Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2002-05-06
2004-03-30
Kumar, Shailendra (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S606000
Reexamination Certificate
active
06713649
ABSTRACT:
BACKGROUND
The present invention relates to a process for the preparation of formic acid.
More recent processes for the preparation of formic acid on an industrial scale start from methyl formate, which is easily accessible by carbonylation of methanol. The methyl formate is subsequently hydrolyzed, with the formic acid acting as catalyst. Since both the hydrolysis and the re-esterification are catalyzed, an equilibrium becomes established in which all four components, methyl formate, water, formic acid and methanol, are present in high proportions.
This results in problems in performing the reaction. It is not possible to shift the equilibrium by removing the desired process products by distillation since the methyl formate (boiling point 32° C.) has a significantly lower boiling point than methanol (boiling point 65° C.) and formic acid (boiling point 101° C.). It would therefore be favorable to shift the equilibrium to the formic acid side by means of an excess of water.
Further problems occur in working up the aqueous formic acid. Formic acid and water form an azeotrope which contains 77.5% by weight of HCOOH and boils at 107.1° C. at 101.3 kPa. The aqueous formic acid formed on hydrolysis of methyl formate has an acid content of from about 20 to 60% by weight. Pure or more highly concentrated formic acid therefore cannot easily be recovered from these dilute aqueous formic acid solutions by distillation.
U.S. Pat. No. 2,160,064 proposes separating the azeotrope by distillation at various pressures. To this end, the dilute acid is first separated at relatively high pressure into water as the top product and a formic acid-rich azeotrope as the bottom product. This azeotrope is subsequently distilled again in a second column operated at relatively low pressure. This gives formic acid as the top product and an azeotrope having a lower acid content than that from the first distillation step as the bottom product. The azeotrope from the second step is fed back into the first step.
In a practical implementation, the distillation is carried out at a pressure of from approximately 202.6 to 303.9 kPa. This causes the composition of the azeotrope to shift toward a higher acid content. Theoretically, the azeotrope should contain from approximately 84 to 85% by weight of formic acid at 253.2 kPa. When the distillation is carried out in practice, the formic acid content in the still of the first distillation column never exceeds a proportion of from 81 to 82% by weight. The second distillation is carried out at atmospheric pressure or somewhat below atmospheric pressure. This means that the amount of formic acid distilled off can correspond to the difference between the compositions of the two azeotropes. Owing to the small differences, the columns must have a very high number of theoretical plates and be operated at very high reflux ratios. At a reflux ratio of R=2.3, the number of theoretical plates for the first distillation column is 15. The second column has, at a reflux ratio of R=10, 18 theoretical plates. Furthermore, the azeotrope formed as the bottom product in the second distillation must be fed back to the first distillation step.
Both owing to the high bottom temperature (125 to 135° C.) in the first column and owing to the high residence time of the formic acid, high losses of yield due to decomposition of the formic acid must be accepted. Furthermore, the aggressive nature of aqueous formic acid means that distillation columns made from special materials must be used in order to avoid excessive corrosion. Owing to the large product streams in circulation and the high energy consumption, the process described is therefore unsuitable for use on an industrial scale.
A switch has therefore been made to removing the formic acid from its mixture (with water) by extraction with water, with the extractant and the formic acid being separated by distillation in a further step. A process of this type is proposed, for example in EP 0 017 866 B1, where firstly methyl formate is hydrolyzed, and the methanol and excess methyl formate are removed from the resultant hydrolysis mixture by distillation. The bottom product from the distillation, consisting of formic acid and water, is extracted in a liquid extraction with an extractant which principally takes up the formic acid. The preferred extractants proposed are carboxamides, in particular N-di-n-butylformamide, N-di-n-butylacetamide, N-methyl-N-2-heptylformamide, N-n-butyl-N-2-ethylhexylformamide, N-n-butyl-N-cyclohexylformamide, N-ethylformanilide and mixtures of these compounds. Further suitable extractants described include isopropyl ether, methyl isobutyl ketone, ethyl acetate, tributyl phosphate and butanediol formate. The mixture obtained in the extraction, comprising formic acid, the extractant and some of the water, is subjected to a further distillation. A product consisting of all or some of the water introduced into the distillation and some of the formic acid is taken off at the top of the column and fed back in vapor form into the lower part of the first distillation column. The bottom product is a mixture of extractant, possibly some of the water and the majority of the formic acid. This mixture is separated into anhydrous or substantially anhydrous formic acid and the extractant in a further, third distillation column. The extractant is recycled into the process. In a particular embodiment, the first and second distillation steps are combined in a single column. However, the extraction of the formic acid from the aqueous mixture is still carried out in a separate extractor. To this end, the mixture of formic acid and water is removed from the column via a side outlet and fed to the extractor. The mixture of extractant and formic acid and possibly water is discharged from the extractor and fed back below the side outlet of the distillation column. A mixture of formic acid, extractant and possibly water is removed at the bottom of the column and fed to a further distillation column, which corresponds to the third distillation column in the embodiment described above.
The design of large-scale industrial syntheses is determined to a large extent by economic considerations. It is therefore an object of the present invention to provide a process for the preparation of formic acid which employs inexpensive chemicals which are available on a large industrial scale and should not be harmful to the environment, and which can be carried out in smaller plants compared with the processes known from the prior art with the same yield.
BRIEF SUMMARY OF THE INVENTION
We have found that this object is achieved by a process for the preparation of formic acid which comprises the following steps:
a) hydrolysis of methyl formate to give a mixture of water, formic acid, methanol and excess methyl formate;
b) removal of the methanol and excess methyl formate from the mixture of water, formic acid, methanol and excess methyl formate by distillation to give aqueous formic acid;
c) extraction of the aqueous formic acid with at least one formic acid ester to give a mixture of at least one formic acid ester and formic acid;
d) separation of at least one formic acid ester and formic acid by distillation.
DETAILED DESCRIPTION OF THE INVENTION
In a practical implementation on a technical scale it is preferred to use at least one formic ester of the group consisting of ethylene glycol diformate, diethylene glycol diformate, propane-1,2-diol diformate, propane-2,3-diol diformate, Dipropylene glycol diformate, butane-2,3-diol diformate, butane-1,4-diol diformate, benzyl formate, cyclohexyl formate, 2-phenylformate, 2-ethylhexylformate. Those formic acid esters are produced in large scale and are therefore available in huge amounts at low costs. Benzyl formate is most preferred.
Benzyl formate is a colorless liquid with a slight cinnamon odor. It has a density of 1.04 g/cm3 and a boiling point of 202.3° C. With water, benzyl formate forms an azeotrope having a water content of 80% by weight and a boiling point of 99.2° C. Benzyl formate ha
Hladiy Serhiy
Lastovyak Yaroslav
Pazderskyy Yuriy
Starchevskyy Mykhaylo
Keil & Weinkauf
Kumar Shailendra
Puttlitz Karl
LandOfFree
Method for production of formic acid does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for production of formic acid, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for production of formic acid will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3269485