FI93857B - Process for separating citric acid from a fermentation medium with the aid of a polymeric adsorbent - Google Patents

Description

93857

A method for separating citric acid from a fermentation broth using a polymeric adsorbent

The invention relates to the adsorbent separation of citric acid in a solid layer from fermentation broths containing citric acid, carbohydrates, amino acids, proteins and salts. More particularly, the invention relates to a process for separating citric acid from fermentation broths containing it, which process comprises using a non-zeolite polymeric adsorbent which selectively adsorbs citric acid and is selected from the group consisting of a neutral, crosslinked polystyrene non-polymeric a ryl ester polymer, a weakly basic anionic ion exchange resin having tertiary amine or pyridine functional groups, and a strongly basic anion exchange resin having quaternary amine functional groups, and mixtures thereof.

Citric acid is used as a food acidifier and in pharmaceutical, industrial and detergent compositions. The growing popularity of liquid detergents formed using citric acid has mainly caused the worldwide growth of citric acid production to about 320 million ’·· *! per year, which is expected to continue in the future.

• · · · ... · Citric acid is produced by an internal fermentation process of the liquid • ·: .V using molasses and a strain as a micro-organism: V: Aspergillus niger. The fermentation product contains carbohydrates, amino acids, proteins and salts as well as citric acid, which must be separated from the fermentation broth.

»· · · • · · · ·

Currently, two different methods are used to separate citric acid »* ·· ''. The second involves the precipitation of citric acid as the calcium salt. The calcium citrate obtained is acidified with sulfuric acid. In another method, citric acid is extracted from the fermentation broth with a mixture of trilaurylamine, n-octanol and ClO or C 1-4 paraffin. Citric acid is re-extracted from the solvent phase into water using heating • 93857 2. However, both of these methods are complex and expensive and generate significant amounts of waste.

The patent literature has suggested the use of a possible third method for separating citric acid from fermentation broth, which method comprises membrane filtration to remove raw materials or high molecular weight impurities and subsequent adsorption of the impurities as after concentration or precipitation of citric acid as the calcium salt and subsequent acidification with H 2 SO 4, separation of CaSO 4 and treatment with cationic or anionic ion exchange resins. This method, disclosed in EP Patent Application No. 151,470, August 14, 1985, is also a rather complicated and time-consuming method for the separation of citric acid. The process according to the invention, on the other hand, makes it possible to separate the citric acid in one adsorption step and to recover the citric acid from the adsorbent, whereby purified citric acid is obtained using an easily separable desorbent.

. In the process according to the invention, the essential characteristics of which are apparent from the appended claims, the citric acid is separated from the fermentation broth into a polymeric adsorbent selected from the group consisting of a neutral, cross-linked compound. ... · a polystyrene polymer, a non-ionic hydrophobic polyacrylic barrier polymer, a weakly basic anion exchange resin having tertiary amine or pyridine functional groups, and a strongly basic anionic functional resin having a quaternary anionic ion exchange resin mixtures thereof, and is then recovered by desorption with a suitable desorbent under suitable conditions. According to the invention, it has been found that a highly selective separation of citric acid from salts and carbohydrates is achieved by adjusting and maintaining the pH of the feed solution below the first ionization constant of citric acid (pKa, = 3.13). The value to which the pH must be lowered in order to obtain sufficient selectivity to appear to be independent of the concentration of citric acid in the feed mixture; The pH is inversely proportional to the concentration. At concentrations of less than 13% to very low values, the pH may be close to the pKa, 3.13 of citric acid; at a concentration of 13%, the pH may be in the range 0.9 to 1.7, but with 40% citric acid fed, the pH must be reduced to at least 1.2 or below. At higher concentrations, the pH should be even lower, e.g., at a citric acid concentration of 50%, the pH should be 1.0 or below. Thus, it is preferred to keep the pH of the feed mixture in the range of 0.5-2.5, with 0.5-2.2 being most preferred. According to the invention, it has also been found that the adsorption temperature of the polymeric adsorbent used can be reduced by adding acetone or some other low molecular weight ketone to the desorbent, thus avoiding the decomposition of the adsorbent by high temperatures.

The process of the invention for separating citric acid from a feed mixture of citric acid-containing fermentation broth using a polymeric adsorbent as described above can be applied to a process comprising the steps of: (a) maintaining a net flow of liquid through said column of adsorbent; - • · · ***. * In which there are at least three zones in which separate operations take place and which are connected to each other in series, the end zones of the statue being connected to provide a continuous connection between these zones; • · (b) maintaining an adsorption zone in this column, the zone being defined by an adsorbent located between the feed inlet flow at the upstream boundary of the zone and the raffinate outlet stream at the downstream boundary of this zone; (C) maintaining the purge zone immediately upstream of this adsorption zone, wherein this purge zone is defined by an adsorbent located between the extract effluent at the countercurrent boundary of the purge zone and the inlet flow of the feed downstream of said zone;

Ii; • 4 93857 (d) maintaining the desorption zone upstream of said purification zone, wherein said desorption zone is defined by an adsorbent located between the inlet stream of the desorbent at the upstream boundary of this zone and the extract effluent at the downstream boundary of this zone; (e) passing the feed mixture under adsorption conditions to the adsorption zone to effect selective adsorption of citric acid by the adsorbent in the adsorption zone, and removing the raffinate inlet stream containing the non-adsorbed portions of the fermentation broth leaving the adsorption zone; (f) introducing a desorbent into the desorption zone under desorption conditions to displace citric acid from the adsorbent in the desorption zone; (g) removing the extract effluent containing citric acid and desorbent from the desorption zone; (h) directing at least a portion of the effluent extract stream to the separation devices and removing at least a portion of the desorbent under the separation conditions; and (i) periodically transferring the zone boundaries of the feed inlet stream, the raffinate effluent stream, the desorbent effluent stream, and the extract effluent stream through the adsorbent column downstream of the adsorbent zone in the direction of the adsorption zone. »To create currents.

• ♦ t «• · · • ·

The process can produce a raffinate product that contains: an even smaller amount of desorbent. In addition, in the process, a buffer zone can be maintained immediately upstream of the desorption zone, this buffer zone m · being defined by an adsorbent located at the inlet flow of the desorbent at the downstream boundary of the buffer zone and at the outflow boundary of this buffer zone.

• · · • · »5 93857

Details of embodiments of the invention regarding feed mixtures, adsorbents, desorbents and processing conditions are set forth below.

Figure 1 is the concentration of different citric acid species as a function of citric acid dissociation pH, showing the change in the equilibrium point of citric acid dissociation with varying concentrations of citric acid, citrate anions, and hydrogen ion.

Figure 2 shows the effect of pH on the amount of citric acid that the adsorbent is capable of adsorbing.

Figures 3A, 3B and 3C graphically show the pulse experiments of Example I using XAD-4 resin to separate citric acid from a feed containing 13% citric acid at pH 2.4, 1.7 and 0.9, respectively.

Figures 4A, 4B, 4C, 4D and 4E show the pulse experiments of Example II at pH 2.4, 1.7, 0.9, 2.8 and 1.4, respectively, using different adsorbent samples.

Figures 5A and 5B show the pulse experiments of Example III at pH 2.8 and 1.4 at 93 ° C, respectively.

Figures 6A, 6B and 6C show the pulse experiments of Example IV at pH 1.94, 1.13 and 0.5, respectively.

Figures 7A, 7B and 7C show pulse experiments according to Example V. at pH 1.82, 0.5 and 0.3, respectively.

• · «

Figures 8A and 8B show pulse experiments according to Example VI * ··· | at pH 1.5 and 1.0, respectively.

Fig. 9 shows the pulse test according to Example VII and the ad • · · · ... · sorption obtained at lower temperatures (93 ° C resp.

4 5 ° C) by adding 10% acetone to the desorption water.

Figure 10 shows a pulse test according to Example VIII using a weakly basic anion exchange resin with a tertiary amine functionality in a crosslinked acrylic resin matrix to separate citric acid from a feed containing 40% citric acid at pH. 1.6 when desorbing with water; FIGURES 11A, 11B and 11C show pulse experiments according to Example IX at pH 7.0, 3.5 and 2.4, respectively.

* * • · 6 93857

Figures 12, 13A and 13B show pulse experiments according to Example X at pH 1.6 using various samples of a weak basic anion exchange resin having pyridine functionality in a crosslinked polystyrene resin matrix. Citric acid is desorbed with 0.05 N sulfuric acid or water.

Figure 14 shows a pulse test according to Example XIII at pH 1.6.

Figure 15 shows the pulse test of Example XIV at pH 2.2 using a different adsorbent sample of a less basic anion exchange resin having quaternary ammonium functionality in a crosslinked polystyrene resin matrix and desorbed with dilute sulfuric acid.

The following definitions of various terms used in this specification are useful in clarifying the treatments, objects, and advantages of the present invention.

A "feed mixture" is a mixture containing one or more extract components and one or more raffinate components which are separated by the process of the invention. The term "feed stream" means the stream of the feed mixture that is derived from the concept. adsorbent used in the process.

An "extract component" is a compound or type of compound that is more selectively adsorbed by an adsorbent, while a "raffinate component" * · ** is a compound or type of compound that is less selectively adsorbed. In this method, the citric acid is an extract component and the carbohydrate salts are raffinate components. The term "desorbent" generally refers to a material capable of desorbing an extract component. The term "desorption stream" or "desorption input stream" means the flow through which the desorbent passes into the adsorbent. The term "raffinate stream" or "raffinate effluent stream" means the stream through which the raffinate component! removed from the adsorbent. The composition of the raffinate stream can range from substantially 100% desorbent to substantially 100% raffinate components. The term "extract stream" or "extract stream" means • ·. : a flow by which the extract material desorbed by the desorbent 7 93857 is removed from the adsorbent. The composition of the extract stream may also range from substantially 100% desorbent to substantially 100% extract components. At least a portion of the extract stream, and preferably at least a portion of the raffinate stream from the separation treatment, is passed to separation equipment, usually fractionation equipment, in which at least a portion of the desorbent is separated to produce an extract product and a raffinate product. The terms "extract product" and "raffinate product" refer to products prepared by a process comprising the extract component and the raffinate component at higher concentrations, respectively, than those present in the extract stream and the raffinate stream. Although it is possible to prepare very pure citric acid in high yield by means of the process according to the invention, it should be noted that the adsorbent never completely adsorbs the extract component. Similarly, the adsorbent does not completely adsorb the Raffi-r.ate component. As a result, varying amounts of raffinate component are present in the extract stream and similarly, the extract component may be present in varying amounts in the raffinate stream. The extract and raffinate streams are then separated from each other and from the feed mixture on the basis of the concentration ratios of the extract component and the raffinate component which in the stream.

··. More specifically, the ratio of citric acid to the least selectively adsorbed components is the lowest in the raffinate stream, followed by the highest in the feed mixture and the highest in the extract stream. Similarly, the ratio of the concentrations of the least selectively adsorbed '·' components to the more selectively adsorbed citric acid is highest in the raffinate stream, followed by the highest in the feed stream, and lowest in the extract stream.

The term "selective pore volume" of an adsorbent is that volume of adsorbent that selectively adsorbs the extract component from the feed mixture. The term "non-selective pore volume" of the adsorbent is that volume of adsorbent which does not retain the extract component from the feed mixture. This volume comprises those cavities of the adsorbent which do not contain adsorbent bonds and the spaces between the particles of the adsorbent. Selective J pore volume and non-selective pore volume are generally defined as 93857 units of volume and are important in determining the appropriate flow rates of the liquid introduced into the treatment zone to provide efficient treatments using a given amount of adsorption. When the adsorbent "enters" the treatment zone (described in more detail below) used in accordance with one embodiment of the invention, its non-selective pore volume, together with the selective pore volume, transports the liquid to this zone. The non-selective pore volume is used to determine the amount of liquid that flows into the zone upstream of the adsorbent, displacing the liquid in the non-selective pore volume. If the flow rate of the liquid entering the zone is less than the non-selective pore volume of the adsorbent entering this zone, a net flow of liquid into this zone occurs. Because this net flow is its liquid in the non-selective pore volume of the adsorbent, it contains in most cases less selectively attached feed stream components. The selective pore volume of the adsorbent may in certain cases adsorb portions of the raffinate from the liquid surrounding the adsorbent, as in certain cases there will be competition for the extract material. and raffinate material between selective pore volume • · ···. adsorbent sites. If a large amount of raffinate material surrounds the adsorbent compared to the extract material, the raffinate material may be competitive enough to adsorb the adsorbent.

* * • · • · »· • ·. *. * The feed material according to the invention is a fermentation product obtained by the internal fermentation of molasses liquid and the microorganism Aspergillus Niger. This fermentation product may have, for example, the following composition: citric acid 12,9% + 3% salts 6000 ppm. carbohydrates (sugars) 1% «• others (proteins and amino acids) 5% •»:: The salts are K, Na, Ca, Mg and Fe. Carbohydrates are sugars, such as glucose, xylose, mannose and DP2 and DP3 oligosaccharides, and plus up to 12 or more i. Air if unleaved saccharides. The composition of the substance to be treated may vary from the above without still falling outside the scope of the invention. However, juices such as citrus juices are not suitable or appropriate because the other substances they contain are adsorbed simultaneously with citric acid. See. Johnson, J .:

Sci. Food Agric, Vol. 33 (3) s, 287-293.

It has now been found that the separation of citric acid can be greatly improved by adjusting the pH of the feed to a level below the first ionization constant of citric acid. The first ionization constant (pKa 2) of citric acid is 3.13; Handbook of Chemistry & Physics, 53rd Edition, 1972-1973, CRC Press, and consequently the pH of the citric acid feed stream should be less than 3.13. If the pH of a 13% solution of citric acid is e.g. 2.4 or higher, as shown in Figure 3A (Example I), "citric acid breaks through" (desorbs) along with salts and carbohydrates at the beginning of the cycle, indicating that citric acid is not adsorbed. On the other hand, a lower "breakthrough" of citric acid is observed at a pH of 1.7, and no "breakthrough" is observed at a concentration of 0.9 13 3, as shown, for example, in Figures 3B and 3C.

The combined citric acid is present in the aqueous solution in equilibrium with several citrate ions and hydrogen ions. This is evident from the following equations, where the citric acid acid dissociation constants pKaj, pKa2 and pKa ^ at 3.1 ° C are 3.13, 4.74 and 5.40, respectively:

Equation 1 pKaj ^ - 3.13 pKa2 - 4.74 pKa3 = 5.40

HjCA ------- 7 h2ca_1 hca'2 Ca ~ 3 + H + + H + + H + ·. The equilibrium point of citric acid dissociation can be changed by varying the concentration of citric acid, citrate anion, or hydrogen ions. This is shown in Figure 1 when comparing the concentrations of several species of birch skin in solution to pH at 90 ° C. The results show that higher 10 93857 percent higher levels of non-ionized citric acid (H 2 CA) are obtained. when using ionic strength (lower pH). Lowering the pH (increasing the H + ion concentration) gives more non-ionized citric acid while decreasing the amount of -1 -2 -3 citrate anion species (H2CA, HCA and CA) in solution.

Based on the balance of citric acid and the above-mentioned properties of the resin, non-ionized citric acid is separated from other ionic species in the fermentation broth (including citrate ions) using the adsorbent resins described above. However, solutions with lower pH are required to achieve better recovery of citric acid. To determine the static adsorption iso-term of citric acid of a resin of the invention, Amberlite XAD-4, treatment was performed at room temperature, about 25 ° C, as a function of feed pH. Figure 2 shows the results of this study. The results show the adsorption of non-ionized citric acid as the pH is lowered. Without being limited to this definition, it is apparent that the non-ionized citric acid species in solution are adsorbed on the adsorbents of the invention either by an acid-base mechanism or a hydrogen binding mechanism or a mechanism based on a strong relative affinity of these hydrophobic species.

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The desorbents used in the various previously known adsorbent separation methods vary depending on such factors as the nature of the treatment used. In a pendulum bed system in which a selectively adsorbed feed component is removed from the adsorbent by a cleaning stream, the choice of desorbent is less critical, and desorbents comprising gaseous ·. hydrocarbons such as methane, ethane, etc., or other types of gases such as nitrogen and hydrogen may be used at elevated temperature or under reduced pressure, or both, to effectively remove the adsorbed feed component from the adsorbent. However, in such adsorbent separation concepts ·. In conditions which are generally applied continuously, mainly at constant pressure and temperatures, in order to obtain a liquid phase, the desorbent must be chosen correctly to ensure a number of factors. First, the desorbin agent should displace the extract component from the adsorbent even at reasonable flow rates without significantly adsorbing itself, which would adversely prevent displacement of the extract component from the desorbent in the next adsorption step. Expressed as selectivity (discussed in more detail below), it is preferred that the adsorbent be more selective for all other extract components relative to the raffinate component than for its selectivity over the desorbent material over the raffinate component. Second, the desorbents must be compatible with the particular adsorbent and feed mixture. More specifically, they must not reduce or eliminate the critical selectivity of the adsorbent over the extract component compared to the raffinate component. In addition, the desorbents should be such that they can be easily separated from the feed mixture for treatment. Both the raffinate stream and the extract stream are removed from the adsorbent as a mixture with the desorbent, and without a method to separate at least a portion of the desorbent, the purity of the extract product and the raffinate product is not very high and the desorbent agent cannot be reused in the process. As a result, it has been found that each desorbent used in this process must have a significantly different average boiling point compared to the feed mixture so that at least a portion of the desorbent can be separated from the feed components in the extract and raffinate streams. · By simple fractional distillation, which made it possible to reuse the desorbent in the process. The term "substantially different" as used herein means that the average boiling point between the different desorbent and the feed mixture is at least about 5 ° C. Desorbizing agent. the boiling range may be higher or lower than the boiling range of the feed mixture. ’I. desorbents should be readily available and therefore cost-effective.

In the preferred isothermal, isobaric: liquid phase treatment according to the invention, water has been found to be a very effective desorbent. It has also been found that acetone and other low molecular weight ketones, such as methyl ethyl ketone and diethyl glycone, are effective when mixed with water in small amounts up to 15% by weight. Their usefulness is based on their water solubility. However, their advantages are based on their ability to reduce the temperature at which desorption occurs. When using some adsorbents and water as the desorbent, the temperature must be raised to enhance the desorption step. High temperatures can cause premature deactivation of the adsorbent. The solution to this problem during such separation is to add 1 to 15% by weight, preferably 1 to 10% by weight and most preferably 5 to 10% by weight of acetone to the desorbent. A low molecular weight ketone can also affect the stability of the adsorbent in potentially two ways, namely by removing soluble constituents that cause deactivation and effecting regeneration, i.e., removing deactivating agents or altering their effect. A reduction in the desorption temperature of such a separation of about 50 ° C is achieved, for example, by adding 10% by weight of acetone to the desorbent. A reduction of about 5-70 ° C can be achieved by adding 1-15% by weight of acetone to the water used as desorbent. Dilute inorganic acids have also been found to give good results when used as desorbents. Aqueous solutions of sulfuric acid, nitric acid, hydrochloric acid and phosphoric acid and mixtures thereof can be used in amounts corresponding to concentrations * \ 0.01 to 1.0 n (normality), the best results being obtained with dilute sulfuric acid at a concentration of 0.01 to 1, 0 n.

• · ·

It is known that certain properties of adsorbents * / at are highly desirable, if not absolutely necessary, for the successful implementation of selective adsorption treatment. These properties are also important in this method. Such properties include, for example: 1) adsorption capacity. 2) a selective adsorption of the extract component with respect to the raffinate component and a desorbent, and 3) a sufficiently rapid adsorption and desorption of the extract component to the adsorbent and an adsorbent therefrom. , · .The prescribed volume of the extract component is naturally necessary »|

I I

* »» 13 93857 unspecified. Without this ability, the adsorbent is unusable in adsorbent separation. In addition, the greater the ability of the adsorbent to extract the extract component, the better the adsorbent. The higher efficiency of an adsorbent makes it possible to reduce the amount of adsorbent required to separate the extract component of known concentration when using a given feed mixture addition rate. The reduction in the amount of adsorbent required in any adsorption treatment reduces the cost of the separation treatment. It is important that the good initial efficiency of the adsorbent is maintained economically long enough during the separation treatment. Another necessary ability of the adsorbent is to separate the components of the feed stream, i.e. that the adsorbent has a certain adsorption selectivity (B) over one component over another. Relative selectivity can not only be shown for one component relative to another component, but can also be shown between any component of the feed mixture and the adsorbent. Selectivity (B), a term used in this specification, is the ratio of the two components of the adsorbed phase to the ratio of the same two components in the non-adsorbed phase at equilibrium conditions. Relative selectivity is shown below. . lön 2: »· ·

Equation 2 • · • · M ·

Selectivity = (B) = (volume percentage C / volume percentage 0) A

(volume percentage C volume percentage D) U

• · · • 1 * · · i «t * · where in the equation C and D are the two components of the feed expressed as i% by volume, and A and U are the adsorbed and non-adsorbed phases, respectively. Equilibrium conditions prevail when the feed passing through the adsorption layer does not change its composition upon contact with the adsorption layer. In other words, there is no net transfer of the substance between the non-adsorbed and the adsorbed phase. As the selectivity of the two components approaches 1.0, the adsorbent does not adsorb the other, ···. components with respect to the other but are adsorbed (or not adsorbed) both in approximately the same manner with respect to each other.

• · 1> · · · · • «•» • ♦ 14 93857

When the value (3) becomes less than or greater than 1.0, the adsorbent mainly adsorbs one component relative to the other. When comparing the selectivity of the adsorbent with respect to the second component C over the second component D, a value (B) greater than 1.0 indicates that the adsorbent adsorbs predominantly component C. When (B) is less than 1.0, this indicates that component D adsorbs predominantly and more adsorb remains in the non-adsorbed phase and component D in the adsorbed phase. The ideal desorbents are such that their selectivity is about 1 or slightly less than 1 for the extractant components so that all extractant components can be desorbed as one group at reasonable flow rates by the desorbent, that the extract components can replace the desorbent in the next adsorption step. Although separation of the extract component from the raffinate component is theoretically possible when the selectivity of the adsorbent with respect to the extract component relative to the raffinate component is greater than 1, it is preferred that this selectivity approaches 2. As well as relative volatility, the higher the selectivity . Greater selectivity allows a smaller amount of adsorbent to be used. A third important feature is the exchange rate of the extract component of the feed mixture, i. the relative desorption rate of the extract component. This property • · is directly dependent on the amount of desorbent that must be used in the treatment to recover the extract component from the adsorbent. Higher exchange rates reduce the amount of desorbent required to remove the extract component and thus allow for a reduction in processing costs. At higher exchange rates, less desorbent must be pumped through the treatment and separated from the extract stream for reuse in the treatment.

Degradation is a measure of the degree of separation of a two-component system, which can be used to quantify the efficiency of a given adsorbent, desorbent and combination of treatment conditions during separation treatment. Scattering in this specification means the distance between the two centers of vertices divided by the average width of these vertices at 1/2 of the height of the peaks below. The equation for determining the scattering is therefore as follows:

Equation 3 L2 - L1 R = --- = - 1/2 (W 1 + W 2) wherein in formula and L 2 are respectively the distance from the reference point in ml, sa with respect to the peak center O, and and W2 are the peak widths at half-height of the case.

In the experiment of different adsorbents, dynamic test equipment, certain feed mixtures and desorbents were used to determine the adsorption capacity, selectivity and exchange rate of the adsorbent. The apparatus consisted of an adsorption chamber consisting of a helical statue of about 70 ml with inlet and outlet points at opposite ends of the chamber. The chamber was in contact with the temperature control devices and also with the pressure control devices used to make the chamber operate at a predetermined constant pressure. Quantitative and qualitative analytical equipment, such as a refractometer, a polarimeter, and chromatographic equipment, can be connected to the outlet line of the chamber and used to quantitatively or qualitatively determine one or more components of the flow out of the chamber. The pulse test, which was carried out using ·. using this apparatus and the following method, selection was used. and other values in different adsorption systems. The adsorbent was filled to equilibrium with the desorbent used by passing it through the adsorption chamber. At the appropriate time, a feed pulse containing a tracer of known extract and a specific extract component or raffinate component, or both diluted with a desorbent, was injected for several minutes. The desorbent flow is then restarted and. the tracer and extract component or raffinate component (or both) were eluted using liquid-solid chromatography.

«

The effluent can be analyzed continuously or the effluent samples can be collected periodically and subsequently analyzed separately with analytical equipment to generate peak curves for the corresponding component.

Based on the results of the adsorption experiments, its efficiency can be expressed as the pore volume, the retention volume of the extract or raffinate component, the selectivity of one component over another, and the desorption rate of the desorbent over the extract component. The holding volume of the extract or raffinate component can be expressed as the distance between the center of the peak curve of the extract or raffinate component and the peak curve of the tracer or some other known reference point. It is expressed as the volume of desorbent in cubic centimeters pumped during this period, represented by the distance between the peak curves. The selectivity (B) of the extract component over the raffinate component can be expressed as the ratio of the distances between the centers of the peak curve of the extract component and the peak curve of the tracer (or other reference point) to the corresponding distance between the peak curve of the raffinate component and the peak of the tracer component. Exchange of an extract component with the desorbent speed can generally be defined as the peak of the curve half width. The narrower the width of the peak. is, the higher the desorption rate. The desorption rate V can also be determined from the distance between the center of the trace of the tracer and the disappearance of the freshly desorbed extract component. This distance is also the volume of desorbent that has been pumped during this time.

Further evaluation of the preferred adsorption systems and the conversion of these values into a practical separation method will require the best system to be tested in practice in a continuous, countercurrent liquid-solid contact system.

. ·. The general principles of operation of such a device are described in advance. more previously in U.S. Patent 2,985,589. An apparatus for performing laboratory principles that implements these principles is described in U.S. Patent 3,706,812. This apparatus has a plurality of 0 m ... · adsorption layers and a plurality of supply lines that are attached to the manifolds in the floors and terminating in a rotating 17,9857 manifold valve. At a given valve position, the feed and desorbent are passed through two lines and the raffinate and extract streams are removed through the other two lines. All other supply lines are inactive, and when the distribution valve position is shifted by one cycle, all active functions are shifted by one layer. This simulates a state in which the adsorbent moves countercurrent to the liquid flow. Further details of the above-mentioned nonionic adsorbent test apparatus and adsorbent assay technique are set forth in "Separation of Cg Aromatics by Adsorption" by A.J. deRosset, R.W. Neuzil, D.J. Korous and D.H. Rosback, presented at the Society's American Chemical Society, Los Angeles, California meeting on March 28th. - 2.4. 1971.

One group of adsorbents that can be used in the process of the invention are nonionic, hydrophobic, water-insoluble styrene-poly (vinyl) benzene copolymers and their copolymers with monoethylenically unsaturated compounds or polyethylenically unsaturated polyunsaturated towers other than polyethylene unsaturated towers. which include acrylic esters, e.g., those described in U.S. Patent Nos. 3,531,463 and 3,663,467, which are incorporated herein by reference. As disclosed in U.S. Patent No. 3,531,463, these polymers can be prepared as disclosed in U.S. Patent Application No. 749,526, which has resulted in U.S. Patent Nos. 4,221,871, 4,224,415. , 4,256,840, 4,297,220, 4,382,124 and 4,501,826, all of which are incorporated herein by reference. The above adsorbents are manufactured by Rohm and Haas Company and sold under the trademark "Amberlite". Amberlite polymers of the type known to be effective in the practice of the invention are mentioned in the brochures of the above-mentioned company as Amberlite adsorbents XAD-1, XAD-2, XAD-4, XAD-7 and ·. XAD-8 and described in these brochures as a "hard, porous polymer formed by insoluble spheres having a large surface area". The different types of adsorbent Amberlite polymers differ somewhat in physical properties such as porosity, volume percent, density and screen size »• 9 9 9 9

U

is 93857, but even more so on the basis of their surface area, average pore diameter and 2-pole torque. The most preferred adsorbents have a surface area of 10-2000 m / g and most preferably 100-1000 m / g. These properties are shown in the following table.

table 1

Properties of polymeric Amberlite adsorption XAD-1 XAD-2 XAD-4 XAD-7 XAD-8

Chemical poly-poly-poly-acrylic-acrylic nature styrene styrene styrene ester ester

Porosity% by weight 37 42 51 55 52

Actual wet heat g / cnr 1.02 1.02 1.02 1.05 1.09

Area m2 / g 100 300 780 450 160

Avg. diameter,

Angstrom 200 90 50 90 225

Structure density g / cm3 1.07 1.07 1.08 1.24 1.23:: Nominal · *. part size 20-50 20-50 20-50 20-50 25-50 • · · ·. 2-Na-I torque of functional groups 0.3 0.3 0.3 1.8 1.8 * · 9 ·

The uses of the adsorbent Amberlite polymers disclosed in Rohm and Haas Comapny's brochures include decolorization of the pulp mill bleach waste solution, decolorization of paint * waste, and removal of insecticides from the waste solutions. This, of course, does not suggest a surprising finding according to the invention that the adsorbent Amberlite polymers are effective in separating citric acid from Aspergillus m Niger fermentation broth.

• * • ♦ · * · 9 • · ·· ♦ 93857 19

Another group of adsorbents that can be used in the process of the invention are weak basic anion exchange resins having tertiary amine or pyridine functionality in a crosslinked polymer matrix, e.g. acrylic or styrene. They are very suitable in the form of spheres, have a very uniform polymer porosity, good chemical and physical stability and good abrasion resistance (which is not common in macroreticular resins).

Adsorbents, such as those described above, are manufactured by Rohm and Haas Company and sold under the trademark "Amberlite". Such Amberlite polymers are known to be effective for the purposes of the invention and are referred to in the Rohm and Haas Company brochures as Amberlite adsorbents XE-275 (IRA-35), IRA-68, and are described in these brochures as "insoluble in conventional solvents, and having an open structure for efficient adsorption and de-sorption of large molecules without losing their efficiency due to fouling by organic matter ". Also suitable are resins AG-3X4A and AG4-.X4, manufactured by Bio Rad, and similar resins sold by Dow Chemical, such as Dowex 66 and Dow test resins, which can be prepared from U.S. Patents 4,031,038,9 • and 4,098,867. methods.

9 9 9 9 9 '· The various polymeric adsorbents in this category · differ to some extent in terms of physical properties such as porosity, volume percentage, structural strength and nominal particle size, and even more in terms of surface area 9, average pore diameter and 2-pole moments. The most preferred adsorbents have a surface area of 10-2000 m 2 / g and preferably 100-1000 m 2 / g. Of the above. The special features of the products have been described in the literature and technical brochures published by the manufacturers, such as the products presented in Chapter 2 of the tau - / *, to which reference is made in this connection. Other types of products can also be used.

• * • · • · 9 9 »9 • ♦ • 9 9 9 9 9 · •

Mm ^ mmrnmrn— ^ · β— ........... i - ——, - 93857 20

Table 2

Adsorbent_ Matrix Type References AG3-4A Polystyrene Chromatography Electrophoresis (Bio Rad) Immunochemistry Molecular

Biology - HPLC - Price T.ist M April 1987 (Bio Rad) AG4-X4 Acrylic Chromatography Electrophoresis

Immunochemistry Molecular Biology - HPLC - Price List M April 1987 (Bio Rad)

Dow Polystyrene U.S. Patent Nos. 4,031,038 and Experimental 4,098,867 Resins

Dowex 66 Polystyrene Material Safety Data Sheet printed 17.2. 1987 (Dow Chemical USA) IRA-35 Acrylic Amberlite Ion Exchange Resins (XE-275) (XE-275) Rohm & Haas Co. 1975 IRA-68 Acrylic Amberlite Ion Exchange Resins-

Amberlite IRA-68

Rohm & Haas Co. April 1977

Applications of the polymeric Amberlite adsorbents described in the literature published by Rohm and Haas Comany include the decolorization of the pulp mill bleach waste solution. to, decolourisation of paint waste and removal of insecticides from t · waste solutions. The present invention has not been disclosed in the literature for the efficient separation of chimeric acid from polymeric Amberlite adsorbents from Aspergillus 0 9 '·' Niger fermentation broth.

• · 0 9 9

A third group of adsorbents that can be used in the process of the invention are strongly basic anion exchange resins having quaternary ammonium functionality in a crosslinked polymer matrix, i. di -: *; vinylbenzene crosslinked acrylic or styrene resins.

*. They are very suitable in the form of spheres and have a uniform polymeric porosity and good chemical and physical stability. In the present case, these resins may be gel-like (or "gel-type") or "macroreticular", a term used in the current literature, namely Kun and Hetherington: "A Progress Report on the Removal of Colloids From Water by Macroreticular Ion Exchange Resins ", paper presented at the International Water Conference (Pittsburgh, PA. October 1969), reproduced by Rohm and Haas Comapny. In current adsorption technology, "the term microreticular refers to a gel structure per se, pore size that is atomic in size and depends on the swelling properties of the gel," while "macroreticular pores and true porosity means structures with pores larger than pores. Their size and shape are not significantly affected by changes in the environment, for example those due to variations in osmotic pressure ", while the dimensions of the gel structure" depend significantly on environmental conditions ". In "classical adsorption", the terms microporous and macroporous normally refer to pores longer than 20 A and larger and 200 A. Pores with a diameter between 20 A and 200 A are transfer pores. "The authors use the term" macroreticular "in its sense. instead of defining the novel ion exchange resins of the invention "having both a microreticular and a macroreticular pore structure. The former means the distance between the chains and the cross-linking points of the swollen gel structure, and the latter pores which do not form part of the actual chemical structure. The macroreticular part of the structure may in fact »·» comprise micro-, macro- and transitional pores depending on the pore size distribution. ”(The above quotations are from page 1 of Kun et al.) Adsorbents with a macroreticular structure also have good abrasion resistance (which is not common with conventional macroreticular resins).

• · In this specification, references to "macroreticular" thus refer to adsorbents of the type described which have two types of porosity, such as Kun and Hethesing. have defined it. The terms "gel" and "gel type" are used herein in their conventional sense.

• · · 9 · 1 * · «· · • · ·« · · • ^ 93857

When considering ion exchange resins containing a quaternary ammonium function according to the invention, the quaternary amine has a positive charge and can form an ionic bond with a sulfate ion. The ion exchange resin containing a quaternary ammonium anion has a weak basic property in the sulfate form, which in turn can adsorb citric acid due to the acid-base reaction.

P - N + (R) 3 or P - N + - (R) 2 (C2H4OH) 0 "O" ·· 1 .. .. I ..

: O = S = O:: O = S = O: l- + l_ + O - H - C.A. O - H -C.A.

wherein P = resin group R = lower alkyl, C3-3 C.A. = citrate ion

Adsorbents, e.g., those described above, are manufactured by Rohm and Haas Company and sold under the trademark "Amberlite". Amberlite polymers known to be effective for the purposes of the invention are disclosed in Rohm and Haas Company's brochures in Amberlite IRA 400 and 900 series and are described in these brochures as "insoluble in all conventional solvents, open in structure to provide efficient adsorption ** and desorption at high molecules without losing their effectiveness due to contamination by organic substances ". Also suitable are resins * Ιψ AG1, AG2 and AGMP-1 manufactured under the tradename Bio Rad, and ♦ I corresponding resins manufactured by Dow Chemical Co., such as Dowex 1, • · 2, 11, MSA-1 and MSA -2, etc. Also useful in the practice of the invention are the so-called moderately basic ion exchange resins which are mixtures of strong and weak base resins. Examples include the following commercially available resins: Bio-Rex 5 (Bio-Rad 1); Amberlite IRA-4 7 and Duolite A-340 (both manufactured by Rohm & Haas). They are [• m useful, e.g., if necessary, such basic ionic /. an exchange resin that is not as basic as strongly resinous · alkaline resins, or one that is more basic than * • · weakly basic resins. 1 · • »23 9 3 8 5 7 The different types of polymeric adsorbents in this group differ to some extent in their physical properties such as porosity, volume percentage, structural strength and nominal particle size, and even more in terms of surface area, average pore diameter and 2 drive hub-torque. The most preferred adsorbents have a surface area of 10-2000 m 2 / g and preferably 100-1000 m 2 / g. The special properties of these materials are described in the literature and technical brochures published by the manufacturer, e.g. those listed in Table 3 and referred to herein.

Table 3

Properties of Adsorbents Adsorption- Matrix Substance_ Resin Type Literature References IRA 458 Acrylic Gee- Amberlite Ion Exchange Resins (Rohm & Haas) Lite Type 1986 & Technical Bulletin IE-207-74 84 IRA 958 Acrylic Mak- Technical Bulletin and Material Grassy Safety Data Sheet Available IRA 900 Technical Bulletin available in Macroporous 3a Amberlite Ion Exchange

Resins, IE-100-66.

• IRA 904 Polystyrene Technical Bulletin, 1979 and Macroporous IE-208/74, Jan. 1974 ·· IRA 910 Polystyrene Technical Bulletin, 1979 and Macroporous IE-101-66, May. 1972 IRA 400, 402 Polystyrene Amberlite Ion Exchange Resins, Macroporous Oct., Sep. 1976, April 1972 and IE-69-62, Oct. 1976 IRA 410 Polystyrene Amberlite Ion Exchange Resins Gel Type IE-72-63, El. 1970 AG 1 Polystyrene Chromatography Electrophoresis (Bio Rad) Gel Type Immunochemistry Molecular

· Biology HPLC, price list M

Apr. 1987 AG 2 Polystyrene Chromatography Electrophoresis Gel Type Immunochemistry Molecular

Biology HPLC, price list M April 1987 24 93857

Table 3 (continued)

Properties of Adsorption Agents Adsorption Matrix Substance__ Resin Type Literature References AG-MP-1 Polystyrene Chromatography Electrophoresis Macroporous Immunochemistry Molecular

Biology HPLC, price list M April 1987

Bio Rex 5 Strong Chromatography Electrophoresis (Bio Rad) and Weakly Immunochemistry Molecular

basic hart- Biology HPLC, price list M

mixture (eg April 1987 AG-2 and AG-3 or AG-4

The adsorbent can be used in the form of a dense solid layer which is contacted alternately with the feed mixture and the desorbent. In the simplest embodiment of the invention, the adsorbent is used in the form of a single static layer, in which case the treatment is only semi-continuous. In another embodiment, two or more stationary layers may be used in the fixed layer together with suitable valves so that the feed mixture is passed through one or more layers of adsorbent while desorbent. 'The ram leads through one or more other layers of the series. Feed mixture and desorbent

• · · I

. ***. the flow can take place either upwards or downwards through the desorbent. Any conventional apparatus for contacting a liquid and a solid in a static layer can be used.

I · • · • ·

However, in a countercurrent system, the countercurrent layer or simulated countercurrent layer is such that they have a much higher separation efficiency than fixed adsorption layer systems and are therefore advantageous - *: *; sinpia. Adsorption and desorption processes in moving bed or simulated moving bed processes. processes, which allows the continuous production of extract and raffinate streams and the continuous use of feed and desorption streams. A preferred embodiment of this method is one that uses a simulated moving flow system based on a moving bed. The processing principles and order of treatment of such a flow system are described in U.S. Patent 2,985,589. Only four inlet lines operate at each time point, namely feed inlet flow, desorbent inlet flow, raffinate outlet flow, and extract outlet flow. Simultaneously with this simulated, upward flow of solid adsorbent, the flow of liquid that fills the pores of the dense layer of adsorbent occurs. Thus, a contact in the opposite direction is maintained, whereby a downward flow of liquid in the adsorption chamber can be provided by means of a pump. As the active fluid inlet moves through the cycle, i. from the top of the chamber to its bottom, circulates the chamber circulation pump through different zones of fluid that require different flow rates. A programmed flow control device may be used to provide and control such flow rates.

The active liquid supply points divide the adsorption chamber into separate zones, each with a different function. In this embodiment of the method according to the invention, it is generally claimed. it is not necessary to use three separate treatment zones to carry out the treatment, although in a few cases a fourth zone may also be used.

; 1 The adsorption zone, zone 1, is defined by the adsorption time located between the feed inlet stream and the raffinate effluent stream. In this zone, the feed is contacted with the adsorbent, the extract component is adsorbed and the raffinate stream is removed. Since the general flow through zone 1 occurs from the feed stream entering this zone, the raffinate flow leaving the zone is considered to be downstream in this zone • when moving from the feed inlet to the raffinate outlet.

* · · · · 26 93857 Immediately upstream of the liquid flow to zone 1, there is a purge zone, zone 2. The purge zone is defined by the adsorbent between the extract effluent and the feed inlet. The basic treatments that take place in zone 2 are the displacement of the raffinate material from the non-selective pore volume of the adsorbent that has migrated to zone 2 by changing the adsorbent to this zone and the desorption of the raffinate material to the adsorbent that has adsorbed the adsorbent. Purification is accomplished by directing a portion of the extract stream exiting zone 3 to zone 2 at the countercurrent boundary of that zone, i.e., the extract effluent so as to provide displacement of the raffinate material. The material flow to zone 2 takes place downstream from the extract discharge stream to the feed inlet stream.

Immediately upstream of zone 2 and of the liquid flowing to zone 2 is the desorption zone, i.e. zone 3. This desorption zone is defined by the adsorbent between the desorbent inlet stream and the extract outlet stream. The purpose of the desorption zone is to allow the desorbent that enters this zone to displace the extract component whose adsorbent is adsorbent. due to previous contact with the »** ... in zone 1 feed during the initial treatment period. The flow of liquid • to zone 3 takes place in substantially the same direction as! *! zones 1 and 2.

• · «· · mm * '· * In a few cases, a buffer zone, zone 4, can be used for myc ~ This zone, defined by the adsorbent between the raffinate effluent and the desorbent inlet, is located, if used, immediately upstream of the liquid flow to zone 4. in order to maintain the amount of desorbent used in the de-sorbing step, in which case part of the raffinate stream which is removed from zone 1 can be led to zone 4 to displace the desorbent in this zone therefrom * · • · • · »• · •» »27 93857 the desorption. Zone 4 should contain sufficient adsorbent so that the raffinate material in the raffinate stream passing from zone 1 to zone 4 can be prevented from entering zone 3 and contaminating the leachate stream flowing from zone 3. In cases where the fourth treatment zone is not used, the raffinate flow from zone 1 to zone 4 must be carefully adjusted so that the flow directly from zone 1 to zone 3 can be interrupted when a sufficient amount of raffinate material is not present in the zone.

Circulation of the feed and discharge streams through the solid bed of adsorbent can be accomplished by using piping in which valves are operated intermittently to vary the supply and discharge streams and to allow fluid flow in countercurrent to the solid adsorbent. Another treatment that can provide a flow of solid adsorbent countercurrent to the liquid involves the use of a rotary poppet valve where the supply and discharge flows are connected to this valve and the lines through which the feed is introduced, the extract is removed, the desorbent is introduced and the raffinate is removed. transferred '*. * in the same direction through the adsorbent layer. Both said ··· [pipe arrangement and poppet valve are known per se.

Various rotary poppet valves that can be used in this process are disclosed in U.S. Patents 3,040,777 and 3,422,848. Both of the above patents describe a rotary V valve having a suitable and the generation of effluent streams from fixed sources can be achieved without difficulty.

In many cases, the treatment zone contains a much larger amount of adsorbent than any other treatment zone. For example, in a few treatments, the buffer zone may contain a smaller amount of adsorbent than the amount of adsorbent required in the adsorption and purification zones. It can also be seen that in cases where a desorbent is used which readily desorbs the extract from the adsorbent, a relatively small amount of adsorbent is required in the desorption zone compared to the amount of adsorbent required in the buffer zone, adsorption zone. or in all of these. Since it is not necessary for the adsorbent to be present in only one column, the invention also includes the use of several chambers or sets of statues.

It is not necessary that all feed or discharge streams be used simultaneously, and in many cases one of the streams may be shut off while the other feeds and discharges the feed. The apparatus which can be used to carry out the method according to the invention may also comprise a series of separate layers connected to interconnectors and fitted with supply and discharge compounds to which different supply and discharge currents can be connected and which can be alternately and periodically varied to provide continuous processing. In a few cases, connecting lines can be connected to transfer points that, during normal processing, do not act as lines through which material is led to and from the processing.

It has been found that at least part of the extract effluent passes to separation devices, whereby at least part of the desorbent can be separated to produce an extract product containing m desorbent at a reduced concentration. Preferably, but not necessary to carry out the process, a portion of the raffinate effluent is also passed to separation devices, wherein at least a portion of the desorbent can be separated to form a desorbent stream that can be reused in the treatment and to form a raffinate product containing at a reduced concentration of desorbent. The separation device is usually formed by a fractionation column having a structure; l and operations are well known in the art.

• «• · · 1: Reference may be made in this connection to U.S. Patent 2,985,589 and to the article" Continuous Adsorptive Processing — A New Separation Technique "(DB Broughton), published in the Society of • ♦ • 29 93857

At the 34th Annual Meeting of Chemical Engineers in Tokyo, Japan on April 2, 1969, referred to herein to clarify the flow diagram of a countercurrent simulated moving bed method.

Although many such adsorbent separation methods can use treatments in both the liquid and vapor phases, the liquid phase treatment is more advantageous because it requires lower temperatures and because an extract product can be obtained in higher yield compared to the treatment in the vapor phase. Under adsorption conditions, the temperature range is about 20-200 ° C, with the range of about 65-100 ° C being most preferred, and the pressure range is from about atmospheric pressure to about 3450 kPa, which values are preferred to ensure a liquid phase. The same temperature and pressure range is used under the desorption conditions as under the adsorption conditions.

The size of the treatment units that can be used in the practice of the invention can vary from experimental scale (e.g., disclosed in U.S. Patent 3,706,812) to factory scale equipment, and flow rates can range from a few milliliters per hour to several thsons per hour.

. The following examples show the selectivity which makes it possible to carry out the method according to the invention. However, these examples do not limit the invention.

M ··· • 9 9 · 9

‘... · Example I

• · ’, ·.! In this example, three pulse experiments were performed using a neutral siren-divinylbenzene polymer as an adsorbent (XAD-4, manufactured by Rohm & Haas Company) to determine the citric acid resolution of this adsorbent at different pH values from its fermentation mixture containing carbohydrates · DP3, DP2, DP2, including glucose, xylose, arabinose and raffinose), and salt ions, including Na +, K +, Mg ++, Ca ++, Fe +++,

Cl, SO 2, PO 2 = and NO 2, amino acids and proteins. The first experiment was performed at pH 2.4 and 4 ° C.

: The other two experiments were performed at pH 1.7 and 0.9. The citric acid was desorbed with water. The composition of the fermentation feed mixture 1 · · was as follows: • · • · • · m 93857

Mixture fed Quantity

Citric acid 12.9%

Salts (K +, Na +, Ca + +, Mg + f, FE +++) 0.60% (6000 ppm)

Carbohydrates (sugars) 1%

Other (SO 4 =, Cl ", PO 4", NO 3 ~, 5% proteins and amino acids)

Water 81.5%

Retention rates and redissolution values were obtained using a pulse pig apparatus and the treatment method described above. The Ad sorbent was tested in a vertical 70 ml column using the following set of treatments in pulse experiments. The desorbent was continuously passed up through the column containing the adsorbent at a nominal liquid flow rate (LHSV) of about 1.0 per hour. The pore volume was determined from the volume of desorbent required to fill the dry filled statue. The flow of desorbent was stopped at the appropriate time and a 10 ml sample of the feed mixture was injected into the column using a sample ring and the flow of desorbent was restarted. Samples of the effluent were automatically collected in a sample collector and their hydrochloric and citric acid content was then analyzed chromatographically. A few . . subsequent samples were also analyzed for carbohydrates, but because they were eluted at approximately the same rate as the carbohydrates, they were not analyzed in these examples, nor were some of the other minor constituents, namely amino acids and proteins. From the analyzes of these samples, the concentrations of the peak curves of the components of the feed mixture were developed. The retention volume of citric acid was calculated by measuring the distance from the center of the salt retention * · volume curve to the center of the citric acid curve. The scattering value R is calculated from Equation 3 previously presented. The separation factor B was calculated as previously described. . a.

• · «» · «• · • m • m« * · 1 · 1 The results of these pulse experiments are shown in the following Table 4.

• »· • · • ♦ · • ·» · # i • · · »• 0 ·

• I I

31 93857

Table 4

Test A - pH - 2.4

Retention Peak width net 0.5 height- Scattering

Ingredient volume della_ (0.5 in height)

Salts 0 14.4 1.39

Citric acid 44.4 49.5 comparison

Test B - pH - 1.7

Retention Peak width net 0.5 height- Scattering

Ingredient volume della_ (0.5 in height)

Salts 0 11.6 1.49

Citric acid 42.2 45.1 comparison

Experiment C - pH - 0.9

Retention Peak width net 0.5 height- Scattering

Ingredient volume della_ (0.5 in height)

Salts 0 13.3 1.4

Citric acid 40.9 45.1 comparison

The results are shown in Figure 3A, which shows that although citric acid is adsorbed more strongly compared to the other ingredients, there is a significant loss of citric acid which remains adsorbed. untreated and excreted with salts and carbohydrates (not shown in • · *). Citric acid differs satisfactorily in the process of Figure 3B, where the results are good, and in the process of Figure 3C, where the results are excellent. The method is obviously preferred at pH 1.7 and below.

'·' However, at pH 2.4 (Figure 3A) it has been found that a considerable amount of citric acid is recovered in the form of citrate H2CA2 in the raffinate together with salts and carbohydrates.

It is clear from this that the ionized solutes must be reduced, as described above, by maintaining a lower pH of the feed, whereby in Equation 1 the equilibrium shifts to the left.

• ·

Example II

This example shows the results obtained using 32,939,557 neutral crosslinked styrene-divinylbenzene copolymer (XAD-4) and neutral crosslinked polyacrylic ester copolymer (XAD-8) and the same feed mixture as in Example I at different pH values, due to its poor pH difference. to be obtained at a pH of 2.4 or higher or above the citric acid ionization constant pKa ^ = 3.13. The separation was performed using the same method and apparatus described in Example I above, except that the temperature was 60 ° C and 5 ml of feed mixture was used.

Figures 4A, 4B and 4C are graphical representations of the results of pulse experiments using copolymer XAD-4 at pH values of 2.4, 1.7 and 0.9, respectively. Figure 4A shows that citric acid. "breaks through" with salts (and carbohydrates). This problem can be partially avoided by lowering the pH to 1.7 in Figure 4B. Excellent separation is achieved by further lowering the pH to 0.9, as shown in Figure 4C. This difference, when adjusting the pH, clearly has good industrial applicability.

Figures 4D and 4E graphically show the results of pulse experiments under the above conditions using copolymer XAD-8 at pH 2.8 and 1.4 and temperatures of 65 ° C, respectively.

• · · ’**. In Figure 4D, performed at pH 2.8, no separation occurs, but the salts, carbohydrates and citric acid elute together. After recovering about 67 ml of citric acid after a small fraction of carbohydrates, salts and citric acid, relatively pure citric acid can be obtained, but the recovery rate is low. In Figure 4E, which was performed at pH 1.4, there is a selectivity between citric acid and carbohydrates and salts, resulting in satisfactory separation and recovery of citric acid.

• · * ·

Example III

m ^ ™ “'h ™ -" This example illustrates the results obtained using ··' neutral crosslinked styrene-divinylbenzene copolymer (XAD-4) and the same feed mixture as in Example I in different • · 33 9 3 8 5 7 To detect poor separation at pH values of 2.4 or higher, the same method and apparatus were used as in Example I, except that the temperature was 93 ° C in quies 5A and 5B and the feed mixture was 10 ml.

Figures 5A and 5B show the results of pulse experiments using copolymer XAD-4 at pH 2/8 and 1.4, respectively. Figure 5A shows that citric acid "breaks through" with salts and carbohydrates. This problem can be avoided by lowering the pH to 1.4 as shown in Figure 5B. Such separation and pH adjustment clearly have industrial applicability.

Example IV

In this example, the method and apparatus of Example I were used. The temperature was 60 ° C and 5 ml of feed mixture was used. The feed mixture was similar to that previously used except that the citric acid concentration was 40%. The effect of concentration on pH was studied. In Figure 6A, also at 60 ° C, the pH of 1.9 is too high to separate citric acid at 40% concentration. By adjusting the pH downwards according to Figures 6B and 6C, mainly lemon is adsorbed. ^ diacid, and excellent separation is obtained at pH II.1 1113 and 0.5. In none of these examples were carbohydrates · ♦ [analyzed, but it can be assumed that the carbohydrates differed together with the salts.

·· »• · · • ·

Example V

Using the three samples of this example, the method and apparatus of Example I were applied. The temperature was 93 ° C and the volume of the feed mixture was 5 ml. The feed mixture was similar to that used previously except that the lemon ·. ·. the acid was concentrated to 40% to determine the effect of pH concentration II. In the process of Figure 7A, the pH of • · Λ 1.8 is still too high at 93 ° C to separate citric acid at 40% concentration. By adjusting the pH downwards, as in Figures 7B and 7C, mainly sulfuric acid is adsorbed and excellent separation is obtained. Again, 34 93857 carbohydrates were not analyzed, but it can be assumed that the carbohydrates separated together with the salts.

Example VI

The pulse experiment of Example I was repeated using two 50% samples of citric acid and copolymer XAD-4 as the adsorbent. In both cases, the desorbent was water. The composition of the feed used was the same as in Example I except that the citric acid was concentrated to 50%. The temperature was 93 ° C. The pH of the first sample was 1.5. As shown in Figure 8A, no citric acid separated. After lowering the pH to 1.0 in the second sample, citric acid separated easily, as shown in Figure 8B. Again, carbohydrates were not analyzed, but were assumed to be eliminated with the salts. The separation according to Figure 8B was defined as good.

Example VII

The separation example shown in Figures 7B and 7C requires high temperatures, e.g., 93 ° C, to achieve 40% citric acid separation due to difficulties in desorbing citric acid from the XAD-4 adsorbent. In this example, they are eliminated; temperatures which adversely affect the service life and handling costs of the adsorbent, and separation may occur. can be easily carried out at 45 ° C using a desorption mixture containing 10% by weight of acetone and 90% of water. In the method of Fig. 9 • · · 0 m '···', a feed mixture containing 40% by weight of citric acid, 4% of carbohydrates and 2% of salts of the following elements was introduced: K +, Na + , Mg ++, Fe +++, Ca ++, and proteins and amino acids, to the pulse test apparatus previously described, and the experiment was performed as described above except that the temperature was 45 ° C. In this experiment, the pH is maintained. was 0.5 and the desorbent contained acetone, such as * · ·. ·, as described above. The retention volume of citric acid was 10.7 ml • · and the decomposition was 0.61, and as a result, the separation could be easily performed.

• · · M »• · • ·» · «· • · • 0 0 35

Example VIII

93857 In this example, four pulse experiments were performed using a weakly basic resin with a tertiary amine-functional hydrogen bound to a sulfate ion in a cross-linked gel-type acrylic resin matrix (AG4-X4, manufactured by Bio Rad Laboratories, Richmond, California), hydrogen bound to a sulfate ion in a crosslinked acrylic resin matrix to determine the ability of this adsorbent to separate citric acid from its fermentation broth containing carbohydrates (DPI, DP2, DP3 and glucose, xylose, arabinose, and, raffinose), and +, Ca ++, Fe +++,

Cl, SO 2, PO 4 and NO 2, amino acids and proteins, at pH 1.6. The first experiment was performed at 75 ° C. Other experiments were performed at 60 ° C. Citric acid was desorbed with water in Pulse Experiment No. 1 (Figure 10) and with sulfuric acid in two concentrations: 0.05 (Pulse Experiment No. 2) and 0.25 N (Pulse Experiment No. 3). Pulse test No. 4 was similar to pulse test No. 2 except that the adsorbent was used after passing 24 volumes of the feed mixture through it. The composition of the fermentation broth was as follows:. Mixture fed Amount • · · ~~ 1 ”1.1 Citric acid 4 0%‘ ··· ’. Salts (K +, Na +, Ca ++, Mg ++, Fe +++) 1.5%

Ml · ·

Carbohydrates (sugars) 4%

Other (SO, =, Cl ", PO, =, NO., -, • · 4 n '. · .1 proteins and amino acids) 5%: X1 Water 49.5%

Retention volumes and separation factor (B) were obtained using the pulse test apparatus and method described in Example I above, except that 5 ml of sample was used. Citric acid. the net retention volume (NRV) was calculated by measuring the distance from the center of the hydrochloric acid curve to the center of the citric acid curve.

V The difference value B was calculated from the retention volumes of the components to be separated.

• M

the ratio of the first salt component (i.e. salts 1) to the retention volume.

• 9 · ♦ 9 9 • · • · • 9 36 93857 The results of these pulse tests are shown in Table 5 below.

Table No. 5

Resin / de- Feed-

Pulse sorption

test_subject_nent N RV B

1 AG4-X4 / water salts 1 1.6 34.25 citric acid 54.8 comparison unknown A 0 offspring unknown B 6.6 8.30 salts 2 54.6 1.00 2 AG4-X4 / 0.05 n H2SO4 salts 3.2 11.87 citric acid 38.0 comparison unknown A 0 residual unknown B 2.7 14.7 3 AG4-X4 / 0.25 n H2SO4 unknown A 0 residual citric acid 26.9 comparison salts 2.3 11.70 unknown B 7.6 3.54 4 AG4-X4 / 0.05 n H2SO4 unknown A 0 prodrug citric acid 38.0 comparison salts 2.4 15.8 unknown B 7.2 5.28 *, The results of pulse tests 2-4 are similar as in Figure: 10. It can be seen from Table 5 that although citric acid is satisfactorily separated in this process in very pure form when water is used, desorption by water is slower than when dilute sulfuric acid is used, which is evident from the higher net retention volume. Once the adsorbent has been aged by passing 24 bed volumes of the feed mixture therethrough, there are no signs of deactivation, as can be seen in Figure 13, which is substantially identical to Figure 11; (performed under identical conditions using fresh adsorbent).

Example IX

The first pulse test according to Example 8 was repeated using: the same method and equipment, except that the temperature was 65 ° C.

Ηη Μ · Μ · Β · η ···· ΒΒη · Ηη · ηη · ΒΗΒηηΒ 37 93857

The desorbent was water. This example describes the results obtained using a macroporous, weakly basic anion exchange resin with a cross-linked polystyrene matrix (Dowex 66) and the same feed mixture as in Example VIII (40% citric acid) in the first two pulse experiments, pH 7.0 and 3.5 (resp. Figs. 11A and 11B) to illustrate the failure of the desired separation when the pH is above the first ionization constant of citric acid pKa ^ = 3.13, and more specifically in these two samples at a pH above 1.7 with a concentration of 40% when citric acid is used. In the third part of the example (Figure 11C), the feed was diluted to 13% citric acid and the pH was lowered to 2.4. Although there is a clear improvement, it is obvious that the pK value and / or concentration must be further reduced to "prevent breakthrough" of citric acid. For example, at a concentration of 13%, it is estimated that the pH must be lowered to about 1.6-2.2.

Figures 11A and 11B graphically show the results of pulse experiments using Dowex 66 resin at pH 7.0 and 3.5, respectively. Figures 11A and 11B show that citric acid "breaks through" together with salts (and carbohydrates) at higher pH values. This problem can be partially avoided by reducing the concentration to 13 ° s and lowering the pH to 2.4, as shown in Figure 11C, which shows that only a small amount of citric acid is not adsorbed and "breaks through" the raffinate, while the largest some of it is adsorbed on the adsorption resin (but not desorbed ·· 'in this figure). This difference, when adjusting the concentration and pH to the optimum level, obviously has good industrial applicability.

Example X

Three more pulse tests were performed under the conditions of Example 8,. unless otherwise stated, using citric acid samples from the same feed mixture, but with two different adsorbents. The de- • · 'sorption agent was 0.05 n H2S <^ 4 in the first two samples (Figs. 12 and 13A), while water was used in the third sample (Fig. 13B). The composition of the feed mixture used was the same as in Example VIII. The temperature was 60 ° C and the pH was 1.6. The adsorbent No. 1 used in the first experiment was a macroporous, pyridine-function, crosslinked divinylbenzene resin having the following formula: CH ..

l J

P - CH2 - N - CH2 -jpj ·· H + so4 = where P is a resin-forming polystyrene group.

The second adsorbent (No. 2) used in the second and third samples was a tertiary amine which also had a pyridine functional group having the following formula: P - ch2 - N - ch2 -fQ j CH- ~ I 2 + = CHOH H SO.

CH3 wherein P is as defined above. Both resins are crosslinked with divinylbenzene. In a few cases, although water is an effective desorbent which provides excellent separation, it is not strong enough to render the adsorbed citric acid fast enough. make the method industrially applicable. See Fig. 13B, where the conditions are the same as when used above • ·! ! adsorbent n.-o 2 and water as desorbent. In this case, the citric acid does not elute until about 95 ml of de-

the sorbent has passed through the adsorbent. Dilute sulfuric acid is therefore the most preferred desorbent, as shown by the results in Figures 12 and 13A. Also from Figures 12, 13A

• · and 13B show that excellent V: separation of citric acid is obtained.

• · * ·

Example XI

The process of Example VIII, its conditions and apparatus were used to separate citric acid from four samples of the same feed mixture using two different resins belonging to the asosorbents described in Example VIII. (except that in the first and fourth samples the column temperature was 50 ° C and the desorbent was 0.05 n H 2 SO 4, and in the second and third samples the pI was 2.2 and the desorbent was dilute sulfuric acid at 0.15 n). Both IRA-68 and IRA-35 resins, manufactured by Rohm and Haar, have an amine function and the following structural formula: R '1 + = P - CH ~ - N: H SO.

2 i 4 R "wherein P is a polyacrylic matrix and R 'and R" = CH 2.

Amberlite IRA-68 (Samples 1, 2 and 3) is a gel type resin. IRA-35 (Sample 4) is a macroreticular resin. Sample 3 was identical to Sample 2 except that the adsorbent had previously been used to separate the bed volume of the feed mixture 69. Samples 1 and 2 are both excellent adsorbents for separating citric acid from its fermentation broth in the pH range 1.6-2.2. Sample 3 shows after the adsorbent is present. . used for a feed volume of 69 layers, the stability of the resin (♦ · 'deactivation has occurred little or not at all) *. · ♦ * in this difference. The net retention volume (NRV) and selective ***** (B) are shown in Table 6 below.

• · · • «• · • ♦ ♦ • · • ·« • t • ♦ «· • · · · · • ♦ • · • · • · ♦ • · • • # * • mw • Ψ · • 0 · 0 9 9 9 0 99 9 9 9 9 909 9 9 0 0 0 9 0 0 0 0 90 0 9 9 0 9 0 0 00 0 9 93857

Table 6 Sample

No. Resin Ingredient NRV B

1 Amberlite salts 5/5 8/24 IRA-68 citric acid 45.3 comparison unknown A 0 progeny unknown B 9.3 4.87 2 Amberlite salts 2.3 12.61 IRA-68 citric acid 29.0 comparison unknown A 0 prodrug unknown B 6.5 4.46 3 Amberlite salts 2.85 10.32 IRA-68 citric acid 29.4 comparison unknown A 0 progeny unknown B 7.0 4.2 4 Amberlite salts 1.3 27.38 IRA-35 citric acid 36.9 comparison unknown A 0 offspring unknown B 5.9 6.25

To compare the adsorbents of Examples I to VII with the adsorbents of Examples VIII to XI, several extract samples were analyzed for the determination of readily carbonizable impurities (RCS) (Food & Chemical Codex (FCC) Monograph No. 3) and potassium content. The amount of RCS was determined as follows: 1 g of extract sample (actual concentration of citric acid was determined) was carbonized at 90 ° C using 10 ml of 95% H 2 SO 4 solution.

:: The carbonated material was examined spectrophotometrically at a wavelength of 500 nm using a 2 cm cell and a 1.27 cm diameter tube, and the amount of RCS was calculated for 50% citric acid solution. The value obtained can be compared with that obtained using this test method in the above-mentioned FCC test and using a standard cobalt solution. Potassium was determined spectroscopically by atomic adsorption. For comparison, the same analytical determinations were performed using the same feed sample, and the RCS value was calculated for 50% citric acid using resins XAD-4, AG4-X4 and adsorbents 1 and 2 according to Example III. · ‘The results are shown in Table 7.

4i 93857

Table 7

Extract quality (RCS / potassium) in the RCS C.Λ. net

Adsorption Desorption calculated (50% retention aid_ substance_ citric acid) ppmK volume XAD-4 H2O 6.86, 8.98 59, 137 13.0 AG4-X4 0.05 n-H2SO4 1.77, 1.42 24, 81 34.8 No. 2 (e.g. X) 0.05 n-H2SC> 4 3.17, 3.33 24, 54 30.8 No. 1 (e.g. X) 0.05 n- H2SO4 2.17 62 31.0 These values indicate a reduction in the RCS and K values of weakly basic resins over neutral resins. In all samples the RCS value had decreased by at least 50% and in two samples the K value had decreased by more than 50%. From the net retention volume, it can be stated that both groups of adsorbents have a good dispersion value, but adsorbents based on strong bases have the disadvantage of somewhat increased cycle lengths. The lengths of the period can be reduced by using sulfuric acid at higher concentrations, e.g. always about 0.2 n and preferably 0.1-0.2 n.

In another embodiment, the citric acid adsorbed on the adsorbent ψ · • · »can be turned in situ to citrate before desorption of 9 m m, e.g. by reaction with alkaline earth metal or alkali metal hydroxide or ammonium hydroxide, and then immediately eluted as metal hydroxide, ammonium hydroxide or ammonium hydroxide. Over time, the adsorbent may be deactivated by unknown impurities, but the adsorbent may be regenerated by rinsing it with a stronger desorbent, e.g. sulfuric acid stronger than the desorbent, an alkali metal. . with a bond or NH 4 OH, or as an organic solvent, e.g. acetone or alcohol.

«» * · * * · • · • 1 * m m m · • · • *

Example XII

42 93857 In this example, two pulse experiments were performed using a gel-type, strongly basic anion exchange resin (IRA 458, manufactured by Rohm & Haas Co.) having the structural formula (1) shown above on page 22 and substituted with three methyl groups to determine the citric acid resolution of the adsorbent. from its carbohydrate fermentation mixture (DPI, DP2, DP3, as well as glucose, xylose, arabinose and raffinose), and salt ions such as Na + r K +, Mg ++, Ca ++, Fe +++, Cl ”, SO 2, PO 4 and NO 2. and proteins, at pH 2.2.

P is acrylic crosslinked with divinylbenzene. Pulse test sample 1 was treated at 50 ° C. Pulse test sample 2 was treated at 60 ° C, but after the bed was aged using 33 bed volumes of feed mixture.

Treatments were then performed using 62 bed volumes without substantial deactivation in the adsorbent. Citric acid was desorbed with a 0.1 N solution of sulfuric acid in each sample. The composition of the fermentation broth was as follows:

Feed mix%

Citric acid 40

Salts (K +, Na +, Ca ++, Mg ++ Fe +++) 1.5

Carbohydrates (sugars) 4: Other (SO. =, Cl ”, PO4 =, NO”, 5: ***; proteins and amino acids) • · · ....: Water 49.5 • · · * «» · m '\ ·' Retention volumes and separation factor were obtained using the pulse test apparatus and method described in Example I above.

The results of these wood tests are shown in Table 8 below.

• ·

* <I

* · »• · ♦ · ♦ 9 9 m •» · · • 1 »• ·» • · · • • «« · · • · • • • 9

Table 8 43 93857 Sample

No. Resin Ingredient NRV B

1 IRA-458 salts 1.0 38.9 citric acid 38.9 comparison unknown S 0 progeny unknown B 6.6 5.89 2 IRA-458 salts 0.9 43.3 citric acid 39.0 comparison unknown A 0 progeny unknown B 7.1 5.49

It is evident that the citric acid separates satisfactorily in this treatment, and when the adsorbent was aged using 33 bed volumes of the feed mixture, there were no signs of deactivation, giving substantially similar results as under the same conditions with fresh adsorbent.

Example XIII

The pulse experiment of Example XII was repeated using additional samples of citric acid and the same feed mixture, but with different macroporous, strongly basic anion exchange resin IRA-958 with quaternary ammonium function and acrylic resin matrix cross-linked with divinyl benzene. . The desorbent was 0.05 n Η250 ^. The composition of the feed mixture used: ** [: was the word as in Example XII. The temperature was 60 ° C and the pH was 1.6. In this experiment, such an asorption agent was used. a resin manufactured by Rohm & Haas and having the structure (1) shown on page 22, wherein R is methyl.

As shown in Figure 14, citric acid begins to elute after 45 ml of desorbent has passed through the adsorbent and is very easily separated from the fermentation broth in very pure recovery with excellent recovery.

• · t f · • ·

Example XIV

• «- - II ·· I —I I

; ·> · <The pulse test according to Example XII was repeated using additional samples of lemon- φ 9 9 · • • · · • 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 «93857 acid and the same feed mixture but different strongly basic anion exchange resin adsorbent AG2-X8 (manufactured by Bio Rad Company) having the structural formula (2) shown above on page 22, wherein R is methyl, together with a crosslinked polystyrene gel-type resin matrix having quaternary ammonium functional groups. The desorbent was 0.15 N H 2 SO 4. The composition of the feed mixture used was the same as in Example XI. The temperature was 50 ° C and the pH was 2.2.

As shown in Figure 15, citric acid begins to elute after 43 ml of desorbent has flowed through the adsorbent and separates very efficiently from the fermentation broth in very pure recovery with excellent recovery.

Further comparing the adsorbents of Examples I-VII to the adsorbents of Examples XII-XIV, several extracts were analyzed for readily carbonized impurities (RCS) (Food & Chemical Codex (FCC) Monograph No. 3) and potassium as described above. The results obtained for each of the adsorbents XAD-4, IRA 458, IRA 959 and AG2-X4, as well as the quality of the adsorbent, are shown in Table 9 below.

Table 9

Extract quality (RCS / potassium) in pulse test • 1 • · ··, RCS unit ppmK CA net · ..1 Adsorbents (calculated (calculated retention ··· desorption Desorbent tu 50% citric acid) 50 % citr volume .. _ _ _ acid) _ XAD-4 H 2 O 13.0 • · IRA 4 58 0.1 n H2SO4 1.5 80 37.9 IRA 958 0.05 n H2SO4 2.73 82 32 AG2-X4 0 , 15 n H2SC> 4 5.3 131 43. These values show that the improvement brought about by the decrease in RCS and K values is clear with strongly basic resins compared to neutral resins. In all samples]: the RCS value was reduced by 40-85% and the K value by 0-20%. Examples • 19 m> »9 9 9% 9 45 93857 XII, XIII and XIV (Figure 4) show that both classes of adsorbents have good resolution, but the adsorbents used have the disadvantage of somewhat longer circulation times. These cycle times can be reduced by using higher concentrations of sulfuric acid up to about 0.2 n, with the most preferred range being 0.1-0.2 n.

According to one embodiment, the citric acid adsorbed by the adsorbent can be converted to citrate in situ before desorption, e.g. by reaction with alkaline earth metal hydroxide, alkali metal hydroxide or ammonium hydroxide, and then immediately eluted using metal hydroxide, ammonium hydroxide or desorbent. Over time, unknown impurities can deactivate the adsorbent, but the adsorbent can be regenerated by rinsing it with a stronger desorbent, e.g. stronger sulfuric acid flowing into the desorbent, alkali metal hydroxide or NH 4 OH, or an organic solvent, e.g. acetone.

· Φ · • · • · • · * m · • · • «• · • t · w a 1 · • ·

Claims (6)

1. A process for separating citric acid from a fermentation j: * medium consisting of a mixture containing citric acid, characterized in that the mixture has a pH value lower than '. citric acid pKa, is contacted with a polymeric adsorbent selected from a neutral cross-linked polystyrene polymer, a nonionic hydrophobic polyacrylic acid ester polymer, slightly basic *: anion exchange resin, exhibiting functional groups of tertiary amir. ·: ··· or pyridine, and a strong basic anion exchange resin, exhibiting functional groups of quaternary amine, and mixtures thereof, under adsorption conditions in which the adsorbent selectively adsorbs the citric acid, after which the citric acid is extracted from the adsorbent with a desorbent agent. or a mixture of water and an inorganic acid, under desorption conditions. 93857 Process according to Claim 1, characterized in that said adsorption and desorption conditions include a tern temperature of from 20 ° to 200 ° C and a pressure of approximately from atmospheric pressure to 3 450 kPa. Method according to claim 1, characterized in that the adsorbent comprises a functional group of tertiary air supported on a matrix consisting of a cross-linked acrylic resin. 4. A method according to claim 1, characterized in that the adsorbent comprises a functional pyridine group supported on a matrix consisting of a cross-linked polystyrene resin. Process according to claim 1, characterized in that the adsorbent is a functional group of quaternary amine supported on a matrix consisting of a cross-linked acrylic resin. Process according to claim 1, characterized in that the adsorbent is a quaternary ammonium salt of pyridine supported on a matrix consisting of a cross-linked polystyrene resin. Method according to any one of claims 1-6, characterized in that it comprises the steps of: • a) maintaining a net fluid flow in a single direction by a ... column of said adsorbent, this column * V; contains at least three zones which have separate operating functions therein and are interconnected in series with the end zones of the column connected to provide a continuous · ··· connection between the zones; B) maintaining in said column an adsorption zone, where at that zone is the adsorbent positioned between the feed inlet stream at an upstream boundary in said * zone and a refinery discharge stream at a downstream boundary in said dross; c) maintaining immediately upstream of said adsorption zone by a purification zone constituted by the adsorbent which is located in an ext ractate feed mix at r-n upstream streams. purification zones ccn ti! Input the input space at a node p. pipe limit in said purification zone; (d) maintaining upstream said purification zone of a desorption zone constituted by a decomposition agent which is located between a desorption agent feed stream at an upstream limit in said zone and. .gsscrum v i. 1 a lower limit of noise in said zone; e) feeding the c in the transfer mixture into adsorption zones. in adsorption conditions for carrying out selective adsorption of citric acid by means of the adsorbent in said adsorption zone and extraction of an electric feed stream, the non-adsorbed grain components in the fermentation zone include the ashes removed; f) feeding the desorbent. into said desorption zone. at dose desorption conditions to effect extrusion of the citric acid from the adsorbent in said desorption zone; j; extraction of an extraction outlet stream containing citric acid and desorption agent from the desorption zone; n) feeding at least a portion of the external outlet effluent to a separator and separating it at separating conditions of the at least one portion of the desorption agent; same: periodic flow through the column of adsorbent i, ···. in the downstream direction with respect to flow in adsorption zones - on of the zone boundaries, which is constituted by c 1 l so far. mood, raff inatutma c n ir.gsc! t the frame desorption agent entry **) the space and exc t at. uc _ ooSsst roms., to act to effect the shift of 3 to 10 zones in the column; 3. A method according to claim 7, characterized in that a buffer zone is maintained directly upstream of said desorption zone, said buffer zone consists of the adsorbent disposed between the desorption medium and the inflow stream of said downstream boundary stream at a downstream boundary. at an up: · - · current limit of said buffer zone. • I