Disproportionation of ethylbenzene

As already stated, isomerization on zeolite HY was always accompanied by disproportionation, even at 180 C. With time on stream, Yo,. Np increases, because these heavy products are most efficiently held by the fresh catalyst. It is an interesting result that, at 180 °C, the yield of naphthalene passed through a maximiun as well. Obviously, under appropriate reaction conditions, the disproportiotuOion of methylnaphthalenes in zeolite HY exhibits an induction period, as does the disproportionation of ethylbenzene in large pore zeolites [39,40]. 

H.G.KarQe,J.Ladebefc.J.Sart>ak,K.Hafada Conversion of Aflcytoenzenes over Zeofite Catalysis liDealkylalion and Disproportionation of Ethylbenzene over Mordenites, Zeolites 2 (1982) 94... 

H.G.Karge,K.Hatada,Y.Zbang.R.FIedoraw Conversion of Alkylbenzenes over Zeotfle Catalysts 1l Dealky1ation and Disproportionation of Ethylbenzene over Faujasite-Type 2bol ites. Zeolites (19 )... 

The disproportionation of ethylbenzene (EB) to benzene (B) and diethylbenzenes (DEB) serves as a case study. This reaction has been introduced by Karge et al. and Weitkamp et al. to compare the activity of different zeolite catalysts [58, 59], and to distinguish between medium- and large-pore zeolites [112, 60], Moreover, since 1994, it has been further developed as a standardized test reaction by the International Zeolite Association (IZA) [55], A general representation of the individual transformations which occur in this type of reaction, is given in the following scheme ... 

Investigations concerning the effects of precoking have been carried out for example on ZSM-5 catalysts for xylene production by disproportionation or alkylation of toluene [102]. During these experiments, an increase of the p-xylene selectivity could be observed. By a defined precoking, it is also possible to generate product-selectivity effects initially not present, as has been shown for the disproportionation of ethylbenzene on HY-zeolites [63]. 

Evaluating the catalytic shape-selectivities of these materials by use of the disproportionation of ethylbenzene (23.24) at 523 K at a conversion of 2% in differential reactor mode, it was observed that larger crystals of sample A gave 85% para-diethylbenzene and 15% meta-diethylbenzene. The smaller crystals of sample B with the smoother aluminium gradient yielded 96% para-diethylbenzene and only 4% meta-isomer. In a second series, samples of crushed large crystals with mean sizes of 1-10 (m were examined. No increase in activity was observed as is expected when the reaction is controlled by the diffusion limitation of molecules in the large crystals. However, this treatment created larger non-selective external surface area and hence a smaller selectivity of 87% para-diethylbenzene for sample B was recorded. 

Three different zeolites (USY-zeolite, H-ZSM-5 and H-mordenite) were investigated in a computer controlled experimental equipment under supercritical conditions using the disproportionation of ethylbenzene as test reaction and butane or pentane as an inert gas. Experiments were carried out at a pressure of 50 bar, a flow rate of 450 ml/min (at standard temperature and pressure), a range of temperatures (573 - 673 K) and 0.8 as molar fraction of ethylbenzene (EB) in the feed. The results showed that an extraction of coke deposited on the catalysts strongly depends on the physico-chemical properties of the catalysts. Coke deposited on Lewis centres can be more easily dissolved by supercritical fluid than that on Brnsted centres. 

In this paper three zeolite catalysts from Sud-Chemie AG (USY-zeolite Si/Al 2.3-2.5, H-ZSM-5 Si/Al 15 and H-mordenite Si/Al 10) have been investigated in a gradientless reactor under supercritical conditions using the disproportionation of ethylbenzene (EBD) as test reaction and butane or pentane as inert. A previous publication reported investigations on those three catalysts at normal pressure and the details about the geometry of the three zeolites [6]. 

It is perhaps easier to introduce a step function into the flow rate to a reactor than to generate a step function in the feed concentration. A recent interesting example 28) involves the disproportionation of ethylbenzene to benzene and diethylbenzenes over an HY zeolite at approximately 500 K. When the flow q is decreased from 120 to 30 ml/min, there is an immediate... 

Figure 3. The relative activity in the disproportionation of ethylbenzene as a function of the pretreatment temperature for NH4Y2.35 (l)x NH4Y2.8 (2), DY4.8 (3)...

The disproportionation of ethylbenzene (EB) to benzene (B) and diethylbenzenes (DEB) is an acid-catalysed reaction that occurs readily on a great variety of acid zeolites [1-6]. Under appropriate conditions, the reaction proceeds without deactivation with a rate which is proportional to the number of Bronsted sites it can be performed at atmospheric pressure in simple fixed-bed flow reactors. Thus, the reaction offers itself as a test reaction for assessing the catalytic activity of zeolites [3-4]. At low temperatures, i.e., below 535 K, excellent stoichiometry to equimolar quantities of benzene and diethylbenzene is observed ... 

The results shown in Figure 1 suggest that the inhibitory effect originates exclusively from the adsorption of diethylbenzenes but not benzene. Therefore, it should be possible to describe the rate, r, of the disproportionation of ethylbenzene by a Langmuir-type expression where the term for the adsorption of the diethylbenzenes, Kdeb [DEB], appears in the denominator ... 

Typical test reactions often used for the characterization of zeolites are the cracking of n-hexane - and disproportionation of ethylbenzene. The catalytic activity of a zeolite is determined by the concentration of protons and the acid strength. 

While the ion exchange with alkaline metal cations does not result in catalysts active in acid-catalysed hydrocarbon reactions and, in contrast, may be carried out to remove any residual activity [1], the incorporation of alkaline earth cations by solid-state reaction should lead to active catalysts. It was shown, however, that the solid-state ion exchange had to be followed by contact with water vapour in order to obtain calcium or magnesium mordenites which are sufficiently active in, for instance, disproportionation of ethylbenzene. This is in full agreement with the IR spectroscopic results which indeed showed that only upon interaction of the heat-treated CaCl2/H-MOR mixture with water vapour were acidic OH groups generated. 

Fig. 9. Selective disproportionation of ethylbenzene at 425 K (1.3 vol % EB in He, 5ml min, m[cat] = 0.25 g). A, over a La-Y (98) catalyst obtained by solid-state ion exchange B, over a conventionally prepared La-Y (96) catalyst.

Fig. 4. Selective disproportionation of ethylbenzene over La,H-Y zeolites. The catalysts were prepared (a) by a solid-state reaction between LaCl3 and the corresponding zeolite and (b) by conventional ion exchange. Experimental conditions T = 182°C 1.3 vol% ethylbenzene in He, total flow 5 ml min-1, m(cat) = 0.25 g. (After...

The large pore zeolite MCM-58 has been synthesized with nsi/nAi-ratios varying from 15 to 35 and also in its new gallosilicate form [Ga]MCM-58 with a ns/noa ratio of 15. The catalytic properties of these materials were characterized using the disproportionation of ethylbenzene and the hydroconversion of n-decane as catalytic tests. MCM-58 and Pt-loaded MCM-58, respectively, proved to be highly active catalysts in these reactions. 

Restricted transition state selectivity is also of importance in the alkylation of benzene with ethylene to give ethylbenzene. High selectivities for ethylbenzene are achieved on H-ZSM-5 owing to suppression of side reactions. These high selectivities were also explained by the fact that the possible bimolecular disproportionation of ethylbenzene is suppressed. 

Figure 9. Selective disproportionation of ethylbenzene (EB) over La,Na-Y catalysts (A) prepared by solid-state reaction between LaClg and Na-Y (for details see text) and (B) prepared by conventional ion exchange in aqueous suspension T[react]=455 K, 1.3 vol% EB in He, 5ml-min, m[cat]=0.25 g (after Ref. [23]).

Conversion of alkylbenzenes over zeolite catalysts. I-Dealkylation and disproportionation of ethylbenzene over... 

Weitkemp carried out the disproportionation of ethylbenzene over a variety of catalysts and concluded that this reaction is a valuable test reaction for the characterization of zeolites of unknown structure. Useful criteria are the presence or absence of... 

A very high / ara-selectivity of inorganic-modified ZSM-5 was also manifested in the disproportionation of ethylbenzene. The results with ZSM-5 modified with magnesium and phosphorus compounds are shown in Table 4.10. The concentration of ara-isomer in the diethylbenzene products was over 99%. ... 

Kaeding WW. Shape-selective reactions with zeolite catalysts V. Alkylation or disproportionation of ethylbenzene to produce p-diethylbenzene. J Catal 1985 95 512-9. 

Fig. 23. Disproportionation of ethylbenzene in a flow-reactor at 425 K after catalyst activation at 725 K in a flow of dry helium, subsequent hydration (1.2 10 Pa water vapor followed by degassing at 625 K) over La,Na-Y catalysts prepared by A solid-state ion exchange and B conventional exchange degree of exchange in La,Na-Y about 98% (after [78], with permission)...

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