Cumene cracking reaction

ILLUSTRATION 12.2 DETERMINATION OF CATALYST EFFECTIVENESS FACTOR FOR THE CUMENE CRACKING REACTION FROM MEASUREMENT OF AN APPARENT RATE CONSTANT... 

The cumene cracking reaction has been studied by a number of investigators because it is a... 

The specific surface area was measured by nitrogen adsorption at -195 C. The cumene cracking reaction was conducted by pulse technique under the following conditions O.IO g catalyst, H, flow rate 75 ml/nin, pulse volume 1 ul. 

Few authors considered the reactivity of hydroxyl groups at catalyti-cally interesting temperatures. In situ infrared spectroscopy showed that in the cumene cracking reaction the 3550 cm-1 hydroxyls in a HY sample are only affected above 325° C. The 3650 cm-1 hydroxyl decreased in intensity at 250° C (6). During the cracking of hexane on a similar sample the gradual deactivation of the catalyst is accompanied by the progressive... 

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. 

Acid catalysts such as zeolites can be readily poisoned by basic organic compounds. One of the earlier studies of the deactivation of silica-alumina cracking catalysts by organic nitrogen compounds such as quinoline, quinaldine, pyrrole, piperidine, decylamine and aniline was done by Mills et al (6). The results of their partial poisoning studies showed an exponential dependence of the catalyst activity for cumene cracking reaction or... 

On the basis of the poisoning studies, the number of active sites of the catalyst were 1.63 x 10 per gram obtained from pyridine poisoning and cumene cracking reaction at 300°C. This number is close to the number reported by Jacobs and Heylen (13) in the study of poisoning with 2,6-methylpyridine of cumene cracking activity of the HY zeolites. 

The cumene cracking reaction was studied at 325°C. The simple kinetic equation... 

ILLUSTRATION 12.3 Determination of Catalyst Effectiveness Factor for the Cumene Cracking Reaction Using the Effective Diffusivity Approach... 

The cumene (isopropyl benzene) cracking reaction is often used as a model reaction for determining the relative activities of cracking catalysts. 

Tphe excellent catalytic activity of lanthanum exchanged faujasite zeo-A lites in reactions involving carbonium ions has been reported previously (1—10). Studies deal with isomerization (o-xylene (1), 1-methy 1-2-ethylbenzene (2)), alkylation (ethylene-benzene (3) propylene-benzene (4), propylene-toluene (5)), and cracking reactions (n-butane (5), n-hexane, n-heptane, ethylbenzene (6), cumene (7, 8, 10)). The catalytic activity of LaY zeolites is equivalent to that of HY zeolites (5 7). The stability of activity for LaY was studied after thermal treatment up to 750° C. However, discrepancies arise in the determination of the optimal temperatures of pretreatment. For the same kind of reaction (alkylation), the activity increases (4), remains constant (5), or decreases (3) with increasing temperatures. These results may be attributed to experimental conditions (5) and to differences in the nature of the active sites involved. Other factors, such as the introduction of cations (11) and rehydration treatments (6), may influence the catalytic activity. Water vapor effects are easily... 

The purpose of the present work is to incorporate aluminum into the framework of SBA-15 during the synthesis in order to create acid sites on the surface of the material directly and to enhance its activity in acid-catalyzed reactions and to study the stability of SBA and AlSBA molecular sieves under various treatments. The influence of these treatments on the pore size, wall thickness and the environment of Al in these materials are investigated in detail. X-ray diffraction (XRD), Electron Microscopy (TEM) and N2 adsorption were used to characterize the structure, the porosity and the stability of these materials. 27Al MAS NMR was used to ascertain the nature and environment of Al, cumene cracking to test the catalytic activity of parent materials and ammonia chemisorption to probe their surface acidity. 

The catalytic activity of SBA and AISBA samples toward cumene cracking were tested in a continuous flow fixed-bed microreactor system with helium (25 mL min 1) as carrier gas. The catalyst load for the tests was 100 mg and the catalyst was preheated at 573 K under helium flow for 3 h. For the reaction, a stream of cumene vapor in helium was generated using a saturator at room temperature. The reaction products were analyzed by gas chromatography. 

The second drawback—that acid colors can be produced by processes other than simple proton addition—is more serious. The case of alumina is an example. Several of the indicators listed in Table I give faint acid colors with samples of pure, activated aluminas that have previously been shown to be inactive for an acid-catalyzed reaction such as cumene cracking (22). However, closer visual examination indicates that the acid... 

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... 

On examinination of the results of the integral-reactor studies, one or more sources of uncertainty were found in each case, which makes the kinetic conclusion drawn from them doubtful. The three major sources of uncertainty are (1) the use of a method which is insensitive to the precise functional forms of the kinetics, (2) the presence of diffusion-transport effects which modify the kinetics, and (3) the presence in the cumene used of strong inhibitors of the cracking reaction. 

Any study of cumene cracking made above 400°C. with commercial cracking catalyst of conventional activity levels, with particle size of approximately 1 mm. or greater (as is the usual practice in integral reactor studies), and with pure cumene will almost certainly be diffusion limited. If this is not the case, it is by virtue of the fact that the cumene contains inhibitors which reduce the reaction rate and, of course, alter the kinetics of the reaction. This can be seen by considering the diffusion results in Table IV and the discussion of effect of inhibitors. 

Thiele (17), Wheeler (12), and Weisz and Prater (1) have given ij vs. curves for some integral-order reaction kinetics. However, the kinetics of cumene cracking does not exhibit a simple constant order. Instead, the order is a function of partial pressure of reactants and products. To determine the jj vs. curve for this kinetics, the diffusion equation... 

In order to determine whether the relationships discovered for coke formation from cumene hydroperoxide might reflect a more general behavior concerning coke formation in cracking reactions, experiments were undertaken with a light East Texas gas oil (LETGO). Such gas oils contain a large variety of inhibitors. 

The best methods known to us Were used to free the cumene from inhibitors of the cracking reaction. The presence of appreciable amounts of inhibitors in the cumene would affect the value of the constant 0 obtained. Let G be such a measured constant and G be the true constant. Then... 

The deactivation of a lanthanum exchanged zeolite Y catalyst for isopropyl benzene (cumene) cracking was studied using a thermobalance. The kinetics of the main reaction and the coking reaction were determined. The effects of catalyst coke content and poisoning by nitrogen compounds, quinoline, pyridine, and aniline, were evaluated. The Froment-Bischoff approach to modeling catalyst deactivation was used. 

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