WO1996004973A1

WO1996004973A1 - Improved spray-drying process for aqueous valuable substance compositions from the group of the wetting, washing and/or cleaning agents

Info

Publication number: WO1996004973A1
Application number: PCT/EP1995/003094
Authority: WO
Inventors: Wilfried Rähse; Kathleen Paatz; Dieter Jung
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1994-08-11
Filing date: 1995-08-03
Publication date: 1996-02-22
Also published as: DE4428388A1

Abstract

A process for spray-drying aqueous compositions of valuable substances and mixtures of valuable substances from the group of the wetting, washing and/or cleaning agents in a vertical tower uses parallel or reverse flows of overheated gasses as drying agent. The process is characterised in that small amounts of a finely powdered water-soluble and/or water-insoluble dry powder are separately introduced into the spray-drying tower, in addition to the aqueous valuable substance compositions. Water-insoluble inorganic fine powders rendered hydrophobic are preferably used. The process is particularly useful for allowing the dried valuable substances to be discharged more easily from spray-drying towers driven with overheated steam as drying gas.

Description

"Improved process for spray drying water-containing recyclable materials from the area of wetting agents, detergents and / or cleaning agents"

The invention relates to the known method of spray drying water-containing preparations of valuable substances or mixtures of valuable substances from the field of wetting agents, detergents and / or cleaning agents, in which the corresponding flowable aqueous preparations are sprayed in upright towers and mixed with an or countercurrent hot gas phase dried to dry powder and then discharged from the spray tower. The type of process that is still common on an industrial scale works with hot fuel gases or hot air as a drying gas phase in a single pass through the spray tower. Corresponding spray drying processes with a circulation of such hot gas phases are also known in the literature, in particular with the aim of achieving self-inerting of the gas phase and thus protecting the material to be dried. Recently, a number of publications by the applicant describe the drying of aqueous preparations of valuable substances and mixtures of valuable substances in the area of application concerned with superheated steam as a hot gas stream, reference is made to the international patent application WO 92/5849 and numerous subsequent applications to this technology of spray drying with superheated steam as the drying gas stream. The associated advantages over the usual spray drying with hot air as the drying gas are manifold. Advantages lie in the absence of oxygen, so that problems with the drying of purely or largely organic materials, for example appropriate surfactants or surfactant mixtures, such as oxidative damage or fire hazards, are avoided. The circulation of the superheated steam also enables a practically emission-free driving style. Further advantages lie in the nature of the material to be dried, which can be obtained in particular as a free-flowing solid material with a microporous structure. The teaching according to the invention described in the following is of fundamental importance for the type of process for spray drying aqueous valuable materials and mixed materials of the subject matter addressed here with the flow of a hot drying gas - regardless of the particular nature of this hot gas flow. However, the procedural measures described in the following bring particular advantages for the type of spray drying with superheated steam as a hot gas stream, so that the teaching according to the invention is essentially described below with reference to this special embodiment. However, the teaching according to the invention is not restricted to this.

A well-known problem area for spray drying lies in the fact that the fine-particle sprayed particles which dry out from the flowable aqueous preparation by dehydration frequently pass through a state of increased surface tack in the course of this drying process before the drying has progressed to such an extent that this non-sticky, free-flowing powder is obtained. In this intermediate stage, there is an increased risk of undesirable caking of the sprayed material on the tower walls and / or undesired adhesion of the particles to one another. These difficulties make it necessary to carefully coordinate the geometric configuration of the spray zone in order to adapt it to the process conditions - for example in mass throughput, the form of hot gas flow in cocurrent and / or countercurrent, possibly with the addition of swirl gas streams and the like. Considerable expenditure has to be made both in the area of investment - in particular the size and dimensions of the spray tower - and in the practical area of drying in order to cope with the difficulties of undesired gluing or coating formation mentioned here.

A certain alleviation of this problem is achieved in the usual spray drying with hot gases or hot air through a constantly open outlet channel in the lower end of the drying container. This not only enables the dry product to be discharged quickly, the false air flowing into the tower also reduces the problem of sticking or caking due to its cooling effect. This procedural aid is not useful when working with superheated steam as the drying gas given. The circulation of this drying gas requires a closed system. This closed design of the drying system working with superheated steam therefore easily leads to an almost flow-free space below the lowest hot steam inlet, the temperature of which corresponds approximately to the inlet temperature of the hot steam. The walls in the lower region of the drying container also have this temperature, unless special precautions are taken. Thermal damage to the particles adhering to the hot housing wall represents a particular risk here.

The problem of caking of thermoplastic materials and other sticky materials on the housing walls of spray dryers is known from the prior art (K. Kröll, drying technology, 2nd volume, dryer and drying process, 2nd edition 1978, Springer Verlag, p. 294). To solve this problem, the walls of the dryers for the corresponding goods are provided with air-flow-through jackets, or blown chambers are circulated on the inside, which blow off the powder with cold air. It is also known that a cool and dehumidified air stream can be fed into the dryer so that it sweeps along the walls as a downward cold air curtain. The supply of cold air or a cold air curtain is carried out in particular for the usually conical discharge funnel at the lower end of the cylindrical drying tower. The cold air is conducted via an annular channel arranged in the attachment area of the cone and an air distribution plate into the interior of a double jacket, the inner wall of which ends below the inlet at approximately a height in which the inner and outer walls come very close. The cold air flows through the narrow annular gap and is forced by this arrangement to flow tangentially to the inner wall of the cone.

Another example of blowing cold air into the discharge cone of a spray drying system can be found in K. Kröll, drying technology, 3rd volume, drying and drying in production, by W. Käst et al., Springer Verlag 1989, page 188, picture 3.20. In this spray tower, cold air is added to the cone via an annular channel. In the usual atomizing dryers operated with hot air as the drying medium these measures are sufficient. In the case of drying with superheated steam and the circulation of the steam, these known measures do not meet the requirement to rule out a substantial risk to the dry material, in particular due to caking and overheating.

In her older German patent application DE-P 4321 361.8, the applicant describes measures to eliminate the sources of danger given here for the special field of spray drying with superheated steam as the drying gas. The process described there is characterized in that a finely divided water mist or water vapor, the temperature of which is below the inlet temperature of the superheated steam, is fed in as an auxiliary fluid in the region of the drying tower below the lowest superheated steam inlet, the auxiliary fluid being supplied via a double jacket can flow in permeable inner wall and the flow continues tangentially and / or radially to the inner wall. The auxiliary fluid can be supplied continuously or intermittently. Further details are contained in the technical teaching of this earlier property right, the disclosure of which is hereby expressly made the subject of the present disclosure of the invention.

The invention is based on the object of proposing further simplifications and improvements for solving the problem area, which are derived from an intermediate surface stickiness of the drying good particles with caking or caking on the inner wall of the vessel with subsequent thermal damage to the good part concerned.

The solution to this problem according to the invention lies in the measure described below in detail, in which small amounts of very fine solid matter in the form of a dry powder are introduced into the interior of the spray drying zone and here in particular into the areas where there is a risk of sticking or caking. This powder or powder-like auxiliary material covers a possibly still sticky outer surface of the material to be dried and thus removes its stickiness to such an extent that the undisturbed free-flowing properties of the material to be dried are ensured, particularly in the problem areas. This reliably prevents both caking of the good particles with one another and, in particular, caking of the good particles on the inner wall of the spray dryer.

Subject of the invention

The invention accordingly relates to the process for spray drying water-containing preparations of valuable substances and mixtures of valuable substances from the field of wetting agents, detergents and / or cleaning agents in an upright tower using hot gases which are driven in cocurrent and / or countercurrent as a drying agent. The process is characterized in that, in addition to and separately from the water-containing valuable substance preparations, small amounts of a finely powdered material to be dried are introduced into the spray tower. This finely divided drying material used as an auxiliary is simply referred to below as "dry powder".

In a particular embodiment, the invention relates to the application of this principle of the process to the drying of water-containing preparations of the valuable substances and valuable substances concerned here, using superheated, circulated steam as drying gas.

Details of the teaching according to the invention

Fine-particle dry powders in the sense of the teaching according to the invention can have a wide variety of properties and can be of inorganic and / or organic origin. For their part, they can be water-soluble and / or water-insoluble. Details of this will be given below. In order to understand the teaching according to the invention, first of all, its physical nature when used in the drying tower and the form of its addition are decisive:

The solid material to be fed into the tower or the endangered tower area is in the form of fine powdered dry material. It is added to the interior of the spray dryer as an additional component, it being essential that the dry powder be separated from the water-containing ones Recyclable materials - not mixed with them - is introduced into the spray tower.

For the selection of suitable forms of supply of the dry powder into the interior of the spray dryer, the sufficiently rapid distribution of the fine powder in the endangered area can be important. As a rule, this is achieved by introducing the dry powder used in a comparatively small amount into the interior of the dryer by means of a gaseous carrier. In the implementation of this working principle, different special configurations are possible, which can also be connected to one another.

In a first embodiment, the dry powder is added to the hot gas stream immediately before or before it enters the dryer interior. It may be preferable to introduce the dry powder into the drying tower by means of one or more auxiliary gas streams. It can be particularly expedient to provide such an entry into the tower inner zones, which are particularly at risk from sticking and / or caking. The partial streams used here as carriers for the dry powder can be partial streams of the drying gas - in particular also partial streams of the superheated steam - but they can also be additional auxiliary gas streams. Such a case exists, for example, when the dry powder is added as an additive to the auxiliary fluid, which according to the teaching of the previously mentioned earlier application DE-P 4321 361.8 is fed into the area of the drying tower below the lowest superheated steam inlet. In this context, the functionality of the auxiliary fluid from the teaching of the earlier application is further reinforced by the use of the dry powder in the sense of the teaching now given. With at least partially tangential flow of such an auxiliary fluid, the rapid, widespread distribution of the dry powder in wall areas that are particularly prone to adhesion is achieved. The radial flow of the auxiliary fluid with the simultaneous addition of fine dry powders according to the invention leads to a reduction in the risk of sticking of the good particles even in the interior of the spray drying room. It may be expedient to feed at least a portion of the dry powder to the interior of the drying tower in the area of the spray nozzles for the aqueous valuable material. Depending on the individual circumstances of the material to be dried and its tendency to form sticky outer surfaces, it may be - if necessary additionally - particularly useful to add fresh dry powder to the surrounding drying gas phase at a later stage of the drying of the particulate material.

In principle, water-soluble and / or water-insoluble, finely divided solids of inorganic and / or organic nature can be used as dry powder. Suitable powders are particularly suitable, which - fed in as a dry, free-flowing solid - are practically non-sticky and / or non-swelling under the drying conditions in the spray tower.

According to an important embodiment of the invention, the dry powder can contain at least a proportion of finely divided free-flowing recyclable materials and / or mixtures of recyclable materials in the specified field of application of the wetting, washing and cleaning agents. In this context, a first interesting embodiment has to be considered in particular:

Spray-dried powders are known to be randomly distributed in terms of their individual particle size. In the practice of the spray drying process, this generally leads to the very fine fraction of the dry material being discharged from the spray drying room together with the drying gas stream. It is generally necessary to separate these very fine fractions of the dried material from the hot gas stream, and this can be done by using filters or separating devices of the cyclone type. The fine material fraction of the primary dry material obtained here can be used as dry powder in the sense of the teaching according to the invention and in particular can be returned to the spray drying zone with auxiliary fluids or partial gas flows.

However, the teaching of the invention is not restricted to this. In further embodiments, selected very finely divided value and / or Auxiliaries of inorganic and / or organic nature are used, which due to their own nature are particularly suitable for the performance level required here. Important special examples for the selection of such drying powders are given below. However, the teaching according to the invention is not restricted to these specifically named representatives. Here, the general technical knowledge of the material properties also applies to other fine-particle solid components.

Particularly good results can be achieved for the teaching according to the invention with highly disperse and essentially water-insoluble inorganic solids, which can be customary valuable components in the field of wetting agents, detergents and / or cleaning agents mentioned here. As an example of such water-insoluble inorganic solids in the field of wiping agents, reference should be made to the builder components based on zeolite in detergent quality, in particular corresponding preparations of zeolite NaA and / or zeolite X. Insoluble detergent builder components of this type are known to be extremely strong small particle sizes, which are generally below 10 μm, for example in the range from 2 to 5 μm. Another finely divided additive, for example in the field of cosmetics, dentifrices and the like, is water-insoluble, finely divided silicas, which are known in particular as so-called "aerosils". This term includes highly disperse silicas with an SiO 2 content of more than 99% by weight. Aerosils are made up of amorphous spherical particles which have a diameter of 10 to 20 nm and an inner surface of, for example, 100 to 400 m ² / g. Aerosils have SiOH groups on their surface, which are linked to one another via relatively weak hydrogen bonds, which leads to the formation of scaffolds. Aerosils are, for example, sales products from Degussa, Hanau / FRG. For more information on their structure, see Seifen-Öle-Fette-Wwachs, 94, 849 (1968).

Another example of a very finely divided inorganic water-insoluble auxiliary in the sense of the definition according to the invention for the dry powder are corresponding metal oxide compounds, in particular aluminum oxide in its various preparations. The dry powders of the type described here - but also the examples of useful materials which are still mentioned - can be used in the commercially customary and in particular non-hydrophobicized embodiment. In an important embodiment of the teaching according to the invention, dry powders are used, at least in part, which contain the corresponding materials in hydrophobicized form. Hydrophobicized aerosils, like the non-hydrophobicized material, are commercial products for a wide variety of uses. In the sense of the use according to the invention, materials which have been rendered hydrophobic can be particularly suitable for preventing the undesirable caking and / or sticking together of the valuable materials.

However, water-soluble organic and / or inorganic solid powders are also suitable as dry powders. Soluble polymer compounds of natural and / or synthetic or semisynthetic origin such as xanthan, starch, cellulose powder and their derivatives such as methyl cellulose and / or carboxymethyl cellulose, in particular with low water retention, may be mentioned here as examples.

Particularly suitable as organic solid components can be very finely powdered compounds with a surfactant character. Examples include fine powder anionic surfactants. Because of their oleophilic molecular constituent, they can achieve comparable effectiveness qualities to the hydrophobized inorganic powders for facilitating and regulating the drying process. However, completely different, very finely divided inorganic and / or organic mixture components from the field of wetting agents, detergents and / or cleaning agents can also be used. Soluble builder components based on alkali metal silicates (the so-called water glasses), adjusting agents such as soda, sodium sulfate and the like may be mentioned here as examples. In particular, reference can be made here to the specialist knowledge and, in particular, the extensive specialist literature on the nature and composition of the area of wetting, washing and cleaning agents mentioned here. The dry powders used according to the invention as auxiliaries generally have considerable BET surfaces. Thus, it may be expedient to use corresponding very fine powders with BET surface areas of at least 5 m 2 / g and in particular of at least 10 m 2 / g. Corresponding surfaces of the dry powder either directly occur in its synthesis in a manner known per se - see, for example, the aerosils with BET surfaces in the range from about 50 to 400% / g - or they can be used as dry powder by appropriate pretreatment coming material can be ensured. Particularly suitable for such a pretreatment is the grinding of a material of initially larger particle size and correspondingly smaller surface area.

The amounts of the dry powder to be used in the spray drying in each particular case are firstly determined by the reliable formation of the inhibition according to the invention with regard to bonding effects. As a rule, this can be achieved with very small amounts of dry powder, which usually make up at most about 10% by weight and preferably at most about 2 to 5% by weight, based on spray-dried valuable material . In general, amounts of the auxiliary substance below 1% by weight, based again on spray-dried material, will suffice. At least that applies to highly effective dry powder, for example of the type of a hydrophobic aerosil. In other embodiments, the targeted use of these auxiliaries in larger quantities may also be desirable. Such cases occur, for example, when the dry powder itself is a desired component of the resulting dry material. Builder components or surfactant components are mentioned here as examples. The optimized amount to be used in each case is also determined from the technical effect sought according to the invention of not causing or triggering excessive and undesired discharge of the added solid fines with the hot gas stream into a secondary separation stage. By varying and adapting the working conditions, an optimization of the desired process result can be set taking into account the technical knowledge. In special cases it may also be desirable to additionally mix and powder the free-flowing solid material discharged from the spray dryer, and preferably in the still warm state, with further portions of the dry powder. Such a case can always exist if, due to their chemical structure, valuable materials or those that are particularly prone to stickiness are processed into free-flowing solid materials in the spray drying process. An example here is anhydrous, free-flowing sugar surfactant powder which is obtained by drying aqueous preparations of alkyl and / or alkenyl oligoglycosides and / or of fatty acid N-alkylpolyhydroxyalkyl amides, in particular in the presence of inorganic and / or organic salts and, if appropriate, other carrier substances become. In this context, reference is made, for example, to the applicant's older German patent application DE P 4340015.9, the disclosure of which is hereby also made the subject of the present disclosure of the invention. The teaching according to the invention changes the technical teaching of the cited earlier application to the effect that dry powders, for example aerosils, in particular in hydrophobicized form, are introduced into the spray tower during the spray drying of water-containing preparation forms of the surfactant components.

To carry out spray drying using superheated steam as the drying gas, reference is also made to the following publications by the applicant: DE-A 4204035, DE-A 4204090, DE-A 4206050, DE-A 4206495 and DE-A 4206521.

B e i s p i e l e

example 1

In a test spray tower of the "Minor Production" type, a slurry consisting of the solids content was composed of

90% by weight Ci2 / l6-cocoalkyl oligoglucoside DP = 1.33 (Plantaren ( ^R ) APG 600) with the following characteristics:

Solid: 50% by weight of active substance: 45% by weight

10% by weight sodium sulfate

dried with superheated steam. The slurry was sprayed from below into the drying tower through a two-component nozzle, the superheated steam used as the propellant gas. The particles move upwards due to the impulse, are deflected and discharged via a double pendulum flap below the tower cone (fountain principle). The superheated steam entered the tower cover and was laterally drawn off below the tower cone. The operating parameters are summarized in Table 1:

Table 1: Process data

Slurry superheated steam

Drying gas propellant for

Dual-substance nozzle

Throughput 15 kg / h 400 m ³ / h 3 m3 / h

Inlet temperature (° C) 80 210 130

Outlet temperature (° C) - 140 -

Pressure (bar) 1.5 0.4 A pyrogenic silica Aerosil ( ^R ) R 972 (from Degussa) with the following characteristics was used as powder material:

Behavior towards water: hydrophobic *

* The silanol groups have been irreversibly replaced by methyl groups

Appearance: loose white powder

BET surface area: approx. 110 m ² / g

Average size of the primary particles: 16 nm

Tamped density: approx. 50 g / 1

Drying loss: <0.5%

Loss on ignition: <2%

SiO 2> 99.8% by weight

AI2O3 <0.05

Tiθ2 <0.03

HC1 <0.05

The Aerosil was sprayed from above through a solid nozzle onto the partially dried surfactant particles. The powder served as a spacer between the particles and thus prevented unwanted agglomeration. The otherwise extremely hygroscopic, adhesive surfactant powder could be discharged through the double pendulum flap as a very free-flowing powder. In addition, the aerosil as an anti-caking agent largely prevented the unwanted caking in the tower. The bulk density was 375 g / 1. The residual moisture was 2.6%. The final product contained 3% powder material.

Example 2

The procedure was as in Example 1. A surfactant mixture was dried out

50% by weight Ci2 / i6 cocoalkyl oligoglucoside DP = 1.33 plantars ( ^R ) APG 600 CS UP, Henkel and 50% by weight Ci2 / i8 fatty alcohol sulfate sulfopone ( ^R ) 1218, Henkel with the following characteristics:

Solid: 55% by weight of active substance: 50% by weight

C chain distribution in the active substance:

C12-14 20-30%

Ci6-18 ^: 70-80%

2% sodium sulfate, based on the surfactant powder, was used as the powdering agent.

The end product showed very good powder properties. The bulk density was 350 g / 1.

Example 3:

The procedure was as in Examples 1 and 2. The solids content of the slurry consisted of

95% by weight Ci2 / i6 cocoalkyl oligoglucoside DP = 1.33 plantars ( ^R ) APG 600 CS UP, Henkel and

5% by weight NaCl

A sodium carboxymethyl cellulose (CMC) A250 from Aqualon was used as the powdering agent.

CMC A250 fine powder:

Purity: 99.5% min.

Sodium chloride: 0.03%

Sodium glycolate: 0.40% max. Degree of substitution: 0.70

Packaging moisture: 8.2% pH in 1% solution: 7.4

Grain size distribution:

> 0.250 mm: 0.5% ax.

<0.075 mm: 80% max.

The APG powder powdered with 5% CMC had a bulk density of 390 g / 1. The APG dried in this way performed very well in the tests with regard to the powder properties (dust test, clump test, sieve analysis).

Example 4:

The procedure was as in Examples 1 to 3. A 65% aqueous paste of a Ci2 / i8- ^fat lk ° h ° l ^{su '} lf ^{' ates} Sulfopon ( ^R ) 1218, Henkel was dried. Water spray in powder form was continuously metered in during the spray drying of the anionic surfactant. Porti1 Ä ( ^R ), Henkel was used as the water glass.

Porti1 A:

Chemical composition:

% SiO 2 54% Na 2 O 27% H 0 19

Weight ratio Siθ2: Na2θ 2.0 - 2.1 molar ratio S1O2: NaH2θ 2.1 - 2.2

Physical data:

Bulk weight: 700 kg / m ³

Grain size distribution: on sieve 0.8 mm approx. 0.5% on sieve 0.4 mm approx. 1.5% on sieve 0.2 mm approx. 10% on sieve 0.1 mm approx. 45% on sieve 0.05 mm approx. 35% through sieve 0.05 mm approx. 10%

The spray-dried and simultaneously powdered surfactant powder was composed of 90% fatty alcohol sulfate and 10% water glass with respect to the dry substance. The bulk density was 340 g / 1. The residual moisture was 2%.

Example 5:

The procedure was as in Examples 1 to 4. A 72% aqueous paste of a fatty alcohol ether sulfate Texapon K14 57θ ( ^R ), Henkel, was dried. The sodium lauryl myristyl ether sulfate as a paste had the following characteristics:

Anionic surfactant> _, 1.504 meq / g

Density (20 ° C) approx. 1 g / cm ³ pH value (3%) 7-10

Nacl <2.5%

Na ₂ S04 <2.0%

Pouring point (DIN-IS03016)> 20 ° C

A water glass Porti1 A ( ^R ) was used for powdering. The powder addition has been adjusted so that 30% water glass with respect to the dry substance is contained in the end product.

Claims

Expectations

1. A process for spray drying water-containing preparations of valuable substances and mixtures of valuable substances from the field of wetting agents, detergents and / or cleaning agents in an upright tower, using hot gases which are driven in cocurrent and / or countercurrent as drying agents, characterized in that that additionally and separately from the water-containing valuable substance preparations small amounts of a fine powder dry material (dry powder) are introduced into the spray tower.

2. The method according to claim 1, characterized in that the dry powder is added directly to the hot gas stream, but preferably introduced into the drying tower by means of an auxiliary gas stream.

3. Process according to claims 1 and 2, characterized in that the dry powder is supplied to the areas of the drying tower which are particularly at risk from adhesions and / or caking.

4. Process according to Claims 1 to 3, characterized in that the dry powder is blown over a wide area at least in wall areas at risk of adhesion.

5. Process according to Claims 1 to 4, characterized in that at least a portion of the dry powder is fed to the interior of the drying tower in the region of the spray nozzles and preferably in the direction of movement of the aqueous valuable material fed in.

6. Process according to Claims 1 to 5, characterized in that finely divided, free-flowing recyclable materials and / or recyclable materials of the specified application range are used as the dry powder.

7. The method according to claims 1 to 6, characterized in that one uses recycled dry material as dry powder and in particular its fines.

8. The method according to claims 1 to 7, characterized in that water-soluble and / or water-insoluble very fine solids of inorganic and / or organic nature are used as the dry powder, which is preferably non-sticky and / or non-swelling, preferably under the drying conditions in the spray tower are and in particular can be hydrophobic.

9. The method according to claims 1 to 8, characterized in that one uses highly disperse and essentially water-insoluble inorganic solids as dry powder, which can also be hydrophobic, where the use of appropriate powders based on aluminum oxide, highly disperse silicas and / or zeolites in detergent quality, can be preferred, the use of very finely divided hydrophobicized silicas being of particular importance.

10. The method according to claims 1 to 8, characterized in that water-soluble organic and / or inorganic solid powders such as water-soluble polymers, for example xanthan, starch, methyl cellulose, carboxymethyl cellulose, but also organic solid components with surfactant character, in particular fine powdered anionic surfactants, or Usual inorganic mixture components from the field of wetting, washing and / or cleaning agents, such as soluble builders and / or adjusting agents, can be used as dry powder.

11. The method according to claims 1 to 10, characterized in that dry powder with BET surface areas of at least 5 m ^ / g, preferably of at least 10 m ² / g, are used.

12. The method according to claims 1 to 11, characterized in that the dry powders are used in the context of spray drying with superheated steam as the drying gas.

13. The method according to claims 1 to 12, characterized in that the Trockeπpulver are fed into a water- or steam-based auxiliary fluid in the drying room, the The addition temperature of this auxiliary fluid can preferably be below the drying temperature of the superheated steam.

14. The method according to claims 1 to 13, characterized in that we at least a portion of the dry powder is fed into the lower region of the drying tower operated with superheated steam as the drying gas.

15. The method according to claims 1 to 14, characterized in that the dry powders are used in quantities not exceeding 10% by weight, preferably not exceeding 2 to 5% by weight, based on the dried material.

16. The method according to claims 1 to 15, characterized in that the spray-dried material - preferably in the still warm state - is additionally mixed with dry powder and powdered.