Ethylbenzene Conversion

In commercial xylene isomerization, it is desirable that the necessary ethylbenzene conversion is accompanied by a minimum conversion (transalkylation) of xylenes, since the latter constitutes a downgrading to less valuable products. The ability of ZSM-5 to convert ethylbenzene via transalkylation in high selectivity, as shown in Table II, leads to high ultimate p-xylene yields in a commercial process. With a simulated commercial feed containing 85% m- and o-xylene and 15% ethylbenzene, we have obtained the data shown in Table III. It is seen that for a given ethylbenzene conversion, the xylene loss... 

Selective xylenes isomerization and ethylbenzene conversion. US Patent 5,143,941. 

Early studies with respect to the dehydrogenation of hydrocarbons to alkenes on oxide catalysts indicated that carbonaceous deposits formed in the early stages of the process on the surface of acidic catalysts act as the real active centers for the oxidative dehydrogenation. The hypothesis was later confirmed377 378 and verified by using carbon molecular sieves. With this catalyst 90% styrene selectivity could be obtained at 80% ethylbenzene conversion.379 Various coals for the synthesis of isobutylene380 and activated carbon in the synthesis of styrene381 were used in further studies. 

Thus when P = 1 bar, a e = 0.70, i.e. the maximum possible conversion has now been raised to 70 per cent. Inspection of equation C shows that the equilibrium conversion increases as the ratio of steam to ethylbenzene increases. However, as more steam is used, its cost increases and offsets the value of the increase in ethylbenzene conversion. The optimum steam ethylbenzene ratio is thus determined by an economic balance. 

Fig. 1.12. Maximum temperature (a) and ethylbenzene conversion (b) during one production cycle for a fixed bed of uniform heat capacity (dotted line), fora structured fixed-bed with inert end sections of higher heat capacity (dashed line), and for latent heat storage inside the catalytic section (solid line) [9].

However, when membrane tubes are inserted in the fluidized-bed reactor, hydrogen is continuously removed from the reaction mixture thus, the main reaction of ethylbenzene dehydrogenation continues to move in the direction of forward reaction. The ethylbenzene conversion and the yield of styrene increase as a result of the selective permeation of hydrogen through the membrane. Both the conversion and the yield exceed those of the industrial fixed-bed reactors and fluidized-bed reactors without membranes. When 16 membrane tubes are used, the selectivity to styrene is expected to be almost 100% due to suppression of by-products such as toluene [Abdalla and Elnashaie, 1995]. A high ethylbenzene conversion (96.5%) along with a high styrene yield (92.4%) is possible under properly selected realistic conditions. 

P10-26b The hydrogenation of ethylbenzene to ethylcyclohexane over a nickel-mordenite catalyst is zero-order in both reactants up to an ethylbenzene conversion of 75% [Ind. Eng. Chem. Res., 280), 260 (1989)]. At 553 K,k = 5.8 mol ethylbenzene/(dm of catalyst, h). When a 100 ppm thiophene concentration entered the system, the ethylbenzene conversion began to drop. 

The substitution of aluminium for boron in zeolites leads to a material with decreased Broensted acidity. These properties have been successfully applied in industrial processes, such as the Assoreni (methyl tertiobuthylether into methanol and isobutene) and Amoco processes (xylene isomerization and ethylbenzene conversion) [1-3]. Recently, the methanol conversion, the alkylation of toluene with methanol and the xylene isomerization on borosilicalites were critically analyzed [4]. 

The Sud-Chemie Group and Criterion Catalysts are the major catalyst developers and manufacturers for the styrene industry. Both companies offer a wide range of catalysts to suit individual processing needs. Ethylbenzene conversion, styrene selectivity, catalyst activity, and catalyst stability can be optimized by selecting the best catalyst or a combination of catalysts for a particular application. Dow and BASF manufacture proprietary catalysts, which have been mainly for use in their own respective technologies. 

Figure 4. Selectivity for ethylbenzene conversion plotted against xylene losses for A MeAPSO s, LZ-105 and SAPO s.

While the present study has not examined the performance of zeolite based catalysts, Table V summarizes patent literature data(23b) for a mordenite and platinum/alumina mixture. Data for the Pt and SAPO-11 mixture obtained under similar conditions are presented for comparison. The mordenite catalyst is significantly less selective than SAPO-11, giving 25.6% ethylbenzene conversion with only 0.5% net xylene production. 

The data obtained with high ethylbenzene feed shows even more dramatically the efficient conversion of ethylbenzene to xylenes over the SAPO-ll-containing catalyst. Thus at 23.6% ethylbenzene conversion, a nearly 13% increase in xylene yield is observed. 

Borosilicate catalysts provide high approach to thermodynamic equilibrium of the xylenes, and offer high selectivity in the conversion of ethylbenzene (8.12.22.50 ). In addition, they have been shown to be less prone to the effects of thermal and steam treatments than corresponding aluminosilicate zeolite catalysts (51). The catalytic activity of borosilicate catalysts was demonstrated to be a function of the structural boron content of the molecular sieve (22.36,50). In addition, the by-product distribution obtained from a borosilicate catalyst in a xylene isomerization/ethylbenzene conversion process was found to be distinctive (50), with high transethylation reactivity relative to transmethylation. 

Reactions 1, 2 and 3 are expressed in terms of ethylbenzene conversion. The sum of these conversions gives the total conversion of ethylbenzene. 

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