Cracking of cumene

The Kinetics of the Cracking of Cumene by Silica-Alumina Catalysts Charles D. Prater and Rudolph M. Laqo... 

ZSM-5 Cracking of cumene and heavy oil Higher cracking activity Higher yield to light olefins [55]... 

Corrigan et al. [Chem. Eng. Prog., 49 (603), 1953] have investigated the catalytic cracking of cumene over a silica-alumina catalyst at 950 °C. 

Chromium zeolites are recognised to possess, at least at the laboratory scale, notable catalytic properties like in ethylene polymerization, oxidation of hydrocarbons, cracking of cumene, disproportionation of n-heptane, and thermolysis of H20 [ 1 ]. Several factors may have an effect on the catalytic activity of the chromium catalysts, such as the oxidation state, the structure (amorphous or crystalline, mono/di-chromate or polychromates, oxides, etc.) and the interaction of the chromium species with the support which depends essentially on the catalysts preparation method. They are ruled principally by several parameters such as the metal loading, the support characteristics, and the nature of the post-treatment (calcination, reduction, etc.). The nature of metal precursor is a parameter which can affect the predominance of chromium species in zeolite. In the case of solid-state exchange, the exchange process initially takes place at the solid- solid interface between the precursor salt and zeolite grains, and the success of the exchange depends on the type of interactions developed [2]. The aim of this work is to study the effect of the chromium precursor on the physicochemical properties of chromium loaded ZSM-5 catalysts and their catalytic performance in ethylene ammoxidation to acetonitrile. 

The activity of zeolite catalyst for the cracking of cumene was measured at several onstream periods at cumene flow rates of u = 0.01 mol/s and 0.32 mol/s (IECPDD 22 609, 1983). The results are tabulated. Taking the relation to be... 

Benzene and propylene are made by cracking of cumene over a silica-alumina catalyst at constant volume in a batch reactor. Initial content of cumene is 9.9%, the remainder inert. The pressure is 20 atm. The tabulated data are of t in sec against x fraction converted (Fogler, 331, 1992), The... 

The disproportionation and isomerization of trimethylbenzene(TrMB) were studied at 200°C using a continuous fixed bed reactor. The reactant TrMB was diluted with nitrogen in a molar ratio of 1 9. The cracking of cumene was carried out at 400 C using a pulse reactor. The catalyst was treated in a stream of nitrogen for 1 h at a desired temperature in the range 400-600°C prior... 

As expected from the TPD results, Al-sapo was more active for the cracking of cumene on a per weight of catalyst basis than Al-mont. In order to compare the catalytic activity on a basis of active sites, we evaluated the number of active sites on these catalysts. TPD spectra were measured with varying the temperature of ammonia adsorption. Typical results on Al-mont are shown in Fig. 2. By integrating these spectra, the concentration of acid sites corresponding to different strength of acidity can be determined. 

It is noted that the microporous effect was greater in the disproportionation of 1,2,4-TrMB than in the cracking of cumene. As shown in the previous paper [14], the disproportionation of 1,2,4-TrMB at 200°C proceeds via a bimolecular transition state and obeys the second order kinetics. In contrast, the cracking of cumene is the first order kinetics with respect to cumene concentration. Thus, it seems that the microporous effect is exerted more significantly in the second order reaction (disproportionation) than in the first order reaction (cracking) if pore structure plays an important role in localizing concentration of reactant molecules. 

Table 13 collects values of adsorption coefficients of some compounds determined by means of this equation from experiments on the cracking of cumene on an aluminosilicate catalyst. 

The acidic nature of NiCaY after reduction of the metal can be illustrated by using the model reaction of cracking of cumene. Figure 3 shows the catalytic activity at various temperatures and the yields of the products. The catalyst possesses high activity even at 200°C, where the conversion is 20.5 mole %. At 400° C the activity increases and the conversion reaches 97.1 mole %. At 200°C dealkylation is accompanied by disproportionation with formation of diisopropylbenzene. With increasing temperature the disproportionation decreases, while hydrogenolysis of the alkyl chain is strongly increased. 

Fig. 16. Cracking of cumene at 500°C over samples of chlorided alumina (22). (Reprinted with permission of N. V. Boekhandel Drukkerij, Leiden.)...

Lewis acid centers, which were thought to be the primary catalytic sites. Boreskova et al. (51) studied the poisoning effect of quinoline on the cracking of cumene over Na, H—Y zeolite and observed a linear decrease in activity with the amount of quinoline added until a constant level of activity was reached. The catalytic activity was attributed to trivalent aluminum centers (Lewis acids), which were poisoned by coordinately bound quinoline. In a similar study of cumene cracking, Turkevich et al. (50) also concluded on the basis of magnetic resonance experiments that Lewis centers were the active sites. 

Catalytic activity measurements and correlations with surface acidity have been obtained by numerous investigators. The reactions studied most frequently are cracking of cumene or normal paraffins and isomerization reactions both types of reactions proceed by carbonium ion mechanisms. Venuto et al. (219) investigated alkylation reactions over rare earth ion-exchanged X zeolite catalysts (REX). On the basis of product distributions, patterns of substrate reactivity, and deuterium tracer experiments, they concluded that zeolite-catalyzed alkylation proceeded via carbonium ion mechanisms. The reactions that occurred over REX catalysts such as alkylation of benzene/phenol with ethylene, isomerization of o-xylene, and isomerization of paraffins, resulted in product distribu-... 

Cumene Cracking Reactions on Separated Fractions. Cumene cracking reactions were tested on a gravimetric setup the basic flow diagram for the reactor system is shown in Figure 1. The reactor determines both the activity of the catalyst (cracking of cumene to benzene and propylene) and the instantaneous rate at which coke is deposited on the catalyst (polymerization of the propylene). Conversion of the cumene is adjusted to exclude the amount of cumene disproportionation which yields benzene and diisopropyl benzene. 

In this paper we shall review the information found in the literature concerning the kinetics of cracking of cumene on silica-alumina. We shall also present some new experimental studies which take into account the precautions outlined in the preceding reference. 

The cracking of cumene has received considerable attention in recent years as a reaction typical of one class of cracking reactions, namely dealkylation of aromatics. Among the studies of cumene cracking found in the literature there are several attempts to determine the kinetics of... 

Column II of Table IV gives, for each particle size, the rate of cracking of cumene above which diffusion phenomena will influence the observed kinetics for the silica-alumina catalyst described. Column III of Table IV gives the temperature at which these rates are observed for very pure cumene. This temperature was determined from the experi-... 

Effect of Distillation and Chromatographing Procedures on Rate of Cracking of Cumene by a Silica-Alumina Catalyst... 

Fig. 4. Time course of the rate of cracking of cumene by silica-alumina catalyst at 420°C. and atmospheric pressure.

Fig. 9. Rate of cracking of cumene containing cumene hydroperoxide at 420°C. as a function of absolute pressure. The solid lines are theoretical curves derived from the kinetics scheme [Eq. (9)].

Fig. 10. Rate of cracking of cumene at atmospheric pressure as a function of mole fraction of cumene hydroperoxide present. The solid curve is a plot of Eq. (11), where the values of kiBo and 0 were determined from pure-cumene pressure studies and the value of Ki was determined from pressure studies with cumene containing cumene hydroperoxide.

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