CA1126756A - Method for producing salts of carboxymethyloxysuccinic acid - Google Patents

Abstract

cC 678 ABSTRACT OF THE DISCLOSURE
An improved method for the conversion of alkaline earth metal carboxymethyloxysuccinates to trialkali-metal carboxymethyloxysuccinate is disclosed wherein certain carbonate, bicarbonate, sesquicarbonate and hydroxide species are utilized and the pH is regulated to about 10 to about 11.5. The product so produced is low in calcium impurities and contains substantially no sulfate impurities.

Description

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METHOD FOR PRODUCING SALTS OF CARBOXYMETHYLOXYSUCCINIC ACID
This process relates to an improved method for the conversion of alkaline earth metal carboxymethyloxysuccinates to trialkali metal carboxymethyloxysuccinates, particularly the trisodium salt, hereafter referred to as sodium CMOS or Na3CMOS wherein the abbreviation "CMOS" refers to the tricarboxylate anion derived from carboxymethyloxysuccinic acid. These trialkali metal salts are useful as builders and metal sesquistrants.
The preferred method for preparing salts of carboxymethyl-oxysuccinic acid is described in U.S. Patents 3,914,297 and3,692,685, and comprises a reaction between maleic acid and glycolic acid under basic conditions in the presence of alkaline earth metal ions, preferably calcium. The reaction is generally carried out at about 60 to about 200C at a pH of about 8 to about 12.5, with 10.5 to 12.5 being preferred, the pH being measured at room temperature ~25C) using~a pH meter equipped with a standard pH combination electrode or separate glass and reference electrodes for measuring pH. Adjustments to pH are preferably made with an alkaline earth metal hydroxide. The - 20 resultant alkaline earth metal salt of CMOS is then reacted with an alkali metal carbonate to give a precipitate of alkaline earth metal carbonate and a solution of the alkali metal CMOS salt.
The alkaline earth metal carbonate is then removed by filtration or centrifugation.
It has been found that complete removal of the insoluble alkaline earth carbonate is often difficult. One of the problems encountered is the small particle size of the precipitate as described in U.S. Patent 3,821,296. Such small particle size impedes the rate of filtration and has been the subject of both 30 U.S. 3,821,296 and 4,058,560 and of Canadian patent application No. entitled "A PROCESS FOR THE PRODUCTION OF SALTS

OF CARBOXYMEHTYLOXYSUCCINIC ACID" said application being filed concurrently herewith.

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~126756 Applicant finds that when alkali metal carbonate is added in a stoichiometric amount, theoretically sufficent to precipitate all the alkaline earth metal ions, incomplete preci~itation occurs.
This is believed due to the presence of excess calcium hydroxide in 5 the reaction mixture. This calcium hydroxide reacts as follows:

(OH)2 CO3 CaCO3+20H

The liberation of hydroxide ions in this reaction results in a high pH, above 12, which, in turn, resluts in a small, but not insignificant reverse reaction. There is, therefore, a small 10 amount of partially soluble calcium hydroxide present, which does not precipitate, unless a large excess of carbonate ions are present.
It is noteworthy that the presence of calcium ions in the Na3CMOS product is highly undesirable for two reasons. First, 15 the calcium ions combine with the carboxymethyloxysuccinate anions thus consuming some of the building capacity of the product.
Secondly, it has been found that calcium ions in the Na3CMOS, - particularly when traces of fumarate salts are present also, interact with sodium silicate components of detergent formulations 20 producing a silica floc. This interaction is particularly troublsome when formulating li~uid detergents with Na3CMOS
and silicate components. For acceptable detergent processing, therefore, it has been found desirable to keep the level of calcium impurities in CMOS salt preparations as low as possible:
25 preferabl~ below about 0.5% and more pre~era~ly below about 0.2%
and most preferably below about 0.1~ basis Na3CMOS; these percentages are calculated using the formula:
~Ca- Na3CMOS) x 100%
In the past, in order to achieve essentially complete 30 precipitation of the calcium carbonate, an excess of alkali metal carbonate (generally about 10%) has been utilized. This method, however, has the following disadvantages:
X 1) It is wasteful in the amount of carbonate usedi and;

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- 2) The excess carbonate maintains the pH above about 12 where a reverse Michael reaction may occur on prolonged standing especially at high temperatures. The high pH is also less desirable from a safe handling poi~t of view.
In the past, the second disadvantage has been dealt with by lowering the temperature of th~ reaction mixture (e.g. to 60C), treating the resulting mixture with sodium carbonate and then filtering off the precipitated calcium carbonate. ~he solution of Na3CMOS obtained from the filtration step is then neutralized with a mineral acid such as sulfuric acid to lower the pH to a more acceptable level of about 10 to about 11. While this procedure of using excess carbonate and makin~ a pH adjustment subseguent to filtration of the calcium carbonate generally provides satisfactory results, it further introduces soluble inorganic electrolyte arising from the an~ons of the neutralizing mineral acid. Thus, when sulfuric acid is used, sodium sulfate is introduced into the Na3C~OS product. The presence of sodium sulfate is generally not objectionable when`the sodium CMOS is to be used in powdered detergent compositions, which normally utilize sodium sulfate as a filler. When, however, the sodium CMOS is to be used in liquid detergent compositions, especially the heavy duty type, the presence of sulfate is undesirable since additional inorganic electrolytes may cause instability problems, due to saIting out effects. Expensive formulation modifications, such as inclusion higher levels of hydrotrope, may be required in such cases.
Sodium sulfate may be separated from sodium CMOS by an extra purification step such as crystallization or salting out precip-itations with a solvent such as methanol or ethanol. T~ishowever, increases the cost of the process, and it is desirable to avoid the presence of sulfates entirely.
Accordingly, it is an object of this;inventi~n to provide trisodium carboxymethyloxysuccinate having low inorganic X 35 electrolyte impurities associated with it.

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-It is also an object of this invention to provide an improved process for preparing the alkali metal salts of carboxymethyloxysuccinic acid having both low residual calcium levels and low inorganic electrolyte impurities.
These and other objects of the invention will become more apparent in the detailed description of the invention which follows.

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' ~ 1 26~ ~ - cC~78 , DETAILED DESCRIPTION OF THE INVENTION
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~ In the course of the instant invention, calcium CMOS, Ca3 (CMOS)2, may be prepared by the aforementioned con-ventional method described in U.S. Patents 3,914t297 and 3,692, 685. In that method maleic ancl glycolic aclds are reacted in ~
an alkaline aqueous solution, in the presence of alkaline earth metal ions preferably calcium. The mixture, containin~ the calcium CMOS, is then reacted with a small excess of a mixture of carbonates and bicarbonates; the total molar amount of carbonate and bicarbonate should be at least about 1% greater - than the molar amount of~ alkaline earth metal present in the mixture with about 3% to about 6% excess being preferred.
Higher amounts r above 6% can aIso be used but are wasteful of reagent and are generally unnecessary. During the ConVerSiQn ~- 15 the carbonate and bicarbonate mixture may be added to the calclum ~OS slurry or the calcium CMOS slurry may be added to the carbon-~ .... ~
' ` - ate and bicarbonate-mixture. ~ ' -' Among the compounds which may be used to supply the carbonate and bicarbonate ions are the alkali metal,(particularly ' sodium~ carbonates, bicarbonates, sesquicarbonates r and carbon dioxide, and mixtures thereof. The precise ratio of carbonate and bicarbonate added is not critical since the amount of each which is presen-t will depend on the pH and this may be'adjusted . .
with any alkali hydroxide such as sodium hydroxide, for example.' A diagram displaying the carbonate and'bicarbonate present at a particular pH may be found in The Journal of the Water Pollution Control Federationr December, 1970 t p. 2036 which is incorporated herein by reference.
It has been determined that excellent precipitation of CaCO3 in the aforementioned conversion occurs at a pH between about 10 to about 11.5, with about 10.6 to about 11.0 being .

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~ h i preferred. Once the desired carbonate and bicarbonate mixture has been added, the pH may be further adjusted with, for example, an alkali metal hydroxide if more alkalini-ty is desired or with carbon dioxide if more acidity is desired. In this way, only alkali metal ca~ g~ and carhonate and blcarbonate anionS
need be added to the reaction mixturei and therefore, in-troduction of sulfates is eliminated.
~rypically~ an amount of sodium bicarbonate or ses-quicarbonate equal in moles to about 10 to about 30% of the amount of calcium in moles present is added to the reaction mixture. The remainder of the carbonate ion is added as sodium carbonate. The adaition of the two may be done simultaneously' or in any sequence. The pH of the reaction mixture which is usually about 9 to about 10, is then adjusted by slowly adding a solution o~ sodium hydroxide until the pH is stable at about 10.7'. Dilute or concentrated sodium hydroxide solution may be - used. Also, short holding periods (e.g. about 5 to about 20 -- minutes) aIter each addition of carbonate species ~i.e. NaHCO3, sesquicarbonate or Na2CO3) or the pH adjustment may be employed advantageously but'are not critical to the invention. At this C point the precipitate is removed by filtration or precipitation.
It has been discovered that the lowest levels of ca'lci~n in the filtrate can be obtained when the filtration is carried out at about 80 to about 100C and preferably about 90 to about 100C. While not wishing to be held to any particular theory, applicant believes that the calcium CMOS chelate is less stable in this temperature range, making more calcium availa~le for precipitation. Heretofore, filtrations were generally carried out at about 60C. ' cC678 ' ~ Z67 5 The filtrate of this process, which contalns small amounts of carbonate and bicarbonate ions, may be use~ directly for formulating liquid deter~ent ~ormulation~ or may be concentrated to ~orm a slurry of Na3CMO~ or may be partially s or completely dried by conventional techniques to produce a solid hydrate form or substantially anhydrous form. The carbonate and bicarbonate present may easily be eliminated in the'process of manufacturing a detergent product by direct addition Qf the acid in the form of an anionic detergent ac-tive, such as a sulfonic acid. Excess carbon dioxide is liberated, and the product formed is, for example, the sodium salt of the ' desired detergent active together with CMOS salt species - with substantially no inorganic electrolyte impurities other than the trace amounts that may be introduced as impurities in the glycolic acid'reactant. -such a product prepared from -sodium Cl~S made by the process of the present invention and ' '~linear alkylbenzenesulfonic'~~acids-(i.e LAS acids) is - admirably suited for incorporation in light and heavy duty li~uid-detergent formulations. The final pH of the finished - 20 ~ormulation in such cases is adjusted by the use o~ the desired alkaline reagent such as alkali metal hydroxides, ammonium hydroxide or organic amines such as monoethanolamine, diethanol-amine, triethanolamine, isopropanolamine, di-isopropanolamine and tri-isopropanolamine.
In the above described process, "calcium" may be replaced by any alkaline earth metal~ and "sodium" by any alkali metal.
The following examples are designed to further illustrate the invention and are in no way intended to limit the scope thereof. ~11 parts and proportions set forth therein are on weight basis unless other~ise indicate~.

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Maleic anhydride, 19.6 grams (0.2 mole) is ground to a powder and added to 100 g wa-ter in a 1 liter, 3 neck Morton flask equipped with a mechanical stirrer and reflux condenser. Glycolic acid, 23.9 g of 70~ solution (O.Z2 moles) is added followed immediately by 25.8 grams (0.35 moles) of 100% calcium hydroxide, sufficient to raise the pH to 11.5, measured at room temperature. Ap~roximately, 17 ~ o additional water is added to the reaction mixture via rinsing while making lQ pH measurements on samples of the reaction mixture. Since 0.20 moles calcium hydroxide is needed to completely neutralize the maleic acid and 0.11 moles to completely neutralize the glycolic acid, there are, therefore, abou-t 0.04 moles excess calcium hydroxiae in the reaction mixture. The mixture is heated ~o reflux and maintained at reflùx with-vigorous agitation for one hour.
About 40 ml water is added to dilute the reaction mixture and the a~itation is reduced to a slow rate (about - 80 RPM) with the temperature maintained at 80C. Then 18.05 g (0.0799 mole) sodium sesquicarbonate(Na2co~ NaHCO3 2H~O) is added, followed by 21.82 grams (0.2058 mole) o~ sodium carbon-- -ate. After each addition, the mixture is a~ita-ted for about 10 minutes. Sufficient 1~ sodium hydroxide, about 30 ml~ is then added to bring the pH to 10.7.
The reaction mixture at 80C is filtered by suction through Whatman #l filter paper to remove calcium carbonate.
The filtrate lS analyzed and found to contain 0.016 Ca and 14.6~ Na3CMOS or 0.07% Ca basis Na3CMOS.

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ExaMpLEs 2 - 15 _ ~ Example 1 is repeated making various suhstitutions - for the sesquicarbona-te-and carhonate mixture. r~esults are in Table 1. The abbreviation "sesqui" re~ers to sodium sesqui-carbonate i.e. Na2C03'NaHC03'2H20. ~Initial levels of Ca and dilution water varied slightly from that in Example 1).
Compare the results of Examples 4-14, and especially 6-14, of the invention versus the resùlts of Examples 1-3 which show poor or undesirable results with respect to calcium ion level or final pH or both.-- - , . . . ,. ~, .
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- . EXAMPLE 16 . . :

Example 1 is repeated with the exception that the sesquicarbonate and carbonate mixture is replaced by sufficient sodium carbonate-to raise the pH to 11.5, Carbon dioxide is then bubbled through the solution until the pH drops to . 11Ø The solution is.then filtered as previously.

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Claims (9)

THE EMODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In the process of producing a trialkali metal carboxymethyloxysuccinate from an alkaline earth metal carboxymethyloxysuccinate wherein:
a) said alkaline earth metal carboxymethyloxysuccinate is reacted, in an aqueous reaction mixture, with an alkali metal carbonate to produce a solution of said trialkali-metal carboxymethyloxysuccinate and a precipitate of insoluble alkaline-earth metal carbonate;
and b) said precipitate is separated from said solution;
the improvement comprising reacting said alkaline-earth metal carboxymethyloxysuccinate with an alkali metal carbonate and alkali metal bicarbonate mixture at a pH of about 10 to about 11.5, said carbonate and bicarbonate species and pH
regulation being supplied by a compound selected from the group consisting of alkali metal carbonates, bicarbonates, sesqui-carbonates, and hydroxides, carbon dioxide, and mixtures thereof, the total molar amount of carbonate and bicarbonate ions in said mixture being at least 1% more than the molar amount of alkaline earth metal ions present in the initial reaction mixture.

2. The method of claim 1, wherein said alkaline earth metal ions are calcium ions.

3. The method of claim 2 wherein said alkali metal is sodium.

cC678

4. The method of claim 3 wherein the pH of said reaction mixture is about 10.6 to about 11Ø

5. The method of claim 4 wherein said pH is about 10.7.

6. The method of claim 3 wherein the calcium carbonate is separated from the trisodium carboxymethyloxy-succinate solution by filtration at a temperature of about 80°C to about 100°C.

7. The method of claim 3 wherein the total molar amount of carbonate plus bicarbonate is about 3% to about 6% more than the molar amount of calcium ions.

8. The method of claim 7 wherein said total molar amount is 5% more than the molar amount of calcium ions.

9. The method of claim 3 wherein a digestion period of 5 to about 20 minutes is employed after the reaction of said alkaline-earth metal carboxymethyloxysuccinate with the carbonate and bicarbonate and pH regulations species.