Dehydrogenation alkyl aromatics

The generation of caibocations from these sources is well documented (see Section 5.4). The reaction of aromatics with alkenes in the presence of Lewis acid catalysts is the basis for the industrial production of many alkylated aromatic compounds. Styrene, for example, is prepared by dehydrogenation of ethylbenzene made from benzene and ethylene. 

We shall not treat cracking processes here due to the complexity of these high-temperature (usually around 500°C) reactions. However, cycloalkane dehydrogenation to aromatics (Appendix A2.4.4), alkane isomerization and olefin alkylation (leading to branched alkanes from linear ones) occur via such carbocation rearrangements. 

Unsaturated residue formed during catalytic reactions that produced paraffins and olefins is the source of alkyl aromatics and nonvolatile residue. When HZSM-5 catalyst is employed, aromatic alkyl chain sizes are restricted to C4 or smaller. The pores of HZSM-5 are large enough to allow formation of small alkyl aromatics by cyclization and dehydrogenation of surface species, but formation of fused unsaturated coke precursors are inhibited. Unlike HZSM-5, larger HY pores facilitate the formation of larger nonvolatile unsaturated coke precursors. 

Reaction Rate Constants and Activation Energies of Reactions of Dehydrogenation of Alkyl Aromatic Hydrocarbons... 

The use of carbon molecular sieves (CMSs) as catalysts for the oxidative dehydrogenation of alkyl aromatics was described in a patent by Lee [54]. Higher conversions and selectivities were reported with molecular sieve carbons with pore sizes in the range 0.5 to 0.7 nm (Carbosieve G from Supelco, and MSC-V from Calgon) than with activated carbon. This work may have triggered subsequent interest for CMS in ODE. 

Often the equilibrium position of a reversible process is such that the conversion to product is low at reasonable holding times (i.e., flow rates and reactor volumes). For example, the dehydrogenation of saturated alkanes and alkyl aromatics to produce alkenes and aryl-alkenes and hydrogen is a very important case in point ... 

An extensive study of the reactions of pure hydrocarbons, including alkanes, cycloalkanes, alkenes and aromatics has been made in the presence of hydrogen, these catalysts are active for (1) isomerization of alkanes, cycloalkanes, and alkyl-aromatics, (2) hydroisomerization of alkylcyclo-pentanes to aromatics, and (4) dehydrogenation of alkanes and cyclohexanes to aromatics. The activity and selectivity of these catalysts are dependent primarily on (1) the hydrogenation-dehydrogenation component used and its concentration, (2) the acidity of the oxide support, and (3) the reaction conditions. The effect of these factors on the conversion of pure hydrocarbons as well as the mechanism of these reactions will be discussed. 

The copper-mediated dehydrogenative alkylation of aromatic compounds is less investigated, compared to the alkynylation and arylation in Sects. 2.1 and 2.2. The limited successful example includes the quinoline-containing benzamide and... 

Supported metal oxide catalysts are widely employed in industrial applications alkane dehydrogenation, olefin polymerization, olefin metathesis, selective oxidation/ammoxida-tion/reduction of organic molecules (alkyl aromatics and propylene), and inorganic emissions (N2O, NO , H2S, SO2, and VOC) [1,3,7,11-13]. The initial industrial applications of supported metal oxide catalysts were limited to hydrocarbon dehydrogenation/hydro-genation and olefin polymerization/metathesis reactions. In more recent years, the number of applications of supported metal oxide catalysts for oxidation reactions has grown significantly due to their excellent oxidation characteristics in the manufacture of certain... 

Alkyl groups attached to aromatic rings are oxidized more readily than the ring in alkaline media. Complete oxidation to benzoic acids usually occurs with nonspecific oxidants such as KMnO, but activated tertiary carbon atoms can be oxidized to the corresponding alcohols (R. Stewart, 1965 D. Arndt, 1975). With mercury(ll) acetate, allyiic and benzylic oxidations are aJso possible. It is most widely used in the mild dehydrogenation of tertiary amines to give, enamines or heteroarenes (M. Shamma, 1970 H. Arzoumanian. 1971 A. Friedrich, 1975). 

Arylation of Aromatic Compounds. In contrast to Friedel-Crafts alkylations, arylations of aromatics are not as well known, and usually require drastic conditions. They iaclude (/) dehydrogenating condensation (SchoU reaction) (2) arylation with aryl haUdes and (J) arylation with dia2onium hahdes. 

Future Developments. The most recent advance in detergent alkylation is the development of a soHd catalyst system. UOP and Compania Espanola de Petroleos SA (CEPSA) have disclosed the joint development of a fixed-bed heterogeneous aromatic alkylation catalyst system for the production of LAB. Petresa, a subsidiary of CEPSA, has announced plans for the constmction of a 75,000 t/yr LAB plant in Quebec, Canada, that will use the UOP / -paraffin dehydrogenation process and the new fixed-bed alkylation process (85). 

Styrene is manufactured from ethylbenzene. Ethylbenzene [100-41-4] is produced by alkylation of benzene with ethylene, except for a very small fraction that is recovered from mixed Cg aromatics by superfractionation. Ethylbenzene and styrene units are almost always installed together with matching capacities because nearly all of the ethylbenzene produced commercially is converted to styrene. Alkylation is exothermic and dehydrogenation is endothermic. In a typical ethylbenzene—styrene complex, energy economy is realized by advantageously integrating the energy flows of the two units. A plant intended to produce ethylbenzene exclusively or mostly for the merchant market is also not considered viable because the merchant market is small and sporadic. 

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