Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-12-02
2001-04-17
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06218574
ABSTRACT:
The present invention relates to a process for purifying long-chain dicarboxylic acid, more particularly, a process for purifying long-chain dicarboxylic acid from a liquid containing a long-chain dicarboxylic acid and/or a salt thereof.
Long-chain dicarboxylic acid is a metabolic product obtainable from the fermentation of n-alkane by microorganisms. The fermentation liquid is a complex multi-phase system which contains unreacted n-alkane, cells of microorganisms and fragments thereof, unutilized culture medium and metabolites, secretion substances of the microorganism and the like, especially in which a large amount of impurities, such as proteins and coloring materials, will have serious adverse effect on the purity and appearance of the product.
At present, the process for purifying the long-chain dicarboxylic acid is typically classified into two types: a solvent process and an aqueous phase process. Though the problems mentioned above can be solved by using the solvent process, its application is significantly restricted by the problems such as high investment, residual alkane and solvent in the product, safety of production and so on. The aqueous phase process can overcome the defects that the solvent process has, but the purity and color appearance of its product cannot attain to a higher level. For example, JP56026193 and JP56026194 disclose an aqueous phase process for separating dicarboxylic acid, wherein the operation steps comprise alkalifying and stewing the end fermentation liquid, centrifuging to remove mycelia, adding siliceous earth to adsorb unreacted reactants and by-products, then filtering, acidifying and crystallizing the filtrate. Finally, the product of dicarboxylic acid is obtained after filtration and drying. The main problem existing in the processes mentioned above is the autolysis of cells during alkalifying and stewing, thereby the impurities such as proteins and coloring materials in cells are dissolved into the fermentation liquid, consequently the purity of total dicarboxylic acid product is only 98.5% at highest, and the coloring materials in the product are difficult to be removed. The product is then light tawny in appearance.
The object of the present invention is to provide an aqueous phase process for purifying long-chain dicarboxylic acid from a liquid containing a long-chain dicarboxylic acid and/or a salt thereof so as to improve the purity of product, decrease the chroma of product and provide the product with higher quality.
Directing to the defects existing in the prior art, the present invention further purifies long-chain dicarboxylic acid product by using crystallization of monosalt of long-chain dicarboxylic acid. It has been found upon research that the monosalt of long-chain dicarboxylic acid has very weak ability to adsorb the coloring materials. Consequently, during crystallization of monosalt of the long-chain dicarboxylic acid, the soluble proteins and coloring materials remain in the mother liquid when the monosalt of long-chain dicarboxylic acid is filtered. So this process has a dual function of removing both proteins and coloring materials, thus the purity of the long-chain dicarboxylic acid product is improved and the chroma of the product decreases.
Thus the present invention provides a process for purifying long-chain dicarboxylic acid from a liquid containing a long-chain dicarboxylic acid and/or a salt thereof comprising the steps of:
I. adjusting the pH value of said liquid containing a long-chain dicarboxylic acid and/or a salt thereof to6.2-7.0 to form a monosalt of long-chain dicarboxylic acid;
II. dissolving the monosalt of long-chain dicarboxylic acid by heating to obtain a solution containing the monosalt of long-chain dicarboxylic acid;
III. crystallizing the solution obtained from the above step by cooling, and filtering the solution to obtain a filter cake of the monosalt of long-chain dicarboxylic acid and a filtrate;
IV. dissolving the filter cake of the monosalt of long-chain dicarboxylic acid obtained in the above step by heating;
V. converting the monosalt of long-chain acid into long-chain dicarboxylic acid; and
VI isolating the long-chain dicarboxylic acid.
The present invention is suitable for use with any liquid that contains a long-chain dicarboxylic acid and/or a salt thereof. An example of such a liquid is the fermentation liquid obtained through fermentation of an n-alkane by microorganisms.
The present invention applies to any long-chain dicarboxylic acid. Preferably, the long-chain dicarboxylic acid may be a C
10
-C
18
long-chain dicarboxylic acid or a mixture of C
10
-C
18
long-chain dicarboxylic acids.
The present invention utilizes a distinct property of the monosalt of long-chain dicarboxylic acid, that is, its weak ability to adsorb the coloring materials. So it is important to properly adjust the pH value of the liquid so as to ensure that the dicarboxylic acid is converted into its monosalt form completely. Suitable pH value is from 6.2 to 7.0, preferably from 6.5 to 6.8. Acids and bases used to adjust the pH value are those which are commonly used in the art for this purpose, including organic and inorganic acids and bases. Examples of such acids are sulfuric acid, nitric acid, hydrochloric acid and phosphoric acid. Examples of such bases are alkali metal hydroxides, such as sodium hydroxide and potassium hydroxide.
Where the liquid from which the long-chain dicarboxylic acid to be purified is a fermentation liquid of an n-alkane, said liquid is advantageously treated by conventional method to remove the mycelia which may be present in the liquid prior to being processed by the process of the present invention. The treated liquid may be adjusted with an acid to 6.2-7.0. Alternatively, said fermentation liquid may be acidified directly, for example to a pH value of 2.0-4.0, preferably with heating, without removal of the mycelia. This may cause some of the proteins in the fermentation liquid to be denatured and precipitated. Then, the acidified liquid may be filtered to obtain a filter cake of long-chain dicarboxylic acid containing mycelia, leaving soluble proteins and part of the coloring materials in the filtrate. Optionally, alkanes remaining in the fermentation liquid may be separated from the liquid before the filtration is carried out. An alkali solution is added to the filter cake to obtain a liquid that is now ready to be processed by the process of the present invention.
After the dicarboxylic acid is converted into its monosalt form by pH adjustment, said liquid is heated by conventional means to dissolve the monosalt of the dicarboxylic acid. The solution obtained is cooled such that the monosalt of dicarboxylic acid is crystallized from the solution. Alternatively, the solution containing the monosalt of long-chain dicarboxylic acid is filtered to remove solids prior to being crystallized.
After crystallization, the solution is filtered to obtain a filter cake of the monosalt of dicarboxylic acid and a filtrate. The filter cake obtained is dissolved in an aqueous solvent (for example, water), preferably with heating. The filtrate obtained may be treated with an adsorbent to remove coloring materials and soluble proteins. The treated filtrate may be used for dissolving the filter cake mentioned above. Said adsorbent is selected from conventional adsorbents which are suitable for the removal of coloring materials and soluble proteins, for example, active carbon and active clay. The amount of the adsorbent added may be 0.5-3% by weight based on the weight of the filtrate and the treatment with the adsorbent may be carried out at 20-60° C. for 15-30 minutes.
After the filter cake of the monosalt of dicarboxylic acid is completely dissolved, the monosalt of dicarboxylic acid is converted to its acid form by any of conventional methods. For example, the monosalt may be acidified with an acid to a pH value of 2.0-4.0, preferably with heating to 80-95° C.
Alternatively, where a fermentation liquid is acidified directly prior to being processed by the process of the present
Gao Dacheng
Liu Shuchen
Zhang Jiangang
Calve John N.
China Petro-chemical Corporation
Geist Gary
Shanks & Herbert
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