Disproportionation Of Ethylbenzene Research Articles

STUDY OF CATALYTIC BEHAVIOURS OF THE SPINEL STRUCTURE NdxMg1- xAl2O4 COMPOSITION WITH ZSM-5 ZEOLITE IN ETHYLBENZENE DISPROPORTIONATION

Nanosized (10–15 nm) powders of spinel structures NdxMg1–xAl2O4 were obtained by low-temperature combustion of aluminium, magnesium, neodymium nitrate solutions, diethylmalonate, and hydrazine monohydrate with further calcination of nanopowders at 1000 °C, which were used in the preparation of catalytic compositions with ZSM-5 zeolite. The obtained catalytic compositions were characterized by X-ray diffraction, pyridine adsorption, and low-temperature nitrogen adsorption. The acidic properties and porosity of the catalysts were altered by controlling the concentration of nanopowder (1.0–7.0 wt.%) in the catalytic composition. The interaction of the modifier with HZSM-5 zeolite leads to a decrease in specific surface area and pore volume, as well as reduse of strong Bronsted acid sites (B) and an increase in the concentration of medium Lewis acid sites (L), resulting in a change in the B/L ratio from 3.61 to 0.23. The ongoing variations contributed mainly to an enhancement of the para-selectivity of the catalytic composition in the ethylbenzene disproportionation reaction. The catalytic composition of 5% Nd0.1Mg0.9Al2O4 with a pore volume of 0.15 cm3/g and an acid site B/L ratio of 0.27 demonstrates a maximum selectivity to p-diethylbenzene of 75.6% with a conversion of ethylbenzene of 23.7%.

Selective mono-alkylbenzene disproportionation over silylated MFI zeolite

Silica chemical vapor deposition (Si-CVD) technique was applied in the silylation of ZSM-5 zeolite to enhance para isomer product selectivity in the disproportionation of toluene (TDP) and ethylbenzene (EBDP). A threshold value in Si-CVD deposition for enhancement in para isomer selectivity in TDP and EBDP was determined. Beyond the threshold value, the para selectivity increased with increasing silica deposition amount. Upon Si-CVD modification, while the micropore size of the MFI zeolite stayed the same with the parent MFI zeolite, the enhancement in para selectivity could be due to the passivation of external active sites. The p-diethylbenzene isomer selectivity of>99 % was demonstrated at EB conversion up to 35 %. Nevertheless, p-xylene isomer product selectivity of around 83 % was obtained only at a reasonable conversion level of 20 %. The difference in selectivation efficiency between TDP and EBTDP reactions could be attributed to the difference in the relative ratio of reaction kinetics rate to the diffusion rate in associated with different reaction temperature range.

Xylene isomerization side reactions over Beta zeolite: Disproportionation and transalkylation of C8 aromatics and toluene

An experimental and parametric behavior study of disproportionation and transalkylation between C8 aromatics and toluene were carried out over mono-functional acid Beta zeolite with a SiO2/Al2O3 ratio of 35 (BEA35). The experiments were performed in liquid phase under the following conditions: 453, 473, and 493 K and 2.1 MPa. Ethylbenzene disproportionation and ethylbenzene-toluene transalkylation were identified as the main side reactions; therefore, the kinetics of both reactions were estimated. Both reactions were verified to be second-order with no signs of competition for the adsorption sites under the studied conditions. Additionally, ethylbenzene disproportionation and ethylbenzene-toluene transalkylation, undergo through a deethylation-ethylation mechanism, the activation energies were 66 and 57 kJ/mol respectively. Furthermore, the existence of parallel reactions, as well as the feed concentration, showed no effect on the p-diethylbenzene selectivity. Selectivity towards the para-isomer was observed only at very low conversions. Finally, an analytical solution was developed for the system showing excellent agreement with the experimental data.

Alkyl transfer reactions on solid acids. The disproportionation of ethylbenzene and toluene on H-mordenite and HY zeolites

ABSTRACTThe disproportionation of ethylbenzene and toluene have been compared on two zeolites, H-mordenite and HY. The online examination of products as a function of time on stream reflect the different processes occurring on the two zeolites. The relative activities expressed on a unit aluminium center basis, are in line with their relative cracking (n-heptane) activities reported by others, showing that no extraneous factors affect activity. The data set provides a baseline for the activity of these two zeolites for future use in comparing other more complex alkylation reactions involving mononuclear and binuclear aromatic molecules.

Crystal dimension of ZSM-5 influences on para selective disproportionation of ethylbenzene.

Crystal size and crystal dimensions are vital role in shape selective feature. Para selective disproportionation of EthylBenzene (Dip-EB) was investigated over ZSM-5 synthesized in acidic medium. The catalysts were prepared by hydrothermal process with various Si/Al ratios (50, 75 and 100) using fluoride ion precursor. This fluoride ion precursor dissolves the ZSM-5 nutrients below it neutral pH between 4 and 6. The synthesized material was subjected into various physico chemical characterizations such as XRD, SEM, TGA and BET analyses. The XRD patterns showed high crystalline nature and their resulting SEM images were also indicate thin prismatic crystals of large dimension compared with alkaline medium synthesized one. The BET results earned good textural property. Catalytic activity of vapor phase Dip-EB was carried out between 523 and 673 K. As their result, diethylbenzene (DEB) isomers were obtained, but para selective Diethylbenzene (p-DEB) was observed higher than others. The high selectivity towards p-DEB was due to large crystal dimension of ZSM-5 catalysts synthesized in fluoride medium. Hence it is good commercial application for petrochemical feed stock production.

Shape-selective catalysis by phosphate modified ZSM-5: Generation of new acid sites with pore narrowing

Pore narrowing of ZSM-5 was carried out by phosphate modification technique and shape selectivity was evaluated for alkylation, disproportionation reactions and competitive reaction of ethylbenzene and meta-xylene. Catalysts were characterized by XRD, FTIR, MAS NMR, NH3-TPD, PZC etc. Post synthesis modification of ZSM-5 by phosphate treatment generated new kinds of acid sites with pore narrowing. Even though there was a change in acid site strength, these active sites efficiently catalyzed toluene alkylation with methanol, ethylbenzene alkylation with ethanol and disproportionation of ethylbenzene. These active sites formed monolayer islands over catalyst surface and narrowed the pore opening resulting in high para-selectivity. Decrease in pore volume by phosphate modification has a direct correlation with increase in shape selectivity. Constraint index for modified catalysts obtained from competitive reaction of ethylbenzene and m-xylene was used to determine extent of pore narrowing by phosphate modification.

Effect of N2 and O2 on selective disproportionation of xylene mixed ethylbenzene over highly active silylated HZSM-5

The influence of carrier gases such as nitrogen and air (78 % N2 and 21 % O2) on catalytic activity and its stability etc., over modified H-ZSM-5 (pore size regulated by silylation) for the selective formation of Para-diethylbenzene (p-DEB) by xylene mixed ethylbenzene (EB) disproportionation is discussed. The comparison of plane and modified HZSM-5 catalysts using different carrier gases viz., nitrogen and air on pure EB and xylene mixed EB feeds are presented. The disproportionation reaction with xylene mixed EB feed in the presence of air over HZSM-5TS (8 % silica deposited) is observed to be more active and selective as far as p-DEB formation is concerned. Reaction kinetics of EB disproportionation with first-order power law model at different temperatures and W/F (weight of the catalyst/reactant feed rate), with pure EB and xylene mixed EB feed are also discussed. The reaction rate constants are within 0.0668–0.0969 dm3/g h and the activation energy of the reaction is calculated to be 30.16 kJ/mol. The catalyst stability (100 h) in the presence of carrier gas is also studied in detail.

Stability of the Reaction Intermediates of Ethylbenzene Disproportionation over Medium-Pore Zeolites with Different Framework Topologies: A Theoretical Investigation

The strain energies of the main reaction intermediates (i.e., monoethylated diphenylethane (mEDPE) and diethylated diphenylethane (dEDPE) derivatives), which can be formed during ethylbenzene (EB) disproportionation over six 10-ring zeolites with different framework topologies, as well as over the large-pore zeolite Y, were determined by the density functional theory calculations in order to more precisely investigate the effects of the pore structure of medium-pore zeolites on their formations. It was found that while the strain energies of mEDPE and dEDPE intermediates in zeolite Y, MCM-22 and TNU-9, were always lower than 19.6 kJ mol(-1), some of them were characterized by considerably higher energies (>32.8 kJ mol(-1)) when positioned in the intersection channels of ZSM-5 and ZSM-57. As expected, in addition, all the mEDPE and dEDPE derivatives embedded in TNU-10 and ZSM-22 with narrower 10-ring channels were strongly distorted, giving them much higher strain energies (>37.7 kJ mol(-1)), which were in excellent agreements with our recently reported experimental results (J. Phys. Chem. C 2010, 115, 16124). This led us to conclude that the size and shape of void spaces in the medium-pore zeolites play a crucial role in governing the type of mEDPE and dEDPE formations during the EB disproportionation. Our work also shows that the strain energies of various reaction intermediates confined within zeolites with different pore topologies could be regarded as a useful quantitative means in better understanding the shape-selective nature of this important class of microporous crystalline catalysts.

“Ideal” bifunctional catalysis over Pt-acid zeolites

The conditions of “ideal” bifunctional catalysis were specified on the example of two reactions involved in major refining and petrochemical processes, the hydroisomerisation of n-alkanes (n-Cx) and of ethylbenzene (EB) over PtHzeolites. In both cases, the balance between the hydrogenating and acid functions (CPt/CH+) was shown to affect positively the activity (actually the turnover frequency of the acid sites), the stability and the selectivity of the bifunctional catalysts. Optimal catalytic characteristics were obtained for CPt/CH+ values high enough so that the acid catalysed steps be rate-limiting, provided however, an additional condition is satisfied: low number of acid sites between two Pt sites in order that only one skeletal transformation of n-Cx intermediates could occur or distance between zeolite protonic sites sufficient for limiting the demanding reaction of ethylbenzene disproportionation. The location of the active acid sites which determines their access by the olefinic intermediates plays also an essential role; the highest selectivity values were obtained with sites located at the micropore mouth of the zeolites, after however blockage by carbonaceous deposits of the accessibility to the non-selective inner sites. The only limitation of the corresponding catalysts is their low activity related to the low concentration of zeolite outer sites, which should be easily overcome by preparing zeolite samples with larger outer surface. The generalisation of this analysis to other reactions should facilitate the design of the “ideal” bifunctional catalysts, opening the route to cleaner commercial processes.

Kinetics modeling of disproportionation and ethylation of ethylbenzene over HZSM-5: Effects of SiO2/Al2O3 ratio

This article deals with the effects of SiO2/Al2O3 ratio of HZSM-5 catalysts in disproportionation and ethylation of ethylbenzene to produce para-diethylbenzene (p-DEB). The physicochemical characterization of the catalyst samples shows that the variation of SiO2/Al2O3 has minimal impact on the crystallinity of HZSM-5 samples. On the other hand, the acidity of the materials decreased while specific surface area increased with increasing the SiO2/Al2O3 ratios. The catalytic experiment in the CREC Riser Simulator shows that low temperature favors the EB ethylation reaction while higher temperature is favorable for disproportionation. The DEB selectivity is found to be significantly higher in ethylation of EB with ethanol than disproportionation. Among the five HZSM-5 catalysts, the sample with SiO2/Al2O3=80 gives highest EB conversion and is more selective to DEB although the p-DEB/m-DEB for the catalysts are comparable with other samples. The value of the activation energy for EB cracking is comparable to the activation energy of EB disproportionation which is consistent to the high benzene selectivity in this route. During the EB ethylation with ethanol, a small amount of benzene was formed via the cracking of EB, which is reflected by higher activation energy of the EB cracking reaction. The kinetics analysis also confirms that during EB ethylation, the disproportionation and cracking of EB is negligible. In EB ethylation, the HZSM-5 catalyst with SiO2/Al2O3=80 requires lowest amount of activation energy to form DEB which is reflected in higher DEB selectivity of the catalyst.

Dodecatungstophosphoric Acid Supported on Acidic Clay Catalyst for Disproportionation of Ethylbenzene in the Presence of C8 Aromatics

Vapor-phase disproportionation of ethylbenzene (EB) to diethylbenzene (DEB) in a single step is industrially relevant. Diethylbenzene is an important raw material for the conversion of divinylbenzene monomer. Conventionally, it is prepared from diacetophenone by reduction. It is also prepared by vapor-phase alkylation of ethylbenzene with ethylene/ethanol using zeolitic catalysts. In the current work, the efficacy of dodecatungstophosphoric acid (DTPA) supported on acid-treated clay has been evaluated in the disproportionation of ethylbenzene. A 20% (w/w) DTPA/K-10 clay catalyst was found to be efficient and robust. An industrial feed having different compositions of ethylbenzene and xylene isomers was used for the experimentation. Hence, they were expected to hinder the movement of reactant molecules on the catalyst surface. It was observed that irrespective of feed composition the concentration of the xylene isomers was intact in the product. There was no other byproduct formation like p-ethylmethylbenzene. Optimization of process parameters is presented. The effect of varying the concentration of aromatic compounds in the feed on ethylbenzene conversion and product distribution over the plain clay (K-10) and heteropolyacid-loaded clay catalyst have been discussed. The effect of catalyst bed length to inner diameter of reactor (L/D) ratio on the ethylbenzene conversion and selective formation of p-diethylbenzene (p-DEB) are also discussed.

Mechanistic Investigations of Ethylbenzene Disproportionation over Medium-Pore Zeolites with Different Framework Topologies

Ethylbenzene disproportionation has long been recognized as a useful test reaction for distinguishing between medium- and large-pore zeolites because medium-pore materials show neither an induction period nor a diethylbenzene deficit, unlike large-pore ones. Hence, the mechanism of this reaction over all medium-pore zeolites has been regarded as simply monomolecular to date. Here, we demonstrate that the pore architecture of medium-pore zeolites strongly influences the type of main reaction intermediates of ethylbenzene disproportionation and, thus, that of the prevailing reaction mechanism: dual-cycle diphenylethane-mediated, bimolecular diphenylethane-mediated, or monomolecular ethyl-transfer reaction pathway. To our knowledge, our study provides more manifest experimental evidence for the transition state shape selectivity in zeolite catalysis than has ever been reported.

In situ regeneration of ZSM-5 used in the ethylbenzene disproportionation under supercritical conditions

A study of the ethylbenzene disproportionation at a wide range of reaction pressures, from gas to supercritical conditions, was carried out in order to determine the influence of the reaction media properties, such as density, on the reaction parameters and especially on the deactivation by coke deposition. Pressure does not only favour the ethylbenzene disproportionation but also the formation of ethylene, a well-known coke precursor, by dealkylation reactions. However, coke extraction is also favoured by pressure, leading to an equilibrium between coke formation and extraction at high pressures, which is called in situ regeneration. So that, under certain supercritical conditions such as 400 °C and 91 bar, the reaction media properties make possible to obtain high ethylbenzene conversion and reduced deactivation by coking.

ChemInform Abstract: Insights into Reaction Mechanisms in Heterogeneous Catalysis Revealed by in situ NMR Spectroscopy

AbstractReview: 58 refs.

Effect of reactant density inside supercages of zeolite La,Na-Y on the mechanism of the ethylbenzene conversion

Zeolites La,Na-Y are important catalysts for industrial FCC units due to their acidic properties and stability. The ethylbenzene disproportionation on this zeolite was suggested as a standard test reaction for acidic zeolites by the Catalysis Commission of the International Zeolite Association (IZA). The present work provides solid-state 13C NMR spectroscopic evidence that various amounts of reactants inside the supercages of zeolites La,Na-Y obviously affect the catalytic behavior of ethylbenzene reaction. At 453 K, diphenylethane was only detected on zeolite La,Na-Y with three ethylbenzene molecules per supercage. This intermediate, however, did not occur on samples with low loading (1 or 2 EB molecules per supercage). On zeolite La,Na-Y loaded with one molecule ethylbenzene per supercage, dealkylation and realkylation of ethylbenzene occurred at 548 K without any side-reactions. However, side-reactions of oligomerization, hydride transfer, and aromatization were observed on samples with high ethylbenzene loading, which promotes the catalyst deactivation. In addition, the zeolites La,Na-Y with high loadings of ethylbenzene show a higher reactivity and more complex reaction mechanisms.

ChemInform Abstract: On the Question of Aromatic Ring Expansion-Contraction for Conversions with a ZSM-5 Catalyst.

Toluene, labeled with {sup 14}C in either the methyl position or uniformly in the aromatic ring, did not undergo a measurable amount of either ring expansion-contraction or ring degradation to produce ethene at temperatures up to 350{degrees}C. Ethylbenzene dealkylation and disproportionation and xylene isomerization occur to produce equilibrium mixtures of diethylbenzenes or xylenes under these reaction conditions; hence, ring expansion-contraction must be much slower than these isomerization reactions.

Optimisation of Ethylbenzene Conversion and Selectivity of p-diethylbenzene Using Differential Evolution Technique via OLS Modelling

This paper delves into the application of a robust optimisation tool, differential evolution (DE), to the disproportionation of ethylbenzene (EB) to produce the commercially important para-diethylbenzene (p-DEB). Through the application of this technique, EB conversion and selectivity of the p-DEB product are maximised against the three input variables of temperature, pressure and liquid hourly space velocity (LHSV), using a model. The catalytic process is represented by a multi-input multi-output (MIMO) orthogonal least-square (OLS) algorithm, using historic data. The optimised solutions are experimentally verified and show significant improvement in the p-DEB conversion and selectivity.

Supercritical fluids as reaction media in the ethylbenzene disproportionation on ZSM-5

Ethylbenzene disproportionation over HZSM-5, was studied in a wide range of temperatures and pressures including supercritical conditions, aiming to determine the effect of variations in reaction media properties on reaction parameters, focusing on the potential advantages of supercritical conditions, previously discussed in literature. The effect of pressure on conversion has been explained in terms of changes in the reaction media produced by pressure variations, whereas at high pressure conditions temperature has effect not only on the kinetics but also on media density. Pressure dos not have effect on the selectivity to the main product, diethylbenzene; however temperature should be taken into account since above certain temperatures secondary reactions are favoured. Conversion close to the equilibrium one has been reached at 400 °C and 45 bar, demonstrating that supercritical fluids are a satisfactory reaction media for ethylbenzene disproportionation.

Insights into reaction mechanisms in heterogeneous catalysis revealed by in situ NMR spectroscopy

This tutorial review intends to show the possibilities of in situ solid state NMR spectroscopy in the elucidation of reaction mechanisms and the nature of the active sites in heterogeneous catalysis. After a brief overview of the more usual experimental devices used for in situ solid state NMR spectroscopy measurements, some examples of applications taken from the recent literature will be presented. It will be shown that in situ NMR spectroscopy allows: (i) the identification of stable intermediates and transient species using indirect methods, (ii) to prove shape selectivity in zeolites, (iii) the study of reaction kinetics, and (iv) the determination of the nature and the role played by the active sites in a catalytic reaction. The approaches and methodology used to get this information will be illustrated here summarizing the most relevant contributions on the investigation of the mechanisms of a series of reactions of industrial interest: aromatization of alkanes on bifunctional catalysts, carbonylation reaction of methanol with carbon monoxide, ethylbenzene disproportionation, and the Beckmann rearrangement reaction. Special attention is paid to the research carried out on the role played by carbenium ions and alkoxy as intermediate species in the transformation of hydrocarbon molecules on solid acid catalysts.

Diethylated Diphenylethane Species: Main Reaction Intermediates of Ethylbenzene Disproportionation over Large-Pore Zeolites

GC/MS evidence for the build-up of diethylated diphenylethane species, as well as of monoethylated diphenylethane derivatives, inside the LaNa-Y cavities during ethylbenzene disproportionation is presented. The role of the former species as reaction intermediates was found to become greater than that of the latter ones with increasing time on stream. A new dual-cycle mechanism for diethylbenzene formation over large-pore zeolites is proposed based on the overall results presented here.