CA1129668A - Granulation process - Google Patents
Granulation processInfo
- Publication number
- CA1129668A CA1129668A CA341,643A CA341643A CA1129668A CA 1129668 A CA1129668 A CA 1129668A CA 341643 A CA341643 A CA 341643A CA 1129668 A CA1129668 A CA 1129668A
- Authority
- CA
- Canada
- Prior art keywords
- charge
- particles
- gas stream
- granules
- calcium sulfate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- A—HUMAN NECESSITIES
- A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
- A01N—PRESERVATION OF BODIES OF HUMANS OR ANIMALS OR PLANTS OR PARTS THEREOF; BIOCIDES, e.g. AS DISINFECTANTS, AS PESTICIDES OR AS HERBICIDES; PEST REPELLANTS OR ATTRACTANTS; PLANT GROWTH REGULATORS
- A01N25/00—Biocides, pest repellants or attractants, or plant growth regulators, characterised by their forms, or by their non-active ingredients or by their methods of application, e.g. seed treatment or sequential application; Substances for reducing the noxious effect of the active ingredients to organisms other than pests
- A01N25/12—Powders or granules
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
- C01F11/466—Conversion of one form of calcium sulfate to another
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B18/02—Agglomerated materials, e.g. artificial aggregates
- C04B18/021—Agglomerated materials, e.g. artificial aggregates agglomerated by a mineral binder, e.g. cement
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
- C04B20/10—Coating or impregnating
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
- C05G5/00—Fertilisers characterised by their form
- C05G5/40—Fertilisers incorporated into a matrix
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/54—Particles characterised by their aspect ratio, i.e. the ratio of sizes in the longest to the shortest dimension
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Ceramic Engineering (AREA)
- Health & Medical Sciences (AREA)
- Civil Engineering (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Pest Control & Pesticides (AREA)
- General Health & Medical Sciences (AREA)
- Inorganic Chemistry (AREA)
- Agronomy & Crop Science (AREA)
- Geology (AREA)
- Plant Pathology (AREA)
- Toxicology (AREA)
- Dentistry (AREA)
- Wood Science & Technology (AREA)
- Zoology (AREA)
- Environmental Sciences (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
- Glanulating (AREA)
Abstract
ABSTRACT
GRANULATION PROCESS
Sorbent, calcium sulfate dihydrate-containing granules are produced by dispersing particulate calcium sulfate hemihydrate into a generally helical turbulent gas stream, contacting the dispersed hemihydrate particles with an aqueous binder in an amount sufficient to wet and agglomerate the particles and to initiate hydration of the hemihydrate to the corresponding dihydrate, and mechani-cally agitating the resulting dispersion so as to pack the wetted particles into granules while hydration takes place.
Thereafter the produced granules are recovered from the gas stream and, if necessary, dried.
GRANULATION PROCESS
Sorbent, calcium sulfate dihydrate-containing granules are produced by dispersing particulate calcium sulfate hemihydrate into a generally helical turbulent gas stream, contacting the dispersed hemihydrate particles with an aqueous binder in an amount sufficient to wet and agglomerate the particles and to initiate hydration of the hemihydrate to the corresponding dihydrate, and mechani-cally agitating the resulting dispersion so as to pack the wetted particles into granules while hydration takes place.
Thereafter the produced granules are recovered from the gas stream and, if necessary, dried.
Description
~3L2~668 Background of the Invention This invention relates to granular sorptive carriers, and more particularly to methods for producing granular sorptive carriers using calcium sulfate hemi-hydrate. The sorptive carrier granules produced ac-cording to this invention are substantially neutral and are useful as inert carriers for chemicals and particu-larly for agricultural chemicals.
A number of solid materials are widely used as carriers for agricultural chemicals, such as insecticides, herbicides, fertilizers, and the like. The agricultural chemicals are combined with such a carrier for convenient dissemination by various distributor means.
In some types of agricultural carriers, the chemical or active ingredient contained therein is in solid form, usually as a powder or as small particles or granules, and is admixed with the carrier, the mixture then being formed into pellets. With other types of carriers, the carrier is in the form of particles or granules into which the active ingredient, in liquid form, is sorbed. With yet another type of carrier the active ingredient is adhered to the carrier surface.
Agricultural carrier material can be used in many forms, such as powder, particles, granules, or pel-lets. For ease of handling, and for other reasons, mate-rials having a granule size in a range which would pass through a 20-mesh screen and be retained on a 60 mesh screen (U.S.A. Standard Sieve Series) are commonly used.
With such size granules, it is important that the gran-ules maintain their structural integrity and thus sizeduring initial fabrication as well as during subsequent storage, marketing, and application. In many applica-tions, it is important that the particles or granules be of a size that does not pass through the 60-mesh screen so as to reduce the probability that some of the particles or granules are so small as to form dust. It is also important that the particles maintain their size and con-dition so that they do not form dust, or turn to dust, i~2~8 owing to degradation during storage or use, or owing to general abrasion or attrition during manufacturing, handling, storing, transporting and application with mechanical devices to agricultural soil. Dust is ob-jectionable because of the well known problems with dustspreading in the air and on persons and animals, and being inhaled by workers making or handling such carriers.
Many naturally-occurring mineral carriers that are used with agriculturally active ingredients, includ-ing certain types of pesticides, have a degree of surfaceacidity which varies depending upon the crystalline and molecular structure of the mineral. It is thought that the surface acidity arises as a result of a non-uniform distribution of electric charge in or on the surface or the mineral particles. A large number of electric charges may exist at certain areas on a surface of a mineral car-rier particle and these are referred to as acid sites or electrophilic centers. The strength of these centers varies depending upon the composition of the surface and the degree of distortion in the structure which brings about the non-uniform distribution of the electrical surface charges. The surface acidity on a mineral car-rier particle can affect the reactivity of that mineral particle with the agricultural chemical carried thereon.
It is thought that the surface acidity, and specifically the acid centers, have a catalytic effect with respect to the decomposition of the particular chemical. It has been found that with some pesticidal chemicals, the catalytic ac~ivity of the acid sites, with respect to inducing or accelerating decomposition, can be much re-duced by deactivation of the acid sites with certain organic or inorganic materials which preferentially share their electrons with the mineral to form a bond which is stronger than that which may be formed between the agri-cultural chemical and the acid center itself. The addi-tion of any deactivator material, usually in amounts of up to 6 or 8 percent by weight of the carrier adds an ~z~6~;8.
undesirable cost to the formulation of the agricultural chemical-laden carrier. Thus, it would be desirable to provide a method for producing a substantially neutral and inert carrier for agricultural chemicals, and es-pecially for pesticides, which has little or no surfaceacidity and which does not require the addition of any deactivator material.
A sorbent carrier for liquid chemicals should have a relatively high sorptivity, or a sorptivity which is at least high enough to prove commercially satisfac-tory.
In the case of sorbent materials, the porosity of the material is usually related to the sorbency char-acteristics of the material. Further, a generally low dry bulk density is usually a characteristic of the more sorbent materials. Generally, as particle or granule size increases, the bulk surface area decreases for a given number of granules. Since sorptivity is princi-pally a surface phenomenon and a function of the pore density within a surface, it would be desirable to pro-, vide a method for producing a carrier granule having a size small enough to present a relatively high bulk sur-face area and having a pore density high enough such that the sorp~ivity is commercially satisfactory.
In order that a granulated carrier functions properly and does not degrade through abrasion or attri-tion into dust under mechanical stress during manufacture, packaging, storing, shipping and use, the carrier granules must exhibit adequate mechanical strength. Thus, it would be desirable to provide a method for producing a carrier granule which has relatively high mechanical strength or resistance to attrition while minimizing the concurrent generation of an undesirable amount of small, dust-size particles.
The present invention provides a very effecti~e method for controlled manufacture of relatively low-density, gypsum-containing granules that are eminently 1~2~ 8 suitable as carriers for agricultural chemicals and -that are resistant to attrition. Additionally, the low-density, gypsum-containing granules produced according to the method of this invention are also useful as oil and grease sorbents, as sorbents for household pet toilets, and for similar applications.
_ mmary of the Invention According to the method of the present invention, a particulate charge containing calcium sulfate hemihydrate (CaSO4.1/2H20) is treated with an aqueous binder in an amount sufficient to wet and agglomerate the particles of the charge, and to initiate hydration of the calcium sulfate hemihydrate present while being subjected to vigorous mechanical action. The charge particles and aqueous binder are fed into a confined elongated space in which a generally helical turbulent gas stream is generated. The charge and aqueous binder orm a substantially uniform dispersion of the particles within the turbulent gas stream which dispersion is subjected to mechanical agitation so as to pack the wetted particles into granules. Thereafter the granules are recovered from the gas stream.
Thus, in accordance with the present invention, there is provided a method for producing sorbent calcium sulfate dihydrate-containing granules which comprises: providing a particulate charge comprising finely divided calcium sulfate hemihydrate particles having a size that passes through a 60 mesh screen, said charge containing calcium sulfate hemihydrate in an amount of at least about 35 percent by weight of the charge; providing a confined elongated space and generating a generally helical turbulent gas stream within said space; feeding said charge into said gas stream so as to provide a substantially uniform disper-sion of said particles in said gas stream, the space time for the particulate cnarge within the turbulent gas stream being about 1.4 x 10 4 hours to about 1 x 10 3 hours; introducing into said ~r~ ~
~; ~
~LZ916~3 dispersion an aqueous binder in an amount sufficient to wet and agglomerate said particles, and to initiate hydration of said calcium sulfate hemihydrate while in said dispersion; mechanically agitating said dispersion such that the flow of said dispersion is substantially the same as that of said gas stream so as to pack the wetted particles into granules; and recovering the granules thereby produced.
The present invention may also be defined as a method for producing sorbent calcium sulfate dihydrate-containing granules which comprises: providing a particulate charge comprising sor-bent particles having a size that passes through a 60 mesh screen and at least about 35 percent by weight of the charge of plaster of Paris particles mixed therewith mechanically agitating a gas within a confined, elongated space so as to produce a generally helically shaped turbulent gas stream therein; feeding said charge into the produced gas stream at a substantially uniform rate so that the space time for the particulate charge within the turbulent gas stream being about 1.4 x 10 hours to about 1 x 10 3 hours; feeding an a~ueous binder into the produced gas stream sub-stantially simultaneously with said charge in an amount sufficientto wet the particulate charge and to initiate hydration of said plaster of Paris particles; continuing said agitation for a time period sufficient to form granules; and recovering the produced granules.
The granules produced in accordance with this method have a relatively high mechanical strength or resistance to attrition -to mechanical stresses during manufacture, packaging, storing, shipping and other uses. Additionally, the sorbent carriers made in accordance with this invention are relatively inert and have sorptivities which are high enough for commercial use as sorbent materials. Still another advantage of -the method of this in-vention is that the particle size distribution of the produced - 4a -granules can be controlled within a relatively narrow range.Yet another benefit of the method of this invention is that the sorptive granules produced have a bulk density which is lower than that of naturally occurring gypsum particles and, as discussed hereinabove, provide higher sorptive capacity than naturally occurring - ~b -IL2~8 gypsum particles of similar size. Numerous other advan-tages and features of the present invention will become readily apparent from the following detailed description of the invention, the accompanying examples, and from the appended claims.
Descri tion of the Preferred Embodiments P
While the method of this invention is suscept-ible of embodiment in many different forms, specific embodiments will be herein described in detail, with the understanding that the present disclosure is to be con-sidered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated.
All references made herein to sieve analysis, screen mesh sizes, particle sizes, and the like are ex-pressed using the designations of U.S.~. Standard Sieve Series-ASTM Specification E-11-70.
In accordance with the method of this invention, sorbent calcium sulfate dihydrate (CaSO4 2H2O) or gypsum-containing ~ranules are produced by first providing aparticulate charge comprising finely divided calcium sul-fate hemihydrate (CaSO4 1/2H2O) particles with or without other particulate absorbent material being present. This charge contains at least about 35 percent by weight cal-cium sulfate hemihydrate, commercial grades of which arealso known as plaster of Paris. Preferably, the particu-late charge contains at least about 50 percent by weight plaster of Paris.
In order for the granulation process of this invention to be most successful, substantially all of the particles in the charge r and particularly the plaster of Paris particles, should be wet with an aqueous binder as will be discussed in greater detail hereinbelow. Conse-quently, the charge particles should be of a small enough diameter such that they may be so wet. It has therefore been found beneficial to use charge particles whose sizes ~2~
are such that they will pass through a 60-mesh screen.
More preferably, and beneficially, the charge particles, and therefore plaster o~ Paris particles, should be of a size such that the particles will pass through a 325-mesh screen.
The charge may also be comprised of other sor-bent particles, i.e., supplemental sorbent materials, in addition to the plaster of Paris particles. These other sorbent particles may be selected from an extremely wide range of organic as well as inorganic materials. As is the case of the plaster of Paris, preferably substantially all particles of the other sorbent materials present in the charge should be wetted by the aqueous binder during the granulation process. It is also beneficial to have the particle size of the other sorbent materials similar to that of the plaster of Paris, i.e., particles having a size such that they will pass through a 60-mesh screen, and most preferably particles of sizes which will pass through a 325-mesh screen.
Particularly useful such other sorbent particles or supplemental sorbent materials include inorganic mate-rials such as absorbent clay minerals, vermiculite, diatomaceous earth, pumice~ Portland cement, gypsum, activated carbon, and the like. Particulate botanical materials such as ground corn cobs, oat mill feed, soybean mill feed, alfalfa meal, coconut meal, ground cottonseed hulls, ground rice hulls, chopped hay, wood flour, and the like are also useful for the present purposes.
Particulate absorbent clay minerals are particu-larly preferred. These materials are natural, earthy pro-ducts composed primarily o~ hydrous aluminum silicates.
Small amounts of non-clay materials may also be present.
Typical absorbent clay minerals are montmorillonite, kaolin, illite, halloysite, vermiculite, the sodium and calcium bentonites (clays largely composed of montmorillonite but may contain beidellite, attapulgite, and similar minerals), attapulgite, sepiolite, and the like. Calcium bentonite is a particularly preferred clay mineral for the present purposes. Calcium bentonite can range in color from a cream, off-white, to a dark reddish tan color and is fre-quently referred to in the trade under designations such as Mississippi brown, Georgia brown and Georgia white clays.
Gypsum containing particles such as those made in accordance with this invention but whose sizes are such that they are either too large to be commercially useful and therefore have been crushed for reuse, or those whose sizes are too small for commercial use can also be simply added back into the charge of a subsequent preparation of sorbent granules.
Additionally, the particulate charge may also contain coloring materials, should variously colored granules be desired, and also agents which may retard or hasten the hydration reaction and therefore the setting into a solid state of the plaster. Retarding agents are usually of a colloidal nature such as glue, sawdust, blood, packing-house tankage, and the like. Hastening agents are frequently crystallized salts such as sodium chloride, sodium sulfate, sodium carbonate, and the like.
The granules of this invention are produced in a reactor having a confined, elongated space which often may be tubular. Within this space a ~enerally helical turbulent gas stream is generated, e.g., by rotating im-pellers, vanes, or similar means, and the particulate charge is introduced therein. The introduced particulate charge is suspended in the turbulent gas stream, is sub- --jected to mechanical agitation within the confined space, wetted by the aqueous binder, and follows a generally helical path which is substantially the same as that of the turbulent gas stream. The preferred gas is ambient air. However, heated or cooled air may be employed as well as other gases such as nitrogen, carbon dioxide, argon and the like.
66~3 For optimum agitation of the suspended particu-late charge along its path in the reaetor, the mechanical agitation is induced by a series of impellers whieh are spaced along the length of the reactor. Each of the im-pellers preferably is eomprised of a plurality of bladesor paddles which impinge on the suspended particulate charge and on the wet granules as they are formed. In preferred reactors, the angle o~ the blades or paddles may be changed as desired to thereby control the degree of physical agitation produced by each impeller as well as the residence time of the suspended particulate charge within the reactor.
A reactor which has been found useful for prac-ticing the present invention is commercially available from the Strong-Scott Mfg. Co. of Minneapolis, Minnesota, under the trade name TURBULIZER. A TURBULIZER is de-seribed by its manufaeturer as a "h;igh speed eontinuous mixer," and a suggested use for it is the de-agglomeration and homogenizakion of solids. However, it has now been found that this machine, when operated in a certain manner can also be used to make granules from very small parti-cles, or fines. The designation of a Strong-Scott TURBULI-ZER as a reaetor in which the method of this invention can be aceomplished, is for illustrative purposes only, sinee the method of this invention is not limited to using only this particular reactor brand or reactor design.
In earrying out the method of this invention, as the reactor's meehanical agitation is begun, a turbulent helical gas flow is generated within the reactor by the rotating reactor paddles or vanes therein. As a partieu-late charge is fed into the reactor, the particles consti-tuting the charge enter the gas stream and create therein a substantially uniform dispersion of the charge particles.
An aqueous binder is also introduced into the reactor in an amount sufficient to wet the charge particles and ini-tiate hydration of the calcium sulfate hemihydrate while i6~
the particles are in the dispersion created within the reactor. Thus, a new dispersion containing gas, water, supplemental sorbent particles (if present),and hydrating calcium sulfate hemihydrate is produced. Within the reac-tor, the aqueous binder preferably wets substantially allof the charge particles and in so wetting causes the cal-cium sulfate hemihydrate to begin its conversion to the dihydrate. The calcium sulfate hemihydrate, as it is in the process of hydrating, under the influence of the mechanical agitation that takes place within the reactor along the aforementioned helical gas flow agglomerates with the various other materials present within the reac-tor to form substantially spherical absorbent granules.
The aqueous binder used in this method is prefer-ably water as it is received from the tap. Distilled ordeionized water may also be used. ~dditionally, additives may be included into the water such as polymeric materials which aid the granulation process and also add some mechan-ical strength to the granular product of this invention.
Examples of polymeric materials which may be used in the water include but are not limited to polyvinyl alcohol containing resins, soluble acrylic resins as well as water insoluble but dispersible acrylics as are used in forming paints and the like.
It is preferred that the particulate charge and aqueous binder are fed into the reactor and gas stream substantially simultaneously, thus, a fore-run of the particulate charge does not emerge from the reactor prior to the desired product nor does the aqueous binder emerge prior to the granulated product.
The amount of aqueous binder used is a function of its water content, and the amount of calcium sulfate hemihydrate tplaster of Paris) present in the charge. The amount of water used should be near the stoichiometric amount required to convert the calcium sulfate hemihydrate to calcium sulfate dihydrate, i.e., plaster of Paris, to ~2~G~
gypsum. Preferably, the amount of water used is in slight excess over that which would be required by the stoichio-metry of the hydration reaction. At the stoichiometric point, about 6 weights of plaster of Paris would consume about 1 weight of water. Most preferably, water should not be used at more than about 25 percent of the weight of the plaster, or said in a different fashion, the most preferable weight ratio between plaster of Paris and water fed to the reactor at any given time is about 4 weights of plaster of Paris to one weight of water.
Granules prepared in accordance with the prefer-red amounts of water emerge from the reactor slightly damp, but as the hydration reaction is allowed to continue, the granules dry by themselves. It is assumed that the water which causes the dampness either evaporates into the sur-roundings, or more likely, it is used to continue hydration of the plaster into gypsum. If substantially more water is used than that within the preferred range, the mechanical strength of the granules may suffer. Also, the granules leaving the reactor must be dried, which requirement adds another step and therefoxe increases the cost of produc-tion.
As the reactor hereinabove described is one which does not allow a significant amount of backmixing, the aqueous binder should be fed into the reactor in a quantity which is sufficient to hydrate that portion of the particu-late charge which is also being fed. Thus, it is preferred that the aqueous binder be fed into the reactor and its gas stream at a rate such that the weight of aqueous binder fed is no greater than about 25 percent by weight of the charge which is simultaneously being fed.
The manner in which the aqueous binder is fed into the reactor may vary. Thus, if water alone is used as the binder, it may be fed in the form of steam or water vapor. Additionally, an aqueous binder may be fed as a liquid stream to be broken up by the mechanical agitators.
~2~
Preferably, it is fed as a liquid in particulate form, i.e., as a spray or fog. Several different types of ori-fices are known in the art for spraying aqueous solutions or dispersions and particular choices of these orifices or nozzles are left to be chosen by those skilled in the art depending upon the particular type of granule desired, the particle size of the charge being fed, the binder being used, and the particular requirements of the reactor which is chosen.
The size of the produced granules is dependent to a large extent on the processing time of the particu-late charge within the reactor. In general, the longer the processing time the larger will be the average size, i.e., diameter of the produced granules. However, for any given reactor, the time elapsed in processing one reactor volume of dispersed particulate charge to be granulated at steady state conditions, the space time, should be at least 0.5 seconds to allow for wetting of the plaster of Paris particles and formed granule compaction by mechanical agitation.
Space time, ~,can be calculated by dividing the reactor volume by the volumetric flow rate of reactor output. The reciprocal of space time ~, is space velocity, S, i.e., 5 = l/~.
As an example, using a granulation reactor having a reactor volume of about 3.35 cubic feet, such as Turbuli-zer Model T-l~, granules predominantly in the 20/60 mesh size, i.e., passing through a 20-mesh screen and retained on a 60-mesh screen, can be produced at a rate of about 2500 pounds/hour while feeding through the reactor about 2000 pounds/hour of commercial grade plaster of Paris and about 500 pounds/hour of water as a finely divided spray together with ambient air as carrier gas at a rate of about 270 cubic feet per minute or about 16,200 cubic feet/hour.
Accordingly, the approximate space time for the foregoing granulation process is about 2 x 10-4 hours.
66E~
In general, it has been found that a space time of about 1.4 x 10-4 hours to about 1 x 10-3 hours is pre-ferable in producing granules by the method of this inven-tion such that at least about 20 weight percent of the granules will pass through a 20-mesh screen and be re-tained on a 60-mesh screen. Space times of aboutl.8 x 10-4 hours to about 2.2 x 10-4 hours are preferred for produc-ing granules whose sizes are such that at least about 85 weight percent of the granules will pass through a 20-mesh screen and be retained on a 60-mesh screen.
The granules produced by the method of this in-vention generally have a dry bulk density of about ~0 pounds per cubic foot and less, depending on the constitu-ents that are present, and preferably of about 40 to about lS 55 pounds per cubic foot. These granules generally have a surface hardness of less than about 40 percent attrition and a liquid holding capacity of at least about 30 percent by weight.
The fact that the surface hardness of the gran-ules of this invention is less than about 40 percentattrition is an indication that the granule of the pre sent invention is particularly well suited for commercial use as a carrier for liquid chemicals, and especially as a carrier for agricultural chemicals, which are sorbed in or on the granule and which can be deposited upon agricul-tural sites by spreading the granules on such sites using ordinary agricultural implements. Specifically, the rela-tively high surface hardness imparts a degree of mechanical strength or resistance to attrition under the mechanical stresses encountered during the formulation process, during packaging, and shipping, as well as during use wh~n the granules are spread by mechanical apparatus on agricultural sites.
The relatively high surface hardness further con-tributes to a relatively low dustability characteristic ofthe granule. That is, the granule o the present invention, ~3L2~68 having a relatively high surface hardness, has a lesser tendency to break down and form small dust particles or "fines" which are generally undesirable because the fines spread through the air and are transported to areas where they are not wanted and also because they may be inhaled by animals and/or workers handling the granules.
The calcium sulfate dihydrate granules of the present invention provide granules which are substantially inert with respect to the agricultural chemicals for which they are intended to serve as a carrier. It is believed that this carrier material has few, if any, catalytic sites or acid sites, which tend to cause or accelerate decomposition of various chemicals abs~rbed on the gran-ules. Thus, the use of deactivator compounds i5 not ordinarily required with this granule to neutralize acid centers as is required with many other types of carriers.
It is to be noted that the calcium sulfate dihy-drate granule of the present invention has a bulk density of less than about 55 pounds per cubic foot when prepared in accordance with the method of the present invention to be described hereinafter. This compares favorably with the bulk density of naturally occurring gypsum (calcium sulfate dihydrate) of between 65 and 70 pounds per cubic foot.
Though this reduction in bulk density cannot be currently satisfactorily explained, such a reduction in bulk density is highly desirable because it is some indication of the sorptivity capability. The oil holding capacity of the granules of the present invention is at least about 30 per-cent by weight, and may reach 100 percent depending on the granule constituents. The water holding capacity of these granules is about the same, to slightly higher than the oil holding capacity.
The preferred size of the granule of the present invention falls within a range wherein the granule will pass through a 20-mesh screen and be retained on a 60-mesh screen. This size granule has dry flow characteristics and 66~
handling characteristics that make it eminently suitable for use as a carrier of agricultural chemicals.
The presence of fines in the charge affects the surface hardness of the ultimately produced absorkent granule, thus the surface hardness can also be regulated by controlling the amount of fines present in the parti-culate charge to the reactor. In general, the particulate charge can contain up to about 50 percent by weight fines.
The higher the concentration of these fines in the charge the lower will be the surface hardness of the ultimately produced granules.
A number of examples will be presented herein-after for the purposes of further illustrating and dis-closing the present invention. These examples are by way of illustration, and are not to be taken as limiting.
With each example, there $s provided a tabula-tion of parameters relating to the initial charge of mate-rial, the process conditions, and the characteristics of the final product. Certain terms or properties that have been used or referred to in the pre~3ent specification, including the following examples, axe defined or deter-mined as follows:
1) "Bulk Density" is the measured loose packed density of the agglomerated product when dried to no more than 1 wt.-~ free moisture. A 250 ml. graduated cylinder is completely filled with the product without tamping.
The bulk density in pounds per cubic foot is determined by dividing the weight of the sample in grams by the volume of the sample in milliliters and multiplying by the factor 62.43.
A number of solid materials are widely used as carriers for agricultural chemicals, such as insecticides, herbicides, fertilizers, and the like. The agricultural chemicals are combined with such a carrier for convenient dissemination by various distributor means.
In some types of agricultural carriers, the chemical or active ingredient contained therein is in solid form, usually as a powder or as small particles or granules, and is admixed with the carrier, the mixture then being formed into pellets. With other types of carriers, the carrier is in the form of particles or granules into which the active ingredient, in liquid form, is sorbed. With yet another type of carrier the active ingredient is adhered to the carrier surface.
Agricultural carrier material can be used in many forms, such as powder, particles, granules, or pel-lets. For ease of handling, and for other reasons, mate-rials having a granule size in a range which would pass through a 20-mesh screen and be retained on a 60 mesh screen (U.S.A. Standard Sieve Series) are commonly used.
With such size granules, it is important that the gran-ules maintain their structural integrity and thus sizeduring initial fabrication as well as during subsequent storage, marketing, and application. In many applica-tions, it is important that the particles or granules be of a size that does not pass through the 60-mesh screen so as to reduce the probability that some of the particles or granules are so small as to form dust. It is also important that the particles maintain their size and con-dition so that they do not form dust, or turn to dust, i~2~8 owing to degradation during storage or use, or owing to general abrasion or attrition during manufacturing, handling, storing, transporting and application with mechanical devices to agricultural soil. Dust is ob-jectionable because of the well known problems with dustspreading in the air and on persons and animals, and being inhaled by workers making or handling such carriers.
Many naturally-occurring mineral carriers that are used with agriculturally active ingredients, includ-ing certain types of pesticides, have a degree of surfaceacidity which varies depending upon the crystalline and molecular structure of the mineral. It is thought that the surface acidity arises as a result of a non-uniform distribution of electric charge in or on the surface or the mineral particles. A large number of electric charges may exist at certain areas on a surface of a mineral car-rier particle and these are referred to as acid sites or electrophilic centers. The strength of these centers varies depending upon the composition of the surface and the degree of distortion in the structure which brings about the non-uniform distribution of the electrical surface charges. The surface acidity on a mineral car-rier particle can affect the reactivity of that mineral particle with the agricultural chemical carried thereon.
It is thought that the surface acidity, and specifically the acid centers, have a catalytic effect with respect to the decomposition of the particular chemical. It has been found that with some pesticidal chemicals, the catalytic ac~ivity of the acid sites, with respect to inducing or accelerating decomposition, can be much re-duced by deactivation of the acid sites with certain organic or inorganic materials which preferentially share their electrons with the mineral to form a bond which is stronger than that which may be formed between the agri-cultural chemical and the acid center itself. The addi-tion of any deactivator material, usually in amounts of up to 6 or 8 percent by weight of the carrier adds an ~z~6~;8.
undesirable cost to the formulation of the agricultural chemical-laden carrier. Thus, it would be desirable to provide a method for producing a substantially neutral and inert carrier for agricultural chemicals, and es-pecially for pesticides, which has little or no surfaceacidity and which does not require the addition of any deactivator material.
A sorbent carrier for liquid chemicals should have a relatively high sorptivity, or a sorptivity which is at least high enough to prove commercially satisfac-tory.
In the case of sorbent materials, the porosity of the material is usually related to the sorbency char-acteristics of the material. Further, a generally low dry bulk density is usually a characteristic of the more sorbent materials. Generally, as particle or granule size increases, the bulk surface area decreases for a given number of granules. Since sorptivity is princi-pally a surface phenomenon and a function of the pore density within a surface, it would be desirable to pro-, vide a method for producing a carrier granule having a size small enough to present a relatively high bulk sur-face area and having a pore density high enough such that the sorp~ivity is commercially satisfactory.
In order that a granulated carrier functions properly and does not degrade through abrasion or attri-tion into dust under mechanical stress during manufacture, packaging, storing, shipping and use, the carrier granules must exhibit adequate mechanical strength. Thus, it would be desirable to provide a method for producing a carrier granule which has relatively high mechanical strength or resistance to attrition while minimizing the concurrent generation of an undesirable amount of small, dust-size particles.
The present invention provides a very effecti~e method for controlled manufacture of relatively low-density, gypsum-containing granules that are eminently 1~2~ 8 suitable as carriers for agricultural chemicals and -that are resistant to attrition. Additionally, the low-density, gypsum-containing granules produced according to the method of this invention are also useful as oil and grease sorbents, as sorbents for household pet toilets, and for similar applications.
_ mmary of the Invention According to the method of the present invention, a particulate charge containing calcium sulfate hemihydrate (CaSO4.1/2H20) is treated with an aqueous binder in an amount sufficient to wet and agglomerate the particles of the charge, and to initiate hydration of the calcium sulfate hemihydrate present while being subjected to vigorous mechanical action. The charge particles and aqueous binder are fed into a confined elongated space in which a generally helical turbulent gas stream is generated. The charge and aqueous binder orm a substantially uniform dispersion of the particles within the turbulent gas stream which dispersion is subjected to mechanical agitation so as to pack the wetted particles into granules. Thereafter the granules are recovered from the gas stream.
Thus, in accordance with the present invention, there is provided a method for producing sorbent calcium sulfate dihydrate-containing granules which comprises: providing a particulate charge comprising finely divided calcium sulfate hemihydrate particles having a size that passes through a 60 mesh screen, said charge containing calcium sulfate hemihydrate in an amount of at least about 35 percent by weight of the charge; providing a confined elongated space and generating a generally helical turbulent gas stream within said space; feeding said charge into said gas stream so as to provide a substantially uniform disper-sion of said particles in said gas stream, the space time for the particulate cnarge within the turbulent gas stream being about 1.4 x 10 4 hours to about 1 x 10 3 hours; introducing into said ~r~ ~
~; ~
~LZ916~3 dispersion an aqueous binder in an amount sufficient to wet and agglomerate said particles, and to initiate hydration of said calcium sulfate hemihydrate while in said dispersion; mechanically agitating said dispersion such that the flow of said dispersion is substantially the same as that of said gas stream so as to pack the wetted particles into granules; and recovering the granules thereby produced.
The present invention may also be defined as a method for producing sorbent calcium sulfate dihydrate-containing granules which comprises: providing a particulate charge comprising sor-bent particles having a size that passes through a 60 mesh screen and at least about 35 percent by weight of the charge of plaster of Paris particles mixed therewith mechanically agitating a gas within a confined, elongated space so as to produce a generally helically shaped turbulent gas stream therein; feeding said charge into the produced gas stream at a substantially uniform rate so that the space time for the particulate charge within the turbulent gas stream being about 1.4 x 10 hours to about 1 x 10 3 hours; feeding an a~ueous binder into the produced gas stream sub-stantially simultaneously with said charge in an amount sufficientto wet the particulate charge and to initiate hydration of said plaster of Paris particles; continuing said agitation for a time period sufficient to form granules; and recovering the produced granules.
The granules produced in accordance with this method have a relatively high mechanical strength or resistance to attrition -to mechanical stresses during manufacture, packaging, storing, shipping and other uses. Additionally, the sorbent carriers made in accordance with this invention are relatively inert and have sorptivities which are high enough for commercial use as sorbent materials. Still another advantage of -the method of this in-vention is that the particle size distribution of the produced - 4a -granules can be controlled within a relatively narrow range.Yet another benefit of the method of this invention is that the sorptive granules produced have a bulk density which is lower than that of naturally occurring gypsum particles and, as discussed hereinabove, provide higher sorptive capacity than naturally occurring - ~b -IL2~8 gypsum particles of similar size. Numerous other advan-tages and features of the present invention will become readily apparent from the following detailed description of the invention, the accompanying examples, and from the appended claims.
Descri tion of the Preferred Embodiments P
While the method of this invention is suscept-ible of embodiment in many different forms, specific embodiments will be herein described in detail, with the understanding that the present disclosure is to be con-sidered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated.
All references made herein to sieve analysis, screen mesh sizes, particle sizes, and the like are ex-pressed using the designations of U.S.~. Standard Sieve Series-ASTM Specification E-11-70.
In accordance with the method of this invention, sorbent calcium sulfate dihydrate (CaSO4 2H2O) or gypsum-containing ~ranules are produced by first providing aparticulate charge comprising finely divided calcium sul-fate hemihydrate (CaSO4 1/2H2O) particles with or without other particulate absorbent material being present. This charge contains at least about 35 percent by weight cal-cium sulfate hemihydrate, commercial grades of which arealso known as plaster of Paris. Preferably, the particu-late charge contains at least about 50 percent by weight plaster of Paris.
In order for the granulation process of this invention to be most successful, substantially all of the particles in the charge r and particularly the plaster of Paris particles, should be wet with an aqueous binder as will be discussed in greater detail hereinbelow. Conse-quently, the charge particles should be of a small enough diameter such that they may be so wet. It has therefore been found beneficial to use charge particles whose sizes ~2~
are such that they will pass through a 60-mesh screen.
More preferably, and beneficially, the charge particles, and therefore plaster o~ Paris particles, should be of a size such that the particles will pass through a 325-mesh screen.
The charge may also be comprised of other sor-bent particles, i.e., supplemental sorbent materials, in addition to the plaster of Paris particles. These other sorbent particles may be selected from an extremely wide range of organic as well as inorganic materials. As is the case of the plaster of Paris, preferably substantially all particles of the other sorbent materials present in the charge should be wetted by the aqueous binder during the granulation process. It is also beneficial to have the particle size of the other sorbent materials similar to that of the plaster of Paris, i.e., particles having a size such that they will pass through a 60-mesh screen, and most preferably particles of sizes which will pass through a 325-mesh screen.
Particularly useful such other sorbent particles or supplemental sorbent materials include inorganic mate-rials such as absorbent clay minerals, vermiculite, diatomaceous earth, pumice~ Portland cement, gypsum, activated carbon, and the like. Particulate botanical materials such as ground corn cobs, oat mill feed, soybean mill feed, alfalfa meal, coconut meal, ground cottonseed hulls, ground rice hulls, chopped hay, wood flour, and the like are also useful for the present purposes.
Particulate absorbent clay minerals are particu-larly preferred. These materials are natural, earthy pro-ducts composed primarily o~ hydrous aluminum silicates.
Small amounts of non-clay materials may also be present.
Typical absorbent clay minerals are montmorillonite, kaolin, illite, halloysite, vermiculite, the sodium and calcium bentonites (clays largely composed of montmorillonite but may contain beidellite, attapulgite, and similar minerals), attapulgite, sepiolite, and the like. Calcium bentonite is a particularly preferred clay mineral for the present purposes. Calcium bentonite can range in color from a cream, off-white, to a dark reddish tan color and is fre-quently referred to in the trade under designations such as Mississippi brown, Georgia brown and Georgia white clays.
Gypsum containing particles such as those made in accordance with this invention but whose sizes are such that they are either too large to be commercially useful and therefore have been crushed for reuse, or those whose sizes are too small for commercial use can also be simply added back into the charge of a subsequent preparation of sorbent granules.
Additionally, the particulate charge may also contain coloring materials, should variously colored granules be desired, and also agents which may retard or hasten the hydration reaction and therefore the setting into a solid state of the plaster. Retarding agents are usually of a colloidal nature such as glue, sawdust, blood, packing-house tankage, and the like. Hastening agents are frequently crystallized salts such as sodium chloride, sodium sulfate, sodium carbonate, and the like.
The granules of this invention are produced in a reactor having a confined, elongated space which often may be tubular. Within this space a ~enerally helical turbulent gas stream is generated, e.g., by rotating im-pellers, vanes, or similar means, and the particulate charge is introduced therein. The introduced particulate charge is suspended in the turbulent gas stream, is sub- --jected to mechanical agitation within the confined space, wetted by the aqueous binder, and follows a generally helical path which is substantially the same as that of the turbulent gas stream. The preferred gas is ambient air. However, heated or cooled air may be employed as well as other gases such as nitrogen, carbon dioxide, argon and the like.
66~3 For optimum agitation of the suspended particu-late charge along its path in the reaetor, the mechanical agitation is induced by a series of impellers whieh are spaced along the length of the reactor. Each of the im-pellers preferably is eomprised of a plurality of bladesor paddles which impinge on the suspended particulate charge and on the wet granules as they are formed. In preferred reactors, the angle o~ the blades or paddles may be changed as desired to thereby control the degree of physical agitation produced by each impeller as well as the residence time of the suspended particulate charge within the reactor.
A reactor which has been found useful for prac-ticing the present invention is commercially available from the Strong-Scott Mfg. Co. of Minneapolis, Minnesota, under the trade name TURBULIZER. A TURBULIZER is de-seribed by its manufaeturer as a "h;igh speed eontinuous mixer," and a suggested use for it is the de-agglomeration and homogenizakion of solids. However, it has now been found that this machine, when operated in a certain manner can also be used to make granules from very small parti-cles, or fines. The designation of a Strong-Scott TURBULI-ZER as a reaetor in which the method of this invention can be aceomplished, is for illustrative purposes only, sinee the method of this invention is not limited to using only this particular reactor brand or reactor design.
In earrying out the method of this invention, as the reactor's meehanical agitation is begun, a turbulent helical gas flow is generated within the reactor by the rotating reactor paddles or vanes therein. As a partieu-late charge is fed into the reactor, the particles consti-tuting the charge enter the gas stream and create therein a substantially uniform dispersion of the charge particles.
An aqueous binder is also introduced into the reactor in an amount sufficient to wet the charge particles and ini-tiate hydration of the calcium sulfate hemihydrate while i6~
the particles are in the dispersion created within the reactor. Thus, a new dispersion containing gas, water, supplemental sorbent particles (if present),and hydrating calcium sulfate hemihydrate is produced. Within the reac-tor, the aqueous binder preferably wets substantially allof the charge particles and in so wetting causes the cal-cium sulfate hemihydrate to begin its conversion to the dihydrate. The calcium sulfate hemihydrate, as it is in the process of hydrating, under the influence of the mechanical agitation that takes place within the reactor along the aforementioned helical gas flow agglomerates with the various other materials present within the reac-tor to form substantially spherical absorbent granules.
The aqueous binder used in this method is prefer-ably water as it is received from the tap. Distilled ordeionized water may also be used. ~dditionally, additives may be included into the water such as polymeric materials which aid the granulation process and also add some mechan-ical strength to the granular product of this invention.
Examples of polymeric materials which may be used in the water include but are not limited to polyvinyl alcohol containing resins, soluble acrylic resins as well as water insoluble but dispersible acrylics as are used in forming paints and the like.
It is preferred that the particulate charge and aqueous binder are fed into the reactor and gas stream substantially simultaneously, thus, a fore-run of the particulate charge does not emerge from the reactor prior to the desired product nor does the aqueous binder emerge prior to the granulated product.
The amount of aqueous binder used is a function of its water content, and the amount of calcium sulfate hemihydrate tplaster of Paris) present in the charge. The amount of water used should be near the stoichiometric amount required to convert the calcium sulfate hemihydrate to calcium sulfate dihydrate, i.e., plaster of Paris, to ~2~G~
gypsum. Preferably, the amount of water used is in slight excess over that which would be required by the stoichio-metry of the hydration reaction. At the stoichiometric point, about 6 weights of plaster of Paris would consume about 1 weight of water. Most preferably, water should not be used at more than about 25 percent of the weight of the plaster, or said in a different fashion, the most preferable weight ratio between plaster of Paris and water fed to the reactor at any given time is about 4 weights of plaster of Paris to one weight of water.
Granules prepared in accordance with the prefer-red amounts of water emerge from the reactor slightly damp, but as the hydration reaction is allowed to continue, the granules dry by themselves. It is assumed that the water which causes the dampness either evaporates into the sur-roundings, or more likely, it is used to continue hydration of the plaster into gypsum. If substantially more water is used than that within the preferred range, the mechanical strength of the granules may suffer. Also, the granules leaving the reactor must be dried, which requirement adds another step and therefoxe increases the cost of produc-tion.
As the reactor hereinabove described is one which does not allow a significant amount of backmixing, the aqueous binder should be fed into the reactor in a quantity which is sufficient to hydrate that portion of the particu-late charge which is also being fed. Thus, it is preferred that the aqueous binder be fed into the reactor and its gas stream at a rate such that the weight of aqueous binder fed is no greater than about 25 percent by weight of the charge which is simultaneously being fed.
The manner in which the aqueous binder is fed into the reactor may vary. Thus, if water alone is used as the binder, it may be fed in the form of steam or water vapor. Additionally, an aqueous binder may be fed as a liquid stream to be broken up by the mechanical agitators.
~2~
Preferably, it is fed as a liquid in particulate form, i.e., as a spray or fog. Several different types of ori-fices are known in the art for spraying aqueous solutions or dispersions and particular choices of these orifices or nozzles are left to be chosen by those skilled in the art depending upon the particular type of granule desired, the particle size of the charge being fed, the binder being used, and the particular requirements of the reactor which is chosen.
The size of the produced granules is dependent to a large extent on the processing time of the particu-late charge within the reactor. In general, the longer the processing time the larger will be the average size, i.e., diameter of the produced granules. However, for any given reactor, the time elapsed in processing one reactor volume of dispersed particulate charge to be granulated at steady state conditions, the space time, should be at least 0.5 seconds to allow for wetting of the plaster of Paris particles and formed granule compaction by mechanical agitation.
Space time, ~,can be calculated by dividing the reactor volume by the volumetric flow rate of reactor output. The reciprocal of space time ~, is space velocity, S, i.e., 5 = l/~.
As an example, using a granulation reactor having a reactor volume of about 3.35 cubic feet, such as Turbuli-zer Model T-l~, granules predominantly in the 20/60 mesh size, i.e., passing through a 20-mesh screen and retained on a 60-mesh screen, can be produced at a rate of about 2500 pounds/hour while feeding through the reactor about 2000 pounds/hour of commercial grade plaster of Paris and about 500 pounds/hour of water as a finely divided spray together with ambient air as carrier gas at a rate of about 270 cubic feet per minute or about 16,200 cubic feet/hour.
Accordingly, the approximate space time for the foregoing granulation process is about 2 x 10-4 hours.
66E~
In general, it has been found that a space time of about 1.4 x 10-4 hours to about 1 x 10-3 hours is pre-ferable in producing granules by the method of this inven-tion such that at least about 20 weight percent of the granules will pass through a 20-mesh screen and be re-tained on a 60-mesh screen. Space times of aboutl.8 x 10-4 hours to about 2.2 x 10-4 hours are preferred for produc-ing granules whose sizes are such that at least about 85 weight percent of the granules will pass through a 20-mesh screen and be retained on a 60-mesh screen.
The granules produced by the method of this in-vention generally have a dry bulk density of about ~0 pounds per cubic foot and less, depending on the constitu-ents that are present, and preferably of about 40 to about lS 55 pounds per cubic foot. These granules generally have a surface hardness of less than about 40 percent attrition and a liquid holding capacity of at least about 30 percent by weight.
The fact that the surface hardness of the gran-ules of this invention is less than about 40 percentattrition is an indication that the granule of the pre sent invention is particularly well suited for commercial use as a carrier for liquid chemicals, and especially as a carrier for agricultural chemicals, which are sorbed in or on the granule and which can be deposited upon agricul-tural sites by spreading the granules on such sites using ordinary agricultural implements. Specifically, the rela-tively high surface hardness imparts a degree of mechanical strength or resistance to attrition under the mechanical stresses encountered during the formulation process, during packaging, and shipping, as well as during use wh~n the granules are spread by mechanical apparatus on agricultural sites.
The relatively high surface hardness further con-tributes to a relatively low dustability characteristic ofthe granule. That is, the granule o the present invention, ~3L2~68 having a relatively high surface hardness, has a lesser tendency to break down and form small dust particles or "fines" which are generally undesirable because the fines spread through the air and are transported to areas where they are not wanted and also because they may be inhaled by animals and/or workers handling the granules.
The calcium sulfate dihydrate granules of the present invention provide granules which are substantially inert with respect to the agricultural chemicals for which they are intended to serve as a carrier. It is believed that this carrier material has few, if any, catalytic sites or acid sites, which tend to cause or accelerate decomposition of various chemicals abs~rbed on the gran-ules. Thus, the use of deactivator compounds i5 not ordinarily required with this granule to neutralize acid centers as is required with many other types of carriers.
It is to be noted that the calcium sulfate dihy-drate granule of the present invention has a bulk density of less than about 55 pounds per cubic foot when prepared in accordance with the method of the present invention to be described hereinafter. This compares favorably with the bulk density of naturally occurring gypsum (calcium sulfate dihydrate) of between 65 and 70 pounds per cubic foot.
Though this reduction in bulk density cannot be currently satisfactorily explained, such a reduction in bulk density is highly desirable because it is some indication of the sorptivity capability. The oil holding capacity of the granules of the present invention is at least about 30 per-cent by weight, and may reach 100 percent depending on the granule constituents. The water holding capacity of these granules is about the same, to slightly higher than the oil holding capacity.
The preferred size of the granule of the present invention falls within a range wherein the granule will pass through a 20-mesh screen and be retained on a 60-mesh screen. This size granule has dry flow characteristics and 66~
handling characteristics that make it eminently suitable for use as a carrier of agricultural chemicals.
The presence of fines in the charge affects the surface hardness of the ultimately produced absorkent granule, thus the surface hardness can also be regulated by controlling the amount of fines present in the parti-culate charge to the reactor. In general, the particulate charge can contain up to about 50 percent by weight fines.
The higher the concentration of these fines in the charge the lower will be the surface hardness of the ultimately produced granules.
A number of examples will be presented herein-after for the purposes of further illustrating and dis-closing the present invention. These examples are by way of illustration, and are not to be taken as limiting.
With each example, there $s provided a tabula-tion of parameters relating to the initial charge of mate-rial, the process conditions, and the characteristics of the final product. Certain terms or properties that have been used or referred to in the pre~3ent specification, including the following examples, axe defined or deter-mined as follows:
1) "Bulk Density" is the measured loose packed density of the agglomerated product when dried to no more than 1 wt.-~ free moisture. A 250 ml. graduated cylinder is completely filled with the product without tamping.
The bulk density in pounds per cubic foot is determined by dividing the weight of the sample in grams by the volume of the sample in milliliters and multiplying by the factor 62.43.
2) "Water Absorption" is determined by the fol~
lowing procedure. First, a sample of about 50 grams from the dried product is weighed to the nearest 0.1 gm. and poured into a glass tube measuring 9 inches in length and 30 mm. in internal diameter. The glass tube is maintained in a vertical position and one end of the tube is covered with a Number 18-mesh screen. Fine particles passing through the screen are collected and returned to the top of the tube. The glass tube is held on a tripod stand and positioned at a 30 angle to the horizontal. A 100 ml.
graduated cylinder is placed under the tube at the screen.
75 ml. of water is introduced from a pipette through the open end of the 9-inch-long glass tube to the sample. The water is absorbed by the sample until the saturation point is reached and the surplus water begins draining into the graduated glass cylinder. This step is continued until all portions of the sample in the tube are wet. After insuring that no part of the sample in the ' tube is dry, the tube is allowed to drain for 30 minutes.
Next, since 75 ml. of water was initially present in the ; pipette, and since any water not absorbed by the sample in the tube is collected in the graduated cylinder below the tube, the amount of water absorbed is equal to the initial 75 milliliter quantity minus the volume of water collected in the graduated cylinder. This amount is divided by the weight of the sample in grams to provide the absorption capacity of the sample in units of ml./gm.
lowing procedure. First, a sample of about 50 grams from the dried product is weighed to the nearest 0.1 gm. and poured into a glass tube measuring 9 inches in length and 30 mm. in internal diameter. The glass tube is maintained in a vertical position and one end of the tube is covered with a Number 18-mesh screen. Fine particles passing through the screen are collected and returned to the top of the tube. The glass tube is held on a tripod stand and positioned at a 30 angle to the horizontal. A 100 ml.
graduated cylinder is placed under the tube at the screen.
75 ml. of water is introduced from a pipette through the open end of the 9-inch-long glass tube to the sample. The water is absorbed by the sample until the saturation point is reached and the surplus water begins draining into the graduated glass cylinder. This step is continued until all portions of the sample in the tube are wet. After insuring that no part of the sample in the ' tube is dry, the tube is allowed to drain for 30 minutes.
Next, since 75 ml. of water was initially present in the ; pipette, and since any water not absorbed by the sample in the tube is collected in the graduated cylinder below the tube, the amount of water absorbed is equal to the initial 75 milliliter quantity minus the volume of water collected in the graduated cylinder. This amount is divided by the weight of the sample in grams to provide the absorption capacity of the sample in units of ml./gm.
3) "Oil Absorption`' was determined in accordance with the test specified in Bulletin P-A-1056, Federal Spec-ification/ Absorbent Material, Oil and Water (For Floors and Decks), issued by the General Services Administration of the United States of America. The observed absorption capacity is reported in units of ml./gm.
4) "Surface Hardness" is reported as percent aitrition and is determined as follows: A nest of two standard testing sieves, sieve No. 8 and sieve No. 60, each having a circular shape and an eight-inch diameter are selected for use with a Ro-Tap mechanical sieve machine manufactured by W. S. Tyler Co. of Dayton, Ohio. An ali-quot of 100 grams, weighed to the nearest 0.1 gm., is with-drawn as a sample from the granulated product. The sample is placed on the No. g sieve in the sieving machine for 5 minutes of shaking. The material passing through both the , No. 8 sieve and the No. 60 sieve and ending up in the col-lecting pan beneath the No. 60 sieve is rejected along with any larger material unable to pass through the No. 8 sieve.
50 grams of material retained on the No. 60 sieve is placed in a pan along with 300 grams of 1/4-inch diameter steel balls and hand mixed. The pan is then shaken in the mechanical sieving machine for 20 minutes without the tapping arm engaged. The contents of the pan are placed on the top, No. 8, sieve and allowed to fall through to the No. 60 sieve and retaining pan below the No. 60 sieve. The steel balls are removed from the No. 8 sieve and the ma-chine is mechanically sieved for 5 minutes with the tapping arm engaged. The material that is passed through the No.
60 sieve is then weighed. The hardness, in terms of "break down percent" or attrition is calculated by dividing the weight of the material that has passed through the No. 60 sieve by 50 grams and multiplying by 100.
50 grams of material retained on the No. 60 sieve is placed in a pan along with 300 grams of 1/4-inch diameter steel balls and hand mixed. The pan is then shaken in the mechanical sieving machine for 20 minutes without the tapping arm engaged. The contents of the pan are placed on the top, No. 8, sieve and allowed to fall through to the No. 60 sieve and retaining pan below the No. 60 sieve. The steel balls are removed from the No. 8 sieve and the ma-chine is mechanically sieved for 5 minutes with the tapping arm engaged. The material that is passed through the No.
60 sieve is then weighed. The hardness, in terms of "break down percent" or attrition is calculated by dividing the weight of the material that has passed through the No. 60 sieve by 50 grams and multiplying by 100.
5) "Liquid Holding Capacity". In testing liquid holding capacity (dry flow), a low viscosity organic liquid having a specific gravity of 1 gm./ml. is used. A one to one mixture (by weight) of Heavy Aromatic Naphtha and ortho chloro toluene will give the desired specific gravity and viscosity, and be relatively non-volatile. The procedure is as follows: -(A) Place 20 grams of granules in an 8 ounce French square bottle.
(B) Add 5-gram increments of liquid to the gran-ules and for each increment sha~e the bottle (a) until no granules cling to the sides or (b) for 5 minutes.
(C) When sufficient liquid has been added that granules still cling to the sides of the glass after 5 minutes of shaking, add l-gram increments of dry granules (with a 5 minute shaking interval for each addition until the point is reached where no granules cling to the sides of the container). At this point the liquid holding capa-city (L.H.C.) is calculated as follows:
~z~
cc (or grams) of liquid % L.H.C. = - X 100 grams of granules + grams of liquid
(B) Add 5-gram increments of liquid to the gran-ules and for each increment sha~e the bottle (a) until no granules cling to the sides or (b) for 5 minutes.
(C) When sufficient liquid has been added that granules still cling to the sides of the glass after 5 minutes of shaking, add l-gram increments of dry granules (with a 5 minute shaking interval for each addition until the point is reached where no granules cling to the sides of the container). At this point the liquid holding capa-city (L.H.C.) is calculated as follows:
~z~
cc (or grams) of liquid % L.H.C. = - X 100 grams of granules + grams of liquid
6) The "Screening Distribution Analysis" pre-sented in each example summarizes the results of a standard test to determine the distribution of granule sizes in the product charge. At the end of the granulation process, the batch of produced granules was dried. Thereafter, five standard circular, 8-inch diameter sieves or mesh screens were used in the analysis and were placed in nested, de-scending order with respect to screen size (mesh opening).Approximately 200 grams of the granule product was placed on the top sieve, and the sieves were shaken for five min-utes using a Ro-Tap mechanical sieve machine. The weight retained on each tared sieve was converted to percent retention of the 200-gram sample and is listed in the tab-ulation for each example under the sieve or mesh number on which it is retained. A listing of a pair of sieve or mesh numbers separated by a virgule t/) indicates that the granules had passed through the first number sieve or screen and had been retained on the second number sieve or screen. A sieve or mesh number preceded by a plus (+) sign indicates that the granules were retained on the sieve or screen, whereas a sieve or mesh number preceded by a minus (-) sign indicates that the granules passed through the sieve or screen.
A model T-l~ Strong-Scott TURBULI~ER reactor was used to granulate commercial grade plaster of Paris. About 1900 pounds of plaster of Paris per hour were fed to the reactor together with a water spray at a rate of about 25 percent by weight of the plaster of Paris feed rate. The produced gypsum granules were then recovered and dried.
About 2200 pounds of gypsum granules per hour were obtained having a bulk density of about 57 pounds per cubic foot and the following screen analysis:
6~i8 Screen ~ by Weight -+ 4 0.3 + 6 1.3 + 8 2.6 + 10 2.1 + 12 4.3 -~ 16 15.0 + 20 23.9 + 60 40.4 - 60 10.1 100.0 A Model T-14 Strong-Scott TURBULIZER reactor was used to granulate a mixture of about 50 weight percent Canadian plaster and about 50 weight percent Mississippi brown clay having a particle size passing through a 60-mesh screen. Prior to granulation the particulate mate-rials were pre-blended in a cement mixer having a~out four cubic eet capacity.
; 20 Turbulizer Operating Conditions Feed Rate: 1850 ~/hr Water Feed Rate: 1.5 gal/min Output: 2600 #/hr, wet 2000 #/hr, dry Shaft Speed: 728 rpm Paddle Setting: 45o Power Draw: 20 amps, with surges to 60 amps, at240 volts Wet granules were recovered from the reactor and dried as a fluidized bed under the following conditions:
Inlet Temperature: 90C.
Final Outlet Temperature: 40C
Batch Size: 75 # wet Time Required per Batch: 25-30 min Damper Settings: 100% Inlet 100% Outlet ~2~1668 The dried granules were then subjected to a size reduction operation.
Crusher and Screen Operating Conditions Throughput: 800-1000 #/hr Number of Passes: 4 to 5 Before size reduction:
Yield, Wt.-%
Screen Batch #1 Batch #2 Batch #3 + 20 55 S0 37 After 1st pass at crushing the + 20 from Batch ~3:
Screen Yield, Wt.-%
+ 2072 After 2nd pass using + 20 from 1st ;pass:
Screen Yield, Wt.-%
+ 2083 20/60 9 ,~
After 3rd pass using ~ 20 from 2nd pass:
Screen Yield, Wt.-%
+ 2051 - 60 18 .~.
Overall yield on Batch #3:
Screen Yield, Wt.-%
~ 20 31 ~Z~6~
Product Evaluation Bulk Density:
Loose 44.0 #/ft.3 Packed 47.8 #/ft.3 O'Haus 41 #/ft.3 Absorption:
Oil 0.9 ml/gm Water 0.8 ml/gm Hardness 25.3%
Free Moisture 1.1%
Bound Moisture 11.4%
pH 7.2 Color grey pKa 1.5 negative 3.3 positive Screen Analysis Screen Wt.-%
o ~ 30 17.2 + 40 34.1 50 41.1 6.1 - 60 1.5 The same reactor as in Example 2, above, was used to granulate a mixture of about 60 weight percent Canadian plaster and about 40 weight percent Mississippi brown clay having a particle size passing through a 60-mesh screen.
The foregoing mixture was prepared by blending the afore-mentioned materials in a cement mixer having about four cubic feet capacity.
Turbulizer Operating Conditions Feed Rate: 18g0 #/hr Water Feed Rate: 1.63 gal/min Output: 2700 #/hr, wet 2070 #/hr, dry ~i2~66B
Shaft Speed: 728 rpm Paddle Setting: 45O
Power Draw:20 amps,withsurges to 60 amps, at 240 volts The wet granulated output from the reactor was recovered and dried as a fluidized bed under the following conditions:
Inlet Temperature: 90C.
Final Outlet Temperature: 40C.
Batch Size: 75 # wet T.ime required per Batch: 20-25 min Damper Settings: 100% Inlet 100% Outlet The obtained dry granules were then subjected to size re-duction.
Crusher and Screen Operating Condit:ions Throughput 800-1000 #~hr Number of passes 4 to 5 Before size reduction:
Yield, Wt.-%
_ _ Screen Batch #1 Batch #.2 Batch #3 + 20 54 45 51 After crushing + 20:
_ Yield, Wt.-%
Screen Batch #1 Batch #2 Batch #3 30+ 20 0 0 0 Overall yield of 20/60:
Weighted Batch #1 Batch #2 Batch #3 Average 68~ 60% 70% 68%
i68 Product Evaluation .
Bulk Density:
Loose 44.9 #/ft.3 Packed 49.8 #/ft.3 O'Haus 44 #/ft.3 Absorption:
Oil 0.8 ml/gm Water 0.8 ml/gm Hardness 25.5 Free Moisture 1.1 Bound Moisture 11.0 pH 7.1 Color grey pKa 1.5 negative 3.3 positive Screen Analysis Screen Wt.-%
+ 20 0 ~ 30 19.6 + 40 35.9 ~ 50 37.2 + 60 5.5 - 60 1.8 ; The foregoing specification and data are intended as illustrative of the present invention and are not to be taken as limiting. Variations in processing parameters within the spirit and scope of the invention disclosed hereinabove are possible and will readily present them-selves to one skilled in the art.
A model T-l~ Strong-Scott TURBULI~ER reactor was used to granulate commercial grade plaster of Paris. About 1900 pounds of plaster of Paris per hour were fed to the reactor together with a water spray at a rate of about 25 percent by weight of the plaster of Paris feed rate. The produced gypsum granules were then recovered and dried.
About 2200 pounds of gypsum granules per hour were obtained having a bulk density of about 57 pounds per cubic foot and the following screen analysis:
6~i8 Screen ~ by Weight -+ 4 0.3 + 6 1.3 + 8 2.6 + 10 2.1 + 12 4.3 -~ 16 15.0 + 20 23.9 + 60 40.4 - 60 10.1 100.0 A Model T-14 Strong-Scott TURBULIZER reactor was used to granulate a mixture of about 50 weight percent Canadian plaster and about 50 weight percent Mississippi brown clay having a particle size passing through a 60-mesh screen. Prior to granulation the particulate mate-rials were pre-blended in a cement mixer having a~out four cubic eet capacity.
; 20 Turbulizer Operating Conditions Feed Rate: 1850 ~/hr Water Feed Rate: 1.5 gal/min Output: 2600 #/hr, wet 2000 #/hr, dry Shaft Speed: 728 rpm Paddle Setting: 45o Power Draw: 20 amps, with surges to 60 amps, at240 volts Wet granules were recovered from the reactor and dried as a fluidized bed under the following conditions:
Inlet Temperature: 90C.
Final Outlet Temperature: 40C
Batch Size: 75 # wet Time Required per Batch: 25-30 min Damper Settings: 100% Inlet 100% Outlet ~2~1668 The dried granules were then subjected to a size reduction operation.
Crusher and Screen Operating Conditions Throughput: 800-1000 #/hr Number of Passes: 4 to 5 Before size reduction:
Yield, Wt.-%
Screen Batch #1 Batch #2 Batch #3 + 20 55 S0 37 After 1st pass at crushing the + 20 from Batch ~3:
Screen Yield, Wt.-%
+ 2072 After 2nd pass using + 20 from 1st ;pass:
Screen Yield, Wt.-%
+ 2083 20/60 9 ,~
After 3rd pass using ~ 20 from 2nd pass:
Screen Yield, Wt.-%
+ 2051 - 60 18 .~.
Overall yield on Batch #3:
Screen Yield, Wt.-%
~ 20 31 ~Z~6~
Product Evaluation Bulk Density:
Loose 44.0 #/ft.3 Packed 47.8 #/ft.3 O'Haus 41 #/ft.3 Absorption:
Oil 0.9 ml/gm Water 0.8 ml/gm Hardness 25.3%
Free Moisture 1.1%
Bound Moisture 11.4%
pH 7.2 Color grey pKa 1.5 negative 3.3 positive Screen Analysis Screen Wt.-%
o ~ 30 17.2 + 40 34.1 50 41.1 6.1 - 60 1.5 The same reactor as in Example 2, above, was used to granulate a mixture of about 60 weight percent Canadian plaster and about 40 weight percent Mississippi brown clay having a particle size passing through a 60-mesh screen.
The foregoing mixture was prepared by blending the afore-mentioned materials in a cement mixer having about four cubic feet capacity.
Turbulizer Operating Conditions Feed Rate: 18g0 #/hr Water Feed Rate: 1.63 gal/min Output: 2700 #/hr, wet 2070 #/hr, dry ~i2~66B
Shaft Speed: 728 rpm Paddle Setting: 45O
Power Draw:20 amps,withsurges to 60 amps, at 240 volts The wet granulated output from the reactor was recovered and dried as a fluidized bed under the following conditions:
Inlet Temperature: 90C.
Final Outlet Temperature: 40C.
Batch Size: 75 # wet T.ime required per Batch: 20-25 min Damper Settings: 100% Inlet 100% Outlet The obtained dry granules were then subjected to size re-duction.
Crusher and Screen Operating Condit:ions Throughput 800-1000 #~hr Number of passes 4 to 5 Before size reduction:
Yield, Wt.-%
_ _ Screen Batch #1 Batch #.2 Batch #3 + 20 54 45 51 After crushing + 20:
_ Yield, Wt.-%
Screen Batch #1 Batch #2 Batch #3 30+ 20 0 0 0 Overall yield of 20/60:
Weighted Batch #1 Batch #2 Batch #3 Average 68~ 60% 70% 68%
i68 Product Evaluation .
Bulk Density:
Loose 44.9 #/ft.3 Packed 49.8 #/ft.3 O'Haus 44 #/ft.3 Absorption:
Oil 0.8 ml/gm Water 0.8 ml/gm Hardness 25.5 Free Moisture 1.1 Bound Moisture 11.0 pH 7.1 Color grey pKa 1.5 negative 3.3 positive Screen Analysis Screen Wt.-%
+ 20 0 ~ 30 19.6 + 40 35.9 ~ 50 37.2 + 60 5.5 - 60 1.8 ; The foregoing specification and data are intended as illustrative of the present invention and are not to be taken as limiting. Variations in processing parameters within the spirit and scope of the invention disclosed hereinabove are possible and will readily present them-selves to one skilled in the art.
Claims (20)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for producing sorbent calcium sulfate dihydrate-containing granules which comprises: providing a particulate charge comprising finely divided calcium sulfate hemihydrate particles having a size that passes through a 60 mesh screen, said charge containing calcium sulfate hemihydrate in an amount of at least about 35 percent by weight of the charge; providing a confined elongated space and generating a generally helical turbulent gas stream within said space; feeding said charge into said gas stream so as to provide a substantially uniform dis-persion of said particles in said gas stream, the space time for the particulate charge within the turbulent gas stream being about 1.4 x 10-4 hours to about 1 x 10-3 hours; introducing into said dispersion an aqueous binder in an amount sufficient to wet and agglomerate said particles, and to initiate hydration of said calcium sulfate hemihydrate while in said dispersion; mechanically agitating said dispersion such that the flow of said dispersion is substantially the same as that of said gas stream so as to pack the wetted particles into granules; and recovering the granules thereby produced.
2. The method of claim 1 wherein said charge contains at least 50 percent by weight calcium sulfate hemihydrate.
3. The method of claim 1 wherein said charge contains solid sorbent particles in addition to calcium sulfate hemihydrate.
4. The method of claim 1, wherein said binder is liquid water and said gas is air.
5. The method of claim 1, wherein said binder is liquid water and said gas is air and the water and particulate charge are fed into said gas stream substantially simultaneously.
6. The method of claim 5 wherein the amount of said water fed into said dispersion is no more than about 25 percent of the weight of said calcium sulfate hemihydrate being fed into said gas stream.
7. A method for producing sorbent calcium sulfate dihydrate-containing granules which comprises: providing a particulate charge comprising sorbent particles having a size that passes through a 60 mesh screen and at least about 35 percent by weight of the charge of plaster of Paris particles mixed therewith mechanically agitating a gas within a confined, elongated space so as to produce a generally helically shaped turbulent gas stream therein; feeding said charge into the produced gas stream at a substantially uniform rate so that the space time for the particulate charge within the turbulent gas stream being about 1.4 x 10-4 hours to about 1 x 10-3 hours; feeding an aqueous binder into the produced gas stream substantially simultaneously with said charge in an amount sufficient to wet the particulate charge and to initiate hydration of said plaster of Paris particles; continuing said agitation for a time period sufficient to form granules; and recovering the produced granules.
8. The method of claim 7 wherein said binder is water and said gas is air.
9. The method of claim 8 wherein said charge contains at least 50 weight percent plaster of Paris.
10. The method of claim 9 wherein said water is fed into said gas stream at a rate such that the weight of water fed is no greater than 25 percent by the weight of said charge being fed.
11. The method of claim 10 wherein said sorbent particles are inorganic materials which are members of the group consisting of an absorbent clay mineral, vermiculite, diatomaceous earth, pumice, Portland cement, gypsum and activated carbon.
12. The method of claim 10 wherein said sorbent particles are sorbent,particulate botanical materials.
13. The method of claim 10 wherein said charge includes absorbent clay in the form of fines in an amount of up to about 50 percent by weight of the charge.
14. The method in accordance with claim 13 wherein said absorbent clay fines are particles having a size that passes through a 60-mesh screen.
15. The method in accordance with claim 13 wherein said absorbent clay fines have particles of a size that passes through a 325-mesh screen.
16. The method in accordance with claim 10 wherein said plaster of Paris has a particle size that passes through a 325-mesh screen.
17. The method in accordance with claim 10 wherein said air stream is at about ambient temperature.
18. The method in accordance with claim 10 wherein the space time for said particulate charge within the turbulent gas stream is about 1.8 x 10 4 hours to about 2.2 x 10 hours.
19. The method in accordance with claim 7 wherein said aqueous binder is steam.
20. The method in accordance with claim 7 wherein said aqueous binder is a liquid and is fed into said gas stream in particulate form.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1492179A | 1979-02-26 | 1979-02-26 | |
| US14,921 | 1979-02-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1129668A true CA1129668A (en) | 1982-08-17 |
Family
ID=21768560
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA341,643A Expired CA1129668A (en) | 1979-02-26 | 1979-12-11 | Granulation process |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1129668A (en) |
| DE (1) | DE3002653A1 (en) |
| GB (1) | GB2045221B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4876091A (en) * | 1986-09-08 | 1989-10-24 | Clarke Jr John L | Gypsum-based insecticide pellets and method of manufacture |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0122010B1 (en) * | 1983-03-07 | 1988-11-02 | Metropolitan Mosquito Control District | Timed release delivery means for delivery of active agent to spatially separated terrain locations and compositions comprised thereby |
| US5339769A (en) * | 1993-07-13 | 1994-08-23 | The Dow Chemical Company | Process for making an absorbent composition |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1189902A (en) * | 1914-05-08 | 1916-07-04 | Charles C Armstrong | Lock or fastening device for hinged box members. |
| US3480387A (en) * | 1966-11-15 | 1969-11-25 | Central Glass Co Ltd | Method for producing gypsum pellets |
-
1979
- 1979-12-11 CA CA341,643A patent/CA1129668A/en not_active Expired
-
1980
- 1980-01-25 DE DE19803002653 patent/DE3002653A1/en active Granted
- 1980-02-22 GB GB8005973A patent/GB2045221B/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4876091A (en) * | 1986-09-08 | 1989-10-24 | Clarke Jr John L | Gypsum-based insecticide pellets and method of manufacture |
| US4917837A (en) * | 1986-09-08 | 1990-04-17 | Clarke Jr John L | Gypsum-based insecticide pellets and method of manufacture |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2045221B (en) | 1983-02-02 |
| DE3002653C2 (en) | 1988-11-24 |
| DE3002653A1 (en) | 1980-09-04 |
| GB2045221A (en) | 1980-10-29 |
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