US2862242A - Comminution method - Google Patents

Description

1958 J. B. JONES ETAL 2,862,242

HEATER COMMINUTION METHOD Filed Sept. 16, 1957 w w w w.

JAMES B. JONES I 2 BY JOHN L. STRAUGHN ATTORNEY United States Patent COMIVIINUTION METHOD James B. Jones and John L. Straughn, West Chester, Pa., assignors to Aeroprojects, Inc., West Chester, Pa., a corporation of Pennsylvania Application September 16, 1957, Serial No. 685,361

13 Claims. (Cl. 1847.3)

The present invention relates to a method for forming particles from solid materials which are not brittle at room temperatures.

Numerous materials, particularly organic compounds having relatively high molecular weights, such as a variety of waxes and related materials, are solids at room temperatures, yet are not brittle and cannot be pulverized into fine particles by conventional grinding or fracturing techniques. Prior methods for abrasively grinding these materials, as by rendering such materials brittle by reducing their temperatures to greatly depressed temperatures, through the use of refrigerants like liquid air, liquid nitrogen, etc., have not proved satisfactory. Thus, the cost of the refrigerant is considerable, and moreover, the material may prove difficult to fracture even when rendered brittle by such methods.

An alternative prior method is spray drying wherein the material to be comminuted is dissolved in a solvent, and the solution is sprayed into a large chamber under conditions such that the solvent is evaporated, leaving the solute in finely divided.form. This method while successful in some cases has a number of serious disadvantages, in particular, the difficulties concomitant with the removal of the solvent by evaporation, and the possibility of chemical interreaction between the solid material and the solvent. Moreover, the initial and operational costs of spray drying are frequently excessive.

An object of the present invention is to provide a highly efficient method by which finely divided solid particles can be obtained from a material which cannot be readily fractured or subdivided into finely divided particles at room temperatures.

A different object of the present invention is the provision of a method by which a solid may be comminuted to aerosol size particles, that is particles within the size range of a maximum dimension of sixty microns, and preferably below ten microns.

A still different object of the present invention is the provision of a method for forming solid particles suitable for solid powder blending, formation of dusting powder mixtures, etc.

A further object of the present invention is the provision of a method by which a solid may be comminuted into very fine particles within a relatively narrow particle size range. I v

A still further object of the present invention is the provision of a method for comminuting solids to a particle size of five microns in diameter or less.

which solidify relatively rapidly on contact with a gas at ambient or relatively low temperatures. As examples of materials which may be used in the process of our invention may be mentioned: meltable metallo-organic com pounds such as copper stearate, cobalt linoleate, lithium stearate, and magnesium stearate; meltable non-metallic elements such as elemental sulfur, and phosphorous; meltable inorganic compounds such as sodium hydroxide, and tetrasodium pyrophosphate; meltable metallic elements and alloys such as sodium, aluminum, bismuth alloys and stainless steel; meltable resins and polymers such as polyethylene, gums, amber, asphalt, polyethylene waxes, benzoin, copal, the so-called Carbowaxes which are polyethylene glycol water soluble waxes produced by Carbide and Carbon Chemical Corporation, New York, N. Y.;,

meltable polyols and sugars such as pentaerythritol, and sorbitol; meltable insecticides and pesticides such as DDT (dichlorodiphenyltrichloroethane), and benzene hexachloride; both natural fats and waxes and synthetic fats and waxes such as glycerine monostearate, carnauba wax, paralfin waxes, beeswax, microcrystalline petroleum Waxes such as Cardis-l obtained from Warwick Chemical Company, Division of Sun Chemical Corporation, Wood River Junction, Rhode Island; meltableorganic compounds such as salicylic acid, anthracene, stearic acid, and cetyl alcohol; meltable food products such as hydrogenated shortening; meltable pharmaceutical compounds such as steroid derivatives like testosterone propionate; and meltable chelating agents such as ethylene diamine tetraacetic acid.

In the process of our invention, the material is melted by being heated to a temperature above its melting point and is contacted while in its molten form with a rapidly moving propellant gas, preferably a gas moving at supersonic speeds, which gas has been heated to a temperature approximating the temperature of the molten material. The contact between the molten material and the rapidly moving stream of gas effects comminution of the molten material, which is then contacted with an atmosphere maintained at-a temperature appreciably below the melting point of the material, whereby solidification of the material into finely divided distinct particles is effected.

For the purpose of illustrating the invention there is shown in thedraWings-a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

Another object of the present invention is the provision Referring to the figures wherein like reference characters refer to like parts: Figure 1 is a schematic embodiment of apparatus suitable for practicing the method of the present invention. Figure 2 is a longitudinal section through a nozzle useful for the practice of the present invention.

Referring to the drawings and initially to Figure 1 wherein a schematic embodiment of apparatus suitable for the practice of the present invention is shown, 10 designates the container or tank for the solid material which is to be comminuted. In the specific embodiment of the present invention here illustrated, such material consists of glycerine monostearate, which is a waxy material having a melting point of approximately F. This material is relatively soft and non-brittle, and therefore cannot be pulverized by conventional grinding apparatus into particles having a size of ten microns or smaller, as its pulverization by mechanical abrasion will cause the pulverized particles to join together at the particle interfaces with resultant agglomeration. This material may be heated in air to well above its melting point,

as for example it may be heated to a temperature of 200 F. without any deleterious effect thereto. Alternatively,

stearic acid, or a wax, such as beeswax may be com- Patented Dec. 2, 1958 regulated soas to avoid. temperatures at which deleterious material should beraised to a temperature sufiiciently above its melting point so that loss of heat due to conduction and other-heat losses while the molten material is passed'through the system does not result in its solidification with resultant plugging of thepump and/ or conduits.

Themolten wax is conveyed through line 14 to metering-pump 16. In metering pump 16'the molten material is raised to the-pressure necessitated by the nozzle or generator that is utilized.

From metering pump 16'the'pressurized molten material is conveyed through line18-to booster heater 20 whereinit is heated to a'temperature appreciably above its-melting point, namely to a temperature of about 200- F. 7

The heated and pressurized molten material is conveyed from booster heater 20 through line 22, temperature-indicator 24, line 26-and thence to generator 28. Temperature indicator 24 maybe interconnected, by means well known to the art, to booster heater 20 to achieve closely regulated temperature control. Alternatively, booster heater 20 may be provided with a conventional thermostatic control for regulating the temperature of the molten material passing therethrough. The operation of generator '28 and the-comminution of the molten material will be discussed below.

The propellent gas for generator 28 should be an inert gas, namely one which does not chemically interreact with the glycerine monostearate, when such material is in its molten condition. We have found that air is suitable as a propellent gas for this material; although the air may be diluted with an inert diluent, such as carbon dioxide, to avoid the possibility of anexplosive mixture. Other inert gases such as nitrogen, carbon dioxide, helium, and other inert propellent gases may be used.

The propellent gas is passed from line 30 through pressure gauge 32 and line 34 to pressure control-valve 36. Pressure control valve 36 comprises'means for regulating the pressure of the propellent gasto the generator 28. From pressure control valve 36 the gas is passed through line 38 to heat-exchanger 40, wherein; it is heated to a temperature.approximating theternperature of the molten material in line 26, namely to a temperature of about 200 F. The propellent gas is passed from heat-exchanger 40 through line 42, temperature indicator 44, and line 46 to generator'28.

An example of an excellent generator is that disclosed in copending applicationfor U. S. Letters' Patent Serial No. 441,039, filed July 2, 1954, entitled"Apparatus and Method for Generating Aerosols in the name of James B. Jones.

The generator 28 shown in Figure 2 is that of the aforesaid Serial No. 441,039. However, in place of such generator 28, thegenerator shown in copending patent application Serial No. 632,332, filed January '3, 1957, for Process for Generating Aerosols and Apparatus Therefor in the name of James Byron Jones which utilizesa gas barrier may be substituted, as may other generators which operate generally likethe aforesaid generators and'which produce dispersions of the moltenmaterial into particles having very small dimensions, such as into particles within the aerosol particle size range and within a narrow range of particle sizes within such, aerosol particle size range.

Referring particularly toFigure 2 wherein the presently preferred generator 28-is shown in detail, this generator comprises a liquid conduit 52 which mates with and is a continuation of conduit 26. The liquid conduit 52 discharges the molten glycerine monostearate through outlet 54. Generator 28 also includes a conduit 48 for the propellent gas; conduit 48 mating with and being a continuation of conduit 46. As seen, in Figure 2, cona duit 52 is coaxial with conduit 48, and its outlet 54 concentrically surrounds that portion of conduit 48 proximate outlet 50.

A barrier designated 56 is retained by means of yoke 58 at a spaced axial distance from outlet 50. The face 60 of barrier 56 is juxtaposed to outlets 50 and 54. The propellent gas, namely the heated air, is pressurized to above about 1.5 atmospheres, preferably above 1.7 atmospheres and issues through outlet 50 at supersonic or nearly supersonic velocity, drawing the molten glycerine monostearate from outlet 54 into a. sleeve-like envclope around the discharge gas stream. As this compressed gas stream carrying the envelope of. molten ma? terial approaches barrier 56, it. is drastically distorted from a unidirectional or. axial stream into a substantially radial or disk-like pattern radiating outwardly of the axial flowing stream. The sleeve-like. mass of partially disrupted substance, having higher unit mass than the gas stream, impinges into the gas stream, where maximum distortion thereof is taking place, and is further broken down. We have found that, when, such substances are properly fed into the field of a distorted, high velocity, gas stream withthe generating apparatus as set forth according to this invention, exceedingly finely divided solid particles are produced insubstantially large quantities at substantially high rates, at low gas consumption, and at low gas pressures.

The finely divided molten particles are rapidly cooled to ambient temperature by falling through the atmosphere surrounding the generator 28, and may be collected as finely divided, solid particles with a chamber encompassing the generator. The temperature of such chamber may be lowered to:,below normal room temperature (e. g. below 65 F.), as to a temperature of 50 F. to facilitate hardening of the'molten wax particles. Pref erably, with organic compounds, such as glycerinc monostearate, which may form explosive mixtures with oxygen, the atmosphere, surrounding generator 28 is confined (as by inserting the; generator 28 within ajchamber) and an inert gas such as carbon dioxide introduced therein. A safe oxygen level for glycerine monostearate is 10-12 percent; Theintroduction of carbon dioxide into the chamber may advantageously be utilized to effect lowering of the. oxygen content, and also lowering of the chambers temperature.

We have found that it is possible to comminute the particles in accordance with the process'of our invention to very fine particles, as for example, to particles having diameters less than sixty microns, and in particular, diameters of as little as five microns or less.

Moreover, We have found that it is possible by the method of the present invention to obtain particles within a relatively narrow size range.

As illustrative of the subject inventionthere are set forth below the following examples:

Example I Elementalsulphur obtained 'aschemically p ure" sulphur which had a'melting' point of between 220 F. and 230 F. was aerosolized in accordance with the present invention at a temperature of-between 290 F. to 300 F. with nitrogen. The nitrogen pressure at the instant of aerosolization' was one hundred pounds per square inch and its temperature 400 F.

Under the aforesaid conditions aerosolized sulphur particles were obtained of which ninety weight percent had a particle size of less than twenty microns.

Example III A bismuth alloy consisting of 38.4 weight percent of bismuth, 30.8 weight percent of lead, 15.4 weight percent of tin, and 15.4 weight percent of cadmium which had a melting point of 158 F. was aerosolized in accordance with the present invention at a temperature of between 275 F. to 300 F. using nitrogen as the aerosolizing gas. The nitrogen pressure was one hundred pounds per square inch and the nitrogen temperature was 400 F.

Under the aforesaid conditions aerosolization of the bismuth alloy was achieved to the extent that ninety weight percent of the aerosolized particles had a particle size of less than fifteen microns.

I Example IV Example V Yellow beeswax which hada melting point of between 143 F. to 149 Fjand a flash point of 450 F. was aerosolized at 175 F. with air. The air pressure was one hundred pounds per square inch and the air temperature at aerosolization was 400 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles lay in the particle size range of from one to five microns.

Example V1 Pentaerythritol, which had a melting point of between 340 to 350 F. was aerosolized at 510 F. to 520 F. with nitrogen. The nitrogen pressure at aerosolization was one hundred pounds per square inchand the nitrogen temperature at aerosolization was 380 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a size of less than ten microns.

Example VII A polyethylene wax having the molecular weight of about 2,000, a melting point of 210 F. to 220 F., and a viscosity of between fifty and one hundred centipoises at 400 F. was pumped as a liquid at-320 F. to 330 F. and aerosolized at 425 F. to 450 F. with air. The air pressure was one hundred pounds per square inch at aerosolization and the air temperature 400 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a size of less than three to four microns.

Example VIII A hard wax mixture obtained from Atlas Powder Company, Wilmington, Delaware, comprising a mixture of 83.3 weight percent of Atmul 84, a glycerine monostearate, 11.7 weight percent of sorbitan monostearate, marketed by Atlas Powder Company under its trademark Span '60, and 5.0 weight percent of polyoxyethylene sorbitan mono- ,stearate marketed by Atlas Powder Company under its trademark Tween 60 and having a melting point of F. aerosolized at 225 F. to 235 F. with air. The air pressure at aerosolization was ninety to one hundred and ten pounds per square inch and the air temperature 340 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a size of less than five microns.

Example IX A glycerine monostearate wax having a melting point of about 150 F. was aerosolized at 225 F. with air. The air pressure at aerosolization was one hundred pounds per square inch and the air temperature 300 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a size of less than fifteen microns.

Example X Stearic acid having a melting point of F; was aerosolized with air at 300 F. The air pressure at aerosolization was one hundred pounds per square inch and the airtemperature 400 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a size of less than ten microns.

Example XI Carnauba wax having a melting point of F. to F. was aerosolized at 250 F. with air. The air pressure at aerosolization Was one hundred pounds per square inch and the air temperature 300 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a particle size of less than ten microns.

Example XII DDT (dichloro-diphenyl-trichloroethane) having a melting point of 160 F. to 230 F. was aerosolized at 250 F. to 275 F with nitrogen. The nitrogen pressure at aerosolization was one hundred pounds per square inch and the nitrogen temperature was 350 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a particle size of less than five microns.

Example XIII Example XIV A commercial hydrogenated shortening comprising hydrogenated triglycerides of saturated and unsaturated fatty acids, namely Crisco made by Procter and Gamble of Cincinatti, Ohio, was aerosolized at 190 F. to 210 F. with air. The air pressure at aerosolization was one hundred pounds per square inch and the air temperature 340 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a size of less than ten microns.

ExampleX V A wax made up of sixty weight percent of hard glycerine monostearate designated Atmul 84 and forty weight percent of plastic glycerine monostearate designated Atmul 80, obtained from Atlas Powder Company, Wilmington, Delaware, which had a melting point of between 140 F. to 150 F., was aerosolized at 220 F. with air. The

7- air pressure at aerosolization was one hundred pounds per square inch and the air temperature 200 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a size of less than fifteen microns.

Example XVI Technical grade potassium hydroxide was aerosolized at a liquid temperature of 660 F. and a gas temperature of 750 F.

Under the aforesaid conditions ninety weight percent of the aerosolized particles had a size of less than microns.

This application is a continuation-in-part of our copending application Serial No. 512,730, filed June 2, 1955, now abandoned.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. A method for forming finely divided solid particles within a relatively narrow size range from non-brittle pliable solids, which method comprises heating a solid of the aforesaid type above its melting temperature, contacting arapidly moving stream of an inert gas with a coaxially enveloping stream of said molten solid, impinging the rapidly moving stream of gas upon a barrier and deflecting it at an angle to its normal direction of movement, said deflection of the gas stream comminuting said enveloping molten solid stream into finely divided particles within a narrow particle size range, and rapidly solidifying said particles by moving said particles through a gaseous atmosphere maintained at a temperature appreciably below the melting point of the solid.

2. A method in accordance with claim 1 in which the rapidly moving stream of gas is heated above the melting point of the solid.

3. A method in accordance with claim 1 in which the rapidly moving stream of gas is moving at supersonic velocities.

4. A method in accordance with claim 1 in which the solid particles are solidified by moving through a gaseous atmosphere maintained at a temperature below 65 F.

5. A method in accordance with claim 1 in which the solid is a high molecular Weight polymer.

6. A method in accordance with claim 1 in which the solid is a wax.

7. A method in accordance with claim 1 in which the solid is glycerine monostearate.

8. A method in accordance with claim 1 in which the solid-is ametal.

9. A method in accordance with claim 1 in which the solid is a hydrocarbon wax.

10. A method in accordance with claim 1 in which the solid is an organic compound. 4

11. A method for forming finely divided solid particles within a relatively narrow size range from non-brittle pliable solids, which method comprises heating a solid of the aforesaid type above its melting temperature, contacting a stream of an inert gas which is at a temperature above the melting point of the solid and which is moving at a supersonic velocity with a coaxially enveloping stream of said molten solid, impinging the gas stream upon a barrier and deflecting it at an angle to its normal direction of movement, said'deflection of the gas stream comminuting said enveloping molten solid'stream into finely divided particles within a narrow particle size range, and rapidly solidifying said particles by moving said particles through a gaseous atmosphere maintained at a temperature below F.

12. A method for forming finely divided particles of glycerine monostearate within a narrow particle'size range, which method comprises melting the glycerine monostearate, heating said glycerine monostearate to about 200 F., contacting a stream of an inert gas which is moving at a supersonic velocity and is at a temperature of about 200 F. with a coaxially enveloping stream of said molten glycerine monostearate, impinging the rapidly moving stream of 'gas upon a barrier and deflecting it at an angle to its normal direction of movement, said deflection of the gas stream comminuting the molten stream into finely divided particles within a narrow size range, and rapidly solidifying said finely divided particles of glycerine monostearate by moving said particles through a gaseous atmosphere, said gaseous atmosphere being maintained at a temperature below 65 F.

13. A method in accordance with claim 12 in which the rapidly moving gas stream comprises a mixture of air and carbon-dioxide.

References Cited in the file of this patent UNITED STATESPATENTS 1,329,845 Overbeck Feb. 3, 1920 2,072,375 McCallum Mar. 2, 1937 2,284,023 Scripture May 26, 1942 2,711,570 Sindeband June 28, 1955 FOREIGN PATENTS 609,560 Great Britain Oct. 4, 1948 58,784 Netherlands Jan. 15, 1947

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