Benzene from toluene dealkylation

HDA [Hydrodealkylation] A proprietary dealkylation process for making benzene from toluene, xylenes, pyrolysis naphtha, and other petroleum refinery intermediates. The catalyst,... 

HDA [HydroDeAlkylation] A proprietary dealkylation process for making benzene from toluene, xylenes, pyrolysis naphtha, and other petroleum refinery intermediates. The catalyst, typically chromium oxide or molybdenum oxide, together with hydrogen gas, removes the methyl groups from the aromatic hydrocarbons, converting them to methane. The process also converts cresols to phenol. Developed by Hydrocarbon Research with Atlantic Richfield Corporation and widely licensed worldwide. 

UOP Benzene Toluene Thermal dealkylation process produces high-purity benzene from toluene 41 1992... 

Houdry Litol Production of benzene from toluene 50 600 Co, Mo Hz Hydrogenation of unsaturated compounds hydrocracking of non-aromatics desulfurization, dealkylation and dehydrogenation of naphthenes lead to higher benzene yields... 

Houdry dealkylation (HDA) Production of benzene from toluene 45 max. 750 Hz Benzene yield up to 99 %... 

A typical catalytic hydrodealkylation scheme is shown ia Figure 3 (49). The most common feedstock is toluene, but xylenes can also be used. Recent studies have demonstrated that and heavier monoaromatics produce benzene ia a conventional hydrodealkylation unit ia yields comparable to that of toluene (51). The use of feeds containing up to 100% of C —aromatics iacreases the flexibiUty of the hydrodealkylation procedure which is sensitive to the price differential of benzene and toluene. When toluene is ia demand, benzene suppHes can be maintained from dealkylation of heavy feedstocks. 

Biphenyl has been produced commercially in the United States since 1926, mainly by The Dow Chemical Co., Monsanto Co., and Sun Oil Co. Currently, Dow, Monsanto, and Koch Chemical Co. are the principal biphenyl producers, with lesser amounts coming from Sybron Corp. and Chemol, Inc. With the exception of Monsanto, the above suppHers recover biphenyl from high boiler fractions that accompany the hydrodealkylation of toluene [108-88-3] to benzene (6). Hydrodealkylation of alkylbenzenes, usually toluene, C Hg, is an important source of benzene, C H, in the United States. Numerous hydrodealkylation (HDA) processes have been developed. Most have the common feature that toluene or other alkylbenzene plus hydrogen is passed under pressure through a tubular reactor at high temperature (34). Methane and benzene are the principal products formed. Dealkylation conditions are sufficiently severe to cause some dehydrocondensation of benzene and toluene molecules. 

The most common by-product losses are due to transalkylation, dealkylation, saturation and cracking. Transalkylation results in toluene, trimethylbenzenes, methylethyl benzenes, benzene and ClOAs. These are the best by-products to have, because they are the easiest to react back into C8A in a transalkylation unit (if the aromatics complex is so equipped) without any loss of carbon atoms [59-61]. Dealkylation results in benzene, toluene, methane and ethane. The benzene and toluene are aromatics and represent valuable by-products, but the C1-C6 nonaromatics represent carbons that are lost from the complex as less valuable LPG and fuel gas. 

The same commercial Bi—Mo—P—O catalyst was used in a study by Van der Wiele [347], which included the oxidation of the xylenes at 400— 500° C. In contrast to the oxidation of toluene, dealkylation cannot be neglected. Table 33 presents an example of the product distribution at a 71—74% conversion level for both the xylenes and toluene. Remarkably, substantial amounts of the dialdehyde are only formed from p-xylene, while an enhanced benzene production is found in the case of o-xylene. The reaction schemes shown on p. 208 are proposed the combustion reactions, applicable to each component in the scheme are left out for simplicity. 

The dealkylation of toluene is a prime source of benzene, accounting for about one-half of toluene consumption. The production of diisocyanates from toluene is increasing. As a component of fuels, the use of toluene is lessening. Toluene takes part in several industrially important syntheses. The hydrogenation of toluene yields methyl cyclohexane (C6HnCH3), a solvent for fats, oils, rubbers, and waves. Trinitrotoluene [TNT, CH3C6H2(N02)3] is a major component of several explosives. When reacted with sulfuric acid, toluene yields o- and p-toluene sulfonic acids... 

Description Aromatics are produced from naphtha in the Aromizing section (1), and separated by conventional distillation. The xylene fraction is sent to the Eluxyl unit (2), which produces 99.9% paraxylene via simulated countercurrent adsorption. The PX-depleted raffinate is isomerized back to equilibrium in the isomerization section (3) with either EB dealkylation-type (XyMax) processes or EB isomerization-type (Oparis) catalysts. High-purity benzene and toluene are separated from non-aromatic compounds with extractive distillation (Morphylane ) processes (4). Toluene and C9 to Cn aromatics are converted to more valued benzene and mixed xylenes in the TransPlus process (5), leading to incremental paraxylene production. 

Dealkylation of EB and cracking of non-aromatics preferentially occurs in the top bed. The bottom bed promotes isomerization of xylenes, while minimizing loss of xylenes from side reactions. The reactor effluent is cooled by heat exchange, and the resulting liquid and vapor phases are separated in the product separator (3). The liquid is then sent to a fractionator (4) for recovery of benzene and toluene from the isomerate. 

More than 90% of today s petrochemicals are produced from refineiy products. Most are based on the use of C2-C4 olefins and aromatics finm hydrocarbon steam cracking units, which are even more closely linked to refineries. In North America, the feedstock for steam cracker units have generally been ethane, propane, or LPG. As a result, most of the propylene and aromatics have been provided by FCC units and catalytic reformers. In maity other parts of the world where naphtha feed has been more readily available, suppUes of propylene and aromatics have been produced directly by steam cracking. When necessary, the catalytic dehydrogenation of paraffins or dealkylation of toluene can balance the supply of olefins or benzene. In Table 7.2 some of the catalytic processes that convert olefins and benzene from a steam cracker into basic petrochemicals for the modem chemical industry are shown. 

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). 

Petroleum-derived benzene is commercially produced by reforming and separation, thermal or catalytic dealkylation of toluene, and disproportionation. Benzene is also obtained from pyrolysis gasoline formed ia the steam cracking of olefins (35). 

Extractive distillation, using similar solvents to those used in extraction, may be employed to recover aromatics from reformates which have been prefractionated to a narrow boiling range. Extractive distillation is also used to recover a mixed ben2ene—toluene stream from which high quaUty benzene can be produced by postfractionation in this case, the toluene product is less pure, but is stiU acceptable as a feedstock for dealkylation or gasoline blending. Extractive distillation processes for aromatics recovery include those Hsted in Table 4. 

Transalliyiation. A chemical reaction involving the movement of a group from one molecule to another molecule, dealkylating the first, alkylating the second. An example would be the reaction in which two molecules of toluene form benzene and j -lene, which involves a quick two-step of a methyl group and a hydrogen between toluene molecules (also called disproportionation). 

Benzene and para-xylene are the most sought after components from reformate and pygas, followed by ortho-xylene and meta-xylene. While there is petrochemical demand for toluene and ethylbenzene, the consumption of these carmot be discussed in the same way as the other four. Toluene is used in such a large quantity in gasoline blending that its demand as a petrochemical pales in comparison. Fthylbenzene from reformate and pygas is typically dealkylated to make benzene or isomerized to make xylenes. On-purpose production of petrochemical ethylbenzene (via ethylene alkylation of benzene) is primarily for use as an intermediate in the production of another petrochemical, styrene monomer. Ethylbenzene plants are typically built close coupled with styrene plants. 

To examine selectivity relationships, the following classification of o-ethyltoluene products is proposed for simplification ethylbenzene, toluene, and benzene are dealkylation products p- and m-ethyltoluene are isomerization products. Formation of m- and p-xylenes must have involved skeletal rearrangements to have been produced from o-ethyltoluene. Accordingly, these compounds are counted as isomerization products. In all cases studied, toluene was the major dealkylation product, and m- and... 

Toluene is convened 10 benzene by hydrodemethylation either under thermal or catalytic conditions. Benzene produced from this source generally supplies 25-30% of the total benzene demand. The feedstock is usually extracted toluene, but some reformers are operated under sufficiently severe conditions or with selected feedstocks to provide toluene pure enough to be fed directly to the dealkylation unit without extraction. 

The feed to an aromatics complex is normally a C6+ aromatic naphtha from a catalytic reformer. The feed is split into Cg+ for xylene recovery and C7 for solvent extraction. The extraction unit recovers pure benzene as a product and C7+ aromatics for recycling. A by-product of extraction is a non-aromatic C6+ raffinate stream. The complex contains a catalytic process for disproportionation and transalkylation of toluene and C9+ aromatics, and a catalytic process for isomerization of C8 aromatics. Zeolitic catalysts are used in these processes, and catalyst selectivity is a major performance factor for minimizing ring loss and formation of light and heavy ends. The choice of isomerization catalyst is dependent on whether it is desired to isomerize ethylbenzene plus xylenes to equilibrium or to dealkylate ethylbenzene to benzene while isomerizing the xylenes. Para-selectivity may also be a desired... 

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