AND COMPOSITION THEREOF

TECHNICAL FIELD

This disclosure relates to a process of preparing 2-(l,2-dicarboxyethylamino) butanedioic acid (hereinafter also referred to as 'iminodisuccinic acid' or 'IDS'), salts and optical isomers thereof. The present disclosure further relates to systems, apparatus, and the like, for preparing IDS.

BACKGROUND

Chelating agents have been employed in a variety of ways for a number of years. Many chelating agents such as ethylenediaminetertraacetic acid (EDTA), nitrilotriacetic acid (NT A), and various phosphonates such as diethylenetriaminemethylenephosphonic acid (DTMPA) are not fully biodegradable and have obvious environmental drawbacks. Some of aforementioned chelating agents such as NTA have also been classed as carcinogenic and EDTA has been shown to contain NTA as by-product of its synthesis. Phosphonates contain formaldehyde (a known carcinogen) which is also a by-product from commercial synthesis.

Iminodisuccinic acid (IDS) is an alternative chelating agent that is readily biodegradable. IDS as prepared in this work is manufactured from comparatively benign chemicals using manufacturing techniques known in the art. Iminodisuccinic acid and its salts may find use as chelating agents in numerous applications such as in the fields of detergents and cleaning compositions, pharmaceuticals, cosmetics, agriculture, electroplating, building materials, textiles and pulp and paper manufacture.

Various methods of preparing IDS are known. For example, US 6,107,518 describes preparing iminodisuccinic acid alkali metal salts via a reaction of maleic acid and ammonia in an aqueous medium in the presence of alkali metal hydroxides pressurized to 20 bar. GB 1,306,331 describes the preparation of iminodisuccinic acid from maleic acid and ammonia in a molar ratio of 2:3 to 2:5 at temperatures of 60°C to 155°C. US 7,183,429 describes a process for the preparation of iminodisuccinic acid ammonium metal salts by reaction of maleic anhydride, alkali metal hydroxides, ammonia and water in a first stage to give iminodisuccinic acid ammonium salts and their subsequent reaction with metal oxides, metal hydroxides or other metal salts in a second stage. Van Westrenen et al, Reel. Trav. Chim. Pays-Bas, 109, 474 (1990) describes the reaction of Na ₂ -maleate with Na2-aspartate resulting in 22% yield of Na4-iminodisuccinate. There was a large proportion of fumarate side product formed (70%).

JP 05-320109 describes the synthesis of Na4-iminodisuccinate from maleic anhydride, aspartic acid and alkali/alkaline earth metal base such as NaOH or Ca(OH) ₂ . The process is said to produce a high yield with low impurities by using higher concentration (>20 wt% each) of starting materials although such results were not obtained when the present inventors attempted to reproduce the disclosed process (please see Comparative Examples 1 and 2 below). The process is also said to be relatively rapid. However, the process produces a firm dough-like intermediate at higher concentrations (>20 wt% of each reactant) that is difficult to mix using conventional chemical processing equipment thus limiting the commercial viability of this process (please see Comparative Example 2 below). The process also contains a higher proportion of unreacted Na ₂ -aspartate than commercially available NaHDS.

SUMMARY

The present disclosure provides, at least in part, a process to prepare iminodisuccinic acid salts using maleic anhydride, aspartic acid, and a base in water. In an example, maleic anhydride and aspartic acid are added at certain concentrations to a reactor. A base, such as NaOH, is then added to neutralize the reactants. A slurry is produced preferably having a viscosity of about 1,000 cps or less. Preferably the pH is raised to about 10 or above to achieve a homogenous clear solution. Water is distilled out of the reactor to increase the concentration of reactants and the solution is then heated to reflux and the reaction allowed to proceed for a certain period. Yields of over 85% of the theoretical yield can be achieved.

The present disclosure also provides, at least in part, a process for the preparation of iminodisuccinic acid salts, the process comprising: (a) combining maleic anhydride and aspartic acid to form a slurry; (b) adding a base in water to said slurry such that the resulting composition has a pH of about 10 or greater and a viscosity of about 10000 cps or less; (c) distilling off the water until the concentration of maleic anhydride and aspartic acid is about 35 wt% or less; and (d) mixing the reactants and allowing them to react to form iminodisuccinic acid salt.

The present disclosure also provides, at least in part, a composition comprising: (a) about 35 wt% or less maleic anhydride; (b) about 35 wt% or less aspartic acid; (c) water; and (d) a base; wherein said composition has a temperature of about 80°C or less, a pH of about 10 or greater and a viscosity of about 10000 cps or less.

The present disclosure also provides, at least in part, a system for preparing iminodisuccinic acid salts using maleic anhydride, aspartic acid and a base in water. The present disclosure also provides, at least in part, an apparatus for preparing iminodisuccinic acid salts using maleic anhydride, aspartic acid and a base in water.

This summary does not necessarily describe all features of the invention. Other aspects, features and advantages of the invention will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention. DETAILED DESCRIPTION

As used herein, "a" or "an" means "one or more".

As used herein, "reactor" means any vessel or container suitable for containing the reactants.

As used herein, "about" indicates a quantity within 10% of the stated value. The present disclosure provides, at least in part, a process to prepare, and a system and apparatus for preparing, iminodisuccinic acid (IDS) salts using maleic anhydride (MA), aspartic acid (AspA) and a base in water.

While not wishing to be bound by theory, embodiments of the present process may provide a high yield of IDS. For example, achieving yields of about 50% or more, about 60% or more, about 70% or more, about 75% or more, about 80% or more, about 82% or more, about 85% or more, about 88% or more, or about 89% or more, of the theoretical yield might be possible.

While not wishing to be bound by theory, embodiments of the present process may provide a process with a reaction time of less than about 48 hrs, such as for example, about 24 hrs or less, about 22 hrs or less, about 20 hrs or less, about 18 hrs or less, about 16 hrs or less, about 14 hrs or less, about 12 hrs or less, about 10 hrs or less, about 9 hrs or less, about 8 hrs or less, about 7 hrs or less, about 6 hrs or less, about 5 hrs or less.

While not wishing to be bound by theory, embodiments of the present process may provide a process that may be operated without the need for high pressures which necessitate more expensive equipment and may be more dangerous. While embodiments do not require high pressure to proceed efficiently, this does not exclude the use of high pressure which may further increase reaction rates and decrease reaction times.

In certain embodiments of the present disclosure, MA and water are mixed to form maleic acid (MAcid). In a reactor, aspartic acid is mixed with the MAcid. A base is added to the reactor and the pH raised to about 10 or above forming a slurry. Preferably, the slurry has a viscosity at 20°C of about 10000 cps or less, about 8000 cps or less, about 6000 cps or less, about 4000 cps or less, about 3000 cps or less, about 2000 cps or less, about 1000 cps or less, about 500 cps or less, about 100 cps or less.

The MAcid is provided at any suitable concentration such as, for example, about 35 wt% or less, about 30 wt% or less, about 25 wt% or less, about 24 wt% or less, about 23 wt% or less, about 22 wt% or less, about 21 wt% or less, about 20 wt% or less, about 19 wt% or less, about 18 wt% or less, about 17.5 wt% or less, about 17 wt% or less, about 16.5 wt% or less, about 16 wt% or less, about 15.5 wt% or less, about 15 wt% or less, about 14.5 wt% or less, about 14 wt% or less.

The AspA is provided at any suitable concentration such as, for example, about 35 wt% or less, about 30 wt% or less, about 25 wt% or less, about 24 wt% or less, about 23 wt% or less, about 22 wt% or less, about 21 wt% or less, about 20 wt% or less, about 19 wt% or less, about 18 wt% or less, about 17.5 wt% or less, about 17 wt% or less, about 16.5 wt% or less, about 16 wt% or less.

In processes according to the disclosure, AspA, MA and water may be combined in any suitable ratio. For example, the AspA, MA and water may be in a molar ratio of 1 : 1- 1.2:5-35. Preferably, MA and water are employed in a molar ratio of 1 :4-35, such as 1 :6- 22 or 1 : 8-20. Preferably, AspA and water are employed in a molar ratio of 1 :4-35, such as 1 :6-22 or 1 :8-20. Base may be metered into the reactor (such as by, but not limited to, stirring) to prepare MAcid salt and AspA salt in solution. The addition of base is exothermic and the rate of addition of base to the reactor is preferably controlled so that the reaction temperature does not rise above about 80°C to prevent the isomerization of maleic acid to fumaric acid. The temperature can be kept below 80°C during the addition of the base in various ways such as, for example, slow addition of base or a faster addition of base with the aid of cooling such as a heat exchanger. After addition of the base, the pH of the solution is preferably about 10 or greater, about 10.2 or greater, about 10.4 or greater, about 10.6 or greater, about 10.8 or greater, about 11 or greater, about 11.2 or greater, about 11.4 or greater, about 11.6 or greater, about 11.8 or greater, about 12 or greater. The base may be any suitable material such as, but not limited to, a metal hydroxide (MOH) where the metal is alkali or alkaline or an organic base such as but not limited to ammonium hydroxide (NH4OH). For example, M may denote Li, Na or K when it is an alkali or Mg or Ca when it is alkaline. Preferred for use here are Na, K or Ca, particularly Na. The amount of MOH employed may be any suitable. For example, 1 mole equivalents of base for every mole of carboxylic acid group may be present in the reactant mixture. While not wishing to be bound by theory, employing less than 1 mole equivalents of base may lead to a decrease in product yield and a slower reaction rate, while employing more than 1 mole equivalents of base may lead to lower reaction yields and increased malic acid side-products. The slurry may be at any suitable temperature such as, for example, about 10°C or greater, about 15°C or greater, about 20°C or greater, about 25°C or greater, about 30°C or greater, about 35°C or greater, about 40°C or greater. The temperature may be, for example, about 100°C or lower, about 95°C or lower, about 90°C or lower, about 85°C or lower, about 80°C or lower, about 75°C or lower, about 70°C or lower. While not wishing to be bound by theory, it is believed that by starting at lower concentrations of ingredients, the slurry produced during neutralization does not get so thick that stirring becomes an issue. After the base has been added and the reactants are dissolved, water may be distilled off until the reactants have reached the desired reaction concentration. For example, the concentration of each reactant may be about 10% or greater, about 12% or greater, about 14% or greater, about 16% or greater, about 18% or greater, about 20% or greater. The concentration of each reactant may be about 42% or lower, about 41% or lower, about 40% or lower, about 39% or lower, about 38% or lower, about 37% or lower, about 36% or lower, about 35% or lower. While not wishing to be bound by theory, it is believed that increasing the concentration of reactants in the proper ratio in the reactor has the technological advantage of increasing yields and shortening reaction time (t) (please see Example 1 and Comparative Example 1). After distilling out the water, the reactants remain dissolved in solution without any precipitation or solids forming.

The reactants are then heated at the reaction temperature (T) over a desired reaction time (0.

T may be any suitable temperature such as, for example, about 80°C or greater, about 85°C or greater, about 90°C or greater, about 95°C or greater, about 100°C or greater, about 105°C or greater, about 110°C or greater. T may be about 150°C or less, about 140°C or less, about 130°C or less, about 120°C or less, about 118°C or less, about 115°C or less. Preferably the reactants are heated to reflux (for example 112°C).

Time (0 may be any suitable time such as, for example, about 0.1 hour or more, about 0.5 hour or more, about 1 hour or more, about 2 hours or more, about 3 hours or more, about 4 hours or more, about 5 hours or more, about 6 hours or more, about 7 hours or more. Time (t) may be about 48 hours or less, about 36 hours or less, about 24 hours or less, about 20 hours or less, about 18 hours or less, about 16 hours or less, about 14 hours or less, about 12 hours or less, about 10 hours or less, about 8 hours or less.

The process described herein is able to produce IDS salts in high yields and produces little to no waste since the water that is distilled off is reused to dilute the product to its desired final concentration. By carrying out the reaction in less water, the product precipitates out of solution when it reaches a high enough concentration (e.g. greater than 40 wt%). When the product precipitates out, the reaction is driven further toward completion. The IDS precipitate formed during synthesis dissolves easily in water during dilution to desired commercial concentrations.

In an embodiment of the present disclosure, excess maleic acid, relative to the aspartic acid, is added to the reactor. The excess compensates for the loss in maleic acid due to isomerisation to fumaric acid. The addition of excess may increase yield and/or rate of reaction. For example, the ratio of maleic acid to aspartic acid in the reactor may be about 1 : 1 or greater, about 1.05: 1 or greater, about 1.1 : 1 or greater, about 1.15: 1 or greater, about 1.2: 1 or greater. The AspA and MAcid slurry is converted into the AspA salt and Macid salt dissolved in solution by metering in base in water. The secondary variant of this process may be advantageous where adjusting the amount of water in the produced slurry affect the ability to effectively stir the reaction while also affecting the reaction rate and t.

The IDS salt produced starts to precipitate out of solution at >40wt% during reaction reflux (112°C). The precipitation of IDS out of solution when the concentration has reached >40wt% may be beneficial because it drives the reaction to further completion, increasing yields and lowering fumaric acid side products. It has been shown from previous work in Reel. Trav. Chim. Pays-Bas 109, 474 (1990) that the reaction mechanism involves a carbanion intermediate which is in equilibrium with the product and side product (Scheme I). The reaction is tracked by HPLC, and IDS salts are obtained in yields of great than about 75%, such as about 80% or greater, about 88% or greater, of theoretical yield. The sum of all side products and unreacted starting materials may amount to about 25% or less, preferably about 20% or less, about 15% or less, about 11% or less. The water that was distilled off during concentration may be added back to the reactor to dilute the product to the desired final concentration.

Scheme 1. Mechanism of reaction in the synthesis of IDS salts.

It is contemplated that different parts of the present description may be combined in any suitable manner. For instance, the present examples, methods, aspects, embodiments or the like may be suitably implemented or combined with any other embodiment, method, example or aspect of the invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. Unless otherwise specified, all patents, applications, published applications and other publications referred to herein are incorporated by reference in their entirety. If a definition set forth in this section is contrary to or otherwise inconsistent with a definition set forth in the patents, applications, published applications and other publications that are herein incorporated by reference, the definition set forth in this section prevails over the definition that is incorporated herein by reference. Citation of references herein is not to be construed nor considered as an admission that such references are prior art to the present invention.

Use of examples in the specification, including examples of terms, is for illustrative purposes only and is not intended to limit the scope and meaning of the embodiments of the invention herein. Numeric ranges are inclusive of the numbers defining the range. In the specification, the word "comprising" is used as an open-ended term, substantially equivalent to the phrase "including, but not limited to," and the word "comprises" has a corresponding meaning.

The invention includes all embodiments, modifications and variations substantially as hereinbefore described and with reference to the examples and figures. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims. Examples of such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way.

EXAMPLES

Example 1

1.25 moles of maleic anhydride (122.6 grams) are added to 180 grams of water and stirred for 30 minutes to produce a maleic acid solution. To the stirring mixture, 1.25 moles of aspartic acid (166.4 grams) are added to create a slurry. To this slurry, 5 moles of a 50% NaOH solution (400 grams, 100% base equivalent) are added slowly, thereby maintaining the temperature of the slurry below 80°C. During the addition of base, the consistency of the slurry first thickens, but then thins out again after >60% of the base is added. After all the base is added, the solution is clear and homogenous. 209.6 grams of water is then distilled out to generate a reaction mixture containing 22.0 wt% and 25.2 wt% for maleic acid and aspartic acid, respectively. The reaction mixture is then heated to 112-115°C and stirred for 8 hours. After 2 hours, the NaJDS starts to precipitate out of solution and the reaction mixture transitions from a clear solution to milky white solution (>40 wt% Na4lDS in solution) and eventually to a white paste. The reaction is completed after 8 hours. The solids content is determined by HPLC.

Na4lDS yields of 89.8% of theory (based on moles of aspartic acid added) are achievable in the foregoing synthesis. The solution appears as a thick white paste where concentration of NaJDS is 57.4 wt%. Water is added to the thick paste to dissolve NaJDS and to dilute the concentration of NadDS down to 34 wt%. The solids content of the final solution is determined by HPLC and may contain 34.2 wt% NadDS, 4.1 wt% Na ₂ -Aspartate, 1.0 wt% Na ₂ - Maleate and 1.4 wt% Na ₂ -Fumarate.

Example 2

The same experiment as Example lis carried out, except that the mole ratio of reactants is modified to 128.7 grams of maleic anhydride (1.313 moles), 166.4 grams of aspartic acid (1.25 moles) and 410 grams of 50% NaOH (5.13 moles, 100 equivalent). After the base is added, 215 grams of water is distilled out to generate a reaction mixture containing 22.7 wt% and 24.8 wt% for maleic acid and aspartic acid, respectively. The reaction mixture is then heated to 112-115°C and is stirred for 8 hours. After 1.5 hours, the NaJDS starts to precipitate out of solution and the reaction mixture transitions from a clear solution to milky white solution (>40 wt% NaJDS in solution) and eventually to a white paste. The reaction was complete after 8 hours. The solids content is determined by HPLC.

NaJDS yields of 89.2% of theory (based on moles of aspartic acid added) are achievable in the foregoing synthesis. The solution appears as a thick white paste where concentration of NaJDS is 56.1 wt%. Water is added to the thick paste to dissolve NaJDS and dilute the concentration of NaJDS down to 34 wt%. The solids content of the final solution is determined by HPLC and may contain 34.7 wt% NaJDS, 3.7 wt% Na ₂ - Aspartate, 1.4 wt% Na ₂ -Maleate and 1.4 wt% Na ₂ -Fumarate.

Comparative Example 1

A mole of maleic anhydride (98.1 grams) is dissolved in 211 grams of water and stirred for 30 minutes to produce a maleic acid solution. To the stirring mixture, 1 mole of Aspartic acid (133.1 grams) is added to create a slurry. To this slurry, 4 moles of 50% NaOH solution (320 grams, 100% base equivalent) are added slowly maintaining the temperature of the slurry below 80°C. When approximately 20-60% of the total base is added, the consistency of the slurry becomes a free flowing paste. After >65% of the base is added, the solution begins to thin out and is a clear free flowing liquid after all the base has been added.

The desired concentration of maleic acid and aspartic acid in the reaction mixture is 15.2 wt% and 17.5 wt%, respectively. The reaction mixture is heated to 112-115°C and stirred for 20 hours.

The solids content is determined by HPLC. Na4lDS yields of 75.4% of theory (based on moles of aspartic acid added) are achievable in the foregoing synthesis.

Comparative Example 2 The same experiment is carried out as Comparative example 1, except that the concentration of solids is increased by decreasing the amount of water added to 80 grams and increasing the reactants to 147.1 grams of maleic anhydride (1.5 moles), 199.7 grams of aspartic acid (1.5 moles) and 480 grams of 50% NaOH (6 moles, 100 equivalent). After about 20% of the required base is added, the mixture begins to assume the consistency of dough and may not be stirred effectively. 40 grams of water is then added to improve the fluidity of the mixture. The desired concentration of maleic acid and aspartic acid in the reaction mixture is 18.4 wt% and 21.1 wt%, respectively. The reaction mixture is then heated to 112-115°C and stirred for 20 hours. The solids content were determined by HPLC. NaJDS yields of 82.0% of theory (based on moles of aspartic acid added) are achievable in the foregoing synthesis.