METHOD AND COMPOSITIONS FOR THE CONTROL OF DUST

Abstract: Dust is suppressed by contacting a dust-producing material with an emulsion containing (a) 20-99.5% of water and, correspondingly, (b) 80-0.5% of a composition compris­ ing from 0.1% to 20% of at least one methacrylate polymer, a minimum of 70% of at least one hydrophobic liquid and 0.01% to 10% of at least one emulsifying surfactant, all percentages being by weight. The above described emul­ sions and the composition (b) are novel.

Description: This invention relates to dust suppression. More particularly, though not exclusively, it relates to coal dust suppression. The term "dust suppression" as used herein, means the prevention or reduction of the extent to which fine particules become airborne or suspended in air. Dust is generated in significant quantities during the mining, handling, transportation, and storage of coal and coal refuse; dust is also generated during the processing, transportation and handling of such materials as rock, ores (for example iron ore), grains, taconite, sulphur, copper, limestone, gypsum, fly ash, cement, bauxite, ash, sinter, coke, mineral concentrates and fertilizers (such as potash and phosphates). Road dust is also a problem. In coal-mining applications, mechanical and chemical methods for dust control are known. For example, dust-collection equipment is used in mining operations. Also, water is commonly used to prevent dust particles from becoming airborne. Additionally, aqueous solutions containing surfactants may be used for dust control (see U.S. Patents US-A-3,690,727 and US-A-4,136,050). Aqueous foam compositions have also been used to suppress dust (see U.S. Patents US-A-3,954,662, US-A-4,000,992 and US-A-4,400,220). U.S. Patent US-A-4,316,811 discloses the use of an aqueous solution of polyethylene oxide for dust control. U.S. Patent US-A-4, 169,170 discloses the use of an aqueous composition comprising an asphalt emulsion or a black liquor lignin product and a water-soluble methoxylated alkylphenol or sulphosuccinate wetting agent to form a crust layer, which provides protection against the loss of coal due to wind or the action of a coal-transportation device. The present invention provides a composition comprising from 0.1% to 20% of at least one methacrylate polymer, a minimum of 70% of at least one hydrophobic liquid and 0.01% to 10% of at least one emulsifying surfactant, all percentages being by weight. Also in accordance with the invention 20-99.5% by weight of water and, correspondingly, 80-0.5% by weight of such a composition, are formed into an emulsion, and such emulsions constitute another embodiment of the present invention. Also in accordance with the present invention, the emulsion is used to provide a dust suppressant. It has excellent penetration, binding and wetting properties and also provides efficient and inexpensive coverage of the material being treated. After application, the dust control agent provides a tacky water-resistent coating which effectively prevents dusting while additionally acting as an antifreeze agent. The present invention provides excellent dust suppression relative to contemporary dust suppressants, and can be used to control dusting and windage loss at stock piles and during material handling and transport. It is also effective when applied to hauling roads around coat preparation plants, mills and mining sites. The emulsions and method of the invention constitute a notable advance in the art since they minimize the disadvantages of commonly used dust suppressants, such as compositions comprising water and surfactants. These disadvantages include (1) low persistence: with light usage, dust control may be only temporary due to evaporation; (2) adverse affect on BTU (calorific) values: with heavy application, the effective BTU value of the coal being treated may be reduced; (3) expense: known coal-dust suppressants are costly; (4) freezing: many coal-dust suppressants currently in use do not aid in the prevention of freezing, and may, in fact contribute to it; and (5) spontaneous combustion: conventional coal-dust suppressants may contribute to spontaneous combustion due to the heat of wetting. The amount of emulsion that is effective in inhibiting or eliminating dusting of the material being treated is at least 0.1 Kg of emulsion per metric ton of the material on a total solids basis. For surface treatment, at least 0.1 Kg of emulsion/m² surface area of the material being treated must be added. Preferred dosages are 0.1-80 Kg per metric ton and 0.1-50 Kg/m² for total contact and surface treatment, respectively. Especially preferred dosages are 2-20 Kg/metric ton and 2-15 Kg/m², for total contact and surface treatment, respectively. The emulsions are prepared by first combining at least one methacrylate polymer with at least one hydrophobic liquid. For use, this admixture may then be emulsified into water by use of at least one emulsifying surfactant, which is preferably added to the methacrylate polymer/hydrophobic liquid composition. An effective amount of emulsifying surfactant must be used, with the term "effective amount" referring to that concentration of surfactant or surfactants necessary to provide a consistent stable emulsion. The preferred emulsifying surfactant dosage ranges from 0.1-6% by weight of the polymer/hydrophobic liquid/surfactant composition. Any methacrylate polymer can be used. As used herein, "methacrylate polymers" are those polymers prepared from (1) one or more monomers having the generic formula CH₂=C(CH₃)COOR, where R is a straight or branched C₁₋₁₂, preferably C₄₋₁₂, alkyl group or (2) one or more of the above-described monomers in combination with any monomer having the generic formula CH₂=CH-COOR¹, where R¹ is any straight or branched C₁₋₆ alkyl group, alone or in combination. Additionally, R and R¹ include straight or branched alkyl groups such as 2-ethylhexyl and 2-ethylbutyl, in which from one to three of the hydrogens of the above defined straight or branched alkyl groups is/are replaced by a methyl, ethyl or propyl group. Thus, the backbone of R may contain up to 12 carbon atoms, and methyl, ethyl or propyl groups may be substituted for up to 3 of the hydrogens on these 12 carbon atoms. Similarly, for R¹, the backbone of R¹ may contain up to 6 carbon atoms, and methyl, ethyl or propyl groups may be substituted for up to three of the hydrogens on these 6 carbon atoms. Preferred methacrylates are homopolymers of methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, 2-ethyl butyl methacrylate, and 2-ethylhexyl methacrylate, including all their isomers. The especially preferred methacrylates are homopolymers of 2-ethyl hexyl methacrylate and isodecyl methacrylate. Molecular weight of the methacrylate is not critical. However, it is preferred that the methacrylate have a molecular weight in excess of 2,000, as determined by light-scattering techniques. The term hydrophobic liquid, as used herein, is defined as a liquid that is not miscible with water. Any hydrophobic liquid can be used. The preferred hydrophobic liquids are mineral oils, fuel oils, diesel fuels or oils, kerosene, naphthas, petroleums, and blends of aromatic and aliphatic hydrocarbons containing four or more carbon atoms in the molecule, alone or in combination. The especially preferred hydrophobic liquids are fuel oils, diesel fuels or oils, kerosene, and mixtures of such liquids. Preferred compositions contain, by weight, 0.1 to 10% of at least one methacrylate polymer on an active basis, 0.1 to 6% of at least one emulsifying surfactant and at least 84% of at least one hydrophobic liquid. These compositions preferably comprise 30-70% by weight of the emulsions, with the balance being water. Blends of methacrylates can be used, as can blends of various hydrophobic liquids. For example, a composition comprising a methacrylate polymer and kerosene may be prepared. The kerosene improves the viscosity properties of the methacrylate polymer. This composition may be further diluted with a second hydrophobic liquid, e.g. a diesel fuel to number 5 fuel oil. The second hydrophobic liquid is preferably heavier and more viscous than the kerosene, thereby promoting better binding of the fine dust particles. The kerosene:heavy second oil ratio in the above composition can range from 1:20 to 20:1, preferably 1:10 to 10:1 and especially 1:1 to 1:6, on a weight basis. The total weight of the hydrophobic phase, however, remains at at least 70% by weight of the polymer/hydrophobic liquid/surfactant composition. The emulsions are oil-in-water emulsions, i.e. water is the continuous phase and the hydrophobic liquid is the dispersed phase. Any surfactant that functions as an emulsifier can be used. The emulsion preferably comprises, by weight, 30%-70% especially 45-55%, water and 70%-30%, especially 55-45%, hydrophobic liquid/polymer/emulsifying surfactant composition. However, emulsions comprising up to 99.5% water can be used in certain applications, such as when coal having a moisture content greater than 10% is being treated. Nonionic or anionic emulsifying surfactants can be used, alone or in combination. Nonionic emulsifying surfactants must have high HLB (hydrophile-lipophile balance) numbers, i.e. HLB values greater than or equal to 8.0. High HLB values indicate that these surfactants are strongly hydrophilic, and that they are good oil-in-water emulsifiers. Additionally, the preferred emulsifying surfactants should have good wetting, binding and penetration characteristics. The preferred emulsifying surfactants are (1) nonionic surfactants having an HLB value greater than 8.0, such as polyoxyethylene ethoxylates, polyethylene glycol ethers, alcohol ethoxylates, and alkyl phenyl ethoxylates; and (2) anionic surfactants such as phosphate ester-containing surfactants, sulphosuccinates, alkyl sulphates, ethoxylated alkyl phenol sulphates, alkyl ether sulphates, fatty ester sulphates, sulphated alcohol ethoxylates, and their salts. Especially preferred are polyethylene glycol ethers of linear alcohols, alkyl phenol ethoxylates, phosphate ester-containing surfactants, alkyl ether sulphates and sulphosuccinates, and their salts, e.g. sodium and potassium salts. Preferred examples of polyethylene glycol ethers of linear alcohols include, but are not limited to, those sold under the trade marks Tergitol 155-5, Tergitol 155-7 and Tergitol 155-9, all of which are available from Union Carbide Corporation, and which have 5, 7 and 9 moles EO and approximate HLB values of 10.5, 12.1 and 13.3, respectively. A preferred alkyl phenol ethoxylate is an ethoxylated octyl phenol (degree of ethoxylation, n = 10) having an HLB value of approximately 13.5. A preferred example of a phosphate ester-containing surfactant is sold under the trade mark Gafac RS-610, which is described as a phosphate ester free acid with an aliphatic hydrophobic base, which is available from GAF Corporation. Preferred alkyl ether sulphates are sodium salts of alkyl ether sulphates. Preferred examples of sulphosuccinates include sodium dioctyl sulphosuccinate, such as that sold under the trade mark Aerosol OT-75, disodium ethoxylated alcohol hemi-ester of sulphosuccinic acid, such as that solid under the trade mark Aerosol A-102, and disodium ethoxylated nonylphenol hemi-ester of sulphosuccinic acid, such as that sold under the trade mark Aerosol A-103, all available from American Cyanamid Company. Combinations of emulsifying agents may also be used to formulate the dust suppressants of the invention. The final emulsification step can be and preferably is conducted at the dust treatment site. This method saves the cost of transporting water. Thus, a composition of the invention comprising at least one methacrylate polymer, at least one hydrophobic liquid and at least one emulsifying surfactant is prepared and transported to the treatment site. Immediately prior to application, the composition is emulsified into water. The water is used as an inexpensive means to transport and distribute the dust suppressant. Water may form 20-99.5%, by weight, of the final emulsion. The amount of water may be optimized, however, so as not to substantially lower the BTU value of the dust suppressant or cause freezing in cold temperatures. The emulsion can be formulated using any of several known technologies, including injection of the composition into a water line, which may or may not contain an in-line mixing device, or use of an agitated vessel. The dust-suppressant emulsions of the invention are suitable for use on any material prone to create dust, including rock, ores (such as iron ore), taconite, sulphur, copper, limestone, gypsum, flyash, cement, bauxite, ash, sinter, coke, mineral concentrates and fertilizers, including but not limited to potash and phosphate fertilizers. These emulsions are also excellent agents for the control of road dust. If the material being treated is water-soluble, the water content of the emulsion should be minimized. In such cases, 20-30% water, by weight, is preferred. The dust suppressant emulsions of the invention are especially effective when applied to coal by any of the commonly known techniques, including spraying or otherwise contacting the coal with the dust-suppressant emulsions. Spraying is preferred. Preferably, all of coal being treated, i.e. not only its surface, such as the surface area of a pile of coal or the coal in a railway waggon, is contacted with the emulsion. Thus, a preferred method of treating coal is to spray the coal with the emulsion while loading it into or onto a transportation device, such as a railway waggon, lorry or conveying system. However, surface spraying can also be used. Use of the dust suppressants of the invention minimizes or eliminates dusting of the coal during transport and subsequent handling while additionally protecting against freezing and possibly enhancing the BTU value of the coal. Dust suppression is excellent due to the persistence of the emulsions, their exceptional penetrating qualities and their ability to agglomerate and bind fine coal particles, i.e. those less than 10 µm in diameter, to more coarse coal. Also, emulsions containing up to 50% water may enhance the BTU value of the coal, while providing freeze protection. Additionally, the compositions of the present invention can be used without water in applications where water cannot be tolerated or is undesirable. The following Examples are illustrative. All parts and percentages are by weight unless otherwise stated. EXAMPLES 1-6 Coal dust suppressant emulsions were prepared by mixing 250 g diesel fuel with 50 g of a composition comprising 6% 2-ethylhexyl methacrylate polymer and 94% kerosene. 3 g (active basis) of an emulsifying agent was then added. (Various emulsifiers were used, as shown below). Acceptable emulsifying agents produced stable dispersions of the composition into water, on a 1:1 weight basis (i.e. 303 g of water). The following surfactants were used: Aerosol OT-75, which is a 75% active sodium dioctyl sulphosuccinate, available from American Cyanamid Company; Tergitol 15S-3, 15S-5, 15S-7 and 15S-9, which are polyethylene glycol ethers of linear alcohols having 3, 5, 7 and 9 moles of EO, respectively, available from Union Carbide Corporation. EXAMPLES 7-15 Transportation tests were run on sub-bituminous coals being shipped via rail. The coal of Examples 7-14 had an inherent moisture level of approximately 8% and an energy value of approximately 6,000 Kcal/metric ton (25J/kg). The coal of Example 15 had an inherent moisture level of approximately 10.5% and an energy value of approximately 5700-5800 Kcal/metric ton (24J/kg). The journey in each case was approximately 800 miles (1288 km). Dust suppression efficacy was recorded at the unloading site. Results are shown in Table 2, below. In Examples 7-15, the following dust suppressants were evaluated: water, DCF-20 foam (commercially available from Calgon Corporation, Pittsburgh, Pennsylvania), ammonium lignosulphonate (commercially available from Alchem, Inc., as Alchem, (3WF943), calcium lignosulphonate (commercially available from Benetech, Inc.), DCL-1870 anionic surfactant (commercially available from Calgon Corporation), Alchem 8 A08 polymer binder (commercially available from Alchem, Inc.), the emulsion of Example 2 and a 1:99 hydrophobic liquid-surfactant-polymer:water emulsion (weight:weight basis) which contained 1% of the kerosene/diesel fuel/Aerosol OT-75/2-ethyl hexyl methacrylate admixture of Example 2 and 99% of water.

Claims: A composition for use in dust suppression comprising from 0.1% to 20% of at least one methacrylate polymer, a minimum of 70% of at least one hydrophobic liquid and 0.01% to 10% of at least one emulsifying surfactant, all percentages being by weight. A composition as claimed in Claim 1, in which the methacrylate polymer is (1) one or more monomers having the generic formula CH₂=C(CH₃)COOR, where R is a straight or branched C₁₋₁₂ alkyl group or (2) one or more of the above-described monomers in combination with any monomer having the generic formula CH₂=CH-COOR¹, where R¹ is a straight or branched C₁₋₆ alkyl group, alone or in combination, or (3) one or more monomers of group (1) or group (2) where R and R¹ are as defined above except that 1, 2 or 3 of the H atoms of R or R¹ is replaced by a C₁₋₃ alkyl group. A composition as claimed in Claim 1 or 2 in which the hydrophobic liquid is one or more of mineral oils, fuel oils, diesel fuels or oils, kerosene, naphthas, petroleums and blends of aromatic and aliphatic hydrocarbons containing four or more carbon atoms in the molecule. A composition as claimed in Claim 3 in which the hydrophobic liquid comprises kerosene and a second, heavier component that is a diesel fuel or oil or a fuel oil. A composition as claimed in any preceding claim in which the emulsifying surfactant is one or more nonionic surfactants having an HLB value greater than 8.0 and/or one or more anionic surfactants that is a sulphosuccinate, phosphate-ester-containing surfactant, alkyl sulphate, ethoxylated alkyl phenol sulphate, alkyl ether sulphate, fatty ester sulphate or sulphated alcohol ethoxylate, or salt thereof. A composition as claimed in Claim 1 in which the methacrylate polymer is a homopolymer of 2-ethylhexyl methacrylate or isodecyl methacrylate, the hydrophobic liquid is kerosene, a diesel oil or fuel, a fuel oil, or a combination thereof, and the emulsifying surfactant is a polyethylene glycol ether of linear alcohols having at least 5 moles EO, ethoxylated octyl phenol, sodium dioctyl sulphosuccinate, a disodium ethoxylated alcohol hemi-ester of sulphosuccinic acid, a disodium ethoxylated nonyl phenol hemi-ester of succinic acid, a phosphate ester free-acid with an aliphatic hydrophobic base, or a sodium salt of an alkyl ether sulphate. An emulsion useful as a dust suppressant containing, (a) 20-99.5% of water and, correspondingly, (b) 80-0.5% of a composition as claimed in any preceding claim. An emulsion as claimed in Claim 7, comprising, by weight, (a) 30-70% water (b) the balance a composition comprising 0.1-10% of at least one methacrylate polymer on an active basis, 0.1-6% of at least one emulsifying surfactant and at least 84% of at least one hydrophobic liquid. A method of suppressing dust, comprising contacting a dust-producing material with an effective amount of an emulsion as claimed in Claim 7 or 8. A method as claimed in Claim 9 in which the dust-producing material is coal, rock, ores, taconite, sulphur, copper, limestone, gypsum, fly ash, cement, bauxite, ash, sinter, coke, a mineral concentrate, a fertilizer or road dust. A method of suppressing coal dust, comprising contacting coal with an emulsion comprising (a) 20-99.5% by weight water and (b) the balance a composition as claimed in Claim 6, in which the emulsion is added at a dosage of at least 0.1 Kg/metric ton on a total solids basis or at a dosage of at least 0.1 Kg/m² on a surface area basis.

Inventors: REY, PAUL A., ROBERTS, BRIAN G.
Applicants: CALGON CORPORATION
Application year: 1986
Main classification: C10L9
IPC codes: C08L33, C10L10, C10L9, C08L21, B65G69, C10L5, C08L7, B65G3, C09K3