Tar acid

If the third substance dissolves in both liquids (and the solubility in each of the liquids is of the same order), the mutual solubility of the liquids will be increased and an upper C.S.T. will be lowered, as is the case when succinic acid or sodium oleate is added to the phenol - water system. A 0 083 molar solution of sodium oleate lowers the C.S.T. by 56 -7° this large effect has been applied industrially in the preparation of the disinfectant sold under the name of Lysol. Mixtures of tar acids (phenol cresols) do not mix completely with water at the ordinary temperature, but the addition of a small amount of soap ( = sodium oleate) lowers the miscibility temperature so that Lysol exists as a clear liquid at the ordinary temperature. 

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. 

Large-scale recovery of light oil was commercialized in England, Germany, and the United States toward the end of the nineteenth century (151). Industrial coal-tar production dates from the earliest operation of coal-gas faciUties. The principal bulk commodities derived from coal tar are wood-preserving oils, road tars, industrial pitches, and coke. Naphthalene is obtained from tar oils by crystallization, tar acids are derived by extraction of tar oils with caustic, and tar bases by extraction with sulfuric acid. Coal tars generally contain less than 1% benzene and toluene, and may contain up to 1% xylene. The total U.S. production of BTX from coke-oven operations is insignificant compared to petroleum product consumptions. 

The chemical oil contains ca 50 wt % naphthalene, 6 wt % tar acids, 3 wt % tar bases, and numerous other aromatic compounds. The chemical oil is processed to remove the tar acids by contacting with dilute sodium hydroxide and, in a few cases, is next treated to remove tar bases by washing with sulfuric acid. 

The main impurity in cmde 78°C coal-tar naphthalene is sulfur which is present in the form of thionaphthene (1—3%). Methyl- and dimethylnaphthalenes also are present (1—2%) with lesser amounts of indene, methylindenes, tar acids, and tar bases. 

Not good for services where soHds, tars, acidic gases are expected stream should be condensed once before coming in contact with membrane to remove low boilers if possible. 

The only valuable components in low temperature tar are the phenols and an oil fraction distilled over the range of 180—310°C, which is collected for tar-acid recovery is taken. A typical primary distillation is given in Table 3. 

Coumarone—Indene Kesins. These should be called polyindene resins (17) (see Hydrocarbon resins). They are derived from a close-cut fraction of a coke-oven naphtha free of tar acids and bases. This feedstock, distilling between 178 and 190°C and containing a minimum of 30% indene, is warmed to 35°C and polymeri2ed by a dding 0.7—0.8% of the phenol or acetic acid complex of boron trifluoride as catalyst. With the phenol complex, tar acids need not be completely removed and the yield is better. The reaction is exothermic and the temperature is kept below 120°C. When the reaction is complete, the catalyst is decomposed by using a hot concentrated solution of sodium carbonate. Unreacted naphtha is removed, first with Hve steam and then by vacuum distillation to leave an amber-colored resin. It is poured into trays, allowed to cool, and broken up for sale. 

First, the tar acids were removed from the naphtha fractions of light oils and, in the case of CVR tars, carboHc oil. The oils were then mixed with 25—35% sulfuric acid. After separation of the sulfates, the aqueous solution was diluted with water and the resinous material skimmed off. The diluted sulfate solution was boiled to expel any neutral oils, dried by the addition of soHd caustic soda or a2eotropically with ben2ene, and fractionated to yield pyridine, 2-methylpyridine (a-picoline), and a fraction referred to as 90/140 bases, which consisted mainly of 3- and 4-methylpyridines and 2,6-dimethylpyridine (2,6-lutidine). Higher boiling fractions were termed 90/160 and 90/180 bases because 90% of the product distilled at 160 and 180°C, respectively. 

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 next stage in the recovery and refining of tar acids, water and pitch ate removed from the cmde tar acids in a continuous-vacuum still heated by superheated steam or circulating hot oil. The aqueous phenol overhead distillate is recycled, the stream of once-mn tar acids is refined, and the phenoHc pitch bottoms are burned. 

The once-mn tar acids are fractionated in three continuous-vacuum stills heated by superheated steam or circulating hot oil. These stills contain 40—50 bubble trays and operate at reflux ratios between 15 and 20 1. The overhead product from the first column is 90—95% phenol from the second, 90% (9-cresol and from the third, a 40 60 y -cresol—p-cresol mixture. Further fractionation gives the pure products. 

At other refineries, only two continuous stills in series are used, but these ate of 80—100 plate efficiency and yield pure grades of phenol and o-cresol and a base mixture of cresols, xylenols, and higher boiling tar acids. The latter are fractionated batchwise to various saleable grades of cresyHc acids. 

Fractionation columns in tar-acid refineries are generally operated under vacuum and heated by high pressure steam or circulating hot oil. Calandtia in the reboders, condensers, mndown lines, and receiving tanks are constmcted of stainless steel, or, in the case of the condensers, of tin or nickel. 

Cast-iron column shells are satisfactory, but stainless-steel bubble or valve trays are preferred. A flow sheet of a typical tar acid extraction and refining plant is shown in Figure 3. 

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. 

T, % tar acids, is defined as the percentage by volume extracted by 10% aqueous caustic soda. 

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). 

Miscellaneous Sources of Benzene. Benzene has been recovered from coal tar. The lowest boiling fraction is extracted with caustic soda to remove tar acids. The base washed oil is then distiUed and further purified by hydrodealkylation. 

The development of natural gas as a fuel source in the UK has led to reductions in tar acid supplies and this has prompted the petrochemicals industry to make... 

At one time the requirement for phenol (melting point 41°C), eould be met by distillation of eoal tar and subsequent treatment of the middle oil with eaustic soda to extraet the phenols. Such tar acid distillation products, sometimes containing up to 20% o-cresol, are still used in resin manufacture but the bulk of phenol available today is obtained synthetically from benzene or other chemicals by such processes as the sulphonation process, the Raschig process and the cumene process. Synthetic phenol is a purer product and thus has the advantage of giving rise to less variability in the condensation reactions. 

Chemical Designations - Synonyms Cresylic Acids Hydroxytoluenes Methylphenols Oxytoluenes Tar Acids Chemical Formula CH3C3 H4OH. 

The austenitic irons are also useful in some circumstances for handling organic acids such as dilute acetic, formic and oxalic acids, fatty acids and tar acids. They are more resistant to organic acids than unalloyed cast irons, e.g. in acetic acid the austenitic irons show corrosion rates 20-40 times lower than the ferritic iron (Table 3.51). 

Phenolics, e.g. tar acids (clear soluble phenolics), non-coal tar (chloroxylenol), bisphenol (triclosan)... 

Many of the phenols which are used in household and other commercial disinfectant products are produeed from the tar obtained by distillation of coal or more recently petroleum. They are known as the tar acids. These phenols are separated by fractional distillation according to their boiling point range into phenol, cresols, xylenols and high boiling point tar acids. As the boiling point increases the properties of the products alter as shown ... 

Phenolsolvan A process for extracting phenols from coke-oven liquor and tar acids from tar by selective solvent extraction with di-isopropyl ether (formerly with -butyl acetate). Developed by Luigi in 1937. 

Synroc Synroc. tantalum Kroll (1). tantalum carbide Menstruum, tar acids Phenolsolvan. 

The Lurgi gasifiers used by Sasol operate at "low" temperatures and consequently phenols, and "tars" are "distilled" from the coal at the top of the gasifier, and carried out with the raw gas. On condensation two liquid phases are formed, "tar" and "gas liquor" (water). The "tar acids" (phenol, cresols etc) are dissolved in the "gas liquor" which is fed to the Phenosolvan unit where the acids are recovered by counter current extraction with butyl acetate or diisopropyl ether. The crude tar acids are fractionated to yield phenol, ortho, meta and para cresol and xylenols. The phenol is further refined to produce a high purity, colourless and stable product. Phenol is used mainly in the production of formaldehyde resins while the cresols are used as flotation frothers and in the manufacture of pesticides etc. 

Chemically bound nitrogen in coal is converted to NH in the gasifier and the ammonia ends up in the "gas liquor" (water) phase. After extraction of the tar acids in the Phenosolvan process, the liquor is steam-stripped to remove the NH which is then purified. 

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