GB1575469A

GB1575469A - Recovery of glycine and iminodiacetic acid

Info

Publication number: GB1575469A
Application number: GB13255/77A
Authority: GB
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co
Priority date: 1976-03-29
Filing date: 1977-03-29
Publication date: 1980-09-24
Also published as: IT1075138B; SE7703448L; FR2346317A1; DE2713472A1; NL7703323A; JPS52118421A

Description

(54) RECOVERY OF GLYCINE AND IMINODIACETIC ACID (71) We, W.R. GRACE & CO., a Corporation organised and existing under the laws of the State of Connecticut, United States of America, of 1114 Avenue of the Americas, New York, New York 10036, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particuarly described in and by the following statement: This invention relates to the recovery of glycine and iminodiacetic acid from an aqueous solution containing their sodium salts (sodium glycinate and disodium iminodiacetate).

In the prior art glycine was prepared by: (a) hydrolyzing glycinonitrile which was prepared by the reaction of glycolonitrile and ammonia in an aqueous medium with an aqueous alkaline earth metal hydroxide to form an alkaline earth metal salt of the amino monoacetic acid (glycine); and (b) treating the alkaline earth metal salt with carbon dioxide to form the free amino acid (which remains in solution) and an alkaline earth metal carbonate (which precipitates).

The amino acid (glycine) was then recovered. This method, as applied to the preparation of glycine, is taught by US Patent No. 2,388,189.

It is desirable to replace the alkaline earth metal hydroxide with sodium hydroxide because the latter has a lower equivalent weight than strontium and barium hydroxides, is more soluble than the alkaline earth metal hydroxides, is easier to handle under plant conditions, and the ions of sodium, unlike those of barium, (a preferred alkaline earth metal hydroxide) are not toxic. However, such substitution introduces a complication in the separation and recovery of the amino acid (glycine) because sodium cabonate, unlike the alkaline earth metal carbonates, is readily soluble in water, thereby to render the separation and recovery of pure or substantially pure glycine difficult.

Glycinonitrile where prepared by the reaction of glycolonitrile and ammonia in an aqueous medium generally contains iminodiacetonitrile (IDAN) which is formed as a side product during the reaction whereby glycinonitrile is produced. The ratio of glycinonitrile to IDAN can vary from about 1:0 to 1:0.1 depending on reaction conditions and the relative ratios of the reactants. During hydrolysis of the glycinonitrile with aqueous caustic soda to form sodium glycinate the side product IDAN is also hydrolyzed to form IDANa2 (disodium iminodiacetate). It is undesirable from the economic and environmental standpoints to discard this IDANa2 or the product of reduced sodium content (monpsodium monohydrogen iminodiacetate (IDANaH) formed when sodium glycinate solution containing the IDANa2 is acidified.

Our invention provides a method for separating and recovering such IDANa2 as IDA.

IDA can be prepared by a route originated by Eschweiler (Ann. 1894, 278, 229-239) wherein IDAN is formed by the reaction of HMTA (hexamethylene tetramine) and HCN in an aqueous medium. The IDAN is saponified by reaction with aqeuous barium hydroxide to yield the barium salt of IDA which is converted to free IDA and barium sulfate by reaction with sulfuric acid. The IDA is separated from the by-product barium sulfate and recovered. This particular process has been satisfactory because of low yields, the time required to complete the preparation, the relatively low quality of the IDA produced, the toxicity of soluble barium compounds, and the inconvenience and expense of using barium hydroxide.

Improved processes for preparing IDAN are taught by U.S. Patent No. 3,167,580, U.S.

Patent 3,412,137, and U.S. Patent 3,904,668. According to 3,167,580 the HMTA of Eschweiler is replaced with acid stabilized aqueous formaldehyde and ammonia while according to 3,412,137 Eschweiler's rreactants (HMTA and HCN) are used in aqueous acetic acid. In 3,904,668 HCN, HMTA and glycolonitrile are reacted to form IDAN.

It is desirable to replace Eschweiler's barium hydroxide with sodium hydroxide because the latter is cheaper, has a lower equivalent weight, is more soluble, is easier to handle under plant conditions, and sodium ions, unlike barium ions, are not toxic. However, such substitution introduces a complication in the separation and recovery of the IDA product because, unlike Eschweiler's soluble barium sulfate by-product, sodium sulfate (the by-product obtained where Eschweiler's barium hydroxide is replaced with sodium hydroxide) is readily soluble, thereby to render the separation and recovery of pure or substantially pure IDA difficult.

IDAN prepared by the above-mentioned methods generally contains glycinonitrile as a side product with the ratio of IDAN to glycinonitrile varying from about 1:0 to 1:1 depending on reaction conditions and relative ratios of the reactants. During hydrolysis of the IDAN with aqueous caustic soda to form IDANa2 the side product glycinonitrile is also hydrolyzed to form sodium glycinate which is then present in the IDANa2 product. It is undesirable from the economic and environmental standpoints to discard this sodium glycinate or the product (glycine sulfate or glycine hydrochloride) formed when the IDANa2 containing the sodium glycinate contaminant is acidified to about pH 2-2.8 with sulfuric acid or hydrochloric acid to form IDA.

Our invention provides a method for recovering such sodium glycinate as glycine.

The ratio of IDAN to glycinonitrile obtained in such methods can as is well known, be varied over wide ranges by controlling the ratios of reactants and reactive contitions.

A process for preparing both IDA and glycine via the IDAN/glycinonitrile route from an admixture comprising both IDAN and glycinonitrile in ratios of IDAN to glycinonitrile of about 1:0.01 or 1:1.0 is now a reality because of the instant invention which provides a method for preparing, separating, and recovering IDA and glycine from the admixture of IDANa2 and sodium glycinate obtained by hydrolyzing such admixture of IDAN and glycinonitrile.

Solid components (glycine, IDA, sodium sulfate, or sodium chloride, respectively), of the respective slurries formed in the process of our invention can be separated from the respective mother liquors comprising said slurries by filtration, centrifugation, or decantation.

Thus our invention starts with an aqueous solution containing sodim glycinate (sodium aminomonoacetate) and sodium iminodiacetate; the formation of such a solution is an inherently desirable modification of the prior art but is of no use unless one can recover the glycine and IDA in economic amounts. The method of solving this problem provided by the present invention consists of three stages.

In the first stage, the starting solution is acidified to convert the sodium salts to compounds having no sodium content or less sodium content than the starting salts, by addition of a mineral acid which is sulfuric acid or hydrochloric acid; at pH 4.5 to 8.5 the sodium glycinate is converted to glycine and the sodium salt of the mineral acid (sodium sulfate or sodium chloride, according to the acid used), and the disodium iminodiacetate is converted to monosodium monohydrogen iminodiacetate (IDAHNa) and the sodium salt of the mineral acid. The acidification in the first stage may be more aggressive, to a pH in the range 2 to 2.8, and this converts the amino acid salts to glycine sulfate or glycine hydrochloride, and iminodiacetic acid, together with the sodium salt of the mineral acid.

Some of the acid for acidification may be provided by the mother liquor which is recycled, as described below.

In the second stage of the process there are three distinct recovery steps, for precipitation and separation of, respectively, the sodium salt of the mineral acid, the glycine and the iminodiacetic acid; these three recovery steps can be in any order. For recovery of the sodium sulfate or sodium chloride, water is evaporated until a desired amount of the sodium salt has precipitated.

For recovery of the iminodiacetic acid, the pH is lowered by acidification to 2 to 2.8 (this may have been done as the first stage of the process, and if it has not been done then it must be done in the second stage), so that the IDA is precipitated and then the precipitate is removed.

For recovery of the glycine, the solution containing it is cooled at a pH of 4.5 to 8.5 so that glycine is precipitated for removal; if the IDA is removed (at pH 2 to 2.8) before recovery of glycine, then the pH of the mother liquor left after removal of IDA must be raised by addition of alkali to 4.5 to 8.5, and addition of alkali in this way can be sufficient to precipitate glycine even without cooling.

At above pH 4 IDANa2 is converted to IDAHNa which is more soluble than glycine but at about pH 2 IDAHNa is converted to IDA which is less soluble than glycine.

In the third stage of the process, the mother liquor left after removal of the mineral acid sodium salts, the precipitated glycine and the precipitated IDA is recycled to the first stage.

Thus the process of this invention can be worked in a number of different sequences, and seven preferred sequences are summarised in the following table.

TABLE - POSSIBLE SEQUENCES IN STAGE TWO First Separation Second Separation Third Separation Embodiment Product Method Product Method Product Method A Na2SO4 evapor- Glycine cool IDA precipitate or ate at pH 2-2.8 NaCl B Na2SO4 evapor- IDA cool Glycine precipitate or ate at pH 4.5 NaCl C IDA precip- Na2SO4 evapor- Glycine cool itate at or ate pH 2-2.8 NaCl D IDA precip- Glycine precip- Na2SO4 evaporate itate at itate at or pH 2-2.8 pH 4.5 NaCI E Glycine cool Na2SO4 evapor- IDA precipitate or ate at pH 2-2.8 NaCl F Glycine cool IDA precip- Na2SO4 evaporate itate at or pH 2-2.8 NaCl G Na2SO4 evapor- IDA precip- Glycine precipitate or ate itate at at pH 4.5 NaCl pH 2-2.8 These various embodiments will now be described in further detail.

Embodiment A of this invention is directed to a process for: (A) preparing glycine, iminodiacetic acid, and sodium sulfate or sodium chloride from a first aqueous system comprising sodium glycinate and disodium iminodiacetate; and (B) separating such glycine, iminodiacetic acid, and sodium sulfate or sodium chloride, said process comprising:: (a) adjusting the pH of the first aqueous system to 4.5-8.5 with sulfuric acid or hydrochloric acid to form a second aqueous system comprising NaaSO4 or NaCI, glycine, and monosodium monohydrogen iminodiacetate; (b) evaporating water from the second aqueous system'to form a first slurry comprising precipitated Na2SO4 or NaCI and a first mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; (c) separating the precipitated Na2SO4 or NaCl from the first mother liquor at a temperature effective for such separation;; (d) cooling the separated first mother liquor to a temperature effective for precipitating glycine to form a second slurry comprising the precipitated glycine and a second mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine and dissolved monosodium monohydrogen iminodiacetate; (e) separating the precipitated glycine from the second mother liquor at a temperature effective for such separation; (f) adjusting the pH of the separated second mother liquor to about 2-2.8 to precipitate iminodiacetic acid and to form a third mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine sulfate or glycine hydrochloride, and dissolved iminodiacetic acid (g) separating the precipitated iminodiacetic acid from the third mother liquor at a temperature effective for such separation; and (h) recyling at least a portion of the separated third mother liquor to the first aqueous system or to step "(a)".

In the preferred forms of this embodiment A: 1. After the separated third mother liquor (or a portion (e.g., about 90-98% (or 60-90%) thereof)) has been recycled to step "(a)" its (the third mother liquor's) excess sulfuric acid or hydrochloric acid (including that present as glycine sulfate or glycine hydrochloride) is utilized after the recycle along with such amount of H2SO4 (or HC1) as may be required to adjust the pH of the first aqueous system to 4.5-8.5.

2. Where the sodium glycinate content of the first aqueous system is less than about 20-45%, water can be evaporated from the first aqueous system to reduce the water content thereof and to form a "concentrated" first aqueous system having a sodium glycinate content of about 20-45%. The resulting concentrated first aqueous system can be sent forward to step "(a)".Alternatively: (a) water can be evaporated after adjusting the pH to about 4.5-8.5 in step "(a)" of said embodiment A to form a "concentrated" second aqueous system which can be sent forward to step "(b)" of said embodiment A or (b) all of the evaporation (where processing a first aqueous system having such low sodium glycinate content (i.e., a sodium glycinate content of less than about 10-20%)) can be conducted in step (b) of said embodiment A where the evaporation of water can be continued until the dissolved glycine content of the resulting first slurry is about 15-30%.

In another preferred embodiment ("Embodiment B") this invention is directed to a process for: (A) preparing glycine, iminodiacetic acid, and sodium sulfate or sodium chloride from a first aqueous system comprising sodium glycinate and disodium iminodiacetate; and (B) separating such glycine, iminodiacetic acid, and sodium sulfate or sodium chloride, said process comprising:: (a) adjusting the pH of the first aqueous system to about 2-2.8 with sulfuric acid or hydrochloric acid to form a second aqueous system comprising Na2SO4 or NaCl, glycine sulfate or glycine hydrochloride, and iminodiacetic acid; (b) evaporating water from the second aqueous system to form a first slurry comprising precipitated Na2SO4 or NaC1 and a first mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine sulfate or glycine hydrochloride, and iminodiacetic acid; (c) separating the precipitated Na2SO4 or NaCI from the first mother liquor at a temperature effective for such separation;; (d) cooling the separated first mother liquor to a temperature effective for precipitating iminodiacetic acid to form a second slurry comprising the precipitated iminodiacetic acid and a second mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine sulfate or glycine hydrochloride, and dissolved iminodiacetic acid; (e) separating the precipitated iminodiacetic acid from the second mother liquor at a temperature effective for such separation; (f) adjusting the pH of the separated second mother liquor to about 4.5-8.5 to precipitate glycine and to form a third mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; (g) separating the precipitated glycine acid from the third mother liquor at a temperature effective for such separation; and (h) recycling at least a portion of the separated third mother liquor to the first aqueous system or to step "(a)".

In preferred forms of the Embodiment B: 1. 90 to 98% of the third mother liquor is recycled to step "(a)" of said Embodiment.

2. Where the disodium iminodiacetate content of the first aqueous system is less than, about 15-25%, water can be evaporated from the first aqueous system to reduce the water content thereof and to form a "concentrated" first aqueous system having a disodium iminodiacetate content of about 15-25%. The resulting concentrated first aaqueous system can be sent forward to step "(a)" of said Embodiment B.Alternatively: (a) water can be evaporated after adjusting the pH to about 2-2.8 in step "(a)" of said Embodiment to form a "concentrated" second aqueous system which can be sent forward to step "(b)" of said Embodiment B; or (b) all of the evaporation (where processing a first aqueous system having such low disodium iminodiacetate content (i.e., an iminodiacetate content of less than about 25%)) can be conducted in step (b) of said Embodiment B where the evaporation of water can be continued until the dissolved iminodiacetic acid content of the resulting first slurry is about 20%.

In another preferred embodiment ("Embodiment C") this invention is directed to a process for: (A) preparing glycine, iminodiacetic acid, and sodium sulfate or sodium chloride from a first aqueous system comprising sodium glycinate and disodium iminodiacetate; and (B) separating such glycine, iminodiacetic acid, and sodium sulfate or sodium chloride, said process comprising:: (a) adjusting the pH of the first aqueous system to about 2-2.8 with sulfuric acid or hydrochloric acid to form a first slurry comprising precipitated iminodiacetic acid and a first mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine sulfate or glycine hydrochloride, and dissolved iminodiacetic acid; (b) separating the precipitated iminodiacetic acid from the first mother liquor at a temperature effective for such separation (c) adjusting the pH of the first mother liquor to 4.5-8.5 and evaporating water therefrom to form a second slurry comprising precipitated Na2SO4 or NaCl and a second mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved monosodium monohydrogen iminodiacetate, and dissolved glycine; (d) separating the precipitated Na2SO4 or NaCl from the second mother liquor at a temperature effective for such separation;; (e) cooling the second mother liquor to a temperature effective for precipitating glycine to form a third slurry comprising precipitated glycine and a third mother liquor comprising water, dissolved monosodium monohydrogen iminodiacetate, dissolved Na2SO4 or NaCl, and dissolved glycine; (f) separating the precipitating glycine from the third mother liquor at a temperature effective for such separation; and (g) recycling at least a portion of the separated third mother liquor to the first aqueous system or to step "(a)".

In especially preferred embodiments of this invention as recited in Embodiment C, supra: 1. 90-98% of the separated third mother liquor is recycled to step "(a)" of Embodiment C.

2. Where the disodium iminodiacetate content of the first aqueous system is less than about 15-25%, water can be evaporated from the first aqueous system to reduce the water content thereof and form a "concentrated" first aqueous system having a disodium iminodiacetate content of about 15-25%. The resulting concentrated first aqueous system can then be sent forward to step "(a)" of said Embodiment C.Alternatively: (a) water can be evaporated after adjusting the pH to about 2-2.8 in step "(a)" of said Embodiment B to form a "concentrated" second aqueous system which can be sent forward to step "(b)" of said Embodiment C; or (b) all of the evaporation (where processing a first aqueous system having such a low disodium iminodiacetate content (i.e., a disodium iminodiacetate content of less than 25%)) can be conducted in step (b) of said Embodiment B where the evaporation of water can be continued until the dissolved iminodiacetic acid content of the resulting first slurry is about 20-30%.

In another preferred embodiment ("Embodiment D") this invention is directed to a process for . (A) preparing glycine, iminodiacetic acid, and sodium sulfate or sodium chloride from a first aqueous system comprising sodium glycinate and disodium iminodiacetate; and (B( separating such glycine, iminodiacetic acid, and sodium sulfate or sodium chloride, said process comprising:: (a) adjusting the pH of the first aqueous system to about 2-2.8 with sulfuric acid or hydrochloric acid to form a first slurry comprising precipitated iminodiacetic acid and a first mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine sulfate or glycine hydrochloride, and dissolved iminodiacetic acid; (b) separating the precipitated iminodiacetic acid from the first mother liquor at a temperature effective for such separation; (c) forming a second slurry comprising precipitated glycine and a second mother liquor comprising water, dissolved monosodium monohydrogen iminodiacetate, dissolved Na2SO4 or NaCl, and dissolved glycine by adjusting the pH of the separated first mother liquor to 4.5-8.5 e.g. with sodium hydroxide at a temperature effective for forming such slurry; and (d) separating the precipitated glycine from the second mother liquor at a temperature effective for such separation; (e) evaporating water from the second separated mother liquor to form a third slurry comprising precipitated Na2SO4 or NaCI and a first mother liquor comprising water, dissolved na2SO4 or NaCl, dissolved monosodium monohydrogen iminodiacetate, and dissolved glycine; (f) separating the precipitated Na2SO4 or NaC1 from the third mother liquor at a temperature effective for such separation; (g) recycling at least a portion of the separated third mother liquor to the first aqueous system or to step "(a)".

In other embodiments of this invention as recited in Embodiment D, supra: 1. A portion, 90-98% or 60-90%, of the separated third mother liquor is recycled to step "(a)" of Embodiment D.

2. Where the disodium iminodiacetate content of the first aqueous system is less than about 25%, water can be evaporated from the first aqueous system to reduce the water content thereof and to form a "concentrated" first aqueous system having a disodium iminodiacetate content of about 15-25%. The resulting concentrated first aqueous system can then be sent forward to step "(a)" of said Embodiment D. Alternatively the water can be evaporated after adjusting the pH to about 2-2.8 in step "(a)" of said Embodiment D to form a "concentrated" second aqueous system which can be sent forward to step "(b)" of said Embodiment D.

In another preferred embodiment ("Embodiment E") this invention is directed to a process for: (A) preparing glycine, iminodiacetic acid, and sodium sulfate or sodium chloride from a first aqueous system comprising sodium glycinate and disodium iminodiacetate; and (B) separating such glycine, iminodiacetic acid, and sodium sulfate or sodium chloride, said process comprising:: (a) adjusting the pH of the first aqueous system to about 4.5-8.5 with sulfuric acid or hydrochloric acid to form a second aqueous system comprising glycine, monosodium monohydrogen iminodiacetate, and Na2SO4 or Nail; (b) cooling the second aqueous system to a temperature effective for precipitating glycine to form a first slurry comprising precipitated glycine and a first mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine and dissolved monosodium monohydrogen iminodiacetate if the second aqueous system is not already at such temperature ; (c) separating the precipitated glycine from the first mother liquor at a temperature effective for such separation;; (d) evaporating water from the separated second mother liquor to form a second slurry comprising precipitated Na2SO4 or NaCI and a second mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; (e) separating the precipitated Na2SO4 or NaC1 from the second mother liquor at a temperature effective for such separation; (f) adjusting the pH of the separated second mother liquor to about 2-2.8 to precipitate iminodiacetic acid and to form a third mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine sulfate or glycine hydrochloride, and dissolved iminodiacetic acid; and (g) separating the precipitated iminodiacetic acid from the third mother liquor at a temperature effective for such separation; and (h) recycling at least a portion of the separated third mother liquor to the first aqueous system or to step "(a)".

In a preferred form of this Embodiment, the sodium glycinate content of the first aqueous system is less than a value in the range 20-45%, water can be evaporated from the first aqueous system to reduce the water content thereof and to form a "concentrated" first aqueous system having a sodium glycinate content in the range 20-45%. The resulting concentrated first aqueous system can be sent forward to step "(a)" of said Embodiment E.

Alternatively: (a) water can be evaporated after adjusting the pH to about 4.5-8.5 in step "(a)" of said Embodiment E to form a "concentrated" second aqueous system which can be sent forward to step "(b)" of said Embodiment E; or all of the evaporation (where processing a first aqueous system having such low sodium glycinate content (i.e., a sodium glycinate content of less than about 20%)) can be conducted in step (b) of said Embodiment E where the evaporation of water can be continued until the glycine content of the resulting first slurry is about 15-30%.

In another preferred embodiment ("Embodiment F') this invention is directed to a process for: (A) preparing glycine, iminodiacetic acid, and sodium sulfate or sodium chloride from a first aqueous system comprising sodium glycinate and disodium iminodiacetate; and (B) separating such glycine, iminodiacetic acid, and sodium sulfate or sodium chloride, said process comprising:: (a) adjusting the pH of the first aqueous system to 4.5-8.5 with sulfuric acid or hydrochloric acid to form a second aqueous system comprising glycine, monosodium monohydrogen iminodiacetate, and Na2SO4 or Nail; (b) cooling the second aqueous system to a temperature effective for precipitating glycine to form a second slurry comprising the precipitated glycine and a first mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine and dissolved monosodium monohydrogen iminodiacetate if the second aqueous system is not already at such temperature; (c) separating the precipitated glycine from the first mother liquor at a temperature effective for such separation; ; (d) adjusting the pH of the separated first mother liquor to about 2-2.8 to precipitate iminodiacetic acid and to form a second mother liquor comprising water, dissolved Na2SO4 or Nail, dissolved glycine sulfate or glycine hydrochloride, and dissolved iminodiacetic acid; (e) separating the precipitated iminodiacetic acid from the second mother liquor at a temperature effective for such separation; (f) evaporating water from the separated second mother liquor to form a third slurry comprising precipitated Na2SO4 or NaC1 and a third mother liquor comprising water, dissolved Na2SO4 or Nail, dissolved glycine, and dissolved iminodiacetic acid; (g) separating the precipitated Na2SO4 or NaC1 from the first mother liquor at a temperature effective for such separation; and (h) recycling at least a portion of the separated third mother liquor to the first aqueous system or to step "(a)", supra.

In preferred forms of Embodiment F, where the sodium glycinate content of the first aqueous system is less than about 45%, water can be evaporated from the first aqueous system to reduce the water content thereof and to form a "concentrated" first aqueous system having a sodium glycinate content of about 20-45%. The resulting concentrated first aqueous system can be sent forward to step "(a)" of said embodiment F. Alternatively, water can be evaporated after adjusting the pH to about 4.5-8.5 in step "(a)" of said Embodiment F to form a "concentrated" second aqueous system which can be sent forward to step "(b)" of said Embodiment F.

In another preferred embodiment ("Embodiment G") this invention is directed to a process for: (A) preparing glycine, iminodiacetic acid, and sodium sulfate or sodium chloride from a first aqueous system comprising sodium glycinate and disodium iminodiacetate; and (B) separating such glycine, iminodiacetic acid, and sodium sulfate or sodium chloride, said process comprising:: (a) adjusting the pH of the first aqueous system to about 4.5-8.5 with sulfuric acid or hydrochloric acid to form a second aqueous system comprising Na2SO4 or NaCl, glycine, and monosodium monohydrogen iminodiacetate; (b) evaporating water from the second aqueous system to form a first slurry comprising precipitated Na2SO4 or NaCl and a first mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; (c) separating the precipitated Na2SO4 or NaCI from the first mother liquor at a temperature effective for such separation;; (d) adjusting the pH of the first mother liquor to about 2-2.8 and cooling to a temperature. effective for precipitating iminodiacetic acid to form a second slurry comprising the precipitated iminodiacetic acid and a second mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine sulfate or glycine hydrochloride, and dissolved iminodiacetic acid; (e) separating the precipitated iminodiacetic acid from the second mother liquor at a temperature effective for such separation; (f) adjusting the pH of the separated second mother liquor to about 4.5-8.5 to precipitate glycine and to form a third mother liquor comprising water, dissolved Na2SO4 or Nail, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; (g) separating the precipitated glycine from the third mother liquor at a temperature effective for such separation; and (h) recycling at least a portion of the separated third mother liquor to the first aqueous system or to step "(a)".

The process of the invention then, comprises (a) preparing glycine, iminodiacetic acid, and sodium sulfate or sodium chloride from a first aqueous system comprising sodium glycinate and disodium iminodiacetate; and (b) separating and recovering such glycine, iminodiacetic acid, and sodium sulfate or sodium chloride. This is done according to the sequence of steps recited above.

The product glycine and the product IDA obtained may be contaminated with sodium sulfate or sodium chloride. In such event the separated contaminated (crude) glycine and/or the separated contaminated (crude) IDA can be purified by recrystallizing from water or by washing with water, preferably water saturated with glycine or IDA, respectively. Where the contaminant is sodium chloride, cold wash water (e.g., water at about 3-20"C or 5-10"C) can be used. Where the contaminant is sodium sulfate such wash water should have a temperature of about 33"C or higher (e.g., 34-45"C or 35-40"C).

The separated (or separated and recrystallized or separated and washed) glycine and IDA can be dried (preferably at about 60-100 C or 100-130"C). Vacuum drying can be used with excellent results.

The separated sodium sulfate or sodium chloride can also be dried (preferably at 33-100"C or 100-140"C). Vacuum drying can be used.

We prefer to crystallize and separate sodium sulfate in the process of this invention at a temperature above about 80 "C. We especially prefer to crystallize and separate sodium sulfate or sodium chloride at 90-100 c; however other temperatures both higher and lower are operable.

We prefer to crystallize and separate glycine and IDA in the process of our invention at temperatures below 40 "C, preferably below 25 "C. Where separating precipitated (crystallized) glycine or IDA from a mother liquor containing more than about 5 % of dissolved sodium sulfate we prefer to operate at a temperature of about 33-45"C or 35-40"C. Where the mother liquor is substantially free of sodium sulfate but contains appreciable amounts of sodium chloride (but is not saturated with sodium chloride at about 5-45"C) we prefer to separate precipitated (crystallized) glycine or IDA from mother liquor at about 5-45"C or 20-30"C.

Where water is evaporated in our process to bring about the precipitation (crystallization) of sodium sulfate or sodium chloride, such evaporation can be conducted at a temperature at which glycine and/or IDA will also cyrstallize, provided that separation of the sodium sulfate or sodium chloride from the mother liquor in which it (the Na2SO4 or NaCl was precipitated) is conducted at a temperature such that substantially all of the glycine and/or IDA present in the system will be dissolved in said mother liquor.

Adjustments of pH which are made to precipitate (crystallize) glycine or IDA can be made at a temperature so high that glycine or IDA will not precipitate, provided that the step wherein glycine or IDA is separated from a mother liquor is made at a temperature such that a substantial quantity of the glycine or IDA present in the system will be present as solid (crystalline) glycine or IDA.

The embodiments set forth above recite first aqueous systems containing sodium glycinate and IDANa2 in such ratios (e.g., preferably mole ratios of glycine to IDA in the range 1: 4 to 1:0.8) that both glycine and IDA will be separated in the respective separation steps of the first pass of such first aqueous system through the process.

Where working with a first aqueous system containing a major amount of sodium glycinate and a minor amount of IDANa2, or vice versa, (i.e., a first aqueous system having a mole ratio of sodium glycinate to IDANa2 such that glycine or IDA but not both will be separated on the first (or second, or third, etc.) pass or (cycle)) a number of cycles must be run before the concentration of the minor component will be built up to the point at which the acid corresponding to the minor component (i.e., glycine where sodium glycinate is the minor component and IDA where IDANa2 is the minor component) will precipitate.

Alternatively, the steps (pH adjustment and/or temperature adjustment) which cause the acid corresponding to the minor component to precipitate can be omitted through several cycles until the recycled liquor contains a sufficient quantity of the minor component (or the acid corresponding thereto) to insure precipitation of such acid when the system is submitted to the pH and/or temperature adjustments designed to cause the acid corresponding to the minor component to precipitate.

In another alternative embodiment the minor component of the acid corresponding to the minor component can be added to the first aqueous system in an amount sufficient to cause the acid corresponding to the minor component to precipitate in the first cycle of the process. Alternatively, an amount of the minor component (or the acid corresponding thereto) sufficient to cause precipitation of the minor component in the first cycle can be added when (or just before) adjusting the pH or temperature in the first cycle to a range effective for precipitating the acid corresponding to the minor component in the first cycle.

Precipitated (crystallized) sodium sulfate or sodium chloride, glycine, and IDA can be separated from the respective mother liquors from which they crystallize by filtration, decantation, or centrifugation. We generally prefer to use centrifugation.

A quantity of the first aqueous system can be used (in place of or admixed with sodium hydroxide) to increase the pH of a system having a pH of about 2.2-2.8.

The instant invention will be better understood by referring to the following specific but nonlimiting examples and procedures. It is understood that said invention is not limited by these examples and procedures which are offered merely as illustrations; it is also understood that modifications can be made without departing from the invention.

The examples were actually run.

The procedures, while not actually run, will illustrate certain embodiments of our invention.

Example 1 A mixture containing 16.1% disodium iminodiacetate and 6.8% sodium glycinate was prepared by mixing 10.00 kg of a technical 20% disodium iminodiacetate solution and 2.39 kg of a technical 35% sodium glycinate solution.

To 4000 g of this solution was added 623 g of concentrated H 2SO4 to adjust the pH to 2.3.

1026 g of water was evaporated from this solution. The resulting concentrated first solution was cooled to 35"C and stirred for 1 1/2 hours, thereby forming a first slurry comprising precipitated IDA and a first mother liquor. This slurry was centrifuged. The separated IDA was washed with water and dried at 500C. 233 g of dry solid containing 100% IDA was recovered. 3230 g of the first mother liquor was adjusted to pH 6.0 by the addition of 203 g of 50% NaOH to form a second solution. 1428 g of water was evaporated from this second solution to form a second slurry comprising precipitated Na2SO4 and a second mother liquor.This second slurry was centrifuged at a temperature above 80"C and the separated Na2SO4 was washed with water and dried at 50"C. 560 g of dry Na2SO4 and 1284 g of second mother liquor were recovered.

The second mother liquor was cooled to 350C and stirred at 350C overnight, but no crystallization occurred. The pH of this liquor was then adjusted to 2.3 by the addition of 155 g of concentrated H2SO4 to form a third solution. This solution was evaporated to remove 47 g of water and then cooled to 35"C to form a third slurry comprising precipitated IDA and a third mother liquor. After stirring for 1 1/2 hours at 350C this third slurry was centrifuged. The separated IDA was washed with about 5 ml of water and dried at 500C.

172 g of crude (ca. 66%) IDA and 1651 g of third mother liquor were recovered.

The pH of the third mother liquor was increased to 6.0 by the addition of 171 g of 50% NaOH to form a fourth solution. This solution was evaporated to remove 427 g of water to form a fourth slurry comprising precipitated Na2SO4 and a fourth mother liquor. This fourth slurry was centrifuged at a temperature above 80"C. and the separated Na2SO4 was washed with water and dried at 50 C. 232 g of dry Na2SO4 and 650 g of fourth mother liquor were recovered.

The fourth mother liquor was cooled to 35"C. and stirred at 35"C. overnight. A fourth slurry comprising precipitated glycine and a fourth mother liquor was formed. This slurry was centrifuged and the separated glycine was washed with water and dried at 500C. 123 g of crude (ca. 79%) glycine and 335 g of fourth mother liquor were recovered.

The two IDA crops and the glycine crop were analyzed by gas chromatography. The IDA crops contained less than 1% glycine, and the glycine contained less than 1% IDA. The fourth mother liquor is recycled to initial mixture containing IDANa2 (disodium iminodiacetate) and AMANa (sodium aminomonoacetate) when the process is used commercially.

Example 2 A mixture containing 19.7% sodium glycinate and 8.7% disodium iminodiacetate was prepared by mixing 5.00 kg of technical 35% sodium glycinate and 3.87 kg of technical 20% disodium iminodiacetate.

To 4000 g of this solution was added 617 g of concentrated H2SO4 to pH 6.0. The resulting first solution was evaporated to remove 1818 g of water and to form a first slurry comprising precipitated Na2SO4 and a first mother liquor. This slurry was centrifuged at 80"C. The separated Na2SO4 was washed with water and dried at 500C. 647 g of dry Na2SO4 and 1837 g of first mother liquor were recovered.

The first mother liquor was cooled to 350C and stirred at 350C for 1 1/2 hours to form a second slurry comprising precipitated glycine and a second mother liquor. This second slurry was centrifuged and the separated glycine was washed with water and dried at 50"C.

322 g of 85% glycine was recovered.

The second mother liquor was acidified to pH 2.3 by the addition of 266 g of concentrated H2SO4 and cooled to 35"C. A third slurry comprising a mixture of precipitated Na2SO4 and IDA and a third mother liquor was formed. This slurry was stirred at 35"C for about 2 hours and then centrifuged. The separated solid was washed with about 5 ml of water and dried at 50"C. The recovered dry solid weighed 388 g and contained 46% IDA.

The glycine and IDA crops were analyzed by gas chromatography. The IDA contained less than 1% glycine and the glycine contained less than 1% IDA.

The third mother liquor is recycled to initial mixture of IDANa2 (disodium iminodiacetate) and ADANa (sodium aminodiacetate) when the process is used commercially.

PROCEDURE 1 A mixture of 1.0 kg mole of 30% aqueous hexamethylenetetramine and 1.0 kg mole of 44% aqueous formaldehyde can be reacted with 7 kg moles of hydrogen cyanide by the process of our co-pending Patent Application No. 37231/76 (Serial No. 1561144) which teaches the preparation of IDAN by the reaction of HMTA, formaldehyde, and HCN in an aqueous system. The resulting solution will contain a mixture of iminodiacetonitrile and glycinonitrile in a mole ratio of about 3:1. This solution can be added to 7.2 kg moles of 30% NaOH at a temperature above 50"C. When the addition is complete, the solution can be boiled until ammonia free and the total weight of the resulting ammonia free solution can be adjusted to 2390 kg.This solution will contain about 20% disodium iminodiacetate and about 4% sodium glycinate; said solution can be designated "Product from Procedure 1" or "Solution from Procedure 1".

PROCEDURE 2 One kg mole of aqueous 60% glycolonitrile can be added to 2.5 kg moles of aqueous 28% ammonia in a stirred pressure vessel at a temperature of 60-80"C.

and held at this temperature for 30 minutes, thereby producing 247 kg of solution containing about 22% glycinonitrile. This solution can be added to 1.02 kg moles of 30% NaOH at a temperature above 50"C. and then boiled until ammonia free and the weight of the resulting ammonia free solution can be adjusted to 280 kg. This solution will contain about 30% sodium glycinate and 7.6% disodium iminodiacetate; said solution can be designated "Product from Procedure 2" or "Solution from Procedure 2".

PROCEDURE 3 Run No. 1: To a 2 kg portion of the product of Procedure 1 can be added sufficient sulfuric acid to reduce the pH to 2.3; the temperature of the resulting acidified system can be adjusted to a temperature above 80"C, and the concentration thereof can be adjusted as required (e.g., by evaporating water therefrom or by adding water thereto) to produce a first solution which is nearly saturated. The first solution can be cooled to 35"C to form a first slurry comprising precipitated IDA and a first mother liquor. The precipitated IDA can be separated from the first mother liquor by centrifuging at 35"C. The separated IDA can be recovered.The separated first mother liquor can be concentrated by evaporating water therefrom to form a second slurry comprising precipitated Na2SO4 and a second mother liquor. The precipitated Na2SO4 can be recovered. Ninety-five percent of the separated second mother liquor can be combined with a fresh 2 kg portion of solution form Procedure 1 and the above recited steps can be repeated.

The above sequence of steps can be repeated one or more times, thereby permitting the concentration of glycine to increase to a level sufficiently high to permit separation of glycine in a subsequent (e.g., 4th) cycle by the method in Run No. 2, of this Procedure, infra.

Run No. 2: The pH of the separated first mother liquor from the last cycle (e.g., 4th cycle) of Run No. 1, supra, can be increased to 6 by adding sodium hydroxide thereto to cause about 40% of the contained glycine to precipitate. The resulting third slurry comprising the precipitated glycine and a third mother liquor can be stirred for 2 hours at 35"C and centrifuged at 35"C to separate the precipitated glycine from the third mother liquor. The separated glycine can be recovered. The separated third mother liquor can be concentrated by evaporating water therefrom to form a fourth slurry comprising precipitated sodium sulfate and a fourth mother liquor.The precipitated Na2SO4 can be separated from the fourth mother liquor by centrifuging at a temperature above 80"C. The separated sodium sulfate can be recovered.

Run No. 3: Ninety-five percent of the separated fourth mother liquor from Run No. 2 of this procedure (Procedure 3) ~ or separated fourth mother liquor obtained from a later recited step of this run (Run No. 3 of Procedure 3)~~ can be combined with a fresh 2 kg portion of solution from Procedure 1 and the pH of the resulting mixture can be adjusted to 2.3 with sulfuric acid. The temperature of the resulting acidified system can be adjusted to a temperature above 80 C, and the concentration thereof can be adjusted as required (e.g., by evaporating water therefrom or by adding water thereto) to provide a first solution which is nearly saturated. The first solution can be cooled to 350C to form a first slurry comprising precipitated IDA and a first mother liquor.The precipitated IDA can be separated from the first mother liquor by centrifuging at 350C. The separated IDA can be recovered. The separated first mother liquor can be concentrated by evaporating water therefrom to form a second slurry comprising precipitated Na2SO4 and a second mother liquor. The precipitated Na2SO4 can be separated from the second mother liquor by centrifuging at a temperature above 80"C. The separated Na2SO4 can be recovered. The pH of the separated first mother liquor can be increased to 6 by adding sodium hydroxide thereto to cause about 40% of the contained glycine to precipitate.The resulting third slurry comprising the precipitated glycine and a third mother liquor can be stirred for 2 hours at 35"C and centrifuged a 35"C to separate the precipitated glycine from the third mother liquor. The separated glycine can be recovered. The separated third mother liquor can be concentrated by evaporating water therefrom to form a fourth slurry comprising precipitated sodium sulfate and a fourth mother liquor. The precipitated Na2SO4 can be separated from the fourth mother liquor by centrifuging at a temperature above 80"C. The separated sodium sulfate can be recovered, and, as stated supra, ninety-five percent of the separated fourth mother liquor can be combined with a fresh 2 kg portion of solution from Procedure 1 and the above-recited method (i.e., the method recited in Run No. 3 of Procedure 3) can be repeated.

PROCEDURE 4 Run No. 1: This run can be conducted in a manner identical with that used in Run No. 1 of Procedure 3.

Run No. 2: The second mother liquor from the last cycle (e.g., 4th cycle) of Run No. 1, supra, can be combined with a fresh 2000 g portion of the product of Procedure 1 and a third slurry of precipitated IDA and a third mother liquor can be formed by the general method of Run No. 1, supra, in which the first slurry is formed. The precipitated IDA may be separated from the third mother liquor by centrifuging. The pH of this third mother liquor can be increased to 6 by adding sodium hydroxide thereto. Water can be evaporated from the resulting system to produce a fourth slurry comprising precipitated sodium sulfate and a fourth mother liquor. Said fourth slurry can be centrifuged to separate the precipitated sodium sulfate from the fourth mother liquor.This mother liquor can be cooled to 35 to form a fifth slurry comprising precipitated glycine and a fifth mother liquor.

Glycine can be separated from the fifth slurry by centrifuging and then recovered.

Run No. 3.: The general method of Run No. 2 of this procedure (i.e., Procedure 4) can then be repeated over an indefinite number of cycles wherein ninety-five percent of the separated fifth mother liquor can be combined with a fresh 2 kg portion of product from Procedure 1 and the above recited steps of Run No. 2 of this procedure (i.e., Procedure 4) can be repeated.

PROCEDURE 5 Run No. 1: To a 2 kg portion of the product of Procedure 1 can be added sufficient sulfuric acid to reduce the pH to 6. This system can be concentrated by evaporating sufficient water therefrom to cause about 40-50% of the contained sodium sulfate to precipitate, and to form a first slurry comprising the precipitated sodium sulfate and a first mother liquor. The precipitated sodium sulfate can be separated from the first mother liquor by centrifuging. The pH of the first mother liquor can be reduced to 2.3 by the addition of sulfuric acid. The temperature can be adjusted to 35"C., to cause IDA to precipitate and to form a second slurry comprising the precipitated IDA and a second mother liquor. After stirring for about 2 hours the precipitated IDA can be separated from the second mother liquor by centrifuging and recovered.Ninety-five percent of the separated mother liquor can be combined with a fresh 2 kg portion of solution from Procedure 1 and the above recited steps can be repeated.

The above sequence of steps can be repeated one or more times, to cause the concentration of glycine to increase to a level sufficiently high to permit separation of glycine in a subsequent (e.g., 4th) cycle by the method in Run No. 2, of this Procedure (i.e., Procedure 5), infra.

Run No. 2: The pH of the separated second mother liquor from the last cycle (e.g., 4th cycle) of Run No. 1; supra, can be increased to 6 by adding sodium hydroxide thereto to cause about 40% of the contained glycine to precipitate. The resulting third slurry comprising the precipitated glycine and a third mother liquor can be stirred for 2 hours at 35"C and centrifuged at 350C to separate the precipitated glycine from the third mother liquor. The separated glycine can be recovered.

Run No. 3: The general method of Run No. 2 of this Procedure (i.e., Procedure 5) can be repeated over an indefinite number of cycles wherein, in each such cycle, ninety-five percent of the separated third mother liquor can be combined with a fresh 2 kg portion of solution from Procedure 1 and the above recited steps of Run No. 2 can be repeated.

PROCEDURE 6 The general method of Procedure 5 can be carried out except that the pH of the first slurry of Runs No. 1, 2, and 3 can be adjusted to 2.3 rather than being maintained at 6 as in Run No. 1 of Procedure 5, supra. Where using this modification of the method recited in Procedure 5, the pH of the separated first mother liquor will be 2.3 at the time of separation. Accordingly~ unlike the method recited in Procedure 5~~no further adjustment of the pH of said mother liquor will be required in the method of this Procedure (i.e., Procedure 6). Alternatively, sufficient sulfuric acid can be added to a 2 kg portion of the product from Procedure 1 to reduce the pH to 2.3 rather than to 6; this will cause the first slurry to have a pH of 2.3 rather than 6.

PROCEDURE 7 Run No. 1: To a 2 kg portion of the product of Procedure 2 can be added sufficient sulfuric acid to reduce the pH to 6. This resulting system can be evaporated to cause about 50% of the contained sodium sulfate to precipitate and form a first slurry comprising the precipitated sodium sulfate and a first mother liquor. The sodium sulfate can be separated and recovered by centrifuging the first slurry at a temperature above 80"C. The separated first mother liquor can be cooled to 350C and stirred for 2 hours to form a second slurry comprising precipitated glycine and a second mother liquor. The glycine can be separated and recovered by centrifuging the second slurry. Ninety-five percent of the separated second mother liquor can be combined with a 2 kg portion of fresh product from Procedure No. 2 and the above recited steps can be repeated.

The above sequence of steps can be repeated one or more times, thereby permitting theconcentration of IDANaH to increase to a level sufficiently high to permit separation of IDA in a subsequent (e.g., 4th) cycle by the methods of Run No. 2, of this Procedure (Procedure 7), infra.

Run No. 2: In the next (e.g., 4th) cycle, the first slurry, second slurry, and second mother liquor can be formed by the general method of Run No. 1 of this Procedure.

The pH of the second mother liquor of this cycle (e.g., 4th cycle) can be adjusted to 2.3 by the addition of sulfuric acid. The resulting third slurry, comprising precipitated IDA and a third mother liquor, can be cooled to 35"C and stirred at 350C for 2 hours and then centrifuged to separate the precipitated IDA from the third mother liquor. The separated IDA can be recovered.

Run No. 3: The general procedure of Run No. 2 of this procedure (i.e., Procedure 7) can be repeated over an indefinite number of cycles wherein 95% of the third mother liquor can be combined with a 2 kg portion of the product of Procedure 2 and the general method of Run -No. 2 repeated.

PROCEDURE 8 Run No. 1: To a 2 kg portion of the product of Procedure 2 can be added sufficient sulfuric acid to reduce the pH to 6; the temperature of the resulting acidified system can- be adjusted to a temperature above 80 , and the concentration thereof can be adjusted as required (e.g., by evaporation of water therefrom or the addition of water thereto) to produce a first solution which is nearly saturated. The first solution can be cooled to 35"C to form a first slurry comprising precipitated glycine and a first mother liquor. The precipitated glycine can be separated from the first mother liquor by centrifuging at 35"C.

The separated glycine can be recovered. The separated first mother liquor can be concentrated by evaporating water therefrom to form a second slurry comprising precipitated Na2SO4 and a second mother liquor. The precipitated Na2SO4 can be separated from the second mother liquor by centrifuging at a temperature above 80"C. The separated Na2SO4 can be recovered. Ninety-five percent of the separated second mother liquor can be combined with a fresh 2 kg portion of solution from Procedure 2 and the above recited steps can be repeated.

The above sequence of steps can be repeated one or more times, to permit the concentration of monosodium monohydrogen iminodiacetate to increase to a level sufficiently high to permit separation of IDA in a subsequent (e.g., 4th) cycle by the method in Run No. 2 of this Procedure (Procedure 8), infra.

Run No. 2: In the next (e.g., 4th) cycle of Run No. 1 of said Procedure 8, the first slurry, second slurry and separated second mother liquor can be formed. The pH of the separated second mother liquor can be decreased to 2.3 by adding H2SO4 thereto to cause about 40% of the contained IDA to precipitate. The resulting third slurry, comprising the precipitated IDA and a third mother liquor, can be stirred for 2 hours at 350C and centrifuged at 35"C to separate the precipitated IDA from the third mother liquor.

Run No. 3: The general method of Run No. 2 of this Procedure (i.e., Procedure 8) can then be repeated over an indefinite number of cycles wherein, in each cycle, 95% of the third mother liquor can be combined with 2 kg of product of Procedure 2 and the method of Run No. 2 repeated.

PROCEDURE 9 Run No. 1: To a 2 kg portion of the product of Procedure 2 can be added sufficient H2SO4 to reduce the pH to 6. The temperature of the resulting acidified system can be reduced to 35"C and the resulting first slurry, comprising precipitated glycine (about 40-50% of the total contained glycine being precipitated) and a first mother liquor, can be stirred for 2 hours. The first slurry can be centrifuged to separate the precipitated glycine from the first mother liquor. The separated glycine can be recovered. Water can be evaporated from the separated first mother liquor to form a second slurry comprising precipitated Na2SO4 and a second mother liquor. The precipitated Na2SO4 can be separated from the second mother liquor by centrifuging at a temperature above 80"C. The separated Na2SO4 can be recovered. Ninety-five percent of the separated second mother liquor can be combined with a fresh 2 kg portion of solution from Procedure 2 and the above recited steps can be repeated.

The above sequence of steps can be repeated one or more times, thereby permitting the concentration of monosodium monohydrogen iminodiacetate to increase to a level sufficiently high to permit separation of IDA in a subsequent (e.g., 4th) cycle by the method in Run No. 2, of this Procedure (Procedure 9), infra.

Run No. 2: In the next (e.g., 4th) cycle, a first mother liquor can be formed by the method of Run No. 1 of this Procedure. Sulfuric acid can be added to this first mother liquor to decrease the pH to 2.3, thereby forming a third slurry comprising precipitated IDA and a third mother liquor. After stirring for 2 hours, the third slurry can be centrifuged. The separated IDA can be recovered. Water can be evaporated from the separated third mother liquor, thereby forming a fourth slurry comprising precipitated Na2SO4 and a fourth mother liquor. The precipitated Na2SO4 can be separated from the fourth mother liquor by centifuging the fourth slurry. The Na2SO4 can be recovered.

Run No. 3: The general method of Run No. 2 of this Procedure (i.e., Procedure 9) can then be repeated over an indefinite number of cycles wherein 95% of the separated fourth mother liquor can be combined with a 2 kg portion of product from Procedure 2 and the above recited steps of Run No. 2 of this Procedure (i.e., Procedure 9) can be repeated indefinitely.

WHAT WE CLAIM IS: 1. A process for recovering the amino acids glycine and iminodiacetic acid from an aqueous solution containing sodium glycinate and disodium iminodiacetate, which comprises: (1) acidifying the aqueous solution with sulphuric acid or hydrochloric acid, thereby converting the sodium salts of the amino acids to compounds having no sodium content or having lower sodium content than the starting salts, and forming the sodium salt of the sulphuric or hydrochloric acid used for acidification, (2) then, in any desired sequence (a) evaporating water from the solution to precipitate the sodium sulphate or sodium chloride, and recovering said sodium sulphate or chloride, (b) separately recovering precipitated iminodiacetic acid from the solution, the precipitation of iminodiacetic acid being effected by acidification to a pH of 2-2.8 either as step (1) of the process or subsequently, (c) separately recovering precipitated glycine, the precipitation of glycine being effected at pH 4.5 to 8.5 by cooling the solution or, when it follows precipitation of iminodiacetic acid at pH 2-2.8, by increasing the pH to 4.5-8.5, and then (3) recycling the mother liquor after the sodium salts, iminodiacetonitrile and glycine have been precipitated and recovered, to step (1) together with fresh starting solution.

2. A process according to claim 1, in which in step (1) the solution is acidified to a pH of 4.5 to 8.5 thereby forming a second aqueous system comprising (i) sodium sulphate or sodium chloride, (ii) glycine and (iii) monosodium monohydrogen iminodiacetate.

3. A process according to claim 1, in which in step (1) the solution is acidified to a pH of 2 to 2.8 thereby forming a second aqueous system comprising (a) sodium sulphate or sodium chloride, (b) glycine sulphate or glycine hydrochloride and (c) iminodiacetic acid.

4. A process according to claim 2, which comprises (a) acidifying the solution with sulphuric acid or hydrochloric acid, (b) evaporating water from the second aqueous system to form a first slurry comprising precipitated Na2SO4 or NaCl and a first mother liquor comprising water, dissolved Na2SO4 or Nail, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; (c) separating the precipitated Na2SO4 or NaCl from the first mother liquor at a temperature effective for such separation; (d) cooling the separated first mother liquor to a temperature effective for precipitating glycine to form a second slurry comprising the precipitated glycine and a second mother liquor comprising water, dissolved Na2SO4 or Nail, dissolved glycine and dissolved monosodium monohydrogen iminodiacetate;; (e) separating the precipitated glycine from the second mother liquor at a temperature effective for such separation; (f) adjusting the pH of the separated second mother liquor to 2-2.8 to precipitate iminodiacetic acid and to form a third mother liquor comprising water, dissolved NaaSO4 or NaCl, dissolved glycine sulphate or glycine hydrochloride, and dissolved iminodiacetic acid; and (g) separating the precipitated iminodiacetic acid from the third mother liquor at a temperature effective for such separation.

5. A process according to claim 2, in which step (2) comprises (b) cooling the second aqueous system to a temperature effective for precipitating glycine to form a first slurry comprising precipitated glycine and a first mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine and dissolved monosodium

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. concentration of monosodium monohydrogen iminodiacetate to increase to a level sufficiently high to permit separation of IDA in a subsequent (e.g., 4th) cycle by the method in Run No. 2, of this Procedure (Procedure 9), infra. Run No. 2: In the next (e.g., 4th) cycle, a first mother liquor can be formed by the method of Run No. 1 of this Procedure. Sulfuric acid can be added to this first mother liquor to decrease the pH to 2.3, thereby forming a third slurry comprising precipitated IDA and a third mother liquor. After stirring for 2 hours, the third slurry can be centrifuged. The separated IDA can be recovered. Water can be evaporated from the separated third mother liquor, thereby forming a fourth slurry comprising precipitated Na2SO4 and a fourth mother liquor. The precipitated Na2SO4 can be separated from the fourth mother liquor by centifuging the fourth slurry. The Na2SO4 can be recovered. Run No. 3: The general method of Run No. 2 of this Procedure (i.e., Procedure 9) can then be repeated over an indefinite number of cycles wherein 95% of the separated fourth mother liquor can be combined with a 2 kg portion of product from Procedure 2 and the above recited steps of Run No. 2 of this Procedure (i.e., Procedure 9) can be repeated indefinitely. WHAT WE CLAIM IS:

1. A process for recovering the amino acids glycine and iminodiacetic acid from an aqueous solution containing sodium glycinate and disodium iminodiacetate, which comprises: (1) acidifying the aqueous solution with sulphuric acid or hydrochloric acid, thereby converting the sodium salts of the amino acids to compounds having no sodium content or having lower sodium content than the starting salts, and forming the sodium salt of the sulphuric or hydrochloric acid used for acidification, (2) then, in any desired sequence (a) evaporating water from the solution to precipitate the sodium sulphate or sodium chloride, and recovering said sodium sulphate or chloride, (b) separately recovering precipitated iminodiacetic acid from the solution, the precipitation of iminodiacetic acid being effected by acidification to a pH of 2-2.8 either as step (1) of the process or subsequently, (c) separately recovering precipitated glycine, the precipitation of glycine being effected at pH 4.5 to 8.5 by cooling the solution or, when it follows precipitation of iminodiacetic acid at pH 2-2.8, by increasing the pH to 4.5-8.5, and then (3) recycling the mother liquor after the sodium salts, iminodiacetonitrile and glycine have been precipitated and recovered, to step (1) together with fresh starting solution.

monohydrogen iminodiacetate if the second aqueous system is not already at such temperature; (c) separating the precipitated glycine from the first mother liquor at a temperature effective for such separation; (d) evaporating water from the separated second mother liquor to form a second slurry comprising precipitated Na2SO4 or NaCl and a second mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; (e) separating the precipitated Na2SO4 or NaCl from the second mother liquor at a temperature effective for such separation; (f) adjusting the pH of the separated second mother liquor to 2-2.8 to precipitate iminodiacetic acid and to form a third mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine sulphate or glycine hydrochloride, and dissolved iminodiacetic acid; and (g) separating the precipitated iminodiacetic acid from the third mother liquor at a temperature effective for such separation.

6. A process according to claim 2, in which step (2) comprises: (b) cooling the second aqueous system to a temperature effective for precipitating glycine to form a second slurry comprising the precipitated glycine and a first mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine and dissolved monosodium monohydrogen iminodiacetate if the second aqueous system is not already at such temperature; (c) separating the precipitated glycine from the first mother liquor at a temperature effective for such separation; (d) adjusting the pH of the separated first mother liquor to 2-2.8 to precipitate iminodiacetic acid and to form a second mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine sulphate or glycine hydrochloride, and dissolved iminodiacetic acid;; (e) separating the precipitated iminodiacetic acid from the second mother liquor at a temperature effective for such separation; (f) evaporating water from the separated second mother liquor to form a third slurry comprising precipitated Na2SO4 or NaCl and a third mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine, and dissolved iminodiacetic acid; and (g) separating the precipitated Na2SO4 or NaCl from the first mother liquor at a temperature effective for such separation.

7. A process according to claim 2, in which step (2) comprises: (b) evaporating water from the second aqueous system to form a first slurry comprising precipitated Na2SO4 or NaCI and a first mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; (c) separating the precipitated Na2SO4 or NaCl from the first mother liquor at a temperature effective for such separation;; (d) adjusting the pH of the first mother liquor to 2-2.8 and cooling to a temperature effective for precipitating iminodiacetic acid to form a second slurry comprising the precipitated iminodiacetic acid and a second mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine sulphate or glycine hydrochloride, and dissolved iminodiacetic acid (e) separating the precipitated iminodiacetic acid from the second mother liquor at a temperature effective for such separation; (f) adjusting the pH of the separated second mother liquor to 4.5-8.5 to precipitate glycine and to form a third mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; and (g) separating the precipitated glycine from the third mother liquor at a temperature effective for such separation.

8. A process according to claim 3, in which step (2) comprises: (b) evaporating water from the second aqueous system to form a first slurry comprising precipitated Na2SO4 or NaCl and a first mother liquor comprising water, dissolved Na2SO4 or NaCI, dissolved glycine sulphate or glycine hydrochloride, and iminodiacetic acid; (c) separating the precipitated Na2SO4 or NaCI from the first mother liquor at a temperature effective for such separation; (d) cooling the separated first mother liquor to a temperature effective for precipitating iminodiacetic acid to form a second slurry comprising the precipitated iminodiacetic acid and a second mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine sulphate or glycine hydrochloride, and dissolved iminodiacetic acid; ; (e) separating the precipitated iminodiacetic acid from the second mother liquor at a temperature effective for such separation; (f) adjusting the pH of the separated second mother liquor to 4.5-8.5 to precipitate glycine and to form a third mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved glycine, and dissolved monosodium monohydrogen iminodiacetate; and (g) separating the precipitated glycine acid from the third mother liquor at a temperature effective for such separation.

9. A process according to claim 3, in which the acidification causes the iminodiacetic acid to precipitate and step (2) comprises (b) separating the precipitated iminodiacetic acid from the first mother liquor at a temPerature effective for such separation; (c) adjusting the pH of the first mother liquor to 4.5-8.5 and evaporating water therefrom to form a second slurry comprising precipitated Na2SO4 or NaCl and a second mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved monosodium monohydrogen iminodiacetate, and dissolved glycine; (d) separating the precipitated Na2SO4 or NaCl from the second mother liquor at a temperature effective for such separation;; (e) cooling the second mother liquor to a temperature effective for precipitating glycine to form a third slurry comprising precipitated glycine and a third mother liquor comprising water, dissolved monosodium monohydrogen iminodiacete, dissolved Na2SO4 or Nail, and dissolved glycine; and (f) separating the precipitated glycine from the third mother liquor at a temperature effective for such separation.

10. A process according to claim 3, in which the acidification causes the iminodiacetic acid to precipitate and step (2) comprises: (b) separating the precipitated iminodiacetic acid from the first mother liquor at a temperature effective for such separation; (c) forming a second slurry comprising precipitated glycine and a second mother liquor comprising water, dissolved monosodium monohydrogen iminodiacetate, dissolved Na2SO4 or NaCl, and dissolved glycine by adjusting the pH of the separated first mother liquor to 4.5-8.5 e.g. with sodium hydroxide at a temperature effective for forming such slurry; (d) separating the precipitated glycineXfrom the second mother liquor at a temperature effective for such separation;; (e) evaporating water from the second separated mother liquor to form a third slurry comprising precipitated Na2SO4 or NaCl and a first mother liquor comprising water, dissolved Na2SO4 or NaCl, dissolved monosodium monohydrogen iminodiacetate, and dissolved glycine; and (f) separating the precipitated Na2SO4 or NaCI from the third mother liquor at a temperature effective for such separation.

11. A process for preparing glycine, which comprises reacting glycolonitrile and ammonia in aqueous medium to form a solution of glycinonitrile contaminated with aminodiacetonitrile, and reacting said solution with sodium hydroxide to hydrolyse the glycinonitrile thereby forming an aqueous solution containing sodium glycinate and disodium iminodiacetate, and then recovering glycine and iminodiacetic acid therefrom by a method claimed in any preceding claim.