CZ16892A3 - process of extractive separation of citric acid from fermentation broth - Google Patents

Abstract

The method of the extractive separation of citric acid from fermentation broth containing 8 to 20% by weight of citric acid during which the fermentation broth is put into intensive contact with a concentrated solution of trialkylamine with alkyl groups with 8 to 12 carbon atoms in a mixed diluent containing 20 to 50% by weight of n-octanol or 2-ethyl hexanol as the polar high-boiling constituent, and 10 to 55% by weight of n-hexan, n-heptan or a mixture of aliphatic hydrocarbons as the inert constituent, and the obtained organic phase is then diluted with the inert constituent in a ratio of 0.5 to 2 in relation to the original content of the mixed diluent and is put into counter-current contact with water at a temperature of 65 to 100 degrees C and the added inert constituent is removed from the organic phase by distillation, and the resulting concentrated trialkylamine solution is cooled and then used again for countercurrent contact with the fermentation broth.

Description

Technology .......

The invention relates to the extraction separation of citric acid from a fermentation broth containing from 8 to 20% by weight. citric acid, wherein the fermentation broth is in intense countercurrent contact with a concentrated solution of a trialkyl amine of C 8 -C 12 alkyl groups in a mixed diluent containing a polar high-boiling and non-polar low-boiling inert component.

Background. techniques

Currently, most of the citric acid available on the market is produced by fermenting starch, sugar or molasses with a suitable strain of Aspergillus niger. The aqueous solution of the feedstock with the addition of nutrients and other substances is fermented with oxygen either superficially or submergedly to form citric acid, and after removal of the mycelium, a fermentation broth containing in addition to 8 to 15¾ citric acid also proteins, carbohydrate and nutrient residues and other impurities.

So far, the separation of citric acid from the fermentation broth is most often accomplished by precipitating calcium citrate, separating it and releasing the acid therefrom with an aqueous sulfuric acid solution. This method is described, for example, in the Ullmans Encyclopedia der technischen Chemie, 8and 9, 624-636. Verlag Chemie Weinheim, 1975. Using starch as a raw material, a method for separating impurities from the fermentation broth was proposed in succession by filtration, ultrafiltration, charcoal purification, and ion exchange.

Furthermore, a number of methods for separating citric acid from the fermentation broth by extraction were proposed. Since citric acid is highly hydrophilic in nature, conventional organic solvents for its extraction are poorly effective. The tertiary amines (hereinafter Irialkylamine-TAA) having carbon chains of 8 to 12 carbon atoms, which form complex compounds with citric acid, have proven to be the most efficient extracting agent. However, these amines are very viscous and must be diluted with a suitable organic diluent for practical use. Some organic solvents behave as so-called inert diluents which do not affect the extraordinary ability of tertiary amines. These include, for example, aliphatic hydrocarbons such as hexane, heptane and the like.

Polar solvents and solvents protonating as aliphatic ketones, alcohols or chlorinated hydrocarbons are active since they significantly increase the extraction capacity of TAA. It has also been proposed to use combined diluents composed of inert and active solvents. In terms of extraction, citric acid resembles other organic acids such as acetic, propionic, lactic fumaric, malonic, maleic and succinic acids, but is the most difficult to extract from these acids. Ways? extractive separation have usually been designed for these general ^f · acids and of their application to citric acid is fraught with difficulties. The drawbacks in terms of extraction tend to be the lack of ability of a given combination of TAA with a diluent to extract acid from the aqueous phase, which leads to losses in practice, toxicity of extractant components, or unsuitable properties for the separation of citric acid from organic extract.

In the case of inert solvents, a second organic phase may be formed during the extraction. This is described, for example, in Wennersten R .: The extraction of citric acid from fermentation broth using a solution of tertiary amine. J.Chem.Tech. Biotechnol.,

33B, 85-84 (1983); Kertes A.S., King C.J .: Extraction Cheers of Fermentation Product Carboxylic Acids. Biotechnology and Bioengineering, 28, 269-282 (1986).

The main difficulty in using TAA to separate citric acid from the fermentation broth is the separation of the acid from the organic extract. All of the proposed procedures assume the reextraction of the acid into water or an aqueous solution of suitable reagents. The difficulty is that the better the extracting agent for citric acid is the chosen amine solution in the diluent, the more difficult it is to extract the acid from it. To overcome this difficulty, it has been proposed (Bauer U., Marr R., Riickl W., Siebenhofer M .: Extraction of citric acid from aqueous solutions. Chem. Biochem. Eng. Q., 2, 230-232 (1988) to re-extract the acid It has also been proposed (Pooke L.3., King CJ: Regeneration of carboxylic acid-amine by extracting it with an aqueous solution of volatile amine). Ing.

Eng. Chem. Res., 30, 923-929 (1991) to re-extract carboxylic acids from a TAA solution with an aqueous solution of a volatile amine such as trimethylamine, which is then separated by distillation.

It has also been suggested (Baniel AM, Blumberg R., Hajdu K.: Recovery of Acides from Aquatic Solutions. US Pat. 4,275,234 (1981)) to re-extract carboxylic acids at elevated temperature with water, since the extraction capacity of TAA decreases with increasing temperature and facilitates A drawback of the previously known combinations of TAA and diluents is that they have little ability to extract the acid from the aqueous phase in terms of extraction.

Finally, it has been proposed (Tamada J.A., King C.J .: Extraction of carboxylic acids with amine extractants. 3. Effect of temperature, water coextraction and process considerations.

Ind.End.Chem.Res., 29, 1333-1338 (1990), take advantage of the fact that the extraction capacity of TAA for carboxylic acids decreases when diluted with an inert diluent, dilute the extract with this diluent and distil the inert diluent after re-extraction of the acid with water. Alternatively, the TAA can be dissolved in a mixture of a volatile polar solvent and a low volatile inert diluent and, prior to reextracting, a portion of the polar solvent to reduce the extraction ability of the mixture.

Said methods of separating citric acid from the fermentation broth have various disadvantages. The method based on the precipitation of calcium citrate leads to a large consumption of calcium hydroxide and sulfuric acid; per ton of citric acid, up to 2.5 tonnes of waste calcium sulfate are produced. The aqueous citric acid solution obtained must be freed from a considerable amount of sulphate and calcium ions by costly ion exchange prior to crystallization.

Methods based on extraction with a TAA solution and reextraction with an aqueous solution of formic acid or TAA are energy intensive, since perfect separation of these agents from citric acid is difficult. Method based on extraction of acid with TAA solution in cold and re-extraction of acid with water under increased .....

temperature is relatively easy to carry out with some carboxylic acids, for example succinic acid. From this acid, a distribution coefficient of 5 can be achieved by extraction with trioctylamine in methyl isobutyl ketone at 25 ° C, which is sufficient to obtain a high yield of acid. When reextracted at 75 ° C, this coefficient drops to 0.8, so that the extractant can be largely regenerated and at the same time a sufficient, high acid concentration in the aqueous solution for crystallization can be achieved.

In the case of citric acid, it has not been possible to prepare a diluent or a mixture of diluents which provides a similarly advantageous range of distribution coefficients as a function of temperature.

In other words, the diluents which have been proposed so far allow either a good yield of citric acid when extracted from the fermentation broth, but do not ensure sufficient reextraction of the aqueous reextract, or vice versa.

_s - When inert or weakly polar diluents are used, a higher organic saturation of TAA with citric acid results in a second organic i

phase, so that the capacity of the extraction agent is very limited (see Wennersten, cited above), when the strongly polar diluents are used, a sufficient reduction in the distribution coefficient cannot be achieved by increasing the temperature. A similar difficulty occurs when using the organic phase dilution method prior to reextraction with an inert diluent. Dilution methods of TAA with a mixture of volatile polar and non-volatile inert diluents cannot be used for citric acid for food use, as polar volatile solvents are either too water soluble or toxic (eg chlorinated hydrocarbons),

SUMMARY OF THE INVENTION It is an object of the present invention to separate the citric acid from all the above-mentioned substances by extraction and to obtain an aqueous solution thereof by back-extraction, which solution is then worked up by crystallization to anhydrous acid or its monohydrate.

SUMMARY OF THE INVENTION

The principle of the extraction separation of citric acid from the fermentation broth is that for countercurrent contact of the fermentation broth with a solution of trialkylamine in a mixed diluent, n-octanol or 2-ethylhexanol in an amount of 20 to 50¾ wt. and as an inert component n-hexane, n-heptane or a mixture of aliphatic hydrocarbons boiling at 60 to 110 ° C, in an amount of 10 to 55¾ wt.%, based on the whole solution of trialkylamine and mixed diluent, and that the obtained organic phase is diluted in a ratio of 0.5 and 2, based on the original content of the mixed diluent, and countercurrently contacted with water at 65-100 ° C and the added inert component is removed from the organic phase by distillation, and after cooling the trialkylamine solution is reused countercurrent contact with the fermentation broth.

The ratio of the mass flow rates of the fermentation broth to the concentrated trialkylamine solution is preferably 0.5 to 0.9, and the ratio of the mass flow rates of water to the organic phase diluted with the inert component is 0.1 to 0.2.

The effect of the process is further enhanced if the countercurrent contact of the diluted organic phase with water is performed under vibration.

The process of the invention has a number of advantageous properties and effects. No raw materials are consumed and no waste is generated except for the extracted fermentation broth. The extraction agent used is non-toxic. The energy requirements for heating and distillation are low due to the low specific evaporation temperatures of the organic substances used. In this case, the proposed process makes it possible to obtain an aqueous solution of citric acid having a concentration of 23 to 29%, which means that it achieves a significant concentration and thus a saving of thermal energy in the subsequent crystallization.

In the process according to the invention it is also important to apply the vibrational movement during extraction and reextraction. The vibratory tray columns are characterized by high extraction efficiency and also allow foaming solutions contaminated with surfactants, which is the case with fermentation broth.

The following are examples of carrying out the process of the invention without limiting its scope.

DETAILED DESCRIPTION OF THE INVENTION Example 1

Fermentation broth containing 9¾ wt. citric acid was countercurrently extracted in an extractor column with removal tray with trioctylamine solution in a mixture of 2 parts by weight of n-octanol and 3 parts by weight of n-heptane, the solution containing 1.5

1 mole of amine per kg. thinners. The ratio of the mass flow rate of the aqueous phase to the δ of the organic phase expressed as water and diluent flow rate was 0.5.

The extraction was carried out at 25 ° C, the extractor had an efficiency corresponding to 4 theoretical stages. The extract was counter-currently contacted with ^one clean water in a ratio of mass flow

I of water and diluent in aqueous and organic phase 0,2 at 75 ° C in a vibratory tray extractor which has | efficiency corresponding to 6 theoretical degrees. The organic acid-free phase was re-cooled to 25 ° C and used to extract the fermentation broth; this working cycle was repeated until the concentrations of the aqueous raffinate from the extraction and the aqueous extract from the re-extraction were stabilized. The steady-state concentration of citric acid in the aqueous raffinate was 1.9 wt%. and in the aqueous reextract was 16.0 wt. This corresponds to a yield of 80% and a relative thickening of the aqueous citric acid solution 1.8 times.

l · Example 2

The fermentation broth as in Example 1 was subjected to extraction under the same conditions, after which the extract obtained was diluted with n-heptane such that the weight amount of heptane added was equal to the original amount of the mixture of octanol and heptane. The organic phase so treated was re-extracted countercurrently with water at a ratio of the mass flow rate of water and diluent in organic phase 0.2 at 25 ° C in the same apparatus as in Example 1.

Subsequently, the composition of the organic phase was distilled off by distilling off the heptane, and the cycle was repeated until the output concentrations of the aqueous phases from both extra steps were stabilized. The concentration of citric acid in the aqueous raffinate from the extraction was 6.5% by weight, the concentration of citric acid in the aqueous reextract 3.3% by weight. This corresponds to a yield of 29% and a relative concentration of an aqueous citric acid solution of 0.37.

Example 3

The fermentation broth as in Example 1 was subjected to extraction under the same conditions, after which the organic phase was diluted with n-heptane as in Example 2 and reextracted with water at a water to organic phase weight ratio of 0.2 but at 75 ° C. After reextraction, n-heptane was distilled off from the organic phase as in Example 2. After stabilization, the following results were obtained: the concentration of citric acid in the aqueous raffinate from the extraction was 0.025% by weight, the concentration of acid in the aqueous extract of the reextraction was 10.6% . This corresponds to an acid yield of 99.7% and a concentration of 1.18. .

Example 4

The fermentation broth as in the previous examples was extracted under the same conditions and the extract was diluted with n-heptane as in Example 3. and re-extracted countercurrently with water at 75 ° C at a water to diluent weight ratio of 0.12. The following procedure was the same as in Example 3. After stabilization, the following results were obtained: the concentration of citric acid in the aqueous solution was 0.025 wt%, the concentration of the acid in the aqueous extract of reestraction was 16.5 wt%. This corresponds to an acid yield of 99.2% and a concentration of 1.83.

Example 1 shows that some extraction of the fermentation broth at 25 [deg.] C and reextraction at 75 [deg.] C results in a certain increase in the acid concentration in the aqueous phase; but the extraction yield is insufficient. Example 2 shows that when using reextraction with dilution of the organic phase with an inert solvent, the results are completely unacceptable. However, Example 3 shows a completely unexpected effect of a combination of both reextraction methods. Under otherwise unchanged conditions, the yield in the reextraction radically increased and at the same time a slight increase in the acid concentration in the reextract was achieved: compared to the concentration in the fermentation broth. Finally, the example shows that by adjusting the ratio of the phase flow rates in the reextraction, it can be achieved. The concentration is higher than that of reextraction using a temperature alone. This example also indicates the unexpected advantageous properties of the invention, namely the possibility to influence the flow rate ratio change phases in the reextraction _of significant thickening without causing changes in the yield of extraction.

This makes it possible, for example, to compensate for variations in the concentration of citric acid in the fermentation broth after fermentation, so that it does not affect the reextract concentration and thus the inlet conditions of subsequent evaporation and crystallization.

i. Industrial Applicability

The process according to the invention can be used in any production of citric acid based on fermentation.

Claims (3)

Process for extracting citric acid from a fermentation broth containing 8 to 12¾ wt. citric acid, in which the fermentation broth is in intensive countercurrent contact with a concentrated solution of a trialkyl amine having alkyl groups of 8 to 12 carbon atoms in a mixed diluent containing characterized in that n-octanol or 2-ethylhexanol in an amount of 20 to 50% by weight of n-octanol or 2-ethylhexanol is used as polar component. and, as an inert component, n-hexane, n-heptane or a mixture of aliphatic hydrocarbons boiling in the range of 60 to 110 ° C, in an amount of 10 to 55 µm. and that the organic phase obtained is diluted with an inert component in a proportion of 0.5 to 2 relative to the original content of the mixed diluent and brought into countercurrent contact with water at a temperature of 65 to 100 ° C. after which the added inert component is removed from the organic phase by distillation and the concentrated trialkylamine solution thus obtained is, after cooling, reused for tiproud contact with the fermentation broth. The method of claim 3, wherein the ratio of the mass flow rates of the fermentation broth to the concentrated trialkylamine solution is 0.3 to 0.9 and the ratio of the mass flow rates of water to the organic phase diluted with the inert component is 0.1 to 0. 2. .Λ 3. A process for extracting citric acid according to claim 1 or 2, wherein the countercurrent contact of the diluted organic phase with water is performed under vibration.