Catalytic Cracking Of Cumene Research Articles

A Simple Method of Preparation of High Silica Zeolite Y and Its Performance in the Catalytic Cracking of Cumene

A series of high silicon zeolites Y were prepared through direct synthetic method by using silica sol as the silicon source and sodium aluminate as the aluminum source. The effects of alkalinity and crystallization time of the process of synthesis were investigated. To separately reveal the crystalline structure, element content, morphology, and surface areas, the as-synthesized zeolite Y was characterized by powder X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and N2adsorption-desorption isotherms (BET). The results show the as-synthesized zeolite Y with high relative crystallization and uniform morphology; the SiO2/Al2O3ratio was about 4.54~6.46. For an application, the zeolite cracking activity was studied with cumene as the probe molecules.

Poisoning effect of nitrogen compounds on the transformation of model hydrocarbons and real feed under catalytic cracking conditions

The effect of the content and nature of nitrogen compounds on the distribution of target products in transforming model hydrocarbons under cracking conditions over equilibrium zeolite-containing catalyst was studied. Using cracking of n-undecane as an example, a nearly 50% drop in the conversion and in yields of propane-propene (PPF) and butane-butene fractions (BBF) was observed when the pyrrol content in the feed was raised to 3000 ppm of nitrogen. Increasing the nitrogen content in the feed led to a nonlinear reduction in the rate constants of n-undecane cracking. It was found that the dependence of the yields of PPF, BBF, and isobutane in BBF on the conversion remained constant upon the cracking of n-undecane with various of nitrogen compounds; poisoning was likely to proceeds only because the acidic sites of the catalyst were blocked. The high poisoning effect of pyrrol and indole upon the cracking of n-undecane and decalin (strong proton donors) was observed along with the formation of ammonia. Quinoline exhibited high poisoning ability in the catalytic cracking of cumene with low [H]-donor activity. Quinoline poisoned catalysts to a greater degree than indole, during the catalytic cracking of non-hydrofined vacuum gasoil with a high content of aromatic structures. Indole exhibited the highest poisoning ability in processing heavy hydrocracking residue which was rich of paraffin-naphthene hydrocarbons.

Mesoporous Y zeolite with homogeneous aluminum distribution obtained by sequential desilication–dealumination and its performance in the catalytic cracking of cumene and 1,3,5-triisopropylbenzene

The aluminum–silicon distribution and mesoporosity of Y zeolites prepared by sequential NaOH desilication and ammonium hexafluorosilicate (AHFS) dealumination are compared with that of Y samples prepared via AHFS dealumination only. AHFS treatment led to severe non-uniform dealumination and substantial surface silicon deposition. Y samples obtained by sequential desilication and dealumination had substantially better dealumination uniformity and aluminum–silicon distribution. The mesopore formation in these zeolites is discussed in detail. The desilication creates defects in the framework of the parent NaY zeolite. These defects improve the intra-crystalline transport and induce mesopore formation during dealumination. The desilication- plus dealumination-treated zeolites showed higher initial activity and lower deactivation tendency in the case of 1,3,5-triisopropylbenzene cracking, and higher conversion rate of cumene than those zeolites modified by AHFS treatment only. These catalytic data indicate that the former could be a viable catalyst in the catalytic cracking of heavy hydrocarbons.

Hydrocracking of heavy oil using zeolites Y/Al-SBA-15 composites as catalyst supports

A series of Y/Al-SBA-15 composites were prepared by a two-step synthesis procedure in mild acidic medium. The materials were characterized by powder X-ray diffraction (XRD), N2 sorption isotherms and TEM techniques. Catalytic cracking of cumene and 1,3,5-tri-isopropylbenzene was carried out as the probing reactions on these composites. The XRD results showed that these materials are composites of Al-SBA-15 and Y zeolite. N2 sorption isotherms and TEM displayed that these composites were abundant in micropores and mesopores. At the same time, the mesopores may communicate with the␣micropores in some domains, which may result in the high catalytic activities of Y/Al-SBA-15 composites for the␣cracking of both small-molecule (cumene) and large-molecule (1,3,5-tri-isopropylbenzene) hydrocarbons. The existence of mesopores may also make the acid sites easily accessible for reactants. Catalysts of W–Ni supported on Y/Al-SBA-15 and modified Y zeolites with mesopores were prepared by impregnation method, and the hydrocracking of heavy oil was performed on these catalysts. The catalyst using zeolite Y/mesoporous Al-SBA-15 composites as support gave higher yield of diesel compared to the catalysts using modified zeolite Y as support. In addition, the higher aromatics potential of heavy naphtha and the significantly lower BMCI (U.S. Bureau of Correlation Index) of tail oil revealed Y/Al-SBA-15 composite catalyst possessed integrated performance in the hydrocracking of heavy oil. These results proved that the combination of Y zeolites and mesoporous Al-SBA-15 plays a great role in improving the performance of catalysts for hydrocracking heavy oils.

Synthesis, Characterization and Catalytic Activities of Mesoporous AlMSU-X with Wormhole-Like Framework Structure

Mesoporous AlMSU-X molecular sieves with high acidity have been prepared from preformed beta nanoclusters under strong acidic conditions in the presence of nonionic TX-100 as structure directors. These materials were characterized by XRD, HRTEM, N2-adsorption, 27Al MAS NMR, NH3-TPD, IR-pyridine adsorption and catalytic cracking of cumene and 1,3,5-triisopropylbenzene. The experimental results showed that Al heteroatoms had been successfully incorporated into the framework structure of mesoporous MSU-X, and so-produced catalysts exhibited superior catalytic properties.

An experimental study of fluid catalytic cracking in a downer reactor

First results of an experimental study of the fluid catalytic cracking (FCC) process in a new type of reactor, the downflow gas–solids reactor or ‘downer’, are presented. A bench-scale experimental set-up has been constructed, the downer with an inner diameter of 25 mm and a length of 800 mm being the central part of it. As a first step in the development and characterisation of this reactor, catalytic cracking of cumene has been chosen as a model reaction. In a temperature range of 743–823 K, catalyst-to-oil (CTO) ratios up to 25 and residence times of 60–350 ms, conversions were between 10 and 70%. Comparison to modelling results, on the basis of a plug flow model, showed that the measured conversions were lower than expected on the basis of the calculations. The higher the solids mass flux, the greater the difference between the two, indicating that incomplete break-up of the solids stream entering the downer — with particle clusters negatively affecting transfer processes to and from the individual particles — might be the cause for these reduced conversions.

Textural, Structural and Catalytic Properties of Cr2O3/SiO2 Catalysts

Four chromia/silica samples containing 5–30 wt% CrIII were prepared by impregnation methods and calcined at 773–1173 K. Nickel, molybdenum and vanadium oxide-impregnated Cr2O3/SiO2 samples were also prepared by impregnation and were subjected to the same thermal treatment. The textural parameters of all the samples prepared were determined from the adsorption of nitrogen at 77 K, while X-ray diffraction (XRD) and differential thermal analysis (DTA) techniques were used to elucidate their structures. The catalytic properties of the solids so prepared in the catalytic cracking of cumene were investigated using a pulse microcatalytic technique. The surface areas evaluated for the various Cr2O3/SiO2 samples studied were found to decrease gradually on increasing their CrIII content, the calcination temperature and on addition of Ni, Mo and V oxides. DTA and XRD studies demonstrated the absence of any interaction between the SiO2 and Cr2O3, with the latter being the only phase capable of detection by these techniques. Samples impregnated with Ni, Mo and V ions also showed no interaction between these ions and Cr2O3 and SiO2, with only the corresponding oxides being detected. The results obtained for the catalysis studies also indicated that the cracking of cumene depended on the metal content, impregnant cations and thermal treatment of the solids employed.

The Catalytic Cracking of Cumene Interpreted as a Chain Mechanism

Recent publications on the chain mechanism of catalytic cracking have focused on paraffin cracking. Before we apply the concepts developed in those papers to olefins, we present the intermediate case of cumene cracking or, more generally, the dealkylation of aromatics. The benzene ring of cumene with its {pi} bonding character suggests that initiation in this case may not involve protolysis as it does in paraffin cracking but proceeds by proton addition to the benzene ring. At the same time, it has been reported that the benzene ring stays intact during the cracking process and dealkylation is the major reaction observed. By examining the product distribution and the initial molar selectivity data of any catalytic cracking reaction, a catalytic cracking chain mechanism can be developed using the principles previously defined. 10 refs., 3 tabs.

Surface and acidic properties of some mixed oxide catalysts in relation to their catalytic activities

A series of silica-alumina catalysts were prepared to contain different proportions of alumina. The catalysts were calcined at 773–973 K. Another series of silica-titania catalysts of different chemical compositions were prepared and calcined between 773 and 973 K. The textural properties (surface area and pore structure) of the catalysts were determined by low-temperature nitrogen adsorption at 77 K. The surface acidity (acid amount and acid strength) was determined for each catalyst by thermal programmed desorption (TPD) of pyridine. The catalytic cracking of cumene at 673–773 K and the catalytic conversion of isopropanol at 473–593 K were investigated using microcatalytic technique. Cracking of cumene is a first-order catalytic reaction which takes place on relatively strong acid sites and the reaction is structurally sensitive. Dehydration of isopropanol on mixed oxide catalysts is a zero-order reaction and proceeds on most of the acid sites. Dehydration of isopropanol is related to the surface acid density and is structurally insensitive.

The Catalytic Cracking of Cumene

Abstract Science, by its very nature, aspires to the orderly arrangement of knowledge in a way which will allow predictive interpolation and even cautious extrapolation into unstudied regions of performance on the basis of known data. So it is that in the study of kinetics many sophisticated attempts have been made to calculate the rate parameters for some of the simplest gas-phase reactions from basic physical measurements. Most such attempts have so far ended in failure, and kinetics remains basically an experimental science.

Comments on the Interpretation of the Mechanism of Formation of Minor Products Accompanying the Catalytic Cracking of Cumene

Abstract The article “The Catalytic Cracking of Cumene” by Corma and Wojciechowski [11 discusses, among other things, mechanisms of formation of minor products accompanying dealkylation of isopro-pylbenzene. The mechanistic schemes advanced by the authors by artfully exhibited drawings seem to violate accepted principles of cationic reactions and ignore known facts of catalytic hydrocarbon conversions.

The catalytic cracking of cumene: The kinetics of the dealkylation reaction

In a previous paper [ J. Catal. 31, 74 (1973)] the Campbell-Wojciechowski mechanism for cumene cracking was applied to cumene conversion data obtained on various mesh sizes of LaY catalyst in order to study the effects of diffusion on the model parameters. Here, the diffusion free region is isolated and the intrinsic kinetics are determined. The activation energy for the dealkylation reaction is found to be 22.5 kcal/mole, which is in good agreement with results reported by other workers. Furthermore, when this value of activation energy is used in an analysis of the energetics of the reaction, it is shown that endothermic chemisorption of cumene must be assumed in order to construct a plausible picture of the reaction energy surface. It is also shown that diffusion limitations affect the rate of catalyst decay to a different extent than they affect the rate of reaction. This confirms our belief that the standard experimental procedure to test the significance of intraparticle diffusion must be modified in a manner suggested in a previous publication [ Canad. J. Chem. Eng. 54, 197 (1976)] in order to avoid misinterpreting the results of diffusion studies on decaying catalysts.

The catalytic cracking of cumene on aging catalysts: II. An experimental study

The time on stream theory of catalyst decay is applied to data obtained by cracking cumene on a lanthanum-exchanged Y-sieve catalyst. It is shown that the theory describes the observed phenomena correctly. As a result it can be reported that the system cumene-LaY exhibits Class II behavior and that poisoning reactions remove two active sites per deactivating event. The activation energy for the cracking reaction is found to be 19.5 kcal/gmole.

Effects of metal acetate salts on the catalytic cracking of cumene over silica-alumina

A study was made of the effects of metal acetate salts on the ability of a commercial silica-alumina catalyst to promote the conversion of cumene to benzene and propylene. The typical effect of the salts was to reduce the conversion. The extent of this reduction was determined by the amount, size, valence, and chemical type of the poisoning cation. Graphs of percent conversion versus the area (or volume) of catalyst surface actually covered by poisoning metal ions showed three distinct activity curves with the alkali metala exhibiting greatest, the alkali earth metals poorest, and zinc and cadmium an intermediate poisoning ability. Very small amounts of divalent metal cations showed a small promoting action. Acetic acid had no effect on conversion. The results suggest that cracking occurred on acid sites present in clusters on the catalyst surface and that site blocking and chemical neutralization both contributed to the poisoning of the catalyst.

Study on the pulse reaction technique: II. Dealkylation and disproportionation of cumene

The catalytic cracking of cumene on a silica-alumina catalyst was studied by the pulse technique with a rectangular pulse. The effect of pulse width on the conversion predicted in the previous paper was verified experimentally: The conversion increases with decreasing pulse width, and the reverse reaction can be neglected when pulse width is zero, where the relation between the conversion and the contact time is the same as that usually observed in the first order irreversible reaction. The activation energy of the forward reaction was found to be 24.4 kcal/mole from the conversion at zero pulse width. The effect of pulse width on the yield of diisopropylbenzene was also studied. The yield of diisopropylbenzene was independent of pulse width, from which it was concluded that diisopropylbenzene was formed in the disproportionation of cumene.

Effect of uniformity of fluidization on catalytic cracking of cumene

AbstractThe effect of uniformity of fluidization on the catalytic cracking of cumene, with a silicaalumina catalyst, was studied in a 3‐in.–diameter reactor operated at 800°F. Superficial gas velocities were varied from 0.06 to 0.24 ft./sec. for bed heights of 1.5, 3, 5, and 8 in. The percentage conversion in a fluidized bed was found to be lower than in a fixed bed and to be dependent on the type of catalyst support used. A porous plate support was up to 30% more efficient than a screen support, which is attributed to its better gas‐distribution characteristics and to its ability to introduce the discontinuous phase as smaller gas bubbles. Indications are that the first few inches of bed are very effective in bringing in contact the continuous and discontinuous phase, and therefore most of the conversion due to the interaction of the two phases takes place here. This can be explained in terms of the rapid growth of gas bubbles as they proceed through the bed.