WO2001083401A1

WO2001083401A1 - Carnallite having reduced moisture absorption and method of producing it

Info

Publication number: WO2001083401A1
Application number: PCT/IL2000/000835
Authority: WO
Inventors: Meir Elam; Sara Ben-Ari; Nestor Leiderman
Original assignee: Dead Sea Works Ltd.
Priority date: 2000-05-04
Filing date: 2000-12-14
Publication date: 2001-11-08
Also published as: IL135984A; IL135984A0; AU2001218818A1

Abstract

Carnallite material having reduced moisture absorption, which comprises carnallite particles typically having a diameter of from 0.5 to 10 mm, coated with a soft wax that is solid at room temperature. The amount of the soft wax may be at least 0.05 %, or from 0.15 to 3 %, by weight of the weight of the uncoated carnallite particles. The soft wax may be prevalently constituted by paraffinic hydrocarbon compounds, such as about 90 % paraffins and isoparaffins having from 20 to 40 carbon atoms. Up to 40 wt% of paraffinic oil may be added to the soft waxes.

Description

CARNALLITE HAVING REDUCED MOISTURE ABSORPTION AND METHOD OF PRODUCING IT

Field of the Invention

This invention relates to carnallite having reduced moisture absorption, reduced corrosive properties, and substantially unchanged solubility in water, whereby it may be stored, handled and shipped in bulk in free-flowing conditions, and used as a fertilizer or fertilizer component or for any other purpose. The invention further relates to a method of producing said carnallite.

Background of the Invention

Carnallite is a mineral having the formula KCl.MgCl2.6H2O and is a valuable potassium-magnesium mineral. It is per se a fertilizer, and it is also a good raw material for the production of various types of fertilizers and may be useful for other applications. Carnallite sources, however, are concentrated in specific geographic locations, so that the mineral must be shipped to locations in which it is processed or utilized. Carnallite is a very hygroscopic material and in storage quickly absorbs considerable amounts of moisture, amounts that depend on the relative humidity of the storage or shipping environment. As a result, not only is extra weight added to the material, increasing shipping costs, but the material is no longer free-flowing, which hampers the storing, handling and shipping operations. Additionally, carnallite is corrosive, as are chlorides in general, and, when wet, attacks metal containers in which it may be stored and shipped.

The problems relating to hygroscopicity and corrosiveness of carnallite have not been solved by the art and it is the general purpose of this invention to solve them. It is therefore a purpose of this invention to provide a carnallite material that has reduced moisture absorption.

It is another purpose of this invention to provide carnallite granules that are free-flowing.

It is a further purpose of this invention to provide carnallite granules that have reduced moisture absorption, yet substantially the same solubility and rate of dissolution in water as raw granules of comparable sizes.

It is a still further purpose of this invention to provide a carnallite material that has reduced corrosiveness.

It is a still further purpose of this invention to reduce dust formation in the storing and handling of carnallite.

It is a still further purpose of this invention to provide a method for producing a carnallite material having reduced moisture absorption, free flowability and reduced corrosiveness.

Other purposes and advantages of the invention will appear as the description proceeds.

Summary of the Invention

The carnallite material having reduced moisture absorption and corrosiveness, according to the invention, is in the form of particles, which are particles of carnallite compound KCl.MgCl2.6H2O, coated with a soft wax that is sohd at room temperature. Preferably, the carnallite material particles have a diameter of from 0.5 to 10 mm, and also preferably, the amount of the soft wax is at least 0.05% by weight and is preferably from 0.15 to 3.0% by weight of the weight of the particles of the raw carnallite compound.

The soft waxes that are used according to the invention comprise and are prevalently constituted by paraffinic hydrocarbon compounds. The term "soft waxes", as used in this specification and claims, should be construed as meaning waxes that have a needle penetration of 20-100 mm/10 at 25 °C, measured according to ASTM D 1321.

More preferably said soft waxes additionally have the following physical properties:

Melting point 30°C-120°C, preferably 40°C -80°C (ASTM D 938)

Density (at room temperature), 0.7-0.9 g/cm²

Viscosity (at 100 °C), 2-7 cst (ASTMD 445)

Flash Point, >100 °C, preferably >150 °C.

The melting point is chosen in each case according to the weather conditions at the carnallite production site, the shipping route, the destination of the carnallite product and the availability of the wax.

The soft waxes are chemically inert. They are preferably about 90% paraffins and isoparaffins C H2n+2 having from n=20 to n=40 carbon atoms. The remaining portion is constituted generally by cycloparaffins, small amounts of paraffinic oils (mineral oils, n between 12 and 18) and sometimes paraffins with more than 40 carbon atoms. The soft waxes may contain small amounts of aromatics and alcohols with high molecular weight. The soft waxes provide an effective protection against moisture, that is not provided by other coating materials, and yet do not substantially affect the solubility of the carnallite granules, as will be set forth better hereinafter. The soft waxes are often produced in the form of solutions in mineral oils and may contain surface active agents. The mixture may contain up to 50 wt% of mineral oil, but preferably up to 5 wt%, to obtain enhanced protection against moisture.

The method for producing carnalhte material having reduced moisture absorption and corrosiveness, according to the invention, comprises applying a molten soft wax, which is solid at room temperature, onto the carnalhte compound granules. Hereinafter, the raw carnallite compound will be called "uncoated carnallite" or only "carnalhte", and the material obtained by the invention will be called "coated carnallite". The application of the molten wax to the uncoated carnallite can be effected e.g. by spraying molten wax onto the carnalhte granules; or, alternatively, by adding the sohd wax to carnalhte which is heated to above the melting point of the wax, causing this latter to spread over the carnallite and adhere to it while cooling.

The coated carnallite particles, obtained according to the invention, are free-flowing and their dissolution rate in water is about the same as that of the uncoated carnallite. This is surprising, since the waxes used according to the invention are water-insoluble, and would be expected to prevent or at least to delay and/or reduce the dissolution of the coated carnalhte. When the coated carnallite is dissolved in water, the waxes separate and float on the water.

Because of the aforesaid surprising behavior, the coated carnalhte particles are suitable for direct use, as such, as fertilizer, once dissolved in water in the same way and the same amounts conventionally used for uncoated carnallite, and said use is one of the aspects of the invention. The hygroscopicity of a material can be quantitatively characterized by a parameter which is the critical relative humidity (CRH), viz. the relative humidity of the atmosphere above which the material will absorb a significant amount of moisture, while below it will not absorb a significant amount; or, in other words, it is the relative humidity at which the partial vapor pressure of the water in the air equals the water vapor pressure over a saturated solution of the material. The CRH is, of course, a function of the temperature. The CRH of carnalhte is about 50-55% at ambient temperatures.

Detailed Description of Preferred Embodiments

Waxes having the physical and chemical characteristics set forth hereinbefore are commercially available on the market. Examples of such waxes are those listed in the following Table, in which the first column gives the names that are used herein to designate each wax, the second column gives the corresponding trade names, and the third column the producer.

SW55 WASO - 30S Haifa Basic Oils

HSW WASO - 30 Haifa Basic Oils

80HW 80% WASO - 30 + 20%PW573 Haifa Basic Oils

NF275 Novoflow 98275 Holland Novochem B.V.

EXP501 Lilamin AC-XP 99012501 Akzo Nobel

N 276 Novoflow 98276 Holland Novochem B.V.

EXP502 Lilamin AC-XP 99012502 Akzo Nobel

AC-7H Lilamin AC-7H Akzo Nobel

AC-61H Lilamin AC-61H Akzo Nobel

AC-601H Lilamin AC-601H Akzo Nobel

EXP 4423 CECA S.A. The Waso waxes are solid saturated hydrocarbons (Cas No. 64742-61-6). They have specific weights about 0.85, molecular weight 300-500, melting point 42-56 °C and boiling point at atmospheric pressure 240 °C. Novoflow 98275 has a boiling point of 315 °C, a pour point of 40 ±6 °C, a density at 20 °C of 0.830 g/cm³ and a kinematic viscosity at 100 °C of about 4 mm²/sec (DIN 53211/4). Novoflow 98276 has a melting point of 45 °C, a boiling point of 315 °C, a flash point higher than 180 °C and a decomposition temperature higher than 130 °C.

Lilamin AC-XP 99012501 is a mixture of nonionic waxes, not containing alkyl amines. It has a density at 70 °C of 0.798 kg/m³, a flash point higher than 150 °C, and a dynamic viscosity, mPas, 70 °C, of 10. Lilamin AC-7H is a mixture of nonionic waxes in mineral oil, has a density at 70 °C of 0.900 kg/m³, a flash point higher than 150 °C, and a dynamic viscosity, mPas, 70 °C, of 29. Lilamin AC-61H is a blend of hydrophobic waxes and cationic surface active compounds in mineral oil, has a density at 70 °C of 0.820 kg/m³, a flash point higher than 150 °C, and a dynamic viscosity, mPas, 70 °C, of 10. Lilamin AC-601H is a blend of hydrophobic waxes and cationic surface compounds in mineral oil, has a flash point higher than 150 °C, and a dynamic viscosity, mPas, 70 °C, of 29.

EXP 4423 is a preparation based on fatty amines solution in a mineral oil. At 80 °C it has a density of about 818 kg/m³ and a viscosity of 43 mPa.s, a sohdification point of 61 °C and a flash point above 100 °C. More data can be found in Product Information leaflets issued by each producer.

The following Examples relate each to specific waxes used at various percentages by weight on the weight of the uncoated carnallite. The uncoated carnallite is in granules. A typical example of its granulometry is set forth hereinafter. For agricultural applications, particles size and distribution is important because of standardized spreading equipment and the practice of the blending of various fertilizers. Generally, two size ranges are widely apphed. In the Americas, particles that pass 6 mesh Tyler mesh sieve (3.35 mm) and retain on 16 mesh Tyler sieve (1.00 mm), are used. In Europe and East Asia, particles of the size range of 2-4 mm are used. These size prescriptions should be considered as defining preferred embodiments of this invention. However, particles as large as 10 mm, for a purpose such as de-icing, are also within the scope of the invention.

The moisture absorption tests, the results of which will be set forth hereinafter, were carried out according to the modified procedures of IFDC S-100 and S-101 tests (Manual for Determining Physical Properties of Fertilizer, D.W. Rutland, IFDC, Muscle Shoals, Al., 2^nd ed., 1993). A 10 g sample is placed in a preweighed shallow cup. The particles are 2-4 mm or 4—8 mm and form, approximately, a monolayer at the bottom of the cup. The cup with contents is accurately weighed on the analytical balance. Then it is placed in the humidity chamber at 30°C and at 61% or 70% or 79% or at 89% relative humidity, usually for 24 hours. The sample cups were removed from the chamber for weighings and examinations, after fixed periods of time, and returned to the humidity chamber to complete the 24 hour period. The moisture absorption is expressed as a percent weight increase from the original sample. FW is the Final Weight of the sample and IW is the Initial Weight of the sample.

The CRH of carnalhte is 50-55%. It is important to note that every soluble material, at humidities above its CRH, continues to absorb moisture, until it becomes a solution in which vapor pressure is in equihbrium with the partial water pressure in the air. The time to reach equihbrium at a certain temperature and humidity, in the case of coated material, depends, among other factors, on the effectiveness of the coating.

A typical moisture absorption, expressed as the percent weight increase from the initial value, after a 24 hour exposure to different relative humidities at 30°C, is given in Table I. For comparison, data for other chemicals, in particular fertilizers, are given in the same table, along with the CRHs of commercial materials, and of pure materials. All of the materials were commercial "fertilizer grade", except NaCl, AN and bischofite, which were of higher purity.

Table I Weight Increase (%) after 24 hr

AN - Ammonium Nitrate, "explosive grade"

Bischofite - MgCl₂-6H₂0

DAP - Diammonium Phosphate

The method for coating the carnallite, according to the invention, comprises applying a wax in sohd state to the uncoated carnallite granules at temperatures above the melting point of the wax, causing the wax to spread over the carnallite, and then allowing the wax to solidify. A preferred way of carrying out this method comprises effecting the coating in a revolving drum. The wax may be melted and sprayed, through a conventional nozzle, onto the carnallite, which is kept a temperature between room temperature to the melting point of the wax, and preferably at about this latter, while the drum revolves and consequently the carnallite granules are subjected to a tumbhng and mixing action. When the desired amount of wax has been sprayed, the coated carnallite is allowed to cool and the wax solidifies, while the drum still revolves.

The following Examples illustrate the invention, but do not constitute a limitation.

Example 1 Granular carnallite, 2-4 mm particle size, was sprayed with different amounts of molten SW55 wax (m.p. 54-56°C) in a rotating drum. Table II shows the weight increase, in percent from the initial weight, of a single run of different samples (each sample is an average of triplicate), during a total of 24 hours exposure in a humidity chamber at 30°C and four humidities. The data in Table II show a large decrease in moisture uptake of the coated samples, as compared to the uncoated one (called herein "blank samples") and the moisture uptake decreases as the weight percent of the coating increases. Moreover, the rate of moisture uptake of the coated samples decreases with time, in comparison with that of the blank samples, as shown in Table III. Table III corresponds to Table II, but lists the weight increases of the coated carnalhte, relative to those of the blank carnalhte, which is set to 100. The percentages in the first column are the weight percentages of the coating relative to the weight of the uncoated carnalhte.

Table II Weight increase (%) of blank and SW55 coated samples of carnallite

Table III Relative to blank value (% of blank) of data from Table II

Example 2

This example is similar to Example 1, except that the weight increase is shown only after the 24 hr. period of exposure at different humidities, and the data are averages of several runs (the samples for every run were prepared and tested separately). Table IV corresponds to Tables II and III combined.

Table IV

Averaged Weight Increase (%) Averaged Relative to Blank Values

The figures in the first column are the weight percentages of the coating relative to the weight of the uncoated carnallite.

Example 3

This example is similar to Example 2, except that the wax used is HSW (m.p. 42-48°C). Table V corresponds to Table IV.

Table V

Averaged Weight Increase (%) Averaged Relative to Blank Values

The figures in the first column are the weight percentages of the coating relative to the weight of the uncoated carnallite. The same is true of Tables VI, VII and VIII.

Example 4

This example is similar to Example 2, except that the wax used is 80HW (m.p. 46-51°C). Table VI corresponds to Table IV.

Table VI

Averaged Weight Increase (%) Averaged Relative to Blank Values

Example 5

This example is similar to Example 2, except that the wax used is NF275 (m.p. 37-43°C). Table VII corresponds to Table IV. Table VII

Averaged Weight Increase (%) Averaged Relative to Blank Values

Example 6

This example is similar to Example 2, except that the wax used is EXP501 (m.p. 40-50°C). Table VIII corresponds to Table W.

Table VIII

Averaged Weight Increase (%) Averaged Relative to Blank Values

Example 7

Granular carnallite, 4-8 mm particle size, was coated with 1% of HSW wax by two methods: (1) the molten wax was sprayed on the carnalhte in a rotating drum; (2) the sohd wax was added to hot carnalhte (110°C) in a rotating drum. Also, the carnalhte was coated with 1% 80HW wax by the second method. The three coated samples and an uncoated sample were checked for moisture absorption, as described above. Table IX corresponds to Table IV.

Table K

Example 8

This example is similar to Example 2, except that the wax used is NF276 (m.p. 45°C). Table X corresponds to Table IV.

Table X

Averaged Weight Increase (%) Averaged Relative to Blank Values

Example 9

This example is similar to Example 2, except that the wax used is EXP502. Table XI corresponds to Table IV. Table XI Averaged Weight Increase (%) Averaged Relative to Blank Values

Example 10

This example is similar to Example 2, except that this is a single run and the carnallite was coated with 0.6% of different waxes. Table XII corresponds to Table IV.

Table XII

Averaged Weight Increase (%) Averaged Relative to Blank Values

Example 11

The rate of dissolution was tested by a Hanson SR2 dissolution apparatus, paddle method, usually used for pharmaceutical purposes. The carnal te (coated or uncoated) was poured into the flask which contained 800 ml of distilled water at 30°C. The paddle started to rotate at 100 rpm and the dissolution rate was measured by means of conductometer. It was found that the time needed to complete the dissolution was almost identical for uncoated carnalhte and carnallite coated with 1% of HSW wax. It took about 2, 3, 4, 5 and 6 minutes to dissolve 5, 40, 120, 200 and 300 grams of either coated or uncoated carnalhte in 1 liter of water respectively.

While some embodiments of the invention have been described by way of example, it will be apparent that the invention can be carried by the skilled person out with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims.

Claims

1. Carnallite material having reduced moisture absorption, which comprises carnallite particles coated with a soft wax that is sohd at room temperature.

2. Carnallite material according to claim 1, wherein the carnalhte particles have a diameter of from 0.5 to 10 mm.

3. Carnalhte material according to claim 1, wherein the amount of the soft wax is at least 0.05% by weight of the weight of the uncoated carnallite particles.

4. Carnalhte material according to claim 3, wherein the amount of the soft wax is from 0.15 to 3% by weight of the weight of the uncoated carnalhte particles.

5. Carnallite material according to claim 1, wherein the soft wax is prevalently constituted by paraffinic hydrocarbon compounds.

6. Carnalhte material according to claim 5, wherein the soft waxes are about 90% paraffins and isoparaffins having from 20 to 40 carbon atoms.

7. Carnalhte material according to claim 5, wherein up to 40 wt% of paraffinic oil is added to the soft waxes.

8. Carnallite material according to claim 1, wherein the soft wax has needle penetration at 25 °C, 20-100 mm/10.

9. Carnalhte material according to claim 1, wherein the soft wax has the following physical properties:

Melting point 30°C-120°C

Density (at room temperature), 0.7-0.9 g/cm²

Viscosity (at 100 °C), 2-7 cst

Flash Point, >100 °C.

10. Carnallite material according to claim 1, wherein the soft wax has a melting point of 40°C -80°C.

11. Carnallite material according to claim 1, wherein the soft wax has a flash point >150 °C.

12. Carnallite material according to claim 1, which is free-flowing.

13. Carnallite material according to claim 1, having a dissolution rate in water similar to that of uncoated carnallite.

14. Carnallite material according to claim 1, having a dissolution rate such that 5, 40, 120, 200 and 300 grams thereof are dissolved under stirring in about 2, 3, 4, 5 and 6 minutes respectively, in 1 liter of distilled water, at 30°C.

15. Carnallite having the dissolution rate of claim 14 for the whole concentration range of the carnallite, up to saturation, at room temperature.

16. Method of making carnallite material having reduced moisture absorption, which comprises applying a molten soft wax, which is solid at room temperature, onto the carnallite granules.

17. Method according to claim 16, comprising melting the wax and sprying the molten wax onto the carnalhte in a revolving drum.

18. Carnalhte material according to claim 1, for use as fertilizer.

19. Use of carnallite material, according to claim 1, as fertilizer, substantially as described in the specification.

20. Carnalhte material having reduced moisture absorption, substantially as described and exemplified.