Benzene, toluene, xylenes feedstock

Table 4. Extractive Processes for the Separation of Benzene—Toluene—Xylene Mixture from Light Feedstocks ...

The raw material has to be washed to remove impurities. Diluted sodium hydroxide allows the removal of phenols and benzonitrile, and diluted sulphuric acid reacts with pyridine bases. The resulting material is distilled to concentrate the unsaturated compounds (raw feedstock for coumarone-indene resin production), and separate and recover interesting non-polymerizable compounds (naphthalene, benzene, toluene, xylenes). Once the unsaturated compounds are distilled, they are treated with small amounts of sulphuric acid to improve their colour activated carbons or clays can be also used. The resulting material is subjected to polymerization. It is important to avoid long storage time of the feedstock because oxidation processes can easily occur, affecting the polymerization reaction and the colour of the coumarone-indene resins. 

Petrochemicals and fossil fuels entail chemicals produced from hydrocarbon feedstocks, such as crude oil products and natural gas. They include such chemicals as hydrocarbons and industrial chemicals (e.g., alcohols, acrylates, acetates), aromatics (e.g., benzene, toluene, xylenes), and olefins (e.g., ethylene, propylene, butadiene, methanol). 

Proof of the existence of benzene in the light oil derived from coal tar (8) first established coal tar and coal as chemical raw materials (see Feedstocks, 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 liquid 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). 

Toluene, Benzene, and BTX Reeoveiy. The composition of aromatics centers on the C - and Cg-fraction, depending somewhat on the boihng range of the feedstock used. Most catalytic reformate is used directiy in gasoline. That part which is converted to benzene, toluene, and xylenes for commercial sale is separated from the unreacted paraffins and cycloparaffins or naphthenes by hquid—hquid extraction or by extractive distillation. It is impossible to separate commercial purity aromatic products from reformates by distillation only because of the presence of azeotropes, although comphcated further by the closeness in boihng points of the aromatics, t/o-paraffin, and unreacted C -, C -, and Cg-paraffins. 

The feedstock is usually extracted toluene, but some reformers are operated under sufftciendy severe conditions or with selected feedstocks to provide toluene pure enough to be fed directiy to the dealkylation unit without extraction. In addition to toluene, xylenes can also be fed to a dealkylation unit to produce benzene. Table 20 Hsts the producers and their capacities for manufacture of benzene by hydrodealkylation of toluene. Additional information on hydrodealkylation is available in References 50 and 52. 

Since toluene is nothing more than benzene with a methyl group attached, creating one from another is relatively easy. Benzene, toluene, and for that matter, xylenes too, are coproduced in the processes just described—coke making, cat reforming, and olefin plants operations. The ratio of benzene to the other aromatics production is rarely equal to the chemical feedstock requirements.. fo.r the three. One method for balancing supply and demand is toluene hydrodealkylation (HDA). This process accounts for 10—15% of the supply of benzene in the United States and is a good example of what can be done when one or more coproducts are produced in proportions out of balance with the marketplace. 

The olefins—ethylene, propylene, and the butylenes—are derived from natural gas and petroleum. Methane is the major constituent in natural gas. The aromatics— benzene, toluene, and the xylenes— are derived from petroleum. About 90% by weight of the organic chemicals in the world comes from natural gas and petroleum. But actually only 3% of this crude oil and 6% of refinery output in the U.S. is processed into chemicals, with the rest going as various fuels. Although we are a small user of the petroleum industry, this 3-6% going to petrochemical feedstock is important to us ... 

Petroleum feedstock, natural gas and tar represent the main production chain drivers for the petrochemical industry (Bell, 1990). From these, many important petrochemical intermediates are produced, including ethylene, propylene, butylenes, butadiene, benzene, toluene, and xylene. These essential intermediates are then converted to many other intermediates and final petrochemical products, constructing a complex petrochemical network. Figure 1.4 depicts a portion of the petrochemical alternative routes to produce cellulous acetate. 

The two-zone plume interception treatment technology is designed to treat chlorinated and nonchlorinated organic compounds in groundwater using a sequence of anaerobic and aerobic conditions. The in situ technology has been applied to aquifers contaminated with benzene, toluene, ethylbenzene, and xylenes (BTEX) petroleum products hydrocarbons coal tar wastes and industrial feedstock chemicals. The technology does not treat metals. 

Deep Catalytic Cracking. 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 liquid product. The liquid product contains predominandy benzene, toluene, and xylene (see BTX processing). This process is being developed by SINOPEC in China (42,73). SINOPEC is currendy converting one of its fluid catalytic units into a demonstration unit with a capacity of 60,000 t/yr of vacuum gas oil feedstock. 

Petroleum and Petrochemical Processes. I he first large-scale application of extraction was ihe removal of aromatics From kerosene to improve its burning properties. Solvent extraction is also extensively used to meet ihe growing demand for the high purity aromatics such as benzene, toluene, and xylene (BTXl as feedstocks for the petrochemical industry. Additionally, Ihe separation of aromatics from aliphaties is one of the largesi applications of solvent extraclion. 

Separation of the C2 stream to produce high-purity ethylene and ethane requires a large tower, sometimes the largest one in the plant. Separation of the C3 stream to produce high-purity propylene and propane also requires a large tower, and in some plants it is the largest one. Separation of butadiene from the C4 stream, if performed, is usually accomplished by extractive distillation. Aromatics are frequently recovered and separated to obtain benzene, toluene, and xylenes, especially when heavy feedstocks are used. 

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