The generation of dust during transport and handling of material has long been recognized as an economic loss and a health hazard. In general there are four ways to prevent dust generation using a chemical solution. Two are temporary: using foam to form a physical blanket over the material, usually when it is on a conveyor belt, or using surfactants in water to wet the dusting material and prevent dust generation through multiple handling points. These remedies last only as long as the foam remains intact or the material remains wet. The second two approaches focus on longer-term dust control. They involve applying a chemical binder to the surface of a stock pile or railcar to form a crust, preventing wind-born loss, or to treat the entire mass of material with a binder, cementing the smaller dust particles to larger particles on a semi-permanent basis. The former approach, depending on the choice of binder, can form a crust lasting over a year. The latter, depending on the choice of binder, can render a dusting material effectively non-dusting for a time ranging from days to months. We report here an improvement of the latter technology.
There have been any number of compositions put forth over many decades to address this. Most of these center around handling coal. As early as 1931, Wallace (U.S. Pat. No. 1,910,975) taught the application of hygroscopic sugary materials such as molasses to prevent dusting in coal. Of greater note is Work et. al.'s (U.S. Pat. No. 2,250,287) 1940 recognition that a “ . . . strong, abrasion-resistant coating . . . ” was preferred as a dust-proofing agent for coal. While the use of calcium chloride and other hygroscopic salts to retain moisture on coal had been previously taught, in 1943 Kleinicke et al. (U.S. Pat. No. 2,436,146) added organic gels such as starch, gelatin, or agar to enhance the performance of these salts. More recently, Trechock et al. (U.S. Pat. No. 3,711,318) taught the use of film-forming compositions including sodium silicate, asphalt, coal tar, and molasses to substantially reduce <325 mesh dust production on coke briquettes. In 1974, Salyer et al. (U.S. Pat. No. 3,954,662) taught the use of copolymers of vinyl esters and unsaturated dicarboxylic acids and anhydrides with wetting agents to suppress dust on coal. Beck et al. (U.S. Pat. No. 4,055,471) reported the use of waste sulfite liquor (lignosulfonates) to suppress dust on coal before feeding it to a coking oven. It is worth noting that at about this time, Callahan et al. (U.S. Pat. No. 4,369,121) reported the use of water-soluble nonionic cellulose ethers to form a pile seal over the surface of stockpiles, however he did not teach the use of this composition as a dust-proofing agent for treating the bulk of the aggregate, nor did his composition contain a plasticizer. Shimizu et al. (U.S. Pat. No. 4,428,984) later taught the use of a polyhydridic alcohol; preferably glycerin, and a wetting agent as a dust-reducing treatment. Fenton (U.S. Pat. No. 4,469,612) taught the use of polyacrylates and copolymers of acrylics as dust agglomerating agents specifically for use with oil-shale derived fines. Kittle (U.S. Pat. No. 4,561,905) taught the use of foamed heavy process oil to suppress coal dust. At almost the same time, Siddoway et al. (U.S. Pat. No. 4,582,511) taught the use of sugar or molasses as a body treatment to suppress coal dust. Yan's (U.S. Pat. No. 4,462,196) use of a gelatinized starch illustrates yet another possible composition for suppressing coal dust. Roberts et al. (U.S. Pat. No. 4,650,598) taught the advantage of adding a small amount of a polyacrylate or polymethacrylate to kerosene in an oil in water emulsion for dust control on coal. This is very similar to Roe's (U.S. Pat. No. 4,780,233) teaching of using polyisobyutlyene to enhance the effectiveness of oil in an oil in water emulsion for dust control. The two previous patents taught the use of kerosene or mineral-based oils and this contrasts with Zinkan's (U.S. Pat. No. 4,801,635) approach of using anionic and nonionic water soluble (non-cellulosic) polymers with a wetting agent. Returning to petroleum-based compositions, Wajer et al. (U.S. Pat. No. 5,192,337) taught the use of petroleum resin diluted with mineral oil to reduce dusting on coal. Roe et al. (U.S. Pat. No. 5,194,174), at roughly the same time, taught the use of polyvinyl alcohol with cross-linkers, wetting agents, and plasticizers for dust control. Of particular note is the work of Winstanley et al. (U.S. Pat. No. 5,223,165), which teaches the use of alkyl glycosides for dust control. While the alkyl glycosides are wetting agents and the focus of the patent, the use of hydrophilic binders including cellulose derivatives in combination with the wetting agents is taught. Again, nowhere is there any mention of the use of a plasticizer to enhance dust suppression. Roe (U.S. Pat. No. 5,271,859) discussed dust control methods at high temperature; that is, greater than 250° F., using nonionic cellulose ethers. There are additional patents covering the use of a variety of binders to render materials non dusting. Included in that list would be teachings related to the use of cationic polymers (Roe, U.S. Pat. No. 5,256,444); lignosulfonate plus additives (Bennet, U.S. Pat. Nos. 5,310,494; 5,578,239); hydrated grain endosperm (Rogers et al., U.S. Pat. No. 5,658,486); distillation bottoms from 1,6-hexanediol production (McNabb et al., U.S. Pat. No. 5,820,787); and molasses and oil or simply molasses protein (Rahm et al., U.S. Pat. No. 6,086,647; Wolff et al., U.S. Pat. No. 6,790,245).
From the references set forth above, it is apparent that there are a variety of options available to render a material non-dusting. However the majority of the above treatments rely on a strong binder to perform their function. As was taught by Work et al. in 1940, strength is essential as it relates to the basic mechanism by which dust is suppressed. Dust is suppressed when a composition binds the loose particles of the bulk material together. The stronger the bond between the bulk material particles, the less likely dust will separate from the substrate on mechanical agitation.
Of note to this disclosure is Roe's (U.S. Pat. No. 5,271,859) teaching of the use of water-soluble cellulose ethers with an additional wetting agent or plasticizer at temperatures above 250° F. as a dust palliative. In particular, Roe's claimed invention specifically calls for the addition of either a plasticizer or a wetting agent but not both.
Water-soluble cellulose ethers are well-known in the coatings industry. Their behavior with plasticizers has been studied extensively. As long ago as 1940 it was recognized that the addition of a plasticizer weakened the tensile strength of cellulose ether films (Kropscott, U.S. Pat. No. 2,226,823). Oakley (U.S. Pat. No. 2,653,108) made a similar observation. More recently Part et al. (Park, H. J., Weller, C. L., Vergano, P. J., and Testin, R. F.; Journal of Food Science, 58, #6, 1993 pp 1361-1364) quantified the same behavior specifically in methyl cellulose and hydroxypropyl methyl cellulose using, among other plasticizers, propylene glycol and glycerin (2,3-hydroxy-1-propanol). A DOW Corporation website discusses not only strength, but film toughness and Young's Modulus (http://dowwolff.custhelp.com/app/answers/detail/a_id/2357/˜/methocel-effect-of-plasticizers-on-film-properties-in-tablet-coatings). In every case the addition of glycerin or propylene glycol weakened the films. It is therefore a surprising and unexpected result that the addition of a plasticizer to dust control formulas similar to those described by Roe would result in improved strength.
The present invention is provided to solve the problems discussed above and other problems, and to provide advantages and aspects not provided by prior dust suppression fluids of this type. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings.