The Photochemistry of Ketene the Reactions of Methylene with Toluene and P-Xylene in Vapor Phase (II)

In the photolysis of ketene with toluene in the vapor phase, ethylbenzene, xylenes, 2-methylcycloheptatriene-1, 3, 5, and three unidentified compounds are found as the products of the reactions of methylene with toluene. In the ketene-p-xylene system, p-ethyltoluene, 1,2,4-trimethylbenzene, 1,4-dimethylcyclohepatriene-1,3,5, and three unidentified compounds are obtained as the products of the reactions of methylene with p-xylene. The reaction mechanism is discussed.     

Isothermal Phase Equilibrium Studies on the Binary Mixtures of some Alkylbenzenes

Abstract

The gas chromatographic method proposed by us for simple and accurate measurement of isothermal phase equilibria has been applied to the binary mixtures formed by alkylbenzenes amongst themselves. Results on the binary mixtures of: benzene - toluene, toluene + o-xylene, toluene + p-xylene, toluene + ethylbenzene, ethylbenzene + o-xylene and ethylbenzene + p-xylene are presented in this paper. The present measurements on benzene + toluene system at 40°C are in good agreement with the isothermal phase equilibrium data available in the literature.     

Formation of ring-retaining products from the OH radical-initated reactions of o-, m-, and p-xylene

The ring-retaining products formed from the OH radical-initiated reactions of o-, m-, and p-xylene in the presence of NO_x have been identified and their formation yields determined. Experiments were carried out at 298 ± 2 K and in the presence of 740 torr total pressure of air. The products observed, and their yields, were: from o-xylene, o-tolualdehyde, 0.0453; 2-methylbenzyl nitrate, (0.0135 + 5.5 × 10^?17 [NO₂]); 2,3-dimethylphenol, 0.097; 3,4-dimethyl-phenol, 0.064; 3-nitro-o-xylene, 0.0059; 4-nitro-o-xylene, (0.0111 + 9.9 × 10^?17 [NO₂]); from m-xylene, m-tolualdehyde, 0.0331; 3-methylbenzyl nitrate, 0.0061; 2,4-dimethylphenol, 0.099; 2,6-dimethylphenol, 0.111; 4-nitro-m-xylene, 0.0018; 5-nitro-m-xylene, (0.0032 + 1.6 × 10^?17 [NO₂]); from p-xylene, p-tolualdehyde, 0.0701; 4-methylbenzyl nitrate, 0.0082; 2,5-dimethylphenol, 0.188, 2-nitro-p-xylene, (0.0120 + 2.8 × 10^?17 [NO₂]), where the NO₂ concentration is in molecule cm^?3 units. The nitro-xylene data are consistent with our recent product study of the corresponding reactions of benzene and toluene and indicate that under the experimental conditions employed the dimethylhydroxycyclohexadienyl radicals reacted with NO₂ and not with O₂. When combined with literature ring-cleavage product yields, these data show that ca. 55–80% of the reaction pathways are accounted for.     

Investigations on poly(vinyl chloride). II. Pyrolysis of chlorinated polybutadienes as model compounds for poly(vinyl chloride)

The pyrolysis of chlorinated polybutadienes (CPB) was investigated by using a pyrolysis gas chromatograph. CPB corresponds to poly(vinyl chloride) (PVC) constructed with head–head and tail–tail linkages of the vinyl chloride unit. Benzene, toluene, ethyl-benzene, o-xylene, styrene, vinyltoluene, chlorobenzenes, naphthalene, and methylnaphthalenes were detected in the pyrolysis products from CPB above 300°C, and no hydrocarbons could be detected at 200°C. The pyrolysis products from CPB were similar to those from PVC and new products could not be detected. Lower aliphatics, toluene, ethylbenzene, o-xylene, chlorobenzenes, and methylnaphthalenes were released more easily from pyrolysis of CPB than from PVC; amounts of benzene, styrene, and naphthalene formed were small. These results support the conclusion that recombination of chlorine atoms with the double bonds in the polyene chain takes place and that scission of the main chain may depend on the location of methylene groups isolated along the polyene chain during the thermal decomposition of PVC.     

Catalytic Conversion of Biomass-Derived Polyols into Para-xylene over SiO2-Modified Zeolites

This work proved that biomass-based polyols (sorbitol, xylitol, erythritol, glycerol and ethanediol) were able to be converted into high-value chemical (p-xylene) by catalytic cracking of polyols, alkylation of aromatics, and the isomerization of xylenes over the SiO₂-modified zeolites. Compared to the conventional HZSM-5 zeolite, the SiO₂-containing zeolites considerably increased the selectivity and yield of p-xylene due to the reduction of external surface acidity and the narrowing of pore entrance. The influences of the methanol additive, reaction temperature, and types of polyols on the selectivity and yield of p-xylene were investigated in detail. Catalytic cracking of polyols with methanol significantly enhanced the production of p-xylene by the alkylation of toluene with methanol. The highest p-xylene yield of 10.9 C-mol% with a p-xylene/xylenes ratio of 91.1% was obtained over the 15wt%SiO₂/HZSM-5 catalyst. The reaction pathway for the formation of p-xylene was addressed according to the study of the key reactions and the characterization of catalysts.     

Catalytic properties of zeolites MCM-22 and NU-87 in disproportionation of toluene

The catalytic properties of MCM-22 and NU-87 were investigated for the disproportionation of toluene to produce benzene and xylene, and the results were compared with those obtained over mordenite, beta and ZSM-5. It turns out that dealumination of MCM-22 removes selectively the acid sites from the external surface and thus suppresses the secondary isomerization of p-xylene, enhancing the para-selectivity. This indicates that the dealuminated MCM-22 is a promising catalyst for the selective formation of p-xylene from toluene disproportionation. This revised version was published online in June 2006 with corrections to the Cover Date.     

m-Xylene Isomerization in SAPO-11/HZSM-5 Mixed Catalyst

The catalytic isomerization of m-xylene was studied over a solid acid silicoaluminophosphate type SAPO-11, mixed to HZSM-5 zeolite. The reaction was processed varying the temperature and weight hourly space velocity, using a fixed bed continuous flow reactor. The m-xylene suffers isomerization to p-xylene and o-xylene by molecular displacement of methyl groups. The mixed catalyst was selective to p-xylene at 623 K and 2.5 h⁻¹ with a maximum p/o ratio of 2.05. The ethylbenzene formation was not observed in the products. In this process an apparent activation energy of the order of 13.9 kJ mol⁻¹ was obtained. This revised version was published online in June 2006 with corrections to the Cover Date.     

Renewable \begin{document}$p$\end{document}-Xylene Production by Co-catalytic Pyrolysis of Cellulose and Methanol

This work developed a one-step process for renewable p-xylene production by co-catalytic fast pyrolysis (co-CFP) of cellulose and methanol over the different metal oxides modified ZSM5 catalysts. It has been proven that \begin{document}${\rm{L}}{{\rm{a}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}$\end{document}-modified ZSM5(80) catalyst was an effective one for the production of bio-based p-xylene. The selectivity and yield of p-xylene strongly depended on the acidity of the catalysts, reaction temperature, and methanol content. The highest p-xylene yield of 14.5 C-mol% with a p-xylene/xylenes ratio of 86.8% was obtained by the co-CFP of cellulose with 33wt% methanol over 20%\begin{document}${\rm{L}}{{\rm{a}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}$\end{document}-ZSM5(80) catalyst. The deactivation of the catalysts during the catalytic pyrolysis process was investigated in detail. The reaction pathway for the formation of p-xylene from cellulose was proposed based on the analysis of products and the characterization of catalysts.     

Vapour–liquid equilibria of butyl acetate with aromatic hydrocarbons at 298.15 K

Vapour pressures of butyl acetate?+?benzene or toluene or o- or m- or p-xylene were measured by static method at 298.15?±?0.01?K over the entire composition range. The activity coefficients and excess molar Gibb's free energies of mixing (G ^E) for these binary mixtures were calculated by fitting vapour pressure data to the Redlich–Kister equation using Barker's method of minimizing the residual pressure. The G ^E values for the binary mixtures containing benzene are positive; while these are negative for toluene, ortho, meta and para xylene system over the whole composition range. The G ^E values of an equimolar mixture for these systems vary in the order: benzene?>?m-xylene?>?o-xylene?>?p-xylene?>?toluene     

Rate constants for the gas-phase reactions of the OH radical with a series of aromatic hydrocarbons at 296 ± 2 K

Using a relative rate method, rate constants have been determined at 296 ± 2 K for the gas-phase reactions of the OH radical with toluene, the xylenes, and the trimethylbenzenes. Using the recommended literature rate constant for the reaction of OH radicals with propene of (2.66 ± 0.40) × 10^?11 cm³ molecule^?1 s^?1, the following rate constants (in units of 10^?12 cm³ molecule^?1 s^?1) were obtained: toluene, 5.48 ± 0.84; o-xylene, 12.2 ± 1.9; m-xylene, 23.0 ± 3.5; p-xylene, 13.0 ± 2.0; 1,2,3-trimethylbenzene, 32.7 ± 5.3; 1,2,4-trimethylbenzene, 32.5 ± 5.0; and 1,3,5-trimethylbenzene, 57.5 ± 9.2. These data are compared with the literature values.     

The mass spectra and ionization potentials of the neutral fragments produced during the electron bombardment of aromatic compounds

A mass spectrometer equipped with a dual ionization chamber ion source has been used to characterize directly the neutral species produced in the dissociative ionization of gases by electron impact. Neutral fragment mass spectra have been obtained for the electron ionization and fragmentation of benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene and isotopically labeled toluene. The neutral fragment mass spectra correlate well with the structures of the molecules. The abundant species in the neutral fragment mass spectra also correlate reasonably well with the abundant complementary positive ions of the normal mass spectra. Ionization potentials have been determined for the abundant neutral species produced. Where comparisons with values reported elsewhere are possible, the agreement is usually within ±0.2 eV or less.     

Catalytic Conversion of 1,2,3-Trimethylbenzene Over HY Zeolite

The reaction of 1,2,3-trimethylbenzene (1,2,3-TMB) over HY zeolite was investigated in a fixed-bed flow reactor at 200-300 °C under atmospheric pressure. The reaction products include toluene, pentamethylbenzene and isomers of xylene, 1,2,3-TMB and tetramethylbenzene. Based on the time-on-stream theory, the types and initial selectivities of these products were determined from plots of product selectivity. 1,2,4-TMB is initially produced from 1,2,3-TMB via isomerization whereas o-xylene, m-xylene, 1,2,3,4- and 1,2,3,5-tetramethylbenzene were primarily formed by disproportionation of 1,2,3-TMB. Isomerization and disproportionation obeyed first- and second-order kinetics, respectively; both reactions proceeded via a carbonium ion mechanism with the former occurring by methyl transfer on the benzene ring whereas the latter proceeded through the diphenylmethane transition state. The activation energies are 31.6 and 37.2 kJ mol^?1 for isomerizaion and disproportionation, respectively.     

Speed of Sound and Isentropic Compressibilities of N-Methylcyclohexylamine with Benzene and Substituted Benzenes at 303.15 K

Abstract

New experimental sound velocity and density data for binary mixtures of N-methyl-cyclohexylamine with benzene, toluene, o-xylene, m-xylene, p-xylene, chlorobenzene, bromobenzene and nitrobenzene at 303.15K have been reported. The sound velocity data were also used to compute the isentropic compressibilities (K_s ). The deviation in isentropic compressibilities (ΔK_s ) from ideal behaviour suggests that the existence of weak dipole-induced dipole and dipole-dipole interactions between unlike molecules.     

The stability of suspensions of multiwalled carbon nanotubes in organic solvents in the presence of triton X-165

The stability of suspensions of multiwalled carbon nanotubes in isopropanol, toluene, and p-xylene has been studied. Suspensions of multiwalled carbon nanotubes in isopropanol (unlike those in toluene and p-xylene) display high aggregation stability, which is explained by the formation of repulsive solvation layers as a result of interactions between the polar solvent and nanotube surface. The addition of a nonionic surfactant, Triton X-165, noticeably increases aggregate sizes and accelerates sedimentation processes in nanotube suspensions in isopropanol, while, in toluene and p-xylene, the aggregate sizes decrease and the nanotube suspensions are stabilized.     

Design and Development of Zeolite-Based Catalytic Processes for Aromatics Production

Processes for the production of xylenes, which occur in an integrated aromatic complex, are discussed. A brief overview of the work carried out at Indian Petrochemicals Corporation Limited for the development of zeolite-based catalytic processes for the production of aromatics is presented. This includes xylene isomerization, transalkylation and disproportionation of C₇ and C₉ aromatics for maximization of xylenes, selective disproportionation of toluene and selective alkylation of mono-alkylaromatics to p-dialkylbenzene. Achievements in the commercialization of zeolite-based catalysts and processes for isomerization of m-xylene to p- and o-xylene along with dealkylation of ethylbenzene, and for selective ethylation of ethylbenzene to produce p-diethylbenzene are highlighted.     

Desorption of BTEX from activated charcoal using accelerated solvent extraction: evaluation of occupational exposures

A procedure for the determination of benzene, toluene, ethylbenzene and o-xylene, m-xylene and p-xylene (BTEX) in occupational environments is proposed. These compounds are extracted from activated charcoal using accelerated solvent extraction. Operational parameters are optimized and quantitative recovery is obtained using acetonitrile as the extraction solvent and 1-mL extraction cells, a preheat time of 2 min, a temperature of 160 °C, a pressure of 1,500 psi, a static period of 5 min, a flush volume of 110%, two cycles and a purge time of 90 s. Determination of BTEX compounds is carried out by gas chromatography using a flame ionization detector. The recoveries, obtained for a confidence level of 95%, are 91 ± 4, 100 ± 3, 104 ± 2, 93 ± 4, 99 ± 2 and 99 ± 2% for benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene, respectively. The detection limits are 0.5 μg for benzene, 0.7 μg for toluene and 1.0 μg for the other compounds. The proposed procedure has been applied to real samples collected in several workplaces, like a microbiology laboratory, an analytical chemistry laboratory, a printer’s, a car repair shop and a petrol station. From the results obtained, it can be concluded that the occupational exposures determined are always acceptable because they are lower than the tenth part of the recommended exposure limits (VLA-ED and VLA-EC).     

Isothermal Phase Equilibria Through Gas Chromatography for Petrochemical Processing

Abstract

A gas chromatographic technique has been used to measure the isothermal phase equilibria likely to be of importance in petrochemical processing. The measurements on the binary mixtures formed by chlorobenzene with some aromatic hydrocarbons (toluene, o-xylene, p-xylene) and aliphatic alcohols (ethanol, 1-propanol, 1-butanol) are given in this paper. Our measurements on chlorobenzene + 1-propanol mixtures are in good agreement with the literature data.     

Mechanism for selective <Emphasis Type="Italic">para</Emphasis>-disproportionation of toluene on pentasil-based catalysts

We propose a bimolecular mechanism for disproportionation of toluene to form benzene and para-xylene via protonation of the toluene molecule at the methyl group, reaction of the carbocation formed with the para position of the next toluene molecule, and α-scission of the complex obtained. The mechanism presumes formation of methyl diphenyl methane as a byproduct of disproportionation.     

Inversion of the Kirkwood–Buff Theory of Solutions: Application to Tetrahydrofuran + Aromatic Hydrocarbon Binary Liquid Mixtures

The Kirkwood–Buff (K-B) integrals play an important role in characterizing the intermolecular interactions in liquid mixtures. The interaction is represented by the K-B parameters, G _AA,G _BB, and G _AB, which reflect correlation between like-like and like-unlike species in the mixture. The K-B integrals of binary mixtures of tetrahydrofuran with benzene, toluene, o-xylene, m-xylene, p-xylene and mesitylene at 298.15 K and atmospheric pressure have been computed from the experimental data of ultrasonic speed and density. We have used the similar inverse procedure (as proposed by Ben-Naim) to compute the K-B parameters of the mixture, in which thermodynamic information on mixtures, such as partial molar volumes, isothermal compressibility and experimental data of partial vapor pressures were used. A new route has been incorporated by using regular solution theory in the computation of excess Gibbs energy for obtaining the partial vapor pressures of binary liquid mixtures. The low values of excess entropy, S ^E≈0, obtained for these mixtures indicate the applicability of regular solution theory to the mixtures. The values of the K-B parameter, G _AB, obtained using this procedure indicate that the correlation/affinity between THF and aromatic hydrocarbon molecules follows the order: benzene > toluene > o-xylene > m-xylene > p-xylene > mesitylene, which is in good agreement with the results obtained from the trends exhibited by the excess functions of these mixtures.     

Polymerization of α-halogenated p-xylenes with base

Various α-halo-p-xylenes have been polymerized with base yielding p-xylylene polymers. The reaction involves a 1,6-dehydrohalogenation to give a xylylene which then polymerizes. α,α′-Dichloro-p-xylene forms poly-α-chloro-p-xylylene and polymers containing stilbene units; α,α,α′,α′-tetrachloro-p-xylene gives poly-α,α,α′-trichloro-p-xylylene; alkyl, aryl, and halogen ring-substituted α-chloro-p-xylenes give the corresponding ring-substituted poly-p-xylylenes. The more halogens in the α positions (up to five), the weaker the base necessary for dehydrohalogenation. Sodium hydroxide in methanol will polymerize tetrachloro-p-xylene, while potassium tert-butoxide in refluxing p-xylene is necessary to polymerize α-chloro-p-xylenes. Stilbenes are formed when α-halo-p-xylenes are reacted with potassium tert-butoxide in polar solvents such as dimethyl sulfoxide.