Cumene cracking reaction rate

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

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. 

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. 

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. 

For each run in a differential reactor the plug flow performance equation was used to obtain the reaction rate of cumene cracking as follows ... 

The cumene cracking activities over zeolites with different amounts of pyridine, quinoline and aniline adsorption were studied. The reaction rate data of cumene cracking were treated by linearization of eq. (11) as follows ... 

Surface Characterization of the Stabilized Catalyst by Probe Molecule Reaction. HZSM-5 obtained from PQ Zeolite was chosen to study the mechanism of stabilization in light naphtha aromatization. The reactions of both molecules were carried out over stabilized and unstabilized HZSM-5. We assumed first order kinetics with respect to each reactant concentration and first order decay of each reaction, and calculated initial rate constants. Figure 6 shows the initial rate constants of cumene cracking and triisopropyl-benzene cracking over the stabilized and the unstabilized catalysts. 

The catalytic work on the zeolites has been carried out using the pulse microreactor technique (4) on the following reactions cracking of cumene, isomerization of 1-butene to 2-butene, polymerization of ethylene, equilibration of hydrogen-deuterium gas, and the ortho-para hydrogen conversion. These reactions were studied as a function of replacement of sodium by ammonium ion and subsequent heat treatment of the material (3). Furthermore, in some cases a surface titration of the catalytic sites was used to determine not only the number of sites but also the activity per site. Measurements at different temperatures permitted the determination of the absolute rate at each temperature with subsequent calculation of the activation energy and the entropy factor. For cumene cracking, the number of active sites was found to be equal to the number of sodium ions replaced in the catalyst synthesis by ammonium ions up to about 50% replacement. This proved that the active sites were either Bronsted or Lewis acid sites or both. Physical defects such as strains in the crystals were thus eliminated and the... 

It has been pointed out by others 2, 4, 6) that even the best grades of cumene accumulate inhibitor of the cracking reaction during storage. The cracking rate of such a sample can often be increased by more than an order of magnitude if the cumene is either vacuum distilled at room temperature or passed through a column of fresh burnt clay and silica gel. 

Cumene is cracked in a recycle reactor over commercial H-ZSM5 extrudates during a pulse experiment. The results are compared to those obtained from steady state measurements. A linear model for diffusion, adsorption and reaction rate is applied to reactants and products. In contrast to literature it is shown that if the Thiele modulus is greater than 5, the system becomes over parameterised. If additionally adsorption dynamics are negligible or not measurable, only one lumped parameter can be extracted, which is the apparent reaction constant found from steady state experiments. The pulse experiment of cumene is strongly diffusion limited showing no adsorption dynamics of cumene. However, benzene adsorbed strongly on the zeolite and could be used to extract transient model parameters. 

The cracking of cumene into benzene and propylene was carried out in a fixed bed ol zeolite particles at 362°C and atmospheric pressure, in the presence of a large excess of nitrogen. At a point in the reactor where the cumene partial pressure was 0.0689 atm, a reaction rate of 0.153 kmol/kgcathr was observed. 

Figure 14-3. Effect of the temperature of calc. 1 on cumene cracking activity of Ca -PTSM. Reaction temp.= 300 C, W/F= 33 g-cat. h/mol, flow rate of carrier gas= 600 ml/h.

Cumene cracking was used as a model reaction (Guisnet 1985) to detect the active acid sites in A1-PSBCS(0) and A1-PSBCS(3.0). The reaction was carried out in a pulse microreactor. The catalyst was calcined in air at 400 C for 3 hours, crushed, and screened to 40/60 mesh. A catalyst of 0.20g was preheated for Ih at 400°C under a nitrogen stream of flow rate=30 cmVmin,... 

A commercial cumene cracking catalyst is in the form of pellets with a diameter of 0.35 cm which have a surface area. Am, of 420 m g and a void volume, Vm, of 0.42cm g. The pellet density is 1.14g cm. The measured l -order rate constant for this reaction at 685K was 1.49cm s g . Assume that Knudsen diffusion dominates and the path length is determined by the pore diameter, dp. An average pore radius can be estimated from the relationship fp = 2Vm/Am if the pores are modeled as noninterconnected cylinders (see equation 4.94). Assuming isothermal operation, calculate the Thiele modulus and determine the effectiveness factor, tti, vmder these conditions. 

A catalyst for cracking cumene is available commercially in the form of 0.35 cm diameter pellets. These pellets have a specific surface area of 420 m2/g and a void volume of 0.42 cm3/g. If the apparent first-order rate constant for this reaction is 1.49 cm3/sec-g catalyst at 412 °C, determine the effectiveness factor of the catalyst. 

Despite the presence of sites that strongly chemisorb a variety of molecules, pure silica gel is catalytically inactive for skeletal transformations of hydrocarbons. However, as has recently been emphasized by West et al. (79), only trace amounts of acid-producing impurities such as aluminum need be present in pure silica gel to provide catalytic activity— especially when a facile reaction such as olefin isomerization is used as a test reaction. They found that addition of 0.012% Al to silica gel resulted in a 10,000-fold increase in the rate of hexene-1 isomerization at 100°C over the pure gel. An earlier study by Tamele et al. (22) showed that introduction of 0.01% wt Al in silica gel produces a 40-fold increase in cumene conversion when this hydrocarbon is cracked at 500°C. The more highly acidic solids that are formed when substantial concentrations of metal oxides are incorporated with silica are discussed in following sections. 

This model has been successfully used by Kato et al. (1979) to interpret results for the reactant conversion in the case of catalytic cracking of cumene in a packed fluidized bed under conditions of no deactivation. When catalyst deactivation exists, the authors have shown that for reactions with high initial rate constants (>1.0 L/s), the reactant conversion can be calculated by assuming perfect mixing of particles in the bed. For reaction with lower initial rate constants (<0.3 L/s), the assumption of plug flow of particles within the bed seems adequate. 

A number of acid catalyzed reactions have been examined in which the PILCS were compared to zeolites. Shabtai et al. [47] compared the rates of reaction for dealkylation of cumene and 1-isopropylnaphthalene and for cracking of polycyclic naphthenes catalyzed by a pillared montmorillonite with rates of these reactions catalyzed by a Y-type zeolite. In each case the PILC, whether in the H or rare earth form, was found to have a higher activity. When the reactant molecule was larger than the zeolite windows, the rates of the PILC-catalyzed reaction were much greater than those of the zeolite-catalyzed reaction. Some of the data are summarized in Table V. 

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