Recovery of IDA and glauber's salt from waste crystal liquors

Abstract: The separation and recovery of iminodiacetic acid and sodium sulfate decahydrate from sodium sulfate solutions such as the liquor generated in the production of iminodiacetic acid are disclosed. The separation is accomplished by adjusting the temperature of the sodium sulfate solutions to crystallize the iminodiacetic acid and sodium sulfate decahydrate. Nitrilotriacetic acid optionally can be isolated prior to the crystallization of the IDA and sodium sulfate decahydrate.

Description: This invention relates to the recovery of iminodiacetic acid and Glauber's Salt (Na₂SO₄·10H₂O) from sodium sulfate solutions such as the liquor generated in the process of producing iminodiacetic acid. Typical prior art processes for the recovery of iminodiacetic acid from sodium sulfate solutions are disclosed in U.S. Patents 3,808,269 and 4,299,978. U.S. Patent No. 3,808,269, the disclosure of which is herein incorporated by reference, discloses a process of recovering iminodiacetic acid (IDA) from a starting aqueous solution of sodium sulfate and the amino acid having a temperature above about 33°C and containing at least 5% amino acid. The process comprises adjusting the pH of the starting solution to 1.5-3 to form an IDA precipitate and a first mother liquor; separating the IDA precipitate from the first mother liquor; and recovering the separated IDA. Sodium sulfate can then be precipitated from the first mother liquor by adjusting the temperature so as to prevent precipitation of IDA.. U.S. Patent No. 4,299,978, the disclosure of which is herein incorporated by reference, discloses a process for separating an "iminodiacetic acid component" from an aqueous glycine solution including IDA. The process comprises adding sulfuric acid in the presence of a sodium salt to the aqueous solution so as to lower the pH to 1.5 or less, whereby an "iminodiacetic acid component" is crystallized from the solution, and separating the precipitated IDA component. Glycine can thus be efficiently recovered with minimal levels of IDA. Glauber's salt is not generated. The foregoing references use processes where the precipitation of sodium sulfate with the amino acid is avoided. These processes generated waste liquor streams which include a substantial amount of product. Streams such as this have heretofore been discarded. Other approaches to the recovery of amino acids include U.S. Patent No. 3,510,575 where glycine is separated from NH₄Cl, and U.S. Patent No. 4,691,054 where amino acids are isolated by ion exchange from systems that are substantially free of inorganic ions (such as sodium sulfate). The problems of the prior art have been overcome by the present invention which provides a process for separating IDA and Glauber's Salt from amino carboxylate containing solutions such as the waste liquors generated from the production of IDA. It is therefore an object of the present invention to provide a process to minimize generation of waste from the production of IDA. It is a further object of the present invention to provide a process for the recovery of value from the waste generated from the production of IDA. It is still a further object of the present invention to provide a process which reduces disposal costs in the production of IDA. According to the present invention, these and other objects which will become more apparent, are accomplished by providing a process for separating IDA and sodium sulfate decahydrate from an aqueous solution comprising IDA and sodium sulfate, which comprises: a. forming a slurry which is a solid mixture of IDA and sodium sulfate decahydrate and a mother liquor by, for example, adjusting the temperature of the aqueous solution to a level sufficient to crystallize the IDA and Glauber's Salt; and b. separating the solid mixture from the mother liquor. The mixed crystals can be recycled to a point in the IDA production process. Nitrilotriacetic acid (NTA) optionally can be isolated prior to crystallizing the IDA and Glauber's Salt. The process of preparing IDA from the corresponding nitrile can be accomplished according to the following sequence of reactions: HN(CH₂CN)₂ + 2H₂O +2NaOH → HN(CH₂COONa)₂ + 2NH₃ HN(CH₂COONa)₂ + H₂SO₄ → HN(CH₂COOH)₂ + Na₂SO₄ Much of the amino acid now sent to waste in the IDA purge liquor from IDA production processes can be recovered, and optionally recycled, in the process of the present invention. This can be accomplished either batchwise or in a continuous process by forming a slurry comprising precipitated IDA and sodium sulfate decahydrate, and mother liquor. In one embodiment of the batch process, aqueous solutions containing IDA and sodium sulfate, such as waste liquor and recycled liquor produced in the process for the production of IDA, are charged to a cooling crystallizer, eg at a temperature of about 40°C. The mixture is cooled, eg at a rate of about 5.8°C/hr, to a temperature effective for precipitating the amino acid and Glauber's Salt, eg about 5°C. IDA seed crystals can be added, for example at about the saturation temperature of IDA in the solution. Glauber's Salt seed crystals can be added, for example at about the saturation temperature of sodium sulfate decahydrate in the solution. The solid, which is a mixed wet cake comprising IDA and Glauber's Salt, is separated from the mother liquor by, for example, centrifugation. The solid can be recycled to an earlier point in the production process. A portion of the mother liquor (eg, 50%) can be recycled to the crystallizer, to reduce the slurry density, for example. In a second embodiment of the batch process, NTA is isolated prior to the cooling crystallization of IDA and sodium sulfate decahydrate. The process comprises: a. forming a first slurry consisting essentially of precipitated nitrilotriacetic acid and a first mother liquor; b. separating the precipitated nitrilotriacetic acid from the first mother liquor; c. forming a second slurry consisting essentially of precipitated iminodiacetic acid and sodium sulfate decahydrate and a second mother liquor; and d. separating the precipitated iminodiacetic acid and sodium sulfate decahydrate from the second mother liquor. The first slurry may be formed by adjusting the pH of the aqueous solution to a pH effective to precipitate NTA therefrom, eg by lowering the pH of the solution from about 2.6 to about 2.1 with, for example, sulfuric acid, to decrease the solubility of NTA. NTA seed crystals can be added to stimulate NTA crystallization. A typical starting solution obtained from the production process of IDA has a composition of about 2.9% NTA, 6.3% IDA and 22.6% Na₂SO₄ by weight. The saturation temperature of NTA in such a solution after acidification to about pH 2.1 is greater than 40°C. Sodium sulfate decahydrate precipitates from the mother liquor after NTA separation and after neutralization with, for example, sodium hydroxide back to about the pH of the starting aqueous solution, eg a pH of about 2.6, at a temperature of about 27°C. The mother liquor can be cooled to a temperature of about 5°C. In another embodiment, a continuous crystallization can be used. Thus the present invention provides a process for the continuous separation of iminodiacetic acid and sodium sulfate decahydrate from an aqueous solution comprising iminodiacetic acid and sodium sulfate, which process comprises: a. preparing a slurry of iminodiacetic acid, sodium sulfate decahydrate and liquor at about the temperature specified in step c; b. feeding said slurry into a crystallizer; c. feeding said aqueous solution comprising iminodiacetic acid and sodium sulfate into said slurry while cooling to maintain the temperature at a level effective for precipitating iminodiacetic acid and sodium sulfate decahydrate; and d. withdrawing said slurry and separating iminodiacetic acid and sodium sulfate decahydrate therefrom. A slurry of IDA, Glauber's Salt and liquor is prepared at the operating temperature (eg, about 5°C). Fresh waste liquor is fed into the stirring slurry while cooling to maintain the operating temperature. The preferred residence time of the solution in the crystallizer is about 2 hours. Both the IDA and Glauber's Salt crystallize since the crystallizer operates at a temperature below the saturation temperature of both. Slurry is constantly withdrawn and subjected to separation. A portion of the liquor can be returned to the crystallizer. The aqueous solution in step c may be fed into the slurry in the crystallizer, or at a point prior to where the slurry enters the crystallizer. Separation is preferably accomplished by centrifugation, although other forms of separation such as filtration or decantation could be used. Suitable centrifuges include the traditional vertical perforated bowl centrifuge, which provides excellent separation of entrained liquor. A speed setting corresponding to a centrifugal force of about 500g-1000g can be used, with a force of 900-1000g being most preferable. In the IDA production process, wash water can be used to wash the cake generated in the IDA production step free of sodium sulfate. However, this wash causes some of the IDA in the cake to redissolve. Further, this water dilutes the liquor. By excluding the wash water, this redissolution and dilution are minimized. The temperature at which the IDA and Glauber's Salt are precipitated is a function of the concentration of the amino acid and the sodium sulfate in the solution. The typical waste purge stream from the process for the production of IDA has a composition of about 6% IDA and about 23% sodium sulfate by weight. The preferred temperature to which such a solution should be cooled is about 5°C. Those skilled in the art will be able to determine the necessary temperature to which the particular stream must be cooled to precipitate IDA and Glauber's Salt. Separation of precipitate can be carried out at more than one temperature during the cooling, to maintain a workable slurry density. for example. The resulting liquor can be recycled to the crystallizer. An IDA stream having the aforementioned composition precipitates because of the decreased solubility at about 5°C as compared to its solubility in the starting solution having a temperature of about 40°C. Simultaneously, solvent (i.e., water) is being removed as Na₂SO₄ crystallizes as Na₂SO₄·10H₂O. Because this water becomes part of the solids in the slurry, the slurry density becomes high. In the continuous system, the slurry density can be adjusted appropriately by continuously recycling saturated 5°C mother liquor back to the crystallizer. The recovered solid, which is a mixture of IDA, Glauber's salt and some entrained liquor, can be recycled to the mix tank that contains the feed to a Na₂SO₄ crystallizer in the IDA production process. Water is added to the solid to create a pumpable stream. In another embodiment the present invention provides a process for recovering iminodiacetic acid from an aqueous solution consisting essentially of sodium sulfate, iminodiacetic acid, and water, said solution having a temperature above 33°C and comprising at least about 5% iminodiacetic acid by weight, wherein said process comprises: a. forming a first slurry consisting essentially of a first crop of precipitated iminodiacetic acid and a first mother liquor by adjusting the pH of the starting solution to 1.5-3; b. separating the first crop of precipitated iminodiacetic acid from the first mother liquor and recovering the separated iminodiacetic acid; c. forming a second slurry at a temperature effective for preventing the precipitation of iminodiacetic acid therefrom and consisting essentially of precipitated sodium sulfate and a second mother liquor analysing at least 5% dissolved iminodiacetic acid by evaporating water from the first mother liquor; d. separating the precipitated sodium sulfate from the second mother liquor while maintaining the second slurry and the second mother liquor at a temperature effective for preventing iminodiacetic acid from precipitating therefrom; e. forming a third slurry consisting essentially of a second crop of precipitated iminodiacetic acid and a third mother liquor by cooling the second mother liquor to 33-40°C; f. separating the second crop of precipitated iminodiacetic acid from the third mother liquor and recovering the separated iminodiacetic acid, g. cooling said third mother liquor to a temperature effective for precipitating iminodiacetic acid and sodium sulfate decahydrate to form a fourth slurry, the fourth slurry comprising a mixture of precipitated iminodiacetic acid and sodium sulfate decahydrate and a fourth mother liquor; and h. separating the precipitated iminodiacetic acid and sodium sulfate decahydrate from the fourth mother liquor; optionally comprising the further step of recycling at least a portion of the fourth mother liquor to step g. In another embodiment the present invention provides a process for recovering iminodiacetic acid from an aqueous solution consisting essentially of sodium sulfate, iminodiacetic acid, and water, said solution having a temperature above 33°C and comprising at least about 5% iminodiacetic acid by weight, wherein said process comprises: a. forming a first slurry consisting essentially of a first crop of precipitated iminodiacetic acid and a first mother liquor by adjusting the pH of the starting solution to 1.5-3; b. separating the first crop of precipitated iminodiacetic acid from the first mother liquor and recovering the separated iminodiacetic acid; c. forming a second slurry at a temperature effective for preventing the precipitation of iminodiacetic acid therefrom and consisting essentially of precipitated sodium sulfate and a second mother liquor comprising at least 5% by weight dissolved iminodiacetic acid by evaporating water from the first mother liquor; d. separating the precipitated sodium sulfate from the second mother liquor while maintaining the second slurry and the second mother liquor at a temperature effective for preventing iminodiacetic acid from precipitating therefrom; e. forming a third slurry consisting essentially of a second crop of precipitated iminodiacetic acid and a third mother liquor by cooling the second mother liquor to 33-40°C; and f. separating the second crop of precipitated iminodiacetic acid from the third mother liquor and recovering the separated iminodiacetic acid, g. preparing a fourth slurry of iminodiacetic acid, sodium sulfate decahydrate and a fourth mother liquor at about the temperature specified in step i; h. feeding said fourth slurry into a continuous crystallizer; i. continuously feeding said third mother liquor into said fourth slurry while cooling to maintain the temperature in a range effective for precipitating iminodiacetic acid and sodium sulfate decahydrate to form a fifth slurry, said fifth slurry comprising a mixture of precipitated iminodiacetic acid and sodium sulfate decahydrate and a fifth mother liquor; and j. continuously separating the precipitated iminodiacetic acid and sodium sulfate decahydrate from the fourth mother liquor; optionally comprising the further step of continuously recycling at least a portion of the fifth mother liquor to step i. The embodiments just described may optionally be followed by the steps of recycling at least a portion of the separated or precipitated iminodiacetic acid and sodium sulfate decahydrate to step c, and/or adding iminodiacetic acid seed crystals to the third mother liquor prior to cooling the third mother liquor, and/or adding sodium sulfate decahydrate seed crystals during the cooling of the third mother liquor, eg at about the saturation temperature of sodium sulfate decahydrate in the third mother liquor. The instant invention is illustrated by the following Examples. In the Examples which follow the percentages are all percentages by weight. EXAMPLE 1 1250 g of IDA liquor containing 6.4% IDA, 2.7% NTA, and 23.0% Na₂SO₄ was charged to a 1 liter crystallizer and equilibrated at 40°C. Five g of IDA seed crystals was added, then the mixture was linearly cooled at a rate of 5.8°C/hr. Five grams of Na₂SO₄·10 H₂O (Glauber's Salt) seed crystals was added at the saturation temperature of 27°C. At 13°C about two thirds of the very heavy crystal slurry was centrifuged. The liquor was returned to the crystallizer and the mixture of this liquor and the remaining one third of the slurry was cooled to 5°C. The 5°C slurry was stirred for 1 hour and then centrifuged. A total of 525 grams of liquor and 695 grams of wet cake was recovered. After air-drying (during which most of the water of crystallization was lost), the cake was found to contain 18.5% IDA, 0.7% NTA, and 67.8% Na₂SO₄; thus, 85% of the IDA and 90% of the Na₂SO₄ contained in the liquor were recovered in the cake. EXAMPLE 2 The process of Example 1 was repeated, but 45 grams of 96% H₂SO₄ was added to the liquor to reduce the pH from the original 2.7 down to 2.0. The air-dried recovered cake contained 15.0% IDA and 6.1% NTA. The heavy contamination of the recovered solid demonstrated that this mode of operation was unsatisfactory. EXAMPLE 3 The process of Example 2 was repeated except that after acidification to pH 2.0 the liquor was seeded with NTA, stirred 2 hours at 40°C, and then centrifuged to remove the crystallized NTA. The liquor was returned to the crystallizer, seeded with IDA, and cooled as described in Example 1. The NTA crop contained 83% NTA, 4.1% IDA, and 5.0% Na₂SO₄. The IDA crop was contaminated with 3.2% NTA which was considered unsatisfactory. EXAMPLE 4 2500 grams of a new lot of IDA liquor containing 6.3% IDA, 3.0% NTA, and 23.3% Na₂SO₄ was charged to a 2 liter crystallizer and equilibrated at 40°C. 72 grams of 96% H₂SO₄ was added to pH 2.1. 10 grams of NTA seed was added, then the mixture was stirred for 2 hours. Additional H₂SO₄ was added as needed to maintain this pH. The precipitated NTA was separated on a centrifuge and washed. The liquor was returned to the crystallizer and re-equilibrated to 40°C. 82.8 grams of 50% NaOH was added to bring the liquor back to the original pH of 2.7. 10 grams of IDA seed was added and the batch was linearly program cooled to 5°C over 6 hr. At 27°C 5.0 grams of Glauber's Salt seed was added to initiate crystallization of Glauber's Salt. To maintain a workable slurry density, at both 25°C and 15°C about two thirds of the slurry was centrifuged, with the centrate being immediately returned to the crystallizer. The remaining slurry was centrifuged at 5°C. None of these crops was washed. The recoveries were:

Claims: A process for separating iminodiacetic acid and sodium sulfate decahydrate from an aqueous solution comprising iminodiacetic acid and sodium sulfate, said processing comprising: a. forming a slurry which is a solid mixture of iminodiacetic acid and sodium sulfate decahydrate, and a mother liquor; and b. separating the solid mixture from the mother liquor. A process according to claim 1, wherein the slurry is formed by adjusting the temperature of the aqueous solution. A process according to claim 1 or 2 comprising the further step of recycling at least a portion of the separated mother liquor to step a. A process according to any one of the preceding claims further comprising adding iminodiacetic acid seed crystals to said aqueous solution prior to step a. A process according to claim 4 wherein said seed crystals are added at about the saturation temperature of iminodiacetic acid in said solution. A process according to any one of the preceding claims further comprising adding sodium sulfate decahydrate seed crystals during the formation of the slurry in step a. A process according to claim 6 wherein the sodium sulfate decahydrate seed crystals are added at about the saturation temperature of sodium decahydrate in said aqueous solution. A process according to any one of the preceding claims wherein said aqueous solution has a temperature of about 40°C prior to step a. A process according to any one of claims 2 to 8 wherein the temperature is adjusted by cooling at a rate of about 5.8°C/hr. A process according to any one of claims 2 to 9 wherein said solution is cooled to a temperature of about 5°C. A process according to any one of the preceding claims wherein said separation is accomplished by centrifugation. A process according to any one of claims 2 to 11, wherein step a comprises cooling said solution to a temperature effective for producing a solid mixture of iminodiacetic acid and sodium sulfate decahydrate, and a mother liquor. A process according to any one of claims 2 to 12 wherein said solution has a temperature of about 40°C prior to a step a and said process comprises: a. cooling the solution to a temperature effective for precipitating iminodiacetic acid and sodium sulfate decahydrate; b. during said cooling step adding sodium sulfate decahydrate seed crystals at about the sodium sulfate decahydrate saturation temperature of said solution; and c. separating the precipitate. A process according to any one of the preceding claims wherein the aqueous solution further comprises nitrilotriacetic acid, and said process comprising a. forming a first slurry consisting essentially of precipitated nitrilotriacetic acid and a first mother liquor; b. separating the precipitated nitrilotriacetic acid from the first mother liquor; c. forming a second slurry consisting essentially of precipitated iminodiacetic acid and sodium sulfate decahydrate and a second mother liquor; and d. separating the precipitated iminodiacetic acid and sodium sulfate decahydrate from the second mother liquor. A process according to claim 14 wherein the first slurry is formed by adjusting the pH of the aqueous solution to a pH effective to precipitate nitrilotriacetic acid therefrom. A process according to claim 15 wherein the pH is adjusted to about 2.1. A process according to claim 15 or 16 wherein the pH is further adjusted after separation of the precipitated nitrilotriacetic acid to about the pH of the starting aqueous solution. A process according to any one of claims 15 to 17 wherein the pH is further adjusted after separation of the precipitated nitrilotriacetic acid to about 2.6. A process for the continuous separation of iminodiacetic acid and sodium sulfate decahydrate from an aqueous solution comprising iminodiacetic acid and sodium sulfate, which process comprises: a. preparing a slurry of iminodiacetic acid, sodium sulfate decahydrate and liquor at about the temperature specified in step c; b. feeding said slurry into a crystallizer; c. feeding said aqueous solution comprising iminodiacetic acid and sodium sulfate into said slurry while cooling to maintain the temperature at a level effective for precipitating iminodiacetic acid and sodium sulfate decahydrate; and d. withdrawing said slurry and separating iminodiacetic acid and sodium sulfate decahydrate therefrom. A process according to claim 19 wherein the residence time of said solution in said crystallizer is about two hours. A process according to claim 19 or 20 further comprising recycling a portion of the liquor resulting from said separation to said crystallizer. A process according to claim 19, 20 or 21 wherein the separation is accomplished by centrifugation. A process according to any one of claims 19 to 22 wherein the aqueous solution in step c is fed into the slurry in the crystallizer. A process according to any one of claims 19 to 23 wherein the aqueous solution in step c is fed into the slurry at a point prior to where said slurry enters said crystallizer. A process for recovering iminodiacetic acid from an aqueous solution consisting essentially of sodium sulfate, iminodiacetic acid, and water, said solution having a temperature above 33°C and comprising at least about 5% iminodiacetic acid by weight, wherein said process comprises: a. forming a first slurry consisting essentially of a first crop of precipitated iminodiacetic acid and a first mother liquor by adjusting the pH of the starting solution to 1.5-3; b. separating the first crop of precipitated iminodiacetic acid from the first mother liquor and recovering the separated iminodiacetic acid; c. forming a second slurry at a temperature effective for preventing the precipitation of iminodiacetic acid therefrom and consisting essentially of precipitated sodium sulfate and a second mother liquor analysing at least 5% dissolved iminodiacetic acid by evaporating water from the first mother liquor; d. separating the precipitated sodium sulfate from the second mother liquor while maintaining the second slurry and the second mother liquor at a temperature effective for preventing iminodiacetic acid from precipitating therefrom; e. forming a third slurry consisting essentially of a second crop of precipitated iminodiacetic acid and a third mother liquor by cooling the second mother liquor to 33-40°C; f. separating the second crop of precipitated iminodiacetic acid from the third mother liquor and recovering the separated iminodiacetic acid. g. cooling said third mother liquor to a temperature effective for precipitating iminodiacetic acid and sodium sulfate decahydrate to form a fourth slurry, the fourth slurry comprising a mixture of precipitated iminodiacetic acid and sodium sulfate decahydrate and a fourth mother liquor; and h. separating the precipitated iminodiacetic acid and sodium sulfate decahydrate from the fourth mother liquor. The process according to claim 25 comprising the further step of recycling at least a portion of said fourth mother liquor to step g. A process for recovering iminodiacetic acid from an aqueous solution consisting essentially of sodium sulfate, iminodiacetic acid, and water, said solution having a temperature above 33°C and comprising at least about 5% iminodiacetic acid by weight, wherein said process comprises: a. forming a first slurry consisting essentially of a first crop of precipitated iminodiacetic acid and a first mother liquor by adjusting the pH of the starting solution to 1.5-3; b. separating the first crop of precipitated iminodiacetic acid from the first mother liquor and recovering the separated iminodiacetic acid; c. forming a second slurry at a temperature effective for preventing the precipitation of iminodiacetic acid therefrom and consisting essentially of precipitated sodium sulfate and a second mother liquor comprising at least 5% by weight dissolved iminodiacetic acid by evaporating water from the first mother liquor; d. separating the precipitated sodium sulfate from the second mother liquor while maintaining the second slurry and the second mother liquor at a temperature effective for preventing iminodiacetic acid from precipitating therefrom; e. forming a third slurry consisting essentially of a second crop of precipitated iminodiacetic acid and a third mother liquor by cooling the second mother liquor to 33-40°C; and f. separating the second crop of precipitated iminodiacetic acid from the third mother liquor and recovering the separated iminodiacetic acid, g. preparing a fourth slurry of iminodiacetic acid, sodium sulfate decahydrate and a fourth mother liquor at about the temperature specified in step i; h. feeding said fourth slurry into a continuous crystallizer; i. continuously feeding said third mother liquor into said fourth slurry while cooling to maintain the temperature in a range effective for precipitating iminodiacetic acid and sodium sulfate decahydrate to form a fifth slurry, said fifth slurry comprising a mixture of precipitated iminodiacetic acid and sodium sulfate decahydrate and a fifth mother liquor; and j. continuously separating the precipitate iminodiacetic acid and sodium sulfate decahydrate from the fourth mother liquor. A process according to claim 27 comprising the further step of continuously recycling at least a portion of said fifth mother liquor to step i. A process according to any one of claims 25 to 28 comprising the further step of recycling at least a portion of said separated or precipitated iminodiacetic acid and sodium sulfate decahydrate to step c. A process according to any one of claims 25 to 29 further comprising adding iminodiacetic acid seed crystals to the third mother liquor prior to cooling said third mother liquor. A process according to any one of claims 25 to 30 further comprises adding sodium sulfate decahydrate seed crystals during the cooling of said third mother liquor. A process according to any one of claims 25 to 31 wherein the sodium sulfate decahydrate seed crystals are added at about the saturation temperature of sodium sulfate decahydrate in said third mother liquor.

Inventors: THUNBERG JON C, THUNBERG, JON C.
Applicants: HAMPSHIRE CHEMICAL CORP, HAMPSHIRE CHEMICAL CORPORATION
Application year: 1990
Main classification: C07C227
IPC codes: C01D5, C07C229, C07C227