GB2135689A - A process for the preparation of aqueous, non-sedimenting dispersions - Google Patents

Abstract

Starch and urea are used as anti-sedimentation agents for aqueous dispersions of solid particulate materials. The method is particularly useful for the stabilisation of fertiliser suspensions.

Description

SPECIFICATION A process for the preparation of aqueous, nonsedimenting dispersions The invention relates to a process for the preparation of aqueous, non-sedimenting dispersions by dispersing solid particles in water, characterized in that before the preparation of the dispersion starch and urea are dispersed either separately or in form of a previously mixed product in an aqueous medium or in a dispersion already containing the solid particles.

It is known that the particles of the brine falling into the size range of the colloid sediment extremely slowly, thus a sedimentation equilibrium sets in. The particles of the suspensions representing the rougher size range sediment relatively rapidly if their density is greater than that of the medium (Erdey-Gruz, T.-Schay, Cs.: Theoretical Physical Chemistry, Tankönyvkiadó, Budapest, 1964, pp. 226-233).

If there are both colloids and particles falling in the rougher size range in the systems, the particles falling in the bigger size range and sedimenting relatively rapidly precede the smaller particles, they can stick together with them and sediment in a manner not characteristic for small particles, in a manner characteristic for polydisperse systems with high speed, as a consequence of the so-called orthokinetic coagulation (Dr. BuzBgh A.: Practice for Colloids, Tankönyviadó, Budapest, 1962, pp. 1 43-149).

At a great number of industrial processes the aim is to prepare systems sedimenting well, mainly at the separation of substances in solid and liquid state as e.g. at the dehydration of different sludges or at the sheet formation in paper-making industry. However, at another part of the industrial processes the aim is to increase the-stability, to prevent the sedimentation, e.g. at the preparation of the boring slurry for the petroleum exploitation, at the preparation of different emulsions or if dispersions have to be transported, stored. Characteristic examples for this are the preparation of filler suspensions in the paper-making industry, the stabilization of paraffin-, bitumen emulsions applicable for different aims or of different plant protective emulsions and the preparation of the different fertilizer dispersions, too.

At the stabilization of suspensions nowadays the preparation of suspended fertilizers is one of the fields developing most dynamically and being most important from an economical point of view.

Therefore the principles, the practice and the detailed questions of the stabilization are discussed as an example of suspended fertilizers.

The storing and transport of the different fertilizers in powder form is connected with much loss, the inequality at their dispersing is always disadvantageous; the dispersing of a fertilizer having different active agents is possible only by several operational steps. These problems can be avoided by suspensions prepared with fertilizers possessing different active agents if no sedimentation disturbing the applied operational steps in the course of the preparation, the storing, the transport and the dispersion takes place.

The naming of the suspended fertilizers is confusing. Without any doubt the solid fertilizer components used for the preparation fall under the rough dispersion range. The size and the quality of the particles in the solution of the components show a complicated picture due to the different interactions taking place in the solution, the double salt formation processes, particle sedimentation and so on. The quality of the particles in these systems and their size, respectively, in dependence of the substance quality has not been examined by scientifically detailed examinations; therefore these systems were named in sum-without the analysis of the particle size-as dispersions. This definition allows the separate and, respectively, common presence of particles falling both in the colloidal and in the rough disperse size range.

With suspensions electrolytes are used for stabilizing against sedimentation of usual manner.

They cause electrostatic repelling power between the particles and thus prevent their linking up.

Naturally this method cannot be used in the case of a medium of fertilizer dispersions consisting of a strong electrolyte solution.

For the stabilization of dispersions so-called macromolecular colloids, too, can be used which increase the viscosity of the medium and thus make difficult the sedimentation of the particles but cover the particles like a coat, thereby preventing the linking up, too. For this purpose gelatine, lignine sulfonic acid and, respectively, the derivatives thereof, sorbite, glucose etc. can be applied.

For the stabilization of suspended fertilizers synthetic silicates, different silicic acid derivatives, colloidal silicate brine, magnesium-aluminium silicates are proposed; furthermore natural silicates, such as betonite, illite, attapulgit etc.

belonging to the clay minerals are used.

Optionally dispersing agents on phosphate base are used beside the clay minerals. Beside the dispersing and stabilizing agents the importance of the effect of the mechanical reduction is stressed. The relating prior art is disclosed e.g. in Buzagh's Practice for Colloids (Tankanyvkiad6, Budapest, 1962, pp. 11 9-125, 143-1 49 and 176-1 99), furthermore in German patent specification No. 1,667,798 and U.S. patent specification No.3,579,321.

A relatively good stability can be obtained by the described methods but in most of the cases the already sedimented components have to be repeatedly homogenized from time to time in the thus-stabilized systems.

A further problem resides in the relatively high price of the industrial products, caused by the material and energy demand. At the natural and different industrial by-products, however, the great difference in quality is a difficulty for the stabilization. Optionally the value of a method considered as applicable can be decreased if the stabilizing agent has a chemical composition foreign to the substances of the soil.

The invention aims to ensure a process rendering possible the stabilization of suspensions with agents being at disposal in a sufficient quantity and equal quality and being relatively cheap, applicable without any special chemical transformation and principally not differing from the natural soil components.

The invention is based on the recognition that this aim can be solved with the help of starch and urea. Namely, surprisingly it was found that the rapidly sedimenting starch and urea together do not only not sediment but prevent the sedimentation of the solid particles of the dispersion, too.

This recognition is still more surprising if one takes the literature (Handbook of Paper Industry, Chief Editor: György Vamps, Müszaki KQnyvkiad6, Budapest, 1980, pp. 120-122 and 143) according to which the starch can generally be transformed by oxidative, enzymatic, basic or acidic decomposition into a non-sedimenting system and the thus-obtained product is generally known not as stabilizing agent but just as coagulator, clarifying or sedimenting agent.

Accordingly the essence of the invention is that before the preparation of the dispersion starch and urea are dispersed either separately or in form of a previously mixed product in an aqueous medium or in a dispersion already containing the solid particles.

The starch quantity used for stabilization amounts to 1 to 50 per cent by weight, advantageously 2 to 10 per cent by weight, related to the water. The urea quantity is at least identical with that of the starch but at most the fiftyfold, advantageously the two- to tenfold quantity thereof.

The starch can be used advantageously in a not-decomposed form, in the form of natural substances containing starch. The starch and the urea may preferably be used in the form of a dry mixture.

The process according to the invention provides a non-sedimenting, well-flowable and easily shakable system from mixtures, having various compositions, which are water-soluble in different degrees and consists of inorganic and/or organic compounds. Thus the process fulfils several necessities at a higher level than the prior art:: - suspensions can be stabilized by substances which are not foreign to the natural components of the soil, the living organisms; - the process does not restrict to certain groups of different materials but ensures the necessary stabiiity at the use of disperse particles of various chemical compositions, too; - at fertilizer suspensions one of the stabilizing components, the urea, can be considered as the natural component thereof; it renders possible to extend the field of application of the starch which is an important product of the industry basing on the agricultural production;; - the starch has not to be isolated from its natural form, it acts at the use of milling products of different plant substances containing starch, e.g. cereals and so on.

Further details of the process according to the invention and the effects to be obtained with it are demonstrated with the help of the following non-limiting examples.

Comparative Example 1 40 g of starch were dispersed under constant stirring in 500 ml of water. A settling cylinder with a volume of 250 ml and a 2.5 ml scale in the range between 100 and 250 ml was filled with the dispersion. The volume of the sedimented substance was read after 1,2 and 24 hours, then the character of the sedimentation was determined by surveying after 24 hours.

Already after one hour the sediment of the starch in the settling cylinder fell in the undivided range under the 100 ml marking. The sediment formed an extremely solid and very hardly shakable layer in 24 hours.

Comparative Example 2 One proceeded as in counter Example 1, with the difference that further 200 g of urea were dispersed under stirring. In the course of the stirring the urea was dissolved, a sedimentation examination could not be performed.

Comparative Example 3 One proceeded as in counter Example 1, with the difference that instead of starch 1 50 g of antrachinone were dispersed. Already after one hour the sediment of the antrachinone in the settling cylinder fell in the undivided range under the 100 ml marking. The sediment formed an extremely solid and hardly shakable layer in 24 hours.

EXAMPLE 1 One proceeded as in counter Examples 1 to 3 with the difference that in the water 200 g of urea, 40 g of starch and 150 g of antrachinone were dispersed in 500 ml of water under stirring.

No sedimentation could be observed in the settling cylinder after one and, respectively 2 hours; after 24 hours still 5 mi of clear medium could be seen above the sediment. After the 24hour sedimentation no sediment formed, the dispersion remained homogeneous and easily shakable.

Comparative Example 4 One proceeded as in counter Example 2, with the difference that instead of 200 g of urea 200 g of potassium chloride were dispersed. In the course of the stirring only a part of the potassium chloride dissolved. After filling the suspension formed in the saturated KCI-solution an extremely rapidly sedimenting system was obtained. The sediment fell already after one hour into the undivided range under the 100 ml marking. The sediment formed an extremely solid and hardly shakable layer within 24 hours.

Comparative Example 5 One proceeded as in counter Example 2, with the difference that monoammonium-phosphate was dispersed. In the course of the dispersing a part of the monoammoniumphosphate dissolved.

The saturated monoammoniumphosphate suspension sedimented rapidly in the settling cylinder, already after one hour the sediment fell in the undivided range under the 100 ml marking.

After 24 hours the sediment was loose, but its volume was extremely small, the shaking-up did not mean any particular problem.

Comparative Example 6 One proceeded as in Comparative Example 5, with the difference that in the course of the suspending 150 ml of 25 per cent ammonium hydroxide were added to the suspension. The suspension sedimented in the 250 ml settling cylinder slower than it was observed in counter Example 5 but despite this fact the volume of the sediment fell slightly under the 100 ml marking.

The sediment was relatively well-shakable after 24 hours.

EXAMPLE 2 One proceeded as in counter Example 1 or 2, with the difference that 500 g of urea and 250 g of starch admixed previously in dry state were dispersed in 500 ml of water. The thus-prepared system possessed an extremely high viscosity, the shaking-up was made difficult by the viscosity.

The system did not sediment even after 24 hours.

EXAMPLE 3 One proceeded as in Example 1, with the diference that according to the ratio nitrogen: phosphorus:potassium 1:0.5:0.5 1 870 g of urea, 40 g of starch, 1000 g of monoammonium phosphate, 900 g of 25 per cent ammonium hydroxide and 880 g of potassium chloride were dispersed in 650 ml of water. The thus-obtained dispersion with a 40 per cent active agent content did not sediment in the settling cylinder after 1 and, respectively, 2 hours. After 24 hours 7.5 ml of a clear medium were formed over the surface of the suspension. No sediment was formed. The suspension could easily be shaken up.

EXAMPLE 4 One proceeded as in Example 3, with the difference that according to the ratio nitrogen: phosphorus:potassium 1 ::0 720 g of urea, 1000 g of monoammonium phosphate as well as 40 g of starch were dispersed in 30 ml of water and 900 g of ammonium hydroxide. The thusobtained dispersion with an active agent content of 40% did not sediment in the 250 ml settling cylinder within 1 and, respectively, 2 hours. After 24 hours 5 ml of clear medium were formed over the surface of the suspension. Homogenization was not necessary. A sediment was not formed.

The suspension could easily be shaken.

EXAMPLE 5 One proceeded as in Example 3, with the difference that according to the nitrogen: phosphorus:potassium ratio of 1:1:1 900 g of ammonium hydroxide, 1000 g of monoammonium phosphate, 720 g of urea, 880 g of potassium chloride and 40 g of starch were dispersed in 71 0 ml of water. The thus-prepared dispersion with an active agent content of 40% did not sediment in the 250 ml settling cylinder after 1 and, respectively, 2 hours. After 24 hours 10 ml of clear medium were formed over the surface of the suspension. A sediment was not formed. The suspension could easily be shaken up.

EXAMPLE 6 One proceeded as in Example 3, with the difference that according to the nitrogenphosphorus-potassium ratio of 1:1:2 720 g of urea, 1000 g of monoammonium phosphate, 900 g of ammonium hydroxide, 1 860 g of potassium chloride and 50 g of starch were dispersed in 920 ml of water. The dispersion did not sediment after 1 and, respectively, 2 hours. After 24 hours 2.5 ml of clear medium were formed over the surface of the suspension. No sediment was formed. The suspension could easily be shaken.

EXAMPLE 7 One proceeded as in Example 3, with the difference that according to the nitrogenphosphorus-potassium ratio of 1:2:3 300 g of ammonium hydroxide, 280 g of urea, 1000 g of monoammonium phosphate, cereal milling product containing 40 g of starch, and 1350 g of potassium chloride were dispersed in 1100 ml of water. The dispersion did not sediment in the settling cylinder after 1 and, respectively, 2 hours.

After 24 hours 12.5 ml of clear medium were formed over the surface of the suspension. No sediment was formed. The suspension could easily be shaken up.

EXAMPLE 8 125 g of urea, 1250 g of monoammonium phosphate, 375 g of ammonium hydroxide, 20 g of starch and 2656 g of potassium chloride were dispersed in 1 750 ml of water. The thus-formed dispersion containing 40% of active agent did not sediment in the 250 ml of settling cylinder after 1 and, respectively, 2 hours. After 24 hours 1 5 ml of clear medium were formed. A sediment was not formed, The suspension could easily be shaken up.

Claims (12)

1. An aqueous dispersion of solid particulate material which contains starch and urea as anti sedimentation agents.

2. A dispersion as claimed in claim 1 which contains 1 to 50% by weight starch, relative to the water content.

3. A dispersion as claimed in claim 2 which contains 2 to 10% by weight of starch.

4. A dispersion as claimed in any one of the preceding claims in which the amount of urea present is at least the same as the amount of starch.

5. A dispersion as claimed in claim 4 in which the amount of urea present is 2-10 times the amount of starch, by weight.

6. A dispersion as claimed in any one of the preceding claims wherein the starch used is a natural (untreated) starch.

7. A dispersion as claimed in any one of the preceding claims wherein the solid particulate material is a fertiliser composition.

8. A dispersion as claimed in claim 7 wherein the fertiliser composition contains ammonium phosphate, ammonium hydroxide and potassium chloride.

9. A dispersion as claimed in claim 1, substantially as described herein in any one of Examples 1 to 8.

1 0. A process for the preparation of a dispersion as claimed in any one of claims 1 to 8 which comprises introducing the starch and urea into the aqueous medium either before or after the solid particulate material is introduced.

11. A process as claimed in claim 10 wherein the starch and urea are used in the form of a dry mixture.

12. A process as claimed in claim 10, substantially as described herein in any one of Examples 1 to 8.