GB2046748A

GB2046748A - Process for preparing mixtures of alkali metal salts and calcium salts of carboxylic acids of 1-3 carbon atoms

Info

Publication number: GB2046748A
Application number: GB8010363A
Authority: GB
Original assignee: Verdugt BV
Current assignee: Verdugt BV
Priority date: 1979-03-30
Filing date: 1980-03-27
Publication date: 1980-11-19
Also published as: NL7902506A; DE3011306A1; GB2046748B; FR2452474B1; FR2452474A1

Abstract

Mixtures of alkali metal and calcium salts of carboxylic acids of 1-3 carbon atoms, possessing a larger bulk density and consequently a lower dusting tendency than normally, are prepared by subjecting a free, water-containing mixture of 50-95% of one or more alkali metal salts and 50-5% of one or more calcium salts of these acids to a drying treatment.

Description

SPECIFICATION Process for preparing mixtures of alkali metal salts and calcium salts of carboxylic acids of 1-3 carbon atoms The formates, acetates and propionates of sodium and calcium are known preservation agents which are used for various purposes, for example in fodder and in the preparation of bread. For many of these purposes mixtures of alkali metal and calcium salts are used, for instance mixtures of sodium propionate with calcium propionate and/or calcium acetate. A practical drawback of these salts is that they are usually only available in powdered form, which tend to be very dusty, which makes them difficult to use.In principle, it is possible to prepare each of these salts in the form of well-shaped crystals by letting them crystallize slowly from a suitable solvent, but this leads to an unacceptable expensive preparation, and also the mixing of such larger crystals into the material to be preserved is more difficult. Granulation of the powdery mixture is also possible, but this means an additional process step and for commercial operation a very high plant investment is necessary.

In the past, the applicant has tried to solve the dusting problem by preparing mixtures of 8387% calcium propionate, 1 0-1 2% powdery sodium propionate and 35% water. With this some decrease of dusting is attained, but the results were not constant and therefore the dusting problem remains.

It is known to prepare a liquid mixtures of these salts which, if desired, may also contain propylene glycol; vide Dutch Patent Application 7612827 and 7710608. This does solve the dusting problem, but because of the high water content, transportation costs are high.

The problem of dusting of alkali metal salts is also discussed in German OLS 1900564, but in this case the salts involved are alkali metal chlorides. In that case the solid salts are treated with a concentrated CaCI2 solution and with either a spluble organic acid or phosphoric acid or a salt thereof.

Surprisingly it has now been found that certain free water-containing mixtures of the alkali metal salts and calcium salts in a particular ratio can be dried to yield powders having a considerably larger untamped bulk density (and accordingly also a higher tamped bulk density) than is obtained by drying each of the components alone and then mixing. These more compact powders consequently are substantially dust-free, and also they ocupy iess volume per unit weight, which means a saving in transportation costs.

Accordingly, the invention provides a process for preparing mixtures of alkali metal salts and calcium salts of carboxylic acids of 13 carbon atoms, which comprises forming an aqueous composition containing a mixture of from 5095% by weight of the alkali metal salt or salts and from 550% by weight of the calcium salt or salts, and drying the aqueous composition sufficiently rapidly to obtain substantially simultaneous crystallisation of the alkali metal and calcium salts.

Among the alkali metal salts the sodium salts are preferred in practice, because they are cheap and easily available. However, the potassium salts are also suitable.

It is remarked that of course ions of the various salts are present in the water phase. In the case that salts of various acids are present, the final product, by recombination of the ions, may also contain salts which as such had not been added to the starting mixture.

The preferred salt mixtures used in this invention are mixtures of 5095% sodium propionate with one or more calcium salts. Particularly preferred are binary and ternary mixtures of 6080% sodium propionate with 4020% calcium propionate and/or calcium acetate.

The process of the invention can be carried out extremely simply. Mixtures of the salts which contain free water are eas::v available, especially because the salts are often prepared from solution anyway. The mixtures need not be completely liquid since supersaturated systems which contain solid salts may also be used. The minimum amount of water in fact is determined by the drying apparatus used. The preferred technique is spray-drying in which case a solution is preferred by spray-drying apparatus is commercially available which can handle pastes having a thick liquid consistency. The upper amount of water in the starting mixture is unlimited, but for economic reasons it is of course undesirable to have to evaporate excessive amounts of water.Therefore, one preferably starts from a mixture having a solids content of at least 10% and even more preferably at least 20%.

One may use any industrial drying method, and even laboratory methods in general are suitable.

The only requirement which should be taken into account is that one should not dry excessively slowly, because then consecutive crystallization of the salts could occur instead of simultaneous crystallization, in which case the benefit of this invention is probably not attained. Such a slow method, however, anyway does not enter into consideration for practical use. In practice particularly suitable drying methods are spray-drying and roll-drying.

As mentioned already, the obtained mixtures are relatively heavy and show little or no dusting, this in contrast to the powdery salts per se or mixtures of these powdery salts which have been prepared dry.

In the case of the binary mixtures of alkali metal salts and calcium salts of different acids, for example mixtures of sodium propionate with calcium acetate, amounts of calcium salts of 5-3q% by weight, based on the mixture of the salts, are preferred In the case of the binary mixtures of alkali metal and calcium salts of the same acid, for instance mixtures of sodium and calcium propionate, amounts of calcium salt of 10- -40% by weight, based on the salt mixture, are preferred. In the case of the ternary mixtures the amount of alkali metal salt, for instance sodium propionate, based on the salt mixture, is preferably 6080% by weight, and the ratio between the two other components can be chosen arbitrarily.

Of course, one can incorporate further usual additives in the mixtures of the invention, for example propylene glycol or an anti-caking agent, such as calcium phosphate.

The effect of the invention is further elucidated hereinbelow with the aid of comparative experiements.

In all cases the starting mixture contained 30% salt and 70% water on a weight basis. The mixtures were sprayed in a drying tower having an eveporation capacity for water of 30 kg/hour. The solutions were introduced into the tower with a temperature of 500 C; the air for drying was introduced with a temperature of 3000C and the mixtures left the tower with a temperature of 9 C. The products were separated with the aid of a cyclone. Consequently, the only factor which was varied was the composition of the starting salt mixture.

The determination of the unpacked and packed bulk density of the samples was carried out according to Din 53194 with the aid of a tamping-volume meter (produced by J. Engelsman, Ludwigshafen) having a calibrated cylinder of 250 ml.

The unpacked bulk density was determined by filling the tared cylinder with the powder to be examined up to 250 ml and determining the weight of the powder. The unpacked bulk density is (1000/250) x weight of powder, expressed in kg/m3.

The packed bulk density is determined by placing the cylinder filled with powder in a shaking apparatus, whereafter the apparatus is operated for such a time that the powder has obtained a constant volume. If this volume is expressed as a, the packed bulk density is (1000/a) x weight of powder, expressed in kg/m3.

The -resuls of these experiments are summarized in the following table.

Composition of starting salt in % by weigth Unpacked Packed bulk density, bulk density, Na- K- Ca- Na- Ca- Ca- kg/m kg/m propionate propionate propionate acetate acetate formate 100 380 500 100 340 400 100 330 420 100 280 400 100 390 490 100 450 730 90 10 480 610 85 15 500 630 70 30 570 770 a) 70 30 580 790 a) 95 5 440 580 70 30 720 960 69 30 1 680 900 66 29 5 680 900 70 5 25 650 840 60 20 20 680 900 70 30 600 830 80 20 510 650 80 20 660 850

a) Duplicate experiments.

Claims

1. A process for the preparation of substantially dust-free powdered mixtures containing alkali metal and calcium salts of the same or different carboxylic acids of 1-3 carbon atoms. which comprises forming an aqueous composition containing a mixture of from 5095% by weight of the alkali metal salt or salts and from 5-50% by weight of the calcium salt or salts, and drying the aqueous composition sufficiently rapidly to obtain substantially simultaneous crystallisation of the alkali metal and calcium salts.

2. A process according to claim 1, wherein a salt mixture is used which contains 5095% sodium propionate.

3. A process according to claim 2, wherein a ternary salt mixture is used which contains 60-80% sodium propionate.

4. A process according to any one of the preceding claims, wherein the calcium salt is calcium acetate and/or calcium propionate.

5. A process according to any one of the preceding claims, wherein the aqueous composition is dried by spray-drying.

6. A process according to any one of the preceding claims, wherein the aqueous composition is an aqueous solution of said alkali metal and calcium salts.

7. A process according to any one of the preceding claims, wherein the aqueous composition contains at least 10% by weight of said salt mixture based on the total composition.

8. A process according to claim 7, wherein the aqeuous composition contains at least 20% by weight of said salt mixture based on the total composition.

9. A dry, powdered salt mixture containing at least one alkali metal and at least one calcium salt of the same or different carboxylic acid of 1-3 carbon atoms, when prepared by a process according to any of the preceding claims.