Coke oven benzole

DISTAPEX A process for removing aromatic hydrocarbons from pyrolysis gasoline or coke-oven benzole by extractive distillation with added N-methyl pyrrolidone. The operating temperature is at least 170°C. Developed by Lurgi. First announced in 1961 by 1993, 22 plants had been built. 

Lurgi 01 Gas Chemie GmbH Benzene/toluene Pyrolysis gasoline, reformate, coke oven benzole Extractive distillation using N-methylpyrrolidone as solvent has high yield, low utilities 22 2000... 

The light oil consists principally of benzene, toluene and xylenes in terms of its composition, it resembles coke-oven benzole. The naphthalene fraction, recovered as a 4% yield of the crude oil, contains 42% naphthalene along with mainly methylnaphthalenes. 

Although Charles B. Mansfield, a disciple of August W.von Hofmann, detected the presence of toluene in coal tar in 1849, it found only limited application at first as a chemical raw material. However, this changed in World War I, when toluene was used in the production of the explosive trinitrotoluene (TNT). Up to the turn of the century, coal tar and coke-oven benzole remained the only source of toluene, but during the World War I it was also produced by fractional distillation of aromatic crude oils from the Far East (e.g. Borneo, Java). 

The most important sources for BTX aromatics are reformer gasoline, pyrolysis gasoline and coke oven benzole. Reformer gasoline is the major source in countries where the production of ethylene is primarily based on gas, so that production of pyrolysis gasoline is relatively low this applies particularly to the United States, where around two-thirds of its ethylene is produced from wet natural gases. With a share of around 75%, reformer gasoline is therefore the major raw material for BTX aromatics in the USA. 

Hydrogenation is currently the most important method for pretreatment of coke oven benzole. The BASF/Scholven process has proved particularly effective, operating at temperatures between 300 and 400 °C with molybdenum or cobalt/ molybdenum catalysts and treating the benzole with various gases containing hydrogen, under pressure (20 to 50 bar). By this process the sulfur content of the refined product is reduced to below 0.5 ppm. 

Liquid-liquid extraction and extractive distillation are most commonly used to separate non-aromatics from coke-oven benzole, pyrolysis gasoline and reformer gasoline. 

In azeotropic distillation, on the other hand, the additive and the component to be separated form an azeotrope i. e. a mixture boiling at a given temperature and with a constant composition. Azeotropic distillation can only be used to refine highly-enriched mixtures of aromatics, such as occur in coke-oven benzole, whereas extractive distillation can also be used to separate aromatics which are present in low concentrations. As early as World War I toluene used in the production of explosives was obtained by extractive distillation, using phenol as the extractive material. 

The most important benzene aromatics in terms of quantity are benzene and p-xylene. Since the production from reformer gasoline, pyrolysis gasoline and coke-oven benzole is frequently inadequate to meet the demand, isomerization, disproportionation and dealkylation methods have been developed to complement the direct production from aromatics mixtures. 

Benzole pressure refining Hydrogenation of coke oven benzole 20-50 350 Co, Mo H2 Reduction of sulfur to below 0.5... 

Isolation of styrene from coke-oven benzole or coal tar light oil is no longer of any practical significance styrene, however, has to be separated from these coal-... 

In 1883, Viktor Meyer first detected thiophene in coke-oven benzole, where it is present in concentrations of around 1%. (Because of the close relationship between thiophene and benzene, Meyer took the name kryptophen ( hidden in benzene ) into consideration.) Recovery of thiophene from coke-oven benzole, which is possible by the reaction of thiophene with concentrated sulfuric acid to thiophenesulfonic acid, is not used industrially since the synthesis is more economical. 

From the beginning of industrial aromatic chemistry there have been fundamental new developments in the production of aromatics. Until the 1920 s, coal tar and coke-oven benzole were virtually the sole sources of aromatics available on an industrial scale. Coal tar contains a host of widely used aromatic compounds, such as benzene, toluene, naphthalene, anthracene and pyrene, as well as styrene and indene. In addition coal tar contains some important recoverable aromatic compounds with hetero atoms, such as phenols, anilines, pyridines and quinoline. 

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). 

Blended coal is first heated in coke ovens to produce coke. This process is known as carbonization. The gas produced during carbonisation is extracted and used for fuel elsewhere in the steelworks. Other by-products (such as tar and benzole) are also extracted for further refining and sale. Once carbonised, the coke is pushed out of the ovens and allowed to cool. 

The production of coke involves the heating of coal in the absence of air, called the carbonization or destructive distillation of coal. Carbonization, besides its main purpose of production of coke, also results in a coproduct called coke oven gas from which various liquid products such as tar, benzol, naphthalene, phenol, and anthracene are separated. There are two main types of carbonization based on the temperature to which the coal is heated in the absence of air. One type is low-temperature carbonization (LTC) the other is high-temperature carbonisation (HTC). Some features of LTC and HTC are listed in Table 1.28. The LTC Process is mainly carried out to manufacture domestic smokeless fuel. This presentation, however, concentrates on the HTC process by which metallurgical coke is produced. 

Continuing further with the recovery aspects from coke oven gas reference may be drawn to the recovery of light oil (crude benzol). In a typical process used, the coke oven gas (from which benzol is to be recovered) after removal of tar, ammonia etc. is passed through the benzol scrubber where the benzol vapours are scrubbed by wash oil flowing countercurrent to the gas. Benzolised wash oil is then pumped to the recovery section where the crude benzol, absorbed in the wash oil is stripped off by steam. The steam vapour mixture, com-... 

During the conversion of coal to coke required for the production of pig iron, crude gases or coke oven gases are formed, together with benzols and tars (coal tars). The carbonization balance depends on the volatile matter index of the coal feedstock. On the average, one ton of dry coal yields ... 

Benzols are essentially produced by the purification of crude gas, with a small part produced by tar distillation. Coke oven gas has the following average composition ... 

The coking process in these ovens also produces such by-products as coke oven gas ammonia, which is converted to ammonium sulfate coal tar, which can be distilled into useful secondary products like pitch, anthracene oil, naphthalene, etc. and benzol for producing chemical products such as benzene, toluene, and xylene. 

Coal tar light oil, or crude benzole, is similar in chemical composition to the crude benzole recovered from the carbonization gases at gas works and in coke-oven plants. The main components are benzene, toluene, and xylene(s) with minor quantities of aromatic hydrocarbons, paraffins, naphthenes (cyclic aliphatic compounds), and phenols, as well as sulfur and nitrogen compounds. 

Large-scale carbonization of hard coal is performed at temperatures between 1,000 and 1,200 °C. The production of blast-furnace coke takes 14 to 20 hours. Each ton of coal yields 750 kg of coke, 370 m coke-oven gas, 35 kg of crude tar, 11 kg benzole, 2.4 kg ammonia and 150 kg water. Figure 3.11 shows the quantitative flow chart for a coke plant with a daily coal throughput of 7,0001. The blastfurnace gas is supplied by the blast furnaces which are linked for energy supply (underfiring) to the coke ovens. 

Figure 4.3 shows the flow diagram of the recovery of benzole from coke oven gas by distillation. 

Table 4.5 compares the basic data for benzole and refined benzene produced by hydrogenation with coke oven gas. 

Benzole after hydrogenation with coke oven gas... 

Field test data showing the effects of natural gas composition and flow rate are given by Enneking (1966). The use of adsorption to recover hydrocarbons from gas streams at refineries and petrochemical plants is described by Cantrell (1982). The recovery of benzol (a benzene-rich light oil) from manufactured and coke-oven gas streams was formerly an important application of activated carbon adsorption, but is no longer considered significant. A typical benzol removal installation is described by Howell (1943) and Walker et al. (1944). Hydrocarbon recovery processes are not described in detail herein because of their similarity to solvent recovery processes and the fact that they are intended primarily for recovery, not gas purification. 

---