Method for producing metal-organic frameworks

Abstract

The present invention relates to a method for the preparation of a metal-organic framework structure compound, the metal-organic framework structure compound being prepared such as well as the use of the metal-organic framework structure compound being prepared such as adsorbent.

Claims

1. A method for the preparation of a metal-organic framework structure compound comprising the steps of: reacting at least one metal salt comprising a metal cation which is selected from the group consisting of the transition metals and Al as well as combinations thereof, with a linker compound, wherein the reaction is conducted at a pressure of less than 1.5 bar in aqueous solution, and wherein the linker compound is an isophthalate.

2. The method according to claim 1, wherein the aqueous solution comprises less than 10% by volume of organic solvents.

3. The method according to claim 1, wherein the reaction is conducted at a temperature of 80 to 120 C.

4. The method according to claim 1, wherein the reaction is conducted over a period of time of 10 hours or less.

5. The method according to claim 1, wherein the linker compounds are structures of the general Formula 2: ##STR00002## wherein the groups R1 to R4 are independently from each other selected from hydrogen, hydroxyl, nitro, amino, methyl, ether and halogenide groups as well as combinations thereof.

6. The method according to claim 1, wherein the metal salt is selected from the group consisting of iron and aluminum salts.

7. The method according to claim 1, wherein to the aqueous solution a base is added.

8. The method according to claim 1, wherein the reaction is conducted at the boiling point of the reaction medium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the N.sub.2 sorption isotherm, the filled squares describe the adsorption curve and the empty squares describe the desorption curve;

(2) FIG. 2 shows the N.sub.2 sorption isotherm, the filled squares describe the adsorption curve and the empty squares describe the desorption curve;

(3) FIG. 3 shows the water sorption isotherm obtained with this substance

(4) FIG. 4 shows the measured powder diffractogram, as a comparison the diffractogram of vanadium MIL-59 which is isostructural is shown;

(5) FIG. 5 shows the N.sub.2 sorption isotherm; and

(6) FIG. 6 shows the powder diffractogram of CAU-10-H.

DETAILED DESCRIPTION OF THE INVENTION

(7) In a first aspect, this object is solved by a method for the preparation of a metal-organic framework structure compound in which at least one metal salt comprising a metal cation which is selected from the group consisting of the transition metals and Al as well as combinations thereof is reacted with a linker compound, characterized in that the reaction is conducted in an aqueous solution at a pressure of 1.5 bar or less. Here, the linker compound is selected from the group consisting of substituted and unsubstituted isophthalates as well as combinations and mixtures thereof.

(8) According to the present invention, isophthalates or derivatives thereof are structures of the general Formula 2.

(9) ##STR00001##

(10) Preferably, the groups R1 to R4 are independently from each other selected from hydrogen, hydroxyl, nitro, amino, methyl, ether and halogenide groups as well as combinations thereof. In preferable embodiments all groups R1 to R4 are hydrogen. In preferable embodiments R3 is selected from amino, nitro, hydroxyl, methyl ether and methyl group.

(11) In embodiments according to the invention the linker compound is selected from isophthalates. According to the present invention, the term isophthalates also comprises their derivatives, in particular derivatives comprising a substitution at the position 2, 4, 5 or 6. As suitable substituents hydroxyl, nitro, amino, methyl, ether and halogenide groups as well as combinations thereof can be mentioned.

(12) According to the invention, the reaction is conducted in aqueous solution. Since many aromatic dicarboxylic acids are occasionally characterized by poor solubility in water, it is according to the invention to use the isophthalates. The isophthalates are used in the form of their salts, preferably as sodium, potassium, or ammonium salts.

(13) Preferred metals are Fe, Co, Ni, Zn, Zr, Cu, Cr, Mo, Mn, Al, Pd and combinations thereof, wherein particularly preferred are Al, Fe, Cu, Cr, Zr as well as combinations thereof. In also preferred embodiments the metals are selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn as well as combinations thereof. In particularly preferred embodiments the metal is selected from Al and Fe. Especially in the case of the use of aluminum it is possible to prepare extremely water-stable framework structure compounds. Preferably, the metals are used in the form of their water-soluble salts, particularly the sulfates, nitrates, carbonates, chloride oxides or halogenides. But also other salts each can be used.

(14) According to the present invention, reacting in aqueous solution preferably means that substantially no organic solvents are used in the reaction medium. Advantageous aqueous solutions comprise less than 10% by volume, in particular less than 5% by volume, further preferably less than 2% by volume and particularly preferably less than 1% by volume of organic solvent such as DMF. In preferable embodiments the reaction medium does not at all contain any organic solvent. The proportion of water in the aqueous solution is in particular higher than 50% by volume, more preferably at least 70% by volume, particularly higher than 80% by volume and particularly preferably at least 90% by volume or at least 99% by volume.

(15) In special embodiments short-chain alcohols having carbon chain lengths of 1 to 4 carbon atoms, in particular ethanol, can be used in the reaction media of this invention. Their proportion is preferably limited to at most 20% by volume, more preferably at most 10% by volume of the solvent used.

(16) The main issue of the present invention is a new synthesis approach in which, different from prior art, a substantially pressure-less synthesis is conducted. As a further aspect, the present invention preferably comprises the use of solutions of the educts and not of solids and/or suspensions. In particular, in combination with the pressure-less synthesis, this is an advantage. So, as solvent preferably water can be used, and a pressure reactor is not required.

(17) Therefore, in a preferable design of the method according to the present invention the reaction is conducted at a pressure of at least 900 mbar, particularly at least 1 bar. In preferable embodiments the pressure is at most 1.2 bar or at most 1.1 bar. Thus, the reaction can be conducted at atmospheric pressure. From that direct economic advantages follow, when the preparation method is translated into an industrial scale. For example, a continuous production can be realized by removing product being prepared from the process. This can be achieved by filtration. An advantageous design of the method according to the present invention comprises the isolation of the metal-organic framework structure compound being prepared by means of filtration. Isolation of the product by means of filtration can be realized in a continuous method in an easier manner than the isolation by means of centrifugation.

(18) Furthermore, the working-up is substantially easier, since only one step of washing is necessary and no thermal activation for removing, for example, residues of DMF.

(19) As a result, with that the recyclability is significantly increased, and the residues of the synthesis batch can directly be introduced into the clarification plant without any further post-treatment. Thus, also the product is directly free of organic solvent.

(20) In a preferable design of the method according to the present invention the reaction is conducted at a temperature of 80 to 120 C., particularly 90 to 110 C. In one embodiment the reaction temperature is at most 100 C. The reaction is in particular conducted at the boiling point of the reaction medium.

(21) A further technical advantage of the synthesis methodology according to the present invention is that, compared with the poor solubility of the aromatic dicarboxylic acid (isophthalic acid), the aromatic dicarboxylate (isophthalate) can easily be dissolved in water. In particular, when it should be translated into an industrial scale, this results in advantages, since the reaction time is considerably reduced, from 12 h, such as in literature, to, for example, 6 h or 3 h in a flask. As a consequence thereof a higher STY (space-time yield) can be achieved. Therefore, in a preferable design of the method according to the present invention the reaction is conducted over a period of time of 10 hours or less, in particular of 8 hours or less, particularly preferably 6 hours or less.

(22) In a further preferable design of the method according to the present invention the reaction is conducted under irradiation of the aqueous solution with microwaves. But also other methods for heating the reaction vessel which are common for a person skilled in the art are according to the present invention.

(23) In contrast to the synthesis which is known from literature, according to preferred methods according to the present invention the starting materials are aromatic dicarboxylates (isophthalates) and not the aromatic dicarboxylic acid (isophthalic acid) which is characterized by poor solubility in water. Therefore, in the synthesis which is known from literature due to the poor solubility it is necessary to use DMF as a solvent and an increased temperature.

(24) For the method according to the present invention each arbitrary isophthalate can be used. Preferably used are sodium isophthalates, potassium isophthalates, ammonium isophthalates and mixtures thereof.

(25) In principle, for the method according to the present invention, all metal salts being described above can be used. Preferably used are iron and aluminum salts.

(26) In contrast to the synthesis which is known from literature preferably aluminum sulfate in combination with sodium dicarboxylate (e.g. sodium isophthalate) as well as at the same time an inorganic base, particularly sodium hydroxide, calcium hydroxide, potassium hydroxide, ammonia or sodium aluminate in a solution and in a glass vessel instead of a Teflon vessel are used.

(27) In the first instance, the use of Al sulfate is not obvious, since the formation of minor phases, in particular alunite (KAl.sub.3[(OH).sub.6(SO.sub.4).sub.2]), is considerably increased. For avoiding or for minimizing the formation of these minor phases, preferably potassium hydroxide, sodium hydroxide, calcium hydroxide, ammonia or sodium aluminate is added as a base. Here, sodium aluminate is used as combined metal source and base which is not taught in literature. Accordingly, in a preferable design of the method according to the present invention as metal salt aluminum sulfate is used. In a further preferable design of the method according to the present invention a base is added to the aqueous solution. Preferably, the base is selected from the group consisting of ammonia, sodium hydroxide, potassium hydroxide, sodium aluminate and potassium aluminate. Particularly preferable is sodium aluminate.

(28) In an alternative preferable design of the method according to the present invention as metal salt iron(III) chloride is used.

(29) The metal-organic framework structure compounds which are prepared by the method according to the present invention being described here are characterized by a particularly high resistance against water. Preferably, the metal-organic framework structure compound has a specific surface area according to BET of 500 m.sup.2/g or more.

(30) The metal-organic framework structure compounds produced according to the present invention are used as an adsorbent, wherein the adsorbed material (adsorbate) is preferably water, ethanol, methane, CO.sub.2, H.sub.2 or a mixture thereof. Preferable is particularly the use of the metal-organic framework structure compounds being described herein for applications such as gas storage, catalysis, dehumidification and heat transformation (e.g. heat pumps, refrigerating machines).

(31) With the method according to the present invention high yields of more than 90%, based on the linker compound, can be achieved. The metal-organic framework structure compounds being prepared with this method have the same or larger surfaces areas, the same or higher capacities with respect to gas sorption and thus the same or better technical properties than metal-organic framework structure compounds being prepared according to a prior art method. In addition, the metal-organic framework structure compounds which have been prepared by reaction in aqueous solution are characterized by the absence of residues of organic solvents.

(32) The present invention will be explained in greater detail by means of the following examples.

EXAMPLES

(33) For the samples to be investigated at the beginning of the ageing process being independent on cycles a starting measurement with nitrogen (N.sub.2) at 77 kelvins was conducted on a NOVA 3000e of the company Quantachrome. Via the nitrogen measurement at 77 kelvins information about the change of the pore structure (distribution of the pore radii), pore volumes as well as about the internal surface area (BET) can be gathered. For removing humidity and foreign gases from the samples, before the actual measurement, they were baked out in high vacuum for 24 h at 120 C. Subsequently, the dry weight of the sample was measured by means of an analytical balance of the company Sartorius with the class of accuracy I. Subsequently, complete isotherms in adsorption and desorption were measured and evaluated. The relative pressure range was between p/p0=0.05-0.999 in the case of adsorption and p/p0=0.999-0.1 in the case of desorption. The pore volume was calculated according to the density functional theory (DFT) and according to the model of Dubinin and Astakhov (DA). The internal surface area was calculated according to the model of Brunauer-Emmett-Teller (BET) between p/p0=0.05 and 0.15.

Comparative Example 1

(34) Synthesis:

(35) 200 mg of 1,3-isophthalic acid (1,3-H.sub.2BDC, 1.20 mmol), dissolved in 1 mL of N,N-dimethyl formamide (DMF), were mixed with 800 mg of Al.sub.2(SO.sub.4).sub.3*18H.sub.2O, dissolved in 4 mL of H.sub.2O, and treated in a Teflon-lined steel autoclave for 12 hours at 135 C.

(36) Working-Up:

(37) After allowing to cool down to room temperature the product was filtrated and washed with water in an ultrasonic bath. The white solid obtained was dried and subsequently activated at 120 C. in vacuum for 24 hours.

(38) The specific surface area of the product was S.sub.BET=525 m.sup.2/g and the pore volume was 0.27 cm.sup.3/g.

Comparative Example 2

(39) Synthesis:

(40) A solution of 0.75 mol (125 g) of isophthalic acid in 600 ml of DMF and 2400 ml of water and 0.72 mmol (483 g) of Al.sub.2(SO.sub.4).sub.3*18H.sub.2O were heated in a 5000 ml three-necked flask to 135 C.

(41) In a 5 L flask 483 g (0.72 mol) of Al.sub.2(SO.sub.4).sub.3*18H.sub.2O were completely dissolved in 2,4 L of water. To the aluminum sulfate solution 125 g (0.75 mol) of isophthalic acid, dissolved in 600 mL of DMF, were added in portions.

(42) The solution was refluxed under stirring for a period of time of 48 h.

(43) Working-Up:

(44) The solid formed was filtered off with the help of a fluted filter (5-13 m), resuspended in H.sub.2O and placed in an ultrasonic bath for 30 minutes. This procedure was repeated three times. Subsequently, the white solid was dried for 5 days at 90 C. in the drying oven and for 1 day at 120 C. in the vacuum oven.

(45) After the purification 156.8 g of a white solid with S.sub.BET=578 m.sup.2/g were obtained. The single crystalline phase was identified by means of X-ray powder diffraction analysis as CAU-10-H. FIG. 6 shows the powder diffractogram of CAU-10-H.

Embodiment Example 1

(46) Synthesis:

(47) 5 L of a 0.5 M sodium isophthalate solution were prepared by making up sodium hydroxide (199.99 g; 5 mol) and isophthalic acid (415.33 g; 2.5 mol) in a graduated volumetric flask with H.sub.2O to a volume of 5000 ml. Furthermore, 2 L of a 0.5 M aluminum sulfate*18H.sub.2O solution (666.15 g; 1 mol) and 2 L of a 0.5 M sodium aluminate solution (81.79 g; 1 mol), each by making up in a graduated volumetric flask with H.sub.2O to a volume of 2000 mL, were prepared each. For the reaction 2.16 L of sodium isophthalate solution (0.5 M) and 180 mL of ethanol were combined and under stirring 810 mL of aluminum sulfate solution (0.5 M) and 540 mL of sodium aluminate solution (0.5 M) were added. Subsequently, the reaction was conducted for 6 h under reflux and stirring.

(48) Working-Up:

(49) The solid obtained was filtered off, washed with a plenty of water and ethanol and dried over night at 90 C. 207 g (92% yield) of a white powdery solid (S.sub.BET=580 m.sup.2/g) were obtained, and this was identified as CAU-10-H by means of X-ray powder diffraction analysis. The N.sub.2 sorption isotherm is shown in FIG. 1; filled squares describe the adsorption curve and empty squares describe the desorption curve.

Embodiment Example 2

(50) Synthesis:

(51) For the synthesis 100 mL of a 0.5 M sodium isophthalate solution were prepared by making up sodium hydroxide (3.99 g, 0.1 mol) and isophthalic acid (8.30 g; 0.05 mol) in a graduated volumetric flask with H.sub.2O to a volume of 100 ml. Furthermore, 100 mL of a 0.5 M aluminum sulfate*18H.sub.2O solution (33.308 g; 0.05 mol) and 100 mL of a 2 M sodium hydroxide solution (7.99 g; 0.2 mol), each by making up in a graduated volumetric flask with H.sub.2O to a volume of 100 mL, were prepared each. For the reaction 127.5 mL of H.sub.2O, 7.5 mL of ethanol and 90 mL of sodium isophthalate solution were combined and under stirring 45 mL of aluminum sulfate solution and 22.5 mL of sodium hydroxide solution were added. Subsequently, the reaction was conducted for 6 h under reflux and stirring.

(52) Working-Up:

(53) The solid obtained was filtered off, washed with a plenty of water and ethanol and dried over night at 100 C. A powdery solid (S.sub.BET=573 m.sup.2/g) was obtained which was identified by means of X-ray powder diffraction analysis as CAU-10-H. Furthermore, the reaction product contained a minor phase (sodium alunite, NaAl.sub.3(OH).sub.6(SO.sub.4).sub.2; #(ICSD)=44626). The N.sub.2 sorption isotherm is shown in FIG. 2; filled squares describe the adsorption curve and empty squares describe the desorption curve.

Embodiment Example 3

(54) Synthesis:

(55) 5.25 mL of a 0.5 M sodium isophthalate solution was stirred up with 4.5 mL of water. Under stirring 5.25 mL of a 0.5 M FeCl.sub.3 solution were added. Subsequently, the reaction was conducted for 6 h at 95 C. in the microwave under stirring.

(56) Working-Up:

(57) The solid obtained was filtered off, washed with a plenty of water and ethanol and dried over night at 90 C. It was possible to identify it as Fe-MIL-59. FIG. 3 shows the water sorption isotherm obtained with this substance.

Embodiment Example 4

(58) For a further synthesis of Fe-MIL-59 100 mL of m-Na.sub.2-BDC solution (0.5 M) and 50 mL of water were combined and under stirring 100 mL of FeCl.sub.3 solution (0.5 M) were added. The reaction was conducted under vigorous stirring and reflux for 6 hours. The solid obtained was filtered off by means of a very fine filter and the solid was washed thoroughly with water. The product was dried in the drying oven (90 C.) for 3 days. An orange-brown solid was obtained. The yield was 12.55 g (max. 12.8 g, 98%). The powder diffractogram measured is shown in FIG. 4. As a comparison the diffractogram of vanadium MIL-59 which is isostructural is shown.

Comparative Example 3

(59) 7.5 mL of Na.sub.2TDC solution (0.5 M) were provided, and under stirring 5.625 mL of AlCl.sub.3 solution (0.5 M) and 1.875 mL of NaAlO.sub.2 solution (0.5 M) were added. The reaction was conducted for 3 h at 95 C. under stirring in the microwave. The solid obtained was filtrated and washed with water and ethanol. An analysis resulted in a surface area (BET) of 1024 m.sup.2/g and a pore volume=0.4381 cm.sup.3/g. FIG. 5 shows the N.sub.2 sorption isotherm.

(60) From the comparison of Comparative Example 2 and the embodiment examples 1 and 2 it is obvious that the use of isophthalates in aqueous reaction media substantially reduces the reaction time.

(61) Embodiment Example 3 shows that the reaction does not only work with aluminum as the metal component.

(62) Comparative Example 3 shows that the reaction can analogously be conducted with other aromatic dicarboxylic acids.