Liquid-phase Toluene Research Articles

Water-soluble arylhydrazone complexes based on Mn(II) and Cu(II) as catalysts for liquid-phase toluene oxidation

Novel hydrosoluble coordination compounds based on arylhydrazones of β-diketones and bearing first row transition metals, namely [Mn(μ-1κO1,2κO2-HL1)2(H2O)2]n (1) and [Cu(κO1O2N-L2)(DEA)] (2; DEA = diethanolamine), were synthesised and characterized. Their structural features were investigated using single crystal X-ray diffraction. The catalytic performance of the complexes was explored for liquid phase oxidation of toluene in homogeneous medium using aqueous tert‑butyl hydroperoxide (TBHP) and hydrogen peroxide (H2O2) as oxidants. Both catalysts demonstrated activity, producing a mixture of benzaldehyde, benzyl alcohol and benzoic acid. Under optimized conditions, in the presence of catalysts 1 and using an aqueous TBHP solution as oxidant, the oxidation of toluene yielded an overall 42.6 % of oxygenated products. Contrary to what has been regularly reported regarding selectivity for benzaldehyde, benzoic acid was the predominant product in this study (71 %).

Quorum sensing improved the low-temperature performance of biofilters treating gaseous toluene

Biofilters usually have poor VOC removal performance at temperatures lower than 20 °C. In this study, two quorum sensing (QS) enhancement methods, which are addition of exogenous N-acyl-homoserine lactones (AHLs) and inoculation of AHL-producing bacteria, were applied in biofilters treating gaseous toluene at a low temperature of 12 °C. Their effects on biofilter performance and biofilm characteristics were investigated. The results showed that adding exogenous AHLs and AHL-producing bacteria in biofilters raised the average toluene elimination capacity by 39% and 26% respectively, and raised the average mineralization efficiency by 25% and 47% respectively in first 24 days. In addition, the two QS enhancement methods could increase the attached biomass by 48% and 87% respectively and made the biofilm distribute more uniform by increasing its extracellular polymeric substances content and microbial adhesive strength. The two QS enhancement methods resulted in more mesopores in biofilm, lower O/C and (O+N)/C of organic elements in biofilm, and increased the solubility of toluene in liquid phase, which all benefit VOCs mass transfer in biofilters. These results demonstrate that QS enhancement methods have the potential to optimize the biofilm and thus improve the performance of biofilters treating VOCs at a low temperature. This work provides us a new choice to improve industrial-scale biofilters treating VOCs at high latitude regions or in winter.

Single site MIL-101 for novel low-temperature liquid-phase toluene methylation

P-xylene is one of petrochemical products eagerly in demand. Until recently, the process for preparing of p-xylene was done via gas-phase toluene methylation reaction at high temperature using a strong acid catalyst. In this work, high surface area, shape-selective and single-site MIL-101(Cr) was used as a catalyst to perform toluene methylation reaction in a liquid phase at low reaction temperature (60-120 °C). Toluene conversion and p-xylene selectivity are up to 50% and 90%, respectively. Under the optimum operating conditions; 1:1 toluene: methanol molar ratio, the reaction temperature is 120 °C. The catalyst was synthesized via the hydrothermal method and the MIL-101 structure was confirmed by different analytical techniques: TGA, XRD, FTIR and BET surface area. The remarkably high toluene conversion and xylene selectivity at a low reaction temperature, in comparison to previous research, was attributed to the suppression of side reactions that could convert methanol to linear hydrocarbons, and to the inhibition of p-xylene isomerization. This suppression can be attributed to the single site properties and to the uniform pore size distribution of the prepared MIL 101 catalyst. Synthesis and characterization of single-site MIL-101(Cr) were used as a catalyst for toluene methylation reaction in a liquid phase at low reaction temperature (60–120 °C). The results suggest that toluene conversion and p-xylene selectivity are up to 50% and 90%, respectively, under the optimum operating conditions; 1:1 toluene: methanol molar ratio, the reaction temperature is 120 °C.

Ag/ZnO Nanocomposites: Preparation, Characterization and Investigation of the Catalytic Activity for Oxidation of Toluene in Liquid Phase

In this research, Ag/ZnO nanocomposites were prepared and characterized by transition electron microscopy (TEM), the energy dispersive X-ray spectrum (EDS) and X-ray diffraction patterns (XRD). These nanocomposites were used as catalysts for the oxidation of toluene to benzaldehyde and benzoic acid with hydrogen peroxide (H2O2) and tert-butylhydroperoxide (TBHP) as oxidizing agent in the liquid phase. For these Ag/ZnO nanocomposites, acetonitrile was used as a solvent, since all the reagents dissolved and show the highest yields. The oxidation products of toluene are benzaldehyde and benzoic acid. The results of this study showed that oxidant and the catalyst type affected the efficiency of toluene oxidation. TBHP was found to be better oxidizing agent than H2O2 since higher efficiency of product were observed when TBHP was used. The catalytic performance of 2.5%Ag/ZnO nanocomposite was better than the 1% and 5%Ag/ZnO nanocomposites. Under the optimal reaction conditions, the catalytic system of 2.5%Ag/ZnO nanocomposite gave about 76.3% efficiency of toluene.

Framework-Substituted Sn-MOR Zeolite Prepared by Multiple pH-Adjusting Сo-Hydrolysis As Efficient Catalyst for tert-Butylation of Toluene

A series of Sn-MOR samples with different tin species loadings were prepared via a mutiple pH‑adjusting co-hydrolysis method. Their properties were characterized by XRD, XRF, UV–Vis, FT-IR, Py-IR, N2 sorption and SEM techniques. The catalytic performance was evaluated in liquid-phase toluene alkylation with tert-butyl alcohol. The characterization results shows that compared to framework destruction of mordenite for the Sn/MOR sample with floccule prepared by ion exchange method, higher relative crystallinity and larger surface area and pore volume for Sn-MOR samples with walnut morphology can be obtained. The doping with tin species can increase the Lewis acidity and decrease the pore size resulting in both higher toluene conversion and p-tert-butyltoluene (PTBT) selectivity. The Sn-MOR(0.010) sample shows the highest catalytic performance with toluene conversion of 48.0% and PTBT selectivity of 85.6%. It shows high stability: toluene conversion of 45.3% and PTBT selectivity of 87.2% can be obtained even after 5 consecutive runs.

The efficacy and cytotoxicity of iron oxide-carbon black composites for liquid-phase toluene oxidation by persulfate.

This study evaluated the oxidation of toluene (TOL) by persulfate (PS) in aqueous solution in the presence of a Fe3O4-carbon black (CB) composite oxidant system generating sulfate radicals. The cytotoxic activity and oxidative stress generated by these materials were investigated in rat liver Clone 9 cells. The effects of various operating parameters including the pH and concentrations of PS, Fe3O4-CB, and TOL were evaluated to optimize the oxidation process. The results showed that Fe3O4-CB/PS achieved effective removal of TOL under acidic conditions. The TOL degradation efficiency was strongly pH-dependent, where pH3.0 > 6.0 > 9.0. Additionally, the viability of Clone 9 cells exposed to 0-400μg/mL Fe3O4-CB indicated that this material showed low cytotoxicity. A dichlorodihydrofluorescein diacetate assay performed to evaluate the generation of reactive oxygen species indicated that Fe3O4 showed relatively lower toxicity than CB in these cells. Therefore, the cytotoxicity of CB may involve the induction of oxidative stress and physical changes in cell morphology.

Controlled synthesis of CuxMn3.66−xMo3O12 with the citrate sol–gel method for the selective liquid-phase toluene oxidation to benzaldehyde by air

A systematic study on the synthesis of the CuxMn3.66−xMo3O12 using citrate sol–gel technique is presented. The influence of the copper substitution, citric acid concentration and pH of the precursor solution on the exclusive formation of Cu–Mn–Mo polymetallic oxide are studied. The physicochemical properties of as-prepared oxides are characterized by XRD, ICP-MS, SEM, TEM, XPS, FT-IR, BET, and H2-TPR, and their dependence on the conditions of synthesis is explored. It is found that these three synthesis factors remarkably alter the crystal phases and surface structures. The catalytic behaviors of synthesized catalysts for liquid-phase toluene oxidation are evaluated with toluene-catalyst mixture under uniformly distributed conditions. The evaluation reveals that the ratios of Mn3+/Mn2+ as well as Oads/Olat on catalysts play a crucial role in the activity and selectivity. Factors effecting reaction parameters, such as reaction temperature, residence time, catalyst weight, promoter weight, airflow rate and the volume ratio of substrate to solvent, are investigated in detail. The reusability of the catalyst is examined through conducting repeat runs with the same catalyst, exhibiting no significant decline in its activity even after 8 runs. A toluene conversion of 60% with 57.4% selectivity toward benzaldehyde is observed after 4 h over the high-crystalline CuxMn3.66−xMo3O12 nanoparticles.

Kinetics and Mechanism Modeling of Liquid-Phase Toluene Oxidation to Benzaldehyde Catalyzed by Mn–Mo Oxide

In this study, liquid-phase aerobic oxidation of toluene catalyzed by Mn–Mo oxide was conducted in a 1.0 L batch reactor. The macroscopic kinetics of toluene consumption and benzaldehyde generation at 413–443 K were obtained from a combination of experimental observation and hypothetical models. The results clearly showed that both the oxidation rate of toluene and generation rate of the aromatic product were proportional to the concentration of the substrate, the partial pressure of oxygen and the surface area of the catalyst. The energy barrier of toluene oxidation to benzyl alcohol was the highest (≈ 81 kJ mol−1), while that of benzyl alcohol oxidation to benzaldehyde was the lowest (≈ 57 kJ mol−1). Moreover, the activation energy of further oxidation of benzaldehyde in an acetic acid solvent was only slightly lower (≈ 1.9 kJ mol−1) than that of toluene oxidation. Significantly, the transformation of benzyl alcohol indeed contributed to the generation of benzaldehyde and this step conformed to a first-order parallel-consecutive model. Increased reaction temperature and residence time favored the transformation of benzyl alcohol to benzaldehyde. In addition, doping with molybdenum at Mn/Mo = 3/1 enhanced the catalytic performance of the heterogeneous catalyst and was attributed to the presence of a synergetic effect between different metal cations. Regarding the microscopic kinetics, the LH-OS-ND mechanism (Langmuir–Hinshelwood adsorption of reagents on the same type of active sites and non-dissociative adsorption of oxygen) was verified as responsible for the heterogeneous oxidation of toluene. Oxygen and benzaldehyde were weakly adsorbed (ΔHads,Oxy ≈ − 15 kJ mol−1, ΔHads,Bald ≈ − 30 kJ mol−1), but showed strong mobility (ΔSads,Oxy ≈ − 22 J mol−1 K−1), ΔSads,Bald ≈ − 39 J mol−1 K−1). The fundamental intrinsic rates were deduced based on the LH-OS-ND mechanism and showed great consistency with the macroscopic results.

Well-defined dendrimer encapsulated ruthenium SCILL catalysts for partial hydrogenation of toluene in liquid-phase

Dendrimer encapsulated ruthenium nanoparticles (RuDEN) were prepared and immobilized on silica 60 and silica 100. The size of the supported RuDENs was investigated using HRTEM and the generation six G6-RuDEN was found to be the most stable RuDEN upon immobilization. The catalysts were evaluated in the liquid-phase hydrogenation of toluene at a hydrogen pressure of 30bar and 110°C. Several ionic liquids were used as coatings for the G5-RuSil100 catalysts to give various Solid Catalysts with Ionic Liquid Layer (SCILL). In each case the selectivity towards methylcyclohexenes was increased compared to the uncoated catalyst, accompanied by an expected decrease in activity with the highest methylcyclohexene selectivity being observed when using [EMIM][NTf2] as a coating.

Modelling the transport of toluene liquid in protective polymer gloves using a fluorescent dye-tracing technique

The absence of adequate information about the phase change of liquid solvents within polymer-glove walls hinders the complete characterisation of the mass transfer of toluene liquid through the polymer membranes using the data obtained from ASTM F739 method for toluene liquid permeation testing. Therefore, an alternative fluorescent dye-tracing technique is used to account for the transport processes of toluene liquid through polymer gloves. The results of dye penetration experiments show that the displacement of liquid-phase toluene is proportional to the square root of immersion time, indicating that the transport behaviour of liquid-phase toluene is dominated by Fickian diffusion. Furthermore, a linear relationship between the mass sorption of toluene vapour and the sampling time is established, which suggests that the diffusion process in the vapour-phase toluene is governed by Case-II transport. Based on the combined analysis of the results obtained from permeation tests, immersion tests, fluorescent dye-tracer tests, and the pertinent calculations of thermodynamic properties, an evidence-based mechanism for the mass transfer of toluene liquid through the polymer-glove walls is proposed in terms of time-series processes. The model comprises three regimes: a liquid phase, a combined liquid–vapour phase, and a vapour phase of toluene that exist in series within the membrane.

Ionic liquid immobilization on carbon nanofibers and zeolites: Catalyst design for the liquid-phase toluene chlorination

The environmental-friendly chlorination reaction of toluene by trichloroisocyanuric acid (TCCA, C 3 N 3 O 3 Cl 3 ) was investigated applying immobilized ionic liquids (ILs) on different supports. Ionic liquids were grafted either on carbon nanofibers (CNF) or encapsulated in zeolites. Their influence on the chlorination activity as well as on the selectivity in different chlorinated products was studied. An unusually high selectivity toward meta -chlorotoluene was achieved, up to 36%. Hence, the selectivity could be tuned to produce either expected ortho-/para -chlorotoluene or meta -chlorotoluene with a proper support choice. La réaction de chloration du toluène par l’acide trichloroisocyanurique (TCCA) catalysée par des liquides ioniques immobilisés sur des nanofibres de carbone (IL/CNF) ou encapsulés dans des zéolithes (IL/zéolithe) a été étudiée. Un comportement particulier a été observé pour le système IL/CNF, donnant lieu à une sélectivité très élevée de 36 % en l’isomère méta -chlorotoluène. En adaptant la nature du support, on peut aisément moduler la sélectivité envers les différents isomères.

Atom economical Michael addition of indole with methyl vinyl ketone over novel solid acid catalyst sulfated zirconia on silica tubes

Porous structures of inorganic oxides with different morphology are being paid a great deal of attention because of their potential for providing ultra large specific surface areas, exceptionally fine inner pores, and catalytic surface properties. A facetted silica tube functionalized with sulfated zirconia was prepared and used to catalyze Michael addition reaction of indole with methyl vinyl ketone. The effect of mesoporous tubular structure in generation of mild acidic sites on silica is discussed. The reaction is 100% atom economical. The silica tubes were prepared by using tetraethylorthosilicate and (dl)-tartaric acid in basic medium. The support and catalyst were well characterized by XRD, FT-IR, ASAP, SEM and EDXS. The activity was also compared through benzylation of toluene in liquid phase with reference to sulfated zirconia. Several other catalysts were also evaluated. The effects of various parameters on the rate of reaction were investigated. Based on the experimental data, a suitable mechanism was developed and kinetic model deduced.

Precise measurement of thermal conductivity of liquid over a wide temperature range using a transient hot-wire technique by uncertainty analysis

One of the standard methods used to measure the thermal conductivity of liquids is transient hot-wire technique. The principle of this technique is to fit the unbalanced voltage of the hot wire in a bridge circuit using a theoretical model. The uncertainty in the measurement mainly relates to the procedure used and the measuring instruments, which we evaluate for toluene in liquid phase at atmospheric pressure and in the temperature range from −30°C to 90°C using the Guide to the Expression of Uncertainty in Measurement. The uncertainty of the results was estimated to be within ±0.50% below 60°C and ±0.96% at a temperature of 90°C. The maximum departure between recommended values and the results of our experimental runs is 0.31% at the highest temperature, and the thermal conductivity values measured are in good agreement with the recommended values within the level of uncertainty over the whole temperature range.

Effect of electron irradiation on the catalytic properties of supported Pd catalysts

The effect of electron irradiation on the properties of the systems 1% Pd/C, 1% Pd/Al2O3, and 1% Pd/TiO2 is studied in gas-phase and liquid-phase toluene hydrogenation. An increase in the irradiation dose to 120–900 Mrad increases the catalytic activity by a factor of 2–8 relative to that of the original system. XPS data for the Pd/C catalyst suggest that, after irradiation with high-energy electrons, the metal particles are stabilized on the surface of the carbon support, their degree of dispersion is increased, and their sintering is suppressed. These inferences are consistent with the observed changes in catalytic properties.

Mode-focusing in molecules by feedback-controlled shaping of femtosecond laser pulses

The feasibility of mode-selective excitation with broadband femtosecond laser pulses is demonstrated for toluene in liquid phase. A learning-loop optimal control scheme was applied to a stimulated Raman excitation process. Modifications of the phase shape of one of the exciting pulses resulted in dramatic changes of the mode distribution reflected in coherent anti-Stokes Raman spectra. An evolutionary algorithm guided the coherent excitation process to a selective enhancement or suppression of one or more vibrational modes over the complete coherence lifetime spanning several picoseconds. New ways of spectral filtering as well as exciting possibilities of mode-selective studying of chemical reaction dynamics are indicated.

Hydroformylation of 1-hexene in supercritical carbon dioxide using a heterogeneous rhodium catalyst. 3. Evaluation of solvent effects

The heterogeneously catalyzed hydroformylation of 1-hexene in supercritical carbon dioxide is demonstrated as an alternative to homogeneous catalysis through the use of a rhodium–phosphine catalyst tethered to a silica support. Reaction over the heterogeneous catalyst in supercritical CO2 is compared with the use of this catalyst in liquid-phase toluene, and toluene expanded with CO2. Likewise, the performance of the tethered catalyst is compared with a homogeneous rhodium–phosphine catalyst, and shown to be equally effective under identical reaction conditions. Comparable reaction rates were obtained using the heterogeneous rhodium catalyst in supercritical CO2 and CO2-expanded toluene, both of which were superior to the reaction rate with the heterogeneous catalyst in liquid-phase toluene. Initial aldehyde selectivity obtained with the heterogeneous species was also comparable to that obtained with the homogeneous catalyst, but decreased over the course of the reaction. These results demonstrate the value of using phase behavior, and the importance of understanding this behavior in the development and analysis of greener solvent/catalyst systems.

Regioselective Liquid-Phase Toluene Nitration with Modified Clays as Catalysts

Abstract Catalytic mononitration of toluene (yields of 50–81%; turnover at least 850) occurs in the presence of modified clays with useful regioselectivities, such as (o:m:p) = 31:2:67. The nitrating species is extracted from concentrated nitric acid by carbon tetrachloride-acetic anhydride mixture.