Dehydrogenation of alkylaromatics

The reaction mechanism for a very strong one-electron donor centre in the dehydrogenation of alkylaromatic hydrocarbons is similar to that proposed by Krause for ethylbenzene dehydrogenation [reactions (5) and (6)]. The mechanism for n-propylbenzene transalkylation and cyclization on the radical pathway has been suggested. ... 

Debras, G., Grootjans, J., and Delorme, L., Process for the Catalytic Dehydrogenation of Alkylaromatic Hydrocarbons , European Patent 0 482 276 Al issued to FINA Research, S. A. (1992). 

Dehydrogenation of alkylaromatics or paraffins to alkenylaromatics (in particular, styrene), or olefins, on supported bismuth-vanadium oxides. 

IngaUina, P, Carluccio, L., Bellussi, G., et al. (2001). Process for the Preparation of Catalytic Systems for the Oxidative Dehydrogenation of Alkylaromatics or Paraffins, European Patent EP1160011. EniChem S.p.A.-EniTecnologie S.p.A. Assignee. 

This chapter compares the reaction of gas-phase methylation of phenol with methanol in basic and in acid catalysis, with the aim of investigating how the transformations occurring on methanol affect the catalytic performance and the reaction mechanism. It is proposed that with the basic catalyst, Mg/Fe/0, the tme alkylating agent is formaldehyde, obtained by dehydrogenation of methanol. Formaldehyde reacts with phenol to yield salicyl alcohol, which rapidly dehydrogenates to salicyladehyde. The latter was isolated in tests made by feeding directly a formalin/phenol aqueous solution. Salicylaldehyde then transforms to o-cresol, the main product of the basic-catalyzed methylation of phenol, likely by means of an intramolecular H-transfer with formaldehyde. With an acid catalyst, H-mordenite, the main products were anisole and cresols moreover, methanol was transformed to alkylaromatics. 

Dehydrocyclization, 30 35-43, 31 23 see also Cyclization acyclic alkanes, 30 3 7C-adsorbed olefins, 30 35-36, 38-39 of alkylaromatics, see specific compounds alkyl-substituted benzenes, 30 65 carbene-alkyl insertion mechanism, 30 37 carbon complexes, 32 179-182 catalytic, 26 384 C—C bond formation, 30 210 Q mechanism, 29 279-283 comparison of rates, 28 300-306 dehydrogenation, 30 35-36 of hexanes over platintim films, 23 43-46 hydrogenolysis and, 23 103 -hydrogenolysis mechanism, 25 150-158 iridium supported catalyst, 30 42 mechanisms, 30 38-39, 42-43 metal-catalyzed, 28 293-319 n-hexane, 29 284, 286 palladium, 30 36 pathways, 30 40 platinum, 30 40 rate, 30 36-37, 39... 

The cylization of alkylaromatics over platinum catalysts is usually accompanied by isomerization, hydrogenation and dehydrogenation, fragmentation (i.e., hydrogenolysis and cracking), and other reactions. 

Main reactions in CR processes are dehydrogenation of cyclohexane and alkylcylohexanes, cyclization of alkanes, isomerization of n-parafines, alkylcyclopentanes and alkylaromatics, and hydrocracking. Secondary reactions are the demethylation and cracking of cyclic compounds. 

Although V-containing zeolites have already been studied in gas-phase selective oxidations (propane oxidative dehydrogenation, for example [7]) data on the reactivity of these catalysts on the heterogeneous gas-phase selective oxidation of alkylaromatics are not available. Alky-laromatic oxidation has also been done in the liquid phase using H2O2 as oxidant [8]. The... 

Without going into detail we simply note that oxidation of alkylaromatic hydrocarbons with polymer-immobilized catalysts can be considered as a system of successive-parallel reactions including mononuclearic hydroxylation to phenols, oxidation of phenols, oxidative dehydrogenation of hydroquinones, oxidative decomposition of quinones and thermal and catalytic decomposition of peracids. 

Wathever the actual mechanism, oxide clusters, including aklali oxides appeared to be able to catalyze the formation of a carbide species which could react with methanol, thus resulting in an overall alkylation of the side chain of substituted aromatics. Further dehydrogenation of the resulting alkylaromatic was also achieved with such oxide species. 

Acidic zeolites are known for their excellent catalytic activity in cracking and isomerization of hydrocarbons (75). In the absence of metal, however, these catalysts rapidly deactivate due to the formation of carbonaceous products, usually referred to as coke. The carbonaceous residues are mainly formed via alkylaromatics and polyaromatics, which are the result of dehydrogenation, cyclization, and further alkylation processes. The coke deposits lower the catalytic activity by site poisoning and eventually also by pore blocking, which inhibits access of hydrocarbon molecules to the acid sites (286). 

The ZnX and CoX catalysts described in Section J,1 function as dehydrogenation catalysts for olefins, alkylaromatics, and aralkyl-amines. Activity was enhanced by the addition of NH3 to the reactants. As shown in Table XXXVIII, small amounts of butadiene were formed... 

When oligomers of more than six carbons are formed then benzene and alkylaromatics can be obtained through intermediates involving secondary carbenium ions. The cycloalkenes formed by oligomerization would rapidly dehydrogenate either on GajOj, or by hydride transfer on the zeolite since either on... 

Transformations of hydrocarbons promoted by solid metals and their oxides play very important roles in chemical industry [1], Heterogeneous metal-containing catalysts [2] are widely employed for cracking (see, e.g [3]) of oil fractions, oxidation, dehydrogenation, isomerization and many other processes of saturated as well as alkylaromatic hydrocarbons. 

The Cg alkylaromatics fraction is formed by ethylbenzene and the three xylene isomers. Ethylbenzene is used as a raw material to produce styrene by dehydrogenation, or oxidative dehydrogenation. Para-xylene and ortho-xylene are catalytically oxidized to give terephthalic and phthalic acid. The meta-xylene isomer can also be oxidized to give isophthalic acid. The major industrial source of these products is the catalytic reforming of naphthas. The Cyclar process, can also produce xylenes from propane and butane. However, using this process, xylenes are formed less selectively than toluene or benzene in the BTX. 

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