WO1999032599A1

WO1999032599A1 - Method of manufacturing particles

Info

Publication number: WO1999032599A1
Application number: PCT/GB1998/003791
Authority: WO
Inventors: John Hibbs
Original assignee: Manro Performance Chemicals Limited
Priority date: 1997-12-19
Filing date: 1998-12-17
Publication date: 1999-07-01
Also published as: GB9726824D0

Abstract

A method of manufacturing laundry detergent particles is disclosed, being an extrusion method in which a builder and surfactant, the latter comprising as a major component a sulphated or sulphonated anionic surfactant, are fed into an extruder, mechanically worked at a temperature of at least 40 °C and extruded through an extrusion head having a multiplicity of extrusion apertures. The extrusion method produces detergent particles having a bulk density of at least 400 g/l, preferably 550-900 g/l.

Description

METHOD OF MANUFACTURING PARTICLES

This invention relates to a method of manufacturing surfactant particles comprising an anionic surfactant.

The great majority of solid preparations for laundry use consist of surfactant granules. There are several methods by which these granules may be produced, but most involve the intimate mixing of solid and liquid components under high shear conditions. In general, liquid components are sprayed onto powders to agglomerate the powders into a granular form. These systems, while widely used, have certain limitations. Certain surfactants used in modern formulations require specialised handling, due to their high melting points, and/or high viscosities. As a result, specialist handling equipment is needed, and spraying may be difficult. These limitations may be overcome by using lower concentration surfactants, but this increases the cost of the process, since added water must be removed. Some processes seek to overcome the problems by using pre-dried surfactant, typically produced by spray-drying. Here a small amount of liquid is added to act as a binding agent. A further limitation of conventional agglomeration systems is that they tend to give a granule of lower bulk density than the feed materials, due to the inclusion of air in the granules. Using conventional raw materials, and agglomeration processes, it is difficult to produce a granular composition with a bulk density in excess of 550 g/1. Furthermore it would be desirable not to have to use spray-dried materials.

A recent trend in consumer laundry products has been towards compact powders. These have bulk densities of over 550 g/1, and in recent products, bulk densities in excess of 800 g/1 have been achieved. Products such as these depend on novel production techniques, many of which are described in patent literature.

EP-A-349200 describes a process for making dense, concentrated detergent granules from a surfactant paste using fine dispersion cold granulation. A preferred temperature range is from about -30°C to about 0°C. The surfactant paste can be introduced into the mixer at an initial temperature in the range about 5-70°C, especially about 20-30°C; it is stated that a temperature greater than about 70°C can lead to poor initial mixing due to increased product stickiness. The paste is preferably cooled to the granulation temperature by addition of dry ice.

EP-A-420317 describes a process in which a liquid acidic surfactant precursor is neutralised by an alkaline inorganic material in a high speed mixer/densifier, followed by the treatment of the resultant granular detergent material in a moderate speed granulator/densifier , whereby it is brought into a deformable state. The detergent material remains granular throughout; caking, balling and dough formation are avoided.

EP-A-340966 describes a process of making a high density particulate detergent composition, involving turbodrying a mixture of an anionic surfactant, water and bentonite. In the process of turbodrying a special piece of equipment called a turbodryer subjects the mixture to centrifugal and axial forces while it is being dried.

US-A-5290496 describes a process for manufacturing granules by a process in which detergent components are mixed together to form a free-flowing premix, for charging a homogenizing unit, for example a twin-screw kneader in which it is kneaded at a moderate temperature, for example at a temperature of 45° to 60°C, and then extruded through specially designed bores in an extruder head, which may be heated to the predetermined extrusion temperature, for example to around 45 to 50°C. The resulting strands are then pelletized. The temperature of the "molding compound" in the kneader is said to be an important parameter. Those molding compounds which are temperature sensitive may have to be cooled during the process to prevent destruction.

In accordance with a first aspect of the present invention there is provided a method of manufacturing particles comprising an anionic surfactant, the method comprising: feeding a feed material comprising an anionic surfactant to an extruder having an extrusion head with a multiplicity of extrusion apertures; mechanically working the material comprising the anionic surfactant, within the extruder, at an elevated temperature, to form an extrudable mass; extruding the mass through an extrusion head to form strands; and forming particles from the strands; wherein the temperature of the mass immediately prior to its extrusion is at least 40°C.

Preferably the temperature of the mass immediately prior to its extrusion is at least 60°C; more preferably at least 70°C; most preferably at least 80°C.

Depending on the design of the extrusion head and the composition of the material, the temperature of the material may increase a few degrees as it is forced through the extrusion head. However, there is not a requirement to use a specially designed extrusion head, as there is with the method of US-A-5290496. Rather, any ordinary multi-aperture axial or radial extrusion head may be used. The apertures thereof may comprise plain cylindrical apertures of diameter not exceeding 2 mm; 0.5- 1.5 mm is a preferred range. Such apertures may be entirely cylindrical or may have a funnel portion on their upstream side, tapering to the main, cylindrical portion.

The maximum temperature of the mass during the method should be such that there is no significant degradation. We have found that, contrary to our expectation, preferred sulphate and sulphonate anionic surfactants may be taken to temperatures well in excess of 80°C, without significant degradation; and in some cases up to 130°C.

In practical terms however it is preferred that the maximum temperature of the material at any stage of the method does not exceed 100°C.

Preferably the mass within the extruder is in a plastic and/or semi-solid form at least when it reaches the extrusion head.

Preferably the mass is plastic and/or semi-solid when it is mechanically worked within the extruder. Preferably the mass is at an elevated temperature when mechanically worked, suitably at least 40°C; preferably at least 60°C; more preferably at least 70°C; most preferably at least 80°C.

Preferably the feed material is added to the extruder at a temperature of at least 40°C, more preferably at least 60°C. It may be added as a solid or in plastic or molten form. The feed material is preferably an anionic surfactant paste, whose activity (i.e. anionic surfactant content) is suitably at least 40%wt, preferably at least 70%wt, most preferably at least 90%wt.

Feed materials whose activity is in the range 40- 85%wt are typically as-prepared anionic surfactants, that is, the direct products of the surfactant manufacturing process. The balance is largely water, additionally with unreacted chemicals from the surfactant manufacturing process. The preferred feed materials of high activity may be prepared by subjecting the as-prepared surfactants to a drying step prior to the extrusion step. Preferably this drying step is not a spray drying step, which tends to give a very dry powder product, but a drying step which can reduce the water content to any predetermined level, preferably between 0 and 25%wt, preferably between 0 and 14%, on weight of anionic surfactant/water in admixture. Examples of equipment which can achieve this include a rotary drum dryer, or a Chemithon turbo-type tube drier, or, most preferably, a wiped film evaporator. Preferably the dried product is a waxy or pasty solid at ambient temperature, not a flowable powder.

In one preferred method a feed material comprises an anionic surfactant which contains 2-10%wt of water, and whose activity is 90-98%wt. It is found that the presence of this water aids the processing of the surfactant, within the extruder and/or during a downstream spheronisation step, if carried out.

Alternatively a dried surfactant may be employed in the feed material, and there may be a separate addition of water to aid processing, either when the feed material is introduced to the extruder, or subsequently. The amount of water present after the addition may be as defined above. In preferred methods however no water is added to the extruder and the desired amount of water is preferably controlled by control of the water content of the feed material. This is preferably controlled not by adding water to a dried anionic surfactant, but by removing water to the extent required, in a prior surfactant drying process.

In a preferred method of the invention the feed material is dried immediately prior to its introduction into the extruder. Preferably it is fed directly from a drier to the extruder, without being actively cooled therebetween.

In some detergent formulations it is desired to have extremely low quantities of water present, or none at all. We have found that in such formulations a non-ionic surfactant may aid the processing of the anionic surfactant within the extruder, and/or their downstream handling. Thus, in one preferred method an anionic surfactant and a non-ionic surfactant are present. The weight ratio of non-ionic surfactant to the anionic surfactant is suitably up to 1 part, preferably up to 0.5 parts, of non-ionic surfactant per part of anionic surfactant (with reference to their active contents).

A non-ionic surfactant, when present, may suitably be added at any stage prior to the stage of mechanical working in the extruder; thus it may be added to the material comprising the anionic surfactant prior to the prior drying step (if carried out); prior to the feeding of the material comprising the anionic surfactant into the extruder; at the same time as the feeding of the material comprising the anionic surfactant into the extruder; or subsequent to the feeding of the material comprising the anionic surfactant into the extruder, through a separate feed point, during or, more preferably, prior to the mechanical working thereof.

The anionic surfactant of the present invention is suitably an anionic organic surfactant, which is usually employed in a soluble salt form, preferably as a alkali metal salt, especially as a sodium salt. Although other types of anionic detergents may be utilized, such as higher fatty acyl sarcosides or conventional "soaps" of fatty acids, the preferred anionic surfactants employed are those which are described as of a sulphonate or sulphate type, which may be designated as sulph(on)ates. These include linear higher alkylaryl sulphonates (for example alkylbenzene sulphonates ) , higher fatty alcohol sulphates, higher fatty alcohol polyalkoxylate sulphates, olefin sulphonates, oc-methyl ester sulphonates and paraffin sulphonates. An extensive listing of anionic detergents, including such sulph(on)ate surfactants, is given at pages 25 to 138 of the text Surface Active Agents and Detergents, Vol. II, by Schwartz, Perry and Berch, published in 1958 by Interscience Publishers, Inc., and is incorporated herein by reference. Usually the higher alkyl group of such anionic surfactants is of 8 to 24, especially 10 to 20 carbon atoms, preferably 12 to 18 carbon atoms, and the alkoxylate content of such anionic surfactants that are alkoxylated (preferably ethoxylated or ethoxylated/propoxylated) is in the range of 1 to 4 alkoxy groups per mole.

One preferred class of anionic surfactants comprise the alkali metal (preferably sodium) alkyl sulphates, preferably having linear C₁₂.₁₈ alkyl groups . One preferred class of anionic surfactants comprise alkali metal (preferably sodium) alkylaryl sulphonates (especially alkylbenzene sulphonates), preferably having linear C₁₀._I3 alkyl groups.

A preferred non-ionic surfactant is a condensation product of a higher fatty alcohol with a lower alkylene oxide, such as ethylene oxide or a mixture of ethylene oxide and propylene oxide. In such non-ionic surfactants the higher fatty moiety will normally be of 12 to 15 carbon atoms and there will usually be present from 3 to 20, preferably 4 to 15 moles of alkylene oxide per mole of higher fatty alcohol.

It is preferred that the particles contain a builder. A builder in particulate form is suitably added to the material comprising the anionic surfactant during or, preferably, prior to the mechanical working thereof. When the material comprising the anionic surfactant is dried the builder is preferably not present during the drying step. It is preferably introduced subsequently, for example added to the material comprising the anionic surfactant prior to feeding into the extruder; at the time that material is fed into the extruder; or, preferably, subsequent to the feeding of the material comprising the anionic surfactant into the extruder, through a separate feed point. Preferably the builder, when present, is added to the material comprising the anionic surfactant within the extruder during or, preferably, prior to the mechanical working thereof, said material already being at an elevated temperature, preferably at least 40°C, more preferably at least 60°C.

Suitable builders include water soluble inorganic salt builders, preferably sodium salts, such as sodium polyphosphates, e.g. sodium tripolyphosphate and sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium sesquicarbonate , sodium silicate, sodium disilicate, sodium metasilicate and sodium borate. In addition to the water soluble inorganic salts, water insoluble builders may also be useful, including the ion exchanging zeolites, such as Zeolite 4A. Organic builders may be employed but if heat sensitive may need to be added after extrusion. Among suitable organic builders are polyacetal carboxylates, as described in US-B-4725455, and water soluble salts of lower hydroxycarboxylic acids, such as sodium citrate and sodium gluconate.

A builder, when present, may suitably be present in an amount of from 0.1-10 parts per part of the anionic surfactant (active content), by weight. When the anionic surfactant is, or is predominantly, an alkali metal alkyl sulphate, the builder may suitably be present in an amount of from 0.2-6 parts per part of the anionic surfactant (active content), by weight, preferably 0.5-5, most preferably 0.7-4 parts, by weight. When the anionic surfactant is, or is predominantly, an alkali metal alkylaryl sulphonate, the builder may suitably be present in an amount of from 0.1-5 parts per part of the anionic surfactant (active content), by weight, preferably 0.1-1, most preferably 0.15-0.5 parts, by weight.

By predominantly we mean that of at least 51%wt of the anionic surfactant (active content) is constituted by the respective sulphate or sulphonate component (active content) .

When we refer herein to the presence of "a" component, for example a builder, we envisage that there may be more than one builder present. When proportions of constituents are given herein there refer to the total content of the respective components , for example the total content of builders.

The main ingredients of the extruded particles are preferably anionic surfactant and builder. Other constituents discussed already are water and non-ionic surfactant. Many other components, which we will call herein "adjuvants" may be desirable for eventual detergent formulations. These may include a polymer, bleaching agent, optical brightener, sequestrant, conditioning agent, anti-foaming agent, filler, colorant, soil release agent, enzyme etc. Further, a hydrotrope may be a useful adjuvant, firstly in preventing the anionic surfactant from becoming sticky as a result of water content and/or water absorption, and secondly in aiding washing processes, by promoting good dissolution. Examples of suitable hydrotropes are alkali metal arylsulphonates, for example sodium xylene sulphonate and sodium toluene sulphonate.

Most adjuvants can be added to the material comprising the anionic surfactant prior to extrusion; for example prior to a prior drying step (when carried out); or subsequent to a prior drying step (when carried out) but prior to feeding of the material comprising the anionic surfactant into the extruder; or at the same time as that material is fed into the extruder; or subsequent to the feeding of the material comprising the anionic surfactant into the extruder, through one or more separate feed points, for example during or, preferably, prior to the mechanism working. Alternatively adjuvants may be blended with the particles after their extrusion and cooling. For some adjuvants which are heat sensitive, such as enzymes, post-extrusion blending may be preferred. Thus, the method of the present invention may produce particles which constitute a ready-to-use multi-component detergent or an intermediate product to be admixed or incorporated with other components, to produce a product for sale.

It should be noted that whereas US-B-5290496 requires a free flowing powder to be fed into a specially designed extruder, in the present invention an anionic surfactant in the form of a solid, semi-solid or paste is preferably fed in. It may be fed in in whatever way is most convenient - for example in lumps or shavings, or poured or pumped in. Other components may be co-fed, without a requirement for them to be carefully blended in; or may be added downstream, via one or more separate feed points. The mixing required to produce a good distribution of the components takes place within the extruder at an elevated temperature; and the mixing takes place most efficiently at temperatures which have previously been considered too high for the processing of the preferred sulphate and sulphonate anionic surfactants. Preferably the material in the extruder is plastic and/or semi-solid, and highly workable, at the temperature employed. Preferably the temperature of the material as it is extruded is higher than the melting or softening point of the anionic surfactant.

It is also significant that the method may produce a granule containing a builder and an anionic surfactant, the primary elements of a detergent formulation, in one straightforward step from the as-supplied builder and surfactant; or in two steps if a prior drying step is employed, for drying the surfactant. No prior agglomeration step is required; indeed no prior mixing step of any kind is required, although prior mixing of certain adjuvants may be carried out, if this is the favoured way of incorporating them.

Surprisingly we have found that an anionic surfactant, and a builder and other components, when present, form an extrudate which has very good physical characteristics, even at temperatures at which the surfactant would normally be in a liquid state, and/or expected to hydrolyse or otherwise degrade. This allows intensive mixing within the extruder barrel, without the need for significant cooling of the mass prior to extrusion. This gives a simple process for the production of dense particles (bulk density 400 to 900 g/1, preferably 550 to 850 g/1) of uniform composition. It is further surprising, that we have found that the physical integrity of certain compositions is such that they may be treated as a "dried" (solid) surfactant ingredient, without a downstream drying process; in preferred processes no forced or active drying process is carried out downstream of the extruder.

Following the extrusion process, it may be necessary to change the appearance and handling characteristics of the extrudate strands. This may be conveniently achieved by means of "chopping" the extrudate to the required length. A spheronising procedure may be carried out, if wished, on the chopped extrudate. Commercial equipment is available for both these options.

If, as is preferred, the particles are not to undergo active or forced drying it may be desirable to actively cool them, for example, in a fluid bed cooler. Alternatively, when desired the free moisture may be removed from the extrudate by a fluid bed dryer, or other suitable drying method. Whereas for the main components definitions have been written in terms of their proportion by weight relative to the anionic surfactant (active content), in relation to the adjuvants we may state that they are preferably present in an amount based on the weight of the particles when ready for sale (whether this be straight after the extrusion step, adjuvants having been added already, or after post-extrusion blending of adjuvants) of 0-30%wt, preferably 0-20%wt, most preferably 0-10%wt.

In accordance with a further aspect of the present invention there are provided particles produced by the method of the invention, as defined herein. Preferably the bulk density of the particles is at least 400 g/1, preferably at least 600 g/1.

Preferably the extruder used has means for measuring the temperature of the material thereof at a plurality of positions along the length of the extruder, means for heating the barrel thereof, extending at least to the extent of the means for measuring the temperature thereof, and means for cooling the barrel thereof, extending at least to the extent of the means for measuring the temperature thereof, and means for controlling the means for heating and the means for cooling, in response to the means for measuring the temperature. Preferably the means for measuring the temperature thereof comprises a plurality of thermocouples, preferably set into the inside surface of the barrel, such as to contact the material in the barrel. Suitably the extruder is coupled to a drier, of a type as defined above, to directly receive the output of the drier.

Whilst the process of the present invention could be useful to prepare a ready-for-sale detergent formulation, the particles produced by the present invention are particularly suitable for use by formulators of laundry powders to deliver multiple ingredients into products . The particles may be admixed into a particulate blend of other ingredients, or may be partly ground, and re- agglomerated to give a fully formulated product. In relation to the former case, the prior art practice is to simply admix particles of relatively pure surfactant, particularly alkyl sulphates, into a powder. The invention offers the same ease of incorporation, with the benefits arising from the prior intimate mixing of the alkyl sulphate with other, often more readily soluble components. In the latter case, ease of formulation is improved by the delivery of multiple components, in the correct formulation ratio, suitably obtained by the process of the invention via a single solids addition.

In both cases, the invention offers a form of product which would be difficult for formulators to achieve without special equipment to make a densified powder. The process used is also more efficient than many formulators' own drying and blending operations, offering energy savings and reduced inventory.

A preferred ready-for-sale detergent formulation containing particles produced by the method of the present invention (whether directly or after post-extrusion addition of one or more adjuvants) suitably comprises (referring to active content where appropriate) 15-85%wt anionic surfactant, 85-15%wt builder, 0-30%wt water, 0- 20%wt non-ionic surfactant, and 0-30%wt adjuvant(s); preferably 20-70%wt anionic surfactant; 80-30%wt builder; 0-10%wt non-ionic surfactant; 0-15%wt water; 0-10%wt adjuvant(s). Preferably the anionic surfactant (active content) and the builder together constitute at least 50%wt, most preferably at least 70%wt, of the total weight. Such a ready-for-sale detergent formulation constitutes a further aspect of the present invention.

The invention will now be further described with reference to the accompanying illustrative examples. For these examples an APV MP 2050 (trade mark) twin screw mixer-extruder was used, with 50 mm diameter screws, and a L:D ratio of 30:1. The barrel of the extruder was electrically heated and water cooled, with independently controlled heating zones. Unless otherwise stated the temperature was measured by means of thermocouples set into the inside surface of the barrel, at intervals along it. The extrusion was either axial extrusion through a standard 0.9 mm noodle plate or radial extrusion via a radial extrusion head, using a 1 mm mesh. The radial extrusion head allowed greater throughputs, and lower operating pressures. In general, for axial extrusions the operating pressures were relatively low, about 10 bar unless otherwise stated. For radial extrusions very low pressures were used; essentially no significant over pressure was applied.

The anionic surfactant feeds were metered into the extruder using a weight-belt feeder. Builders and other solid ingredients were added using a screw feeder, with a loss in weight system. The builders were added at a distance of 9D from the surfactant feed. This allowed the surfactant feeds to be heated and worked, to become fully plastic, before builders were added.

Extrudate temperature itself was measured by quickly collecting a mass of extrudate and immediately measuring the temperature in the centre of the mass by means of a thermocouple probe. Liquid additions were made using a volumetric pump.

The particles were chopped into pieces in standard manner and then spheronisation was carried out in each case, using a CALEVA (trade mark) model 15 Disc spheroniser to give roughly spherical particles of approximately 1 mm diameter.

Example 1

The surfactant used was a paste of sodium alkyl sulphate, based on a C_16.18 alcohol, containing about 70% surfactant (the remainder being water, sodium hydroxide, sodium sulphate, and unreacted alcohol), known as MANRO SNO (trade mark). The molten as-prepared paste was allowed to cool until it solidified, and was broken into small pieces, to allow it to be fed into the extruder.

The paste was fed into the main feed port at a rate of 29.5 kg per hour. This was then conveyed, with mixing and heating along the extruder barrel. The builder

(sodium disilicate and sodium carbonate, 3:1 wt:wt) was added at a rate of 20.5 kg per hour. During the mixing process, the maximum temperature observed was 84°C. The mixture was axially extruded through the 0.9 mm die plate, with the extrudate temperature being between 75 and 80°C.

The extrudate was a white solid, which was easily broken into short lengths . Some of the hot extrudate was spheronised, and some of the spheronised material was subsequently dried by fluid bed drying.

The products obtained were analysed as follows.

In a variation of this example, the surfactant portion of the formulation was added as a molten liquid at about 80°C. It was observed that the temperature profile along the extruder barrel reflected the initial high temperature of the molten feed but from the mixing zone on, there was no significant difference between molten feed and solid feed. It was also demonstrated that using this form of feed material the extrudate could be produced at a rate of 80 kg/hr.

Example 2

In this example, the surfactant feed was based on sodium alkylbenzene sulphonate (LAS). The feed was made by drying a paste of 60% active LAS in a BALESTRA DRYEX (trade mark) wiped film evaporator, to an active content of 96-98%. The dried LAS was fed straight into the main feed port of the extruder at a temperature of 60°C, at a rate of 36.5 kg/hr. The surfactant was heated to 80°C and conveyed and to the mixing zone. The builder used was a blend of zeolite (VEGOBOND AX - trade mark) and sodium carbonate, in the ratio 3:1 wt:wt. The addition rate of builder was 27 kg/hr. The product was axially extruded through the 0.9 mm noodle die, at a higher pressure of 30 bar in this example, with an extrudate temperature of 90- 100°C. Example 3

Sodium C₁₂.₁₈ alkyl sulphate paste was previously dried, as described in the example above. The surfactant was fed into the extruder at a rate of 37.1 kg/hr. This was conveyed and heated to about 80°C. The builder was then added at a rate of 30.8 kg/hr. The builder was sodium disilicate and sodium carbonate, 3:1 wt:wt. It was observed that a small water addition (2.1 kg/hr) improved the downstream spheroniser performance. The extrusion was carried out using the radial extrusion head, with an extrusion temperature of 101°C. The product obtained contained 53% (w/w) of surfactant, 4% water and had a bulk density of 730 g/1. In a variation of the above example, the water was replaced with a non-ionic surfactant (a blend of ethoxylated C ₅ alcohols, mean EO number = 6.2). This also gave a significant improvement in spheroniser performance, the product being more evenly sized with less dusting and reduced the extrusion temperature to 88°C, due to lesser heat gain during the passage through the extrusion head. This product contained 54% of anionic surfactant, 5% of non-ionic surfactant, and had a bulk density of 750 g/1.

Example 4

In a variation of example 3, the dried sodium alkyl sulphate was fed at a rate of 18.2 kg/hr. This was conveyed and heated as previously. The builder (VEGOBOND AX zeolite only) was added at a rate of 29.3 kg/hr, and non-ionic surfactant was added at a rate of 2.5 kg/hr. The extrusion was via the axial head, at a temperature of 84°C. The product obtained contained 37% anionic surfactant, 5.2% non-ionic surfactant, and had a bulk density of 640 g/1. Example 5

Dried sodium alkyl sulphate was fed as previously, at a rate of 10.7 kg/hr. Builder (VEGOBOND AX zeolite : sodium carbonate, 11:1 wt:wt) was added at a rate of 32.5 kg/hr, non-ionic surfactant was added at a rate of 4 kg/hr, and an acrylic-maleic polymer SOKOLAN CP5 (trade mark - an ingredient useful in laundry formulations) was added at a rate of 2.7 kg/hr. The temperature of the extrudate from the radial extruder was 80°C. The composition spheronised well. The product contained 20.2% anionic surfactant, 7.6% non-ionic surfactant, 5% polymer, and had a bulk density of 720 g/1.

Example 6

Sodium C₁₂.₁₆ alkyl sulphate paste was dried as described in example 2. The surfactant was fed into the extruder at a rate of 50.0 kg/hr. This was conveyed and heated to 80°C. No builder or other components were added. The extrusion was carried out using the axial extrusion head with an extrusion temperature of 101°C. The product obtained was substantially pure surfactant particles of very high activity, and of bulk density of 600-750 g/1. The resultant particles could be handled and spheronised without difficulty.

All of the above examples produced particles useful as intermediates, to be used by formulators of laundry powders, in producing washing powders of high density.

All of the above examples were demonstrated on pilot scale equipment. In scaling up to commercial production the following points are to be observed. With production units, many of the additives of interest can be added into the anionic surfactant before it enters the extruder, rather than in the extruder. Such additives could include one or more polymers, hydrotropes (e.g. sodium alkylaryl sulphonates, such as sodium xylene sulphonate) non-ionic surfactants, optical brighteners etc. Moisture content would preferably be controlled at the surfactant drying stage, eliminating water additions and downstream drying.

With a larger extruder more feed points become available. Thus solid feeds which are premixed in the examples may be fed separately. With larger extruders the feed points become relatively more closely packed, so larger extruders can have a lower L:D ratio.

It may be desirable on larger scale equipment to subject the extrudate to forced cooling. This could be achieved using either a fluid bed cooler, or a cooled spheroniser.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment( s ) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method of manufacturing particles comprising an anionic surfactant, the method comprising: feeding a feed material comprising an anionic surfactant to an extruder having an extrusion head with a multiplicity of extrusion apertures; mechanically working the material comprising the anionic surfactant, within the extruder, at an elevated temperature, to form an extrudable mass; extruding the mass through an extrusion head to form strands; and forming particles from the strands; wherein the temperature of the mass immediately prior to its extrusion is at least 40┬░C.

2. A method according to claim 1, wherein the feed material includes a builder.

3. A method according to claim 2, wherein the builder is present in the amount of 0.1-10 parts per part of the weight anionic surfactant (active content) by weight.

4. A method according to any preceding claim, wherein the anionic surfactant is an alkoxylated sulphate or sulphonate.

5. A method according to claim 4, wherein the alkoxylate content of the anionic surfactant is in the range of 1-4 alkoxy groups per mole.

6. A method according to any preceding claim, wherein the anionic surfactant comprises an alkali metal salt of a linear C₁₂._╬╣8 alkyl sulphate.

7. A method according to any of claims 1 to 5, wherein the anionic surfacant comprises an alkali metal salt of a linear C₁₀.₁₃ alkylaryl sulphonate.

8. A method according to any preceding claim wherein the feed material includes a non-ionic surfactant.

9. A method according to claim 8, wherein the weight ratio of non-ionic surfactant to the anionic surfactant is up to 1 part of non-ionic surfactant per part of anionic surfactant.

10. A method according to claims 8 or 9, wherein the non- ionic surfactant is a condensation product of a higher fatty alcohol having 12 to 15 carbon atoms with a lower alkylene oxide, wherein there is present 3-20 moles of the alkylene oxide per mole of higher fatty alcohol.

11. A method according to any preceding claim, wherein the feed material is fed into the extruder at a temperature of at least 40┬░C.

12. A method according to any preceding claim wherein the activity of the anionic surfactant in the feed material is at least 40%wt.

13. A method according to claim 12, wherein the activity of the anionic surfactant in the feed material is at least 70%wt.

14. A method according to claim 13, wherein the activity of the anionic surfactant in the feed material is at least 90%wt.

15. A method according to any preceding claim, wherein the temperature of the mass immediately prior to its extrusion is at least 60┬░C.

16. A method according to any preceding claim, wherein the maximum temperature of the material at any stage of the method does not exceed 100┬░C.

17. A method according to any preceding claim, wherein said apertures are of diameter not exceeding 2mm.

18. A method according to any preceding claim, for the production of detergent particles, wherein the bulk density of the particles is at least 400g/l.

19. A method according to claim 18, wherein the bulk density of the particles is at least 550g/l.

20. A detergent formulation containing particles produced by a method of any preceding claim, the detergent formulation comprising 15-85%wt anionic surfactant, 85- 15%wt builder, 0-30%wt water, 0-20%wt non-ionic surfactant, and 0-30%wt adjuvant(s).

21. A formulation as claimed in claim 19, comprising 20- 70%wt anionic surfactant; 80-30%wt builder; 0-10%wt non- ionic surfactant; 0-15%wt water; and 0-10%wt adjuvant(s).

22. A formulation as claimed in claim 20 or 21, wherein the anionic surfactant and the builder together constitute at least 50%wt of the total weight of the formulation.

23. A formulation as claimed in claim 22, wherein the anionic surfactant and the builder together constitute at least 70%wt of the total weight of the formulation.