WO1997024423A1

WO1997024423A1 - Processes for producing solid surfactant compositions with enhanced dissolution rates

Info

Publication number: WO1997024423A1
Application number: PCT/IB1996/001457
Authority: WO
Inventors: James L. Hazen; Mark Einziger
Original assignee: Rhone-Poulenc Surfactants & Specialties, L.P.
Priority date: 1995-12-28
Filing date: 1996-12-20
Publication date: 1997-07-10
Also published as: AU1039697A

Abstract

The processes involve the incorporation in the solid surfactant of particles of citric acid. In each of the processes melted surfactant is mixed with solid citric acid particles, and the mixture is then solidified. In each of the processes, the citric acid particles comprise from about 1 to 8 weight percent of the combined weight of surfactant and citric acid. The various processes may additionally involve extrusion, spray-coating, or spraying combined with blending.

Description

PROCESSES FOR PRODUCING SOLID SURFACTANT COMPOSITIONS WITH ENHANCED

DISSOLUTION RATES

Field of the Invention The present invention relates to a process for the preparation of solid surfactant compositions and the compositions produced thereby which have dissolution rates in water much higher than those of the surfactants alone.

Background of the Invention

Surfactants have many end-use applications well known to those in the art wherein it is desirable to be able to alter and/or control the dissolution rate of the surfactant once it is intimately admixed with water. In certain situations, it becomes desirable to slow the rate at which surfactants solubilize. for example, when used in toilet bowl cleaning cakes. More often, it is desired to increase the rate at which the solid surfactant dissolves into the aqueous medium.

This enhanced rate of dissolution would be desirable, for example, in dishwashing or powdered laundry detergent situations. Therefore, attempts to control the times of solid surfactant solubiiization have taken various forms, such as using incorporated binders and/or effervescent compositions, extrusion granulation, membrane encapsulation, or tableting. i.e.. compression of the surfactant-containing compositions, all of which processes have attendant disadvantages.

For example, encapsulation is highly dependent upon the quality of the encapsulating material and may release the compositions in discrete packages.

The compaction process is an extremely difficult way to control the release of surfactant material for slight variations in composition properties, e.g.. tackiness, particle size. etc. can have dramatic impact on the dissolution rate even under fixed, uniform compacting pressure. Pure extrusion processing to prepare melt-admixed granules, such as is taught in EP 501.798A1 has the disadvantage of always intimately admixing all of the components thus inherently placing a restriction on the individual components that can be utilized in such a process, i.e.. they must be compatible. Furthermore utilization of solid surfactant and active material compositions in extruder processes, without more, tend to realize compaction problems as discussed above.

Utilization of additives to effect an effervescent action i.e. to realize gas generation, usually carbon dioxide, is a well known technique in the art to increase the aqueous dissolution rate of a solid composition containing surfactants as taught for example, in US Patent Nos. 5.180.587: 5.213.808: and 5.236.689. Usually such gas generating disintegrants use various combinations of dibasic and tribasic organic carboxylic acids such as citric, fumaric, phthalic, maleic, malic, oxalic, adipic, glutaric. 2-methyl glutaric. succinic and tartaric or mixtures of any of them with carbonates or hydrogencarbonates including the lithium, sodium, and potassium salts thereof or mixtures of them. This gas generating technique has the attendant disadvantages of having, by necessity, additional material present in the compositions, i.e.. the carbonate or hydrogencarbonate. as well as the high loadings of the reactants necessary to produce sufficient gas to affect the desired break-up of the particles.

It would be advantageous if a process means relatively insensitive to minor process or product variations were available to avoid the above identified problems of the prior art processes and to increase the rate at which solid surfactants, preferably solid nonionic surfactants dissolve in aqueous medium. More preferably, it would be advantageous to have a process and compositions wherein solid nonionic surfactant compositions dissolve more rapidly in aqueous solution than the surfactants alone and also said process would permit i) incompatible components to be incorporated into a single granule and ii) preferential or sequential exposure of selected components to the aqueous media. Summary of the Invention It is an object of the present invention to realize processes for preparing solid surfactant compositions, preferably solid nonionic surfactant compositions with significantly enhanced and easily predictable and controllable aqueous dissolution rates. This is accomplished by incorporating from about 1 to about 8 weight percent of solid citric acid having a particle size range between about 50 and about 200 U.S. Standard mesh: said weight percent based on the combined weight of the surfactant and citric acid in the paniculate or granular product.

Detailed Description of the Invention

It has been discovered that the time for complete dissolution in water of certain solid surfactants, and surfactant compositions, preferably nonionic surfactants can be significantly reduced by the incorporation of from about 1 weight percent to about 8 weight percent, preferably from about 3 weight percent to about 7 weight percent, and most preferably between about 5 weight percent and 7 weight percent, of solid citric acid having a particle size range between about 50 and about 200 U.S. Standard mesh based on the combined weight of the surfactant and citric acid in the granular product. That is, the citric acid particles in the final solid surfactant composition should be such that they would pass through a 50 mesh screen but not pass through a 200 mesh screen. The processes used for preparing the solid granule or particle compositions of the present invention must be such that the processing temperature exceeds the melting point of the solid surfactant i.e.. the surfactant, which is solid at room temperature or slightly above, must be liquid during processing and the processing temperature cannot exceed the melting point of citric acid i.e., about 153°C. In other words, during the preparation of the compositions of this invention, the citric acid must remain in a solid particulate state. Furthermore, the admixing of the particulate citric acid with the liquid, i.e.. the melted surfactant, preferably should take place with agitation in order to prevent segregation or settling out of the citric acid particles. The preferred processes for preparing the compositions of the instant invention are extruding and spray coating.

In the extrusion process, the solid surfactant is melted in a first zone of an extruder, preferably from about 50°C to about 150°C: particles of citric acid are then added in a second zone of the extruder, downstream of the first: the composition is then mixed under moderate shear in a third zone of the extruder, downstream of the second zone; and finally, the composition is extruded through a die, preferably with a cutter head. After allowing the pellets to cool, the compositions optionally can be ground to any desired smaller size.

The second, and more preferred process for preparing the granular compositions of the instant invention is a spray coating process.

By ''spray-coating^" is meant a process whereby the solid surfactant is melted and coated upon the citric acid particles while still in the molten state. This can be accomplished by spraying the molten surfactant onto the citric acid particles within, for example, a coating blender. Of course, it is anticipated that other material, especially particulate material may also be present in the blender with the citric acid during the spray-coating process. For example, actives and other adjuvants may be present if the final granules are being prepared for use in the agricultural or pharmaceutical industries.

Complete coating of the citric acid and other particles initially present in the blender prior to spraying is not always necessary but. rather the degree of completeness of the coating is often determined by specific requirements, such as the need to isolate the citric acid or another component from other incompatible additives.

Furthermore, the sprayed citric acid compositions, while still in a tacky state, can be continuously rumbled to partially agglomerate or granulate the individual particles so as to yield dry flowable granules. It is also anticipated that additional material can be introduced into the blender during this tacky state tumbling so as to adhere the added material to the outside of the granules being produced. Thus a final multi-component composition can be produced wherein the components will be in a uniform weight percent distribution desired for a specific end use and the components will not separate upon shipping and/or significant handling.

Certain solid surfactants, for example certain anionic taurates. may prove to be difficult to melt in the limited temperature range of this invention and so it is anticipated that certain solid surfactants may need to be solubilized by the addition of a solvent during the heating step.

The anionic surfactants of this invention are those known in the art which are solid or of a hard, nontacky wax consistency at room temperature, inclusively called "solid" and include the ethoxylated and non-ethoxylated higher alkyls. alkylbenzenes, alkylnaphthalenes; diphenyloxides. and olefin sulfates. sulfonates. and disulfonates; the higher alkyl or alkylamido sulfosuccinates: the higher alkyl sulfosuccinamates: naphthalene-formaldehyde condensates; the higher alkyl isethionates; and the higher alkyl N-methyl taurates. Also included are the higher alkyl or alkaryl ether carboxylates and the mono and di higher alkyl or alkaryl phosphate esters which are solid at room temperature.

The nonionic surfactants whose dissolution rates can be enhanced by the processes

of this invention are those known in the art which are solid or of a hard, nontacky wax consistency at room temperature, inclusively called "solid". Among the preferred nonionics are the following:

A) Amides such as:

i) Alkanolamides of the formula - O

II / R'

R C N

\ R"

wherein R^* and R" each can be -H, -CH₂CH₂OH, or -CH₂ - CH-OH:

II CH, ii) ethoxvlated alkanolamides of the formula -

O (CH,-CH,-O\H

II /

R- C-N / ^{*^}^- (CH CH O)_yH; and in) ethylene bisamides of the formula -

O

II

R-C H N-CH,-CH₂-N

H ^ ^\ C-R

O

Esters such as: i) fatty acid esters of the formula - O

II R-C-O-R,;

ii) glycerol esters of the formula - O R - C - O - CH₂ - CH - CH₂ - O - R,

OH;

iii) ethoxvlated fatty acid monoesters of the formula -

O

I! R-C-O(CH-,CH₂O)-R,; iv) sorbitan esters of the formula -

HO OH

v) ethoxvlated sorbitan esters of the formula -

H-(OCH₂CH₂)_π-O

H

Ethoxylates such as: i) alkylphenol ethoxylates of the formula ^■

ii) alcohol ethoxylates of the formula R - O - (CH_:CH₂O)_nH; iii) tristyrylphenol ethoxylates of the formula

(OCH₂CH₂)_nOH

iv) mercaptan ethoxylates of the formula - R - S - (CH₂CH₂O)_nH

End-capped and EO/PO block copoiymers such as: i) alcohol alkoxylates of the formula -

CH₃

I

R-(OCH₂CH₂)_x - (O - CH - CH₂)_m - OH:

ii) ethylene oxide/propylene oxide block copoiymers of the formula

CH₃ HO - (CH₂CH₂O)_x (CH₂-CH-O)_m - (CH₂CH₂O\ - H: iii) copoiymers of the formula -

CH₃ CH₃

I I HO(CH-CH₂0)_m-(CH₂CH₂O)_x-(CH₂-CH O), H; iv) chlorine capped ethoxylates of the formula -

R - (OCH,CH₂\Cl; and

v) tetra-functional block copoiymers of the formula -

CH₃ CH₃

I I H (OCH,CH,\ - (OCH CH₂)_m (CH,CH O)_m'-(CH,CH,O)_x.H

/ \

NCH, CH, N

\ ^" /

H (OCH,CH,\ - (OCH CH₂), (CH,CHO)_r - (CH,CH,O\..H j !

CH CH₃ or

CH₃ CH₃

CH₃ CH₃ wherein R is a fany alkyl group, preferably a C₆ - C,, fatty alkyl group, most preferably a C₈ - C_[g fatty alkyl group;

R, is -H or a fatty alkyl group, preferably -H or a C₆ - C,, fatty alkyl group, most preferably -H or a C₈ - C_{l g} fatty alkyl group; x. x', y, y' and n are each independently moles of ethylene oxide preferably 1 to 300: most preferably 1 to 150; and m. m'. 1 and 1' are each independently moles of propylene oxide, preferably 1 to 300: most preferably 1 to 150: with the proviso that the surfactant is a solid at room temperature (24°C), and preferably a solid at 50°C. Mixtures of the above surfactants are acceptable and, in fact, mixtures of the above surfactants with other surfactants that alone are liquid even at room temperature may be acceptable provided that the amount or nature of the liquid surfactant is such that the final particulate product does not exhibit tackiness at room temperature. Preferably, tackiness is not exhibited even at 50°C. The more preferred solid nonionic surfactants are the aforedescribed alkyl alcohol ethoxylates and alkylphenol ethoxylates.

The most preferred solid nonionic surfactant is dinonylphenol ethoxylate ( )100 EO) for it has been discovered that this compound possesses the ability to provide excellent wetting characteristics together with a high melting point. Furthermore, the material exhibits an ability to dissolve in aqueous medium without formation of a gel phase.

Another preferred embodiment of this invention is to spray-coat the molten surfactants, more preferably nonionic surfactants, onto a mixture of diammonium sulfate and citric acid particles.

The preferred process of the instant invention is the spray-coating process which comprises the steps of:

a) adding citric acid particles to a blender chamber;

b) mixing said citric acid to ensure uniform distribution:

c) melting an initially solid nonionic surfactant composition, preferably at a temperature of from about 50°C to less than about 153°C: d) spraying the molten surfactant composition onto the citric acid in said blender chamber with continuous blending to effect a coating and granulation of the citric acid/surfactant particles: and

e) cooling the coated granules.

The more preferred process of the instant spray-coating invention comprises the steps of:

a) adding diammonium sulfate and citric acid to a blender chamber:

b) mixing said diammonium sulfate and citric acid mixture to ensure uniform distribution:

c) melting an initially solid, nonionic surfactant composition, preferably at a temperature of from about 65° to about 95°C.

d) spraying the molten surfactant composition onto the diammonium sulfate and citric acid mixture in said blender chamber with continuous blending to effect a coating and granulation of the particles; and

e) cooling the coated granules, preferably to less than 50°C.

Preferably, the diammonium sulfate and citric acid mixture is initially blended for at least 10 minutes before the spraying step to ensure that the initial crystal sizes are uniformly distributed throughout the batch. The preferred spray blender mixers are those of the Mark VI design manufactured by Continental Rollo or an equivalent.

The amount of diammonium sulfate in the particulate mixture to be spray-coated by the solid nonionic composition can be from about 1 to less than 70 weight percent preferably from about 3 to about 50 weight percent and the citric acid can be present from about 1 to about 8 weight percent based on the combined weight of the surfactant and citric acid in the spray- coated composition.

The essence of the instant invention lies in the discovery that if citric acid particles in the range between about 50 and 200 U.S. Standard mesh are spray-coated or extruded with a solid anionic or solid nonionic surfactant, the dissolution rate of the solid surfactant granular composition in aqueous solution is greatly enhanced. It is theorized that the solid citric acid particles via a wicking action, dissolve; expand; and thus break up the solid surfactant material. Quite possibly the wicking and dissolving action is followed by the citric acid leaching out of the solid surfactant thus increasing the surfactant surface area exposed to the aqueous medium.

Preferably, to aid in providing a unifoim coating and also to avoid undesirable agglomeration, the mixture should continue to be blended for at least three additional minutes after the spraying has ceased. If it is desired to have any additional components adhere to the surface of the coated granules, e.g., if an additional additive is a fine powder and one desires to reduce dusting in the final product the material can be added while the coated granules are still tacky to obtain adherence, i.e.. the material can be added before the coated material is completely cooled. Examples of such optional additional components include anti-foam agents, flow agents, anti-caking agents, stabilizers, inert fillers, gas-generating agents, dyes, and/or any adjuvants particular to the specific end-use application of the resulting product. Optional adjuvants can be added from about 0 to about 20 weight percent of the granular composition. Inert ingredients can be present from about 0 to about 80 weight percent.

One of the distinct advantages of the instant spray-coated, i.e.. multi-layered particle is that it frees the multi-component systems manufacturers. For example, additional adjuvant components which normally would be incompatible with the citric acid or a compound which was initially mixed with the citric acid and then spray-coated, can be made a part of the coated particle by introducing the component after the coating process is completed, but while the multi-layered material is still tacky so that the adjuvant can be adhered to the outer surface, i.e., the component would only be in contact with the outer surfactant composition layer.

Another advantage realized by this adherence contact procedure is that since it allows material to be placed on the outside of the spray-coated particle, it gives the adhered material preferential or advanced exposure to the aqueous media. Thus, one can also selectively sequence the exposure times of certain components of the particle.

The coated surfactant-citric acid composition may be used as is or, if preferred, screened to a desired particle size.

The following specific examples are further illustrative of the present invention, but it is understood that the invention is not limited thereto. All amounts of various ingredients are by weight unless otherwise specified.

In all of the following examples, the dissolution rates were determined as follows (unless indicated otherwise):

A calculated amount of product such that the surfactant weight remained at 2.0 grams is added into a 250 ml beaker filled with 98 ml of deionized water at room temperature while stirring with a magnetic stirrer set to a speed of about 30-50% full scale and a stopwatch started. When complete dissolution is observed, i.e., the solution becomes clear, the time is recorded.

Examples I - Vπi

Citric acid having a particle size range between 50 and 200 mesh (U.S. Standard) is charged into a Continental Rollo mixer, Mark VI blender. A solid surfactant composition is heated to a temperature such that the surfactant composition is melted but below the melting point of the citric acid i.e., about 153°C. The molten surfactant is then sprayed onto the rotating citric acid particles through fine sized 8008E spray tips. The mbcture is blended continuously for three additional minutes to ensure uniform coating and granulation. The mixture is then cooled to room temperature. The granular product is collected through a #8 (U.S. Standard) mesh screen. In these and the following examples, the percentages as indicated in Table I are weight percents based on the combined weight of the surfactant and citric acid in the final formulation. The aqueous dissolution times in minutes:seconds at both room temperature (24°C) and at 40°C of the solid surfactant of similar particle size alone and the granular surfactant/citric acid products of this invention, are set forth in Table I.

TABLE I

1 ) Rhodasurf TB-970 is a long chain linear alcohol ethoxylate

2) Igepal CO-890 is a nonylphenol ethoxylate (40 EO)

3) Igepal DM-880 is a dinonylphenol ethoxylate (49 EO)

4) Antarox F-88 FL is an EO PO/EO block copolymer 5 ) Antarox F- 108 is an EO/PO/EO block copolymer 6) Soprophor S/40P is a trisryrylphenol ethoxylate (40EO)

7) Antarox P- 104 is an EO/PO/EO block copolymer

8) Rhodasurf 870 is a castor oil based alcohol ethoxylate

All of the above are trademarks of proprietary nonionic surfactants sold by Rhone Poulenc.

The resulting dissolution times of the citric acid laced solid nonionic surfactant compositions in Table I indicate the significantly enhanced dissolution rates that can be unexpectedly realized by this invention i.e., by having citric acid particles in the range of from 50 to 200 mesh interspersed within the solid surfactant granules.

Example IX

Following the procedure of Examples I-VTII, citric acid was introduced into a Continental Rollo mixer. Mark VI blender. Sodium oleyl N -methyl taurate. an anionic surfactant sold under the trademark Geropon T-77 by Rhone Poulenc was slightly solubilized by the addition of a solvent and heated to obtain a liquid. The solvent addition was necessary for the solids melting point was too close to that of the citric acid. The liquid surfactant was sprayed onto the tumbling citric acid particles as in Examples I-VIII and processed as set forth in those Examples. The dissolution times at room temperature (24°C) and at 40°C are as indicated in Table II.

TABLE π

Sample As Is As Is 5% Citric Acid 5% Citric Acid

(R.T.) (40°C) (R.T.) (40°C)

Geropon T-77 12:07 6:37 2:51 1:55

The resulting dissolution times indicate the significantly enhanced dissolution rates that can be realized with solid anionic surfactant compositions by utilizing, in the manner described, the particulate citric acid of this invention.

Examples X. XI and XII

A concentrated aqueous solution of citric acid is heated and blended with molten AgRHό DS-420 at 85°C such that the citric acid is present at about 5 weight percent of final solution. AgRHό DS-420 is prepared by blending a flaked dinonylphenol ethoxylate ( >100 EO) (sold under the Rhone-Poulenc trademark Igepal DM-970 FLK) with a sufficient amount of a liquid isodecyl alcohol ethoxylate (4EO) (sold under the Rhone-Poulenc trademark Rhodasurf DA-530) to produce a non-tacky, solid mixture with an 85:15 respectively weight ratio surfactant composition. Although the isodecyl alcohol ethoxylate has an adverse effect on the melting point of the solid dinonylphenol ethoxvlated surfactant, its presence is useful for the improved wetting characteristic it provides, i.e., the lower surface tension realized in the final aqueous solution as a result of its incorporation.

The liquid blend is cooled to solidification; ground; and collected through a #8 mesh screen (U.S. Standard). Dissolution studies, conducted as in the previous examples, indicate no significant increase in dissolution rates over that of comparably sized, solid surfactant alone.

Molten citric acid is blended into molten AgRHό DS-420 at a final concentration level of 5 weight percent; cooled to solidification: and ground to obtain a final particulate product which is collected through a #8 mesh (U.S. Standard). Dissolution studies, conducted as in the previous examples, indicate no significant increase in dissolution rates over that of comparably sized, solid surfactant alone.

Finely powdered citric acid. i.e.. particles of citric acid which easily pass through a 400 mesh screen (U.S. Standard), is tumble blended as in Example I and processed according to the methods of that example using AgRHό DS-420. Dissolution studies, conducted as in the previous examples, indicate no significant increase in dissolution rates over that of comparably sized, solid surfactant alone.

Examples XIII - XXVm

Diammonium sulfate and. where indicated in Table III. citric acid particles in the range of from about 50 to about 200 mesh (U.S. Standard) in an amount sufficient to realize 5 weight percent acid based on the combined weight of the acid and surfactant in the final granulated product is charged into a Continental Rollo mixer Mark VI blender. The sulfate and acid are rotationally blended for about 10 minutes. A solid, nonionic surfactant i.e., AgRHό DS-420 is heated at a temperature of about 85°C until the surfactant composition is melted. The molten surfactant is then sprayed onto the rotating diammonium sulfate and citric acid mixture through fine sized 8008E spray tips. The mixture is blended continuously for three additional minutes to ensure uniform coating and granulation. The mixture is then cooled to room temperature and the coated granular product is collected through a #8 mesh screen (U.S. Standard). The "assay" in Table III indicates the weight percent, based on the total weight of the final granular product of the surfactant on the granules. One can anticipate that the higher the assay, the thicker the solid surfactant coating and thus, the longer the dissolution time.

TABLE πi

Dissolution Time (Sec) Dissolution Time (Sec) W/O Citric Acid W Citric Acid

54 52 56 56 58

37 41 62

89 88

51 51 57 102 98

99

* Citric acid was dissolved in the surfactant before coating.

The resulting dissolution times of these most preferred solid nonionic surfactant compositions indicate the greatly enhanced dissolution rates that can be achieved via utilization of the particulate citric acid in the methods of this invention. In addition to the aforementioned enhanced dissolution: incompatibility avoidance; and preferential dissolution advantages, the coated products of the preferred modifications of this invention also realize a very uniform particle size together with excellent attrition resistance. Serendipitously. the process is significantly less energy intensive and more capital cost effective than other melt-admixing processes, e.g.. extrusion processes of the prior art.

Although the present invention has been described and illustrated with reference to specific examples, it is understood that modifications and variations of composition and procedure are contemplated within the scope of the following claims:

Claims

What is claimed is:

1. A method of prepaπng solid anionic or nomomc surfactant compositions havmg enhanced aqueous dissoluϋon rates compπsmg the steps of:

melting the solid anionic or nomomc surfactant below about 153°C;

intimately mixing with said melted surfactant from about 1 to about 8 weight percent of citπc acid particles in the range of from about 50 to about 200 mesh (U S. Standard) said weight percent based on the combmed weight of the citπc acid and surfactant; and

solidifying the resulting composition.

2 A method of prepaπng solid anionic or nonionic surfactant compositions havmg enhanced aqueous dissolution rates compπsmg the steps of

melting the solid anionic or nonionic surfactant below about 153°C,

intimately mixing with said melted surfactant from about 1 to about 8 weight percent of citπc acid particles in the range of from about 50 to about 200 mesh (U.S Standard) said weight percent based on the combined weight of the citπc acid and surfactant;

extrudine said intimate mixture: and

solidifying the extrudiate

3. A method of preparing solid anionic or nonionic surfactant compositions having enhanced aqueous dissolution rates comprising the steps of:

melting the solid anionic or nonionic surfactant below about 153°C ; spray-coating with said melted surfactant from about 1 to 8 weight percent of citric acid particles in the range of from about 50 to about 200 mesh (U.S. Standard), said weight percent based on the combined weight of the surfactant and citric acid:

cooling; and

10 granulating the coated citric acid composition.

4. The method of claim 3 wherein the solid surfactant is nonionic.

15 5. A method of preparing solid anionic or nonionic surfactant compositions having enhanced aqueous dissolution rates comprising the steps of:

a) mixing citric acid particles in the range of from 50 to 200 mesh (U.S. Standard) in a blending chamber;

20 b) melting nonionic surfactant below about 153°C;

c) spraying the molten surfactant onto the citric acid particles with continuous blending to achieve coating and granulation of the acid particles: and o 3 d) cooling the coated particles wherein said citric acid comprises from about 1 to about 8 weight percent of the composition, said weight percent based on the combined weight of the citric acid and surfactant.

6. The method of claim 5 wherein prior to the spraying step, diammonium sulfate is added to the blending chamber.

7. The method of claim 1 with the proviso that the intimate mixing occurs essentially in the absence of a gas-generatingly effective amount of a carbonate or hydrogencarbonate.