Method for the Production of Formic Acid

Abstract

The present invention relates to a process for preparing formic acid by thermally decomposing ammonium formates of tertiary amines A, wherein the tertiary amine A on which the ammonium formate is based has a boiling point at atmospheric pressure in the range from 105 to 175° C.

Description

FIG. 1 which follows and the example illustrate the process according to the invention in more detail.

FIG. 1 shows a schematic of a continuous configuration of the process according to the invention, in which ammonium formate is prepared by hydrolyzing methyl formate with water in the presence of the tertiary amine. To this end, water, methyl formate and tertiary amine are fed into the hydrolysis reactor A as stream 1. The reactor effluent is decompressed and fed into the distillation column B. The distillation residue of column B which comprises ammonium formate and water is fed into a further distillation column C as stream 3. In column C, the thermal dissociation of the ammonium formate takes place, and aqueous formic acid is drawn off at the top of the column in a concentration of from 70 to 85% by weight (stream 4). The distillation residue of column C which comprises substantially the tertiary amine A and small amounts of formic acid is drawn off as stream 5, if appropriate enriched with fresh base (stream 6) and combined with the water and methyl formate starting materials (stream 10) and recycled into the hydrolysis reaction as stream 1.

At the top of the column B, the methanol present in the reactor effluent (2) of the hydrolysis A and any unconverted methyl formate are drawn off and fed to a distillative separation into methyl formate and methanol (column D) as stream (7). The unconverted methyl formate is drawn off at the top of column D as stream (8) and combined via (8′) with the stream of the starting materials (stream 1) and recycled thus into the hydrolysis A. Substantially pure methanol is obtained as the bottoms of column D and is discharged as stream 9 and can be fed to other uses, for example the preparation of methyl formate.

Example: General Method for the Hydrolysis of Methyl Formate and Subsequent Thermal Decomposition of the Resulting Ammonium Formate

In a continuous stirred vessel having a reactor capacity of 200 ml, a mixture of methyl formate, water and 2,6-dimethylpyridine in a molar ratio of 1:1:0.9 was fed at a feed rate of 570 g/h. The reactor temperature was 120° C. and the pressure 12 bar.

The reaction mixture was decompressed into the middle of a bubble-cap tray column having a diameter of 30 mm and a height of 3 m (30 bubble-caps), so that a mixture of 78 g/h of methanol and 56 g/h of methyl formate was drawn off at a top temperature of 43° C. and a reflux ratio of 2.

The bottom product of the first column was introduced into a randomly packed column (diameter 30 mm, height 2 m, reflux ratio 3) operated at 400 mbar. The bottom temperature was about 125° C. At a top temperature of 79.5° C., 120 g/h of a mixture of formic acid and water distilled off at a formic acid content of 85%. The bottom product obtained was the tertiary amine which contained up to about 3% by weight formic acid. This was recycled quantitatively into the hydrolysis reaction.

The resulting formic acid had a low color number which did not rise even after several days of storage.

Claims

1. A process for preparing formic acid by thermally decomposing ammonium formates of tertiary amines A, wherein the tertiary amine A has a boiling point at atmospheric pressure in the range from 105 to 175° C.

2. The process according to claim 1, wherein the tertiary amine A has a pKa in water at 25° C. in the range from 4 to 9.

3. The process according to claim 2, wherein the tertiary amine A is a pyridine compound.

4. The process according to claim 1, wherein the decomposition of the ammonium formate is carried out at a reaction temperature of not more than 130° C.

5. The process according to claim 1, wherein the thermal decomposition is configured as a distillation in which formic acid and, where present, water are distilled out of the ammonium formate-containing reactant.

6. The process according to claim 1, wherein the ammonium formate is prepared by hydrolyzing methyl formate in the presence of a tertiary amine A.

7. The process according to claim 6, wherein the hydrolysis of the methyl formate is carried out up to a conversion in the range from 50 to 95%.

8. The process according to claim 6, wherein the mixture obtained in the hydrolysis is subjected to a first distillation in which the majority of methanol and any unconverted methyl formate are distilled out of the mixture obtained in the hydrolysis, and the resulting residue is subjected to a second distillation to decompose the ammonium formate, in which formic acid and, where present, water are distilled off

9. The process according to claim 1, wherein the tertiary amine A is recycled into the reaction.

10. The process according to claim 2, wherein the decomposition of the ammonium formate is carried out at a reaction temperature of not more than 130° C.

11. The process according to claim 3, wherein the decomposition of the ammonium formate is carried out at a reaction temperature of not more than 130° C.

12. The process according to claim 2, wherein the thermal decomposition is configured as a distillation in which formic acid and, where present, water are distilled out of the ammonium formate-containing reactant.

13. The process according to claim 3, wherein the thermal decomposition is configured as a distillation in which formic acid and, where present, water are distilled out of the ammonium formate-containing reactant.

14. The process according to claim 4, wherein the thermal decomposition is configured as a distillation in which formic acid and, where present, water are distilled out of the ammonium formate-containing reactant.

15. The process according to claim 2, wherein the ammonium formate is prepared by hydrolyzing methyl formate in the presence of a tertiary amine A.

16. The process according to claim 3, wherein the ammonium formate is prepared by hydrolyzing methyl formate in the presence of a tertiary amine A.

17. The process according to claim 4, wherein the ammonium formate is prepared by hydrolyzing methyl formate in the presence of a tertiary amine A.

18. The process according to claim 5, wherein the ammonium formate is prepared by hydrolyzing methyl formate in the presence of a tertiary amine A.