Process for preparing raw materials for washing agents

Details Process for preparing raw materials for washing agents Process for preparing raw materials for washing agents

1999-08-25

2001-02-20

Douyon, Lorna A. (Department: 1751)

Cleaning compositions for solid surfaces, auxiliary compositions

Cleaning compositions or processes of preparing

Heterogeneous arrangement

C510S457000, C510S470000, C510S495000, C510S501000, C510S504000, C159S006300, C159S047100

Reexamination Certificate

active

06191097

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the contact drying of aqueous surfactant pastes in a horizontal thin-layer evaporator or dryer.
2. Discussion of Related Art
Anionic and amphoteric or zwitterionic surfactants are important ingredients of solid detergents and bar soaps. The detergents are normally produced by spraying an aqueous, generally highly alkaline slurry of the ingredients and drying the slurry with hot inert gases flowing in countercurrent. However, since this conventional spray drying process is accompanied by serious pollution of the waste air with organic material, there is a need for alternative, ecologically more favorable drying processes. These include in particular the contact drying of water-containing surfactant pastes in thin-layer dryers which leads to dry products which can then be processed with the other dried detergent ingredients, for example in mixers, to form the end product.
European patent application EP-A1 0 572 957 (Kao) describes a process for drying alkyl or alkyl ether sulfates in which dilute surfactant pastes are first concentrated to an active substance content of 60 to 80% by weight and are then dried in vacuo at temperatures of 50 to 140° C. in a vertical thin-layer evaporator. However, a major disadvantage of this process is that, because drying is carried out under reduced pressure, the end product has to be removed from the circuit using complicated equipment suitable for operation in a vacuum. The continuous contact with the hot product means that there is always a danger of caking and, hence, operational disturbances which necessitate a complete stoppage of production so that cleaning can be carried out. Another major disadvantage is that the use of a vertical thin-layer evaporator with wall contact of the rotor blades means that a flowable product film has to be maintained on the wall of the evaporator over its entire length in continuous operation in order to avoid mechanical overloading of the evaporator. Accordingly, the process is not suitable for the direct production of a powder, but only for the production of a concentrated hotmelt which has to be separately crystallized (for example in a flaking roller or the like) and then size-reduced.
By contrast, International patent application WO 96/06916 (Unilever) proposes a process for drying water-containing anionic surfactant pastes in a horizontal thin-layer evaporator which operates under a light vacuum to almost normal pressure and at temperatures above 130° C. Another feature of this process is the use of a very high peripheral speed of the stirrers used of at least 15 m/s which virtually rules out direct wall contact and leads to products of satisfactory color. However, in the drying of water-containing anionic surfactant pastes, more particularly aqueous pastes of alkyl sulfates or alkyl ether sulfates, there is basically a risk of unwanted hydrolysis in the product. Even brief reduction of the pH value leads in the presence of water to rehydrolysis, to the formation of inorganic sulfate and to a reduction in the content of washing-active substance. In following the teaching of WO 96/06916, applicants found that a hydrolysis-free product could not be reproducibly obtained over an operating period of several hours.
Accordingly, the complex problem addressed by the present invention was to provide a process for the contact drying of water-containing anionic surfactant and/or amphoteric surfactant pastes which would not have any of the disadvantages mentioned above and which, despite minimal outlay on equipment, would lead under production conditions to hydrolysis-free, free-flowing granules of satisfactory color distinguished by high bulk densities and a uniform particle size distribution.
DESCRIPTION OF THE INVENTION
The present invention relates to a process for the production of solid detergent raw materials by simultaneously drying and granulating water-containing pastes of anionic and/or amphoteric surfactants in a horizontal thin-layer evaporator or dryer with rotating fittings, characterized in that drying is carried at a temperature in the range from 120 to 130° C.
It has surprisingly been found that free-flowing granules of satisfactory color can be obtained only and precisely when the drying temperature is kept in the range mentioned. Even minor upward deviations lead to an unwanted increase in the content of inorganic sulfate while slight downward deviations lead to products with unsatisfactory flow properties. The invention includes the observation that the tendency towards hydrolysis can be further suppressed by carrying out the contact drying process in the presence of (a) 0.05 to 0.5% by weight of alkali metal carbonate and/or (b) an alkaline gas stream. The water is removed preferably by a gas stream and not by applying a vacuum. Another advantage of the process according to the invention is that it gives products of high bulk density (above 600 g/l) which, irrespective of the surfactant paste used, have a very uniform particle size distribution.
Surfactants
Typical examples of anionic surfactants which can be dried by the process according to the invention are soaps, alkyl benzenesulfonates, alkane sulfonates, olefin sulfonates, alkyl ether sulfonates, glycerol ether sulfonates, &agr;-methyl ester sulfonates, sulfofatty acids, alkyl sulfates, fatty alcohol ether sulfates, glycerol ether sulfates, hydroxy mixed ether sulfates, monoglyceride (ether) sulfates, fatty acid amide (ether) sulfates, mono- and dialkyl sulfosuccinates, mono- and dialkyl sulfosuccinamates, sulfotriglycerides, amide soaps, ether carboxylic acids and salts thereof, fatty acid isethionates, fatty acid sarcosinates, fatty acid taurides, N-acyl amino acids such as, for example, acyl lactylates, acyl tartrates, acyl glutamates and acyl aspartates, alkyl oligoglucoside sulfates, protein fatty acid condensates (more particularly vegetable wheat-based products), alkyl (ether)phosphates and sulfates of ring-opening products of olefin epoxides with water or alcohols. Where the anionic surfactants contain polyglycol ether chains, they may have a conventional homolog distribution although they preferably have a narrow homolog distribution. Typical examples of amphoteric or zwitterionic surfactants are alkyl betaines, alkyl amidobetaines, aminopropionates, aminoglycinates, imidazolinium betaines and sulfobetaines. The surfactants mentioned are all known compounds. Information on their structure and production can be found in relevant synoptic works, cf. for example J. Falbe (ed.), “Surfactants in Consumer products”, Springer Veriag, Berlin, 1987, pp. 54-124 or J. Falbe (ed.), “Katalysatoren, Tenside und Mineralöladditive”, Thieme Verlag, Stuftgart, 1978, pp. 123-217.
In the context of the invention, water-containing pastes are understood to be aqueous preparations of the surfactants which have an active substance content of 5 to 80% by weight and preferably 10 to 70% by weight. For energy-related and rheological reasons, it is of advantage to use pastes which have a solids content of at least 30% by weight and preferably 50% by weight and at most 70% by weight. The anionic surfactants are used in the form of their alkali metal, alkaline earth metal, ammonium, alkylammonium, alkanolammonium, glucammonium salts. In other preferred embodiments of the process, alkyl and/or alkenyl (ether)sulfates, sulfosuccinates and/or betaines are dried and processed to light-colored, free-flowing granules.
Alkyl and/or Alkenyl Sulfates
In the context of the invention, alkyl and/or alkenyl sulfates, which are also often referred to as fatty alcohol sulfates, are understood to be the sulfation products of primary alcohols which correspond to formula (I):
R
1
O—SO
3
X  (I)
where R
1
is a linear or branched, aliphatic alkyl and/or alkenyl group containing 6 to 22 and preferably 12 to 18 carbon atoms and X is an alkali metal and/or alkaline earth metal, ammonium, alkylammonium, alkanolammonium or glucammonium. Typical examples of alkyl sulfates which

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