Creosotes

Higher-boiling fractions supply the creosotes, absorbing oils, anthracene, coal tar fuels, road tar, etc. 

Medicinal creosote is a mixture of phenols, chiefly guaiacol and creosol (4-melhyl-2-meth-oxyphenol), obtained by distillation of wood tar. B.p. 480-500 K. It is almost colourless with a characteristic odour and is a strong antiseptic, less toxic than phenol. 

Guaiacol has a very characteristic odour and burning taste its medicinal properties are identical with those of creosote. Used in the preparation of vanillin and paparvarin and for denaturing alcohol. 

Approximately 50—55% of the product from a coal-tar refinery is pitch and another 30% is creosote. The remaining 15—20% is the chemical oil, about half of which is naphthalene. Creosote is used as a feedstock for production of carbon black and as a wood preservative. Because of modifications to modem coking processes, tar acids such as phenol and cresyUc acids are contained in coal tar in lower quantity than in the past. To achieve economies of scale, these tar acids are removed from cmde coal tar with a caustic wash and sent to a central processing plant where materials from a number of refiners are combined for recovery. 

The coal tar first is processed through a tar-distillation step where ca the first 20 wt % of distillate, ie, chemical oil, is removed. The chemical oil, which contains practically all the naphthalene present in the tar, is reserved for further processing, and the remainder of the tar is distilled further to remove additional creosote oil fractions until a coal-tar pitch of desirable consistency and properties is obtained. 

PermeOx is also used to improve the bioremediation of soils contaminated with creosote or kerosene (see Bioremediation (Supplement)), to deodori2e sewage sludges and wastewater (see Odormodification), and to dechloriaate wastewater and effluents. A special formulation of calcium peroxide, made by FMC and sold ia the United States under the trademark Trap2ene, is used for removing metal ions from acidic waste streams such as coal ash leachate and acid mine drainage (see Wastes, industrial). 

Actual water treatment challenges are multicomponent. For example, contamination of groundwater by creosote [8021-39-4], a wood (qv) preservative, is a recurring problem in the vicinity of wood-preserving faciUties. Creosote is a complex mixture of 85 wt % polycycHc aromatic hydrocarbons (PAHs) 10 wt % phenohc compounds, including methylated phenols and the remaining 5 wt % N—, S—, and O— heterocycHcs (38). Aqueous solutions of creosote are therefore, in many ways, typical of the multicomponent samples found in polluted aquifers. 

Fig. 8. The evolution of stoichiometric quantities of carbon dioxide formed from the total photorninerali2ation of 100 ppm of creosote in water under a saturated oxygen atmosphere. A 25-mL sample having 75.5 wt % C was used. The dashed line corresponds to the expected stoichiometric quantity of CO2.

Area repellents are materials that are intended to keep animals away from a broad area. They include predator scent such as Hon or tiger manure, blood meal, tankage such as putrefied slaughterhouse waste, bone tar oil, rags soaked in kerosene or creosote, and human hair (84). Although few controlled tests have been mn on these materials in the past, more recent investigations of predator odors have shown promise (85). 

A typical primary distillation product pattern at a coke-oven tar-processing plant is given in Table 1. At some coke-oven distilleries, only one fraction, designated naphthalene oil, is taken between 180 and 240°C. Two fractions, light creosote or middle oil (230—300°C) and heavy creosote or heavy oil (above 300°C), are taken between the naphthalene oil and pitch. 

In the case of low temperature tar, the aqueous Hquor that accompanies the cmde tar contains between 1 and 1.5% by weight of soluble tar acids, eg, phenol, cresols, and dihydroxybenzenes. Both for the sake of economics and effluent purification, it is necessary to recover these, usually by the Lurgi Phenosolvan process based on the selective extraction of the tar acids with butyl or isobutyl acetate. The recovered phenols are separated by fractional distillation into monohydroxybenzenes, mainly phenol and cresols, and dihydroxybenzenes, mainly (9-dihydroxybenzene (catechol), methyl (9-dihydtoxybenzene, (methyl catechol), and y -dihydroxybenzene (resorcinol). The monohydric phenol fraction is added to the cmde tar acids extracted from the tar for further refining, whereas the dihydric phenol fraction is incorporated in wood-preservation creosote or sold to adhesive manufacturers. Naphthalene Oils. Naphthalene is the principal component of coke-oven tats and the only component that can be concentrated to a reasonably high content on primary distillation. Naphthalene oils from coke-oven tars distilled in a modem pipe stiU generally contain 60—65% of naphthalene. They are further upgraded by a number of methods. 

Liquid tar products, eg, fight oils, cresols, cresyfic acids, creosote oil, and road tars, are generally transported in bulk in insulated mild-steel road or rail tankers. They are loaded at a temperature sufficiently high to ensure delivery at the desired viscosity. Small quantities are generally delivered in dmms that may have to be steam-heated to ensure complete liquidity before discharge. 

Specifications. Tar bulk products are covered by both national specifications and those formulated by the user. For instance, creosote for timber preservation is covered by the American Wood Preserving Association Standards (AWPA) and ASTM D350. 

In the United States creosote specification AWPA PI/89 is intended for the treatment of timber for land and fresh-water use, and the heavier grade AWPA P13/89 for the preservation of marine piling and timber. In the United Kingdom a British Standard Specification, BS. 144/90, Part 1, specifies three grades of creosote two for pressure impregnation and one for bmshing appHcation. The standards of the West European Institute for Wood Preservation (WEI) are often used in Europe. 

The risk of skin cancer by contact with pitch dust has in more recent years been reduced by the transport and handling of pitch as a Hquid or as dust-free flakes or pencils. Nevertheless, in handling coal-tar products, certain precautions should be taken. These have become obligatory in tar distilleries and plants using pitch or creosote. 

Creosote. In coal-tar refining, the recovery of tar chemicals leaves residual oils, including heavy naphtha, dephenolated carboHc oil, naphthalene drained oil, wash oil, strained anthracene oil, and heavy oil. These are blended to give creosotes conforming to particular specifications. 

Creosote oils are by far the most widely used timber preservatives (see Wood). This use dates back to 1850. Eor the treatment of railway ties and marine pilings, the BetheU or fliU-ceU process is preferred. The timber to be treated is charged to a pressure cylinder, which is evacuated to extract the air from the wood ceUs. The cylinder is then filled with hot creosote and the pressure increased to 0.8—1 MPa (ca 8—10 atm) to force the oil into the ceUs. 

When uptake of the oil has ceased, residual creosote is drained from the cylinder and the treated timber is briefly subjected to a vacuum before discharge. 

Timber-preservation creosotes are mainly blends of wash oil, strained anthracene oil, and heavy oil having minor amounts of oils boiling in the 200—250°C range. Coal-tar creosote is also a feedstock for carbon black manufacture (see Carbon, carbon black). Almost any blend of tar oils is suitable for this purpose, but the heavier oils are preferred. Other smaller markets for creosote were for fluxing coal tar, pitch, and bitumen in the manufacture of road binders and for the production of horticultural winter wash oils and disinfectant emulsions. 

The market for tar-based road binders has declined considerably for a variety of reasons. Less cmde tar is available and the profits from the sales of electrode pitch and wood-preservation creosote or creosote as carbon-black feedstock are higher than those from road tar. In most industrial countries, road constmction in more recent years has been concentrated on high speed motorways. Concrete, petroleum bitumen, or lake asphalt are used in the constmction of these motorways. In the United Kingdom, for example, the use of tar products in road making and maintenance had fallen from 330,000 t in 1960 to 100,000 t in 1975 and is less than 100 t in 1994, mainly based on low temperature pitch which is not suitable for electrode or briquetting binders, but which is perfectly satisfactory as the basis for road binders. 

Wood preservatives ate appHed either from an oil system, such as creosote, petroleum solutions of pentachlorophenol, or copper naphthanate, or a water system. Oil treatments ate relatively inert with wood material, and thus, have Htde effect on mechanical properties. However, most oil treatments require simultaneous thermal treatments, which ate specifically limited in treating standards to preclude strength losses (24). 

The best protection for wood against the attack of decay fungi, insects, or marine borers is obtained by applying preservatives under pressure before installation (61,62). Both oil-type preservatives, such as creosote or petroleum solutions of pentachlorophenol, and waterborne preservatives, such as copper-chrome arsenate and ammoniacal-copper arsenate, are used when wood is to be in direct contact with the ground or in the marine environments. 

The principal sources of feedstocks in the United States are the decant oils from petroleum refining operations. These are clarified heavy distillates from the catalytic cracking of gas oils. About 95% of U.S. feedstock use is decant oil. Another source of feedstock is ethylene process tars obtained as the heavy byproducts from the production of ethylene by steam cracking of alkanes, naphthas, and gas oils. There is a wide use of these feedstocks in European production. European and Asian operations also use significant quantities of coal tars, creosote oils, and anthracene oils, the distillates from the high temperature coking of coal. European feedstock sources are 50% decant oils and 50% ethylene tars and creosote oils. 

Imperial Chemical Industries in Great Britain hydrogenated coal to produce gasoline until the start of World War II. The process then operated on creosote middle oil until 1958. As of this writing none of these plants is being used to make Hquid fuels for economic reasons. The present prices of coal and hydrogen from coal have not made synthetic Hquid fuels competitive. Exceptions are those cases, as in South Africa, where there is availabiHty of cheap coal, and fuel Hquids are very important. 

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