BTX processing

See Antiasthmatic agents Expectorants, antitussives, and related agents Prostaglandins. 

Polyesters and alkyd resins Polyester fibers and films 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Name (source) Gravity, °API Sulfur, wt % Vol % of cmde Gravity, °API Octane, research Paraffins, wt % Cyclo-par affins, wt % Aromatics, wt % 

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TURBINE fuels), are both in demand. Solvent extraction is also extensively used to meet the growing demand for the high purity aromatics such as ben2ene, toluene, and xylene (BTX) as feedstocks for the petrochemical industry (see BTX PROCESSING FEEDSTOCKS,PETROCHEMICALS). Additionally, the separation of aromatics from aUphatics is one of the largest appHcations of solvent extraction (see Petroleum, refinery processes survey). 

Benzene [71-43-2] toluene [108-88-3] xylene [1330-20-7] and solvent naphtha are separated from the light oil. Benzene (qv), toluene (qv), and xylene are useful as solvents and chemical intermediates (see Xylenes and ethylbenzene). The cmde light oil is approximately 60—70% ben2ene, 12—16% toluene, 4—8% xylenes, 9—16% other hydrocarbons, and about 1% sulfur compounds (5) (see BTX processing). 

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). 

Cyclic Hydrocarbons. The cyclic hydrocarbon intermediates are derived principally from petroleum and natural gas, though small amounts are derived from coal. Most cycHc intermediates are used in the manufacture of more advanced synthetic organic chemicals and finished products such as dyes, medicinal chemicals, elastomers, pesticides, and plastics and resins. Table 6 details the production and sales of cycHc intermediates in 1991. Benzene (qv) is the largest volume aromatic compound used in the chemical industry. It is extracted from catalytic reformates in refineries, and is produced by the dealkylation of toluene (qv) (see also BTX Processing). 

In general, when the product is a fraction from cmde oil that includes a large number of individual hydrocarbons, the fraction is classified as a refined product. Examples of refined products are gasoline, diesel fuel, heating oils, lubricants, waxes, asphalt, and coke. In contrast, when the product is limited to, perhaps, one or two specific hydrocarbons of high purity, the fraction is classified as a petrochemical product. Examples of petrochemicals are ethylene (qv), propylene (qv), benzene (qv), toluene, and xylene (see Btx processing). 

Exploiting the relative basicity of the xylene isomers, commercial units employ superacids, typically HE—BF, as the acid complexing agent for the separation of / -xylene (feedstock for isophthalic acid) (15). Amoco produces high purity / -xylene at its Texas City facility using the HE—BF process (see Btx processing). Similar processes can be used for the separation of high purity mesitylene and isodurene from their and C q isomers, respectively. 

The principal chemical uses of BTX are illustrated in Figure 1 and Hsted in Table 1 (2). A very wide range of consumer products from solvents to fibers, films, and plastics are based on BTX. The consumption of BTX is approximately in the proportions of 67 5 28, respectively. However, no BTX process gives BTX in these proportions. The economic value of benzene and xylenes (especially -xylene) is normally higher than that of toluene. Because of this, processes that convert toluene to benzene by hydrodealkylation (3) and disproportionate toluene to benzene and xylenes (4) have been commercialized. In addition, reforming processes that emphasize production of either benzene or -xylene [106 2-3] have been described (5). Since these are not classified as BTX processes they are not discussed in detail here. 

BTX processing has come under steadily increasing pressure to reduce emissions and workplace exposures (see Industrial hygiene). Reductions in the permissible levels of both benzene and total aromatics (BTX) in gasoline have been legislated. Whereas all BTX components ate to be controUed, the main focus is on benzene because it is considerably mote toxic than the others and is classified as a known carcinogen (42). 

Deep C t lytic Crocking. This process is a variation of fluid catalytic cracking. It uses heavy petroleum fractions, such as heavy vacuum gas oil, to produce propylene- and butylene-rich gaseous products and an aromatic-rich Hquid product. The Hquid product contains predorninantiy ben2ene, toluene, and xylene (see BTX processing). This process is being developed by SINOPEC in China (42,73). SINOPEC is currentiy converting one of its fluid catalytic units into a demonstration unit with a capacity of 60,000 t/yr of vacuum gas oil feedstock. 

AH commercial processes for the manufacture of caprolactam ate based on either toluene or benzene, each of which occurs in refinery BTX-extract streams (see BTX processing). Alkylation of benzene with propylene yields cumene (qv), which is a source of phenol and acetone ca 10% of U.S. phenol is converted to caprolactam. Purified benzene can be hydrogenated over platinum catalyst to cyclohexane nearly aH of the latter is used in the manufacture of nylon-6 and nylon-6,6 chemical intermediates. A block diagram of the five main process routes to caprolactam from basic taw materials, eg, hydrogen (which is usuaHy prepared from natural gas) and sulfur, is given in Eigute 2. 

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