Powdered economics

The economics of recycling PET are more favorable than recycling HDPE. To iacrease the recycling of HDPE, the separation of bottles made of these two plastics could be omitted and a mixture processed. Coarse, light-colored powders of the two polymers have been prepared by an experimental soHd state shear extmsion pulverization process (55). The powder has been successfully injection molded without pelletization. 

Trends in the field of economics are the centralization of the powder fabrication to enable production on a large scale and the manufacture of low quahty anisotropic materials by a much less expensive technology. An example of the latter is the introduction of alignment during pressing of the raw material mixture in the fabrication route of isotropic materials. 

Bulk Density. Bulk density, or the apparent density, refers to the total amount of space or volume occupied by a given mass of dry powder. It includes the volume taken up by the filler particles themselves and the void volume between the particles. A functional property of fillers in one sense, bulk density is also a key factor in the economics of shipping and storing fillers. 

Economic Jispects. Sodium borohydride is produced ia large quantities mainly as powder and stabilized water solution. Potassium borohydride powder is produced ia lesser amounts. Commercial quantities of sodium borohydride powder sell for ca 55/kg (1992 price) the 12% solution ia caustic soda is priced at ca 47/kg of contaiaed NaBH. ... 

Economic Aspects. The estimated total worldwide market for tartaric acid is 58,000 t and potassium bitartrate (acid basis) is 20,000 t. The majority of tartaric acid consumption, represented by beverage, food, and pharmaceutical appHcations, is shown in Table 10. Potassium bitartrate (cream of tartar) is primarily used in baking powders and mixes. 

Although most lime is sold as quicklime, production of hydrated lime is also substantial. This product is made by the lime manufacturer in the form of a fluffy, dry, white powder, and its use obviates the necessity of slaking. Small lime consumers caimot economically justify the additional processing step that hydration entails. 

Fused-salt electrolysis of K2NbFy is not an economically feasible process because of the low current efficiency (31). However, electrowinning has been used to obtain niobium from molten alkaU haUde electrolytes (32). The oxide is dissolved in molten alkaU haUde and is deposited in a molten metal cathode, either cadmium or zinc. The reaction is carried out in a ceramic or glass container using a carbon anode the niobium alloys with the cathode metal, from which it is freed by vacuum distillation, and the niobium powder is left behind. 

The second and third reactions are economical, but the first is not. The second reaction is used in a process where HCN is oxidized to (CN)2 and hydrolyzed in the presence of a strong acid catalyst to give oxamide. The third reaction is employed in a newly developed process where diaLkyl oxalates are converted to oxamide by the ammonolysis reaction. This reaction easily proceeds without catalysts and quantitatively gives oxamide as a powder. 

It maybe economical, therefore, to use these materials at or near the cutting edge instead of as the whole insert. The development of tools of TiC (40—55%) or TiN (30—60%) in a steel matrix on a steel core using powder metallurgy technology suggests a similar approach for cemented carbides as the need arises. 

Beneficiation (2,11,12,21—27) iavolves a process or series of processes whereby the chemical and/or physical properties and characteristics of raw materials are modified to render the raw material more processible. The extent of beneficiation is determined by a combination of the starting raw materials, the processiag scheme, the desired properties of the product, and economics. Powder cost iacreases with iacreased beneficiation consequently, low value-added clay raw materials used to produce iaexpensive stmctural clay products typically undergo a minimum of beneficiation, whereas higher value-added alumina powders undergo more extensive beneficiation. 

Economic Aspects. The production of bleaching powder has been steadily declining. Peak U.S. production was 133,400 metric tons ia 1923 it decreased to 23,600 t ia 1955 and has not been reported siace. Imports, averagiag 1160 t duriag 1980—1987, came from ladia, Spaia, the Uoited Kiagdom, Germany, and Canada (220). It is probably also manufactured ia some less developed couatries. 

Specific Toothpaste Formulations. Two types of toothpaste formulation predominate. Type 1 is alow abrasive—high solvent toothpaste (Table 1) type 2 is a high abrasive—low solvent toothpaste (Table 2). The most important differences are the ratio of humectant to abrasive and the nature of the abrasive. Type 1 dentifrices were introduced nationally to the U.S. market in 1970 and now constitute the predominant type. Type 2 dentifrices represent a popular earlier formulation, in which economic and scientific considerations related to the abrasive and humectant favored use of a maximum amount of the abrasive component. AH type 1 dentifrices of the early 1990s contain an amorphous hydrated siUca powder as the abrasive. Type 2 dentifrices may contain one or more of many insoluble minerals. 

Economic Aspects. The production of ethyl ether from 1956 through 1973 ranged from 29.5 to 48.6 x 10 kg as reported by Synthetic Organic Chemicals, U.S. Production and Sales. Production was estimated at 13.6-18 X 10 kg in 1986, 12.7 X 10 kg in 1989. Though 1990 U.S. production capacity was estimated at 25.5 x 10 kg, production was estimated as only 12 x 10 kg in 1991 (21). Much of the decrease has been the result of a decline in arsenal demand (smokeless gun powder). List prices for ether have been steadily increasing, and reached 1.12/kg by 1989, refined, tanks (fob). 

The economics seem to be better for systems where dry powdered fresh hme plus ground recycled hme is injected along with a relatively coarse spray which impinges on and dries out from the reagent, as described by Stouffer et al. [Hs EC Res., 28(1) 20 (1989)]. Witnum et al. [9th Ann. Pitt. Coal Prep. Util. Euv. Control Contractors Conf. (1993)] describes an advanced version of that system that has been further optimized to the point that it is competitive with wet hme-stone scrubbing for >90 percent flue gas desirffurization. 

The Majac jet pulverizer (Ho.sokawa Micron Powder Sy.stems Div.) is an opposed-jet type with a mechanical classifier (Fig. 20-55). Fineness is controlled primarily by the classifier speed and the amount of fan air dehvered to the classifier, but other effects can be achieved by variation of nozzle pressure, distance between the muzzles of the gun barrels, and position of the classifier disk. These pulverizers are available in 30 sizes, operated on quantities of compressed air ranging from approximately 0.6 to 13.0 mVmin (20 to 4500 ftV min). In most apphcations, the economics of the use of this type of jet pulverizer becomes attractive in the range of 98 percent through 200 mesh or finer. 

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