Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Utility Patent
1999-08-09
2001-01-02
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S316000, C564S394000, C564S438000
Utility Patent
active
06169187
ABSTRACT:
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 feed solution containing at least one precursor of ascorbic acid, wherein the term precursor of ascorbic acid as used herein is intended to denote compounds that can be converted to ascorbic acid in only a few process steps, as described hereinafter, e.g., compounds selected from the group consisting of salts of ascorbic acid, 2-keto-L-gulonic acid in acid and salt form and derivatives thereof.
As described, e.g., in Kirk-Othmer's
Encyclopedia of Chemical Technology
, Third Edition, ascorbic acid (L-ascorbic acid, L-xylo-ascorbic acid, L-threo-hex-2-enonic acid g-lactone) is the name recognized by the IUPAC-IUB Commission on Biochemical Nomenclature for vitamin C. The name implies the vitamin's antiscorbutic properties, namely, the prevention and treatment of scurvy. L-ascorbic acid is widely distributed in plants and animals. The pure vitamin (C
6
H
8
O
6
, mol. wt. 176.13) is a white crystalline substance derived from L-gulonic acid, a sugar acid, and synthesized both biologically and chemically from D-glucose.
Although natural and synthetic vitamin C are chemically and biologically identical, in recent years a limited amount of commercial isolation from vegetable sources, e.g., rose hips, persimmon, citrus fruit, etc., has been carried out to meet the preference of some persons for vitamin C from natural sources. L-ascorbic acid was the first vitamin to be produced in commercial quantities, and manufacture is based on the well-known Reichstein and Grussner synthesis, which involves the steps of hydrogenation of D-glucose to D-sorbitol; fermentation (oxidation) to L-sorbose; acetonation to bis-isopropylidene-&agr;-L-sorbofuranose; oxidation to bis-isopropylidene-2-oxo-L-gulonic acid, and hydrolysis, rearrangement and purification to L-ascorbic acid.
A fermentation of a carbohydrate to ascorbic acid or to a precursor thereof would be very attractive, saving on operations and on expensive reagents, in addition to its being derived from a natural fermentation process, as opposed to a synthesis involving chemical steps. There are indications that such fermentation route to ascorbic acid is feasible. Yet fermentative industrial production of ascorbic acid faces two major difficulties: (a) the product concentration in the fermentation medium is low; and (b) said product is at least partially a precursor of ascorbic acid rather than the ascorbic acid in its free acid form.
Conversion of said precursor to ascorbic acid and purifying the ascorbic acid by conventional methods without introduction of energy as a driving force would result in a purified product of concentrations similar to those in the feed. Due to its high solubility in water, the cost of ascorbic acid crystallization by water evaporation would be prohibitive. The presence of 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) separation of the precursor, particularly if an ascorbic salt, is more difficult than separation of the acid as separation methods available for salts are usually less selective and of lower yields. Thus, recovery of ascorbic acid from a feed solution comprising a precursor thereof is at present difficult, particularly when the overall precursor concentration in said feed is low. Such feed could result from various sources, such as fermentation to ascorbic acid or to a precursor thereof or from other production process. Those could also be a result of removing ascorbic acid from a feed consisting initially of the acid and its precursor.
Several methods were proposed for combining purification of carboxylic acids with their concentration. In the case of citric acid, it is achieved by the addition of lime to crystallize calcium citrate, which has very low solubility in water. This salt is separated, washed and acidulated with sulfuric acid. Purified and concentrated citric acid is obtained. This method is not applicable for ascorbic acid, as its alkali and alkali earth salts are highly soluble.
A process was proposed in which carboxylic acids were extracted and then displaced from the extractant by a solution of concentrated mineral acids. Both liquid (long chain amines) and solid (resins carrying amine groups) anion exchangers could be considered for this purpose. The purity of the displaced carboxylic acid depends on the preference of the extractant to the mineral acid. Such a process might be applicable for ascorbic acid separation and concentration, provided that the extractant is strong enough to reach high extraction yield, that it shows high preference to the displacing acid, and that the ascorbic acid is stable at the high acidity of the displacing solution.
The regeneration of the anion exchanger would require neutralization by a base. Using HCl as the displacing acid and distilling it of the extractant was proposed, but the high temperatures required and the extractant's decomposition at these conditions are prohibitive. If the anion exchanger is represented by B, the ascorbic acid in the feed solution and in the pure form are AA
F
and AA
P
, respectively, the displacing acid is HCl, and the neutralizing base is NaOH, the equations of the process stages and of the overall reaction are as follows:
B
+
AA
F
=
B
AA
B
AA
+
HCl
=
B
HCl
+
AA
P
B
HCl
+
NaOH
=
B
+
NaCl
+
H
2
O
AA
F
+
HCl
+
NaOH
=
AA
P
+
NaCl
+
H
2
O
&AutoRightMatch;
Reagents are consumed, and a by-product salt of no (or negative) value is produced.
Many methods were suggested for the conversion of anions of salts into the acid form. An example for such conversion method is contacting said aqueous solution containing said salt with a water immiscible cation exchanger in its acid form, which cation exchanger could be in solid form, e.g. a resin, or liquid, e.g. a water immiscible organic acid. On such contact cations from said aqueous solution are adsorbed on or extracted into the said water immiscible cation exchanger and protons are transferred into said aqueous solution where they combine with the anions to form the free acid. The cations carrying cation exchanger is then regenerated with an acid, which results in consumption of more than one mole of said regenerating acid per mole of acid to be converted and formation of more than one mole of an undesired salt.
Preferably, said conversion is effected in a method that does not consume acids and bases as reagents and does not reject salts into the environment. Such methods, also termed salt splitting, convert the salt into the corresponding acid and a basic compound of the cation. Such basic compound is typically hydroxides, bicarbonates and carbonates. 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 separated thereby from impurities present in the feed solution. The acid could be distilled out, if volatile, extracted into a water immiscible extractant or bound to a basic solid adsorbent. The basic compound of the cation could be crystallized out, if of low enough solubility or bound to an adsorbent. The two products could also end up 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 product acid or the product basic compound of the cation are in contact with the feed solution and thereby the two products could react back to the salt. Thus, in order to effect the conversion, at least one of the products needs to be continuously removed. An attractive solution could be extraction of the acid as it forms, or extraction of the anion of the acid and the protons formed on this conversion into an extractant and formation of the product acid therein (based on the availab
Desai Rita
Rotman Alan L.
Williams Morgan & Amerson P.C.
Yissum Research Development Company of the Hebrew University of
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