Coke oven, benzene

The pyrolysis oils are separated from the quench and scrubber oils in the distilation units K 4- and K 7/8 they can be further refined into chemical raw materials by the application of processes used in upgrading coal tar and coke oven benzene. 

HAD Atlantic Richfeld Co., Hydrocarbon Research Inc., Heavy reformate light cycle oil, cracked gas oils from coke ovens Benzene, naphthalene and selected aromatics... 

Proof of the existence of benzene in the light oil derived from coal tar (8) first estabHshed coal tar and coal as chemical raw materials (see Eeedstocks, COAL chemicals). Soon thereafter the separation of coal-tar light oil into substantially pure fractions produced a number of the aromatic components now known to be present in significant quantities in petroleum-derived Hquid fuels. Indeed, these separation procedures were for the recovery of benzene—toluene—xylene (BTX) and related substances, ie, benzol or motor benzol, from coke-oven operations (8) (see BTX processing). 

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. 

Coke-oven tar is an extremely complex mixture, the main components of which are aromatic hydrocarbons ranging from the monocyclics benzene and alkylbenzenes to polycycHc compounds containing as many as twenty or more rings. HeterocycHc compounds containing oxygen, nitrogen, and sulfur, but usually only one heteroatom per ring system are present. Small amounts of paraffinic, olefinic, and partly saturated aromatic compounds also occur. 

Since the 1950s, benzene production from petroleum feedstocks has been very successful and accounts for about 95% of all benzene obtained. Less than 5% of commercial benzene is derived from coke oven light oil. 

Until 1960, coal was the source material for almost all benzene produced in Europe. Petroleum benzene was first produced in Europe by the United Kingdom in 1952, by Erance in 1958, by the Eederal Republic of Germany in 1961, and by Italy in 1962. Coal has continued to decline as a benzene source in Europe, and this is evident with the closure of coke ovens in Germany (73). Most of the benzene produced in Europe is now derived from petroleum or pyrolysis gasoline. In Europe, pyrolysis gasoline is a popular source of benzene because European steam crackers mn on heavier feedstocks than those in the United States (73). 

Some of the principal Japanese producers of benzene are Mitsubishi Petrochemical Co., Ltd., Nippon Steel Chemical Co., Ltd., Sanyo Petrochemical Ltd., and Idemitsu Kosan Ltd. Until 1967, the main source of Japanese benzene was coal-based. Today, approximately 40—45% of benzene production in Japan is based on pyrolysis gasoline (74), about 40% catalytic reformate, and the remainder coke oven light oil and thermal hydrodealkylation. 

Most coal chemicals are obtained from high temperature tar with an average yield over 5% of the coal which is carbonized. The yields in coking are about 70% of the weight of feed coal. Tars obtained from vertical gas retorts have a much more uniform chemical composition than those from coke ovens. Two or more coals are usually blended. The conditions of carbonization vary depending on the coals used and affect the tar composition. Coal-tar chemicals include phenols, cresols, xylenols, benzene, toluene, naphthalene, and anthracene. 

The carbonization by-products are usually refined, within the coke plant, into commodity chemicals such as elemental sulfur (qv), ammonium sulfate, benzene, toluene, xylene, and naphthalene (qv) (see also Ammonium compounds BTX processing). Subsequent processing of these chemicals produces a host of other chemicals and materials. The COG is a valuable heating fuel used mainly within steel (qv) plants for such purposes as firing blast furnace stoves, soaking furnaces for semifinished steel, annealing furnaces, and lime kilns as well as heating the coke ovens themselves. 

Finally, Sec. 112 of the Clean Air Act required that EPA pronml-gate National Emission Standards for Hazardous Air Pollutants (NESHAPs). Between 1970 and 1989, standards were promulgated for asbestos, beiylhum, mercuiy, vinyl chloride, benzene, arsenic, radionuclides, and coke-oven emissions. 

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. 

Raw materials for obtaining benzene, which is needed for the production of alkylbenzenes, are pyrolysis gasoline, a byproduct of the ethylene production in the steam cracking process, and coke oven gas. Reforming gasoline contains only small amounts of benzene. Large amounts of benzene are further produced by hydrodealkylation of toluene, a surplus product in industry. 

During the 1800s, benzene was of limited commercial value, finding use mainly as a solvent. But after the invention of the internal combustion engine and the automobile, it was found that motors ran better when the fuel contained benzene. This added a new economic incentive to recover all of the benzene possible from the steel industry s coke ovens. However, just prior to World War II, the importance of benzene as a chemical intermediate started to be recognized. These dual incentives (gasoline and chemical intermediate) led to new and improved benzene processes based on petrochemistry rather than coal. 

Benzene releases in byproduct recovery operations Naphthalene residues generated in the final cooling tower Sulfur and sulfur compounds recovered from coke oven gas Wastewater from cleaning and cooling (contains zinc, ammonia still lime, decanter tank tar, or tar distillation residues)... 

First, points of release of benzene were identified petroleum refining and coke oven operations (production and extraction releases), use as a chemical intermediate (transportation, storage, use, and waste releases), use in gasoline (use-related release), and use in finished products (use-related release). Benzene also can be a contaminant of most of the derivatives made from it and its use as a solvent was substantial before health concerns arose. The complexity of the chemical systems dependent on benzene is shown in Figure 6. A list of potential releasing products appears in Table II. 

Estimates also were made for 65 coke plants in 12 states. Coke ovens produce benzene as a by-product, but not all of it can be recovered. It has been estimated that benzene contributes about two-thirds of one percent of the coal gas generated. Potential points of emissions from one type of coke battery are illustrated in Figure 7. Emissions from coke ovens were derived from estimated emission factors (based on coke oven product assays and benzene yields) and coal charging rates. 

Figure 7. Schematic diagram of by-product coke oven showing possible atmospheric emission sources for Benzene. (Reproduced with permission from Ref. 3.)...

Fires inside wood-packed benzene scrubbers in coke oven gas plants were attributed to saturation of the wood with naphthalene, and vapour-phase oxidation of the latter to phthalic anhydride, which participates in exothermic free radical chain reactions. 

Benzorbon A process for separating and recovering benzene from coke-oven gas and town gas by adsorption on activated carbon. Developed in 1930 by Luigi. 

Thus ether, which is very extensively used to take up organic preparations, is not completely removed from a much less volatile substance even on the boiling water bath, although the boiling point of this solvent is 35°. The benzene wash of coke ovens is another well-known example which cannot be discussed in detail here. 

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