PROCESS FOR PREPARING A METAL-ORGANIC FRAMEWORK

Abstract

The present invention relates to a process for preparing a magnesium formate based metal-organic framework. The process comprises (a) combining magnesium or magnesium oxide with formic acid; (b) heating the reaction mixture of step (a) at a temperature of between 70° C. and 200° C.; (c) combining formic acid with the reaction mixture of step (b); and (d) heating the reaction mixture of step (c) at a temperature of between 70° C. and 200° C. Steps (c) and (d) may be heated up to 5 times.

Claims

1. A process for preparing a magnesium formate-based MOF, the process comprising: (a) combining magnesium or magnesium oxide with formic acid; (b) heating the reaction mixture of step (a) at a temperature of between 70° C. and 200° C.; (c) combining formic acid with the reaction mixture of step (b); and (d) heating the reaction mixture of step (c) at a temperature of between 70° C. and 200° C.

2. The process according to claim 1, wherein step (a) comprises combining magnesium oxide with formic acid.

3. The process according to claim 1, wherein step (b) is performed at a temperature of between 90° C. and 180° C.

4. The process according to claim 1, wherein step (d) is performed at a temperature of between 90° C. and 180° C.

5. The process according to claim 3, wherein step (b) is performed at a temperature of between 115° C. and 180° C.

6. The process according to claim 4, wherein step (d) is performed at a temperature of between 115° C. and 180° C.

7. The process according to claim 1, wherein step (b) is carried out for between 1 hour and 24 hours.

8. The process according to claim 1, wherein step (d) is carried out for between 1 hour and 24 hours.

9. The process according to claim 1, wherein at least one of step (a) and step (c) is performed with a step selected from grinding, milling, and mixing of the reactants.

10. The process according to claim 9, wherein at least one of step (a) and step (c) is performed with a step selected from grinding, milling, and mixing the reactants for up to 2 hours.

11. The process according to claim 1, wherein at least one of steps (a) and (c) is a mechanochemical step.

12. The process according to claim 11, wherein both (a) and (c) are mechanochemical steps.

13. The process according to claim 12, wherein at least steps (a) and (c) are performed on an extruder.

14. The process according to claim 13, wherein the process is a continuous process.

15. The process according to claim 1, wherein steps (c) and (d) are repeated up to 5 times.

Description

EXAMPLES

[0027] Formic acid (product code 33015) and Magnesium Oxide (product code 220361) were obtained from Sigma-Aldrich.

[0028] BET Surface Areas were measured by adsorbing N.sub.2 gas onto a sample of Mg Formate at 77K over a range of partial pressures using a BELSORP Mini II apparatus. The values of volume of N.sub.2 adsorbed as a function of N.sub.2 partial pressure were used to calculate the BET surface area using the well known BET Equation.

Example 1: Small-Scale Production in a Stainless Steel Shaker Mill

[0029] In a first example, a magnesium formate-based MOF was prepared in a stainless steel Shaker Mill (Retsch MM400), as follows:

[0030] 1 gram of magnesium oxide and 1.87 mls of formic acid were milled in a 25 ml vessel with a 15 mm grinding ball at 30 Hz for 30 minutes. The mixture was then dried at 130° C. under vacuum in a round-bottomed flask in an oil bath for 4 hours. 1.4 mls of formic acid was then introduced, and the mixture was milled at 30 Hz for 30 minutes. The resulting mixture was dried at 130° C. overnight.

[0031] 2.27 g of magnesium formate MOF was produced, which exhibited a BET surface area of 513 m.sup.2/g.

Example 2: Larger-Scale Production in a 250 ml Stainless Steel Planetary Mill

[0032] A magnesium formate-based MOF was prepared in a stainless steel Planetary Mill (Retsch PM100) as follows:

[0033] 25 g of magnesium oxide and 15 mls of formic acid were milled in a 250 ml planetary mill vessel, with two 63 g grinding balls at 400 rpm for 30 minutes. Then, 15 ml of formic acid was introduced into the vessel, and the mixture was milled at 400 rpm for a further 30 minutes. A further 15 ml of formic acid was then introduced, and again the mixture was milled at 400 rpm for 1 hour. The mixture was then dried overnight, at 130° C. Following drying, 15 ml of formic acid was introduced and the mixture was milled at 400 rpm for 30 min. A further 15 ml of formic acid was added, and the mixture was milled at 400 rpm for 30 minutes. The product was then milled at 400 rpm for another 30 minutes. The mixture was then dried overnight, at 130° C. The BET surface area after the second drying step was 460 m.sup.2/g. Following drying, 15 ml of formic acid was added, and the mixture was milled at 400 rpm for 30 minutes. A further 15 mls of formic acid was added and the mixture was milled at 400 rpm for 30 minutes. The product was then milled at 400 rpm for another 30 minutes. The mixture was then dried overnight at 130° C.

[0034] 55 g of magnesium formate MOF was produced, which exhibited a BET surface area of 544 m.sup.2/g.

Example 3: Extrusion

[0035] A magnesium formate-based MOF was prepared by extrusion, as follows:

[0036] 40 g of MgO was mixed with 75 mL of formic acid to form a solid mixture. This was then manually fed into a ThermoFisher Process 11 extruder, at a screw speed of 150 rpm. The barrel of the extruder was 20° C. The extrudate was collected and dried overnight under vacuum at 130° C. BET surface area of the product was determined to be 250 m.sup.2/g. 50 ml of formic acid was added to the product, which was passed through the extruder a second time under the same conditions. Again, the extrudate was collected and dried overnight under vacuum at 130° C. BET surface area of the product was determined to be 32 m.sup.2/g). 12 ml of formic acid was added, and the product was passed through the extruder a third time under the same conditions as previously, before the extrudate was again collected and dried overnight under vacuum at 130° C. The BET surface area after the third drying step was 445 m.sup.2/g, corresponding to commercially viable MOFs, which are marketed with a specification of 400-600 m.sup.2/g. It is likely that a further pass through the extruder would have allowed a BET surface area of >500 m.sup.2/g to be achieved.

[0037] The MgO used in the examples above has a maximum surface area of 165 m.sup.2/g. Higher surface areas are therefore indicative of the formation of the desired MOF. The above results therefore demonstrate that when formic acid is introduced to the reaction mixture after the initial reaction between the magnesium oxide and formic acid has taken place, that the yield of the MOF can be improved, and that sequential performance of these formic acid addition/heating steps, can lead to increasingly improved results. This is significant particularly for continuous processes, such as mechanochemical processes, as it allows a direct route to a commercially viable high-surface area MOF at high yields.