NO135830B - - Google Patents

Description

The invention relates to a method for producing detergent mixtures in powder form by atomizing an aqueous slurry of detergent ingredients into a drying gas stream.

Washing powders are usually made by a method where a gas flow is directed so that the water in the slurry evaporates. The aqueous slurry may have a relatively high temperature relative to the gas, in which case flash evaporation of the water in the slurry occurs during the process, which is sometimes referred to as spray cooling. More often, the aqueous slurry is of relatively low temperature and the gas stream is heated to a higher temperature, and this process is generally referred to as spray drying.

For convenience, the term "spray drying" is used

in the following for all powder-forming processes where aqueous slurries are atomized into drying gas streams.

Conventional spray drying processes are not readily applicable to the production of washing powders with a high content of organic material, due to the risk of fire or explosion if the powder is overheated in the presence of oxygen, which is usually the case when the drying gas is normal air. Furthermore, the effort to lower the content of phosphates, especially condensed phosphate builders such as sodium tripolyphosphate, in detergents has

partial mixtures, due to suggestions that such use of phosphates contributes to eutrophication, have generally gone in the direction of increasing the organic content of washing powders.

The possible organic substitutes for condensed phosphate builders that have been proposed so far include so-called polyelectrolyte builders, e.g. sodium polyacrylate, sodium polymaleate and copolymers thereof, e.g. sodium copolyethylene/maleate, certain oxidized polysaccharides and non-polymeric builders, e.g. sodium oxydiacetate, sodium carboxymethyloxysuccinate and sodium nitrile triacetate. Other preferred organic builders are the water-soluble salts of dicarboxylic acids of the formula R.CH(COOH) (CH2)n•COOH, where n is 0 or 1 and R is a primary or secondary straight-chain alkyl or alkenyl group having from 10 to 20 carbon atoms,

which is described in the applicant's Norwegian patent no. 131,645.

Preferred dicarboxylates are sodium alkenyl succinates which can be prepared by hydrolysis and neutralization of alkenyl succinic anhydrides which are obtained by reaction between maleic anhydride and olefins.

The amounts of builders in detergent mixtures can

be up to as much as 50% by weight, in which case the two-

the organic content of washing powders can sometimes be so

as high as 80% by weight, when the content of organic material in the detergent-active compounds and any additives, e.g. hydrotropes, foam boosters, dirt-carrying agents and fluorescent agents are taken into account. Under these circumstances, when the powders contain more than approx. 50% organic matter, there is a significant risk of fire or explosion if the powders are overdried and overheated during production in conventional spray-drying processes.

According to the invention, a washing powder is produced which contains 50-80% by weight of organic material, consisting of a synthetic detergent-active anionic compound and an organic builder, whereby an aqueous slurry of the detergent ingredients is produced with a content of 20 to 40% by weight of water, and the method is characterized in that the slurry is prepared in a vessel under pressure at a temperature of from 125 to 180°C, after which the mixture is spray-dried in an air stream at a temperature of from 100 to 250°C.

By using this method, it is possible to produce washing powders under conditions which, in the spray drying step, are not so severe that they involve any significant fire or explosion hazard, and the invention can also provide valuable economic benefits in the production of washing powders, both in that the heat required for drying is reduced of the slurry into a powder and by the fact that the capacity in the spray dryer is increased due to the slurry's lower water content. A further advantage lies in the fact that the method will produce powders with a higher bulk density. than conventional spray drying processes.

In conventional washing powder production, it is common to have a water content in the slurry of from approx. 38-50% by weight. In the method according to the invention, the aqueous slurry should contain as little water as practically possible, which is no more than approx. 40% by weight, preferably less than 30% by weight, based on the slurry. The water content can be as low as approx. 20% by weight, calculated on the slurry, under optimal conditions, as explained below.

The conditions used in spray drying are preferably as mild as possible, when it is taken into account that a satisfactory powder production rate will be achieved, with the aim of reducing any fire risk to a minimum, especially when it comes to powders containing the larger amounts of organic material. The gas temperature in the atomization drying stage is preferably from approx. 150 to approx. 200°C. The spray-drying operation is preferably carried out under conditions which make it possible in a single operation to obtain a free-flowing powder, but if desired, e.g. in order to increase the capacity of a spray drying tower, the spray drying conditions can be modified so that the powder that is first produced is still moist, after which the excess water is removed in a subsequent drying operation, e.g. by using a fluidized bed where additional drying gas is passed through the powder, either in a batch process or a continuous process, or by using a pneumatic dryer where the powder is dried by a hot gas while it is being transported.

It will be understood that it is essential to prepare the slurry under pressure in a closed vessel, as elevated temperatures are used. The pressure also serves to transfer the slurry after its production to the atomization dryer and to atomize the slurry before atomization into the gas. The development of the pressure in the vessel is preferably carried out with fresh steam, or, as this tends to raise the water content of the slurry, by means of compressed air or by a combination of both. The pressure in the tub should be such that it gives the atomizing nozzle a pressure of from approx. 2.8 to 4.9 kg/cm 2, but it can go higher, e.g. up to

, 2 <1>

about. 7 kg/cm, while pressure above this is of no noticeable benefit and only greatly increases the costs of the equipment. In practice, a pressure in the vessel of o up to approx. 10.5-14 kg/cm 2. The method according to the invention is only applicable to the production of washing powders where the components are available in a suitable dry form which enables the production of aqueous slurries that contain no more than approx. 40% by weight water. With regard to components which in the powder are in the form of salts of organic acids, which is usually the case for organic detergent builders and anionic detergent-active compounds, the organic acid or its anhydride is preferably neutralized with an alkaline material, e.g. sodium hydroxide, in the slurry. If, on the other hand, the salt is preformed, it generally contains too much water to enable the slurry to be made with the required amount of less than: 40% water. This is because the neutralization of the acids outside the slurry generally requires water in excess to regulate the neutralization arm and to make the product pumpable, and drying the solution of neutralized product to a powder is not economical. However, if a builder salt or an anionic detersive compound is available in a sufficiently dry form, e.g. as a powder or flake, it may be advantageous to use it directly at the slurry.

In the preferred embodiment of the method according to the invention, the main components are mixed, except for the organic builder in acid or arihydride form, and the mixture is heated to a temperature of about. 100 to 140°C. The precursor to the builder is then added, after which it is neutralized,

and hydrolyzed if necessary, in the slurry, and the heat of neutralization causes the temperature and pressure to rise to the desired values for spray drying. This procedure can be performed in batch or continuously.

The method according to the invention is of particular interest for the production of washing powders with alkyl and alkenyl succinates as builders. These materials can easily be

is placed in anhydride form and can be added in this form to the aqueous slurry where hydrolysis and neutralization take place to form the desired water-soluble salts. Some analogous compounds, e.g. alkylthio- and alkyloxysuccinates, can be used in the same way.

Other builders that can be used in the procedure i

according to the invention, includes e.g. the salts of α-sulfonated fatty acids, e.g. α-sulfonated hardened tallow fatty acids, higher alkanesulfonate and -sulfinate/sulfonates, and soaps a and all of these serve as detergency builders in detergent compositions by forming insoluble calcium salts; water-soluble salts of organic acids including oxydiacetic acid, oxysuccinic acid, carboxymethyl-oxysuccinic acid, hydrofuranthetracarboxylic acid and homologues and analogues of these materials, oxidized polysaccharides where the anhydro-glucose rings are opened to form dicarboxylic units as described in the applicant's British patent no. 330,121;

and polyelectrolyte detergency builders, e.g. sodium polyacrylate and sodium polymaleate and copolymers thereof, e.g. sodium copolyethylene/maleate, but it should be noted that in the case of some polyelectrolytes there may be a tendency for these to decarboxylate at the higher temperatures. Many other suitable organic detergency builders are available and are described in the literature, e.g. in "Surface Active Agents and Detergents" by Schwartz, Perry & Berch.

In addition to the organic builders discussed above, the detergent mixtures usually comprise one or more detergent-active compounds, together with the usual optional additives. The synthetic detergent compounds are preferably anionic detergent compounds, which are readily available and relatively cheap, and mixtures thereof. These compounds are usually water-soluble alkali metal salts of organic sulfates

and sulfonates with alkyl radicals containing from approx. 8 to approx.

22 carbon atoms, the term alkyl being used to include the alkyl part of higher acyl radicals.' Examples of such synthetic anionic detergent-active compounds are sodium and potassium alkyl (C8-C20) benzenesulfonates, especially sodium linear sec. -alkyl (C 1-0 -Cl 5 )kenesulfonates; sodium and potassium salts of fatty acid amides of methyl taurine; alkanesulfonates such as those derived by reaction of α-olefins (Cq-C^q) with sodium bisulfite and those derived from reaction of paraffins with SO 2 and Cl 2 and subsequent hydrolysis with a base to produce an arbitrary sulfonate;

and olefin sulfonates, this term being used to cover the material made by reacting olefins, especially α-olefins, with SO 4 and then neutralizing and hydrolyzing the reaction product.

It should be noted that some anionic detergent compounds, e.g. alkyl and alkyl ether sulfates tend to hydrolyze at the higher temperatures that can be used in the method according to the invention.

If desired, non-ionic detergent-active compounds can also be used. Examples include the reaction products of alkylene oxides, usually ethylene oxide, with alkyl (C₁-C₄) phenols, generally 5 to 25 EO; i.e. 5 to 25 units of ethylene oxide per molecule; the condensation products of aliphatic (Cg-C^g) alcohols with ethylene oxide, generally 6 to 30 EO, and products obtained by condensation of ethylene oxide with the reaction products of propylene oxide and ethylenediamine. Other nonionic detersive compounds include long-chain tertiary amine oxides, long-chain tertiary phosphine oxides and dialkyl sulfoxides.

Mixtures of detergent-active compounds, e.g. mixed anionic . or mixed anionic and nonionic compounds,

can be used in the detergent mixtures, especially to give these regulated, low-foaming properties. This is particularly advantageous for products intended to be used in automatic washing machines, which are intolerant of foam.

Proportions of amphoteric or zwitterionic detergent compounds, for example betaines, sulfobetaines and hydroxyalkylmethyl taurines, can also be used in the compositions according to the invention, but this is not normally desired due to their relatively high cost. If any amphoteric or zwitterionic detersive compounds were used, it would generally be in small amounts in mixtures based on the much more commonly used anionic or nonionic

detergent-active compounds.

Many other suitable detergent active compounds are commercially available and are fully described in the literature, e.g.

in "Surface Active Agents and Detergents" by Schwartz, Perry and Berch.

The amount of the synthetic detergent active compound(s) used is generally in the range from approx. 10 to 50%, preferably approx. 15 to 30%, by weight of the mixtures, depending on the desired properties.

Any additives to the detergent mixtures produced according to the invention include foam enhancers, e.g. coconut ethanolamide, hydrotropes, e.g. sodium toluene sulphonate, inorganic salts, e.g. alkaline silicates, sodium carbonate, sodium chloride and sodium sulphate, dirt carriers, e.g. sodium carboxymethyl cellulose, fabric softeners, fluorescent agents, dyes, bactericidal agents, antifungal agents, perfume, enzymes and chemical bleaches, e.g. sodium perborate and peracid precursors. Some of the additives, especially oxygen-releasing bleaches, e.g. sodium perborate, is usually added to the washing powders after they have been prepared by spray drying.

In what follows, the invention will be illustrated by means of examples, where parts and percentages indicate weight.

EXAMPLE 1.

A detergent slurry was prepared by mixing the following ingredients in a stirred reaction vessel at a temperature of 150°C and under a pressure of 2.8 to 3.5 kg/cm 2 .

The water content of the components in the slurry was approx. 16% and, due to the neutralization water and the steam used for heating the slurry, was found by analysis to rise to a total content of 23%. The slurry was atomized through a 4.75 mm atomizing nozzle into a tower where air was passed upwards at a temperature of 150°c and a flow rate of 45.4 kg per hour. minute, for the production of a washing powder which was friable and free-flowing and which contained 6% moisture and 74% organic matter.

EXAMPLE 2.

The procedure from Example 1 was repeated with the exception that the composition of the aqueous slurry was as follows:

The slurry was atomized at a temperature of 150°C through a 3.2 mm atomizing nozzle into an air stream at a temperature of 200°C and a flow rate of 45.4 kg per minute. minute, to produce a powder with 9% moisture and 72% organic matter content, and this product was again brittle and free-flowing.

EXAMPLE 3.

An aqueous slurry was made by mixing the following ingredients in a pressure vessel where the temperature was raised to 160°c.

The slurry with a water content of approx. 32% was atomized at 3.9 kg/cm 2 through a 3.2 mm nozzle into a countercurrent air flow at a temperature of 200°c and then gave a free-flowing powder with approx. 59% organic matter and 5% water.

EXAMPLE 4.

A detergent slurry was prepared at 150°C and

4.2 kg/cm 2 by mixing sodium dodecylbenzene sulphonate and disodium octadecane-1-sulphonate-2-sulphinate with small amounts of additives to give a water content of approx. 28%. The slurry was spray-dried through a 3.2 mm nozzle into a countercurrent air stream at 200°C to form a slow-flowing powder of the following composition:

EXAMPLE 5.

A detergent slurry was prepared at a temperature of 150°C and under a pressure of 5.3 kg/cm 2 by mixing the various detergent ingredients including sodium dodecylbenzene sulphonate and sodium coconut soap, with a water content of 31.5%. The slurry was spray-dried in air at 210°C and gave a free-flowing powder with the following composition:

In a comparative test, a washing powder with the same composition was produced by a spray drying process where the slurry was produced with a water content of approx. 40% and at a temperature of 90°C. The slurry was pumped to a spray drier-

2 etc

tarn at 28 kg/cm and atomized into air at 300 C, so that a free-flowing powder was produced, but with a low bulk density. In that case, the amount of heat needed to evaporate the water and thereby form the powder was increased by approx. 50%.

Claims (2)

1. Process for the production of a washing powder containing 50-80% by weight organic material, consisting of a synthetic washing-active anionic compound and an organic builder, whereby an aqueous slurry of the detergent ingredients is produced with a content of 20 to 40% water by weight, characterized in that the slurry is produced in a vessel under pressure at a temperature of from 125 to 180 oC, after which the mixture is spray-dried in an air stream at a temperature of from 100 to 250°C. 2. Method as stated in claim 1, characterized in that the organic building is formed in the slurry by neutralization of the corresponding organic acid, or by hydrolysis and neutralization of the corresponding organic anhydride.