MXPA99005136A - A process for recovery of ascorbic acid - Google Patents

Abstract

The invention provides a process for the recovery of ascorbic acid from a feed containing at least one precursor of ascorbic acid comprising converting said precursor into at least one product, said at least one product being ascorbic acid in an organic extractant composition, said organic extractant composition comprising at least one secondary or tertiary alkyl amine in which the aggregate number of carbon atoms is at least 20, as a primary extractant, and a polar extraction enhancer compound;wherein said extractant composition comprises at least 2 moles of said polar extraction enhancer compound per one mole of primary extractant;and subjecting said ascorbic acid-containing organic extractant composition to a stripping operation with aqueous solution at a temperature of at least 20°C higher than the temperature at which said conversion is carried out;whereby there is obtained an aqueous solution of ascorbic acid in which the concentration of ascorbic acid is higher than 5%.

Description

PROCEDURE FOR RECOVERY OF ASCORBIC ACID DESCRIPTIVE MEMORY The present invention relates to a process for the production of ascorbic acid. More particularly, the present invention relates to the recovery of ascorbic acid from a stream solution containing at least one precursor of ascorbic acid, wherein the term "ascorbic acid precursor" as used herein is designed to denote compounds that can to be converted to ascorbic acid in only a few procedural steps, as described hereinafter, for example, compounds selected from the group consisting of salts of ascorbic acid, 2-keto-L-gulonic acid in acid and salt form and derived from it. As described, for example in Kirk-Othmer's Encyclopedia of Chemical Technology, third Edition, ascorbic acid (L-ascorbic acid, L-xyl ascorbic acid, L-threo-hex-2-enonic acid g-lactone) is the name recognized by IUPAC-IUB Commission on Biochemical Nomenclature for vitamin C. The name implies the anti-scorbutic properties of the vitamin, that is, the prevention and treatment of scurvy. L-ascorbic acid is widely distributed in plants and animals. The pure vitamin (C6H8 6, mol weight 176.13) is a crystalline white substance derived from L-gulonic acid, a sugar acid, and synthesized both biologically and chemically from D-glucose. Although the natural and synthetic vitamins C are chemically and biologically identical, in recent years a limited amount of commercial isolation from vegetable sources, for example, false fruit rose, plaqueminer, citrus fruits, etc., has been carried out to fulfill the preference of some people for vitamin C from natural sources. L-ascorbic acid was the first vitamin to be produced in commercial quantities, and the manufacture is based on a well-known synthesis of Reichstein and Grussner, which includes the steps of hydrogenation of D-glucose to D-sorbitol; fermentation (oxidation) to L-sorbose; acetone to bis-isopropylidine-a-L-sorbofuranose; Oxidation to bis-isopropylidine-2-oxo-L-gulonic acid, and hydrolysis, rearrangement and purification to L-ascorbic acid. A fermentation of a carbohydrate to ascorbic acid or a precursor thereof would be very attractive, saving on operations and on expensive reagents, in addition to being derived from a natural fermentation process, as opposed to a synthesis involving chemical steps. There are indications that such a fermentation route to ascorbic acid is viable. However, the fermentative industrial production of ascorbic acid faces two great difficulties: (a) the concentration of product in the fermentation medium is low; (b) said product is at least partially a precursor of ascorbic acid rather than ascorbic acid in its free acid form.

The conversion of said precursor to ascorbic acid and the purification of ascorbic acid by conventional methods without introduction of energy with a driving source would result in a purified product of concentrations similar to that in the stream. Due to its high solubility in water, the cost of crystallization of ascorbic acid by evaporation of water would be prohibitive. The presence of the ascorbate acid precursor, rather than the acid or in addition to it, presents the following two problems: (a) for various applications the acid form of the product is desired, and (b) the separation of the precursor, particularly if it is an ascorbic salt, it is more difficult than the separation of the acid since the separation methods available for salts are normally less selective and of lower yields. Therefore, the recovery of ascorbic acid from a current solution comprising a precursor thereof is a present difficulty, particularly when the total concentration of the precursor in said stream is low. Such a current could result from various sources such as fermentation to ascorbic acid or a precursor thereof or from another production process. This could also be a result of removing ascorbic acid from a stream that consists initially of the acid and its precursor. Several methods were proposed to combine the purification of carboxylic acids with their concentration. In the case of citric acid, is achieved by the addition of lime to crystallize calcium citrate, which has a very low solubility in water. This salt is separated, washed and acidified with sulfuric acid. The concentrated and purified citric acid is obtained. This method is not applicable for ascorbic acid, since its alkaline and alkaline earth salts are highly soluble. A procedure was proposed in which the carboxylic acids were extracted and then displaced from the extracted by a solution of concentrated mineral acids. Both liquid anion exchangers (long chain amines) and solids (resins carrying amine groups) could be considered for this purpose. The purity of the displaced carboxylic acid depends on the preference of the extractor to the mineral acid. Such a procedure could be applicable for the separation of ascorbic acid and the concentration, provided that the extractor is strong enough to reach a high extraction yield, which is shown in a high preference to the displacing acid, and that the ascorbic acid is stable in the high acidity of the displacement solution. The regeneration of the anion exchanger would require neutralization by a base. Using HCl as the displacing acid and distilling it from the extractor was proposed, but the high temperatures required and the decomposition of the extractor under those conditions are prohibitive. If the anion exchanger is represented by B, the ascorbic acid in the current solution and in pure form are AAF and AAP, respectively, the displacing acid is HCl, and the neutralizing base is NaOH, the equations of the process steps and of the total reaction are as follows: B + AAF = B AA B AA + HCl = B HCl + AAP B HCl + NaOH = B + NaCl + H2O AAF + HCl + NaOH = AAP + NaCl + H2O The reagents are consumed, and a byproduct salt without value (or negative) is produced. Many methods were suggested for the conversion of salts anions to the acid form. An example of such a conversion method is to contact the aqueous solution containing the aforementioned salt with a non-water miscible cation exchanger in its acid form, which cation exchanger could be in solid form, for example a resin, or liquid, by example an organic acid not miscible in water. With such contact the cations of the aqueous solution are absorbed onto or extracted into the non-water miscible cation exchanger and the protons are transferred into the aqueous solution where they are combined with the anions to form the free acid. The cation exchanger carrying the cations is then regenerated with an acid, which results in the consumption of more than one mole of regenerating acid per mole of acid to be converted and the formation of more than one mole of a desired salt. Preferably, said conversion is effected in a method that does not consume acids and bases as reagents and does not reject salts within the environment. Such methods, also called salt particles, convert the salt into the corresponding acid and a basic compound of the cation. Such a basic compound is typically hydroxides, bicarbonates and carbonates. The separation of these two products is desired so that at least one of those is transferred into another phase. Preferably, both products are transferred into another phase and are therefore separated from the impurities present in the advancement solution. The acid could be distilled outside, if it is volatile, extracted into a non-mixable extractor in water or sent to a basic solid absorber. The basic compound of the cation could be crystallized out, if it is of a sufficiently low solubility or sent to an absorbent. The two products could also end in two aqueous solutions separated by a membrane. All these options suffer from a common problem. During the conversion step the phases consisting of the acid product or the basic compound of the cation product are in contact with the current solution and therefore the two products could react back to the salt. Therefore, in order to effect the conversion, at least one of the products needs to be removed continuously. An attractive solution could be the extraction of the acid as it is formed, or the extraction of the anion from the acid and the protons formed on this conversion inside an extractor and the formation of the acid product therein (based on the available knowledge on acid extraction). , these two cases do not differ easily, at least for some of the acids). Such extraction provides the purification of the product as well as its separation and facilitates the conversion.

Using a relatively weak extractor would result in an extract (organic phase consisting of extracted acid), which is relatively diluted in the product. Therefore, retro-extraction with water to recover the product thereof in an acidic form would also result in a diluted product solution. On the other hand the use of a strong extractor is undesirable, according to the retro extraction of acid from it (in an acidic form) it would result in too diluted product. Therefore, in the US patent. 5,132,456 of King, a strongly basic extractor extracts part of the lactic acid from the neutral solution, which results in an extractor loaded with lactic acid and a basic solution, which could be recycled as a neutralizing medium to the fermentation. The difficulty with such a strong extractor is that it strongly retains the extracted lactic acid. The recovery of the acid extracted by detaching with water results in a very diluted product (retro extraction). The patent of E.U.A. 5, 132, 456 suggests a way to recover carboxylic acid extracted from a strong extractor. It consists of leaching or retro-extraction with an aqueous solution of ammonia or low molecular weight alkylamine, especially trimethylamine (TMA). The resulting aqueous solution of carboxylated ammonia or alkylammonium can be concentrated if necessary, and the carboxylated one can be thermally decomposed to yield the product of carboxylic acid and ammonia or amine which can be condensed and recycled. This process is expensive and complex and gives room for undesired reactions as well as for thermal decomposition, to which ascorbic acid is particularly sensitive. In 1976, the British patent 1, 426,018 was issued and in 1981 the patent of E.U.A. corresponding 4,275,234, directed to the recovery of acids from aqueous solutions. In said patents, the recovery of citric acid, lactic acid, oxalic acid, and phosphoric acid from an aqueous solution of the same acid is illustrated.; in fact, the patent of E.U.A. is specifically limited in its claims to the recovery of one of the four acids mentioned. If the conversion step in the present invention is contemplated as being analogous to a step of subjecting the aqueous solution to extraction in the aforementioned patent, then the present invention as defined herein can be considered as falling formally within the scope of the aforementioned English patent, the relevant teachings of which are incorporated herein by reference, and in this sense the present invention can be seen as constituting a selection thereof. However, as will be further explained below, not only do such patents not teach, suggest, or exemplify the applicability of the process for the recovery of ascorbic acid from a stream containing a precursor thereof, but in fact, from a careful analysis of such patents, one could not expect such a process to be viable for the recovery of ascorbic acid, as is also evidenced by the fact that 20 years have elapsed since the publication of said patent without any person skilled in the art suggesting or applying said process for the recovery of ascorbic acid from said stream. Referring now to the aforementioned patents and teachings thereof, it is found that the method taught therein utilizes the effect of temperature on the extraction of phosphoric and carboxylic acid by amine-based extractors. The term "amine" as used herein means an amine that can not be mixed in water, with a total of at least 20 carbon atoms on its chains. Said patents teach that such amine-based extractors (ABE) lose much of extraction efficiency with the rise in temperature. This loss of efficiency is known as "extraction temperature sensitivity" (TS). The magnitude of this ST can be represented by the ratio of the distribution coefficient at the lowest temperature (DT?) To the distribution coefficient at the highest temperature (Dj2). A high TS provides the purification and concentration of carboxylic acids through the alteration of the temperature between extraction and retro extraction. The acid is extracted from a current solution by an ABE at low temperature, and is then detached or retro-extracted with water at an elevated temperature. The aqueous solution obtained from this retro extraction is, in many cases, more concentrated than in the current solution. This process is known herein as the "oscillatory temperature procedure" (TSP). The attraction of such procedures lies in the fact that the only energy consumption is that of sensible heat, which avoids the undesirable use of chemical energy as a driving force to concentrate the product and saves much from a latent heat of water evaporation in the final concentration. As explained in the patent of E.U.A. 4,275,234: "The concepts of" low temperature "and" high temperature "are not understood in absolute terms, what matters ... is the temperature differential, which will have to be at least 20 ° (centigrade), both for convenience of operation and in order to make both extraction and retro extraction as complete as possible.The extraction can be carried out at temperatures as low as near the freezing point of the aqueous acid solution and the temperature of the retro-extraction can be at or near the boiling point of the extract or water at atmospheric pressure, or if the retro-extraction is carried out under high pressure, at an even higher temperature, provided the temperature and pressure are choose so that the amine remains in the organic phase.In many cases the extraction can be carried out at or near room temperature, and the detachment operation at a temperature of 20 to 40 ° (centigrade) above room temperature. As a rule, the detachment operation is the most effective, the higher the detachment temperature, but the extraction and detachment temperature will be selected in individual cases according to practical factors, such as resistance to corrosion and equipment costs, costs of heating and cooling the currents of the acid solution, the extract and the extractor, the required concentration of the acid released, etc. "" If the aqueous liquid used to detach the extract is water, the retro-extraction is an aqueous solution of the acid free. If desired, the retroretraction operation can thus be conducted so that the retro-extracts are an aqueous solution of a salt of the extracted acid. For example, the retro extraction with an aqueous alkali metal (in this context "alkali metal" includes ammonia) hydroxide solution yields an aqueous solution of the corresponding alkali metal salt of the extracted acid. Or the aqueous extraction fluid may be, for example, an alkali metal chloride solution. In this case, too, the retroretraction contains the corresponding alkali metal salt of the extracted acid while the amine in the extractor is converted to its hydrochloride. This will therefore have to be decomposed, for example with treatment with calcium hydroxide, to reconstitute the extractor. Sometimes it is advantageous to first perform a retro-extraction with water in order to recover most of the acid in the free state. The acid residue remaining in the solvent extract can then be retro-extracted with an alkali metal hydroxide or salt solution. "The most favorable selection of the temperature of the extraction operation and of the extractor compositions, in relation to both the amine and the solvent, will also be determined according to the given condition of particular cases, for example, the type of acid , its concentration in the original aqueous solution, the impurities present in that solution.The main object as far as the extraction and detachment operation will be to achieve a distribution coefficient as favorable as possible for the distribution of the acid between aqueous and organic phases. In the extraction operation, this must be in favor of the extractor; in the detachment operation, in favor of the aqueous phase. "As stated above, the characteristic of said patents is that the retroremoval is performed at a temperature higher than that of the extraction. efficient at room temperature, the retro-extraction at almost 100 ° C provides a retro-extraction, the concentration of which is similar to, or even higher than, that of the stream, in fact, a major part of the production of citric acid in the world relies on this procedure, using tridodecylamine as the primary extractor and 1-octanol as the enhancer [Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Ed., Vol., 6, p.364] .The degree of product concentration In the TSP (the hill-top pumping effect) depends strongly on the magnitude of the TS The thermodynamic explanation for ST is not clear enough. The extraction is exothermic, the equilibrium is exchanged backwards with the rise in temperature. This would be, however, too simple. Therefore, the most exothermic extraction is that of strong mineral acids, but no TS has been discovered for extraction. To the extent of our knowledge, this complex phenomenon was not fully explained in these patents, and no tools were provided to predict the magnitude of ST of the extracted acid structure. The magnitude of ST for the extraction of several carboxylic acids by an extractor composed of 0.5 mol / kg of trilauryl amine (Henkels Alamina 304) and 10% of octanol in a querocenic diluent has not been proven. The results are presented in Table 1 below: TABLE 1 Temperature sensitivity of carboxylic acid extraction per 0.5 mol / kg of Alamine 304 + 10% octanol in kerosene. The temperature sensitivity (ST) is presented as the distribution coefficient at 30 ° C, divided by that at 75 ° C, in several equilibrium concentrations of aqueous phase.

ST in equil ibrio with solutions Aqueous pKa acid of (mol / kg) 0.05 0.2 0.3 0.475 Maleic2 1.93 1.1 1.0 1.0 1.0 Oxoglutaric2 2.57 2.4 1.5 1.3 1.1 Malonic2 2.83 3.6 1.5 1.3 1.1 Tartaric2 3.01 3.4 3.2 2.7 2.4 Citrus3 3.13 6.0 3.1 2.6 2.2 Malic2 3.22 4.0 4.3 4.0 4.0 Gluconic2 3.75 2.1 2.3 2.4 2.6 Lactic1 3.86 2.5 2.4 2.4 2.2 Succinic2 4.2 4.3 4.0 4.0 4.1 Glutárico2 4.4 3.9 4.5 4.5 4.4 Acetic1 4.76 2.3 2.4 2.4 2.4 Butyric1 4.81 2.1 2.0 2.0 1.8 Isobutyric1 4.84 1.9 1.5 1.4 1.1 Propionic1 4.87 1.7 1.5 1.3 1.1 1 Monocarboxylic acid 2 Dicarboxylic acid 3 Tricarboxylic acid It can be seen that ST can depend on the equilibrium concentration of the acid in the aqueous phase and that it varies significantly from one acid to the other. No linear correlation was discovered, however, between ST and acid resistance or other defined characteristic thereof. The strongest ST was discovered for citric acid in the low concentration of 0.05 mol / kg; some dicarboxylic acids show a higher ST than their monocarboxylic analogues. This could indicate a tendency of the ST to increase with an increase in the number of carboxylic groups. Isolating this parameter from the others is difficult.

The extraction of strong mineral acids by ABE is very efficient, reaching stoichiometric levels already in equilibrium with diluted aqueous solutions. This is true even for the weaker straight-chain aliphatic amides, the tertiary ones that reach the stoichiometric extraction of 1 mole of HCl per mole of amine in equilibrium with aqueous solutions of almost 0.5%. High efficiency is also discovered in the extraction of strong carboxylic acids that have a pKa of less than 2.5. The efficiency is, however, much lower by extracting weak carboxylic acids by tertiary amines in a kerosene diluent. This low efficiency is particularly pronounced in the low concentration scale. In order to avoid low extraction yields, extraction improvers are introduced into the extractor. It is well known that polar and protic compounds provide improvement in the extraction of acid by amines. These compounds can act as acid extractors by themselves, but are weaker extractors than amines. The extractors comprising amines and improvers show synergistic effects in most cases, that is, the extraction of acid by such extractors is much higher than the added contribution of the components. In the description of the invention used herein, and to avoid confusion, the term "primary extractor" will be used for long chain amines used for extractions, and the term "improver" will be used for polar and protic extractor components, the extraction power of which is smaller than that of the primary extractors. Suitable improvers are polar, and preferably protic, compounds, including alkanols, ketones, aldehydes, esters and ethers of various molecular weights. The desired extractors should provide high efficiency in extraction (relatively low volumes of extractors, a small number of stages of extractors and high yields), high selectivity, low water miscible, low toxicity (particularly for food grade products) and efficient detachment of the acid extracted from the extract. The acid can be removed from the extractor through interaction with an aqueous solution to form its salt. In most cases, however, the acid is a required product rather than the salt, and the acid recovery of the extract is done by retro-extraction (also called peeling) with water or by distillation, when viable. As is known, high efficiency in current extraction and high efficiency in detachment are conflicting requirements. The retro extraction of the acid extracted from a strong extractor requires high volumes of water and results in the very dilute aqueous solution of the acid (retro extraction). The high cost of product concentration can make the whole process impractical. The distillation of a strong extractor requires high temperatures and can result in the decomposition of the acid and / or the extractor. Extraction enhancers are polar, and preferably, protic compounds that have a very low extraction capacity in themselves, but significantly improve the extraction efficiency of ABE.

The improvement is explained by the stabilization through the solvation of the amine-acid pair. Octanol is used as an improver in the industrial TSP for the production of citric acid. The extraction improvers have, however, an adverse effect on TSP, since the temperature sensitivity decreases with an increase in the content of the improver. This effect is shown immediately in table2.

TABLE 2 Dependence of the extraction temperature sensitivity of citric acid by extractors based on amine Alamin 304 produced by Henkel, where the solvent is kerosene, on amine concentration, enhancer concentration (octanol), and on the aqueous phase equilibrium concentration . The temperature sensitivity is presented as the distribution coefficient ratio at 30 ° C and 75 ° C.

Octanol D30 / D75 amine for mol / kg mol / kq acid concentrations citric acid in equilibrium aqueous solution 0.02 0.5 1.5 mol / kq mol / kg mol / kg 0.2 0.31 30.0 6.4 2.1 0.2 0.62 10.8 2.0 1.3 0.2 2.0 4.9 1.3 1.1 0.5 0.31 31.3 3.7 1.4 0.5 0.62 4.6 1.5 1.1 0.6 2.0 2.1 1.1 1.05 1.0 0.31 10.5 1.2 1.07 1.0 0.62 4.9 1.1 1.01 1.0 2.0 1.8 1.08 1.03 There is, therefore, an exchange between extraction efficiency and the magnitude of ST. Therefore, seeking a higher degree of product concentration in the process leads to a lower efficiency, particularly at the low concentration end, resulting in lower recovery yields, that is, higher product losses. The absolute losses, expressed, for example, by the concentration of product in the raffinate, depends on the shape of the distribution curve at the low concentration end. The proportional loss is determined mainly by the concentration of the acid in the fermentation liquid. The TSP was implemented to recover citric acid from fermentation liquids due to the unique, favorable combination of sensitivity at very high temperature (the highest reported so far) and the relatively high concentration of citric acid in the fermentation liquid, typically 16-18%. Even in these unique conditions, the level of improver should be reduced to a minimum. R. Wennerster I. Chem. Tech. Biotec .. No. 33B, pgs. 85-94 (1983)] studied the effect of the different parameters of extractors and concluded that hydrocarbons are the preferred diluents, since polar diluents reduce the effect of temperature. Cooling below room temperature or preconcentration of the fermentation liquid [patent E.U.A. 4,994,609] are required to avoid further product losses.

The previous limitations brought by Bauer, and others, conclude, in 1989, that a TPS is not yet economical for citric acid, and that the displacement of acid extracted by another (acetic) acid is preferable [Bauer, et al., See Bunsenges, Phys. Chem., Vol. 93, p. 980-984 (1989)]. It is important to note at this point that ascorbic acid does not carry a carboxyl group and is therefore not a carboxylic acid, nor is it a mineral acid. Accordingly, patents and descriptions that are directed to processes for treating or recovering carboxylic and / or mineral acids do not include ascorbic acid within their scope. According to its pKa, ascorbic acid is quite weak, being more than an order of magnitude weaker than citric acid. Its low acidity and high hydrophilicity (because it has 4 hydroxyl groups) reduce its extraction efficiency. The same is also true for ascorbate anion transfer. The extraction efficiency is determined by the dependence of distribution coefficients on the aqueous phase concentration (the shape of the distribution curve). The distribution coefficient at the high concentration end determines the maximum load of the extractor, and therefore, the volume of the extractor in the procedure. The distribution coefficient at the low concentration end determines the ability to achieve complete extraction, and therefore, extraction performance. For extraction of a component of a diluted stream, the extraction performance is very important. Achieving high yields by extracting a relatively weak and highly hydrophilic acid, such as ascorbic acid, from a diluted stream would require high levels of improver. The present invention may not have a step in which the ascorbic acid as such is extracted from solutions containing it. However, the teachings mentioned above regarding the effects of the different parameters on the extraction efficiency are applicable to the effect of those parameters on the efficiency of the conversion. Therefore, high-content improver extractor compositions would lead to lower exhaust volumes and higher recovery yields, particularly in those cases where the precursor concentration is relatively low. Such high efficiency is in conflict with high release efficiency, and therefore leads to more dilute back extraction and vice versa, with the object of a higher product concentration in the process leading to a lower conversion efficiency, resulting in lower recovery returns. Likewise, those properties of ascorbic acid that reduce its extraction are expected to reduce the efficiency of its conversion. The distribution coefficients, for the case of the conversion step in the present invention, would be considered the ratio between the concentration of ascorbic acid in the extractor and the total concentration of precursor in the stream. Even if the extraction of the ascorbic acid has the sensitivity of extraction temperature of citric acid, it would not be considered to use amine-based extractors in the conversion step. This is due to the fact that at a lower level of improver in the extractor, the loss of precursor to the remaining aqueous solution would be extremely high. This is particularly true for those cases where the precursor is an ascorbate salt and the compound containing the cation formed is basic. (Put differently, at lower levels of improver the preferred direction of the reaction would be the reaction of the acid in the extractor with the basic compound to reform the ascorbate salt). On the other hand, at high levels of improver, the sensitivity to temperature decreases, which would not allow a sufficiently high concentration of product in the retroextract. In view of the foregoing, it was extremely surprising to discover that the temperature sensitivity of the extraction of ascorbic acid by amine-based extractors is very high and maintained, even at high levels of improver. Based on this discovery, there is provided, according to the present invention, a method for the recovery of ascorbic acid from a stream containing at least one precursor of ascorbic acid comprising converting the precursor into at least one product, the at least one product being ascorbic acid in an organic extractor composition, the organic extractor composition consisting of a) at least one secondary or tertiary alkyl amine in which the aggregate number of carbon atoms is at least 20, as a first extractant, and b ) a polar extraction enhancing compound, wherein the extractor composition comprises at least two moles of polar extraction enhancing compound per one primary extractor mass, and subjecting the organic extractor composition containing ascorbic acid to a stripping operation with solution water at a temperature of at least 20 ° C higher than the temperature at which the conversion is carried out, thereby obtaining an aqueous solution of ascorbic acid in which the concentration of ascorbic acid is higher than 5%. In a preferred embodiment of the present invention the precursor is a salt of ascorbic acid, preferably an alkaline or alkaline earth salt, preferably an ammonia salt, and a process for the recovery of ascorbic acid from an aqueous stream solution containing at least one salt of ascorbic acid comprising converting the salt into at least two components, first component consisting of a compound of the salt cation, and a second component comprising ascorbic acid in an organic extractor composition comprising a) at least one tertiary or secondary alkyl amine in which the aggregate number of carbon atoms is at least 20, as a primary extractor, and b) a polar extraction enhancing compound wherein the extractor composition comprises at least two moles of polar extraction enhancing compound per one primary extractor mass separating the organic extractor composition containing ascorbic acid from the residual aqueous solution; and subjecting the organic extractor composition containing ascorbic acid to a stripping operation with aqueous solution at a temperature of at least 20 ° C higher than the temperature at which the conversion is carried out where an aqueous solution is obtained. Ascorbic acid in which the concentration of ascorbic acid is higher than 5%. The extractors comprising relatively strong amines as the primary extractor, show almost no sensitivity to temperature on the efficiency of extraction of strong mineral acids. It was however discovered that relatively weak amines show such an effect. An example of such weak amines are the branched chain amines, spaced apart, with branching on a carbon close to the nitrogen atom [Eyal, et al., Solvent Extraction and Ion Exchange, Vol. 9, p. 195-236 (1991)]. These amines are weaker by more than two orders of magnitude than direct chain amines, and weaker than branched chain amines with branching beyond the nitrogen atom. Such amines are too weak to extract the weakest acids and are not suitable for use as primary extractors in the present invention. For simplicity of language, the term "branched chain amines" will be used herein only for relatively weak amines, spaced apart, with branching close to the nitrogen atom. The branched chain amines are very weak to extract many of the carboxylic acids, particularly hydroxycarboxylic acids. The direct chain amines are much more efficient, but a high conversion performance requires the use of extraction improver. This is particularly true for diluted current solutions. However, the stronger the improver is and the higher its content, the lower the sensitivity of extraction efficiency to temperature. Therefore, amine-based extractors, which consist of relatively strong improvers in high proportions of improvers, show high efficiency in conversion, but lose most of the advantages in retro-extraction at higher temperature, according to the patent of USA 4,275,234. According to the known practice, four main options have been suggested for the case of the extraction of phosphoric acid and carboxylic acids, as well as variations and combinations thereof: a) .- The use of a weaker improver or an improver stronger, at a minimum concentration required for the conclusion of extraction (non-optimal extracting composition in extraction, high volume of extractor, many stages in extraction and relatively high losses). This option was chosen for the production of citric acid. b) .- Increase in the temperature scale between extraction and back extraction (costly cooling and high viscosity in extraction, and expensive heating and thermal degradation in the back extraction in which the ascorbic acid is particularly sensitive to said degradation) c) .- Distillation of at least part of the improver from the extract before back extraction (high energy cost, limitation to volatile improvers that in many cases have relatively high solubility in the aqueous streams, requiring additional recovery operations). d) .- Addition to the extract of a polar solvent that acts as suppressor of extraction and removal of this solvent before the use of regenerated extractor (low efficiency and high energy cost). Unlike the previous opinions, a further preferred aspect of the present invention is based on the discovery that the polar organic compounds with steric hindrance of the polar group have, at about room temperature, an improvement effect similar to that of the unimpeded compounds similar, but a lower improvement effect at elevated temperature. As a result, efficient conversion can be achieved using amine-based extractors at approximately room temperature, in combination with suitable amounts of improver, although efficient back-extraction at elevated temperatures is achieved, without having to resort to unduly high back-extraction temperatures and / or the removal of high energy consumption of extractor components, either before or after retroextraction. In light of the foregoing, a method according to the present invention for the recovery of ascorbic acid from a stream containing at least one acid precursor is now provided, in accordance with the preferred embodiments of the present invention. ascorbic, as defined herein above, comprising converting said precursor into at least one product - said at least one product being ascorbic acid - in an organic extractor composition, said organic extractor composition comprising (a) at least one secondary alkylamine or tertiary in which the aggregate number of carbon atoms is at least 20, as a primary extractor, and (b) an organic, polar and sterically hindered extraction enhancing compound having at least 5 carbon atoms, a basic character weaker than that of said primary extractor, and temperature-sensitive extraction enhancing properties, where dich The extractant composition comprises at least 2 moles of said extraction improver compound per one mole of primary extractor.; and subjecting said extractor composition containing ascorbic acid to an extraction operation with aqueous solution at a temperature at least 20 ° higher than the temperature at which said conversion is carried out, wherein said extraction enhancing compound improves both the power of extracting said primary extractor composition, as also facilitates said temperature-sensitive extraction operation, and thereby obtaining an aqueous solution of ascorbic acid in which the concentration of ascorbic acid is more than 5%. In an especially preferred embodiment of the present invention, said precusor is a salt of ascorbic acid, preferably an ammonium, alkaline or alkaline earth salt, and a process for the recovery of ascorbic acid from an aqueous feed solution containing at least one salt of ascorbic acid, comprising converting said salt into at least two components: (i) a compound of the cation of said salt and (ii) ascorbic acid in an organic extracting composition comprising (a) at least a secondary or tertiary alkylamine in which the aggregate number of carbon atoms is at least 20, as a primary extractor, and (b) an organic, polar and sterically hindered extraction enhancing compound having at least 5 carbon atoms. carbon, a basic character weaker than that of said primary extractor, and temperature-sensitive extraction enhancing properties; wherein said extractor composition comprises at least 2 moles of said extraction enhancing compound per one mole of primary extractor; separating said ascorbic acid-containing extractant composition from a residual aqueous solution, and subjecting said ascorbic acid-containing extractant composition to an extraction operation with aqueous solution at a temperature at least 20 ° higher than the temperature at which said conversion is carried out finished; wherein said extraction enhancing compound improves both the extraction power of said primary extractor composition, and also facilitates said temperature-sensitive extraction operation, and thereby obtaining an aqueous solution of ascorbic acid in which the concentration of acid Ascorbic is more than 5%. In said preferred embodiments of the present invention, said polar and sterically hindered organic extraction enhancing compound is preferably selected from the group consisting of alkanols, carboxylic acids, tertiary amines or trialkyl phosphates, having a steric hindrance substituent attached to the carbon bearing said polar group, or a carbon that is alpha, beta or gamma to said carbon. The polar organic compounds, and particularly protics, act as enhancers of the extraction of acid by amines, thanks to their ability to solvate the pair of amine acid ions formed in said extraction. Organic compounds suitable for use as builders in the present invention have at least one polar or protic group whose solvation properties are impeded by the structure of the molecule. The polar group is preferably a hydroxyl, an ester, an aldehyde, a carboxyl, a ketone or an amine, or said polar group may comprise a halogen, sulfur, nitrogen or phosphate atom. The hindrance can be achieved by replacing a hydrogen atom in the alkyl chain with an aiiphatic group, ie branching at the carbon atom carrying the polar group, or at a carbon that is alpha, beta or gamma at said carbon . The improver should be a weaker base than the amine used as the primary extractor in the mixed extractor material. When equilibrating it with an aqueous solution of HCl at 0.1 M in a proportion that provides a molar ratio of improver to HCl of 2, the pH of the aqueous phase will remain below 2. In a similar equilibrium, with the amine acting on its own as the unimproved extractor, the pH of the aqueous phase is increased to about 2.5 or more. In addition to the primary extractor and the organic, polar and sterically hindered enhancer compound, the extractor may comprise a polar or non-polar solvent immiscible with water, for example, an aliphatic or aromatic hydrocarbon, hydrocarbons bearing nitro or halogen substituents and alcohols. In preferred embodiments of the present invention, said polar and sterically hindered extraction enhancing compound is selected from the group consisting of secondary or tertiary alkanols, tris-2-ethylexylamine and tris-2-ethylhexyl phosphate. The present invention also provides an extracting composition for use in a process for the recovery of ascorbic acid from a stream containing at least one precursor of ascorbic acid, said composition comprising (a) at least one secondary or tertiary alkylamine, in which the aggregate number of carbon atoms is at least 20, as a primary extractor; and (b) an organic, polar and sterically hindered extraction enhancing compound having at least 5 carbon atoms, a weaker basic character than said primary extractor, and temperature-sensitive extraction enhancement properties.

In preferred embodiments of the present invention, said extraction composition comprises at least 3 moles of said polar extraction enhancing compound per one mole of primary extractor. In especially preferred embodiments of the present invention, said extraction action carries out the back extraction of at least 80% of the ascorbic acid contained in said organic extractor composition. In the patent of E.U. No. 5,041,563 and EP 133,493 an amine is used as a catalyst in the conversion of 2-ketogulonic acid ester to ascorbic acid, and the amine salt of the product is formed. The next step is to "cut the amine salt of ascorbic acid resulting by liquid-liquid extraction in such a way that the ascorbic acid is recovered in the polar phase and the amine is recovered in the non-polar phase." A suggested way to do this, called liquid-liquid extraction, is the addition of a water / polar solvent and a non-polar solvent to carry out the distribution of the acid in the first and the amine in the latter. In certain cases, an alternative, known as digestion, is to heat with a suitable organic solvent, whereby the amine is transferred to that solvent and ascorbic acid is crystallized. Retroextraction at a temperature higher than that of extraction is not taught in these publications, and thus these references also do not teach or suggest the method of the present invention. Moreover, although the same precursor of ascorbic acid and an amine and a solvent which can be considered as an extraction improver are used are present in the conversion step described herein, that solvent is removed from the reaction mixture before the recovery step. and it is replaced by another solvent, which is a non-polar solvent and which therefore does not act as an improver, but rather as an extractor suppressor. The US patents 2,160,621 and 5,041, 563 both describe a process for the production of acids from the ascorbic acid family, using an amine as a catalyst. Said patents do not teach the separation and purification of the product and therefore obviously do not teach extraction and back extraction in the presence of an extraction improver and the use of the temperature effect of the present invention. The patent of E.U. No. 2,443,487 describes a method for the production of ascorbic acid, in which an amine is used as a catalyst. The specified amines are soluble in water and therefore do not provide a means to separate ascorbic acid. The product, according to said patent, is reacted with sodium hydroxide to displace the amine and sodium ascorbate is crystallized. In this way, this patent also does not teach extraction and back extraction in the presence of an extraction improver, nor the use of the temperature effect of the present invention. The patent of E.U. No. 4,778,902 teaches a method for the removal of a water soluble amine used as a surfactant in the production of ascorbic acid. The amine is removed from the reaction mixture by adsorption on activated carbon. Similarly, Japanese patent 48-15931 and the US patent. 5,637,734 teach the use of an amine as a surfactant in the production of ascorbic acid. None of these patents alone, or in combination, teaches extraction and back extraction in the presence of an extraction improver, nor the use of the temperature effect of the present invention. As will be described and exemplified hereinafter, one of the main advantages of the process of the present invention for the recovery of ascorbic acid is that, after said extraction operation, the remaining organic extractor composition can be recirculated, and the conversion Further carried out with said recirculated organic extractor composition provides yields of at least 90%, and preferably at least 95%. In many cases at least part of the product is desired in free acid form. In those cases water should be used as said aqueous solution in said extraction operation. When a part of the product is desired in the form of free acid and another part of it in the form of a metal ion saltpart of the ascorbic acid part in the organic extracting composition is extracted with water and another part with a solution comprising a base or a salt of said metal ion. In a preferred embodiment, a solution comprising a base of the metal ion is used. Preferably, the base is selected from a group consisting of hydroxides, bicarbonates, carbonates and mixtures thereof. Most preferably, said metal ion is an alkali metal ion, more preferably sodium. It was found that in cases where one part of the product is desired in the form of a free acid and another part in the form of a metal salt, a preferred combined process includes extracting first ascorbic acid in the acid form at the desired ratio extracting with water and then extracting the rest with a solution that includes a base of metal. This combination makes extraction with water more efficient. In this way, the temperature scale between the conversion temperature and that of the extraction temperature may be smaller than in the case where all the extracted acid is extracted with water. Alternatively, the same temperature scale is used and the product of the extraction with water is more concentrated. In said preferred embodiment, said extraction with a solution comprising a metal base can be carried out at any convenient temperature, which does not have to be higher than that of the extraction. In a preferred embodiment of the case in which said precursor is a salt of ascorbic acid, a water-soluble acid is used as an acidulant in the conversion step, making use of the high selectivity of the extractors used. Preferably, said water soluble acid has an acidity similar to that of ascorbic acid or less. In this way, an acid that is less preferred by the extractor than ascorbic acid (HX) is added to the solution consisting of said eritorbate salt. Upon contact with the extract, the ascorbic acid is transferred to the extractor and an HX salt is formed. Alternatively, HX is introduced with the extractor. In another preferred embodiment of the case in which said precursor is a salt of ascorbic acid, HX is added through a membrane instead of directly. In this way, said conversion step is carried out in a unit consisting of at least two compartments separated by a cation exchange membrane. At least one compartment contains said ascorbate salt solution and said organic extractor composition, and at least one adjacent compartment contains a HX solution. In the conversion step, the cations of said ascorbate salt are transferred through the membrane to the aqueous HX solution, forming an HX salt therein. To maintain electroneutrality, the protons of the second aqueous HX solution are transferred to the other compartment and are extracted together with the ascorbate anions to form an ascorbic acid containing an organic extractor composition. In a further preferred embodiment of the case in which said precursor is a salt of ascorbic acid, a solution, preferably an aqueous solution of said salt, is contacted with said extracting composition in the presence of CO2, preferably under a pressure of minus 10 atmospheres A conversion takes place, resulting in a carbonate or bicarbonate of the cation of said ascorbate salt in said ascorbic acid containing the organic extractor composition.

In a preferred embodiment, the ascorbic acid precursor present in said stream is a fermentation product. In a further preferred embodiment, the stream is an aqueous solution and in another preferred embodiment, said solution is a fermentation liquid. Said fermentation liquid is preferably treated before the extraction process. Preferably, said pretreatment consists of operations such as removal of the biomass by methods known per se, e.g., centrifugation, filtration and membrane filtration. If desired, the solution is treated by an adsorbent such as an activated carbon, diatomaceous earth or an adsorbent resin. Other pretreatments include ion exchange, solvent extraction, etc. In another preferred embodiment, the aqueous stream is formed in an extracting fermentation. A solution leaving the fermenter is said stream towards the process of the present invention, and said residual aqueous solution is recirculated to the fermentor, as such or after some treatment. In another preferred embodiment, the precursor in said solution exiting the fermenter is adsorbed, preferably on a basic or extracted resin, preferably by a basic extractor. The basic character of these can be relatively high if needed, for an efficient removal of the solution precursor, which is then recirculated to the fermentor, as such or after another treatment. The adsorbed or extracted acid is scavenged, preferably with a solution of a base to form a solution of a precursor, e.g., a solution of an ascorbate salt, which forms the aqueous stream in the present invention, as such or after adjustments. In the main industrial route for the production of ascorbic acid, the glucose is converted into several steps in 2-keto-L-gulonic acid, which is then converted into ascorbic acid (Reichstein and Grussner, Helv. Chim. Acta, 17, 311-328 (1934). In this way, 2-keto-L-gulonic acid forms a precursor for the production of ascorbic acid. In the Richstein and Grussner procedure, L-ascorbic acid is obtained by heating 2-keto-L-gulonic acid in water at 100 ° C or by esterification and treatment with sodium methoxide in methanol, followed by acidification. Yodice, in WO 87/000839, assigned to Lubrizol Corp., suggests a method for producing L-ascorbic acid comprising: forming a substantially anhydrous 2-keto-L-gulonic acid suspension and a surfactant in an organic support layer and reacting said suspension with a substantially anhydrous hydrogen chloride gas acid catalyst at a temperature from about 40 ° C to about 80 ° C for about 5 hours to convert said 2-keto-L-gulonic acid into ascorbic acid. According to the present invention, a stream containing 2-keto-L-gulonic acid, a derivative thereof or a mixture thereof as a precursor, is converted, preferably in the presence of a catalyst, preferably an acid, to form acid ascorbic in said organic phase composition. Said stream could consist of 2- keto-L-gulonic acid, its derivatives (including salts thereof) or a mixture thereof, in solid form or in a solution. Said solution could be an aqueous solution thereof, e.g., of the type formed by fermentation (said solution could be a fermentation liquid, a pre-treated fermentation liquid, etc.) or a solution in an organic medium. Said solution in an organic medium could be formed by contacting said solid or aqueous solution with a suitable organic medium. Preferably, said organic medium is the organic extractor composition specified for the present invention. Thus, in a preferred embodiment, 2-keto-L-gulonic acid or a derivative thereof in solid form or in an aqueous solution is contacted with an organic extractant composition specified for the present invention., to form an extracting composition comprising said acid or derivatives thereof. Said formed composition is converted, preferably in the presence of a catalyst to form ascorbic acid, in said organic phase composition. Said catalyst is preferably a substantially anhydrous acid and can be introduced in the form of a gas, as a highly concentrated aqueous solution and preferably in an organic medium. Said organic medium is preferably said organic extractor composition specified for the present invention. Said preferred organic medium comprising said acid is preferably formed by the introduction of an organic acid or a mineral acid therein by dissolution or by extraction. Water-immiscible acids and acids stronger than ascorbic acid, when used as a catalyst, remain in the organic medium formed after said conversion, during said extraction operation with water. Thus, in a preferred embodiment, an organic extracting composition as defined above comprising a catalyst acid from a previous step, is contacted with a source of 2-keto-L-gulonic acid or a derivative thereof to form said stream of organic medium containing both acid catalyst and 2-keto-L-gulonic acid or a derivative thereof. Preferably, said medium is homogeneous. If necessary, the composition of said formed medium is adjusted, e.g., by the addition or removal of water, the temperature is adjusted and said conversion is carried out. At the end of said conversion, said organic extractor composition containing ascorbic acid is formed and subjected to said extraction operation. Although the invention will now be described in connection with certain preferred embodiments in the following examples so that aspects thereof can be more fully understood and appreciated, it is not desired to limit the invention to these particular embodiments. On the contrary, it is desired to cover all alternatives, modifications and equivalents that may be included within the scope of the invention defined by the appended claims. Thus, the following examples which include preferred embodiments will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purposes of illustrative description of preferred embodiments of the present invention only, and are presented in the The cause of providing what is believed is the most useful and easily understood description of formulation procedures, as well as the principles and conceptual aspects of the invention.

EXAMPLE A laboratory cell is used, which is composed of two compartments of the same volume, separated with a cation exchange membrane type SM-2 (Neosepta). One of the compartments is filled with a solution at 0.1 mol / kg of sodium ascorbate and an extracting composition, in a weight-for-weight ratio of 1: 2. The extractor is composed of 50% of Alamine 336, the tricaprylamine of Henkel, and 50% of 2-butyloctanol. The other compartment is filled with a solution at 0.2 mol / kg of HCl. After stirring the cell for 50 hours, the concentration of ascorbic acid in the organic extractant composition was 0.2 mol / kg, representing > 90% conversion of sodium ascorbate into ascorbic acid in said extractor. Extraction at 80 ° C of an organic extracting composition containing 0.2 ascorbic acid, in countercurrent stages, results in an aqueous solution of ascorbic acid. The concentration of said acid in the resulting solution is almost one mol / kg.

It will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples, and that the present invention can be incorporated into other specific forms without departing from the essential attributes thereof, and that therefore it is desired that the present embodiments and examples be considered in all respects as illustrative and not as restrictive, reference being made to the appended claims, rather than to the foregoing description, and therefore attempts are made to make all changes that are within the meaning and scale of equivalences of the claims are encompassed by them.

Claims (29)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for the recovery of ascorbic acid from a stream containing at least one precursor of ascorbic acid comprising: converting said precursor into at least one product, said at least one product being ascorbic acid in an extractant composition organic, said organic extractor composition comprises (a) at least one secondary or tertiary alkylamine in which the aggregate number of carbon atoms is at least 20, as a primary extractor, and (b) a polar extraction enhancing compound; further characterized in that said extractor composition comprises at least two moles of said polar extraction enhancing compound per one mole of primary extractor; and said organic extractor composition containing ascorbic acid is subjected to an extraction operation with aqueous solution at a temperature at least 20 ° C higher than the temperature at which said conversion is carried out; whereby an aqueous solution of ascorbic acid is obtained in which the concentration of ascorbic acid is more than 5%.

2. A process for the recovery of ascorbic acid according to claim 1, further characterized in that said precursor is a salt of ascorbic acid.

3. - A process for the recovery of ascorbic acid according to claim 2, further characterized in that said salt is selected from the group consisting of an ammonium, alkaline or alkaline earth salt.

4. A process according to claim 2 for the recovery of ascorbic acid from an aqueous feed solution containing at least one salt of ascorbic acid, comprising: converting said salt into at least two components, a first of said components comprises a cation compound of said salt, and a second of said components comprises ascorbic acid in an organic extractor composition comprising (a) at least one secondary or tertiary alkylamine in which the aggregate number of carbon atoms it is at least 20, as a primary extractor, and (b) a polar extraction enhancing compound; further characterized in that said extractor composition comprises at least two moles of said polar extraction enhancing compound per one mole of primary extractor; said organic extractor composition containing ascorbic acid is separated from said residual aqueous solution; and said organic extractor composition containing ascorbic acid is subjected to an extraction operation with aqueous solution at a temperature at least 20 ° C higher than the temperature at which said conversion is carried out; with which an aqueous solution of ascorbic acid is obtained in which the concentration of ascorbic acid is more than 5%.

5. - A method for the recovery of ascorbic acid according to claim 1, further characterized in that said extracting composition comprises at least 3 moles of said extraction enhancing compound per one mole of primary extractor.

6. A method for the recovery of ascorbic acid according to claim 1, further characterized in that said extraction action carries out the back-extraction of at least 80% of the ascorbic acid contained in said organic extractor composition.

7. A process for the recovery of ascorbic acid according to claim 1, further characterized in that after said extraction operation, the remaining organic extractor composition is recirculated.

8. A process for the recovery of ascorbic acid according to claim 7, further characterized in that the additional conversion carried out with said recirculated organic extractor composition provides yields of at least 90%.

9. A process for the recovery of ascorbic acid according to claim 7, further characterized in that the additional conversion carried out with said recirculated organic extractor composition provides yields of at least 95%.

10. A process for the recovery of ascorbic acid according to claim 1, further characterized in that said stream contains at least one precursor at a concentration of less than 1 mol / kg.

11. A process according to claim 1 for the recovery of ascorbic acid from a stream containing at least one precursor of ascorbic acid, comprising converting said precursor into at least one product, said at least one The product is ascorbic acid, in an organic extractor composition, said organic extractor composition comprising: (a) at least one secondary or tertiary alkylamine in which the aggregate number of carbon atoms is at least 20, as a primary extractor, and (b) an organic, polar and sterically hindered extraction enhancing compound having at least 5 carbon atoms, a weaker basic character than said primary extractor, and temperature sensitive extraction improvement properties.; further characterized in that said extractor composition comprises at least two moles of said extraction enhancing compound per one mole of primary extractor; and said organic extractor composition containing ascorbic acid is subjected to an extraction operation with aqueous solution at a temperature at least 20 ° C higher than the temperature at which said conversion is carried out; wherein said extraction enhancing compound improves both the extraction power of said primary extractor composition, and facilitates said temperature sensitive extraction operation; and thereby obtaining an aqueous solution of ascorbic acid in which the concentration of ascorbic acid is more than 5%.

12. A process according to claim 2 for the recovery of ascorbic acid from an aqueous feed solution containing at least one salt of ascorbic acid, comprising: converting said salt into at least two components: i) a compound of the cation of said salt and (ii) ascorbic acid in an organic extractor composition comprising (a) at least one secondary or tertiary alkylamine in which the aggregate number of carbon atoms is at least 20, as a primary extractor, and (b) an organic, polar and sterically hindered extraction enhancing compound having at least 5 carbon atoms, a weaker basic character than said primary extractor, and extraction improving properties sensitive to temperature; wherein said extractor composition comprises at least 2 moles of said extraction enhancing compound per one mole of primary extractor; said organic extractor composition containing ascorbic acid is separated from said residual aqueous solution; and said organic extractor composition containing ascorbic acid is subjected to an extraction operation with aqueous solution at a temperature at least 20 ° C higher than the temperature at which said conversion is carried out; wherein said extraction enhancing compound improves both the extraction power of said primary extractor composition, and facilitates said temperature-sensitive extraction operation, and thereby obtaining an aqueous solution of ascorbic acid in which the concentration of ascorbic acid is of more than 5%.

13. A method according to claim 11, further characterized in that said organic, polar and sterically hindered extraction enhancing compound is selected from the group consisting of alkanols, carboxylic acids, tertiary amines or trialkyl phosphates having a steric hindrance substituent attached to the carbon that carries said polar group, or to a carbon that is alpha, beta or gamma to said carbon.

14. A method according to claim 13, further characterized in that said substituent is an aliphatic group.

15. A process according to claim 11, further characterized in that said extraction enhancing compound is selected from the group consisting of secondary or tertiary alkanols, tris-2-ethylhexylamine and tris-2-ethylhexyl phosphate.

16. A process according to claim 1, further characterized in that said stream containing said at least one precursor of ascorbic acid is obtained by fermentation.

17. A process for the recovery of ascorbic acid according to claim 1, further characterized in that water is used as said aqueous solution in said extraction operation.

18. A method for the recovery of ascorbic acid according to claim 1, further characterized in that erythorbic acid left in said organic extractor after said extraction operation is extracted with an aqueous solution of a base.

19. A process for the recovery of ascorbic acid according to claim 18, further characterized in that said base is selected from a group consisting of hydroxides, bicarbonates and alkali metal carbonates.

20. A method for the recovery of ascorbic acid according to claim 1, further characterized in that said precursor is selected from the group consisting of salts of ascorbic acid, 2-keto-L-gulonic acid in the form of acid and salt , and derivatives thereof.

21. A process for the recovery of ascorbic acid according to claim 2, further characterized in that said compound of said cation of said ascorbate salt is a basic compound selected from a group consisting of hydroxides, bicarbonates and carbonates.

22. A process for the recovery of ascorbic acid according to claim 2, further characterized in that said cation of said ascorbate salt is selected from a group consisting of ammonium, sodium, potassium, magnesium and calcium.

23. A process for the recovery of ascorbic acid according to claim 21, further characterized in that said basic compound is used to extract ascorbic acid from said organic extractor.

24. - A method for the recovery of ascorbic acid according to claim 21, further characterized in that said basic compound is used in the formation of said feed solution.

25. A process for the recovery of erythorbic acid according to claim 1, further characterized in that said feed solution is a fermentation liquid.

26. A method for the recovery of ascorbic acid according to claim 25, further characterized in that said fermentation liquid is pretreated before said extraction step.

27. A method for the recovery of ascorbic acid according to claim 26, further characterized in that said pretreatment is an operation selected from the group consisting of removal of biomass and treatment with an adsorbent, ion exchanger and a solvent or mixtures thereof.

28. A process for the recovery of ascorbic acid according to claim 27, further characterized in that said removal of biomass is carried out by membrane filtration.

29. A process for the recovery of ascorbic acid according to claim 16, further characterized in that said stream containing said at least one ascorbic acid precursor is obtained by extraction fermentation.