Alkylation Reaction Of Toluene Research Articles

Understanding HZSM-5's shape-selectivity improvement through tiny autonomous dealumination

Abstract The decisive factor that determines HZSM-5's shape-selective capability is obscure due to the interference from zeolite acidity, pore size and crystal size. p-xylene selectivity was found to increase from 45% to 82% in toluene alkylation reaction with the same HZSM-5 catalyst but storage period difference. However, no instrument detectable zeolite acid sites strength, type and quantity changes were observed. NMR revealed slight progressive increase of extra-framework aluminum by dealumination, and nitrogen adsorption-desorption isotherm verified the tiny decrease of micropore volume. Pulse chromatography tests confirmed p-xylene diffusion resistance increase in HZSM-5's channels. The finding made it possible to clarify the interactions between shape-selectivity improvement, p-xylene diffusion resistance increase and extra-framework aluminum while excluding all the other interfering factors, indicating the diffusion resistance control of molecules in HZSM-5's channels is the key to improve its shape-selectivity.

Study by NMR of Liquid-Phase Alkylation of Toluene with Hex-1-ene: Effect of Catalyst on Selectivity

In this work, the selectivity of different solid catalysts in the alkylation reaction of toluene with hex-1-ene has been studied in order to maximize mono-alkylated products. The reaction has been carried out in a fixed-bed reactor, at 120°C. An industrial alkylation catalyst has been used as a reference along with three commercial acid zeolites with difference structures (faujasite, mordenite and beta). All of catalysts achieved total conversion. Mono-alkyltoluenes selectivity was higher than 95% in all cases and formation of di-alkyltoluenes was less than 4.5%. The main products, mono-alkyltoluenes, were identified by Nuclear Magnetic Resonance spectroscopy. This work analyses the effect of physicochemical and structural properties of solid catalysts on the selectivity to the different alkylation products.

Acidity and catalyst performance of two shape-selective HZSM-5 catalysts for alkylation of toluene with methanol

Two shape-selective HZSM-5 catalysts with similar pore size were prepared by silicalite-1 coating or boron modification, respectively. These catalysts samples were characterized by XRD, SEM, NH3-TPD, Py-IR and N2 adsorption–desorption isotherms and tested in the alkylation reaction of toluene with methanol. The results indicated that the boron modification weakened the acidity but increased the total amount of acidity sites, while the silicalite-1 coating led to the decrease of the strong acidity and total acidity. Due to the specific shape-selectivity that the micropore architecture afforded and the increment of the weak acid percentage, both catalysts exhibited a high p-xylene selectivity over 98%. Moreover, the higher toluene conversion would be retained once the strong acid sites in the micropores were remained as many as possible under the premise of the shape-selectivity of pore size.

Core–Shell HZSM-5@silicalite-1 Composite: Controllable Synthesis and Catalytic Performance in Alkylation of Toluene with Methanol

HZSM-5@silicalite-1 catalysts were prepared by the hydrothermal method, and the structure, morphology, acidity and pore texture of core–shell catalysts were studied by XRD, SEM, TEM, NH3-TPD, Py-IR and N2 adsorption/desorption isotherms in detail. Their catalytic performances were tested in the alkylation reaction of toluene with methanol. The results showed that a coating layer was formed in the form of silicalite-1 on HZSM-5. NH3-TPD measurements indicated that HZSM-5@silicalite-1 contained less strong acid sites but more weak acid sites than the parent HZSM-5. The selectivity of p-xylene for toluene alkylation was approximately linear with the percentage of weak acid in total acid. Under the optimal reaction conditions, the conversion of toluene was 34.15%, and the selectivity of p-xylene was 96.77%.

Kinetic modeling and study of H-ZSM-5 coated silicon carbide ceramic foam in toluene methylation to produce xylene

This work deals with the toluene alkylation reaction with methanol catalyzed by commercial H-ZSM-5 coated over SiC foam. The main product is xylene which is a well-known building block of many petrochemicals. The foam has been purchased and H-ZSM-5 was coated on it by dip-coating method. The coated foam was used as a catalyst block to study the reaction of toluene with methanol. The effect of variation of different reaction parameters such as reaction temperature, mole ratio of reactants, W/F ratio, partial pressure, feed rate, number of ceramic block coated with catalyst was investigated. Effect of regeneration of the catalyst has also been studied. In addition, comparison of conversion with pellet and coated one was also studied to confirm the usefulness of ceramic foam as catalyst support to get the best conversion to xylene production.

P-Xylene selectivity enhancement in methanol toluene alkylation by separation of catalysis function and shape-selective function

Catalyst reactivity and selectivity always compromise with each other in most reactions. HZSM-5 catalyst for the methanol toluene alkylation reaction suffers from active site loss when modified by elements such as Si, P, Mg and B to attain high p-xylene selectivity, incurring problems of low toluene conversion and rapid catalyst deactivation. In the present study, the separation of catalysis function and shape-selective function was achieved by epitaxial growing a Silicate-1 layer over HZSM-5 crystal to create an HZSM-5@S-1 catalyst. HZSM-5@S-1 was shown to possess less weak acid sites but more strong acid sites than the parent HZSM-5. With reduced contact time, the catalyst showed increased p-xylene selectivity up to 88% but no obvious degradation in toluene conversion. The enhancement of Silicate-1 shell to PX selectivity was less effective when applied to low Si/Al ratio ZSM-5 samples, due to the re-incorporation of aluminium leached from low Si/Al ratio parental ZSM-5 samples into the newly formed Silicate-1 framework. Benefiting from retaining most of the strong acid sites of HZSM-5, the catalyst showed high toluene conversion with increasing WHSV without apparent deactivation over a 130hours service life test.

Characterization of Alumina and H-ZSM-5 Zeolite and Comparison of their Performance by Toluene Methylation Reaction with Ceramic Foam as Catalyst Support

The present work deals with the characterization and comparison of ceramic foam (dimension 40×40×15mm, 30 pores per inch) supported mesoporous alumina(prepared by the surface hydrolysis of 99% Al metal plate as well as by hydrothermal synthesis of Al(NO3)3.9H2O using pluronic F-127 as structure directing agent), and H-ZSM-5 for the methylation of toluene reaction. The characterization of the catalyst was done by XRD, SEM, Particle size distribution, Ammonia TPD, BET surface area, and pore size distribution. It was observed that alumina prepared with pluronic F-127 shows higher BET surface area (320 m2/g) compared to commercial H-ZSM-5(260 m2/g). Toluene alkylation reaction with methanol was carried out with catalyst coated foam and also with catalyst extrudates (both1g). Conversion obtained was 25-30% at a catalyst loading of 8% on foam for H-ZSM-5 whereas it was 1.26% for alumina coated one. It can also be concluded that catalyst coated ceramic foam exhibits higher conversion compared to pelleted one due to less mass transfer resistance and uniform distribution of catalyst active sites. For any chosen reaction like alkylation, the greater surface area for any catalyst is not the only reason for higher conversion, but the bronsted and lewis acid sites play an important role. Keywords: Ceramic foam, mesoporous alumina, H-ZSM-5, Bronsted acid catalysis, toluene methylation.

Kinetics of toluene alkylation with methanol catalyzed by pure and hybridized HZSM-5 catalysts

A kinetic study of toluene alkylation with methanol was performed over pure HZSM-5, mordenite/ZSM-5 (hybrid of mordenite and HZSM-5), and ZM13 (composite mixture of HZSM-5 and MCM-41 at pH 13). Experimental runs were conducted using a batch fluidized bed reactor at temperatures of 300, 350 and 400°C and reaction times of 3, 5, 7, 10, 13, 15 and 20s. The rate of toluene methylation and toluene disproportionation were studied on the three catalysts (toluene alkylation is usually accompanied by toluene disproportionation on acid catalyst). Based on the results obtained, a simplified power law kinetic model consisting of three reactions was developed to estimate the activation energies of toluene methylation and disproportionation simultaneously. Coke formation on catalysts was accounted for using both reaction time and reactant conversion decay functions. All parameters were estimated based on quasi-steady state approximation. Estimated kinetic parameters were in good agreement with experimental results. The order of alkylation ability of the catalysts was found to be ZM13>HZSM-5>mordenite/ZSM-5, while the reverse is for toluene disproportionation (mordenite/ZSM-5>HZSM-5>ZM13). Thus, alkylation of toluene is most favorable on ZM13 due to combined effect of mesoporosity induced through its synthetic route and acid content. Toluene/MeOH molar ratio of 1:1 was most suitable for toluene alkylation reaction.

FT-IR characterization of [bupy]BF4-MCl3 (M = Al, Fe) ionic liquids using new molecular probe and their alkylation performance

Abstract In the present work, the acidity of [bupy]BF 4 -MCl 3 (M = Al, Fe) ionic liquids was characterized by means of FT-IR technique using acetonitrile as molecular probe. The results show that only Lewis acidity is present in these ionic liquids and the acidity strength of [bupy]BF 4 -AlCl 3 is stronger than [bupy]BF 4 -FeCl 3 . In the alkylation reaction of toluene and 1,3-pentadiene to produce pentenyltoluene, the catalytic activities of these ionic liquids catalysts can be correlated with their Lewis acidity.

Improved selectivity in the toluene alkylation reaction through understanding and optimising the process variables

It has been demonstrated that it is possible to produce p -xylene with >99.9% selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p -xylene on the external acid sites of the catalyst by controlling the contact time. It has been demonstrated that it is possible to produce p -xylene with near-perfect selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p -xylene on the external acid sites of the catalyst by controlling the contact time. This offers a superior route to high selectivity compared to multiple pre-treatments of the catalyst to eliminate external acid sites (for example, by silanisation). Additionally, a high toluene:methanol feed ratio is beneficial because it minimises the methanol dehydration reaction. A further benefit is that the maximum theoretical conversion of toluene is limited, which diminishes p -xylene product inhibition. These findings confirm that toluene alkylation is best operated in a multistage reactor, but also highlight the need for removal of p -xylene as well as addition of methanol between stages. The method of catalyst preparation is not critical, provided that there is sufficient boron present (≥6.5 wt%) and any boron lost through sublimation during the reaction is replenished. It has been found that an active catalyst can be produced in situ by either loading a physical mixture of hydroboric acid and HZSM-5 into the reactor prior to reaction or even placing a bed of hydroboric acid upstream from a bed of HZSM-5. The in situ-formed catalyst readily achieves >99.9% selectivity to the desired p -xylene isomer, under optimised conditions.

Enhanced para-Xylene Selectivity in the Toluene Alkylation Reaction at Ultralow Contact Time

Dramatic improvements in the para-xylene selectivity of the toluene alkylation reaction can be effected by operating the catalytic reaction at ultralow contact time. Unexpectedly, the rate of alkylation is sustained, while unwanted side reactions are suppressed. By demonstrating that contact time directly influences the fate of para-xylene, which is known to form and diffuse preferentially within the zeolite catalyst, we conclude that external mass transfer is a key parameter in controlling selectivity. Even non-optimized catalysts can be made to achieve near-perfect selectivity, without sacrificing conversion.

Crystallization and characterization of high silica silicoaluminophosphate SAPO-5

SAPO-5 with a high Si content have been synthesized by using dipropylamine (DPA) as a template in ethylene glycol (EG) (molar ratio of silica in the reaction gels up to 2.4). Crystallinity and silicon incorporation was confirmed by XRD, XRF, N2 sorption measurement, TG-DTA, SEM, pyridine-TPD and 27Al, 29Si MAS-NMR. These SAPO-5 materials with high Si concentrations show higher activity for toluene alkylation reaction than samples prepared from the gel with up to 0.6 molar ratio of silica.

A theoretical study of the alkylation reaction of toluene with methanol catalyzed by acidic mordenite.

A theoretical study of the alkylation reaction of toluene with methanol catalyzed by the acidic Mordenite (Si/Al = 23) is reported. Cluster DFT as well as periodical structure DFT calculations have been performed. Full reaction energy diagrams of the elementary reaction steps that lead to the formation of the three xylene isomers are given. The use of periodical structure calculations allows one to account for zeolite framework electrostatic contributions and steric constraints that take place in zeolitic catalysts. Especially the steric constraint energy contribution has a significant effect on the energies and bond formation paths. The activation energy barrier of p-xylene formation is found to be approximately 20 kJ/mol lower than the corresponding values for the formation of its isomers. Computed host-guest binding energies according to the DFT method need a correction due to the absence of the dispersive interaction with the zeolite wall. Apparent activation energies obtained with this correction are in good agreement with experimental data.

Kinetics of toluene alkylation with methanol over magnesium-modified ZSM-5

The kinetics of toluene alkylation with methanol has been studied over both unmodified and Mg-modified ZSM-5 catalysts. On the basis of the product distribution obtained over the unmodified zeolite, the following secondary reactions have been considered: methanol dehydration, toluene disproportionation and xylene dealkylation. Power law and Langmuir-Hinshelwood-Hougen-Watson (LHHW) models have been tested for the main toluene alkylation reaction, the best fits to the experimental data being achieved with two models: a second-order power law model and a model based on the Rideal-like mechanism. The first one has been applied to the results obtained with the Mg-modified catalyst, including the effect of the diffusion rate, due to its simpler expression. Over this catalyst p-xylene is the only isomer present in the primary product, hence m- and o-xylene formation takes place by p-xylene isomerization on the external surface catalytic sites. Therefore, the kinetic model developed for the Mg-modified zeolite takes into account, as well as diffusional effects, the influence of p-xylene isomerization over the external zeolite surface, reproducing the experimental product distribution with an average relative error of 6.8%

Reactions of mixtures of toluene and methanol over ZSM-5

Methanol, in the presence of toluene, was completely converted to hydrocarbons above 400 °C. However, depending on the ratio of toluene to methanol in the feed mixture and the reaction severity, only a fraction of the methanol participated in the toluene alkylation reaction, with the remainder being converted to gaseous hydrocarbons. Alkylation is found to be ortho/para-directing over the small-crystal ZSM-5, similar to that found with aluminum chloride and amorphous silica/alumina catalysts, whereas the large crystals showed high para selectivity. The catalytic results are shown to be consistent with the diffusion characteristics of the zeolite.

ChemInform Abstract: Activity and Selectivity of Neodymium Exchanged Zeolites in the Alkylation Reaction of Toluene with Methanol.

ChemInform Abstract: Activity and Selectivity of Neodymium Exchanged Zeolites in the Alkylation Reaction of Toluene with Methanol.

Alkylation of toluene with propene using zeolite catalysts

The catalytic activity of Y-type zeolite for the alkylation reaction of toluene with propene is strongly dependent on the degree of ion-exchange and on the calcination temperature. The activity increases as the sodium ions in Na-form Y zeolite are replaced by hydrogen ions up to at least 90% cation exchange. Optimum activity occurs at activation temperatures around 400 °C when the Brønsted acidity is at a maximum. Ortho-para substitution always predominates, but at low activation temperatures (<400 °C) the p isomer is preferred. This preference is reduced with increasing activation temperature, accompanied by a marked increase in the proportion of the m isomer. Present results indicate that the alkylation proceeds by a carbonium ion mechanism involving Brønsted acid sites on the zeolite surface. There is no correlation between the catalytic activity of the zeolite and its electron-transfer properties. The isomeric composition of the products suggests, however, that the selectivity of the catalysts is a function of their Lewis acidity. These findings, therefore, provide further evidence for the dual nature of zeolite catalysts.

Synthesis of s-Butyltoluene by the Gas Phase Alkylation Reaction of Toluene with 1-Butene Using γ-Alumina-Boria Catalyst

For a selective synthesis of s-P-butyltoluene by an alkylation reaction of toluene with 1-betene, optimal reactioni conditions and suitable catalysts have been found by the authors.In this paper, the experimental results ofthe reaction in gas phase with the alumina boria catalysts using r-alumina as a base are reported. The conclusions may be summarized as follows:1) r-aluminareacted with boric gcid to form strongly acidic centers, as well as with tyand X-alumina, developing activity of toluene alkylation. The total acid amount of the catalyst was distributed uniformly over the acid centers with acid strength Hg ranging from +7.1 to -8.2. The catalysts containing O -vlO wt% boria had much more weak acid centers and Lewis acid ones than those containing more than 15 wt% boria. At the boria contents more than 15 wt% the greater parts of the acid centers were strong acids, considered as Bronsted type, and the acid amount showeda maximum at 15 wt 9Zer boria and this maximum value increased with inCreasing calcina temperature Qf the catalyst, 2) The activity was attributed to the acid centers at strength H, ;-3.0, being directly proportional to its acid amount, When the reaction proceeded with sIight decrease in activity as a result of co:keformation, as may be seen from the above fact and the result shown in 1), the catalyst containing about 15 wt%boria showed the maximum activity that became higher as the calcination temperature increased.3) At transient-state activity(about an hour after the start of run), the toluene conversions and s-butylto1uene(SBT)yields increased as the reaction temperature increased. While at stationary-state activity(five hours after the star of run)they decreased with increasing reac on temperature because of a cataryst decay. Alsg the isomer distribution of SBT at stationary-state activity was slightly dependent on reaction, condition, s, but independent of preparing conditions of the catalyst, and the SBT contained approxi:matly 20% of o-and m-isomer and 60% of p-one.

Liquid Phase Synthesis of sec-Butyltoluenes by Alkylation Reaction of Toluene with 1-Butene

As to synthesis of sec-butyltoluene(SBT) giving the para isomer selectively by alkylation of toluene with 1-butene, the suitable catalysts and optical conditions have been investigated. In this paper, the experimental results of liquid phase reaction utilizing seme Friedel-Crafts catalysts (phosphorus pentoxide, metal halides and so on) are presented.Since the SBT isomers have not been completely identified in previous reports, each one was prepared from the corresponding isomer of brometoluene and was used to identify the reaction products.It was found that phospherus pentoxide gave the para isomer in higher selectivity than the other catalysts. Yields of SBT based on charged 1-butene were 85N90%e and a distribution of the isomer (p-: m-: o-) was 56: 17: 27, when charged molar ratios of toluene, phosphorus pentoxide and 1-butene were 6, O.21 and O.56 at 100Av1200C, respectively. Under these conditions the reaction rate was found to be pseudo-first erder with respect to 1-butene ancl the specific reaction rate was 7800 exp(-9950/R T) min-1.From the result of isomer distributions and anhydrous reaction condition, it might be concluded that the reaction proceeds both through the carbonium ion mechanism with a trace of water and through a mechanism containing direct, coordination cemplexes between 1-butene and the catalyst.

Alkylation on synthetic zeolites: II. Selectivity of p-xylene formation

The influence of the calcination temperature and the degree of cation exchange of NH 4-Y, and the addition of hydrogen chloride to Mn-Y zeolite, in relation to the selectivity of p-xylene formation, was studied for the alkylation reaction of toluene with methanol. It was found that within a certain range of calcination temperature ( i.e., 400–550 °C), p-xylene can be obtained selectively. A proportional relation between the catalytic activity and the selectivity of p-xylene with the degree of cation exchange was also observed. The addition of hydrogen chloride to Mn-Y zeolite has shown a promoting effect in p-xylene selectivity. These behaviors of the treated catalysts can be related to Brönsted acidity. It has also been shown that the alkylation reaction was dominant, while the isomerization reaction of the produced xylene (under the conditions employed) was depressed. It has been established that the p-xylene selectivity is a function of Brönsted acidity.