Benzene by dealkylation

Litol Also called Houdry-Litol. A process for making benzene by dealkylating other aromatic hydrocarbons. It is a complex process which achieves desulfurization, removal of paraffins and naphthenes, and saturation of unsaturated compounds, in addition to dealkylation. The catalyst contains cobalt and molybdenum. Developed by the Houdiy Process and Chemical Company and Bethlehem Steel Corporation. First installed by the Bethlehem Steel Corporation in 1964. Subsequently used at British Steel s benzole refinery, Teesside, England. 

Figure 2.4. Process flowsheet of the manufacture of benzene by dealkylation of toluene (Wells, Safety in Process Design, George Godwin, London, I960). 

Toluene is the most abundant and lowest cost aromatic material. This is a reason to be the valuable raw material for the production of various chemical products. The main chemical use for toluene Is, in fact, production of benzene by dealkylation. The reaction can be carried out either thermally or catalytically using variety of catalysts including supported metals or metal oxides [1-6], amorphous silica-alumina [7] and zeolites [8-19]. The simplest toluene hydrodealkylation reaction is the reaction in which the methyl group is removed in the presence of the forming mainly methane CeHsCHs + H2 —> CeH0 + CH4... 

The Houdry Litol process is widely used to produce benzene by dealkylation the following processes occur concurrently ... 

The predominant uses for toluene are, depending on location, the production of benzene by dealkylation (predominantly in the USA), the application as an aromatic solvent, the production of toluene diisocyanate through nitrotoluene intermediates and the manufacture of the oxidation products benzoic acid, benzalde-hyde and benzyl alcohol. 

If the naphthalene content of petroleum-derived naphthalene fractions is not sufficient for direct recovery, naphthalene enrichment is carried out by dealkylation of methylnaphthalenes, by analogy with the production of benzene by dealkylation of toluene. 

DETOL [DEalkylation of TOLuene] A process for making benzene by dealkylating toluene and other aromatic hydrocarbons. Developed by the Houdry Process and Chemical Company and generally similar to its Litol process for the same purpose. The catalyst is chromia on alumina. Licensed by ABB Lummus Global. Twelve plants had been licensed in 1987. 

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. 

The molecular weight distribution of the feed affects the distribution of the product. If the naphtha is concentrated in the C -Cg range, more benzene and toluene are found in the product. If the feed is weighted to Cg—C q, more xylenes and higher aromatics are found. Some carbon number "shppage" occurs by dealkylation some C s form benzene by losing a methyl group, some CgS form toluene, etc. 

Hydeal [Hydrodealkylation] A process for making benzene by de-alkylating other aromatic hydrocarbons. Generally similar to the Litol process. Developed in the 1950s by UOP and Ashland Oil Company, but abandoned in favor of UOP s THDA process. See dealkylation. 

Reaction (F) represents one of the uses of methanol (reaction (C)), and is also an example in which reaction selectivity is an important issue. The reaction cannot be allowed to go to ultimate completion, since the complete oxidation of CH3OH would lead to C02 and HzO as products. Similarly, in reaction (D), benzene and other (unwanted) products are produced by dealkylation reactions. 

Benzene H one of the most important rnw material in the petrochemical industry The physical pnrpertic of bcn/cnc are well documented in the literature. Most benzene is produced by the petroleum industry hy reforming or by dealkylation of toluene. Styrene accounts tor almost U)tt of benzene usage, Phenol and cyclohexane account for 50% of the rest Che future growth of benzene depends largely on the growth of these three end-use markets. 

As RON depends on the total concentration of aromatics in the reformate, the benzene yield (and concentration in the reformate) can be reduced significantly by increasing the naphtha initial boiling point, but a corresponding amount of heavier aromatics is needed to maintain RON. However, even when all the Cg cyclics were removed from the naphtha, between 1.0 and 1.5 wt% (on feed) benzene, depending on severity, was produced by dealkylation of heavier aromatics. 

The isomerization of xylenes and the dealkylation of ethylbenzene into benzene are other possibilities that have been industrially exploited on a large scale since the mid 1980s. This requires a catalyst that is more effective than mordenite which is not very active in dealkylation. The best-suited catalyst is undeniably ZSM-5 (Table 2). If this zeolite is used in its purely acid form, the ethylene produeed by dealkylation of ethylbenzene at around 350°C is alkylated on another ethylbenzene moleeule mainly to form paradiethylbenzene. some of which is produced industrially by this method. In order to avoid the alkylation reaction in the dealkylation of ethylbenzene, it is necessary to operate under hydrogen pressure ( 1.5 MPa) and to associate a small amount of Pi to the ZSM-5 zeolite, which hydrogenates the ethylene into ethane as it is produced. 

Since in the oxidation of benzene to maleic anhydride, two carbon atoms are lost as CO2, attempts were made early on to produce maleic anhydride from C4 hydrocarbons. With the development of the petrochemical industry, large quantities of C4-cuts became available, from which butene and, by hydrogenation, butane, could be recovered. The use of benzene is in decline, particularly in the USA, since benzene is now produced there, among other routes, by dealkylation of toluene, whereas C4-components are readily available from cat-cracker and ethylene plants. 

The rate of transalkylation, after 0.5 h is faster than the rate of isomerization. The formation of cumene is possible either by transalkylation reaction between DIPB isomers and benzene or dealkylation of DIPB isomers as shovm in reactions (1) and (2) respectively. 

Preparation by dealkylation of 5-tert-butyl-2,4 -dimethoxybenzophenone with aluminium chloride in benzene at 65-70° for 45 h (75%) [9]. 

CH Preparation by dealkylation of 4-hydroxy-5-methyl-2-iso-pro-pylacetophenone with aluminium chloride in chloro-benzene at 50° (53%) [2661]. 

Benzene was first isolated by Faraday in 1825 from the liquid condensed by compressing oil gas. It is the lightest fraction obtained from the distillation of the coal-tar hydrocarbons, but most benzene is now manufactured from suitable petroleum fractions by dehydrogenation (54%) and dealkylation processes. Its principal industrial use is as a starting point for other chemicals, particularly ethylbenzene, cumene, cyclohexane, styrene (45%), phenol (20%), and Nylon (17%) precursors. U.S. production 1979 2-6 B gals. 

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). 

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