Tar, Distillation Fractions

Polynuclear aromatic hydrocarbons (PAH) (a coal-tar distillate fraction) — Solvent extraction and determination by HPLC, GC-FID or GC/MS enzyme immunoassay testing may be applied for semiquantitive determination. 

Anthracene and phenanthrene are stereoisomers that are crystals in pure form. Anthracene is a pale yellow crystal, while phenanthrene exhibits a yellow to brown hue. Besides its common name, anthracene is referred to as anthracin, green oil, or paranaphthalene. The compound is commercially produced by recovery from the coal tar distillation fraction known as anthracene oil or green oil. Anthracene is the key ingredient in the production of anthraquinone. However, it and phenanthrene are also used for the manufacture of dyes, fibers, plastics, and wood preservatives. ° Phenanthrene, also known as phenanthrin, can be produced by high-temperature fractional distillation of coal tar oil. It is additionally used for the oxidation of diphenic acid for use in polymers, as well as the production of chemical softeners, explosives, and some pharma-ceuticals. Recent research has extended the application of both isomers to scintillation counters, semiconductors, and photoconductors. ... 

From a more practical viewpoint, the solvent extraction of bituminous coals has been used as a means of coproducing clean liquid transportation fuels as well as solid fuels for gasification. Coal solvents are created by hydrogenating coal tar distillate fractions to the level of a fraction of a percent, thus enabling bituminous coal to enter the liquid phase under conditions of high temperature (above 400°C [750°F]). The pressure is controlled by the vapor pressure of the solvent and the cracked coal. Once liqnefied, mineral matter can be removed via centrifnga-tion, and the resultant heavy oil prodnct can be processed to make pitches, cokes, as well as lighter products. 

Morgan, T.J., George, A., Alvarez, R, Millan, M., Herod, A.A., Kandiyoti, R. (2008) Characterization of molecular mass ranges of two coal tar distillate fractions (creosote and anthracene oils) and aromatic standards by LD-MS, GC-MS, probe-MS size exclusion chromatography. Energy Fuels, 22, 3275-3292. 

Crude tar is normally distilled in continuous plant into distillate fractions which can vary in boiling range and in name, leaving pitch as a residue. 

The conditions of pyrolysis either as low or high temperature carbonization, and the type of coal, determine the composition of Hquids produced, known as tars. Humic coals give greater yields of phenol (qv) [108-95-2] (up to 50%), whereas hydrogen-rich coals give more hydrocarbons (qv). The whole tar and distillation fractions are used as fuels and as sources of phenols, or as an additive ia carbonized briquettes. Pitch can be used as a biader for briquettes, for electrode carbon after coking, or for blending with road asphalt (qv). 

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. 

There are two serious problems associated with continuous tar distillation. Coal tar contains two types of components highly corrosive to ferrous metals. The ammonium salts, mainly ammonium chloride, associated with the entrained Hquor remain in the tar after dehydration, tend to dissociate with the production of hydrochloric acid and cause rapid deterioration of any part of the plant in which these vapors and steam are present above 240°C. Condensers on the dehydration column and fractionation columns are also attacked. This form of corrosion is controlled by the addition of alkaU (10% sodium carbonate solution or 40% caustic soda) to the cmde tar in an amount equivalent to the fixed ammonia content. 

Carbolic Oils and Tow Temperature Tar Middle Oil, TarMcids. The fractions of some coke-oven tars, distilling in the range of 180—240°C, and the middle oil fraction (180—310°C) from low temperature tars are treated for the recovery of tar acids (19). 

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. 

These specifications include specific gravity, maximum water content, maximum values for toluene- or ben2ene-insoluble material, and maximum amounts distilling at 230°C, 270°C, 315°C, and 355°C. In the case of the AWPA specifications, there are minimum limits to the specific gravities of each of the distillate fractions in the case of the WEI specifications, limits for the contents of ben2o[a]pyrene and water-soluble phenols (tar acids). 

Tar. Before the development of gas chromatography (gc) and high pressure Hquid chromatography (hplc), the quantitative analyses of tar distillate oils involved tedious high efficiency fractionation and refractionation, followed by identification or estimation of individual components by ir or uv spectroscopy. In the 1990s, the main components of the distillate fractions of coal tars are deterrnined by gc and hplc (54). The analytical procedures included in the specifications for tar bulk products are given in the relevant Standardi2ation of Tar Products Tests Committee (STPTC) (33), ISO (55), and ASTM (35) standards. 

Distillation System. The cmde condensate consists of the desired product, some low boiling constituents, and a smaller quantity of high boiling tar. Distillation separates the low boiling components, which are invariably incinerated, followed by the product fraction. Tar accumulates in the stiU ketdes, from which it is periodically removed, again to incineration. Stills work at atmospheric pressure and are vented to the incinerator. 

An electrostatic precipitator is used to remove more tar from coke oven gas. The tar is then sent to storage. Ammonia liquor is also separated from the tar decanter and sent to wastewater treatment after ammonia recovery. Coke oven gas is further cooled in a final cooler. Naphthalene is removed in a separator on the final cooler. Light oil is then removed from the coke oven gas and is fractionated to recover benzene, toluene, and xylene. Some facilities may include an onsite tar distillation unit. The Claus process is normally used to recover sulfur from coke oven gas. During the coke quenching, handling, and screening operation, coke breeze is produced. The breeze is either reused on site (e.g., in the sinter plant) or sold offsite as a by-product. 

N— compounds used as acid inhibitors include heterocyclic bases, such as pyridine, quinoline and various amines. Carassiti describes the inhibitive action of decylamine and quinoline, as well as phenylthiourea and dibenzyl-sulphoxides for the protection of stainless steels in hydrochloric acid pickling. Hudson e/a/. refer to coal tar base fractions for inhibition in sulphuric and hydrochloric acid solutions. Good results are reported with 0-25 vol. Vo of distilled quinoline bases with addition of 0 05m sodium chloride in 4n sulphuric acid at 93°C. The sodium chloride is acting synergistically, e.g. 0-05m NaCl raises the percentage inhibition given by 0-1% quinoline in 2n H2SO4 from 43 to 79%. Similarly, potassium iodide improves the action of phenylthiourea . 

Solvent Naphtha (160° benzol). A mixt of small percentages of benzene and toluene with xylene and higher homologs from coal tar. In crude form, a dark straw-colored liq, bp about 160° (80%), d 0.862—0.892g/cc, flash p about 78°F. When refined, a w-white liq, bp about 160° (90%), d 0.862-0.872g/cc, flash p about 78°F. May be obtained from coal tar by fractional distillation. When nitrated, used in Dynamites (Ref 5)... 

Several thousand compounds are present in petroleum. Few are separated as pure substances. Many of the uses of petroleum can be served by certain fractions from the distillation of crude oil. Typical distillation fractions and their uses are given in Table 7.3 and a distillation unit is shown in Fig. 7.5. The complexity of the molecules, molecular weight, and carbon number increase with the boiling point. The higher boiling fractions are usually distilled in vacuo at lower temperature than their atmospheric boiling points to avoid excessive decomposition to tars. 

Individuals occupationally exposed to coal tars or the naphtha fraction of coal-tar distillate have potentially high exposure to 2,3-benzofuran. Persons living near industrial sources or hazardous waste sites contaminated with 2,3-benzofuran may be exposed to 2,3-benzofuran. There are insufficient data to identify any other populations with potentially high exposure to this compound. 

Utilization of coal and oil shale to produce liquid and gaseous synfuels results in the generation of many hazardous sub-tances. Workers in these synfuel plants are likely to be exposed to potentially carcinogenic materials present in coal tars and oils. Among the various pathways of exposure, skin contamination by direct contact transfer or by adsorption of vapors and particulates into the skin presents a serious occupational health hazard. The skin irritant and potential carcinogenic properties of raw syncrudes and their distillate fractions have been reported (1. 2, 3). 

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