Methylation Of Toluene Research Articles

A Theoretical Investigation of the Methylation of Methylbenzenes and Alkenes by Halomethanes over Acidic Zeolites

The reactivity of chloromethane, bromomethane, and iodomethane over acidic zeolite catalysts has been probed, using the methylation of ethene, propene, and toluene as model reactions. Adsorbed reactants, transition states, and adsorbed products have been investigated. A cluster model has been used to represent the zeolite. Both the associative (direct) mechanism and the dissociative mechanism (via the formation of surface methoxide groups) have been studied. Quantum chemistry predicts that the associative pathway is favored over the dissociative mechanism. A weak trend in reactivity is found among the halomethanes, indicating the following order of reactivity: MeI > MeBr > MeCl. The results are compared with recent theoretical studies on methanol reactivity.

Toluene methylation licensed

Toluene methylation licensed

Activity and basicity of BaO modified zeolite and zeolite-type catalysts

BaO modified zeolite and zeolite-type catalysts provide new and valuable data about the alternative reaction for ethylbenzene and styrene formation—the oxidative methylation of toluene with methane. Over BaO modified X, Y, mordenite, ZSM-5, silicalite and AlPO 4-5 catalysts, the toluene conversion, selectivity and yield of C 8 hydrocarbons (ethylbenzene and styrene) are affected to a different degree by the reaction temperature. Both activity and basicity (measured by TPD of CO 2) are resultant from the combined effect of chemical composition and geometry of zeolite and zeolite-type structures, as well as from the accessibility of BaO modifier to the reagents. The Si/Al atomic ratio determines the catalytic and basic properties within a series of the same structural type. The zeolite and zeolite-type structural geometry determines the accessibility of the introduced BaO. Higher accessibility of BaO used for modification favors the activity. Basicity measurements by X-ray photoelectron spectroscopy (XPS) are mainly sensitive towards the chemical composition of the zeolite and zeolite-type framework.

Basic zeolite and zeolite-type catalysts for the oxidative methylation of toluene with methane

The oxidative methylation of toluene with methane is used as a test reaction for determining the activity, selectivity and yield of C8 hydrocarbons (ethylbenzene and styrene) over different zeolite and zeolite-type catalysts, viz., X, Y, mordenite, ZSM-5, silicalite and AlPO4-5. Selectivity and basicity increase with decreasing Si/Al atomic ratio within the series of the same structural type. The basicity, surface structure and structural integrity are characterized by TPD of CO2, XPS and IRS, respectively.

Gas permeation properties of MFI zeolite membranes prepared by the secondary growth of colloidal silicalite and application to the methylation of toluene

MFI zeolite membranes were prepared by secondary growth on α-alumina microfiltration membranes. Colloidal silicalite, the size of which was ≈100 nm, was used as seed crystals. An MFI membrane, in which the zeolite layer was oriented to the (1 0 1) plane, showed a n-C 4H 10 permeance of 1.5×10 −5 m 3 (STP) m −2 s −1 kPa −1 and a n-/ i-C 4H 10 selectivity of 15 at 150 °C. N 2 permeated faster than He at temperatures lower than 150 °C, probably because of surface diffusion of the adsorbed N 2 in the Henry regime. After ion-exchanging the MFI zeolite membranes from the Na-type to the H-type, the alkylation of toluene with methanol was carried out. A maximal p-xylene selectivity of 80% was achieved using the H-MFI zeolite membranes at 450–500 °C.

Reactivity Descriptors and Rate Constants for Electrophilic Aromatic Substitution: Acid Zeolite Catalyzed Methylation of Benzene and Toluene

The acid zeolite catalyzed methylation of benzene and toluene with methanol to form toluene and ortho-, meta-, or para-xylene is investigated at the B3LYP/6-31G* level of calculation with a T4 cluster representing the zeolite. After geometry optimization of reactants, transition states and products, reaction rate constants, entropy of activation, activation hardness, and local hardness are calculated and used to model the reactions. In general, the ortho and para products are favored over the meta and nonsubstituted products. Through calculation of rate constants and entropy of activation comparison between different reaction mechanisms has been carried out, indicating that the direct and consecutive mechanisms are competitive at higher temperature. The activation hardness correlates well with the activation energy and local hardness is a good parameter for describing intermolecular reactivity in charge controlled reactions.

The Stability with Time-on-Stream of NaBr-Promoted KY Zeolite Catalyst for the Oxidative Methylation of Toluene with Methane

The Stability with Time-on-Stream of NaBr-Promoted KY Zeolite Catalyst for the Oxidative Methylation of Toluene with Methane

Oxidative methylation of toluene with methane using X zeolite catalyst modified with alkali earth oxides

Oxidative methylation of toluene with methane was used to study the catalytic activity, selectivity and yield of C 8 hydrocarbons (ethylbenzene and styrene) of X zeolites, modified with different alkali earth oxides (MgO, CaO, SrO and BaO). It was found that SrO and BaO modified zeolites are more favorable for conversion and C 8 yield than MgO and CaO modified ones. C 8 selectivity is slightly affected by the nature of alkali earth oxide, used for zeolite modification. The effect of temperature, contact time and time-on-stream on the catalytic activity, selectivity and yield of C 8 hydrocarbons were also studied. Basicity results reveal that strong basic sites are generated by introduction of alkali earth oxides. The amount of basic sites increases with oxide molecular size. The nature of alkali earth oxide also affects the amount of crystal phase detectable by X-ray diffraction (XRD). BaO/NaX is the catalyst with the best represented oxide phases. Infrared spectroscopy (IRS) results point to a preserved crystal structure of the zeolite, regardless of the nature of the modifying alkali earth oxide.

BaO/NaX zeolite as a basic catalyst for oxidative methylation of toluene with methane

The oxidative methylation of toluene with methane was studied over a series of BaO/NaX zeolite catalysts. The catalytic properties were estimated with respect to the conversion of toluene, selectivity and yield of C 8 hydrocarbons (ethylbenzene+styrene). The basicity of the catalysts was investigated by temperature-programmed desorption (TPD) of CO 2. It was shown that the increase in the barium content leads to an increase in the amount of basic sites and a corresponding increase in activity. The state of the zeolite crystal structure and that of barium before and after use of the catalysts was registered by X-ray diffraction (XRD) analysis. A preserved crystal structure, existence of differently dispersed BaO and formation of BaCO 3 were detected in the catalysts.

Methylation of Toluene with Methane over ZSM-5 Catalysts

The methylation of toluene with methane in the presence of oxygen over zeolite catalysts is shown to be complicated by extensive disproportionation, hydrodealkylation, and hydrocracking reactions. However, it appears that these undesired reactions can be minimized, to enhance the methylation reaction, by using zeolites with reduced Bronsted acidity.

MgO/NaX zeolite as basic catalyst for oxidative methylation of toluene with methane

Oxidative methylation of toluene with methane was studied over a series of MgO/NaX zeolite catalysts. The effect of MgO on the zeolite was examined by X-ray diffraction (XRD) and temperature-programmed desorption (TPD) of CO 2. The results indicated that the conversion, selectivity and yield of C 8 hydrocarbons (ethylbenzene and styrene) are significantly improved by impregnation of maximum 13 wt.% MgO into the zeolite. The latter catalyst also displays a good stability. It is found that the amount of active sites but not their strength depends on the content of MgO in the zeolite. The catalysts possess well preserved crystal structure and low amount of MgO crystal phase.

Use of isotopic labeling for mechanistic studies of the methanol-to-hydrocarbons reaction. Methylation of toluene with methanol over H-ZSM-5, H-mordenite and H-beta

Methylation of toluene (in one case benzene) with methanol has been investigated over four different zeolites: Small and large crystal ZSM-5, dealuminated mordenite and zeolite beta. The feed ratio methanol/arene was varied over a wide range, mostly >1, using nitrogen or helium as carrier gas. A rather high space velocity was employed (WHSV (methanol + arene): 5–35 h −1). The reaction temperature was 350°C or 375°C. A parallel set of experiments was performed using 13C methanol (99% 13C). The products were analyzed by on-line gas chromatography using a GC–MS system allowing determination of isotopic composition of the more important products, i.e., ethene, propene and the arenes when 13C methanol was employed, otherwise a FID was used. The goal was to obtain mechanistic information, and no attempt has been made to optimize for any particular reaction product. The experiments showed that ethene and propene were isotopically mixed, containing 50–75% 13C. The 25–50% 12C atoms coming from the reactant arene. Over all catalysts the arene was, when fed alone, essentially inert with 0.5% or less conversion, giving neither ethene nor propene in measurable quantities. The isotopic distribution in ethene was indistinguishable from a random distribution. Propene, although being close to, displayed some deviation from randomness. The 12C/ 13C isotopic ratio in propene was equal to that in ethene, and they both varied with the methanol/arene ratio in the feed, but much less so than the variation in feed composition. The results support a pool mechanism where the catalytic activity for converting methanol to hydrocarbons is connected with the presence of adsorbates in the zeolite cavities which add methanol and split off product molecules, notably ethene and propene. Formation of ethene by reaction between C 1 species is at best a minor reaction. While formation of propene may take place by a homologation/cracking mechanism, this route was of minor importance here. Polymethylbenzenes which were formed in many cases displayed a pronounced isotopic scrambling, containing up to six 13C atoms in the benzene ring. Molecules with fewer 13C atoms than the number of added methyl groups were also identified.

Influence of Fe or Zn loading method on toluene methylation over MFI-type zeolite catalysts

Toluene methylation with methanol was investigated on MFI-type zeolite catalysts containing Fe or Zn within the range of 0-2% by weight as an active component. The catalytic performances were compared on catalysts to which Fe or Zn was introduced by different methods, i.e., ion-exchanged and incorporation methods. The prepared catalysts were characterized by XRD, XRF, BET, FTIR and pyridine adsorption technique on in-situ FTIR. The results showed that the incorporated samples, H-Fe, Al-silicate (Si/Fe=150) and H-Zn, Al-silicate (Si/Zn=150), exhibited catalytic activity and xylene selectivities approximately equivalent to those from the ion-exchanged samples, Fe(0.8)/H-MFI and Zn(1.0)/H-MFI, containing nearly the same amount of Fe or Zn. The higherp-xylene selectivity was achieved with H-Fe, Al-silicate (Si/Fe=150) and H-Zn, Al-silicate (Si/Zn=150) because of Bronsted acid strengths weaker than Fe(0.8)/H-MFI and Zn(1.0)/H-MFI. Therefore, the isomerization ofp-isomer produced primarily was suppressed on the incorporated catalysts better than the ion-exchanged ones.

Oxidative methylation of toluene with methane catalyzed by lithium modified molecular sieves

Lithium modified molecular sieves with different structures (X, Y, ZSM-5 and AlPO4-5) were studied as catalysts for oxidative methylation of toluene with methane. LiX zeolite was the most active catalyst for attaining best yields of ethylbenzene and styrene. The effects of basicity, crystallinity and type of structure were examined.

Promotion effects of alkali metal halides on the oxidative methylation of toluene with methane over KY zeolite catalysts

Effects of alkali metal halides promoter on the oxidative methylation of toluene with methane over KY zeolite catalysts were systematically studied. In terms of the catalytic activity for the oxidative methylation of toluene with methane over those catalysts, the following order was observed: NaBr/KY>KBr/KY>NaCl/KY. The C 8 products containing much styrene were gained over alkali metal bromide promoted KY zeolite catalysts. The acidity and basicity of these catalysts were studied by using NH 3-TPD and formic acid-TPD.

Toluene methylation on Al 13- and GaAl 12-pillared clay catalysts

The catalytic activity and selectivity of montmorillonite pillared with Al 13 and GaAl 12 polyoxycations have been investigated at temperatures between 573 K and 673 K for the gas-phase microcatalytic alkylation of toluene with methanol. A mixture of xylenes (XYs) was obtained as the main reaction products: 69% and 74% of xylenes for the Al- and GaAl–PILC catalysts, respectively, at 573 K. Trimethylbenzenes (1,2,4- and 1,2,3-isomers) were also found (31% and 26% for the Al and GaAl catalysts, respectively, at 573 K). The XY-isomer distribution followed the order o> p> m. The influence of the toluene concentration in methanol (2.5; 1.0; 0.5 M) upon the conversion of toluene and the selectivities of the products were also investigated. An increase in toluene molarity produced a decrease in toluene conversion and an increase in xylene selectivity for both the Al and GaAl catalysts. A good correlation was obtained between catalytic activity and increase in acid sites, as determined by pyridine and dimethylpyridine chemisorption in the gas-phase.

Oxidative methylation of toluene with methane catalyzed by cesium modified molecular sieves

Cesium exchanged zeolites (X, Y, and ZSM-5) and cesium impregnated molecular sieve AlPO 4-5 were studied as catalysts for oxidative methylation of toluene with methane. The effects of structure and basicity were examined. XRD analysis indicated that in the exchanged zeolites, cesium was finely dispersed while in the impregnated molecular sieve a CsCl phase was obtained. IR spectroscopy was more informative than XRD analysis as regards the crystallinity of the catalysts after modification with cesium. The most appropriate structure for the best selectivity and yield of ethylbenzene+styrene was found to be that of CsAlPO 4-5. A uniform distribution of the CsCl phase in accessible sites of the crystal lattice of CsAlPO 4-5 was assumed. It was established that the best catalyst CsAlPO 4-5 possessed weak basic sites. The performance of the basic sites was related both to the crystallographic structure and to cesium location.

Effect of preparation of a CsX zeolite catalyst on the oxidative methylation of toluene with methane

The study is devoted to the effect of preparation on the performance of CsX zeolite as basic catalyst for the oxidative methylation of toluene with methane. The conversion, C 8-selectivity and C 8-yield are significantly higher over the impregnated zeolite than those over the ion exchanged one. Intermediate position, but closer to the impregnated zeolite holds the solid-phase ion-exchanged zeolite. The structural characterization, realized by X-ray powder diffraction and IR lattice vibrations, indicates that the zeolite crystal structure is well stabilized and is mainly not influenced by the mode of preparation. Non-framework species (evolved from CsCl) are best presented in the structure of the impregnated zeolite, which is also the most active and selective catalyst of the three catalysts studied. The catalytic behaviour of all catalysts is not directly related to the overall basicity.

Modification of HZSM-5 by CVD of Various Silicon Compounds and Generation of Para-Selectivity

The modification of HZSM-5 zeolite was carried out by a method of chemical vapor deposition of various silicon alkoxides. We thus obtained the HZSM-5 zeolites with the different pore-opening sizes and with the varied extents of inactivation of acid sites on the external surface. Among the various silicon compounds used in this study, the SiOCH3(C3H7)3was effective in selective inactivation of acid sites on the external surface of HZSM-5 zeolite without affecting its intracrystalline void space. From the characterization of the modified HZSM-5 zeolites, and its relationship with the shape selectivity, we concluded that the enhancement of para-selectivity in the methylation of toluene was ascribable more closely to controlling the pore-opening size than to the inactivation of acid sites on the external surface.

Improvement of para-selectivity in methylation of toluene on various MFI-type metallosilicate catalysts

MFI-type metallosilicates incorporating various transition metal elements were synthesized by the rapid crystallization method. Compared with H-ZSM-5, these metallosilicates possess fewer acid sites and weaker acidic strength. In the methylation of toluene with methanol, protonated metallosilicates exhibited lower conversion of toluene, higher para-selectivity and higher yield of paraxylene than H-ZSM-5. Distributions of trimethylbenzene and tetramethylbenzene isomers produced in toluene methylation indicate that the effective pore size (openings and/or channels) of metallosilicates may be smaller than that of ZSM-5, which is more advantageous for formation of the smallest isomers in trimethylbenzenes and tetramethylbenzenes. The relation between the paraselectivity in toluene methylation and the isomerization activity in para-xylene conversion suggests that the para-selectivity could occur exclusively, when isomerization of para-xylene to other isomers could be completely prevented. Therefore, the improvement in para-selectivity on MFI-type metallosilicates should be attributed to both the reduction in effective pore size and the decrease of strong acid sites, on which produced para-xylene would be isomerized to ortho- and meta-xylenes.