TECHNICAL FIELD

The present invention relates to a process for the melt crystallization of amidoacids which leads to improved properties of suspensions made from these melt-crystallized amidoacids. The invention further relates to a process for making suspensions which embodies the melt crystallization process and to suspensions made by this process.

BACKGROUND OF THE INVENTION

Organic peroxyacids are useful as fabric bleaching agents. As such, they are often formulated in the form of either dry, granular compositions, or aqueous suspensions, either of which products can be used in combination with detergent compositions.

European patent publication number 106627 discloses a method for the manufacture of aqueous suspensions of solid organic peroxides whereby peroxides having at least a 5°C difference between their melting points and decomposition temperatures are suspended in aqueous media. In particular, an aqueous phase is prepared by dissolving or dispersing a protective colloid and at least one surface active agent in water. The aqueous phase is mixed with an organic peroxide. This mixture is stirred at a temperature above the melting point of the peroxide long enough to allow the peroxide to be divided into fine particles in an aqueous emulsion. This emulsion is cooled rapidly to form an aqueous suspension of the peroxide.

This process suffers from the disadvantage that it is limited to suspensions of particles of less than 30 μ in diameter as can be seen from the examples wherein particle diameters are in the range of 10-15 μm diameter and from comparative example 1 which demonstrates that a suspension of particles having an average diameter of 50 μ could not be stably suspended by this process.

A similar process is disclosed in Japanese patent publication number J5 9093-044 again employing a protective colloid and a surfactant. This process differs in that the aqueous media is first pre-heated to a temperature above the melting point of the peroxide prior to peroxide addition.

European patent application 517 290 also discloses a process for the preparation of peroxide suspensions wherein the initiator is heated to its melting point, then the initiator is finely divided in water while in the molten state, preferably in the presence of one or more emulsifiers and/or protective colloids, and rapidly cooling the initiator in water so that the initiator is not molten for more than 5 minutes. This process is only suitable to make suspensions of very fine peroxide particles, 90% of which have a diameter of not more than

10 μm. These suspensions are designed for use in PVC polymerization.

Additional methods for suspending some peroxyacids are known from

European Patent publication number 0347 988, European Patent publication number 0435379, European Patent publication number

0 176 124, European Patent publication number 0 160342 and European patent publication number 0201 958, among others. However, none of these publications teaches or suggests a method of preparing a suspension of the present amidoperoxyacids which do not undergo a significant viscosity increase upon storage.

Further, another process for suspending peroxyacids is described in International patent application number PCT/EP 92/02176 filed on 21 September 1992. More particularly, this process comprises the steps of preparing an aqueous suspension having a pH of from 2-6 of a composition comprising at least one amidoperoxyacid agglomerating said aqueous suspension of peroxyacid at a temperature 0-20°C below the melting point of said peroxyacid composition, and cooling said agglomerated peroxyacid composition to a temperature below 30°C.

Although this process provides some improvement over previously known suspension processes for amidoperoxyacids, the resultant suspension still tends to become significantly more viscous when stored at higher temperatures. Thus, this product would require storage at low temperatures in order to maintain its rheological stability.

Accordingly, there exists a need in the art for rheologically stable suspensions of amidoacids, as well as a method for making such rheologically stable suspensions without negatively affecting one or more of the other properties of the bleaching materials and without the need for significant quantities of water-impermeable materials. Further, there is a need in the art for suspensions of large particles containing amidoacids, and, in particular, suspensions of particles having an average diameter greater than about 30 μm.

SUMMARY OF THE INVENTION

The present invention relates to a process for the melt- crystallization of an amidoacid composition which contains at least one amidoacid represented by the formulas I and II:

R ^l -C-N-R ² -C- (0) _n 0H R ⁱ _N-C-R ^a -C- (0) _n 0H

II I II I II II

O R ³ o R ³ 0 o

Formula I Formula II wherein R ^l is selected from Cι_i4 alk(en)yl, ar(en)yl and alkar(en)yl, R ² is selected from alkyl(ene), aryl(ene) and alkaryl(ene) groups containing from 1-14 carbon atoms, R ³ is hydrogen or an alkyl, aryl or an aralkyl group containing from 1 to 10 carbon atoms, and n is 0 or 1; comprising the steps of:

A. preparing an aqueous medium having a pH of from 2-6 comprising water and an effective amount of thickening agent to prevent coalescence of the amidoacid in the water at a temperature above the melting point of the amidoacid composition,

B. heating said aqueous medium to a temperature sufficient to melt the amidoacid composition and form a continuous two phase emulsion thereof, said amidoacid composition being added to said aqueous medium with stirring either before, during or after heating, and

C. cooling said two phase emulsion to a temperature below the crystallization temperature of said amidoacid composition at a controlled cooling rate to crystallize said amidoacid.

The present invention also relates to a process for making suspensions of amidoacids which embodies the above-described melt crystallization process and to suspensions made by this process. It has surprisingly been found that the melt crystallization of the amidoacids at elevated temperature provides suspensions of relatively large amidoacid particles which are physically and chemically stable, and which remain pourable throughout an acceptable storage period, when compared with the prior art suspensions.

The invention and its further advantages will be explained in greater detail in the description which follows.

DETAILED DESCRIPTION OF THE INVENTION

The present invention applies to amidoacids. As used herein, amidoacids includes amidocarboxylic acids as well as amidoperoxycarboxylic acids.

The amidoacids can be represented by the formulas I and II:

R ⁱ _C-N-R ² -C-(0) _n 0H R ¹ -N-C-R ² -C-(0) _n 0H

II I II I II II

O ³ o R ³ O o Formula I Formula II wherein R ¹ is selected from C1.14 alk(en)yl, ar(en)yl, and alkar(en)yl, R ² is selected from alkyl(ene), aryl (ene) and alkaryl(ene) groups containing from 1-14 carbon atoms, R ³ is hydrogen or an alkyl, aryl or an aralkyl group containing from 1 to 10 carbon atoms and n is 0 or 1. These amidoacids and methods for making them are described in U.S. patents 4,634,551 and 4,686,063 and European Patent Application publication number 0445096, all of which are hereby incorporated by reference.

Preferred amidoacids are the amidoperoxyacids of the formula III:

R'-NH-C-R'-C-OOH

II II (in)

0 0 wherein R ^l is an alkyl group containing from 6-12 carbon atoms and R ² is an alkylene group containing 1-6 carbon atoms. The most preferred amidoperoxyacids are 4-nonylamido-4-oxoperoxybutanoic acid and 6-nonylamido-6-oxoperoxyhexanoic acid.

At the end of amidoacid synthesis, the reaction is typically quenched with water and the products are filtered and washed. The wet cake thus obtained may be further processed in accordance with the process of the present invention. Pure amidoacids may also be employed in the process of the present invention.

The first step in the process of the present invention is to prepare the aqueous medium. The aqueous medium is set at a pH of between 2 and 6 by addition of an appropriate amount of pH adjusting agent. The exact pH employed will depend on the amidoacid. For example, with the preferred amidoacids a preferred pH is 2.5-4.5 with pH 3.0 being the most preferred when using an amidoacid of the formula III.

The aqueous medium also contains at least one thickening agent. The thickening agent is employed to adjust the viscosity. In the present process, some thickening agent is added initially to the aqueous medium to provide a structured liquid and to prevent coalescence of the amidoacid composition. Once the melt crystallization process is complete, additional thickening agent can be added.

The thickening agent comprises one or more polysaccharides wherein at least 60% of the saccharide units in the polysaccharide backbone are linked by a 1,4-jS-oxy linkage. More particularly, from the publication, "Applications of Novel Biogums," Clare, K., Chemspec USA '88 Symposium, the structures of several gums are known. This article characterizes the structure of biogums by the units in the backbone and the units in the side chains.

Accordingly, the thickening agents for use in the present invention are polysaccharides having a backbone structure wherein at least 60% of the saccharide units in the backbone are linked by the 1,4-ø-oxy linkage and which polysaccharides are compatible with amidoacids. By

compatible is meant that the polysaccharides do not unduly influence the chemical and/or physical stability of the amidoacids. The desired rheological properties of the aqueous medium can be achieved by use of these polysaccharide thickeners.

Examples of such polysaccharides include natural gums such as xanthan gum, gum arabic, carrageen and agars obtained from seaweed, as well as synthetic gums such as Alpha flo ^® , Rhamsan gum and Whelan gum. A

10 sufficient amount of polysaccharide employed to provide a pourable, physically and chemically stable aqueous medium and generally about 0.1-5 wt% of the total of the aqueous medium and the amidoacid is thickening agent, and more preferably 0.1-1.0 wt% is thickening agent.

15 The aqueous medium may also contain one or more optional ingredients including buffering agents, exotherm control agents, electrolytes and chelating agents, for example.

The electrolyte may be formed in situ from the residual acid present

20 in the amidoacid wet cake, or the electrolyte can be added separately to the aqueous medium. Examples of suitable electrolytes include sodium sulphate, potassium sulphate, magnesium sulphate, aluminum sulphate, sodium nitrate and borate salts. The amount of electrolyte will depend, inter alia, on the specific amidoacid, as well as the 2 ₅ particular aqueous medium. In general, up to about 30 wt.% of the total composition may be electrolyte.

Chelants may also optionally be incorporated in the aqueous medium. Examples of suitable chelants are carboxylates, such as ethylene , _π diamine tetraacetate (EDTA) and diethylene triamine pentaacetate (DTPA) polyphosphates, such as sodium acid pyrophosphate (SAPP), tetrasodium pyrophosphate (TSPP) and sodium tripolyphosphate (STPP); phosphonates, such as ethylhydroxydiphosphonate (Dequest® 2010) and

other sequestering agents sold under the Dequest ^® tradename; dipicolinic acid, picolinic acid, citric acid and 8-hydroxyquinoline; and combinations of the above. Preferably 0.01-10 wt.% of such chelants are employed. More preferably, 0.1-5.0 wt.% of chelant is employed.

The amidoacid composition, and especially amidoperoxyacid compositions, are preferably employed in the form of a wet cake which is fresh from the synthesis process. A typical composition will contain 30-60% by weight of amidoacid, 35-65% by weight water and the balance organic impurities which comprise mainly unreacted starting materials.

The amidoacid composition is mixed into the aqueous medium by a suitable mixing apparatus. For example, a pitch-bladed impeller can be used. The amidoacid composition can be added to the aqueous medium before, during or after heating to a temperature at or above the melting point of the amidoacid composition.

The amidoacid composition may be added to the aqueous medium at any temperature below the decomposition temperature of the amidoacid such as room temperature, but, in a preferred embodiment, the aqueous medium is first warmed to a temperature at or above the melting point of the amidoacid composition. Then, the amidoacid composition is added thereto. In this manner, decomposition of the amidoacid, which may occur at elevated temperatures, is kept to a minimum. Most preferably, the aqueous medium is 0.1-15°C above the melting point of the amidoacid composition when the amidoacid composition is added.

Since an aqueous medium is employed, this places a limitation of 100°C on the melt crystallization temperature. However, amidoacid compositions having a higher melting point can still be melt

crystallized by the present process. More particularly, a material can be added to the aqueous medium to elevate the boiling point. Certain salts and glycols could be employed.

Another alternative is to employ one or more fatty alcohols, fatty acids or fatty esters as diluents in the amidoacid composition whereby the melting point of the amidoacid composition can be depressed below 100°C. A particularly suitable material is lauric acid. References to the melting point of the amidoacid composition do not refer to the melting point of the pure amidoacid, but refer to the melting point of the composition comprising the amidoacid, such as the wet cake.

After addition of the amidoacid composition to the aqueous medium, if necessary, the pH is returned to 2-6 by further addition of the appropriate agent, in this case normally sodium hydroxide.

Then, the aqueous medium is heated to a temperature sufficient to melt the amidoacid composition and stirred until a two phase emulsion of finely divided amidoacid is formed. The emulsion is normally formed in a period of 2-15 minutes. It is desirable to minimize the time at which the amidoacid is kept at a temperature above the melting point in order to minimize decomposition thereof.

Accordingly, it is preferred to add the amidoacid composition to the aqueous medium only after it has be heated. Further, once the emulsion is formed, it is preferable to immediately begin cooling to crystallize the amidoacid.

The cooling of the two phase amidoacid emulsion must be done at a carefully controlled rate, such as 0.1-10.0°C per minute, until crystallization of the amidoacid is complete. If the emulsion is cooled more rapidly, for example by quenching, a poor crystal

structure is formed leading to instability in the crystalline structure of the amidoacid. In order to obtain optimal crystal structure with a minimum of amidoacid decomposition, a cooling rate of 0.5-5.0°C per minute is preferred. Most preferred is a cooling rate of 1-3°C per minute.

The cooling rate specified above applies only in the vicinity of the crystallization temperature of the amidoacid. Since the solubility of the amidoacids in aqueous media is very poor, crystallization is almost complete when the aqueous medium reaches a temperature just below the crystallization temperature. Henceforward, the cooling rate is no longer critical since it can no longer influence the crystal structure. Thus, for an amidoacid composition with a melting point of 67°C, the cooling rate should be controlled in the temperature range of 75°C-60°C to ensure formation of a stable crystal structure. In general the cooling rate is important within about 10°C of the melting point of the amidoacid composition, and, more preferably, the cooling rate is maintained until the suspension attains a temperature at least 5°C below the melting point of the amidoacid composition.

Once cooling is complete, a recrystallized amidoacid product is obtained. This product possesses a more stable crystalline structure, as well as a larger particle size than the amidoacid in the wet cake and therefore lends itself to the production of stable amidoacid suspensions.

The foregoing melt crystallization process can be advantageously employed as an integral part of a suspension process. More particularly, one can advantageously carry out the melt crystallization process in an aqueous suspension media in order to produce stable aqueous suspensions of amidoacids.

When making a suspension, in addition to water, a thickening agent and the other optional ingredients mentioned above, the aqueous suspansion medium may also contain a second polymer. The second polymer improves the physical stability of the suspensions particularly in the case where high concentrations of amidoacid are desired. The second polymer is selected from the group consisting of polyvinyl alcohols, including partially saponified ^' polyvinyl acetates, polyvinyl pyrrolidone, and one or more cellulose derivatives including cellulose ethers. Of particular advantage for use in the current suspensions are methyl cellulose, methyl hydroxypropyl cellulose, methyl hydroxybutyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose. The amount of second polymer is generally from about 0.02 to about 2 wt.% of the suspension.

Any one or more of the thickening agents within the scope of the invention may be combined with any one or more of the second polymers and/or one or more of the other optional ingredients to provide suspensions within the scope of the invention. The aqueous suspension media may also contain one or more additional optional ingredients such as brighteners and perfumes.

In order to make suspensions using the melt crystallization process of the present invention, one carries out the melt crystallization process just as described above until a stable suspension of the amidoacid is obtained. Then, rather than separating out the amidoacid, one simply employs the formed suspension.

In certain cases, it may be desirable to subject the suspension to high shear conditions in order to break up some of the largest agglomerates which are formed during the melt crystallization process. It is generally desirable, in the present invention, to make suspensions with an average particle diameter of 30-100 μ and, more

preferably, an average particle diameter of 40-70 μ . Additional thickening agent may also be added to adjust the viscosity of the suspension to the desired level.

These stable suspensions exhibit good physical and chemical stability, as well as stability under high temperature storage conditions which normally cause significant stiffening of comparable suspensions. The suspensions can be used, for example, as a liquid bleaching agent composition for washing of textiles or bleaching.

The present invention will now be further described by the following examples.

In the following examples, the viscosity is measured by a Brookfield Visco eter Type RVT equipped with a set of spindles. The active oxygen loss was measured by iodometric titration. The pH was measured with a standard pH glass electrode (ex. Ingold) and pH meter (Metrohm) . All suspensions were made in standard glass reactors equipped with pitch bladed glass impellers.

Examples 1-4 and Comparative Example A

Preparation of aqueous suspensions by melt crystallization

As raw material was employed wet cake containing nonylamidoperoxy adipic acid (NAPAA) with an average particle diameter of 15 μm. First, an aqueous suspension medium containing water, thickening agent, second polymer and chelating agent, was prepared and heated to 75°C. Next, the NAPAA wet cake was dosed over a period of 10 minutes with stirring to form a two phase emulsion of a idoperoxyacid melt. Then, the emulsion was then cooled at the cooling rate given in Table 1.

For examples 1-4, the cooling rate refers to the cooling in the temperature range of 75-60°C, whereas for example A the cooling rate refers to cooling in the temperature range of 70-55°C. Brightener and perfume were added and the pH was adjusted to 4.5. The stability data for these materials is presented in Table 1. The formulations for each example were identical and are set forth below.

* Polyviol™ M05-290 (ex. Wacker-Chemie)

2 Tinopal™ CBS-X FWA-49 (Fluorescent Whitening Agent)

3 ex. J.E. Sozio Inc., New Jersey, SZ-4787.

The exact procedure for preparing the suspensions is as follows.

To a 2 liter glass reactor was charged 1100 g. de ineralized water and 3.75 g. dipicolinic acid (DPA) . As the DPA dissolves, the pH drops to 2.0. The pH was then adjusted, with stirring, to 3.0 with caustic soda solution (10% NaOH) . Successively, 4.5 g. Rhodopol™ 23 and 15.0 g. of Polyviol™ M05-290 were sprinkled into the solution with stirring at 300 r.p.m. Thwas aqueous suspension media was then heated to 75°C.

As soon as 75°C was reached, 450 g. NAPAA wet cake containing 39.3 wt% NAPAA was added over a 10 minute period with continued stirring. When all of the NAPAA was melted, a smooth, homogeneous two phase emulsion

was obtained. With a few drops of caustic soda solution the pH was adjusted to 3.0 and jacket cooling was started. From 75-60°C a cooling rate of l°C/min. was employed and stirring was continued at 400 r.p.m. NAPAA crystallization begins at 67°C indicated by a viscosity increase and a slight temperature increase due to the heat of crystallization. At 60°C the cooling was continued more rapidly until ambient temperature was reached.

When the temperature reaches 30°C, 1.5 g. of Brightener FWA-49 was slowly sprinkled into the suspension to enhance the whiteness and brightness. Finally, after reaching ambient temperature, the pH was adjusted to 4.5 with caustic soda solution and the suspension was deagglomerated with an Ultra-Turrax™ for 4 minutes with coarse generator TP 45/2G and 1.5 minutes with the fine generator T 45/6G.

Upon completion of the deagglo eration with the Ultra-Turrax" ^* , the suspension temperature was 30°C. The suspension was again cooled to room temperature with a chilled water bath and vacuum deaerated to remove dispersed air. Finally, an additional 0.15 wt.% of Rhodopol™ 23 thickener was added to adjust the viscosity to the desired level.

Lastly, 0.10 wt.% of Rainforest"" perfume was added to the suspension and the rheological and chemical properties of the suspension were measured over a 10 week storage period at both ambient temperature and at 100°F.

For examples 2-4 and A, the cooling rate was varied. In addition, for each of these examples, the NAPAA was added to the suspension media prior to heating to 75°C. Also, the absolute amounts of each ingredient were varied slightly, by using 1170 g. water and 290 g. NAPAA wet cake in examples 2-4.

Finally, in Example A, 870 g. water and 290 g. NAPAA wet cake were employed and the hot emulsion was cooled by first rapidly cooling to 70°C by adjusting the heating jacket and then by pouring an additional 300 g. of chilled water (1°C) into the emulsion over a 30 second period to cool from 70-55°C. From 55-20°C, the cooling rate was 3°C per minute.

TABLE 1 (page 1)

Example la lb without perfume with perfume

mPas

AvO loss:6.6% after 10 weeks 100°F pH start:4.49 after 10 weeks 3.92

Particle Size Distribution(PSD) (Malvern) _rT_ ^ ^{"^} d 50 d 90 d 99

Density: (kg/m ³ ) start: 1022

4 weeks:

TABLE 1 (page 2)

Suspensions of NAPAA, Nonylamido Adipic Acid (NAAA) and Nonylamidoperoxy Succinic Acid (NAPSA)

In Example 5, the following procedure was employed. A 2 liter glass reactor was charged with 480 g. demineralized water, 2.50 g. DPA and

500 g. NAPSA wet cake. The mixture was stirred at 350 r.p.m. until homogeneous and then 3.0 g. Rhodopol™ 23 and 10.0 g. Polyviol™ M05/290 were added with continued stirring. The pH was adjusted to 3.0 with 10% sodium hydroxide solution and the mixture was heated to 68°C to obtain a two phase emulsion of melted NAPSA. From 68-55°C the cooling rate was l°C/min. Two temperature stabilizations occurred, one at 63°C and one at 59°C. When the temperature reached 55°C, the cooling rate was increased to about 3°C/min and cooling was continued to ambient temperature. At about 40°C, Brightener FWA-49 was added and at 22°C the pH was adjusted to 4.5 with 10% sodium hydroxide solution.

Next the suspension was deagglomerated with the Ultra-Turrax™ as in Example 1 and no extra thickener was required. Before storage, the Rainforest" perfume was added with stirring. The results appear in Table 2 below.

The suspension of Example 6 was prepared by charging a 2 liter glass reactor with 1290 g. demineralized water, 3.75 g. DPA, 180 g. NAAA flakes, 4.5 g. Rhodopol ¹ " thickener and 15.0 g. Polyviol™ M05/290. While stirring the pH of the suspension was adjusted to 3.0 with caustic soda. The suspension was then heated to 87°C to obtain a two phase emulsion. The emulsion was cooled from 87°C-75°C at l°C/min. and then allowed to stand until it reached ambient temperature. At 30°C, 1.5 g. of Brightener 49 was added. The pH is adjusted to 4.5 and deagglomerated with the Ultra-Turrax ^® . Finally, 0.2 Rhodopol ^™ thickener and 0.1% Rainforest™ perfume were added. The results appear in Table 2 below.

TABLE 2

Examples 7-8 and Comparative Example B

Use of Other Additives in the Suspensions

In Example 7, Example 2 was repeated except that 7.5 g. of citric acid were used in place of dipicolinic acid as the chelating agent. The results are given in Table 3.

In Example 8, Example 2 was repeated except that 1 wt.% polyvinyl pyrrolidone was used in place of PVA. The results are given in Table 3.

In Example B, 0.7 wt.% guar gum was used in place of xanthan gum. Guar gum being a polysaccharide which does not contain at least 60% l,4-3-oxy linkages in its polymer backbone, it is outside the scope of the present invention. The results with guar gum are shown in Table 3.

TABLE 3

Exampl e 8

Wei ght Water balance balance balance NAPAA 11.50 11.50 11.50

Comparative Example C

Starting with the same peroxyacid wet cake as was employed in Example 1, a suspension was prepared containing 10.2 wt.% NAPAA, 0.25 wt.% dipicolinic acid, 1.0 wt.% polyvinyl alcohol, 0.5 wt.% xanthan gum and

the balance water by mixing the ingredients with stirring at a temperature below the melting point of the amidoperoxyacid composition. The suspension was then deagglomerated with an Ultra-Turrax™ to provide a suspension with a mean particle size of 13 μm. This suspension was pourable and had an initial viscosity of 270 mPa.s. After 1 week storage at 100°F a gel structure had formed and the suspension was no longer pourable and had a viscosity of more than 10,000 mPa.s.

Example 9 and Comparative Example D

In example 9, the procedure of example 1 was followed except that the aqueous suspension medium contained 1200 g. of demineralized water, 7.5 g. citric acid laq. and 15.0 g. Rhodopol™ thickening agent. A stable emulsion was obtained.

In comparative example D, the procedure of example 9 was followed except that polyvinyl alcohol (Polyviol™ M05/290) was substituted for the Rhodopol™ thickening agent. During heating, clogging of the melting amidoperoxyacid occurred and an unstable emulsion was obtained. If stirring was discontinued, phase separation set in immediately.

The foregoing examples were presented for the purpose of illustration and description only and are not to be construed as limiting the scope of the invention. The subject matter of the invention is to be determined from the claims appended hereto.