WO1995009044A1

WO1995009044A1 - Melt granulation with dielectric heating

Info

Publication number: WO1995009044A1
Application number: PCT/US1994/010585
Authority: WO
Inventors: Roy Quinn Freeman, Iii
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1993-09-29
Filing date: 1994-09-28
Publication date: 1995-04-06
Also published as: AU8010494A

Abstract

A method employing dielectric heating to effect melt granulation and an apparatus therefor, the method employing dielectric heating to melt a meltable component of the composition being granulated.

Description

TITLE MELT GR_ _MJLATION WITH DIELECTRIC HEATING BACKGROUND OF THE INVENTION The present invention pertains to a process and apparatus for making multicomponent granular compositions, comprising at least one meltable component, by heating the composition with microwave or radio frequency energy and melting the meltable component.

Granulation is the binding of fine particles into a relatively larger particle. Granulation makes the composition less dusty, reducing the risk of exposure or explosion and making it easier to measure and convey. As part of the granulation process, the granules may become coated or encapsulated thus reducing the rate of release of the coated or encapsulated component(s) and the potential for exposure to harmful components.

Methods of granulation by melting a meltable-component (melt granulation) are known. They include heating the composition by conducting heat through the granulation chamber walls and/or by employing high-shear mixing. Each of these methods has disadvantages and limitations. One disadvantage is the tendency for a large amount of caked composition to build up on the chamber walls. Another disadvantage is that transfer of heat is not efficient, requiring relatively long hold-up times in the granulation chamber.

We have now found that melt granulation can be effected by microwave (MW) and radio frequency (RF) energy. By using MW or RF energy, the walls of the granulator remain relatively cool and there is little or no melting at the wall surface which would contribute to caking. Also, energy for heating is transferred rapidly so that hold-up times in the granulation chamber are correspondingly short.

SUMMARY OF THE INVENTION This invention concerns a process for preparing a granular composition comprising the steps:

(i) adding the components of the composition, including at least one component which is meltable, to a chamber;

(ii) agitating the mixture of components;

(iii) applying dielectric heating to the mixture of components and melting the meltable component; and

(iv) collecting the melt-formed granular composition from the chamber, whereby the inside chamber walls remain substantially free of caked composition.

This invention also comprises an apparatus for preparing granular compositions comprising: (i) a chamber with agitating means and at least one entrance port; and (ii) an energy source for dielectric heating adjusted to cooperate with (i). BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic drawing of one embodiment of the apparatus of this invention.

Figure 2 is a cross-sectional view along lines 2-2 of Figure 1. Figure 3 is a schematic depiction of an alternative embodiment of this invention. Figure 4 is a schematic drawing of another alternative embodiment of this invention. DETAILED DESCRIPTION OF THE INVENTION

The present invention pertains to melt granulation of a broad range of multicomponent compositions, including those comprising agriculturally active ingredients, pharmaceutical ingredients, detergents, food products and the like. The granules can be used directly, or diluted in a liquid such as water as in the case of a water-dispersible agricultural composition. Granules prepared by this method are particularly useful in controlled release pharmaceutical and agricultural compositions. Definitions

Dielectric Heating: Heating of a substance by microwave and radio frequency energy (hereafter: energy). Substances with a high dielectric loss factor can be heated more readily by this energy than those with a low dielectric loss factor.

Dielectric Loss Factor D F) : An electrical property of insulating materials which is the ratio of energy dissipated to energy stored per hertz of applied energy. The higher the ratio of dissipated energy to stored energy the more readily the material will heat in response to the energy. One method of measuring this property is described in "Measurement of Dielectric Parameters at Microwave Frequencies by Cavity

Perturbation Technique," A. Parakash, et. al., IEEE Transactions on Microwave Theory and Techniques, vol. MTT-27, No. 9, Sept. 1979. The Meltable Component

The meltable component melts (or softens) in a suitable temperature range, typically 40°- 120° C although this varies depending on the application, and is able to bind primary particles together in the form of a granule. Contemplated meltable components include waxes, fatty acids, polymers, surfactants, and others.

In a preferred embodiment, the energy selectively softens the meltable component while the rest of the components of the composition remain relatively cool and thus less energy is needed to accomplish granulation. Knowledge of dielectric loss factors can aid in the choice of components so as to take maximum advantage of selective heating. Other Components

Other components can vary widely depending on the intended end use of the melt- formed granules. For example, in agricultural compositions, the additional components will include the active ingredient as well as inert ingredients such as adjuvants, surfactants, diluents and the like which are normally employed in the industry to prepare melt-formed granular compositions. Pharmaceutical compositions are made in the same way employing the usual range of components that are compatible with the particular formulation being made. In like fashion, detergents, food products, cosmetics and the like can all be made employing the process and apparatus described herein. The application of the present invention to the preparation of water-dispersible and water- soluble granular agricultural compositions is especially preferred.

Meltable components (also referred to as heat activated binders) include polyethylene glycol, polyethylene oxide, polyetho xylated alcohols, glyceryl monostearate, hydrogenated tallow, myristyl alcohol, carnauba wax and stearic acid. Agriculturally active ingredients include herbicides, fungicides, bactericides, insecticides, insect antifeedants, acaricides, miticides, nematocides, and plant growth regulants. Examples of suitable active ingredients include the following: herbicides such as acifluorfen, asulam, atrazine, bensulfuron methyl, bentazon, bromacil, bromoxynil, hydroxybenzonitrile, chloramben, chlorimuron ethyl, chloroxuron, chlorsulfuron, chlortoluron, cyanazine, dazomet, desmediphan, dicamba, dichlorbenil, dichlorprop, diphenamid, dipropetryn, diuron, thiameturon, fenac, fenuron, fluometuron, fluridone, fomesafen, glyphosate, hexazinone, imazamethabenz, imazaquin, imazethapyr, ioxynil, isoproturon, isouron, isoxaben, karbutilate, lenacil, MCPA, MCPB, mefluidide, methabenzthiauron, methazole, metrib uzin, metsulfuron methyl, monuron, naptalam, neburon, nitralin, norflur azon, oryzalin, perfluidone, phenmedipham, picloram, prometryn, pronamide, propazine, pyrazon, rimsulfuron, siduron, simazine, sulfometuron methyl, tebuthiuron, terbacil, terbuthylazine, terbutryn, thifensulfuron methyl, triclopyr, 2,4-D, 2,4-DB, triasulfuron, tribenuron methyl, triflusulfuron, primisulfuron, pyrazosulfuron ethyl, nicosulfuron, and ethametsulfuron methyl, 2-[2,4-dichloro-5-[(2- propynyl)oxy]phenyl-5,6,7,8-tetrahydro-l,2,4-triazolo-[4,3-a]-pyridin-3-(H)-one, methyl 2-[[[[(4,6-dimetho_y-2-pyri__idinyl)amino]carbonyl]amino]sulfonyl]-6-(trifluoromethyl)- 3-pyridinecarboxylate sodium salt, N-[(4,6-dimethoxypyrimidin-2-yl)a__inocarbonyl]-l- methyl-4-(2-methyl-2H-tetrazol-5-yl)-lH-pyrazole-5-sulfonamide and N-[(4,6- dimethoxypyrimidin-2-yl)aminocarbonyl]-l-methyl-4-ethoxycarbonyl-5- pyrazolesulfonamide; fungicides such as carbendazim, thiuram, dodine, chloroneb, captan, folpet, thiophanate-methyl, thiabendazole, chlorothalonil, dichloran, captafol, iprodione, vinclozolin, kasugamycin, triadimenol, flutriafol, flusilazol, hexaconazole, and fenarimol; bactericides such as oxytetracycline dihydrate; acaricides such as hexathizox, oxythioquinox, dienochlor, and cyhexatin; and insecticides such as carbofuran, carbaryl, thiodicarb, deltamethrin, and tetrachlorvinphos. Agriculturally suitable salts of active ingredients can be used in the process and apparatus of this invention.

Pharmaceutically active ingredients that can be employed in the process of this invention utilizing the apparatus of this invention include phenobarbital, meprobamate, d- amphetamine sulfate, ferrous fumarate, tridihexyl chloride and acetazolamide. In fact, any pharmaceutical chemically stable under the process conditions can be employed for formulation into a composition in which the ingredients are adhered together according to the disclosure presented herein. Given this disclosure, one of ordinary skill in the art will have no difficulty in selecting other pharmaceuticals and mixing components for processing by the disclosed procedure in the described apparatus. The Process

Step (i). The component mixture is added to the chamber by any convenient means. If particle size reduction of one or more components is required, this is done prior to admission to the chamber. In the case of batch operation, the components can be added to the chamber individually and blended by the agitation prior to granule formation. Generally, the mixture of components will be blended prior to addition to the chamber. Suitable blenders include ribbon blenders, double cone blenders, orbiting screw blenders, and twin shell blenders. For continuous operation, the blended mixture of components can be fed or metered by standard means such as loss in weight feeders, volumetric feeders, gravimetric feeders, screw feeders.

Although the particle size of the component mixture is only restricted by what could be conveniently processed in the granulation equipment, generally the particle size will be in the range of about 1 to 100 μm and more usually in the range 1 to 50 μm. Likewise, the size of the granules is a matter of convenience and will vary depending on the particular application.

Step (ii). Agitation comprises tumbling, vibration, fluidization and mechanical stirring. These are known to one skilled in the art. Because of design simplicity, tumbling is preferred. Fluidization is less preferred because extensive dust collection is usually needed. Agitation should be sufficient to effect even heating and to prevent the formation of lumps.

Step Cm). Dielectric heating is accomplished by application of MW or RF energy. The ability to heat with this energy is not strongly dependent on wavelength chosen. The most common frequencies allocated for Industrial, Scientific or Medical (ISM) application are: 915 and 2450 MHz for microwave energy and 27 and 40 MHz for radiofrequency energy.

The energy is directed into a chamber where the component mixture is agitating. The power level should be strong enough to heat the meltable component at a rate convenient for the desired operation of the process. Because components have different DLFs, there is the potential for selective heating. In a preferred embodiment, the meltable component is heated preferentially over other components. In a less preferred embodiment, the meltable component is not heated preferentially and only melts as the temperature of the entire composition is raised.

Step (.v.. The granules are collected by standard means. In the case of batch operation, they may be simply dumped or poured into a collection bin. For continuous operation, which is the preferred mode of operation, an exit port is necessary from which granules exiting the granulation chamber can be transported to a collection bin by a belt conveyor, bucket convey, pneumatic conveyor, chain conveyor, vibratory conveyor or some similar system. For either batch or continuous operation, it may be desirable to classif the granules by size after they exit the chamber and this can be done by sieving or other means.

The process of this invention is advantageous over known methods of melt granulation because (1) the composition to be granulated is heated directly by the energy so the walls of the granulation chamber remain relatively cool and the build up of caked composition on the walls is minimal, (2) dielectric heating is rapid so productivity is increased and thus the size of the granulation equipment can be smaller, (3) meltable components can be preferentially heated when their dielectric loss factor is higher than the remainder of the composition, and (4) thermally degradable components not suitable for conventional melt-granulation may be employed in the process of the present invention when employing selective heating of the meltable component. The Apparatus

The chamber can be any suitable design and the method of agitation generally depends on the choice of chamber. Designs for batch operation include (1) a rotating drum with lift flights, (2) a rotating "V" blender, (3) a bin with mechanical stirring similar to a ribbon blender, and (4) a fluid bed. Designs for continuous operation include (1) a rotating cylindrical chamber with lift flights, or (2) a cylindrical chamber with a vibrating bed, where there is continuous feed of component mixture from one end and collection of granules at the other end. The preferred type of design is a rotating chamber with lift flights.

Depending on the nature of the material to be granulated and means for admitting energy, the material of construction of the chamber will differ. If the energy is directed through the chamber wall, at least that portion of the chamber must be made of an energy-transparent material such as polytetrafluoroethylene or quartz. If energy is admitted by means of a waveguide, the preferred material of construction is a high conductivity metal such as stainless steel or aluminum. The energy source can be any standard device for MW or RF generation, including those sold by Microdry Inc., Crestwood, KY (USA); Astex, Inc., Woburn, MA; and, SAIREM, Vaulx-en-Velin, France. The energy can be applied by (1) locating the source inside the chamber, (2) locating the source outside the chamber and directing the energy through a MW or RF transparent chamber wall, or (3) directing the energy through an access port which serves as a waveguide.

Typically, the process of this invention will be operated in an apparatus such as depicted in Figures 1 to 4 according to the following description. One skilled in the art will be able to devise other alternative embodiments based on the description and drawings presented herein.

In an apparatus such as depicted in Figure 1, the granulation chamber is 7, the microwave applicator section is 2_and the microwave source is 3. The components to be granulated are introduced into inlet port 4 and collected at outlet port 5. The apparatus is shown to be tilted at an angle from the horizontal. Although preferred to be tilted, the apparatus need not be tilted necessarily. An internal series of baffles and/or lifting flights can be employed to move the granulated product through the granulation chamber from component inlet port to product outlet port.

Figure 2 is a cross-sectional view along 2-2 of Figure 1 showing typical lifting flights 6 that facilitate the mixing of components shown as granules 7. Figure 3 depicts rotating tube 8 with internal lift flights (not shown). The microwave feed is 9, the inlet port is 77, the outlet is 73 and the microwave termination cap is 72. Motor and gear mechanism 70 rotates tube 8. Rotating points 14 and 75 allow movement of tube 8 which are connected thereto while allowing end sections 14a and 15a to remain stationary, sections 14a and 15a being unconnected to 14_. and 75, so that movement of 8 (and 1_4 and 75) do not cause movement of 14a and 75α.

In Figure 3, the tube can be stainless steel and representative system power could be of the order of 6 KW with component throughput of over 50 kilograms per hour and frequency of, say, 2450 MHz.

Figure 4 represents a small scale apparatus having chamber barrel 16., feeder inlet 27, outlet 24_., and motor and rotating gear mechanism 18_, all located on tiltable platform 22- The microwave input 79 is passed through amplifier 77 and introduced into microwave applicator 23 through microwave inlet nozzle 20. The microwaves heat and melt the meltable components in the granular mixture traversing barrel 16.. In an apparatus such as depicted in Figure 4, the barrel (or tube) can be polytetrafluoroethylene (PTFE) and can contain internal baffles, guides or mixing vanes (flights). Typical energy input into 23_ can be of the order of 900 MHz or higher, and 400 watts of power.

The following Examples are presented to illustrate this invention. definition and Measurement of O-Numbers The relative susceptibility to microwave heating of an ingredient is indicated by the quality (Q) factor. The Q factor is related, inversely, to the DLF, but whereas DLF is an absolute value, Q is only a relative measure of susceptibility. The Q value however is easier to determine than DLF and provides a relative ranking of ingredient susceptibilities which is satisfactory for this invention.

For a dielectric material in a microwave resonant circuit, Q is defined as CO_QU/WL where ω₀ is the angular microwave frequency, U is the stored electromagnetic energy and WL is the energy loss per cycle. Experimentally, Q was determined in an open- ended coaxial resonator at a frequency of 900 MHz using the relationship Q = fr __f where f₀ is the resonant frequency of the microwave cavity and Δf is the frequency bandwidth of the cavity. See for example Collin, R. E. Foundations for Microwave Engineering; McGraw-Hill, 1966, pp 331-362 and Mosig, J.R. et al. "Reflection of an open-ended coaxial line and application to nondestructive measurement of materials"; 7EEE Trans. Instrum. Meas., 1981, Vol. IM-30, pp 46-51.

The value of Q listed below for some typical formulation ingredients is equipment- dependent and is useful in making relative comparisons of susceptibility only. As a rough characterization, a Q of about 550 to 700 is considered to be of low susceptibility (slowly heated by microwave energy), a Q of about 400 to 550 is considered to be of moderate susceptibility and a Q of less than about 350 is considered to be of high susceptibility (rapidly heated by microwave energy).

Melt Component O Number Identity (Vendor. P__ronic® F108 345 Ethylene oxide/propylene oxide block copolymer (BASF)

Carbowax® 8000 403 Polyethylene glycol (Union Carbide) Novel II Εthoxylate 405 Ethoxylated alcohol (Vista) Macol® DNP-150 412 Nonylphenol ethoxylate (PPG Mazer) Hoechst Wax KST 494 Montan wax (Hoechst) Stearic Acid 661 Reagent grade Union Camp Cenwax 664 Paraffin (Union Camp) Εpolene Ε-10 Wax 674 Oxidized polyethylene (Eastman) Paraffin Wax 747 Paraffin wax (Gulf) GE Carnauba Wax 773 Carnauba wax (Baldini) Hoechst Wax S 868 Montan wax (Hoechst)

Wetting Agents Triton® X-120 214 Nonylphenolethoxylate (Rohm and Haas) Morwet® EFW 598 alkyl naphthalene sulfonat e/ alkyl carboxylate (Witco)

Alkanol® XC 600 Alkylnaphthalene sulfonate (DuPont) Aerosol® OTB 612 Dioctylsulfosuccinate (American Cyanamid) Siponate® DS-10 613 Dodecylbenzene sulfonate (Rhone-Poulenc) Dispersants

Reax® 85A 218 Lignin sulfonate (Westvaaco)

Polyfon® H 374 Lignin sulfonate (Westvaaco)

Marasperse® N22 477 Lignin sulfonate (Lignotech)

Norlig® 11D 534 Lignin sulfonate (Lignotech)

Lomar® PW 327 Napthalene sulfonate formaldehyde condensate (Henkel)

Morwet® D425 625 Napthalene sulfonate formaldehyde condensate (Witco)

Methocel F50 377 Ethoxylated cellulose (Dow)

Diluents

Panther Creek Clay 125 Bentonite (American Colloid)

Starch A 217 Starch (Staley)

Dextrin 1895 362 Starch (American Maize)

Barden Clay 407 Kaolin(Huber)

Glacier Talc 551 Talc (Cypress Industries)

Sugar (sucrose) 618 Food Grade

CaCO₃ 674 Reagent grade

Na₂CO₃ 670 Reagent grade

CaSO₄ 661 Reagent grade

K₂SO₄ 660 Reagent grade

NaHCO₃ 623 Reagent grade

Urea 638 Reagent grade

Active Ingredients

Flusilazole 506 Fungicide

Metribuzin 613 Herbicide

Metsulfuron methyl 620 Herbicide

Bromacil 628 Herbicide

Atrazine 631 Herbicide

Glyphosate 633 Herbicide

Linuron 634 Herbicide

Thifensulfiir on methyl 667 Herbicide

Benomyl 655 Fungicide

Cyanazine 654 Herbicide

Tribensulfuron methyl 644 Herbicide EXAMPLES 1-3

The compositions of Examples 1, 2 and 3 were granulated according to the process of this invention as follows.

The active ingredient and diluent component were mixed together and milled. The melt component, which had been sieved to ensure a particle size of less than 20 mesh, was then blended with the milled components to form the composition premix. Component Example 1 Example 2 Example 3

Thifensulfuron methyl 45 g 45 g 45 g

Sugar 6 g 6 g

Panther Creek Clay 6 g

Pluronic F108 (mρ 57°C) 9 g

Stearic Acid (mp 69°C) 9 g 9 g

To form the granules, 2 grams of premix was tumbled in a high density polyethylene (HDPE) vial positioned in the center of a microwave oven cavity by means of a quartz rod. The oven is a cylindrical microwave single mode cavity connected to a 915 MHz microwave generator. The non-conductive, microwave- transparent HDPE vial containing the mixture of components was attached to a dielectric quartz rod positioned along the axis of the cylindrical cavity with the vial at the center of the cavity. The quartz rod, and therefore the vial, was rotated by hand at approximately 45 rpm thereby providing tumbling action of the components while the energy was being applied. For each example, two runs were made. In one run termed "constant power", premix was exposed to 30 watts of power for 30 seconds and the electric field was allowed to vary. In the other run termed "constant electric field", premix was exposed to a constant electric field and the power was adjusted as needed so as to maintain the same electric field for each example, 1-3. Each run is listed separately for each example. Run 1 Run 2

Example 1 Results Premix Constant Power Constant Elect. Field

Weight %>297um (50 mesh) 26 51 35

Weight %149 to 297um 27 16 51

Weight %<149um (100 mesh) 47 33 14 Example 2 Results

Weight %>297um (50 mesh) 17 72 72

Weight %149 to 297um 24 13 19

Weight %<149um (100 mesh) 59 15 9 Example 3 Results Weight %>297um (50 mesh) 24 32 28

Weight %149 to 297um 19 24 44

Weight %<149um (100 mesh) 57 44 28

The results demonstrate that inclusion of at least one low Q component greatly enhances the efficientcy of dielectric heating, and thus binder melting, so that granule formation occurs more readily. In Example 3, where all components have low susceptibility to dielectric heating (high Q), only a small amount of granule growth occured under the dielectric heating conditions employed, as seen by comparing the particle size of the premix to runs 1 and 2. In Example 2, which differs from Example 3 by changing the diluent to one which is highly susceptible to dielectric heating (low Q), substantial granule growth occurs under the same dielectric heating conditions as employed in Example 3. In Example 1, which differs from Example 3 by changing the melt component to one which is highly susceptible to dielectric heating, substantial granule growth also occurs under the same dielectric heating conditions as employed in

Example 3. Less energy, 21 watts, was absorbed in run 2 of Example 3 at constant electric field than in run 2 of Example 2 where 32 watts was absorbed and in run 2 of

Example 1 where 27 watts was absorbed . The sample vial of Example 3 was noticably cooler to the touch than the sample vials of Examples 1 and 2, which is consistent with relatively less energy being absorbed in Example 3 than in Examples 1 and 2.

EXAMPLE 4 The following formulation was employed in an apparatus such as depicted in Fig. 4 operated continuously according to the process of this invention.

Component Grams

Glyphosate wetcake 41.71

Metsulfuron methyl 1.05 Sodium pyrophosphate 30.79

Foamaster® Soap L 0.50

Sugar 1.00

Sodium metasilicate 8.95

Pluronic® F108 16.00 Total 100.00

Glyphosate wetcake is technical glyphosate with about 11% moisture.

Foamaster® Soap L is tallow soap (Henkel Co.).

The granulation chamber was made of PTFE and had an inside diameter of 5.1 cm.

The microwave source, model No. Ml 120 from American Microwave Technology, was 400 watts variable used at 80 watt setting at a wavelength of 915 MHz. In operation, the chamber was rotated at 30 rpm and was inclined 2.5 degrees from horizontal.

All components, except the Pluronic® F108 melt component, were mixed together and milled. The melt component was then blended with these milled components to form the composition premix. With the energy on, the premix was fed to the granulating chamber at a rate of 15 grams per minute using an AccuRate® feeder. The product granules were collected in a dish and analyzed for size.

The sieve size of the product granules versus the premix is as follows:

Product Premix Granules

Weight % > 297 μm (50 mesh) 6.1 79.0

Weight % 149-297 μm 9.9 13.0

Weight % <149 (100 mesh) 84.0 8.0 EXAMPLE 5 In this Example, urea prills are coated with particles of atrazine using Pluronic® F108 as the meltable component. Components were sized, as indicated, by sieving.

Component Grams Urea prills (> 1400 μm) 1.7

Atrazine (<275 μm) 0.1

Pluronic® F108 (<75 μm) 02

2.0 The granules were made by a batch process. The mixture of components was tumbled in a high density polyethylene (HDPE) vial positioned in the center of microwave oven cavity by means of a quartz rod. The oven is a cylindrical microwave single mode cavity connected to a 915 MHz microwave generator. The non-conductive, microwave- transparent HDPE vial containing the mixture of components was attached to a dielectric quartz rod positioned along the axis of the cylindrical cavity with the vial at the center of the cavity. The quartz rod, and therefore the vial, was rotated by hand at approximately 45 rpm thereby providing tumbling action of the components while the energy was being applied. Energy was 30 watts applied for 15 seconds.

After granulation, the urea prills were observed to have an even coating of atrazine particles.

Claims

What is claimed is

1. A process for preparing granular compositions comprising the steps: (i) adding the components of the composition, including at least one component which is meltable, to a chamber;

(ii) agitating the mixture of components; (iii) applying dielectric heating to said mixture of components and melting the meltable component; and (iv) collecting melt-formed granules from the chamber, whereby the inside of the chamber walls remains substantially free of caked composition.

2. A process according to Claim 1 wherein one component of the composition is an agriculturally active ingredient.

3. A process according to Claim 1 wherein one component of the composition is a pharmaceutically active ingredient.

4. A process according to Claim 1 comprising operating the granulation steps i to iii and collecting step iv in a continuous manner.

5. A process according to Claim 2 comprising operating the granulation steps i to iii and collecting step iv in continuous manner.

6. A process according to Claim 3 comprising operating the granulation steps i to iii and collecting step iv in a continuous manner.

7. An apparatus for preparing granular compositions comprising:

(i) a chamber with agitating means and at least one inlet port; and

(ii) an energy source for dielectric heating adjusted to cooperate with (i).

8. An apparatus according to Claim 7 having an outlet port for collecting granular composition made continuously.