrub.
It has been found that a separation of acidic gases from a gas mixture, in particular at relatively low pressure, can be carried out using metal-organic frameworks which have been impregnated beforehand with an amine suitable for a gas scrub.
The acidic gas is preferably carbon dioxide, a sulfur oxide, a nitrogen oxide or hydrogen sulfide. It is also possible for a plurality of acidic gases to be present in the gas mixture. In particular, a plurality of gases selected from among carbon dioxide, a sulfur oxide, a nitrogen oxide and hydrogen sulfide can be present. Particular preference is given to the gas to be separated off being carbon dioxide.
As gas mixture, it is in principle possible to use any gas mixture which comprises at least one acidic gas. The gas mixture is preferably a petroleum raffinate, i.e. typically a gas mixture which comprises hydrocarbons as main components. The gas mixture can also be flue gas, natural gas, town gas or biogas. It is also possible to use mixtures of such gas mixtures. Particular preference is given to the gas mixture comprising at least one of the gases selected from the group of gases consisting of methane, ethane, n-butane, i-butane, hydrogen, ethene, ethyne, propene, nitrogen, oxygen, helium, neon, argon and krypton in addition to the at least one acidic gas.
The separation of carbon dioxide from flue gas is also described in general terms by Dan G. Chapel, Carl L. Mariz, John Ernest, “Recovery of CO2 from Flue Gases: Commercial Trends”, presented at the “Canadian Society of Chemical Engineers annual meeting”, Oct. 4-6, 1999, Saskatoon, Saskatchewan, Canada.
In the process of the invention and also for the metal-organic framework of the invention, it is possible firstly to use a metal-organic framework known in principle from the prior art which is then impregnated with an amine suitable for a gas scrub before the separation is carried out.
Such metal-organic frameworks (MOFs) are described, for example, in U.S. Pat. No. 5,648,508, EP-A-0 790 253, M. O'Keeffe et al., J. Sol. State Chem., 152 (2000), pages 3 to 20, H. Li et al., Nature 402, (1999), page 276, M. Eddaoudi et al., Topics in Catalysis 9, (1999), pages 105 to 111, B. Chen et al., Science 291, (2001), pages 1021 to 1023, DE-A-101 11 230, DE-A 10 2005 053430, WO-A 2007/054581, WO-A 2005/049892 and WO-A 2007/023134.
A specific group of these metal-organic frameworks described in the recent literature is “limited” frameworks in which the framework does not extend infinitely but with formation of polyhedra as a result of specific choice of the organic compound. A. C. Sudik, et al., J. Am. Chem. Soc. 127 (2005), 7110-7118, describe such specific frameworks. These are referred to as metal-organic polyhedra (MOP) to distinguish them.
A further specific group of porous metal-organic frameworks is made up of those in which the organic compound as ligand is a monocyclic, bicyclic or polycyclic ring system which is derived from at least one of the heterocycles selected from the group consisting of pyrrole, alpha-pyridone and gamma-pyridone and has at least two ring nitrogens. The electrochemical preparation of such frameworks is described in WO-A 2007/131955.
The general suitability of metal-organic frameworks for taking up gases and liquids is described, for example, in WO-A 2005/003622 and EP-A 1 702 925.
These specific groups are particularly suitable for the purposes of the present invention.
The metal-organic frameworks of the present invention comprise pores, in particular micropores and/or mesopores. Micropores are defined as pores having a diameter of 2 nm or less and mesopores are defined by a diameter in the range from 2 to 50 nm, in each case in accordance with the definition given in Pure & Applied Chem. 57 (1983), 603-619, in particular on page 606. The presence of micropores and/or mesopores can be checked by means of sorption measurements, with these measurements determining the uptake capacity of the MOF for nitrogen at 77 kelvin in accordance with DIN 66131 and/or DIN 66134.
The specific surface area, calculated according to the Langmuir model (DIN 66131, 66134) of an MOF in powder form (before impregnation) is preferably more than 100 m2/g, more preferably above 300 m2/g, more preferably more than 700 m2/g, even more preferably more than 800 m2/g, even more preferably more than 1000 m2/g and particularly preferably more than 1200 m2/g.
Shaped bodies comprising metal-organic frameworks can have a lower active surface area, but preferably (without impregnation) more than 150 m2/g, more preferably more than 300 m2/g, even more preferably more than 700 m2/g.
The metal component in the framework of the present invention is preferably selected from groups Ia, IIa, IIIa, IVa to VIIIa and Ib to VIb. Particular preference is given to Mg, Ca, Sr, Ba, Sc, Y, Ln, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ro, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb and Bi, where Ln is a lanthanide.
Lanthanides are La, Ce, Pr, Nd, Pm, Sm, En, Gd, Tb, Dy, Ho, Er, Tm, Yb.
With regard to ions of these elements, particular mention may be made of Mg2+, Ca2+, Sr2+, Ba2+, Sc3+, Y3+, Ln3+, Ti4+, Zr4+, Hf+, V4+, V3+, V2+, Nb3+, Ta3+, Cr3+, Mo3+, W3+, Mn3+, Mn2+, Re3+, Re2+, Fe3+, Fe2+, Ru3+, Ru2+, Os3+, Os2+, Co3+, Co2+, Rh2+, Rh+, Ir2+, Ir+,
Ni2+, Ni+, Pd2+, Pd+, Pt2+, Pt+, Cu2+, Cu+, Ag+, Au+, Zn2+, Cd2+, Hg2+, Al3+, Ga3+, In3+, Tl3+, Si4+, Si2+, Ge4+, Ge2+, Sn4+, Sn2+, Pb4+, Pb2+, As5+, As3+, As+, Sb5+, Sb3+, Sb+, Bi5+, Bi3+ and Bi+.
Particular preference is further given to Mg, Al, Y, Sc, Zr, Ti, V, Cr, Mo, Fe, Co, Cu, Ni, Mn, Zn, Ln. Greater preference is given to Al, Mo, Y, Sc, Mg, Fe, Cu, Mn and Zn. Very particular preference is given to Sc, Al, Cu, Mn and Zn.
The expression “at least bidentate organic compound” refers to an organic compound which comprises at least one functional group which is able to form at least two coordinate bonds to a given metal ion and/or one coordinate bond to each of two or more, preferably two, metal atoms.
As functional groups via which the coordinate bonds mentioned can be formed, particular mention may be made of, for example, the following functional groups: —CO2H, —CS2H, —NO2, —B(OH)2, —SO3H, —Si(OH)3, —Ge(OH)3, —Sn(OH)3, —Si(SH)4, —Ge(SH)4, —Sn(SH)3, —PO3H, —AsO3H, —AsO4H, —P(SH)3, —As(SH)3, —CH(RSH)2, —C(RSH)3 —CH(RNH2)2 —C(RNH2)3, —CH(ROH)2, —C(ROH)3, —CH(RCN)2, —C(RCN)3 where R is, for example, preferably an alkylene group having 1, 2, 3, 4 or 5 carbon atoms, for example a methylene, ethylene, n-propylene, i-propylene, n-butylene, i-butylene, tert-butylene or n-pentylene group, or an aryl group comprising 1 or 2 aromatic rings, for example 2 C6 rings, which may, if appropriate, be fused and may each, independently of one another, be appropriately substituted by at least one substituent and/or may each comprise, independently of one another, at least one heteroatom such as N, O and/or S. In likewise preferred embodiments, mention may be made of functional groups in which the abovementioned radical R is not present. In this case, mention may be made of, inter alia, —CH(SH)2, —C(SH)3, —CH(NH2)2, —C(NH2)3, —CH(OH)2, —C(OH)3, —CH(CN)2 or —C(CN)3.
However, the functional groups can also be heteroatoms of a heterocycle. Particular mention may here be made of nitrogen atoms.
The at least two functional groups can in principle be bound to any suitable organic compound as long as it is ensured that the organic compound bearing these functional groups is capable of forming the coordinate bond and is suitable for preparing the framework.
The organic compounds comprising the at least two functional groups are preferably derived from a saturated or unsaturated aliphatic compound or an aromatic compound or a both aliphatic and aromatic compound.
The aliphatic compound or the aliphatic part of the both aliphatic and aromatic compound can be linear and/or branched and/or cyclic, with a plurality of rings per compound also being possible. The aliphatic compound or the aliphatic part of the both aliphatic and aromatic compound more preferably comprises from 1 to 15, more preferably from 1 to 14, more preferably from 1 to 13, more preferably from 1 to 12, more preferably from 1 to 11 and very particularly preferably from 1 to 10, carbon atoms, for example 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms. Very particular preference is here given to, inter alia, methane, adamantane, acetylene, ethylene or butadiene.
The aromatic compound or the aromatic part of the both aromatic and aliphatic compound can have one or more rings, for example two, three, four or five rings, with the rings being able to be present separately from one another and/or at least two rings being able to be present in fused form. The aromatic compound or the aromatic part of the both aliphatic and aromatic compound particularly preferably has one, two or three rings, with one or two rings being particularly preferred. Furthermore, each ring of said compound can independently comprise at least one heteroatom such as N, O, S, B, P, Si, Al, preferably N, O and/or S. The aromatic compound or the aromatic part of the both aromatic and aliphatic compound more preferably comprises one or two C6 rings, with the two rings being present either separately from one another or in fused form. Very particularly preferred aromatic compounds are benzene, naphthalene and/or biphenyl and/or bipyridyl and/or pyridyl.
The at least bidentate organic compound is more preferably an aliphatic or aromatic, acyclic or cyclic hydrocarbon having from 1 to 18, preferably from 1 to 10 and in particular 6, carbon atoms, which additionally has exclusively 2, 3 or 4 carboxyl groups as functional groups.
The at least one at least bidentate organic compound is preferably derived from a dicarboxylic, tricarboxylic or tetracarboxylic acid.
For the purposes of the present invention, the term “derived” means that the at least one at least bidentate organic compound is present in partially or completely deprotonated form. Furthermore, the term “derived” means that the at least one at least bidentate organic compound can have further substituents. Thus, a dicarboxylic, tricarboxylic or tetracarboxylic acid can have not only the carboxylic acid function but also a substituent or a plurality of independent substituents, such as amino, hydroxyl, methoxy, halogen or methyl groups. Preference is given to no further substituent or only an amino group being present. For the purposes of the present invention, the term “derived” also means that the carboxylic acid function can be present as a sulfur analogue. Sulfur analogues are —C(═O)SH or its tautomer and —C(S)SH.
For example, the at least bidentate organic compound is derived from a dicarboxylic acid such as oxalic acid, succinic acid, tartaric acid, 1,4-butanedicarboxylic acid, 1,4-butenedicarboxylic acid, 4-oxopyran-2,6-dicarboxylic acid, 1,6-hexanedicarboxylic acid, decanedicarboxylic acid, 1,8-heptadecanedicarboxylic acid, 1,9-heptadecanedicarboxylic acid, heptadecanedicarboxylic acid, acetylenedicarboxylic acid, 1,2-benzenedicarboxylic acid, 1,3-benzenedicarboxylic acid, 2,3-pyridinedicarboxylic acid, pyridine-2,3-dicarboxylic acid, 1,3-butadiene-1,4-dicarboxylic acid, 1,4-benzenedicarboxylic acid, p-benzenedicarboxylic acid, imidazole-2,4-dicarboxylic acid, 2-methylquinoline-3,4-dicarboxylic acid, quinoline-2,4-dicarboxylic acid, quinoxaline-2,3-dicarboxylic acid, 6-chloroquinoxaline-2,3-dicarboxylic acid, 4,4′-diaminophenylmethane-3,3′-dicarboxylic acid, quinoline-3,4-dicarboxylic acid, 7-chloro-4-hydroxyquinoline-2,8-dicarboxylic acid, diimidedicarboxylic acid, pyridine-2,6-dicarboxylic acid, 2-methylimidazole-4,5-dicarboxylic acid, thiophene-3,4-dicarboxylic acid, 2-isopropylimidazole-4,5-dicarboxylic acid, tetrahydropyran-4,4-dicarboxylic acid, perylene-3,9-dicarboxylic acid, perylenedicarboxylic acid, Pluriol E 200-dicarboxylic acid, 3,6-dioxaoctanedicarboxylic acid, 3,5-cyclohexadiene-1,2-dicarboxylic acid, octanedicarboxylic acid, pentane-3,3-dicarboxylic acid, 4,4′-diamino-1,1′-biphenyl-3,3′-dicarboxylic acid, 4,4′-diaminobiphenyl-3,3′-dicarboxylic acid, benzidine-3,3′-dicarboxylic acid, 1,4-bis(phenylamino)benzene-2,5-dicarboxylic acid, 1,1′-dinaphthyldicarboxylic acid, 7-chloro-8-methylquinoline-2,3-dicarboxylic acid, 1-anilinoanthraquinone-2,4′-dicarboxylic acid, polytetrahydrofuran-250-dicarboxylic acid, 1,4-bis(carboxymethyl)piperazine-2,3-dicarboxylic acid, 7-chloroquinoline-3,8-dicarboxylic acid, 1-(4-carboxyphenyl)-3-(4-chlorophenyl)pyrazoline-4,5-dicarboxylic acid, 1,4,5,6,7,7,-hexachloro-5-norbornene-2,3-dicarboxylic acid, phenylindanedicarboxylic acid, 1,3-dibenzyl-2-oxoimidazolidine-4,5-dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, naphthalene-1,8-dicarboxylic acid, 2-benzoylbenzene-1,3-dicarboxylic acid, 1,3-dibenzyl-2-oxoimidazolidine-4,5-cis-dicarboxylic acid, 2,2′-biquinoline-4,4′-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, 3,6,9-trioxaundecanedicarboxylic acid, hydroxybenzophenonedicarboxylic acid, Pluriol E 300-dicarboxylic acid, Pluriol E 400-dicarboxylic acid, Pluriol E 600-dicarboxylic acid, pyrazole-3,4-dicarboxylic acid, 2,3-pyrazinedicarboxylic acid, 5,6-dimethyl-2,3-pyrazinedicarboxylic acid, 4,4′-diamino(diphenyl ether)diimidedicarboxylic acid, 4,4′-diaminodiphenylmethanediimidedicarboxylic acid, 4,4′-diaminodiphenylsulfonediimidedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,3-adamantanedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 8-methoxy-2,3-naphthalenedicarboxylic acid, 8-nitro-2,3-naphthalenedicarboxylic acid, 8-sulfo-2,3-naphthalenedicarboxylic acid, anthracene-2,3-dicarboxylic acid, 2′,3′-diphenyl-p-terphenyl-4,4″-dicarboxylic acid, (diphenyl ether)-4,4′-dicarboxylic acid, imidazole-4,5-dicarboxylic acid, 4(1H)-oxothiochromene-2,8-dicarboxylic acid, 5-tert-butyl-1,3-benzenedicarboxylic acid, 7,8-quinolinedicarboxylic acid, 4,5-imidazoledicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, hexatriacontanedicarboxylic acid, tetradecanedicarboxylic acid, 1,7-heptanedicarboxylic acid, 5-hydroxy-1,3-benzenedicarboxylic acid, 2,5-dihydroxy-1,4-butanedicarboxylic acid, pyrazine-2,3-dicarboxylic acid, furan-2,5-dicarboxylic acid, 1-nonene-6,9-dicarboxylic acid, eicosenedicarboxylic acid, 4,4′-dihydroxydiphenylmethane-3,3′-dicarboxylic acid, 1-amino-4-methyl-9,10-dioxo-9,10-dihydroanthracene-2,3-dicarboxylic acid, 2,5-pyridinedicarboxylic acid, cyclohexene-2,3-dicarboxylic acid, 2,9-dichlorofluorubin-4,11-dicarboxylic acid, 7-chloro-3-methylquinoline-6,8-dicarboxylic acid, 2,4-dichlorobenzophenone-2′,5′-dicarboxylic acid, 1,3-benzenedicarboxylic acid, 2,6-pyridinedicarboxylic acid, 1-methylpyrrole-3,4-dicarboxylic acid, 1-benzyl-1H-pyrrole-3,4-dicarboxylic acid, anthraquinone-1,5-dicarboxylic acid, 3,5-pyrazoledicarboxylic acid, 2-nitrobenzene-1,4-dicarboxylic acid, heptane-1,7-dicarboxylic acid, cyclobutane-1,1-dicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 5,6-dehydronorbornane-2,3-dicarboxylic acid, 5-ethyl-2,3-pyridinedicarboxylic acid or camphordicarboxylic acid.
The at least bidentate organic compound is more preferably one of the dicarboxylic acids mentioned by way of example above as such.
The at least bidentate organic compound can be derived, for example, from a tricarboxylic acid such as
2-hydroxy-1,2,3-propanetricarboxylic acid, 7-chloro-2,3,8-quinolinetricarboxylic acid, 1,2,3-, 1,2,4-benzenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 2-phosphono-1,2,4-butanetricarboxylic acid, 1,3,5-benzenetricarboxylic acid, 1-hydroxy-1,2,3-propanetricarboxylic acid, 4,5-dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, 5-acetyl-3-amino-6-methylbenzene-1,2,4-tricarboxylic acid, 3-amino-5-benzoyl-6-methylbenzene-1,2,4-tricarboxylic acid, 1,2,3-propanetricarboxylic acid or aurintricarboxylic acid,
The at least bidentate organic compound is more preferably one of the tricarboxylic acids mentioned by way of example above as such.
Examples of an at least bidentate organic compound which is derived from a tetracarboxylic acid are
1,1-dioxidoperylo[1,12-BCD]thiophene-3,4,9,10-tetracarboxylic acid, perylenetetracarboxylic acids such as perylene-3,4,9,10-tetracarboxylic acid or perylene-1,12-sulfone-3,4,9,10-tetracarboxylic acid, butanetetracarboxylic acids such as 1,2,3,4-butanetetracarboxylic acid or meso-1,2,3,4-butanetetracarboxylic acid, decane-2,4,6,8-tetracarboxylic acid, 1,4,7,10,13,16-hexaoxycyclooctadecane-2,3,11,12-tetracarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, 1,2,11,12-dodecanetetracarboxylic acid, 1,2,5,6-hexanetetracarboxylic acid, 1,2,7,8-octanetetracarboxylic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 1,2,9,10-decanetetracarboxylic acid, benzophenonetetracarboxylic acid, 3,3′,4,4′-benzophenonetetracarboxylic acid, tetrahydrofurantetracarboxylic acid and cyclopentanetetracarboxylic acids such as cyclopentane-1,2,3,4-tetracarboxylic acid.
The at least bidentate organic compound is more preferably one of the tetracarboxylic acids mentioned by way of example above as such.
Preferred heterocycles as at least bidentate organic compounds in the case of which a coordinate bond is formed via the ring heteroatoms are the following substituted or unsubstituted ring systems:
Very particular preference is given to optionally at least monosubstituted aromatic dicarboxylic. tricarboxylic or tetracarboxylic acids having one, two, three, four or more rings, with each of the rings being able to comprise at least one heteroatom and two or more rings being able to comprise identical or different heteroatoms. Preference is given, for example, to monocyclic dicarboxylic acids, monocyclic tricarboxylic acids, monocyclic tetracarboxylic acids, bicyclic dicarboxylic acids, bicyclic tricarboxylic acids, bicyclic tetracarboxylic acids, tricyclic dicarboxylic acids, tricyclic tricarboxylic acids, tricyclic tetracarboxylic acids, tetracyclic dicarboxylic acids, tetracyclic tricarboxylic acids and/or tetracyclic tetracarboxylic acids. Suitable heteroatoms are, for example, N, O, S, B, P, with preferred heteroatoms being N, S and/or O. A useful substituent here is, inter alia, —OH, a nitro group, an amino group or an alkyl or alkoxy group.
As at least bidentate organic compounds, particular preference is given to imidazolates such as 2-methylimidazolate, acetylenedicarboxylic acid (ADC), camphordicarboxylic acid, fumaric acid, succinic acid, benzenedicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid (BDC), aminoterephthalic acid, triethylenediamine (TEDA), naphthalenedicarboxylic acids (NDC), biphenyldicarboxylic acids such as 4,4′-biphenyldicarboxylic acid (BPDC), pyrazinedicarboxylic acids such as 2,5-pyrazinedicarboxylic acid, bipyridinedicarboxylic acids such as 2,2′-bipyridinedicarboxylic acids such as 2,2′-bipyridine-5,5′-dicarboxylic acid, benzenetricarboxylic acids such as 1,2,3-, 1,2,4-benzenetricarboxylic acid or 1,3,5-benzenetricarboxylic acid (BTC), benzenetetracarboxylic acid, adamantanetetracarboxylic acid (ATC), adamantanedibenzoate (ADB), benzenetribenzoate (BTB), methanetetrabenzoate (MTB), adamantanetetrabenzoate or dihydroxyterephthalic acids such as 2,5-dihydroxyterephthalic acid (DHBDC), tetrahydropyrene-2,7-dicarboxylic acid (HPDC), biphenyltetracarboxylic acid (BPTC), 1,3-bis(4-pyridyl)propane (BPP).
Very particular preference is given to, inter alia, 2-methylimidazole, 2-ethylimidazole, phthalic acid, isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,2,3-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,3,5-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, aminoBDC, TEDA, fumaric acid, biphenyldicarboxylate, 1,5- and 2,6-naphthalenedicarboxylic acid, tert-butylisophthalic acid, dihydroxybenzoic acid, BTB, HPDC, BPTC, BPP.
Apart from these at least bidentate organic compounds, the metal-organic framework can further comprise one or more monodentate ligands and/or one or more at least bidentate ligands which are not derived from dicarboxylic, tricarboxylic or tetracarboxylic acids.
Suitable solvents for preparing the metal-organic framework are, inter alia, ethanol, dimethylformamide, toluene, methanol, chlorobenzene, diethylformamide, dimethyl sulfoxide, water, hydrogen peroxide, methylamine, sodium hydroxide solution, N-methylpyrrolidone, ether, acetonitrile, benzyl chloride, triethylamine, ethylene glycol and mixtures thereof. Further metal ions, at least bidentate organic compounds and solvents for preparing MOFs are described, inter alia, in U.S. Pat. No. 5,648,508 or DE-A 101 11 230.
The pore size of the metal-organic framework before impregnation can be controlled by selection of the suitable ligand and/or the at least one bidentate organic compound. In general, the larger the organic compound, the larger the pore size. The pore size is preferably from 0.2 nm to 30 nm, particularly preferably in the range from 0.3 nm to 3 nm, based on the crystalline material.
However, larger pores whose size distribution can vary also occur in a shaped body comprising a metal-organic framework before impregnation. However, preference is given to more than 50% of the total pore volume, in particular more than 75%, being formed by pores having a pore diameter of up to 1000 nm. However, a major part of the pore volume is preferably made up by pores from two diameter ranges. It is therefore preferred that more than 25% of the total pore volume, in particular more than 50% of the total pore volume, is formed by pores in the pore diameter range from 100 nm to 800 nm and more than 15% of the total pore volume, in particular more than 25% of the total pore volume, is formed by pores in the diameter range up to 10 nm. The pore distribution can be determined by means of mercury pore symmetry.
Examples of metal-organic frameworks which can be subjected to a subsequent Impregnation are given below. In addition to the designation of the framework, the metal and the at least bidentate ligand, the solvent and the cell parameters (angles α, β and γ and the dimensions A, B and C in A) are indicated. The latter were determined by X-ray diffraction.
Further metal-organic frameworks are MOF-2 to 4, MOF-9, MOF-31 to 36, MOF-39, MOF-69 to 80, MOF-103 to 106, MOF-122, MOF-125, MOF-150, MOF-177, MOF-178, MOF-235, MOF-236, MOF-500, MOF-501, MOF-502, MOF-505, IRMOF-1, IRMOF-61, IRMOP-13, IRMOP-51, MIL-17, MIL-45, MIL-47, MIL-53, MIL-59, MIL-60, MIL-61, MIL-63, MIL-68, MIL-79, MIL-80, MIL-83, MIL-85, CPL-1 to 2, SZL-1, which are described in the literature.
Particularly preferred metal-organic frameworks are MIL-53, Zn-tBu-isophthalic acid, Al-BDC, MOF-5, MOF-177, MOF-505, IRMOF-8, IRMOF-11, Cu-BTC, Al-NDC, Al-AminoBDC, Cu-BDC-TEDA, Zn-BDC-TEDA, Al-BTC, Cu-BTC, Al-NDC, Mg-NDC, Al-fumarate, Zn-2-methylimidazolate, Zn-2-aminoimidazolate, Cu-biphenyldicarboxylate-TEDA, MOF-74, Cu-BPP, Sc-terephthalate. Greater preference is given to Sc-terephthalate, Al-BDC and Al-BTC.
Apart from the conventional methods of preparing the MOFs, as described, for example, in U.S. Pat. No. 5,648,508, these can also be prepared by an electrochemical route. In this regard, reference is made to DE-A 103 55 087 and WO-A 2005/049892. The metal-organic frameworks prepared in this way have particularly good properties in respect of the adsorption and desorption of chemical substances, in particular gases.
Regardless of the method of preparation, the metal-organic framework is obtained in pulverulent or crystalline form. This can be used as such as sorbent either alone or together with other sorbents or further materials. This is preferably effected as loose material. Furthermore, the metal-organic framework can also be converted into a shaped body. Preferred processes here are extrusion or tableting. In the production of shaped bodies, it is possible to add further materials such as binders, lubricants or other additives to the metal-organic framework. It is likewise conceivable for mixtures of frameworks and other adsorbents, for example activated carbon, to be produced as shaped bodies or separately to form shaped bodies which are then used as shaped body mixtures.
The possible geometries of the shaped bodies are in principle not subject to any restrictions. For example, possible shapes are, inter alia, pellets such as disk-shaped pellets, pills, spheres, granules, extrudates such as rods, honeycombs, grids or hollow bodies.
The metal-organic framework is preferably present as shaped bodies. Preferred embodiments are tablets and rodlike extrudates. The shaped bodies preferably have an extension in at least one dimension in space in the range from 0.2 mm to 30 mm, more preferably from 0.5 mm to 5 mm, in particular from 1 mm to 3 mm.
To produce these shaped bodies, it is in principle possible to employ all suitable methods. In particular, the following processes are preferred:
Kneading and shaping can be carried out by any suitable method, for example as described in Ullmanns Enzyklopädie der Technischen Chemie, 4th edition, volume 2, p. 313 ff. (1972), whose relevant contents are fully incorporated by reference into the present patent application.
For example, the kneading and/or shaping can be carried out by means of a piston press, roller press in the presence or absence of at least one binder, compounding, pelletization, tableting, extrusion, coextrusion, foaming, spinning, coating, granulation, preferably spray granulation, spraying, spray drying or a combination of two or more of these methods.
Very particular preference is given to producing pellets and/or tablets.
The kneading and/or shaping can be carried out at elevated temperatures, for example in the range from room temperature to 300° C., and/or under superatmospheric pressure, for example in the range from atmospheric pressure to a few hundred bar, and/or in a protective gas atmosphere, for example in the presence of at least one noble gas, nitrogen or a mixture of two or more thereof.
The kneading and/or shaping is, in a further embodiment, carried out with addition of at least one binder, with the binder used basically being able to be any chemical compound which ensures the desired viscosity for the kneading and/or shaping of the composition to be kneaded and/or shaped. Accordingly, binders can, for the purposes of the present invention, be either viscosity-increasing or viscosity-reducing compounds.
Preferred binders are, for example, inter alia aluminum oxide or binders comprising aluminum oxide, as are described, for example, in WO 94/29408, silicon dioxide as described, for example, in EP 0 592 050 A1, mixtures of silicon dioxide and aluminum oxide as are described, for example, in WO 94/13584, clay minerals as are described, for example, in JP 03-037156 A, for example montmorillonite, kaolin, bentonite, hallosite, dickite, nacrite and anauxite, alkoxysilanes as are described, for example, in EP 0 102 544 B1, for example tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, or for example trialkoxysilanes such as trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane, alkoxytitanates, for example tetraalkoxytitanates such as tetramethoxytitanate, tetraethoxytitanate, tetrapropoxytitanate, tetrabutoxytitanate, or for example trialkoxytitanates such as trimethoxytitanate, triethoxytitanate, tripropoxytitanate, tributoxytitanate, alkoxyzirconates, for example tetraalkoxyzirconates such as tetramethoxyzirconate, tetraethoxyzirconate, tetrapropoxyzirconate, tetrabutoxyzirconate, or, for example, trialkoxyzirconates such as trimethoxyzirconate, triethoxyzirconate, tripropoxyzirconate, tributoxyzirconate, silica sols, amphiphilic substances and/or graphites. Particular preference is given to graphite.
As viscosity-increasing compound, it is, for example, also possible to use, if appropriate in addition to the abovementioned compounds, an organic compound and/or a hydrophilic polymer such as cellulose or a cellulose derivative such as methylcellulose and/or a polyacrylate and/or a polymethacrylate and/or a polyvinyl alcohol and/or a polyvinylpyrrolidone and/or a polyisobutene and/or a polytetrahydrofuran.
As pasting agent, it is possible to use, inter alia, preferably water or at least one alcohol such as a monoalcohol having from 1 to 4 carbon atoms, for example methanol, ethanol, n-propanol, isopropanol, 1-butanol, 2-butanol, 2-methyl-1-propanol or 2-methyl-2-propanol or a mixture of water and at least one of the alcohols mentioned or a polyhydric alcohol such as a glycol, preferably a water-miscible polyhydric alcohol, either alone or as a mixture with water and/or at least one of the monohydric alcohols mentioned.
Further additives which can be used for kneading and/or shaping are, inter alia, amines or amine derivatives such as tetraalkylammonium compounds or amino alcohols and carbonate-comprising compounds such as calcium carbonate. Such further additives are described, for instance, in EP 0 389 041 A1, EP 0 200 260 A1 or WO 95/19222.
The order of the additives such as template compound, binder, pasting agent, viscosity-increasing substance during shaping and kneading is in principle not critical.
In a further, preferred embodiment, the shaped body obtained by kneading and/or shaping is subjected to at least one drying step which is generally carried out at a temperature in the range from 25 to 300° C., preferably in the range from 50 to 300° C. and particularly preferably in the range from 100 to 300° C. It is likewise possible to carry out drying under reduced pressure or under a protective gas atmosphere or by spray drying.
In a particularly preferred embodiment, at least one of the compounds added as additives is at least partly removed from the shaped body during this drying process.
To impregnate the porous metal-organic framework, it is brought into contact with the amine suitable for a gas scrub. Of course, it is also possible to use a plurality of amines. The amine is typically present here in liquid form and is taken up by the porous metal-organic framework without a subsequent drying step being necessary. If the amine is brought into contact in liquid form with the framework, this can be effected in pure form, as a mixture of various amines or in dissolved form, in particular as aqueous solution. If a solution is used, a plurality of amines can also be present in one solution here. It is likewise possible to use a plurality of solutions. However, the amine can also be brought into contact in the gaseous state with the metal-organic framework.
The proportion of amine based on the metal-organic framework can be varied and is, for example, in the range from 1 to 1000 mmol of amine per g of framework, typically in the range from 1 to 100 mmol of amine per g of framework and frequently in the range from 1 to 25 mmol of amine per g of framework.
After impregnation of the porous metal-organic framework with the amine suitable for a gas scrub, the framework typically has a significantly lower specific surface area. This can be explained by the absorbed amine at least partly filling the pores, so that a lower porosity is determined.
Amines which are suitable for a gas scrub are known in the prior art. In general, it is possible an amine of the formula R1N(R2)R3′, R1, R2, R3 are each, independently of one another, hydrogen or a branched or unbranched alkyl radical which has from 1 to 12 carbon atoms and whose carbon chain can be interrupted by one or more —O— or N(R4) groups and the alkyl radical can be unsubstituted or substituted by one or more OH or NH2 groups, where R4 is hydrogen or a branched or unbranched alkyl radical having from 1 to 6 carbon atoms, with the proviso that at least one R1, R2, R3 is different from hydrogen.
R1, R2 together with the nitrogen atom to which they are bound can optionally also form a saturated heteroaliphatic ring which has from 3 to 7 ring atoms and may, if appropriate, have one or more further heteroatoms selected from among —O— and N(R4) and be unsubstituted or substituted by one or more OH or NH2 groups, where R4 is hydrogen or a branched or unbranched alkyl radical having from 1 to 6 carbon atoms.
R1, R2, R3 together with the nitrogen atom to which they are bound can optionally also form a saturated heteroaliphatic bicyclic ring which has from 7 to 11 ring atoms and may, if appropriate, have one or more further heteroatoms selected from among —O— and N(R4) and be unsubstituted or substituted by one or more OH or NH2 groups, where R4 is hydrogen or a branched or unbranched alkyl radical having from 1 to 6 carbon atoms.
The amine can thus be, for example, a monoalkylamine, dialkylamine or trialkylamine. An example is diisopropylamine. Furthermore, it is possible for, for example, the alkyl chain to be interrupted by N(CH3). An example is dimethylaminopropylamine. In addition, alkyl can be substituted by hydroxyl groups. Examples are diethanolamine, monoethanolamine, methyldiethanolamine, diisopropanolamine. Furthermore, the alkyl chain can be interrupted by oxygen and, if appropriate, bear a hydroxyl group as substituent. An example would be diglycolamine. In addition, R1, R2 can form a ring which can, if appropriate, have further ring heteroatoms such as NH. An example would be homopiperazine. It is also possible for R1, R2, R3 to form a bicyclic heterocyclic ring. An example would be urotropin.
The amine suitable for a gas scrub is preferably an amine selected from the group consisting of diethanolamine, monoethanolamine, methyldiethanolamine, diisopropylamine, diisopropanolamine, diglycolamine, 3-dimethylaminopropylamine and homopiperazine. Greater preference is given to diethanolamine, monoethanolamine, methyldiethanolamine, diisopropylamine, diisopropanolamine and diglycolamine. Particular preference is given to diglycolamine.
The step of contacting the gas mixture with the metal-organic framework which has been impregnated according to the invention can be carried out by known methods.
Contacting is preferably carried out at comparatively low absolute pressures. The partial pressure of, in particular, the at least one acidic gas is preferably in the range up to 10 bar, more preferably less than 7.5 bar, more preferably less than 5 bar, more preferably less than 2.5 bar, more preferably less than 1 bar, more preferably in the range from 10 to 500 mbar and in particular in the range from 25 to 250 mbar.
The temperature during contacting is preferably in the range from 0° C. to 50° C., more preferably in the range from 25° C. to 50° C.
Al-2,6-NDC metal-organic framework is prepared from aluminum chloride hexahydrate and 2,6-naphthalenedicarboxylic acid in the presence of N,N-dimethylformamide (DMF) in a manner analogous to example 1 of WO-A 2008/052916. A specific surface area determined by the Langmuir method of 2018 m2/g is obtained.
0.562 g of the framework from example 1 is admixed in a plastic bag with 1.107 g of aminodiglycol (2-(2-aminoethoxy)ethanol) added a little at a time and shaken. A specific surface area determined by the Langmuir method of 3 m2/g is then obtained.
0.519 g of the framework from example 1 is admixed in a plastic bag with 0.830 g of dimethylaminopropylamine added a little at a time and shaken. A specific surface area determined by the Langmuir method of 8 m2/g is then obtained.
0.731 g of framework from example 1 which has been heated overnight at 80° C. is placed in a plastic bag. 1.173 g of homopiperazine which has been melted at 60° C. is added dropwise. The mixture is subsequently shaken.
The framework from example 1 and the impregnated metal-organic framework from example 2 are subjected to a temperature-programmed desorption (TPD) with CO2 pulse chemisorption.
Here, a sample of the frameworks is firstly pretreated by means of a temperature gradient from 30 to 100° C. (5° C./min., 30 min.) under helium (50 cm3/min). A plurality of pulses of 100% CO2 (1 pulse comprises 160 μmol of CO2) are subsequently applied at 40° C.
Up to 4 pulses give an increase in adsorbed CO2 in the case of the metal-organic framework which has been impregnated according to the invention before saturation occurs. The saturation value is about 3250 μg of cumulated adsorbed CO2 per g of framework. In comparison, the unimpregnated framework displays virtually no adsorption.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09155706.6 | Mar 2009 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP10/53530 | 3/18/2010 | WO | 00 | 12/12/2011 |
