US2162690A - Water repellent coating process and product produced thereby - Google Patents

Description

Patented June 20, 1939 UNITED STATES TENT WATER REPELLENT COATING PROCESS AND PRODUCT PRODUCED THEREBY No Drawing.

6 Claims.

It is common knowledge that certain chemical salts such as salts of potash, have a natural tendency to absorb atmospheric and other moisture, and that owing to this tendency, many difficulties are encountered in handling the salts when stored in quantities available for commercial purposes.

Perhaps the principal and most commonly experienced difiiculty found in storing hygroscopic chemical salts, is that the salts, owing to their moist condition, tend to cake together in solid lumps, thereby causing much labor and expense in unloading cars, vessels, storage silos and, in general, in transferring and handling the salts for ultimate use in ore treating plants, or chemical factories, or by dealers and other consumers.

Various expedients have been employed to overcome the above mentioned tendency of such chemical salts to absorb moisture, such as mixing the salts with various inert materials, or even coating the particles with a water-resistant substance, such as oil, but such methods generally are undesirable by reason of dilution of material, and changes in grade and appearance of the same. A treatment of this type likewise materially increases the cost of production of the finished product.

It. is the primary object of the present invention to provide a simple, inexpensive and highly efiicient method of rendering hygroscopic chemical salts moisture-repellent, which has none of the objectionable features mentioned hereinbefore, and which, briefly, consists in applying to the salt particles, a protective coating of a tarry substance in a peculiar and efiective manner.

Broadly considered, the method of coating the salt particles, according to the present invention, consists in mixing the salt material in a damp condition with an oil, and then subjecting the mixture to a drying action, by which the more volatile components of the oil are driven off, leaving a discontinuous tarry coating on the particles.

This coating, applied as described, renders the salt particles water-repellent to the extent that their tendency to take up moisture is eliminated, or at least, greatly minimized, and where the particles are individually prevented from taking up moisture, it follows that they will remain apart and in a sandy and free-flowing condition,

Application September 12, 1936, Serial No. 100,491

thereby evading or lessening any tendency to combine into hard cakes or lumps,

A coating thus applied to the salt particles has little or no effect upon the ultimate solubility of the salts, so that they retain all of their original qualities in use for various purposes.

The process does not aim nor does it result in making the salts insoluble, it being intended solely to overcome the natural hygroscopic property of the salts.

While the process is not limited to any particular method of mixing the oil with the salt, and of subsequently drying the mixture, it is well adapted for use in connection with the process of refining salts as commonly practiced.

In the refining of salts, such as salts of potash, an excess of saturated liquor in which the salts are produced is generally removed by passing the mixture of salts and liquor through a centrifugal dewatering machine, after which the salts, with a small amount of residual moisture, approximately four per cent (4%), are then passed to revolving, fire heated, drum dryers.

In applying the present process, a small amount of suitable oil, Diesel engine fuel oil, for example, is mixed with the damp centrifuged salt in the proportion of about one-third gallon per ton, after which the mixture is passed to the dryer. As a result of this step in the process, the more volatile components of the oil are driven off,

leaving the desired tarry coating on the salt particles.

While Diesel engine fuel oil is well adapted for use in the above described process, different kinds of oil have been found effective, such as crude mineral oils or heavy fractions thereof, animal or vegetable oils, or heavy fractions thereof, in-

cluding,distillates and oleic acid (red oil) etc.,-

and the wordoil as used in the hereunto appended claims should be interpreted as including any fatty acid or other such compound commonly known under the name of oil.

The volatilization step of the process should be at a temperature sufficiently high to drive off the greater part of the volatile components of the oil, and a small amount of moisture in the salts prior to the application of the oleaginous agent, is a desideratum.

Preferably the temperature range for volatilization will be 500 to 700 F., although higher or lower temperatures may be used if desired, and the period of heating is preferably from 3 to 20 minutes, although under certain circumstances longer or shorter heating treatments may be employed.

iii

It will be understood that drying by the volatilization treatment herein described may not satisfactory for all hygroscopic salts under all conditions, and any salts which will be decomposed by the volatilization temperatures employed in the treatment, or which unite with the oleaginous material to form explosive mixtures when heated, should not be subjected to the foregoing treatment, but treated by other methods.

Examples of such salts are potassium nitrate and potassium chlorate. A suitable water-repellent coating may be applied to the surfaces of these materials by the application of films of lime and magnesium soaps, all of which is described in the co-pending application of A. J. Weinig, Serial No. 81,729, filed May 25, 1936, for Process of treating ores.-

In the refining of potassium chloride, the particles of the concentrate, in some instances, are coated with a soapy film of the lime or magnesium type. Subsequent treatment of such material by the above described process results in an emulsification of the oil by the soapy material which assists uniform admixture and surface spreading of the oleaginous material in typical discontinuous form.

The foregoing situation is advantageous in that the quantity of 011 required may be appreciably reduced as a consequence of the better distribution, without impairing the water-repellent properties of the final coating. Therefore, if it is desired to reduce the quantity of oil used, an emulsion of the same can be used in water with emulsifiers such assoaps, sulfonated oils and alcohols, etc. When soaps are used as emulsifiers, small amounts of lime and magnesia salts added to the damp salts increase the effectiveness of the treatment.

Sodium and potassium chlorides, carbonates and sulfates, and all like salts, can be treated in the same manner, if desired.

The coating of particles such as those above enumerated, by the present method may be defined further as involving the eliminating of hydrogen and oxygen from the oleaginous material at a faster rate than carbon is eliminated, and as a result, although some carbon is removed in the treatment, the residue remaining on the particles becomes more and more enriched in carbon as heating progre'sses.

It is to be understood that the heating step of the treatment should be controlled in accordance with properties of the material being coated, and in most instances, it will be undesirable to employ heating temperatures and heating periods which will fuse the particles being coated. Heating to between 600 and 700 F. for a period not exceeding twenty minutes will give good results with mineral, animal or vegetable oils.

Inasmuch as the production of hygroscopic salts, in most instances, involves drying by the application of heat, it will be appreciated that the practice of the present invention involves the utilization of factors already present in the refining operation. The wide variety of oleaginous materials amenable to the treatment permits selection of an oil which is cheap. Therefore, while the process is highly eiiicient in effecting a waterrepellent coating of hygroscopic salts, the coating is attained economically, without any substantial increase in cost of production of the salts in condition for marketing.

What I claim and desire to protect by'Letters Patent is:

1. The process of giving hygroscopic salts a discontinuous water-repellent coating, which comprises applying a surface coating of oil to the salt particles in moist condition, and then subjecting the coated particles to temperatures of from 500 to 700 degrees Fahrenheit for an interval of from three to twenty minutes.

2. The process of rendering salts water-repellent, which comprises applying a surface coating of oil to moist hygroscopic salt particles, said oil being of a character to deposit a tarry residue when its more volatile constituents are removed, and then subjecting the coated particles to a drying action in which volatile constituents of the coating and moisture are driven off, leaving a discontinuous film oftarry residue thereon.

3. The process of rendering salts water-repellent, which comprises applying a surface coating of oil to moist hygroscopic salt particles in the approximate proportion of one third pound oil per ton of salt particles treated, said oil being of a character to deposit a tarry residue when its more volatile constituents are removed, and then subjecting the coating to an evaporating action in which volatile constituents of the coating and moisture are driven off leaving a discontinuous film of tarry residue on the particles.

4. The process of rendering salts water-repellent, which comprises applying a surface coating of fuel oil to hygroscopic salt particles, and then subjecting the coated particles to temperatures of from 500 to 700 degrees Fahrenheit for an interval of from three to twenty minutes.

5. As a new article of manufacture, particles of hygroscopic salts, the exteriors of which are coated with the tarry residue of an oil said coating