Cumene Cracking Research Articles

Natural zeolites for styrene oligomerization

AbstractHydrogen forms of natural mordenite and clinoptilolite were used as catalysts for styrene oligomerization and as matrices to hold the resultant oligomers in order to prepare intense and light-resistant pigments. In contrast to synthetic zeolites of similar pore sizes (mainly H-ZSM-5, H-mordenite), the natural zeolites did not form products with an intense (pink) colouration. H-mordenite samples treated with styrene developed some colour due to styrene oligomers (the chromophore) whereas, in treated clinoptilolites, colour formation was negligible due to the lack of access of styrene molecules into the elliptical channels. The results of catalytic tests for cracking of cumene (cumene and styrene have similar molecular sizes) were consistent with the styrene oligomerization results. They indicate a noticeable catalytic activity with natural H-mordenite and a lack of activity with clinoptilolite. On the other hand, catalytic tests for propan-2-ol decomposition indicate a high activity with both natural zeolites, which confirms the presence of acid sites and their accessibility to small alcohol molecules.

Cracking of cumene on tungsten promoted ceria catalysts

Abstract Tungsten promoted pure and sulfated ceria systems are employed as solid acid catalysts for the vapor phase cumene cracking reaction. The catalytic systems are prepared by the pseudo-template method. The results show the presence of both Lewis and Bronsted acid sites on the catalyst. Upon modification with tungsten oxide, an enhancement in the number of Lewis acid sites is observed. α-methyl styrene is the major product along with some dealkylated products. The influence of reaction conditions such as temperature, flow rate and time on stream on the conversion and selectivity is also investigated. Time on stream studies suggest deactivation of the catalysts presumably because of the coke formation on the acid sites.

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.

Samarium Ion Exchanged Montmorillonite for High Temperature Cumene Cracking Reaction

Montmorillonite clay is cation exchanged with samarium and its catalytic influence in cumene cracking reaction is investigated. Effect of exchange with sodium ions on further exchange with samarium ions is also noted. Acidity measurements are done using Temperature Programmed Desorption (TPD) of ammonia. The retention of basic structure is proved from FTIR spectra and XRD patterns. Elemental analysis result shows that samarium exchange has occurred, which is responsible for the higher catalytic activity. Surface area and pore volume remains more or less unaffected upon exchange. Thermogravimetric analysis indicates the enhanced thermal stability on exchanging. Cumene cracking reaction is carried out at atmospheric pressure in a fixed bed glass reactor at 673 K. The predominance of Brønsted acidity is confirmed from high selectivity to benzene.

Role of the acidity and porosity of MWW-type zeolites in liquid-phase reaction

MWW-type zeolites, MCM-22 and ITQ-2, with a wide range of gel Si/Al ratio were synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), N 2 adsorption and 27Al MAS NMR. Their acid properties were studied via NH 3-temperature programmed desorption (NH 3-TPD), 2,6-di- tert-butyl-pyridine adsorption, infrared spectra of pyridine adsorption (Py-IR), selective poisoning method as well as model acid-catalyzed reactions such as cumene cracking and 1,3,5-tri-isopropylbenzene dealkylation. It is revealed that the delamination process made the catalysts more accessible to bulky molecules but weakened their acid strength. The accessibility of acid sites plays an important role in the liquid phase reactions involving bulky molecules. ITQ-2 has high activity in isomerization of α-pinene because of its abundant accessible acid sites. While for alkylation of hydroquinone, MCM-22 is better due to its higher accessible acid sites of medium-strong strength.

Mesoporous silica–alumina modified by acid leaching as support of Pt catalysts in HDS of model compounds

The potential of mesoporous silica–alumina (MSA) modified by acid leaching as alternative support for Pt catalysts was studied in hydrodesulfurization (HDS) of thiophene and benzothiophene. The supports were characterized by N2 adsorption, XRD, 27AL MAS NMR, electron microscopy (SEM, HRTEM) and by activities in cyclohexene isomerization and cumene cracking. The composition of the catalysts and Pt dispersion were determined by ICP and H2 or CO sorption, respectively. Progressive leaching of the parent MSA from 50% Al2O3 to 11% Al2O3 content led to increase of the BET surface area and exposition of strong acidity. This positively affected the activities of the reduced Pt catalysts in thiophene HDS. Deposition of 1.5wt.% Pt on MSA (11% Al2O3) by using Pt(NH3)4(OH)2 as precursor gave the best catalyst, several times more active in thiophene HDS than the weight equivalents of sulfided CoMo/Al2O3 or reduced Pt/HY zeolite. In benzothiophene reaction, its activity was slightly above that of CoMo/Al2O3 and about twofold compared to Pt/HY.

ChemInform Abstract: Anomalous Behavior of Cumene Cracking in Small-Pore Catalysts.

Abstract The reaction sequence in small-pore catalysts has been postulated to be as follows: adsorption of the reactant from the gas phase to the outside surface of the catalyst to form a condensed-type phase; diffusion of the condensed molecules along the pore walls analogous to surface diffusion, then reaction on active sites, followed by diffusion of the products to the external surface of the catalyst; finally, desorption of the products. This is in contrast to the conventional diffusion, adsorption, and reaction model which is suitable for larger-pore catalysts. Kinetic data from the cumene cracking reaction over REY zeolites are used in this work. The data were obtained at a wide range of temperatures, from 225 to 575°C, sufficient to include the regions of kinetic control and strong pore diffusion. Under these conditions and using the above model, the kinetic and diffusion parameters for cumene cracking are obtained. The intrinsic reaction rate constant and diffusion coefficient over REY zeolites are 2.5 × 106 cm3/g/s and 1.9 × 10−9 cm2/s at 500°C, with activation energies of 33 and 15 kcal/mol, respectively.

ChemInform Abstract: Pillared Tetrasilicic Mica Catalysts Having Fixed Interlayer Ca Ions. Comparison with Other Clays.

Three kinds of Ca2+-modified pillared clays (TSM, taeniolite, and montmorillonite) were prepared from Ca2+-exchanged clays. The cumene cracking activity over the TSM-based catalyst was greatly dependent on the calcination temperature before pillaring, and gave a maximum at 300–400 °C. In contrast, no appreciable increase in the activity with the calcination temperature before pillaring was observed in montmorillonite- and taeniolite-based catalysts. The amount of residual Ca in the modified pillared TSM was increased with a rise in the calcination temperature before pillaring, whereas the amount of Al incorporated through pillaring was decreased, showing the progress of Ca2+ fixation during the stage of thermal treatment of Ca2+-exchanged unpillared TSM. Thus, the cracking activity was greatly enhanced by the fixation of Ca2+. The cracking activity, however, dropped due to a pretreatment above 400 °C, since the Al-pillars which prop silicate layers are reduced while causing a decline in the surface area o...

New Nb and Ta–FAU zeolites—Direct synthesis, characterisation and surface properties

Niobium and tantalum containing Y zeolites were prepared in a one-pot synthesis and via solid-state ion exchange. The first method led to the incorporation of Nb and Ta into the zeolite framework as documented by XRD, UV–vis, XPS and test reactions. The efficiency of the metal introduction was higher for tantalum than for niobium. The presence of Lewis acid sites was proved by pyridine adsorption and cracking of cumene, whereas basic hydroxyls on the surface were evaluated on the basis of 3-methyl-2-cyclopentenone formation in the cyclisation of acetonyl acetone.

Incorporation of highly dispersed aluminum into inner surfaces of supermicroporous silica using anionic surfactant

Incorporation of aluminum on the inner surfaces of mesopores was carried out under hydrothermal conditions for synthesizing mesoporous silica using an anionic surfactant. The synthesis concept was based on ionic interactions between aluminum cations and anionic surfactants, with the latter as templates. We easily obtained aluminum-containing microporous silica with supermicropores. The results of pyridine adsorption and cumene cracking reactions strongly indicated that unlike the materials prepared by the previously reported post synthesis and direct synthesis methods, the larger amount of aluminum incorporated into the materials were effectively present on the inner surfaces of supermicropores.

Genesis of Acid−Base Support Properties with Variations of Preparation Conditions: Cumene Cracking and Its Kinetics

Mixed oxides (Al−Si, Zr−Si, Mg−Si) were synthesized by the sol−gel method at different gelation times. The synthesized supports were impregnated by the incipient wetness method to obtain Ni−Mo, Co−Mo, and Ni−W supported catalysts. Both the supports and catalysts were characterized by N2 physisorption for determining textural properties, and their catalytic activities were tested with isopropyl alcohol (2-propanol) and cumene decomposition in order to evaluate their acid−base properties. According to the obtained products, it was possible to assess qualitatively that Al−Si and Zr−Si supports and their respective catalysts were mainly acidic. In the case of NiMo/AlSi catalyst, high conversion during cumene cracking particularly at higher temperatures was observed. Cracking activity results indicated that surface acidity predominated due to Brønsted acid sites, which are mainly dependent on the support composition as well as their preparation methods. Conversion of isopropyl alcohol leads to the dehydration products, typically propylene with a very low amount of di-isopropyl ether or acetone. NiMo/AlSi catalyst was evaluated for cumene cracking and its kinetic parameters were obtained by applying the Langmuir−Hinshelwood model. The activation energy was found to be 27.75 kcal mol−1 while the heat of adsorption calculated with the Van’t Hoff equation was −14.15 kcal mol−1 taking into account a single-site surface reaction.

Highly acidic mesoporous aluminosilicates prepared from preformed HY zeolite in Na2SiO3 alkaline buffer system

Mesoporous aluminosilicates (YM) were hydrothermally synthesized by assembling zeolite subunits, which were generated by the hydrolysis of HY zeolite in Na2SiO3 aqueous solution, in the presence of cetyltrimethylammonium bromide (CTAB). The Na2SiO3 aqueous solution plays two roles in the synthesis. It provides a moderate alkaline medium with buffering effect for the desilication of HY zeolite and it acts as a supplementary silica source. The desilication of HY zeolite was optimized in terms of reaction temperature and time. Characterizations by XRD, nitrogen isotherms and TEM indicated that YM possessed a well-ordered mesostructure. FT-IR, UV-Raman, 27Al MAS NMR, NH3-TPD, and pyridine-adsorbed IR showed that the characteristics of Y zeolite, such as double six-membered ring subunits, tetrahedral coordination aluminum and high ratio of Bronsted/Lewis acidity sites, were preserved in YM. SEM observation revealed YM possesed a different morphology from either mesoporous MCM-41 or Y zeolite. No separate zeolite crystals were found in the TEM observation. The hydrothermal stability of YM towards refluxed water (120 h) and steam (873 K, 6 h), and the activity in acid-catalyzed cumene cracking (623 K) were compared with MCM-41 prepared with conventional method or parent HY. Because of the uniform structure and surface properties, YM was more hydrothermally stable than MCM-41; it also exhibited more efficient catalytic activitation than MCM-41 and HY in cumene cracking.

THE EFFECT OF OPERATING CONDITION FOR CUMENE CRACKING ON THE PERFORMANCE OF PREPARED HX - ZEOLITE CATALYST

The present study reports the effect of temperature and liquid hourly space velocity (LHSV) on the cumene cracking reaction rate and selectivity by using a laboratory continuous flow unit with fixed bed reactor operating at atmospheric pressure. The prepared HX zeolite was made from Iraqi kaolin with good crystallinity .The activity and selectivity of prepared HX-zeolite was compared with standard HY zeolite and HX zeolite catalysts in the temperature range of 673-823K and LHSV of 0.7-2.5 h-1. It was found that the cumene conversion increases with increasing temperature and decreasing LHSV at 823K and LHSV of 0.7 h-1 the conversions 65.32, 42.88 and 59.42 mol% for HY, HX and prepared HX catalysts respectively and at LHSV of 2.5 h-1 and the same temperature the conversions decrease to 29.24, 12.53 and 22.89 mol%, respectively .It also found that the benzene yield increases with increasing temperature at 823K and LHSV of 0.7 h-1 the benzene yields were 58.79, 38.56 and 54.56 mol% for HY zeolite , HX zeolite and prepared HX zeolite, respectively and the selectivity to benzene is nearly constant over the studied temperatures range. The kinetics of cumene cracking ( the kinetics parameters-rate constant )and activation energy are used in this study to characterize differences between various catalysts. The reaction was found to be first order with activation energy equal to 78.58 , 89.10 and 97.77 kJ/mol for HY, prepared HX and HX , respectively.

Surface functionalization of mesoporous silica SBA-15 by liquid-phase grafting of zirconium phosphate

The introduction of mesoporous silicas in the 1990s has offered new opportunities for the engineering of ordered catalytic nanoreactors, but the acid properties of mesoporous silicas are rather poor. Herein, mesoporous silica (SBA-15) surfaces were functionalized by zirconium phosphate via two methods recently developed in our group. Zr(OPr) 4 and POCl 3 were used as appropriate precursors in both methods. The main difference between these methods lies in whether Zr(OPr) 4 is grafted onto SBA-15 first and POCl 3 second (method 1) or the grafting process takes place in one pot, with SBA-15, Zr(OPr) 4, and POCl 3 altogether (method 2). More zirconium phosphate could be grafted by repeating the above procedures. The materials were characterized by ICP-OES, XRD, N 2 adsorption–desorption, TEM, 31P and 29Si MAS NMR, and NH 3-TPD, and their applications in catalytic isopropanol dehydration, cumene cracking, and metal-ion adsorption were demonstrated. Aluminum phosphate-modified SBA-15 samples could be obtained via these two methods as well. This work enriches the family of metal phosphate-functionalized mesoporous silicas as new solid acid catalysts.

New Aluminosilicate Materials with Hierarchical Porosity Generated by Aerosol Process

This paper underlines the great advantage of using a spray-drying process (aerosol process) to synthesise new families of aluminosilicate materials with a hierarchical porosity from the microporous to the macroporous scales. In concrete terms, high aluminum content mesostructured solids, zeolite - mesostructured aluminosilicate composites and amorphous hierarchical aluminosilicate solids with micro, meso and macroporosity have been successfully synthesised. Notice that the latter family is characterised by non usual acidic properties in cumene cracking catalytic reaction. Such results open then new perspectives in the development of innovating acidic catalysts for hydrocracking reactions.

Ratio of the equilibrium and kinetic acidities of solid catalysts

The feasibility of using the equation log k = const - H0s was examined for solid acid catalysts. Data for the thermoprogrammed dealkylation of cumene showed that the temperature dependence of the strength of the acid sites of the catalyst H0s(T) should be considered in calculating the coefficient . In this case, 1. However, as shown for the isomerization of o-xylene, dimerization of butylenes, dehydration of 2-propanol (2), and the dealkylation of cumene (3), the values found for coefficient are in the range 0.15-0.6 (4) and do not approach 1 as in solution. For example, in the cracking of cumene, an increase in H 0 by six leads to an increase in the rate constant k not by six orders of magnitude but only by a factor of 10. A possible explanation of the low values of is based on the assumption that a proton is not added to the adsorbed molecule but rather polarized hydrogen-bonded complexes are formed (4). In the present work, we have shown that catalytic reactions with proton transfer on the surface in the dealkylation of cumene on acid catalysts may be characterized by "normal" values of 1. In this case, the temperature dependence of the strength of the acid sites of the catalyst is taken into account. Equation (1) clearly reflects the relationship of the equilibrium and kinetic acidities of the catalyst sites and, thus, presupposes a reaction mechanism with consecutive formation of an adsorbed proton-transfer complex with equilibrium constant K s , a transition state with rate constant k, and the reaction products:

Characterization of sulfated zirconia prepared using reference catalysts and application to several model reactions

The sulfated zirconia project was carried out in order to obtain a broad understanding of the preparation, characterization, and application of the solid superacids of sulfated zirconia. The sulfated zirconia catalysts were prepared by the equilibrium adsorption method and the ammonium sulfate kneading method using the reference catalysts JRC-ZRO-2, -3, -4, and -5, supplied by the Reference Catalyst Division of the Catalysis Society of Japan. The catalysts were characterized by elemental analysis, NH 3-TPD, XRD, TG-DTA, CO 2-TPD, Raman spectroscopy, and measurements of the surface area, pore size distribution, coverage (by the BAT method), and heat of Ar adsorption. In order to compare the catalytic activities, we used the prepared catalysts in the isomerizations of butane and n-heptane, hydroisomerization of heptane, aldol condensation, acylation, esterification, and cracking of cumene. The sulfated zirconia prepared using JRC-ZRO-2 by the equilibrium adsorption method showed the highest activity and larger surface area. On the other hand, the kneading method provided catalysts with high reproducibility.

Structural effects of hierarchical pores in zeolite composite

A zeolite composite with MFI and MOR zeolite structures (denoted as MMZ) was prepared by a two-step hydrothermal crystallization, and characterized by X-ray powder diffraction, nitrogen adsorption–desorption, scanning electron microscopy and in situ IR spectrometry of pyridine and 2,6-dimethyl pyridine. The acid catalysis of the composite MMZ was investigated during the catalytic cracking of n-octane and cumene. The results showed that a hierarchical pore system was created in the zeolite composite improving the accessibility of acid sites and diffusivity in the composite material. The diffusivity in the composite was about seven times higher than in the corresponding physical mixture, and the acid accessibility in the composite was 3.4 times as much as in the physical mixture when 2,6-dimethyl pyridine was used as the probe molecule. The conversion of cumene on H-MMZ was three times larger than that on the physical mixture at 423 K.

Crystallization Kinetics and Influencing Factors in the Syntheses of MFI/MFI Core-Shell Zeolites

MFI/MFI core-shell zeolites with a low silica to alumina ratio core and a continuous shell of high silica to alumina ratio were successfully synthesized by a novel two-step procedure. This was done by a secondary growth of the ZSM-5 shell onto the modified ZSM-5 crystals and the pre-treatment step played an important role during the synthesis. Critical factors for the growth of the ZSM-5 shell including synthesis temperatures, periods, and core dosages were summarized. Results from cumene and 1,3,5-triisopropylbenzene (1,3,5-TIPB) cracking reactions showed that the core-shell zeolite and the core crystal had comparable activities for the cumene cracking reaction. Compared to the core crystal, the cracking activity of 1,3,5-TIPB of the core-shell zeolite was reduced by 68%, which coincided with the extent of aluminum reduction on the external surface. These results suggested that the acidity of the core crystals was largely preserved in the MFI/MFI core-shell structure. Crystallization kinetics curves were determined at different synthesis temperatures. The apparent energy of crystallization activation was found to be 26.5 kJ·mol-1 and the activation energy of nucleation was 51.5 kJ·mol-1.

Effect of the Incorporation of Al, Ti, and Zr on the Cracking and Hydrodesulfurization Activity of NiMo/SBA-15 Catalysts

The hydrodesulfurization and cracking activity of NiMo sulfided catalysts supported on Al-, Ti-, and Zr-modified SBA-15 was measured using the HDS of thiophene and cracking of cumene as model reactions. The results were used to analyze the effect of each heteroatom on the two reactions, and the existence of a relationship between HDS activity and the catalysts acid properties. The HDS activity of sulfided NiMo catalysts supported on Al-, Ti-, or Zr-modified SBA-15 depends significantly on the nature of the heteroatom used to modify the SBA-15 support. The HDS activity trend displayed by the catalysts was NiMo/Al20-SBA-15 > NiMo/Ti20-SBA-15 > NiMo/Zr20-SBA-15. This trend was similar for the cumene cracking reaction. The results indicate that Brønsted acidity favors hydrodesulfurization.