Liquid-phase Catalytic Oxidation Research Articles

IR Observation of Selective Oxidation of Cyclohexene with H2O2over Mesoporous Nb2O5

Liquid-phase catalytic oxidation of cyclohexene by H2O2 (35 wt %) over mesoporous Nb2O5 showed considerable conversion and high selectivity for both cis- and trans-1,2-cyclohexanediols in acetonitrile solvent. The mesoporous structure of the catalyst, in addition to its high surface area, was considered to be advantageous for the reaction due to more frequent interaction of molecules with active sites inside pores. Gradual formation of 1,2-cyclohexanediol from the reaction of adsorbed cyclohexene with diluted (10 wt %) H2O2 was observed at room temperature by an in situ infrared (IR) method. The absence of observation of an IR spectrum of 1,2-epoxycyclohexane confirmed that the hydrolysis of the oxidation product occurred immediately. In addition to the conventional stepwise oxidation and hydrolysis to produce 1,2-cyclohexanediol, a direct hydroxylation of cyclohexene was proposed: the production of cis-1,2-cyclohexanediol with about a half amount of trans-1,2-cyclohexanediol suggests the activation of H2...

Catalytic behavior of copper(II) chelate complexes sterically held in zeolite large cavities and fixed on its outer surface by a topological anchor

Catalytic properties of copper(II) tricyclic chelate compounds based on enamino ketone of 3-acetyl-2,4-pentanedione and 1,6-hexametylenediamine fixed on NaY and CaA zeolites by the methods of topological and topologically-anchor retention, respectively, were compared. The mode of fixation of chelates on a support affects the character of the liquid-phase catalytic oxidation of cyclohexene by molecular oxygen. At the topological fixation by a steric retention of a chelate compound in a large cavity of NaY zeolite, the reaction rate related to one reaction center of a metal complex is not proportional to the filling degree that points to inaccessibility for a substrate of catalyst molecules localized in inner cavities of crystallites. In an alternative mode of the catalyst topologically-anchor fixation, when only a ligand fragment is held in CaA zeolite, and catalytically active metal center is turned to the side of the reaction medium, the linear dependence of the cyclohexene oxidation rate on the amount of the chelate on the support is retained within the whole studied range of the surface catalyst concentrations. The catalytic activity of the topologically-anchor fixed Cu(II) chelate compound coincides with its activity in the zeolite absence, which points to a pseudo-homogeneous mode of cyclohexene oxidation. At topologically-anchor fixation of a Cu(II) chelate compound on CaA zeolite diffusion limitations characteristic for the fixation by steric retention are completely eliminated.

Modeling, simulation and analysis of the liquid-phase catalytic oxidation of toluene

The liquid-phase, catalytic oxidation of toluene with air in a continuous stirred tank reactor has become the main technology for producing benzoic acid. Designs are aimed at obtaining high product conversion rates but the reaction is strongly exothermic and therefore it is also important to maintain stable operation to guarantee product quality. However, there is currently no suitable process simulation model available for study. In this paper, a mathematical model of the reaction system is established and validated by comparison to literature data. Steady-state variables were calculated for a series of the operating conditions, using the homotopy continuation method, revealing the existence of multiple steady-state solutions. Two steady-state solutions were found for each operating condition, which had different conversion rates and sensitivities to changes in operating conditions. The operating point having the highest conversion rate was the most sensitive to changes in operating conditions, thus requiring a superior control system. A trade off must be carried out between conversion rate and production stability. Consequently, in practice, a number of factors must be considered simultaneously to select a compromise design.

Preparation, characterisation and testing of catalytic polymeric membranes in the oxidation of benzene to phenol

Liquid-phase catalytic oxidation of benzene to phenol has been studied under mild conditions using catalytic polymeric membranes. They were prepared by dissolving the polymer polyvinylidene fluoride (PVDF) in different solvents, (dimethylacetammide (DMAc), dimethylformammide (DMF) and 1-methyl-2-pyrrolidone (NMP)) and filled with two types of copper oxides catalysts. Membranes were characterised morphologically by scanning electron microscopy (SEM), pore size distribution, contact angle measurements and BET surface area. It was found that DMAc was the best solvent and that membranes filled with the CuO nanopowder catalyst presented an improved wettability to reacting mixture. Reactivity tests, performed at contact time in the range 4–19.4 s between reagents and catalyst, showed a higher phenol concentration using the PVDF membrane filled with the CuO nanopowder rather than CuO powder catalysts. Phenol productivity of 72.5 g phenol g cat −1 h −1 and a phenol yield of 2.3% were obtained in a single pass using a contact time with the catalyst of 19.4 s at 35° C in presence of ascorbic acid.

Kinetics of 2-Methyl-6-acetyl-naphthalene Liquid Phase Catalytic Oxidation

In this paper, a kinetics model for the liquid-phase oxidation of 2-methyl-6-acetyl-naphthalene to 2,6-naphthalene dicarboxylic acid catalyzed by cobalt-manganese-bromide is proposed. The effects of the reaction temperature, catalyst concentration and ratio of catalyst on the time evolution of the experimental concentration for theconstituents including raw material, intermediates and product are investigated. The model parameters are determined in a nonlinear optimization, minimizing the difference between the simulated and experimental time evolution of the product composition obtained in a semi-batch oxidation reactor where the gas and liquid phase were well mixed. Thekinetics data demonstrate that the model is suitable to the liquid-phase oxidation of 2-methyl-6-acetyl-naphthalene to 2,6-naphthalene dicarboxylic acid.

Determining organic impurities in mother liquors from oxidative terephthalic acid synthesis by microemulsion electrokinetic chromatography

In this study, a microemulsion electrokinetic chromatography (MEEKC) method was developed to analyze and detect several aromatic acids (benzoic acid (BA), isophthalic acid (IPA), terephthalic acid (TPA), p-toluic acid ( p-TA), 4-carboxylbenzaldehyde (4-CBA), trimesic acid (TSA), trimellitic acid (TMA), o-phthalic acid (OPA), and hemimellitic acid (HMA)), which are common organic impurities produced by liquid-phase catalytic oxidation of p-xylene to TPA. The effects of microemulsion composition, column temperature, column length and applied voltage were examined in order to optimize the aromatic acid separations. This work demonstrated that variation in the concentration of surfactant (sodium dodecyl sulfate (SDS)) and oil phase (octane) had a pronounced effect on separation of the nine aromatic acids. It was also found that a decrease in column length had the greatest effect on shortening separation time and improving separation resolution for these aromatic acids when compared to that of an increase in column temperature or applied voltage. However, the nature and concentration of cosurfactants and organic modifiers were found to play only minor roles in the separation mechanism. Thus, a separation with baseline resolution was achieved within 14 min by using a microemulsion solution of pH 2.0 containing 3.7% SDS, 0.975% octane, and 5.0% cyclohexanol; and a 50-cm capillary column (effective length of 40-cm) at 26 °C. As a result, the developed MEEKC method successfully determined eight impurities of aromatic acids in the mother liquors produced from the oxidation synthesis of TPA.

Liquid phase catalytic oxidation of isophorone with tert-butylhydroperoxide over Cu/Co/Fe–MgAl ternary hydrotalcites

Abstract Liquid phase catalytic oxidation of isophorone was carried out over M–MgAl ternary hydrotalcites, where M is Cu, Co or Fe, using tert -butylhydroperoxide (TBHP) as an oxidant. The influence of various reaction parameters, namely, substrate/catalyst mass ratio, substrate:oxidant mole ratio, nature of oxidant, solvent, reaction temperature and reaction time on the activity and selectivity for the desired reaction, were studied. The catalysts were synthesized by the coprecipitation technique using metal nitrates and a NaOH/Na 2 CO 3 mixture. Powder X-ray diffraction and thermal analysis of these samples confirmed the presence of hydrotalcite like layered network. Oxidation of isophorone over these catalysts resulted mainly in the formation of ketoisophorone (KIP). A maximum isophorone conversion of 74% with 100% selectivity to KIP was observed over CuMgAl-13 at 333 K up to 48 h using acetonitrile as a solvent, followed by CoMgAl-13 (36%) and FeMgAl-13 (25%). The redox properties of transition metal ions played an important role in driving the reaction and a reaction mechanism involving predominantly free radicals were proposed. An increase in the conversion of isophorone was observed with decreasing substrate/catalyst mass ratio down to 20. With respect to the influence of reaction temperature, the conversion increased up to 333 K and decreased when the temperature was further increased. Among the solvents studied acetonitrile showed maximum conversion and selectivity to KIP, where as methanol showed minimum conversion. An increase in the conversion of isophorone was observed with decreasing molar ratio of isophorone to TBHP. A gradual increase in the conversion of isophorone was observed with reaction time and the maximum conversion was observed at 48 h. Reusable studies showed that the catalysts were stable and reusable up to three cycles without substantial loss of activity.

Kinetics and mechanism of the catalytic reaction between ozone and para-cresol in acetic anhydride

The kinetics of the liquid-phase catalytic oxidation of para-cresol with an ozone-air mixture in the presence of manganese(II) acetate is reported. In an acetic anhydride medium, para-cresol reacts with ozone as para-cresyl acetate, which is formed at the instant the solution to be oxidized is prepared. Under these conditions, the major oxidation products are para-acetoxybenzyl acetate (63.5%) and para-acetoxybenzylidene diacetate (13.7%). The effect of the managanese(II) acetate concentration on the traction selectivity with respect to the oxidation of the methyl group of the substrate is reported. A mechanism consistent with the experimental data available on this catalytic redox reaction is suggested.

Catalytic Liquid Phase Oxidation of Toluene to Benzoic Acid

AbstractThe production of benzoic acid from toluene in the liquid phase with pure oxygen was studied. Investigations have been carried out with a view to determining the most suitable reaction conditions with respect to operating variables including oxygen flow rate, reaction temperature, batch time and catalyst loading. In a series of batch experiments carried out at 4 atm, the optimum values of mole ratio of oxygen to toluene, temperature, reaction time, and catalyst loading were found to be 2, 157 °C, 2 h and 0.57 g/L, respectively. In addition, a kinetic study was carried out by taking into consideration the optimum reaction conditions. The model dependent on the formation of benzyl radical was found to be feasible for describing the catalytic oxidation of toluene to benzoic acid in the liquid phase. The activation energy was determined as 40 kJ/mol.

Simulation and Optimization in the Process of Toluene Liquid-phase Catalytic Oxidation

Liquid-phase oxidation of toluene with air has become the main technology for producing benzoic acid in a reactor at present. Based on the kinetic model of the toluene oxidation process obtained from laboratory and mass balance of key component, a novel model is established to simulate the industrial toluene oxidation process, in which the effects of benzaldehyde and benzyl alcohol are considered and the kinetic parameters are revised by industrial data. The simulation results show that the error of benzoic acid yield is within 3.5%. Based on the simulation model, to maximize the benzoic acid yield, an optimization model is proposed to optimize the operating parameters, including toluene feed-in mass flux and temperature. The optimization result indicates that on the allowable operating conditions, the maximum benzoic acid yield obtained with the reaction temperature at 167.2°C and the mass flux at 104.1 t·h −1 is greater than the current one, which can be used to guide industrial reactor's operation.

Solvent-free oxidation of benzyl alcohol over chromium orthoborate

Abstract The use of CrBO 3 in the catalytic liquid phase oxidation of benzyl alcohol (BzOH) has been investigated for the first time. The reaction was performed under solvent-free conditions without employing any oxidant. Benzaldehyde (BzH), dibenzyl ether (DBzE) and benzyl benzoate (BzB) were obtained as the major reaction products. Influence of the reaction parameters (reaction time, temperature and the amount of catalyst) on the catalytic performance has been studied. A mechanism operating over acidic boron sites has been suggested.

Semicontinuous Studies on the Reaction Mechanism and Kinetics for the Liquid-Phase Oxidation of p-Xylene to Terephthalic Acid

The reaction mechanism and kinetics for the liquid-phase catalytic oxidation of p-xylene to terephthalic acid are briefly reviewed, which indicates that the available literature is not complete when one looks for the industrially applicable mechanism and kinetics. In this work, a detailed radical chain reaction mechanism for the liquid-phase catalytic oxidation of p-xylene to terephthalic acid is proposed. Using several assumptions, a simple fractional-like kinetic model is derived from the assumed reaction mechanism. Several semicontinuous oxidation experiments are carried out at different reactant feed rates and temperatures. The experimental results show that the measured concentrations of liquid-phase reactants increase approximately linearly with time, which indicates that the reaction rate for the liquid-phase reactants is approximately independent from its concentration. The derived kinetic model can explain and correlate these experimental results satisfactorily. By combining the results determined in batch oxidation experiments with the semicontinuous experimental results, the kinetic model parameters are determined by data fitting. The correlated results generally agree with both the semicontinuous and the batch experimental results satisfactorily.

Liquid phase catalytic oxidation of alcohols over mixed metal oxides

Abstract Oxidation of alcohols was studied over CoO–CeO2 using tert-butyl hydroperoxide (TBHP) and n-hexane as a solvent in liquid phase reaction. The catalyst used for this synthetically useful transformation showed considerable level of reusability besides good activity.

Data mining macrokinetic approach based on ANN and its application to model industrial oxidation of p-xylene to terephthalic acid

Considering that kinetics and thermodynamics are coupled with heat and mass transfer effects being present in the liquid-phase catalytic oxidation of p-xylene to terephthalic acid (OXTA) in an industrial type of continuous stirred tank reactor (CSTR) and that the time evolution of the concentration of all the interest intermediate and final products of OXTA in the industrial CSTR cannot be obtained to estimate macrokinetic parameters, a novel data mining macrokinetic approach based on artificial neural network (ANN) was proposed to develop the macrokinetic model of OXTA in the industrial CSTR, which mines intrinsic kinetics and transport phenomena information from the sample data collected from OXTA in the industrial CSTR. Firstly, the reaction orders of OXTA are estimated by the mass transfer-free experiment data in the laboratory semi-batch stirred tank reactor. The kinetics of OXTA in the industrial CSTR is assumed to be zeroth-order with respect to gaseous reactants, 0.65-order with respect to p-xylene, and first-order with respect to the other liquid reactants, respectively. Secondly, ANN is employed to model the influence of the reaction parameters on the rate constants of OXTA in the industrial CSTR. Based on the sample data collected from OXTA in the industrial CSTR, heuristic differential evolution algorithm is employed to adjust the weights and thresholds of the rate constant ANN in such a way that it minimizes the prediction error of the macrokinetic model, and thus the optimal weights and thresholds are obtained and the macrokinetic model of OXTA in the industrial CSTR is developed. The reliability of the macrokinetic model was investigated and the satisfactory results were obtained. Further, a generalized macrokinetic approach for multi-phase reaction in industrial reactor was suggested too.

Discrimination of Active Palladium Sites in Catalytic Liquid-Phase Oxidation of Benzyl Alcohol

Knowledge of the structure of active sites is a prerequisite for the rational design of solid catalysts. Using site-selective blocking by CO and isotope labeling combined with in situ attenuated total reflection infrared (ATR-IR) spectroscopy, we were able to discriminate the different sites involved in the liquid-phase oxidation of benzyl alcohol on Pd/Al(2)O(3). The main reaction, that is, the oxidative dehydrogenation of the alcohol to the corresponding aldehyde, showed only little dependence on structure and occurred on all exposed Pd faces, whereas the undesired product decarbonylation occurred preferentially on hollow sites on (111) Pd faces. This explains why specific blocking of the latter sites, as realized in the industrially used Pd-Bi/Al(2)O(3) catalysts, leads to improved catalytic performance.

Titanium-Containing Mesoporous Materials: Synthesis and Application in Selective Catalytic Oxidation

Titanium-containing mesoporous molecular sieves are of great significance in selective catalytic oxidation processes with bulky molecules. Recent researches and developments on the designing and synthesis of Ti-contaming mesoporous materials have been reviewed. Various strategies for the preparation of Ti-containing mesoporous materials, such as direct synthesis and post-synthesis, are described. Modifications of Ti-containing mesoporous materials by surface-grafting and atom-planting are also discussed. All approaches aimed mainly at the improving of the stability, the hydrophobicity, and mostly the catalytic activity. Structural and mechanistic features of various synthetic systems are discussed. Ti-containing mesoporous materials in liquid phase catalytic oxidation of organic compounds with H 2O 2 as an oxidant is briefly summarized, showing their broad utilities for green synthesis of fine chemicals by catalytic oxidative reactions.

Some Aspects of Heterogeneous Catalytic Liquid Phase Oxidation with Hydrogen Peroxide

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Use of renewables for the production of chemicals: Glycerol oxidation over carbon supported gold catalysts

As a renewable feedstock and due to its high functionality glycerol is an attractive reactant for the production of a large number of valuable compounds. We report on an environmentally friendly alternative to produce chemicals from the glycerol oxidation, which are currently produced either by stoichiometric oxidation processes or by enzymatic routes. We investigate the heterogeneously catalyzed liquid-phase oxidation of glycerol with carbon supported gold catalysts. The prepared nanosized gold catalysts are highly active, so that the reaction could be performed under atmospheric pressure. The influence of the preparation method of the catalysts has been investigated. Moreover, the support effect on the catalytic process has been studied and discussed in terms of pore structure of the investigated carbon materials. The promotor effect of platinum on Au/C catalysts was examined and it could be shown that the presence of Pt increases not only the catalyst activity but also the selectivity. By promoting the gold catalysts with platinum the selectivity to dihydroxyacetone could be increased from 26% (Au/C) to 36% (Au–Pt/C).

Optimum Ratio of Co/Mn in the Liquid-Phase Catalytic Oxidation of p-Xylene to Terephthalic Acid

Liquid-phase catalytic oxidation of p-xylene to terephthalic acid was performed at 150−210 °C over Co−Mn−Br catalyst system. There was an interesting synergistic effect of cobalt and manganese catalyst. In the previous papers (Ind. Eng. Chem. Res. 2005,44, 261−266; 4518−4522; 7756−7760), a lumped kinetic scheme and a fractional kinetic model for the liquid-phase oxidation of p-xylene were proposed and tested, and the effects of catalyst concentration, water content, and guanidine catalyst additive were investigated. In this paper, the synergistic effect of cobalt and manganese on the oxidation kinetics was studied. Experiments of several levels of Co/Mn ratio and temperature were carried out in a semibatch oxidation reactor where the gas and liquid phases were well-mixed. The results showed that the variation of the Co/Mn ratio in the catalyst did affect the activity and selectivity of the catalyst system. For the main reaction, there existed an optimum Co/Mn ratio at which the rates of the latter two slo...

Gas-phase oxidation of alcohols over silver: The extension of catalytic cycles of oxidation of alcohols in liquid-phase

Oxidation of alcohols (including C 2–C 6 alkyl alcohols, cyclohexanol, benzyl alcohol, 1-octanol and allyl alcohol) to corresponding aldehydes or ketones has been performed over silver catalyst; the silver catalyst is highly active and selective to the reaction. The mechanism of oxidations of alcohols is inclined to oxidative dehydrogenation at low temperature region (<550 K). The facets of silver are ideal versatile facets to activate molecular oxygen and generate oxidative, strong basic oxygen species (O δ− ), and weak acidic sites (Ag δ+ ) which can stabilize the organic intermediates, quickly. The facets of silver containing oxygen integrate several active catalytic sites existing in liquid-phase catalytic oxidation of alcohols and make catalytic reaction more effective.