Alkylbenzene, cracking

Also other Type B and C series from Table II are consistent with the above elimination mechanisms. The dehydration rate of the alcohols ROH on an acid clay (series 16) increased with the calculated inductive effect of the group R. For the dehydrochlorination of polychloroethanes on basic catalysts (series 20), the rate could be correlated with a quantum-chemical reactivity index, namely the delocalizability of the hydrogen atoms by a nucleophilic attack similar indices for a radical or electrophilic attack on the chlorine atoms did not fit the data. The rates of alkylbenzene cracking on silica-alumina catalysts have been correlated with the enthalpies of formation of the corresponding alkylcarbonium ions (series 24). Similar correlations have been obtained for the dehydrosulfidation of alkanethiols and dialkyl sulfides on silica-alumina (series 36 and 37) in these cases, correlation by the Taft equation is also possible. The rate of cracking of 1,1-diarylethanes increased with the increasing basicity of the reactants (series 33). 

Raw materials for obtaining benzene, which is needed for the production of alkylbenzenes, are pyrolysis gasoline, a byproduct of the ethylene production in the steam cracking process, and coke oven gas. Reforming gasoline contains only small amounts of benzene. Large amounts of benzene are further produced by hydrodealkylation of toluene, a surplus product in industry. 

Thus hydrochloric acid is a derivative of chlorine. About 93% of it is made by various reactions including the cracking of ethylene dichloride and tetrachloroethane, the chlorination of toluene, fluorocarbons, and methane, and the production of linear alkylbenzenes. It is also a by-product of the reaction of phosgene and amines to form isocyanates. 

A cracking process, the dealkylation of alkylbenzenes, became an established industrial synthesis for aromatics production. Alkylbenzenes (toluene, xylenes, tri-methylbenzenes) and alkylnaphthalenes are converted to benzene and naphthalene, respectively, in this way. The hydrodealkylation of toluene to benzene is the most important reaction, but it is the most expensive of all benzene manufacturing processes. This is due to the use of expensive hydrogen rendering hydrodealkylation too highly dependent on economic conditions. 

The cracking of alkylbenzenes can be treated as a case of aromatic electrophilic substitution (for recent views on this type of reaction see ref. 241) where the attacking agent is either a proton from a surface Br0nsted site or a coordinatively unsaturated surface cation acting as a Lewis site (cf. ref. 238)... 

Fragmentation of alkylbenzenes over silica-alumina occurs exclusively by acid-catalyzed cracking. The reaction selectively cleaves the bond between the phenyl ring and the a-carbon of the side-chain. This occurs more than 100 times more often than the cracking of all the other bonds combined. Cracking rates of secondary alkylbenzenes are about an order of magnitude higher than those of w-alkylbenzenes. 

Herlem et al463 have observed that asphaltene is dissolved in fluorosulfuric acid and the process is accompanied by strong redox reactions (SO2 and HF evolution). The products are mainly functionalized by SO3H groups, but SO2F groups were also detected by XPS. Indeed, model studies with benzene showed the formation of benzenesulfonic acid, diphenylsulfone, and benzenesulfonyl fluoride. For alkylbenzenes, sulfonation was not accompanied by cracking of the alkyl chain. 

Conventional thermal cracking of pure hydrocarbons has been studied extensively in the past, and well-substantiated mechanistic proposals have been outlined (7-19). In contrast, hydropyrolysis of pure model compounds has been studied to a lesser extent and has been confined mostly to low (Ci-C5) paraffins, and simple alkylbenzenes and naphthenoaro-... 

Where relatively high concentrations of H atoms exist, addition of H followed by loss of an alkyl group is an efficient way of reducing alkylbenzenes and polyaromatics to benzene which, of course, is of considerable significance in aromatic cracking processes. 

Watson BA, Klein MT, Harding RH. Catalytic cracking of alkylbenzenes Modeling the reaction pathways and mechanisms. Appl Catal A-Gen 1997 160 13-39. 

It can react with another ethylene molecule, producing a C4 species that can undergo further transformation by alkylation, oligomerization, isomerization or cracking to give other alkylbenzenes and olefins. 

Alkylbenzenes with Side Chains of Three or More Carbons. The products from hydrocracking of alkylbenzenes containing side chains of three to five carbon atoms are relatively simple. Direct dealkylation is the primary cracking reaction. For example, ferf-amylbenzene gives benzene... 

Of the n-alkylbenzenes the effect of toluene equalled that of benzene. The higher alkylbenzenes inhibited both cracking and isomerization. 

Fio. 1. Correlation of cracking of alkylbenzenes over silica-alumina catalyst at 500° (24) by the Taft equation. 

Rase and Kirk 24) have compared the adsorption coefficients of a series of alkylbenzenes calculated for cracking of these hydrocarbons on a silica-alumina catalyst from Eq. (1) with the bond strength of structurally related alkanes and have obtained a linear relation. The correlation coefficient is again high, 0.98. As has been shown in Table I, the corresponding rate constants can be correlated by the Taft equation. However, the plot of log Kj vs a gives a curve. 

Like at low temperature coking occurs rapidly from olefins and from polyaromatics. However at high temperatures, alkylbenzenics (e.g. cumene) and branched alkanes crack rapidly, leading to olefins which are rapidly transformed into coke. Coking is slow only from the monoaromatics such as benzene or toluene and from the linear alkanes which crack slowly [10]. 

C8-16 alkylbenzene Chloro-n-paraffin (C8-22) Tris (2,3-dichloropropyl) phosphate plasticizer, secondary adhesives Chlorinated paraffins (C12, 60% chlorine) Chlorinated paraffins (C23, 43% chlorine) plasticizer, secondary mastics Chlorinated paraffins (C12, 60% chlorine) Chlorinated paraffins (C23, 43% chlorine) plasticizer, secondary paints Chlorinated paraffins (C12, 60% chlorine) Chlorinated paraffins (C23, 43% chlorine) plasticizer, secondary plastics Chlorinated paraffins (C12, 60% chlorine) Chlorinated paraffins (C23, 43% chlorine) plasticizer, secondary synthetic resins Isooctyl palmitate plasticizer, secondary vinyls C12-14 alkylbenzene Chlorinated paraffins (C12, 60% chlorine) Chlorinated paraffins (C23, 43% chlorine) Petroleum distillates, heavy thermal cracked... 

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