WO2009158449A1

WO2009158449A1 - A spray-drying process

Info

Publication number: WO2009158449A1
Application number: PCT/US2009/048559
Authority: WO
Inventors: Hossam Hassan Tantawy; Nigel Patrick Somerville Roberts; Simon Howe; Stuart Andrew Caldwell
Original assignee: The Procter & Gamble Company
Priority date: 2008-06-25
Filing date: 2009-06-25
Publication date: 2009-12-30
Also published as: EP2138565A1; CA2726023A1; BRPI0914675A2; CN102066544A; MX2010014505A; JP2011525215A

Abstract

The present invention relates to a process for preparing a spray-dried powder comprising (i) anionic detersive surfactant; (ii) from 0wt% to 10wt% zeolite builder; (iii) from 0wt% to 10wt% phosphate builder; and (iv) optionally from 0wt% to 15wt% silicate salt; wherein the process comprises the steps of: (a) forming an alkaline slurry in a mixer, the slurry comprising: (v) from 0wt% to 15wt% anionic detersive surfactant; (vi) from 0wt% to 35wt% water; and (b) transferring the alkaline slurry from the mixer through at least one pump to a spray pressure nozzle; (c) contacting an acid anionic detersive surfactant precursor to the alkaline slurry after the mixer and before the spray pressure nozzle to form a mixture; (d) spraying the mixture through the spray pressure nozzle into a spray-drying tower; (e) spray-drying the mixture to form a spray-dried powder; and (f) optionally, contacting an alkalinity source with the alkaline slurry and/or the acid anionic detersive surfactant precursor, and/or the mixture.

Description

A SPRAY-DRYING PROCESS

FIELD OF THE INVENTION

The present invention relates to a spray-drying process.

BACKGROUND OF THE INVENTION

Laundry detergent compositions are typically made by a process that involves the step of spray-drying an aqueous slurry comprising anionic detersive surfactant to form a spray-dried powder. Typically, this spray-drying step is the rate determining step in the production of the laundry detergent powder. This is especially true for low-built formulations that have increased drying loads. With increasing global laundry detergent powder volume demand, many detergent manufacturers' spray-drying towers are running at, or very near, maximum capacity. In order to increase the capacity of their existing spray-drying facilities, detergent manufacturers have to either invest in additional or upgraded spray-drying equipment and/or formulate their spray-dried powder with process aids that increase the formulation complexity of the spray-dried laundry detergent powder.

The inventors have found that by taking at least some of the anionic detersive surfactant from the aqueous slurry in the mixer, and adding its acid precursor at a later stage (i.e. to the alkaline slurry) in the spray-drying process, and by carefully controlling the moisture level of the alkaline slurry in the mixer, the capacity rate of the spray-drying process is significantly increased without the need for investment in additional spray-drying equipment or the need for the incorporation of process aids.

SUMMARY OF THE INVENTION The present invention relates to a process as defined in claim 1.

DETAILED DESCRIPTION OF THE INVENTION

Spray-drying process

The process comprises the steps of: (a) forming an alkaline slurry in a mixer; (b) transferring the alkaline slurry from the mixer through at least one pump to a spray pressure nozzle; (c) contacting an acid anionic detersive surfactant precursor to the alkaline slurry after the mixer and before the spray pressure nozzle to form a mixture; (d) spraying the mixture through the spray pressure nozzle into a spray-drying tower; (e) spray-drying the mixture to form a spray- dried powder; and (f) optionally, contacting an alkalinity source with the alkaline slurry and/or the acid anionic detersive surfactant precursor, and/or the mixture. Each of the process steps are described in more detail below.

Step (a)

In step (a), an alkaline slurry is formed in a mixer. The preferred mixer in step (a) is a crutcher mixer. The alkaline slurry in the mixer is preferably heated, typically in the range of 50⁰C to 90⁰C. Saturated steam can be used to heat the slurry in the mixer. Preferably, all of the liquid components that make up the slurry are heated prior to addition to the mixer, and the slurry is preferably maintained at an elevated temperature in the mixer. These temperatures are preferably in the range of 50⁰C to 90⁰C.

Typically, the residence time of the slurry in the mixer is in the range of from 20 seconds to 600 seconds.

The mixer in step (a) typically has a motor size such that its installed power is in the range of from 5OkW to 10OkW.

Step (b)

In step (b), the alkaline slurry is transferred from the mixer through at least one pump to a spray pressure nozzle. Typically, the alkaline slurry is first transferred to a low pressure line. The low pressure line typically has a pressure in the range of from 4.OxIO⁵ Pa to 1.2xlO⁶ Pa. Typically, the alkaline slurry is then pumped into a high pressure line. The high pressure line typically has a pressure in the range of from 4.0x10 Pa to 1.2xlO⁷ Pa. Typically, a high pressure pump is used to transfer the alkaline slurry from the low pressure line to the high pressure line. Preferably the high pressure pump is a piston pump.

Typically, the alkaline slurry passes through a second mixer during step (b). The second mixer is preferably a slurry disintegrator. The second mixer is typically operated at 1,000 rpm to 3,000 rpm. This second mixer reduces the particle size of the solid material in the slurry. The particle size of the solid material in the slurry at the end of step (b) is preferably less than 2.0mm. This mitigates the risk of blocking the spray pressure nozzle. In step (c), an acid anionic detersive surfactant precursor is contacted to the alkaline slurry after the mixer and before the spray pressure nozzle to form a mixture. Preferably, the acid anionic surfactant precursor is contacted to the alkaline slurry in a low pressure line. However, the acid anionic surfactant precursor may be contacted to the alkaline slurry in a high pressure line. Typically, the temperature of the acid anionic detersive surfactant precursor is in the range of from 20⁰C to 50⁰C when it is contacted with the alkaline slurry. Typically, the ratio of the flow rate of the alkaline slurry to the flow rate of the acid anionic detersive surfactant precursor is controlled. This control is typically achieved by passing the acid anionic detersive surfactant precursor through a mass flow meter, and monitoring the mass flow rate of the alkaline slurry by a loss in weight system installed on a holding tank into which the alkaline slurry is typically transferred prior to it being pumped into the low pressure line. The ratio of the flow rate of the alkaline slurry to the flow rate of the acid anionic detersive surfactant precursor is typically in the range of from 2.5:1 to 25:1, preferably from 5:1, or from 8:1, and preferably to 20:1, or to 15:1.

Step (d)

In step (d), the mixture is sprayed through the spray pressure nozzle into a spray-drying tower. Typically, the mixture is sprayed at a pressure in the range of from 4.0x10 Pa to 1.2xlO⁷ Pa. Typically, the mixture is sprayed at a mass flow rate in the range of from ^OOOkghr ¹ to VO^OOkghr^"1. Typically, a plurality of nozzles are used in the process, preferably the nozzles are positioned in a circumferential manner at different heights throughout the spray-drying tower. The nozzles are preferably positioned in a counter-current manner with respect to the air flow in the tower.

Step (e)

In step (e), the mixture is spray-dried to form a spray-dried powder. Typically, the air inlet temperature is in the range of from 200⁰C to 350⁰C. Typically, the air in-let flow rate is in the range of from 50,000 to 150,000kgm^"3.

Optional step (f)

In optional step (f), an alkalinity source is contacted with the alkaline slurry and/or the acid anionic detersive surfactant precursor, and/or the mixture. The alkalinity source is preferably contacted to the alkaline slurry substantially simultaneously with the acid anionic detersive surfactant precursor. Typically, the alkalinity is contacted to the alkaline slurry and/or the acid anionic detersive surfactant precursor, and/or the mixture at a temperature above 10⁰C; this is especially preferred when the alkalinity source comprises sodium hydroxide.

The alkalinity source can be contacted to the alkaline slurry and/or mixture by injecting the alkalinity source into the low pressure line. Alternative, the alkalinity source, can be injected into the high pressure line.

Typically, the ratio of the flow rate of the alkaline slurry to the flow rate of the alkalinity source is controlled. This control is typically achieved by passing the alkalinity source through a mass flow meter. The control of the mass flow rate of the alkaline slurry is described in more detail above.

Alkaline slurry

The alkaline slurry typically comprises: (a) from Owt% to 15wt% anionic detersive surfactant; and (b) from Owt% to 35wt% water. The alkaline slurry preferably comprises from Owt%, or from above Owt%, and preferably to 30wt%, or to 25wt%, or to 20wt%, or to 15wt%, or even to 10wt% water. The alkaline slurry may be substantially anhydrous. The alkaline slurry typically comprises one or more adjunct detergent ingredients. The alkaline slurry preferably comprises carbonate salt, preferably at least 5wt%, or at least 10wt% carbonate salt. Preferably, the alkaline slurry comprises from Owt% to 10wt%, or from above Owt%, and preferably to 8wt%, or to 6wt%, or to wt%, or to 2wt% anionic surfactant. The alkaline slurry may even be essentially free of anionic detersive surfactant. By essential free of, it is typically meant comprises no deliberately added.

The alkaline slurry may comprise polymeric material. A preferred polymeric material is a carboxylate polymer. The alkaline slurry may comprise at least lwt%, or even at least 2wt% polymeric material.

Preferably, the weight ratio of solid inorganic material to solid organic material present in the slurry is in the range of from 10:1 to 10,000:1, preferably at least 35: 1. The alkaline slurry may comprise less than 10wt% solid organic material, or less than 5wt% solid organic material. The alkaline slurry may even be essential free of solid organic material. For the purpose of the present invention, organic means any hydrocarbon component. Spray-dried powder

The spray-dried powder comprises: (i) anionic detersive surfactant;

(ii) from Owt% to 10wt% zeolite builder; (iii) from Owt% to 10wt% phosphate builder; and (iv) optionally from Owt% to 15wt% silicate salt. The spray-dried powder typically comprises additional adjunct detergent ingredients. Preferably, the spray-dried powder comprises a carbonate salt.

The spray-dried powder typically has a particle size distribution such that the weight average particle size is in the range of from 300 micrometers to 600 micrometers, and preferably less than 10wt% of the spray-dried powder has a particle size greater than 1,180 micrometers, and preferably less than 10wt% of the spray-dried powder has a particle size of less than 150 micrometers.

Typically, the spray-dried powder has a bulk density in the range of from lOOg/1 to 700g/l. The spray-dried powder typically has a moisture content of less than 5wt%, preferably less than 4wt%, or even less than 3wt%. Preferably, the spray-dried powder is white.

Acid anionic detersive surfactant precursor

The acid anionic detersive surfactant precursor preferably comprises C₈-C₂₄ alkyl benzene sulphonic acid. However, any acid anionic detersive surfactant precursor may be used in the present invention.

Anionic detersive surfactant

The anionic detersive surfactant preferably comprises alkyl benzene sulphonate. Preferably the anionic detersive surfactant comprises at least 50%, preferably at least 55%, or at least 60%, or at least 65%, or at least 70%, or even at least 75%, by weight of the anionic detersive surfactant, of alkyl benzene sulphonate. Preferably the alkyl benzene sulphonate is a linear or branched, substituted or unsubstituted, C₈_i₈ alkyl benzene sulphonate. This is the optimal level of the C₈_i₈ alkyl benzene sulphonate to provide a good cleaning performance. The C_8-I8 alkyl benzene sulphonate can be a modified alkylbenzene sulphonate (MLAS) as described in more detail in WO 99/05243, WO 99/05242, WO 99/05244, WO 99/05082, WO 99/05084, WO 99/05241, WO 99/07656, WO 00/23549, and WO 00/23548. Highly preferred C₈-_I8 alkyl benzene sulphonates are linear C ₁₀- ₁₃ alkylbenzene sulphonates. Especially preferred are linear Cio-₁₃ alkylbenzene sulphonates that are obtainable, preferably obtained, by sulphonating commercially available linear alkyl benzenes (LAB); suitable LAB include low 2-phenyl LAB, such as those supplied by Sasol under the tradename Isochem or those supplied by Petresa under the tradename Petrelab^®, other suitable LAB include high 2-phenyl LAB, such as those supplied by Sasol under the tradename Hyblene^®. The anionic detersive surfactant may preferably comprise other anionic detersive surfactants. A preferred adjunct anionic detersive surfactant is a non-alkoxylated anionic detersive surfactant. The non-alkoxylated anionic detersive surfactant can be an alkyl sulphate, an alkyl phosphate, an alkyl phosphonate, an alkyl carboxylate or any mixture thereof. The non- alkoxylated anionic surfactant can be selected from the group consisting of; Ci₀-C_2O primary, branched-chain, linear-chain and random-chain alkyl sulphates (AS), typically having the following formula:

M⁺

wherein, M is hydrogen or a cation which provides charge neutrality, preferred cations are sodium and ammonium cations, wherein x is an integer of at least 7, preferably at least 9; Ci_O-Ci₈ secondary (2,3) alkyl sulphates, typically having the following formulae:

OSO₃ ^" M⁺ OSO₃ ^" M⁺

CH₃(CH₂)_X(CH)CH₃ or CH₃(CH₂)_y(CH)CH₂CH₃

wherein, M is hydrogen or a cation which provides charge neutrality, preferred cations include sodium and ammonium cations, wherein x is an integer of at least 7, preferably at least 9, y is an integer of at least 8, preferably at least 9; C_I0-C_I8 alkyl carboxylates; mid-chain branched alkyl sulphates as described in more detail in US 6,020,303 and US 6,060,443; methyl ester sulphonate (MES); alpha-olefin sulphonate (AOS); and mixtures thereof.

Another preferred anionic detersive surfactant is an alkoxylated anionic detersive surfactant. The presence of an alkoxylated anionic detersive surfactant in the spray-dried powder provides good greasy soil cleaning performance, gives a good sudsing profile, and improves the hardness tolerance of the anionic detersive surfactant system. It may be preferred for the anionic detersive surfactant to comprise from 1% to 50%, or from 5%, or from 10%, or from 15%, or from 20%, and to 45%, or to 40%, or to 35%, or to 30%, by weight of the anionic detersive surfactant system, of an alkoxylated anionic detersive surfactant.

Preferably, the alkoxylated anionic detersive surfactant is a linear or branched, substituted or unsubstituted Ci_2-I8 alkyl alkoxylated sulphate having an average degree of alkoxylation of from 1 to 30, preferably from 1 to 10. Preferably, the alkoxylated anionic detersive surfactant is a linear or branched, substituted or unsubstituted Ci_2-I8 alkyl ethoxylated sulphate having an average degree of ethoxylation of from 1 to 10. Most preferably, the alkoxylated anionic detersive surfactant is a linear unsubstituted Ci_2-I8 alkyl ethoxylated sulphate having an average degree of ethoxylation of from 3 to 7. The alkoxylated anionic detersive surfactant, when present with an alkyl benzene sulphonate may also increase the activity of the alkyl benzene sulphonate by making the alkyl benzene sulphonate less likely to precipitate out of solution in the presence of free calcium cations. Preferably, the weight ratio of the alkyl benzene sulphonate to the alkoxylated anionic detersive surfactant is in the range of from 1:1 to less than 5:1, or to less than 3:1, or to less than 1.7:1, or even less than 1.5:1. This ratio gives optimal whiteness maintenance performance combined with a good hardness tolerance profile and a good sudsing profile. However, it may be preferred that the weight ratio of the alkyl benzene sulphonate to the alkoxylated anionic detersive surfactant is greater than 5:1, or greater than 6:1, or greater than 7:1, or even greater than 10:1. This ratio gives optimal greasy soil cleaning performance combined with a good hardness tolerance profile, and a good sudsing profile.

Suitable alkoxylated anionic detersive surfactants are: Texapan LEST™ by Cognis; Cosmacol AES™ by Sasol; BES151™ by Stephan; Empicol ESC70/U™; and mixtures thereof. Preferably, the anionic detersive surfactant comprises from 0% to 10%, preferably to 8%, or to 6%, or to 4%, or to 2%, or even to 1%, by weight of the anionic detersive surfactant, of unsaturated anionic detersive surfactants such as alpha-olefin sulphonate. Preferably the anionic detersive surfactant is essentially free of unsaturated anionic detersive surfactants such as alpha- olefin sulphonate. By "essentially free of it is typically meant "comprises no deliberately added". Without wishing to be bound by theory, it is believed that these levels of unsaturated anionic detersive surfactants such as alpha-olefin sulphonate ensure that the anionic detersive surfactant is bleach compatible.

Preferably, the anionic detersive surfactant comprises from 0% to 10%, preferably to 8%, or to 6%, or to 4%, or to 2%, or even to 1%, by weight of alkyl sulphate. Preferably the anionic detersive surfactant is essentially free of alkyl sulphate. Without wishing to be bound by theory, it is believed that these levels of alkyl sulphate ensure that the anionic detersive surfactant is hardness tolerant.

Zeolite builder

The spray-dried powder typically comprises from 0% to 10wt% zeolite builder, preferably to 9wt%, or to 8wt%, or to 7wt%,or to 6wt%, or to 5wt%, or to 4wt%, or to 3wt%, or to 2wt%, or to lwt%, or to less than 1% by weight of the spray-dried powder, of zeolite builder. It may even be preferred for the spray-dried powder to be essentially free from zeolite builder. By essentially free from zeolite builder it is typically meant that the spray-dried powder comprises no deliberately added zeolite builder. This is especially preferred if it is desirable for the spray- dried powder to be very highly soluble, to minimise the amount of water-insoluble residues (for example, which may deposit on fabric surfaces), and also when it is highly desirable to have transparent wash liquor. Zeolite builders include zeolite A, zeolite X, zeolite P and zeolite MAP.

Phosphate builder

The spray-dried powder typically comprises from 0% to 10wt% phosphate builder, preferably to 9wt%, or to 8wt%, or to 7wt%,or to 6wt%, or to 5wt%, or to 4wt%, or to 3wt%, or to 2wt%, or to 1 wt%, or to less than 1 % by weight of the spray-dried powder, of phosphate builder. It may even be preferred for the spray-dried powder to be essentially free from phosphate builder. By essentially free from phosphate builder it is typically meant that the spray-dried powder comprises no deliberately added phosphate builder. This is especially preferred if it is desirable for the composition to have a very good environmental profile. Phosphate builders include sodium tripolyphosphate.

Silicate salt

The spray-dried powder optionally comprises from 0% to 20wt% silicate salt, preferably from lwt%, or from 2wt%, or from 3wt%, and preferably to 15wt%, or tol0wt%, or even to 5% silicate salt. Silicate salts include amorphous silicates and crystalline layered silicates (e.g. SKS- 6). A preferred silicate salt is sodium silicate. Carbonate salt

The spray-dried powder typically comprises carbonate salt, typically from 1% to 50%, or from 5% to 25% or from 10% to 20%, by weight of the spray-dried powder, of carbonate salt. A preferred carbonate salt is sodium carbonate and/or sodium bicarbonate. A highly preferred carbonate salt is sodium carbonate. Preferably, the spray-dried powder may comprise from 10% to 40%, by weight of the spray-dried powder, of sodium carbonate. However, it may also be preferred for the spray-dried powder to comprise from 2% to 8%, by weight of the spray-dried powder, of sodium bicarbonate. Sodium bicarbonate at these levels provides good alkalinity whilst minimizing the risk of surfactant gelling which may occur in surfactant-carbonate systems. If the spray-dried powder comprises sodium carbonate and zeolite, then preferably the weight ratio of sodium carbonate to zeolite is at least 15:1.

High levels of carbonate improve the cleaning performance of the composition by increasing the pH of the wash liquor. This increased alkalinity: improves the performance of the bleach, if present; increases the tendency of soils to hydrolyse, which facilitates their removal from the fabric; and also increases the rate, and degree, of ionization of the soils to be cleaned (n.b. ionized soils are more soluble and easier to remove from the fabrics during the washing stage of the laundering process). In addition, high carbonate levels improve the flowability of the spray-dried powder.

Alkalinity source

The alkalinity source preferably comprises sodium hydroxide. The alkalinity source preferably comprises carbonate salt. The alkalinity source preferably comprises silicate salt.

Adjunct detergent ingredients

Suitable adjunct ingredients include: detersive surfactants such as anionic detersive surfactants, nonionic detersive surfactants, cationic detersive surfactants, zwitterionic detersive surfactants, amphoteric detersive surfactants; preferred nonionic detersive surfactants are C_8-I8 alkyl alkoxylated alcohols having an average degree of alkoxylation of from 1 to 20, preferably from 3 to 10, most preferred are Ci_2-I8 alkyl ethoxylated alcohols having an average degree of alkoxylation of from 3 to 10; preferred cationic detersive surfactants are mono-Cό-is alkyl mono- hydroxyethyl di-methyl quaternary ammonium chlorides, more preferred are mono-Cg-io alkyl mono-hydroxyethyl di-methyl quaternary ammonium chloride, mono-Cio-₁₂ alkyl mono- hydroxyethyl di-methyl quaternary ammonium chloride and mono-Cio alkyl mono-hydroxyethyl di-methyl quaternary ammonium chloride; source of peroxygen such as percarbonate salts and/or perborate salts, preferred is sodium percarbonate, the source of peroxygen is preferably at least partially coated, preferably completely coated, by a coating ingredient such as a carbonate salt, a sulphate salt, a silicate salt, borosilicate, or mixtures, including mixed salts, thereof; bleach activator such as tetraacetyl ethylene diamine, oxybenzene sulphonate bleach activators such as nonanoyl oxybenzene sulphonate, caprolactam bleach activators, imide bleach activators such as N-nonanoyl-N-methyl acetamide, preformed peracids such as N,N-pthaloylamino peroxycaproic acid, nonylamido peroxyadipic acid or dibenzoyl peroxide; enzymes such as amylases, carbohydrases, cellulases, laccases, lipases, oxidases, peroxidases, proteases, pectate lyases and mannanases; suds suppressing systems such as silicone based suds suppressors; fluorescent whitening agents; photobleach; filler salts such as sulphate salts, preferably sodium sulphate; fabric- softening agents such as clay, silicone and/or quaternary ammonium compounds; flocculants such as polyethylene oxide; dye transfer inhibitors such as polyvinylpyrrolidone, poly 4-vinylpyridine N-oxide and/or co-polymer of vinylpyrrolidone and vinylimidazole; fabric integrity components such as hydrophobically modified cellulose and oligomers produced by the condensation of imidazole and epichlorhydrin; soil dispersants and soil anti-redeposition aids such as alkoxylated polyamines and ethoxylated ethyleneimine polymers; anti-redeposition components such as carboxymethyl cellulose and polyesters; perfumes; sulphamic acid or salts thereof; citric acid or salts thereof; and dyes such as orange dye, blue dye, green dye, purple dye, pink dye, or any mixture thereof.

EXAMPLES

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. Example 1. A spray-dried laundry detergent powder and process of making it.

Aqueous alkaline slurry composition.

Preparation of a spray-dried laundry detergent powder.

An alkaline aqueous slurry having the composition as described above is prepared in a slurry making vessel (crutcher). The moisture content of the above slurry is 23.1%. Any ingredient added above in liquid form is heated to 70⁰C, such that the aqueous slurry is never at a temperature below 70⁰C. Saturated steam at a pressure of 6.OxIO⁵ Pa is injected into the crutcher to raise the temperature to 90⁰C. The slurry is then pumped into a low pressure line (having a pressure of 5.0x10 Pa).

Separately, 11.4 parts of C₈-C₂₄ alkyl benzene sulphonic acid (HLAS), and 3.2 parts of a 50w/w% aqueous sodium hydroxide solution are pumped into the low pressure line. The mixture is then pumped by a high pressure pump into a high pressure line (having an exit pressure of

8.OxIO⁶ Pa). The mixture is then sprayed at a rate of l,640kg/hour at a pressure of 8.OxIO⁶ Pa and at a temperature of 90⁰C +/-2°C through a spray pressure nozzle into a counter current spray- drying tower with an air inlet temperature of 300⁰C. The mixture is atomised and the atomised slurry is dried to produce a solid mixture, which is then cooled and sieved to remove oversize material (> 1.8mm) to form a spray-dried powder, which is free-flowing. Fine material

(<0.15mm) is elutriated with the exhaust the exhaust air in the spray-drying tower and collected in a post tower containment system. The spray-dried powder has a moisture content of 2.5wt%, a bulk density of 510 g/1 and a particle size distribution such that greater than 80wt% of the spray- dried powder has a particle size of from 150 to 710 micrometers. The composition of the spray- dried powder is given below.

Spray-dried laundry detergent powder composition

A granular laundry detergent composition.

The above laundry detergent composition was prepared by dry-mixing all of the above particles (all except the AE7) in a standard batch mixer. The AE7 in liquid form is sprayed on the particles in the standard batch mixer. Alternatively, the AE7 in liquid form is sprayed onto the spray-dried powder of example 1. The resultant powder is then mixed with all of the other particles in a standard batch mixer.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm".

Claims

CLAIMSWhat is claimed is:

1. A process for preparing a spray-dried powder comprising (i) anionic detersive surfactant;

(ii) from Owt% to 10wt% zeolite builder; (iii) from Owt% to 10wt% phosphate builder; and (iv) optionally from Owt% to 15wt% silicate salt; wherein the process comprises the steps of:

(a) forming an alkaline slurry in a mixer, the slurry comprising:

(v) from Owt% to 15wt% anionic detersive surfactant; (vi) from Owt% to 35wt% water; and

(b) transferring the alkaline slurry from the mixer through at least one pump to a spray pressure nozzle;

(c) contacting an acid anionic detersive surfactant precursor to the alkaline slurry after the mixer and before the spray pressure nozzle to form a mixture;

(d) spraying the mixture through the spray pressure nozzle into a spray-drying tower; (e) spray-drying the mixture to form a spray-dried powder; and

(f) optionally, contacting an alkalinity source with the alkaline slurry and/or the acid anionic detersive surfactant precursor, and/or the mixture.

2. A process according to claim 1, wherein the alkaline slurry comprises from Owt% to 25wt% water.

3. A process according to any preceding claim, wherein the alkaline slurry comprises from Owt% to 5wt% anionic detersive surfactant.

4. A process according to any preceding claim, wherein an alkalinity source is added to the alkaline slurry substantially simultaneously with the acid anionic detersive surfactant precursor.

5. A process according to any preceding claim, wherein the acid anionic detersive surfactant precursor comprises C₈-C₂₄ alkyl benzene sulphonic acid.

6. A process according to any preceding claim, wherein the alkalinity source comprises sodium hydroxide.

7. A process according to any preceding claim, wherein the alkalinity source comprises carbonate salt.

8. A process according to any preceding claim, wherein the alkalinity source comprises silicate salt.