Liquid-phase Oxidation Of Cyclohexane Research Articles

An Efficient and Reusable Catalyst of Bismuth-Containing SBA-15 Mesoporous Materials for Solvent-free Liquid Phase Oxidation of Cyclohexane by Oxygen

Bismuth-containing SBA-15 mesoporous materials with different nsi/nBi ratio was synthesized for the first time through a direct hydrothermal method, and characterized by various physico-chemical techniques. XRD patterns indicate that the synthesized materials have an ordered two-dimensional p6mm hexagonal mesostructure. Transmission electron microscopy and scanning electron microscopy studies show that Bi-SBA-15 has well-ordered hexagonal arrays of mesoporous channels and the morphology of rod-like particles. Raman spectroscopy and UV–Vis DRS show that bismuth atoms in Bi-SBA-15 exist in a highly dispersed state, and locate mainly at tetrahedrally coordinated sites. Thermogravimetric analysis was used to observe the removal of the organic template P123. In the catalytic test, Bi-SBA-15 is found to be a very efficient and reusable catalyst for the oxidation of cyclohexane, in a solvent-free system, with oxygen as oxidant. The influence of different parameters, such as reaction time, reaction temperature, oxygen pressure, and the dosage of catalyst on the oxidation of cyclohexane, is also investigated.

Catalytic epoxidation of α,β-and β,γ-unsaturated bicyclic ketones with hydrogen peroxide

The possibility of preparing epoxides from α,β-and β,γ-unsaturated bicyclic ketones formed as by-products in liquid-phase oxidation of cyclohexane with atmospheric oxygen (a stage in production of caprolactam, adipic acid, and other products) was examined. The reaction products were analyzed by gel chromatography and mass spectrometry.

One-step oxidation of cyclohexane to adipic acid

Liquid-phase oxidation of cyclohexane with Co(III) catalyst and gaseous oxygen was found to be influenced by reaction temperature, catalyst concentration and the duration. Maximum adipic acid product selectivity (77%) with about 85% cyclohexane conversion was attained at 100°C using catalyst: cyclohexane molar ratio 0·08. Under these conditions more than 80% cyclohexane was converted in the first hour, although selectivity to adipic acid continued to increase for the next 5 h. Cyclohexyl acetate and cyclohexyl monoadipate were identified as important intermediates. This study supports the mechanism proposed by Schultz, J. G. D. and Opchenko, A., J. Org. Chem., 38 (21) (1973) 3729.

Kinetic study of oxidation of cyclohexane using complex catalyst

AbstractWith an effort to use a multimetallic catalyst system for oxidation of cyclohexane using oxygen, a binuclear monometallic macrocyclic ZrZr complex was prepared and covalently bonded to modified alumina support. The complex catalyst thus prepared was found to be thermally stable and was completely characterized by CHN, SEM‐EDAX, TGA, and FTIR analysis. We carried out liquid phase oxidation of cyclohexane using molecular oxygen without any solvent, coreactant, or cocatalyst at considerably mild reaction conditions (150°C, 27 atm) with extremely high selectivity. The GC‐MS of the liquid product formed showed the total conversion of as much as 19% having cyclohexanone and cyclohexanol in the ratio of 16:1. To explain the experimental data, a possible reaction mechanism has been proposed and rate constants (assuming single phase) at different temperatures were determined using an optimal curve fitting by applying genetic algorithm. We showed that the steady state approximation cannot be assumed, and for the pressure range studied (7–35 atm), the rate constants thus determined were found to be a function of temperature only. From experiments carried out at different temperatures, we found that for every rate constant, an Arrhenious type relation could be established. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Chromium-containing small pore mesoporous silicas: Synthesis, characterization and catalytic behavior in the liquid phase oxidation of cyclohexane

Abstract Organic–inorganic hybrid mesoporous silica materials containing chromium and various organo trialkoxysilanes (chloropropyl, vinyl, methyl) were prepared by the co-condensation method, in the presence of cetyl trimethyl ammonium surfactants. The hybrid material, containing chromium, retains one X-ray diffractogram (XRD) peak up to a molar ratio of 1:1 between tetra ethyl orthosilicate (TEOS) and organosilane in the synthesis gel. Small pore mesoporous chromium-silica samples can be prepared from the large pore hybrid mesoporous chromium samples by calcination. By this method, the pore size of the material can be tailored into the supermicroporous region, without changing the chain length of the surfactant used in the assembly process, as judged from the XRD and N 2 sorption isotherms. The shrinkage in pore size is dependent on the nature and percentage of the organic pendant groups, such that the chloro propyl and vinyl pendant mesoporous material show more pore size shrinkage than the smaller methyl pendant units. Because of the tailorable pore size and with better textural characteristics, the chromium samples show better catalytic activity in the aerial oxidation reaction of cyclohexane than the conventional chromium-containing mesoporous material, like Cr-MCM-41, under a solvent free system. Among the porous chromium catalysts, the samples prepared using chloro propyl silane show higher cyclohexane conversion and cyclohexanone selectivity and behave as a true heterogeneous catalyst.

One step synthesis of chromium-containing periodic mesoporous organosilicas and their catalytic activity in the oxidation of cyclohexane

Chromium-containing ethane-bridged hybrid mesoporous materials (Cr-PMO) with uniform hexagonal arrangement were synthesized by two different synthesis routes using 1,2-bis(triethoxysilyl)ethane (BTEE) and tetraethyl orthosilicate (TEOS) as silica sources and alkyltrimethyl ammonium salts (ATMA) as surfactants. Powder X-ray diffraction, TEM, N2 adsorption–desorption, FT-IR, in situ FT-Raman, UV–Vis, XPS, 29Si MAS NMR and 13C CP MAS NMR were used to probe the mesoporous structure and the nature of chromium sites in the hybrid catalyst matrix. PXRD, TEM and N2 adsorption–desorption analysis showed that the original hexagonal structure of the materials is maintained after chromium substitution, while FT-Raman, UV–Vis and XPS analysis showed that chromium atoms exist in a highly dispersed state. The catalytic performance of the chromium-containing hybrid samples was tested in the liquid-phase oxidation of cyclohexane with aqueous hydrogen peroxide (H2O2) and non-aqueous tert-butylhydroperoxide (TBHP) as oxidants. The hybrid materials exhibited better catalytic activities and were more stable than the conventional Cr-MCM-41 catalyst. The higher catalytic activity of the new chromium-containing molecular sieves is attributed to the improved hydrophobicity of the materials and to the complementary structural features that facilitates the accessibility of cyclohexane to the active framework chromium sites.

Liquid-phase oxidation of cyclohexene and of tetralin by N 2O in the presence of onium salts under mild experimental conditions

Cyclohexene and tetralin can be oxidized to a slight extent by N 2O in the presence of quaternary ammonium salt promoters under mild experimental conditions. In non-polar solutions, the higher yields of the oxidations of cyclohexene and tetralin are influenced by the donor–acceptor properties of the solvents. The changes in the IR spectrum of N 2O lend further support to the assumption that ion-pair interactions between the solvated oxidant and the onium salts result in an enhanced rate of O-transfer from the oxidant. Onium-decavanadate ion-pair complexes are more effective promoters than simple onium salts.

Catalytic properties of monomeric and oligomeric Cu(II) phenylhydrazono imine chelates immobilized on zeolite with a topological anchor

Heterogeneous catalysts for liquid-phase oxidation of cyclohexene with molecular oxygen were prepared by topological-anchor immobilization on CaA zeolite of a monomeric Cu(II) chelate with N,N′-trimethylenebis(2-methyl-1-benzoylglyoxal 1-phenylhydrazone 2-imine) and of an oligomeric product of its condensation with ethylenediamine. The samples prepared contain surface monomeric and oligomeric Cu(II) chelates oriented toward the reaction medium, which makes them accessible to reactant molecules. The catalytic properties of the above monomeric chelate are preserved in going to the oligomers. The apparent rate constants per metal center for both homogeneous (soluble monomeric chelate) and heterogeneous modes coincide, suggesting the pseudohomogeneous behavior of the supported samples. The topological-anchor immobilization of insoluble oligomeric Cu(II) polychelates on zeolite leads to their more efficient utilization as heterogeneous catalysts and can be considered as one of examples of combining advantages of homogeneous and heterogeneous catalysis.

Liquid phase oxidation of cyclohexane over transition metal incorporated amorphous 3D-mesoporous silicates M-TUD-1 (M = Ti, Fe, Co and Cr)

Redox metals such as Ti, Co, Fe and Cr are incorporated into the framework of TUD-1 (a three-dimensional mesoporous silicate) and characterized by means of XRD, UV–vis and N 2 sorption measurements. The catalytic activity of these materials (M-TUD-1) was tested in the liquid phase oxidation of cyclohexane with tert-butylhydroperoxide (TBHP) as oxidant. Cr- and Co-TUD-1 showed excellent performance in the oxidation of cyclohexane, Cr-TUD-1 being highly selective to cyclohexanone. Leaching of Cr is estimated as 13% during this reaction. In contrast to this it was also proven that the reaction is truly heterogeneous with Co-TUD-1.

Co‐TUD‐1: A Ketone‐Selective Catalyst for Cyclohexane Oxidation

Cobalt-containing mesoporous TUD-1 with different Si/Co ratios (100, 50, 20, and 10) was synthesized by the direct hydrothermal treatment method (DHT) using triethanolamine (TEA) as a template. The prepared samples (denoted as Co-TUD-1) were characterized by XRD, UV/Vis spectroscopy, elemental analysis, N2 sorption measurements, 29Si magic-angle spinning (MAS)-NMR, Raman spectroscopy, and HRTEM. The catalytic performance of Co-TUD-1 samples was tested in the liquid-phase oxidation of cyclohexane with tert-butylhydroperoxide (TBHP) as oxidant under solventless conditions. Higher catalytic efficiency was observed in samples with low Co-loading and thus, most likely isolated CoII active sites, than in samples with high Co-loading and nanoparticles or bulk Co3O4 embedded in the TUD-1 silica.

A novel Ce/AlPO-5 catalyst for solvent-free liquid phase oxidation of cyclohexane by oxygen

Cerium-containing AlPO-5 with an AFI structure has been prepared by hydrothermal synthesis in the presence of HF, and characterized by XRD, XPS, SEM, N2 adsorption/desorption, solid state 27Al, 31P MAS NMR and TG-DTA techniques. The results show that all the samples have good crystallinity, high dispersity of Ce and high surface area, and Ce(III) replaces the position of Al(III) and enters the framework of AlPO-5. Ce/AlPO-5 is a very efficient catalyst for the oxidation of cyclohexane in a solvent-free system with oxygen as an oxidant. In the condition of 0.5 MPa O2 and 413 K for 4 h, the conversion of cyclohexane is 13%, the total selectivity of cyclohexanol and cyclohaxnone is above 92%. In addition, the Ce/AlPO-5 catalyst is very stable in the cyclohexane oxidation system.

Liquid oxidation of cyclohexane to cyclohexanol over cerium-doped MCM-41

Liquid phase oxidation of cyclohexane was carried out under mild reaction conditions over mesoporous Ce-MCM-41 catalysts using aqueous hydrogen peroxide (30%) as oxidant and acetic acid as solvent without adding any initiator. The catalysts exhibited high substrate conversion and good product (cyclohexanol) selectivity and it can be reused once with almost the same activity. The catalyst was characterized by a combination of various physicochemical techniques, such as N 2 physisorption, diffuse reflectance UV–vis, X-ray diffraction and FT-IR.

Fe, Co and Cu-incorporated TUD-1: Synthesis, characterization and catalytic performance in N 2O decomposition and cyclohexane oxidation

Fe, Co and Cu-TUD-1 were prepared with different metal loadings (Si/M ratio = 100, 50, 20 and 10). As a function of increasing metal loading either isolated metal atoms, nano-particles of M-oxide and/or bulk M-oxide crystals in the silicate matrix were obtained, respectively. The materials were fully characterized by means of XRD, UV–vis, elemental analysis, N 2 sorption measurements and HR-TEM. The catalytic performance of the prepared materials was tested in gas phase N 2O decomposition and in liquid phase oxidation of cyclohexane. Results of N 2O decomposition showed that a low M-loading is beneficial for the catalysis and leads to a high TOF, Co-TUD-1 being the most active catalyst. This suggests that the nano-particles observed in many catalysts are not dominating the N 2O decomposition rate, and that active phase entities ranging from isolated to polynuclear sites are the most active. The performance of the TUD-1 catalysts is significantly lower than reported for the microporous Fe, Co and Cu analogues. In the oxidation of cyclohexane with TBHP, Cu-TUD-1 showed the highest activity but also significant leaching. Co-TUD-1 did not show any leaching and is thus the best applicable catalyst in cyclohexane oxidation.

05/01869 Modeling a continuous multistage liquid phase cyclohexane oxidation reactor network: Bhattacharya, A. Chemical Engineering and Processing, 2005, 44, (5), 565–577

05/01869 Modeling a continuous multistage liquid phase cyclohexane oxidation reactor network: Bhattacharya, A. Chemical Engineering and Processing, 2005, 44, (5), 565–577

Bismuth-containing MCM-41: synthesis, characterization, and catalytic behavior in liquid-phase oxidation of cyclohexane

Bismuth-containing MCM-41 was directly synthesized in strongly acidic media with CPBr as the template. It was shown, for the first time, by ICP, XRD, N 2 adsorption/desorption, TEM, SEM, 29Si MAS NMR spectra, UV–vis DRS, and Raman spectroscopy that all of the samples have high surface area and good crystallinity, and all bismuth atoms in Bi-MCM-41 are highly dispersed in the silica-based structure. In addition, XPS spectroscopic data indicate that most of the bismuth enters the internal surface or framework of MCM-41. In the catalytic test, Bi-MCM-41 was found to be a very efficient catalyst for the oxidation of cyclohexane, with oxygen as oxidant, in a solvent-free system, and it behaves truly as a heterogeneous catalyst.

Modeling a continuous multistage liquid phase cyclohexane oxidation reactor network

A model is presented for a continuous multistage liquid phase cyclohexane oxidation reactors-in-series network, which uses, unlike previous efforts, a closed form rate model derived on the basis of the well-known free-radical kinetic mechanism of the oxidation reaction leading to a more generalized representation of the oxygen dependence of the rate. The model calculates the required transport and hydrodynamic parameters by one of the best available set of correlations shown earlier to be successfully used in cyclohexane oxidation in a well-designed laboratory reactor. Process sensitivities with regard to variables such as air rate, residence time, head pressure, inlet air composition and sparger configuration have been predicted. Some of these trends compared very well with the limited published experimental data in a three (35 l) agitated and sparged tank-in-series reactor system, thus partially validating the model. The model has highlighted a fairly generalized way of correlating performance data from a given reactor, namely in terms of a yield–conversion characteristic which can change depending on the mass transfer efficiency and the effective kinetics. Hence, it can aid in plant monitoring and optimization. It has also been shown how to use the same as an aid in preliminary scale-up studies based on laboratory or pilot plant reactor performance data.

Mesoporous VMCM-41: highly efficient and remarkable catalyst for selective oxidation of cyclohexane to cyclohexanol

Liquid phase oxidation of cyclohexane was carried out under milder reaction conditions over mesoporous VMCM-41 molecular sieve catalysts using aqueous hydrogen peroxide as oxidant, acetic acid as solvent, and methyl ethyl ketone as initiator. The catalysts showed high substrate conversion and excellent product (cyclohexanol) selectivity. Although the activity of the catalyst slightly decreased after first recycle, owing to leaching of small amount of non-framework vanadium ions, it, however, remained nearly same thereafter. This observation was further confirmed by washing experiments where the non-framework vanadium ions were removed upon ammonium acetate treatment. Further, the washed catalyst also showed an activity similar to that of the recycled catalyst. Thus, the recycled or washed VMCM-41 behaves truly as heterogeneous catalyst. This observation was complemented and confirmed by both filtrate and quenching studies. The effects of reaction time, temperature, Si/V molar ratio, and catalyst concentration on the catalyst performance were examined in order to optimize the conversion of cyclohexane and selectivity of cyclohexanol. However, the use of strong oxidizing agent, e.g., tertiary butyl hydroperoxide, resulted in the formation of cyclohexanone as the major product. In addition, the use of solvents like methanol, dioxan and acetone showed lower activity.

The role of niobium in the gas- and liquid-phase oxidation on metallosilicate MCM-41-type materials

MCM-41 mesoporous molecular sieves containing Nb, V, and Mo separately and together have been synthesised and characterised by high-resolution transmission microscopy (HRTEM with EDX), N 2 adsorption isotherms, and X-ray diffraction (XRD), and tested in the oxidative dehydrogenation (ODH) of propane in the gas phase and in the liquid-phase oxidation of cyclohexene with hydrogen peroxide. For the first time, it has been documented that the incorporation of niobium during the synthesis of MCM-41 materials results in the formation of defects, the presence of which influences the selectivity in both reactions, ODH of propane to propene and epoxidation of cyclohexene. It is proposed that defect holes, generated by niobium, are convenient for access of reagents to the active species and for making the diffusion easier (particularly important in the liquid-phase reactions). NbO − species plays the role of an electronic promoter in multimetallosilicates NbV- and NbVMoMCM-41, where vanadium is an active species. In the absence of vanadium, niobium species are active in both oxidation processes. The role of acidity in the catalysts used for both oxidation processes is considered.

Structural and Functional Characterization of Redox Mn and Co Sites in AlPO Materials and Their Role in Alkane Oxidation Catalysis

energy occurred concurrently and at similar rates, indicating excellent agreement between these techniques. No H2 Oo r CO 2 were detected during treatment in H2 or CO, respectively, indicating that reduction from Me 3+ to Me 2+ occurred by introduction of protons. These protons are fully removed by treatment in O2 to 773 K, and O2-H2 redox cycles involving reversible proton formation suggest that cations reside within AlPO framework positions, in which protons reside as charge balancing cations at Me 2+ -O-P bridges. H2 consumption rates measured during H2-TPR could be accurately described by Arrhenius-type behavior, and H2/Me ratios showed that only a fraction of all Me cations undergo reversible redox cycles. This fraction was 0.86 for MnAPO-18 (atomic Mn/P ) 0.05); it decreased from 0.68 to 0.40 for MnAPO-5 as Mn/P ratios increased from 0.028 to 0.10. For CoAPO-18 with 0.028 Co/P and CoAPO-5 with 0.40 Co/P, the fractions of redox sites were 0.64 and 0.40, respectively. UV-visible spectra showed no detectable Me 3+ features after thermal treatment in H2. Thus, cations that do not undergo redox cycles remain as permanently divalent cations throughout O2-H2 cycles. The redox-active fraction also decreased during repeated H 2-O2 redox cycles above 773 K, indicating that redox cations convert into permanently divalent sites. This conversion coincides with the evolution of H2O during H2 treatments above 773 K. These findings together with the effects of Me/P ratio on the redox fraction are consistent with a mechanism in which OH groups at divalent framework cation sites recombine to form H2O and an oxygen vacancy. Cyclohexanol and cyclohexanone formation rates during liquid-phase cyclohexane oxidation with O2 on MnAPO-5 samples increased linearly with the number of redox-active sites, suggesting that elementary steps of cyclohexane oxidation involve cycling between Me 2+ and Me 3+ , and require cation sites able to reversibly form charge balancing cationic species.

Kinetic Modeling of Liquid Phase Oxidation of Cyclohexane

AbstractA kinetic model for the liquid phase oxidation (LPO) of cyclohexane has been derived using a reaction network based on a consistent free radical mechanism. It was demonstrated that on embedding this rate model within the overall model of a semi‐batch gas‐liquid reactor (SBR) one can predict the time variation of the dissolved oxygen concentration and the rate of oxygen absorption which compare fairly closely with some well regarded published experimental data. The model is distinguished by easy extendibility and modularity whereby it could be tailored to predict, in the context of a SBR, cyclohexane conversion and ketone‐alcohol (K‐A) product selectivity levels as observed in commercial plants and in the published data on pilot plant experimentation. The model is expected to be of use in the design and scale‐up of LPO reactors.