Cumene cracking, on silica alumina

The Inhibition of Cumene Cracking on Silica-Alumina by Various Substances... 

Figure 7.7 Variation in apparent activation energy with extent of diffusion for cumene cracking on silica/alumina. [After P.B. Weisz and C.D. Prater, Advan. Catalysis, 6, 144, with permission of Academic Press, Inc., New York, NY, (1954).]...

Fig. 10. Poisoning effect of amines on cumene cracking over silica-alumina catalyst 1, quinoline 2, quinaldine 3, pyrrole 4, piperidine 5, decylamine 6, aniline (32). (Reprinted with permission of the American Chemical Society.)...

The work by Mills et al. (32) includes an early example of catalytic titration behavior. Figure 10 taken from their study shows that cumene cracking at 425°C drops sharply as nitrogen bases are chemisorbed in increasing amounts on silica-alumina catalyst. Base effectiveness decreases in the order quinaldine > quinoline > pyrrole > piperidine > decylamine > aniline. 

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. 

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

Fig. 16. The effect of diffusion transport on a zero order kinetics. Pressure dependence in cracking of cumene on silica-alumina, with experimental data of Corrigan et al. (17).

The spectral chemisorption studies described above have been carried out at room temperature. Tachibana and Okuda 95) succeeded in observing a band at 335 mp of an unstable intermediate during the dealkylation cracking of cumene on silica-alumina at 150°C. The band... 

In the elucidation of the kinetics of the cracking of cumene on silica-alumina catalyst, the actions of inhibitors (poisons) on the reaction were studied. These inhibitors compete with cumene for cracking sites. Theoretical analysis leads to an expression from which the equilibrium constant for adsorption of inhibitors on cracking sites can be calculated. 

Various kinds of oxide materials, including single oxides, mixed oxides, molybdates, heteropoly-ions, clays, and zeolites, are used in catalysis they can be amorphous or crystalline, acid or basic. Furthermore the oxides can be the actual catalysts or they can act as supports on which the active catalysts have been deposited. Silica and alumina are commonly used to support both metals and other metal oxide species. Amorphous silica/alumina is a solid acid catalyst, it is also used as a support for metals, when bifunctional (acid and metal) catalysis is required, e.g., in the cracking of hydrocarbons. Other acid catalysts are those obtained by the deposition of a soluble acid on an inert support, such as phosphoric acid on silica (SPA, used in the alkylation of benzene to cumene. Section 5.2.3). They show similar properties to those of the soluble parent acids, while allowing easier handling and fixed bed operation in commercial units. 

The rate constant for the first-order cracking of cumene on a silica-alumina catalyst was measured to be 0.80 cm /(s-gcat) in a laboratory reactor ... 

Further evidence for the need of protons for carboniogenic activity is given by Matsumoto et al. (58), who have shown that NaY, which is inactive for cumene cracking, can be made into an active catalyst by the addition of HCl. This effect of HCl is reversible. In contrast, silica gains no activity on HCl addition, and y-alumina is activated irreversibly by HCl. Similar observations were made by Kolesnikov et al. (51), who found that in the propylation of benzene, a treatment with propyl chloride promotes the activity of NaY and of type X zeolites. 

The possible effect of competing molecular components on the kinetics of a reaction can be illustrated by studies made on the cracking of cumene to propylene and benzene over silica-alumina catalyst in the presence of various diluents in the vapor phase. 

The catalyst used is a commercial catalyst known as the super-D manufactured by Crosfield Chemicals Ltd., UK. It is in the form of particulate spheroid with an average diameter of 81 microns and consists of 15-18% ion exchanged Re sodium Y-zeolites on a support silica-alumina matrix. Heat treatment of catalyst particles at 150°C for 48 hours is undertaken before cracking reaction commenced. The isopropyl benzene (cumene) has the purity higher than 99.5% which was supplied by Fissons Scientific Apparatus. 

Recently Tachibana and Okuda 18) studied the electronic spectrum of cumene adsorbed on a silica-alumina catalyst during its cracking reaction and suggested that a Bronstcd acid contributes to the cracking reaction through the formation of protonated cumene. 

Cumene (isopropylbenzene) cracking by porous silica-alumina catalyst has been studied extensively. This includes studies with respect to coke production (I, M), the maximum depth of active centers (3), kinetics 4), and the effect of diffusion transport phenomena on the kinetics (5). 

Studies (4) made on the cracking of cumene by silica-alumina catalyst show that the kinetics is represented in the temperature range 300-500° by scheme I on top of the following page, where S is cumene, A is a catalytic site, SA is adsorbed cumene, m is benzene, mA is adsorbed benzene, n is propylene, P is an inhibitor, and PA is inhibitor adsorbed on a cracking site. 

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