Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-01-08
2004-06-01
Seaman, D. Margaret (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S512000, C562S526000
Reexamination Certificate
active
06743946
ABSTRACT:
The present invention relates to an improved process for the preparation of 2-hydroxy-4-methylthio-butyric acid (HMTBA) in the form of an aqueous solution and more especially to a process for improved separation from a 2-hydroxy-4-methylthiobutyronitrile (HMTBN) acid hydrolysate mixture. 2-Hydroxy-4-methylthiobutyric acid, an analog of 1-methionine, is used in animal nutrition.
Cummins discloses, in U.S. Pat. No. 3,773,927, a process in which HMTBA is produced by hydrolysis of HMTBN with hydrochloric acid under conditions such that the suspension produced comprises solid ammonium chloride, which is removed by centrifuging. The filtrate is subsequently vacuum distilled to remove the water. This U.S. Pat. No. 3,773,927 discloses a process for the preparation of an aqueous liquid product with a high concentration of HMTBA acid (85 to 90% by mass). This type of product, obtained by such a process, has a strong smell and a dark color and comprises ester oligomers. These characteristics are probably due to the high temperature conditions applied to a product with a low water content during the final dehydration stage. The other disadvantages of this process are a high energy consumption during the same stage and difficulties and losses in yields during the centrifuging or the filtration.
U.S. Pat. No. 2,745,745 discloses the separation of HMTBA by extraction with a water-immiscible organic phase, such as diethyl ether. British Patent No. 915 193 discloses a process for the preparation of calcium salts of HMTBA where the latter is extracted with an ether, such as isopropyl ether or butyl ether, having a boiling point greater than that of ethyl ether. Water is added to form an emulsion, to which calcium carbonate or calcium hydroxide is added to precipitate the calcium salt of HMTBA. This patent does not relate to the preparation of liquid products comprising essentially HMTBA.
Gielkens mentions, in U.S. Pat. No. 3,175,000, that the direct extraction of HMTBA from the hydrolysate gives poor yields. In this patent, the extraction is only used as a secondary recovery means.
U.S. Pat. No. 4,524,077 discloses the liquid-liquid extraction of HMTBA by a water-immiscible organic solvent, preferably methyl isobutyl ketone, and then the recovery of the HMTBA from the extract obtained comprising a minimum of 5% by weight of water on the basis of the mass of HMTBA recovered. The product thus prepared has a lighter color, less of a smell, a lower viscosity and a better thermal stability than the products prepared by the conventional processes described above.
Patent EP 0 330 527 discloses a process for the separation of HMTBA which consists in forming two phases by addition of aqueous ammonia to the hydrolysis solution, each of the phases, the first organic phase comprising the HMTBA and the second aqueous phase comprising the ammonium salt, are subsequently subjected to an evaporation operation, so as to remove the water. The concentrated filtered organic phase is subsequently diluted, so as to adjust its concentration to that of the commercial solution. The ammonium sulfate obtained from the aqueous phase is contaminated by sulfur residues, it often exhibits an unpleasant smell which makes it difficult to sell or which requires additional treatments in order to remove the smell therefrom. The present process requires a large amount of energy during the evaporation of the water from each of the phases obtained after neutralization and an additional treatment stage for the ammonium sulfate, which is also expensive. The present invention has made it possible to solve the abovementioned problems.
DESCRIPTION OF THE INVENTION
The present invention relates to a novel process for the preparation of 2-hydroxy-4-methylthiobutyric acid (HMTBA) and more specifically to a novel process for the separation of HMTBA. This process consists, in a first stage, in adding a neutralizing agent, composed of ammonium hydroxide, to the solution from the hydrolysis with sulfuric acid of 2-hydroxy-4-methylthiobutyronitrile, which results in the separation of the medium into two phases. These two phases are composed of an organic phase, which is subjected to a stage of release of the salts by addition of an organic solvent, and of an aqueous phase, from which residual 2-hydroxy-4-methylthio-butyric acid is exhaustively extracted by addition of an organic solvent.
The system for release of the salts from the organic phase is composed of the addition of a solvent which is not very miscible with water. Mention may be made, among these solvents, of any solvent, chemically compatible with the medium and exhibiting little affinity for water, which makes it possible to dissolve the HMTBA. They can be chosen from ketones, aldehydes, ethers, esters, carbonates or alcohols. They are preferably ketones of low molecular weight, such as methyl ethyl ketone or methyl isobutyl ketone (MIBK), or ethers, such as methyl tert-butyl ether or diisopropyl ether, or carbonates, such as diethyl carbonate. They are more preferably methyl ethyl ketone, methyl isobutyl ketone and ethyl carbonate.
The system for exhaustively extracting the HMTBA from the aqueous phase is composed of the addition of a solvent which is not very miscible with water. Mention may be made, among these solvents, of any solvent, chemically compatible with the medium and exhibiting little affinity for water, which makes it possible to dissolve the HMTBA. They can be chosen from ketones, aldehydes, ethers, esters, carbonates or alcohols. They are preferably ketones of low molecular weight, such as methyl ethyl ketone or methyl isobutyl ketone (MIBK), or ethers, such as methyl tert-butyl ether or diisopropyl ether, or carbonates, such as diethyl carbonate. They are more preferably methyl ethyl ketone, methyl isobutyl ketone and ethyl carbonate.
Each of the stages, release of the salts from the organic phase and exhaustive extraction of the aqueous phase, can be carried out independently of one another or can be carried out jointly during the implementation of the process for the isolation of the HMTBA. It is preferable to carry out these two stages jointly and in a continuous process.
In the case where it is desired to release the salts from the organic solution of HMTBA, the amount of organic solvent which is added to the organic medium composed of HMTBA is according to a solvent/organic solution of HMTBA ratio by weight preferably of greater than 0.3 and more preferably still of between 0.3 and 1. It is obvious that a person skilled in the art will adjust the amount of solvent to be used to the structure of the process. The temperature at which the release is carried out is compatible with the nature of the solvent used and in particular lies below its boiling point.
In the case where it is desired to exhaustively extract the HMTBA from the aqueous solution, it is preferable, according to a better way of implementing the invention, to use an amount of organic solvent with respect to the aqueous solution comprising the inorganic salts, in particular ammonium sulfate, drawn up according to an amount by weight of greater than 0.05 and preferably of between 0.1 and 0.5. The temperature at which the exhaustive extraction is carried out is compatible with the nature of the solvent used and in particular lies below its boiling point.
The following stage consists in evaporating the organic solvent(s) used, which can be alike in the two stages or different. This operation requires less energy than the operation for the removal of water carried out in the prior art.
After evaporation of the solvent or solvents, which are optionally recycled for a fresh operation, an organic phase is obtained which comprises little water and which comprises a greatly reduced amount of salts, which eliminates the filtration phase carried out previously. The phase is subsequently adjusted to the commercial assay of 88% by weight by addition of the water needed.
After two-phase separation between the organic solvent for exhaustive extraction and the aqueous phase comprising the salts, a solution of salt
Carencotte Frederic
Garrait Michel
Gros Georges
Adisseo Ireland Limited
Connolly Bove & Lodge & Hutz LLP
Oh Taylor V
Seaman D. Margaret
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