The method of obtaining citric acid from solutions of alkali citrates

 

(57) Abstract:

The method of obtaining citric acid from enzymatic solutions of alkali citrates includes a bleaching solution, a partial conversion of citrate by electrodialysis, the complete conversion of residual citrates, desalting of the solution and crystallization. Desalting of the solution is carried out by passing liquid through a strongly acidic cation exchanger in the H+-the form and the medium or weakly basic anion exchange resin in the HE--form. Bleaching is carried ionosorption IA-1R in Cl--form. The method allows to increase the purity of the target product, to reduce energy consumption at the stage of electrolysis, to reduce the consumption of ionosorbed and chemicals. 1 C.p. f-crystals, 1 Il.

The invention relates to biotechnology, namely the method of separation of citric acid from solutions of alkali citrates.

Citric acid is widely used in food, perfumery, pharmaceutical, medical and chemical industries.

The traditional method of extraction of citric acid from native solutions microbiological synthesis includes the deposition of lime milk, followed by the dissolution of calcium citrate with sulfuric acid, separating Sul is receiving, the residue, crystallization and drying [1].

With this method of obtaining citric acid production produce large quantities of liquid effluents containing mineral acids and salts, and simultaneously accumulate a large amount of solid waste (gypsum, waste coal, and so on). As a result, the technology becomes cumbersome and time-consuming.

Known methods of isolation of citric acid from native solution by extraction with an organic solvent containing a tertiary amine. From the obtained extract, citric acid extravert water at higher temperatures [2, 3].

In [4] the selection of citric acid from native solution culture liquid (QL) from the fermentation of sugars carry out extraction octane containing tridodetsilamin.

As extractiona the method of separation of substances making too great demands to organic solvents, which must be highly selective, low in the water, having a density different from the density of the solution of the target product to be non-toxic, non-deficient, low-cost and legaliseerimine, this method is lognormality and Dorohoi acid, and citrates.

Typical sorption method of extraction of citric acid and sodium citrate as described in [5]. According to the proposed technology from native solution to obtain citric acid solution is first passed through a strongly acidic cation exchanger in the H+form, and then from a solution of citric acid anions of mineral acids (Hcl, H2SO4H3RHO4) separated by passing the solution through srednednevnoy anion exchange resin in the HE-form.

In this cycle through 1 volume of cation exchange resin can be skipped volume 3 native solution through the anion - 15-17 volumes emerging from the cation column citric acid solution.

Then desalted solution is subjected to obestsvechenny on isosorbide and clarification by passing the solution through a layer of coal. The selection of crystals of citric acid from the clarified solution is carried out in a known manner by vacuum evaporation, crystallization, centrifugation and drying.

The main disadvantage of using sorption method of producing citric acid from the citrate is the fact that when using the yeast Candida lipolytica optimum pH of the fermentation is in the range from 4.0 to 5.5, and in this range and citrate in the citric acid have to be used in the N+-the form of a large volume of cation exchange resin.

If we consider that the use of a large amount of the resin leads to a significant dilution of the original solution at the stage of transformation (1.5-2.0 times), the consumption of large quantities of hydrochloric acid and demineralized water for the regeneration of ion exchange resins and the formation of large amounts of acidic regeneration and adsorption effluent, then the sorption process of transformation of citrate becomes very time consuming and expensive.

Known electrodialysis methods of transformation of citrate in the citric acid.

Method for the production of citric acid using electrodialysis first investigated and patented by the firm Benckiser, Germany [6,7].

By a known method [8] in three - or four electrodialyzers of alkaline citrate, citric acid can be obtained by partial conversion of citrate acid (90-99%), followed by concentration, hot fractional crystallization, centrifugation, and recycling the mother solutions at the stage electrodialysis and crystallization. The work is mainly devoted to the processes and apparatus of obtaining citric acid from citrates, the proposed technological solutions are not potato anions of mineral acids specified technological approaches are difficult to obtain pure crystals of citric acid, that is experimentally proved in the following the above works.

A method of obtaining citric acid from tinatawag citrate [9].

In this way the conversion of alkaline citrate from native solution obtained by the fermentation of n-alkanes yeast was performed by electrodialysis. For bleaching native solution prior to electrodialysis pre-boiled with activated charcoal and filtered. When the electrodialysis fermentation solutions were carried out in four-chamber apparatus using 3 cation-exchange membranes (brand MK-40). Simultaneously with the conversion in electrodialyzer proceeds the concentration of solutions.

The process of electrodialysis was continued until 100% conversion tinatawag sodium citrate (52.7 g/l) citric acid (39,2 g/l).

Closest to the proposed method is the method described in the publication [10].

In this way the conversion of alkaline citrate from native solution obtained by the fermentation of n-alkanes yeast, conducted by electrodialysis. For bleaching native solution pre-boiled with activated charcoal and filtered. When the electrodialysis fermentation solutions were carried out in th is Ana (MA-40).

Simultaneously with the conversion in electrodialyzer proceeds concentration.

Experimental data showed that the cell in which is stored the converted from citrate solution contains 53% citric acid and 47% of impurities in the form of other organic and mineral acids.

On the basis of the above works technical solutions by electrodialysis transformation citrates, we can say that the main disadvantage of electrodialysis method of producing citric acid in all the works is the fact that this native solution is cleared only from cations, present in the solution, all the anions together with citrate pass into the acid form. If we consider that at the subsequent stages of selection citric acid solution after electrodialysis we have to concentrate in 13-15 times (ST. about 72-75%), exemption from anions (CL-, SO42-, RHO43-and so on ) of such viscous solutions using crystallization becomes difficult and the target product is of low quality. Recrystallization of the obtained technical crystals leads to a significant reduction of the yield of the final product.

One of the significant the AI citrate consumes large amounts of electricity, what follows from the experimental results given in [9 and 10].

As indicated in [8], the specific energy consumption for the conversion of citrate to citric acid is significantly increased when the achieved degree of conversion increases, and becomes very high when approaching full conversion of citrate.

To overcome difficulties associated with the use of large amounts of energy, the authors of [8] propose a partial transformation of the electrodialysis alkaline citrate in the citric acid. Next for the Department neprevyshenie citrate from citric acid propose fractional crystallization. It should be noted that, if fractional crystallization provides purification of citric acid solution from the residual alkaline citrates, the cleaning solution of the target product from the inorganic anions, viscous solution in [8] is not mentioned.

In addition, the use of on-stage electrodialysis crude from multiply charged cations native solution leads to contamination of cation exchange membranes and reduce their lifespan [9].

The disadvantages of electrodialysis conversion of citrate in videocasino those salt (one - and disubstituted sodium citrate), which in reality are obtained by fermentation with yeast.

As the pH value translesanas citrate compared with one - and disubstituted about 2 times smaller, therefore, the last two of salt in the solution is relatively well dissociatively and their transformation into acid flows easier. In addition, the number diffundiruyushchii through the cation exchange membrane to sodium ions with less.

The task of the invention is to develop a method of producing citric acid from solutions of alkali citrates.

The technical result that can be obtained using the proposed method lies in the fact that the proposed technological approach provides less power consumption for stage electrodialysis and chemicals and demineralized water on stage IONEX desalting transformation of citrate in the citric acid and obtaining citric acid solution, does not contain extraneous ions.

The essence of the proposed method lies in the fact that the citrate solution is subjected to electrodialysis, the complete conversion of residual citrate and desalting of the solution after the electrodialysis is carried out m in the three electrodialyzer conversion of citrate carry on 85-88%.

For the Department okrashennykh components native solution prior to electrodialysis is passed through ionosorbed in CL-form or layer of activated charcoal.

Before electrodialysis directly before or after bleaching multiply charged cations from native solution is removed by passing it through a carboxylic cation exchange resin in Na+form.

One of the advantages of the proposed method lies in the fact that when the electrodialysis significantly (1.5-1.8 times) reduced energy consumption. This is because in the initial stages, when the concentration of cations in the Central chamber greatest to maintain a constant current density does not have to increase the voltage in the circuit. Energy consumption especially at the last stage increases (when conversion in solution implemented more than 85-88%), as with a decrease in the concentration of sodium ions increases the concentration of citric acid, which is less dissociative than its salt, and increases the electrical resistance of the solution. For complete transformation of citrate in the acid necessary to increase the voltage to keep the current density constant. At this stage increase dramatically UD is possible to complete the full transformation of the residual citrate, compared with the sorption method decreases approximately 8-9 times. This leads to reduction in the same amount of acid and demineralized water required for regeneration sulfonic cation exchanger and reduction of the resulting regeneration and adsorption effluent. The reduction sulfonic cation exchanger leads simultaneously to the decrease in the degree of dilution of the citrate solution.

When the electrodialysis in addition to the conversion and release of cations during the flow of electric current through the membrane together with the counter-ions and cations are transferred and the solvent, which leads to the concentration of citric acid solution.

One of the advantages of electrodialysis method of desalination is that in the cathode section formed sodium hydroxide solution, which can be used as fermenting (for Podarok fermentation solution), and at the stage of regeneration of ion exchange resins.

During electrolysis the transformation of citrate in the citric acid in the solution is determined by three ways:

determination of the pH of the solution (in the beginning of the process);

- determination of the ion concentration of sodium by atomic absorption spectroscopy;in solution was determined by a chemical method [11], and salimonu acid - enzymatic method [12].

The choice of carboxylic cation exchanger, for example KB-P, removal of multiply charged cations from native solution due to the fact that due to the pairwise location of the carboxyl groups in the matrix resin has a high selectivity with respect to the multiply charged cations. In addition, the cation exchange resin has a much higher exchange capacity and easier regenerated. As the native pH of the solution is in the range of 4-6, this corresponds to an operating range of the resin, the resin type is selected correctly.

When the electrodialysis choice of degree of conversion (from 85 to 88%) of citrate in the citric acid due to the fact that in the event of a conversion of less than 85% in the subsequent stage of ionite transformation is necessary to use a relatively larger amount of resin, which, as stated above, leads to the complication of the process.

In the case of conversion higher than 88% of the energy consumption begins to increase sharply.

The choice of the type of resins, in particular KU-2-8, EDE-10P, for ionite conversion of residual citrate and desalting of citric acid solution due to the fact that both resins are chemically durable, and the sky, and Toxicological requirements.

The choice of decolorizing resins, for example, IA-1R, due to the fact that the resin has good decolorizing ability and mechanically strong.

The choice of ion-exchange membranes, such as MK-40, due to the fact that the membrane has good selectivity, has a high electrochemical performance, and satisfactory strength relative to solutions of acids and alkalies, mechanically strong.

The ability of the method is illustrated by the following examples, but is not limited to them.

Example 1. The transformation of the alkaline salts of citrate in the citric acid from native solution is carried out in the three dialysator, the cell which was collected from 2 cation-exchange membranes marks MK-40 intermembrane distance 4 mm

In the anode chamber circulates a 0.3 n solution of sulfuric acid in the cathode of 0.25 n sodium hydroxide solution, and in the Central - native solution of alkaline citrate, obtained by cultivation of a strain of yeast Yarrowla lipolytica in a nutrient medium, where the carbon source used alcohol or waste production. The concentration of sodium citrate (one - and disubstituted at vny solution before electrodialysis under vacuum is passed through activated carbon with a layer thickness of 0.6 see

The current density when the electrodialysis is maintained within the range of 120-140 mA/cm2and the working area of the membrane is 56 cm2.

The electrodes were made of platinized titanium. The volume of all solutions (sodium hydroxide, sulfuric acid, native solution is the same and amounted to 0.75 liters

The solutions in all the cells circulate by means of a pump with a speed of 9 cm/sec.

Conducting electrodialysis conversion of citrate on the above mode shows that within 2 hours - 88,1% of the total citrate is converted to citric acid.

After 88% conversion of citrate process of electrodialysis stop, concentrate replace native clarified solution and the electrodialysis process continues.

For the subsequent stages of purification by electrodialysis at the above mode up to 85-88% conversion of citrate obtained 10.5 l (14 cycles) technical solution of citric acid.

With regard to the content of cations and accompanying citrate anions in the converted solution and the exchange capacity of the used ion-exchange resins for the full oversee citrate and desalting, the solution after electrodialysis in the amount of 10.5 l is passed through poludnevni anion exchange resin, EDE-10P HE--form respectively. After the filing of the citric acid solution the column was washed with distilled water to reduce the concentration of citric acid in the effluent from the anion exchanger fluid to 2.0-2.5 g/L.

Collected desalted solution of citric acid is subjected to the vacuum-evaporation at a temperature of 50-55oC and the pressure of 90 kPa to ST. 69-72% and from one stripped off solution two step crystallization produce pure crystals of citric acid.

The first and second portions of the crystals of citric acid are mixed and dried.

The yield of the final product from native solution considering the return of uterine solutions in the technological cycle is 72%.

The content of the main product - citric acid monohydrate is obtained in crystals is not less than 99.8%, which sootwetstwuet the requirements of GOST 3652-69 jet citric acid.

Because the solubility of solimano acid much more than lemon, it accumulates in the mother solution. Adsorbed on the crystals of citric acid solimena acid by centrifugation and water washing of the crystals of citric acid passes into the mother liquor.

On the basis of that is, it using titration with potassium hydroxide solomonow acid is isolated in the form of montalieu salt.

After water recrystallization technical crystals montalieu salt solimano acid get crystalline product of 98.5% purity.

The output of montalieu salt solimano acids from native solution is 35%.

Example 2. The selection of citric acid from native solution is performed in the same way as described in example 1, except that the selection of the target product was used a solution obtained by fermentation, in which the source of carbon used liquid paraffin. This mineral composition of the fermentation solution is complicated. In particular, the molecules in the solution increased the content of double-cations (CA2+Mg2+), from which before electrodialysis freed by passing discolored native solution through the carboxylic cation exchanger KB-4-2S in Na+-form. Next, the resin is washed with water and the collected solution together with the washing water passed through the electrodialysis.

Conducting electrodialysis conversion of citrate on the above mode shows that the acid from native solution is carried out, as described in example 1, except that the bleaching native solution prior to electrodialysis conduct its passage through ionosorbed IA-1R in CL-form.

Example 4. The selection of citric acid from native solution were carried out as described in example 1, except that on stage desalting using a weakly basic anion exchange resin, for example an-31.

Thus the proposed method allows of citrate solution different mineral composition with less energy and chemicals to obtain purified crystals of citric acid.

Using IONEX method of bleaching native solution allows to increase the degree of discoloration of the solution, while in the technological cycle eliminates the generation of solid waste.

Due to the use of carboxylic cation exchanger for sorption of multiply charged cations from native solution increases the working life of the ion exchange membranes in 3.5 times.

Through the use of weakly - or srednecenovogo of the anion citrate solution is purified from other inorganic anions. In the production of formed relatively less regeneration effluent.

The drawing shows the equilibrium state of citric acid in solution depending on the pH, where CA - citric acid; CANa - one-deputizing sodium citrate; CANa2- disubstituted sodium citrate; CANa3- trehzameshchenny sodium citrate.

Sources of information

1. C. A. Smirnov. Food acids, 1983, S. 151-193.

2. Patent EP 0460854.

3. Patent Czechoslovakia 277812.

4. U.S. patent 5426220.

5. Patent Of Russia 2090611.

6. U.S. patent 3086928.

7. French Patent 2260558.

8. U.S. patent 3968017, 1976, 204-180.R.

9. J. K. Lamb, I. R. Of Kramsach, A. A. Kolesnikov. The selection of citric acid from fermentation solutions by means of electrodialysis. In Proc. of the Biosynthesis of hydroxy acids and ketoacids by microorganisms. Riga: zinatne, 1984, S. 59-66.

10. J. K. Lamb, I. R. Karklina, O. A. Markunas. Study of the process of electrodialysis tinatawag citrate and fermentation fluids in the cells with the intermembrane distance of 3 and 4 mm, In Proc. of "the Biosynthesis of hydroxy acids and ketoacids by microorganisms. Riga: zinatne, 1984, S. 67-72.

11. Shabolovskaya N. A. and other Bakery and candice the population of citric acid from native solutions of alkali citrates, according to which native solution discolor, by electrodialysis perform a partial conversion of citrate solution in citric acid and crystallization get the target product, characterized in that prior to crystallization after partial conversion conducts a full conversion of the residual citrate and desalting of the solution, passing the liquid through a strongly acidic cation exchanger in the H+-the form and the medium or weakly basic anion exchange resin in the HE-form.

2. The method according to p. 1, characterized in that the bleaching native solution is performed by ionosorption IA-1R in Cl--form.

 

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