CA2232133A1 - A process for the production of water-and dust-free sugar surfactant granules - Google Patents

Abstract

Proposed is a new method for preparing granulated anhydrous and non-dusting sugar surfactants of high bulk density, wherein aqueous pastes of a) alkyland/or alkenyloligoglycosides and/or b) fatty acid-N-alkylpolyhydroxyalkyl amides with a solids content of at least 20 wt % are simultaneously pelletized and dried to a residual water content of less than 2 wt % in a horizontal thinfilm evaporator with rotating components, a temperature gradient being applied to the thin-film evaporator from product input to product discharge and a gas treatment being effected with counterflow air.

Description

Henkel KGaA
TTP-]?atentabteilung/Dr. Fabry 445/55-APG/FAG
13th September, 1995 Patent Application A process for the production of water- and dust-free sugar ~urfactant granules Field of the Invention This invention relates to a process for the simul-taneous drying and granulation of water-containing sugar surfactant pastes using a lhin-layer evaporator.

Prior Art Sugar surfactants, for example alkyl oligoglucosides or fatty acid-N-alkyl glucamides, are distinguished by excellent detergent properties and high ecotoxicological compatibility. For this reason, these classes of nonionic surfactants are acquiring increasing significance. Although, hitherto, they have generally been used in liquid formulations, for example dishwashing detergents or hair shampoos, there is now also a market need for solid, water-free formulations which may even be incorporated, for example, in powder-form detergents or syndet soaps.
On an industrial scale, liquid surfactant formula-tions are generally dried by conventional spray drying, in which the water-containing surfactant paste is sprayed in the form of fine droplets at the head of a tower, the droplets encountering hot drying gases flowing in countercurrent. Unfortunately, this technology cannot readily be applied to sugar surfactant pastes because the temperatures required for drying are above the caramelization temperature, i.e. the decomposition temperature of the sugar surfactants. In short, the conventional drying of sugar surfactant pastes results in the formation of carbonized products, in addition to which caking occurs on the walls of the spray drying tower so that they have to be cleaned at considerable expense at short intervals.
Attempts have been made in the past to overcome this problem. For example, German patent application DE-A1 41 02 745 (Henkel) clescribes a process in which a small quantity of 1 to 5~ by weight of alkyl glucosides is added to fatty alcohol pastes which are then conventionally spray dried. Unfortunately, the process can only be carried out in the presence of a large quantity of inorganic salts. According to German patent application DE-A1 41 39 551 (Henkel), pastes of alkyl sulfates and alkyl glucosides which may contain at most only 50~ by weight of the sugar surfactant are sprayed in the presence of mixtures of soda and zeolites.
However, this process only gives compounds with a low surfactant concentration and an inadequate apparent density. Finally, International patent application WO
95/14519 (Henkel) reports on the drying of sugar surfactant pastes wit:h superheated steam.
Unfortunately, this is technically very complicated. In fact, there has not yet been a reliable process which enables high-quality, substantially water-free sugar surfactant powders or granules to be produced, but which does not entail the use of carriers during the drying process. Another problem of known processes is that they do not lead to the particularly preferred heavy powders with an apparent density above 500 g/l and, at the same time, a greatly reduced dust content. However, it is precisely these two parameters which are so important on economical, applicational and safety grounds.

Accordingly, the complex problem addressed by the present invention was to convert water-containing sugar surfactant pastes with minimal outlay on equipment and without any need for inorganic or organic carriers into substantially water-free and dust-free granules which would be distinguished simultaneously by acceptable color quality, by high apparent density, by good flow properties, by satisfactory stability in storage and, in comparison with known products, by at least comparable lo performance properties.

Description of the Invention The present invention relates to a process for the production of water-free and dust-free sugar surfactant granules of high apparent density, in which water-con-taining pastes of a) alkyl and/or alkenyl oligoglycosides and/or b) fatty acid-N-alkyl po:Lyhydroxyalkylamides with a solids content of at least 20~ by weight and preferably in the range from 25 to 75~ by weight are dried in a horizontally arranged thin-layer evaporator with rotating fittings to a residual water content below 2~ by weight, preferably helow 1.5~ by weight and, more preferably, below 1~ by weight and, at the same time, converted into particulate form.
It has surprisingly been found that a horizontally arranged thin-layer evaporator is eminently suitable for converting water-containing sugar surfactant pastes into dry, light-colored, free-flowing and non-tacky granules without any risk of product discoloration and caking on the walls. The products have a high apparent density of 550 to 650 g/l and an average particle diameter of 2.0 to 2.8 mm which leads to a reduction in the unwanted absorption of water and in the caking of the particles.
High stability in storage is also achieved in this way.
At the same time, the particles are dust-free, i.e. the percentage of particles smaller than 200 ~m in diameter is less than 5~ by weight:. This discovery is all the more surprising insofar as, although evaporators of the type mentioned are known in principle for the drying of anionic surfactant pastes r the powders obtained do not meet the requirements mentioned either in regard to their apparent density or in regard to their dust and residual water contents.

Alkyl and/or alkenyl oligoqlycosides Alkyl and alkenyl oligoglycosides are known nonionic surfactants corresponding to general formula (I):

R O-[G]p (I) in which R1 is an alkyl and/or alkenyl radical containing 4 to 22 carbon atoms, G is a sugar unit containing 5 or 6 carbon atoms and p is a number of 1 to 10. They may be obtained by the relevant methods of preparative organic chemistry. EP-A1-0 301 298 and WO 90/03977 are cited as representative of the extensive literature available on this subject.
The alkyl and/or alkenyl oligoglycosides may be derived from aldoses or ketoses containing 5 or 6 carbon atoms, preferably glucose. Accordingly, the preferred alkyl and/or alkenyl oligoglycosides are alkyl and/or alkenyl oligoglucosides.
The index p in general formula (I) indicates the degree of oligomerization (DP degree), i.e. the distribution of mono- and oligoglycosides, and is a number of 1 to 10. Whereas p in a given compound must CA 02232l33 l998-03-l6 always be an integer and, above all, may assume a value of 1 to 6, the value p for a certain alkyl oligogly-coside is an analytically determined calculated quantity which is generally a broken number. Alkyl and/or alkenyl oligoglycosides having an average degree of oligomerization p of 1.1 to 3.0 are preferably used.
Alkyl and/or alkenyl oligoglycosides having a degree of oligomerization of less than 1.7 and, more particularly, between 1. 2 and 1. 4 are preferred from the applicational point of view.
The alkyl or alkenyl radical R1 may be derived from primary alcohols containing 4 to 11 and preferably 8 to 10 carbon atoms. Typical examples are butanol, caproic alcohol, caprylic alcohol, capric alcohol and undecyl alcohol and the technical mixtures thereof obtained, for example, in the hydrogenation of technical fatty acid methyl esters or in the hydrogenation of aldehydes from Roelen's oxosynthesis. Alkyl oligoglucosides having a chain length of C8 to C10 (DP = 1 to 3), which are obtained as first runnings in the separation of technical Ca18 coconut oil fatty alcohol by distillation and which may contain less than 6-g6 by weight of C12 alcohol as an impurity, and also alkyl oligoglucosides based on technical Cg/11 oxoalcohols (DP = 1 to 3) are preferred.
In addition, the alkyl or alkenyl radical R1 may also be derived from primary alcohols containing 12 to 22 and preferably 12 to 14 carbon atoms. Typical examples are lauryl alcohol, myristyl alcohol, cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol, brassidyl alcohol and technical mixtures thereof which may be obtained as 3 5 described above. Alkyl oligoglucosides based on hydrogenated C12/14 coconut oil fatty alcohol having a DP
of 1 to 3 are preferred.

Fatty acid N-alkyl polyhydroxyalkylamides Fatty acid N-alkyl polyhydroxyalkylamides are nonionic surfactants corresponding to formula (II):

R2CO-N-[Z] (II) in which R2CO is an aliphatic acyl radical containing 6 to 22 carbon atoms, R3 is hydrogen, an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms and [Z] is a linear or branched polyhydroxyalkyl radical containing 3 to 12 carbon atoms and 3 to 10 hydroxyl groups.
The fatty acid N-alk:yl polyhydroxyalkylamides are known compounds which may normally be obtained by reduc-tive amination of a reducing sugar with ammonia, an alkylamine or an alkanolamine and subsequent acylation with a fatty acid, a fatty acid alkyl ester or a fatty acid chloride. Processes for their production are described in US 1,985,424, in US 2,016,962 and in US
2,703,798 and in International patent application WO
92/06984. An overview of this subject by H. Kelkenberg can be found in Tens. Surf. Det. 25, 8 (1988).
The fatty acid N-alk.yl polyhydroxyalkylamides are preferably derived from reducing sugars containing 5 or 6 carbon atoms, more particularly from glucose. Accord-ingly, the preferred fatty acid N-alkyl polyhydroxyalkylamides are fatty acid N-alkyl glucamides which correspond to formula (III):

R2CO-N-CH2-CH-CH-CH-CH-CH2OH (III) OH

Preferred fatty acid N-alkyl polyhydroxyalkylamides are glucamides corresponding to formula (III) in which R3 is hydrogen or an alkyl ~roup and R2CO represents the acyl component of caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, palm-itoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, petroselic acid, linoleic acid, linolenic acid, arachic acid, gadoleic acid, behenic acid or erucic acid or technical mixtures thereof. Fatty acid N-alkyl glucamides (III) obtained by reductive amination of glucose with methylamine and subsequent acylation with lauric acid or C12/l4 coconut oil fatty acid or a corresponding derivative are particularly preferred. In addition, the polyhydroxyalkylamides may also be derived from maltose and palatinose.

Drying and granulation in a so-called flash dryer The simultaneous drying and granulation process takes place in a horizontally arranged thin-layer evapo-rator with rotating fittings of the type marketed, for example, by the VRV company under the name of "flash dryer". In simple terms, the flash dryer is a tube which can be heated to different temperatures over several zones. The paste--form starting material, which is introduced by a pump, is projected onto the heated wall by one or more shafts fitted with paddles or plowshares as rotating f:ittings and is dried on the heated wall in a thin layer typically with the thickness of 1 to 10 mm. According to the invention, it has been found to be of advantage to apply a temperature gradient of 170~C (product entrance) to 20~C (product exit) to the thin layer evaporator. To this end, the first two zones of the evaporator for example may be heated to 160~C and the last zone to 20~C. H:igher drying temperatures have not been found to be of advantage in view of the thermal lability of the starting materials. The thin-layer evaporator is operated at atmospheric pressure. Air is passed through in countercurrent (throughput 50 to 150 m3/h). The gas entry temperature is generally in the range from 20 to 30~C while the exit temperature is in the range from 90 to 110~C.
The water-containing sugar surfactant pastes which may be used as starting materials may have a solids content above 20~ by weight and preferably in the range from 25 to 75~ by weight. Typically, their solids content is of the order of 30 to 50~ by weight. The throughput is of course dependent on the size of the dryer, but is typically in the range from 5 to 15 kg/h.
It is advisable to heat the pastes to 40 to 60~C during their introduction.
In addition, after drying, it has proved to be of considerable advantage to transfer the granules, which still have a temperature of around 50 to 70~C, to a conveyor belt, preferably in the form of a vibrating shaft, and rapidly to cool them thereon, i.e. over a period of 20 to 60 seconds, to temperatures of around 30 to 40~C using ambient air. In order further to improve their resistance to the unwanted absorption of water, the granules may also be subsequently dusted with 0.5 to 2~ by weight of silica powder.

Industrial Applications The granules obtainable by the process according to the invention may be subsequently mixed with other ingredients of powder-form surface-active formulations, for example tower powders for detergents. In addition, the powders may readily be incorporated in aqueous preparations. In fact, where the powders are used, no differences in performance properties are observed in relation to the water-containing starting pastes. The granules may also readily:be incorporated in syndet soap formulations, for example together with fatty acids, fatty acid salts, starch, polyglycol and the like.

CA 02232l33 l998-03-l6 Examples Example 1 The granules were produced in a flash dryer of the type manufactured by VRV ',.p.A., Milan, Italy. This is 5 a horizontally arranged thin-layer evaporator (length 1100 mm, internal diameter 155 mm) with four shafts and 22 paddles of which the distance from the wall is 2 mm.
The dryer had three separate heating and cooling zones and a total heat exchange area of, in all, 0. 44 m2 . The dryer was operated at normal pressure. An aqueous paste - heated to 50~C - of a cocoalkyl oligoglucoside (Plan-taren(~' APG 1200, solids content around 50~ by weight) was pumped into the thin-layer evaporator at a throughput of 11. 5 kg/h by a vibrating pump. Heating 15 zones 1 and 2 of the thin-layer evaporator had been adjusted to 160~C while its cooling zone 3 had been adjusted to 20~C. The rotor speed was 24 m/s. Air was passed through the flash dryer at a rate of around 110 m3/h. The gas exit temperature was around 65~C. The 20 predried granules which still had a temperature of around 60~C were transferred to a vibrating chute (length 1 m), exposed to ambient air and cooled to around 4 0~C in 30 s. The granules were then dusted with around 1~ by weight of silica powder (Sipernat~' 50 S).
25 Dry, pure white granules which were still free flowing and lump-free even after prolonged storage in air were obtained and, after incorporation in shampoo formu-lations, did not show any differences in relation to a paste-form comparison product. The characteristic data of the granules are set out: in Table 1:

Table 1 Characteristic data of the flash dryer granules Parameter Granules Particle size distribution [~ by weight]
< 1.0 mm 1.2 1.0 mm 47.8 2.5 mm 16.5 3.2 mm 16.2 4.0 mm 11.3 5.0 mm 4.7 6.2 mm 2.3 Residual water content (Fischer method) [~ by weight] 1.0 Apparent density [g/l] 590 Example 2 The procedure was as in Example 1 except that the glucoside was replaced by cocofatty acid-N-methyl gluc-amide. The temperature in the two heating zones of the flash dryer was increased to 170~C. Pure white, free-flowing lump-free granules with an apparent density of 600 g/l and a residual water content of 0.8~ by weight were again obtained.

Claims (6)

12

1. A process for the production of water- and dust-free sugar surfactant granules of high apparent density in which water-containing pastes of a) alkyl and/or alkenyl oligoglycosides and/or b) fatty acid-N-alkyl polyhydroxyalkylamides with a solids content of at least 20% by weight are dried in a horizontally arranged thin-layer evaporator with rotating fittings to a residual water content below 2% by weight and, at the same time, converted into particulate form.

2. A process as claimed in claim 1, characterized in that alkyl and alkenyl oligoglycosides corresponding to general formula (I):

R1O-[G]p (I) in which R1 is an alkyl and/or alkenyl radical containing 4 to 22 carbon atoms, G is a sugar unit containing 5 or 6 carbon atoms and p is a number of 1 to 10, are used.

3. A process as claimed in claims 1 and 2, characterized in that fatty acid N-alkyl polyhydroxyalkylamides corresponding to formula (II):

R2CO-N-[Z] (II) in which R2CO is an aliphatic acyl radical containing 6 to 22 carbon atoms, R3 is hydrogen, an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms and [Z] is a linear or branched polyhydroxyalkyl radical containing 3 to 12 carbon atoms and 3 to 10 hydroxyl groups, are used.

4. A process as claimed in claims 1 to 3, characterized in that a temperature gradient of 170 to 20°C is applied to the thin-layer evaporator from the product entrance to the product exit.

5. A process as claimed in claims 1 to 4, characterized in that, after leaving the thin-layer evaporator, the still hot granules are further cooled with ambient air on a vibrating chute.

6. A process as claimed in claims 1 to 5, characterized in that, after cooling, the granules are dusted with silica powder.