This invention relates to a process for converting water-containing preparations of washing- and cleaning-active surfactant compounds into storable surfactant granules and into storable detergents in granular form.
Considerable and, at the same time, greatly increasing interest is being shown in the use of oleochemical surfactant compounds in detergents and cleaning products. The primary considerations in this regard are based on the one hand on the fact that surfactant compounds of this type can be obtained from renewable vegetable and/or animal raw materials, although on the other hand it is above all the high ecological compatibility of selected components of this type to which crucial significance is attributed. An example of one such class of oleochemical surfactant compounds are the known fatty alcohol sulfates which are prepared by sulfatization of fatty alcohols of vegetable and/or animal origin containing predominantly 10 to 20 carbon atoms in the fatty alcohol molecule and subsequent neutralization to water-soluble salts, more particularly the corresponding alkali metal salts. Of particular practical significance in this regard are the sodium salts of fatty alcohol sulfates which are based on at least predominantly linear fatty alcohols or corresponding fatty alcohol mixtures containing approximately 12 to 18 carbon atoms in the fatty alcohol molecule. Tallow alcohol sulfates (TAS) containing predominantly saturated C.sub.16-18 residues in the fatty alcohol are already of considerable interest for the production of laundry detergents, more particularly in solid form, although significant detergent properties may also be attributed to fatty alcohol sulfates (FAS) which cover a broader range in regard to the length of their carbon chains. Thus, C.sub.12-18 fatty alcohol sulfates having a high percentage content of the lower fatty alcohols of this range, for example based on coconut oil or palm kernel oil, represent particularly important anionic surfactants for use in detergents and cleaning products. There are numerous references to this effect in the relevant specialist literature, cf. H. Baumann "Neuere Entwicklungen auf dem Gebiet fettchemischer Tenside", Fat Sci. Technol., 92 (1990) 49/50 and the literature cited therein. European patent application 342 917 also describes detergents in which the anionic surfactants consist predominantly of C.sub.12-18 alkyl sulfates.
The economic synthesis of light-colored anionic surfactants based on FAS is now established state of the art. The corresponding surfactant salts accumulate in the form of water-containing preparations in which the water contents may vary from approximately 20 to 80% and, more particularly, from approximately 35 to 60%. Products of this type have a paste-like to cuttable consistency at room temperature, the flowability and pumpability of the pastes being limited or even completely lost for active substance contents of only about 35% by weight, so that the subsequent processing of the pastes, particularly their incorporation in solids mixtures, for example in solid detergents and cleaning products, involves considerable problems. It is possible to obtain free-flowing FAS powders by conventional drying processes, particularly in spray drying towers. However, there are serious limitations in this regard which, in particular, jeopardize the economy of using FAS surfactants on an industrial scale. Tower-dried TAS powder, for example, shows a very low apparent density, so that there are unprofitable aspects to the packaging and marketing of this detergent raw material. However, even in the production of spray-dried powder, safety considerations can necessitate such restrictive operation of the spray drying tower that practical difficulties arise. Thus, safety-based investigations of tower-dried powder based on TAS or FAS having active substance contents of 20% or higher show that the spray drying of formulations of this type is only possible to a very limited extent and, for example, requires tower entry temperatures below 200.degree. C.
Comparable difficulties or other difficulties are involved in the conversion of water-containing, more particularly paste-form, preparations of numerous other washing- and cleaning-active surfactant compounds into storable dry products. Further examples of anionic oleo-chemical surfactant compounds include the known sulfofatty acid methyl esters (fatty acid methyl ester sulfonates, MES) which are prepared by .alpha.-sulfonation of the methyl esters of fatty acids of vegetable and/or animal origin containing predominantly 10 to 20 carbon atoms in the fatty acid molecule and subsequent neutralization to water-soluble monosalts, more particularly the corresponding alkali salts. The corresponding .alpha.-sulfofatty acids or disalts thereof are formed therefrom by ester cleavage and show specific washing- and cleaning-active properties in the same way as mixtures of disalts and sulfofatty acid methyl ester monosalts. However, comparable problems also arise with other classes of surfactants where attempts are made to produce the corresponding surfactant raw materials in solid or granular form, as for example with washing- and cleaning-active alkyl glycoside compounds. To obtain light-colored reaction products, their synthesis generally requires a final bleaching step carried out, for example, with water-containing hydrogen peroxide, so that in this case, too, modern technology leads to the water-containing paste form of the surfactant. Water-containing alkyl glycoside pastes (APG pastes) are more susceptible, for example, to hydrolysis or microbial contamination than corresponding solids. In their case, too, simple drying by conventional methods involves significant difficulties. Finally, however, even the drying of a water-containing paste of the alkali metal salts of washing-active soaps and/or of alkyl benzenesulfonates (ABS pastes) can also involve considerable problems.
It is also desirable, above all for economic reasons, to limit the quantity of water to be introduced into the process as far as possible. Accordingly, the smallest possible quantity of water is best used in the water-containing surfactant pastes. However, the degree of concentration is limited by the viscosity behavior of the water-containing pastes. Only raw materials which can still be processed, i.e. for example are flowable and pumpable, in the process can be introduced into the process. It is known that, particularly for detergents and cleaning products, for example for laundry detergents, important anionic surfactants, such as the alkali metal salts of ABS, fatty alcohol sulfates, fatty acids, .alpha.-sulfonated fatty acids and corresponding .alpha.-sulfofatty acid esters, can only be worked up into flowable and pumpable pastes using relatively considerable quantities of water. Thus, ABS salt pastes and pastes of tallow alcohol sulfates having water contents of 40 to 60% by weight are being processed in practice at the present time. In addition, the paste viscosity of water-containing mixtures of the type in question is still greatly dependent on temperature so that pastes of the type in question cannot be used without difficulties at room temperature and elevated temperatures, for example in the range from 50.degree. to 70.degree. C., have to be applied.
Further investigations in the field in question have revealed dramatic deteriorations in the processability of water-containing mixed pastes in one important special case: the paste viscosity allows ABS and TAS pastes each having solids contents of 50 to 60% by weight to be separately processed. However, if an attempt is made to mix these separately processable pastes to obtain a homogeneous anionic surfactant mixture for subsequent incorporation in detergent formulations, there is a dramatic increase in viscosity in the paste mixture for basically the same solids content. This phenomenon is observed both when the ABS paste is added to the FAS paste and vice versa. Even mixing ratios of 9:1 or 8:2 lead to a solidified, water-containing material which can no longer be processed.
The teaching of U.S. Pat. No. 4,495,092, the entire contents of which are incorporated herein by reference, describes the use of C.sub.8-40 alcohols which are substituted by 1 to 5 hydroxyl groups and/or onto which up to 15 mol ethylene oxide and/or propylene oxide are added per tool alcohol as viscosity regulators for high-viscosity industrial surfactant concentrates of the synthetic anionic surfactant type. Corresponding water-containing pastes of alkyl sulfates, alkylaryl sulfates and .alpha.-sulfofatty acid esters having a surfactant content of at least 30% by weight are mentioned in particular. According to this teaching, the addition of the above-mentioned viscosity regulators in quantities of 1 to 15% by weight, based on the quantity of surfactant, leads to viscosities of the particular surfactant concentrate of at most 10,000 mPa.s at 70.degree. C. (Hoppler falling ball viscosimeter). Mixtures of saturated and unsaturated fatty alcohols containing up to 8 tool EO and/or PO units are particularly preferred viscosity regulators. The viscosity behavior of water-containing pastes of mixed surfactants and, in particular, the dramatic increase in viscosity when water-containing ABS and TAS pastes are mixed is not discussed in this publication.
The problem addressed by the present invention was to provide an alternative method of processing water-containing, more particularly paste-form, surfactant preparations into dry, more particularly free-flowing and concentrated surfactant granules. The invention is based on the disclosure of U.S. Pat. No. 4,495,042, but extends the principles described therein beyond existing knowledge.