Research Advances on Cyclohexane Catalytic Cracking

This article elaborates on the research achievements of domestic and foreign researchers in exploring the conversion pathways and reaction mechanisms of cyclohexane catalytic cracking in recent years.It analyzes the effects of different catalysts and process conditions on the conversion laws of cyclohexane,summarizes the conversion pathways of cyclohexane,and discusses the chemical mechanisms of several main reactions of cyclohexane in catalytic cracking,such as cracking,isomerization,hydrogen transfer,dehydrogenation,and alkylation;Several advanced characterization methods and common research methods were listed,and prospects for future development in this field were proposed based on existing research.

The synthesis of Co-doped SAPO-5 molecular sieve and its performance in the oxidation of cyclohexane with molecular oxygen

Silicoaluminophosphate（SAPO） molecular sieves doped with cobalt（Co-SAPO-5） were synthesized hydrothermally with different concentrations of Co.Each sample was characterized by X-ray diffraction,N2 adsorption-desorption,scanning electron microscopy,ultraviolet-visible spectroscopy,temperature-programmed desorption of NH3（NH3-TPD）,and infrared spectrascopy of adsorbed pyridine（Py-IR）.The results showed that Co was highly dispersed in the Co-SAPO-5 samples.In addition,a part of the Co content had been incorporated into the SAPO-5 framework,while the remainder existed on the surface as extra-framework Co.The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample.However,the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample.As the concentration of Co increased,the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface.NH3-TPD and Py-IR results revealed that the amount of Br（？）nsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample.These values were also higher for samples with higher Co content.The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen.When Co was added to the SAPO-5 catalyst,the catalytic activity of the Co-SAPO-5 catalysts improved.In addition,the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased.However,with a high conversion of cyclohexane（6.30%）,the total selectivity of cyclohexanone（K） and cyclohexanol（A） decreased sharply.The K/A ratio ranged from 1.15 to 2.47.The effects of reaction conditions（i.e.,reaction temperature,reaction time,initial oxygen pressure,and the catalyst amount） on the performance of the Co-SAPO-5 catalysts have also been measured.Furthermore,the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.

Solvent-free selective oxidation of cyclohexane with molecular oxygen over manganese oxides:Effect of the calcination temperature

The effects of calcination temperature on the physicochemical properties of manganese oxide catalysts prepared by a precipitation method were assessed by X-ray diffraction,N2 adsorption-desorption,X-ray photoelectron spectroscopy,H2 temperature-programmed reduction,O2 temperature-programmed desorption,and thermogravimetry-differential analysis.The catalytic performance of each of these materials during the selective oxidation of cyclohexane with oxygen in a solvent-free system was subsequently examined.It was found that the MnOx-500 catalyst,calcined at 500 °C,consisted of a Mn2O3 phase in addition to Mn5O8 and Mn3O4 phases and possessed a low surface area.Unlike MnOx-500,the MnOx-400 catalyst prepared at 400 °C was composed solely of Mn3O4 and Mn5O8 and had a higher surface area.The pronounced catalytic activity of this latter material for the oxidation of cyclohexene was determined to result from numerous factors,including a higher concentration of surface adsorbed oxygen,greater quantities of the surface Mn4＋ ions that promote oxygen mobility and the extent of O2 adsorption and reducibility on the catalyst.The effects of various reaction conditions on the activity of the MnOx-400 during the oxidation of cyclohexane were also evaluated,such as the reaction temperature,reaction time,and initial oxygen pressure.Following a 4 h reaction at an initial O2 pressure of 0.5 MPa and 140 °C,an 8.0% cyclohexane conversion and 5.0% yield of cyclohexanol and cyclohexanone were achieved over the MnOx-400 catalyst.In contrast,employing MnOx-500 resulted in a 6.1% conversion of cyclohexane and 75% selectivity for cyclohexanol and cyclohexanone.After being recycled through 10 replicate uses,the catalytic activity of the MnOx-400 catalyst was unchanged,demonstrating its good stability.

APM3 Molecular Orbital Study on the Conformational Equilibrium of Cyclohexane upon α-Cyclodextrin Inclusion Complexation

用PM3分子轨道方法研究了α -环糊精的包合作用对环己烷构象平衡的影响。发现α -环糊精的包合作用可以改变环己烷的构象平衡。计算结果表明 ,虽然环己烷的椅式构象比船式构象稳定 1 8.5kJ·mol-1,但在α-环糊精的包合物中 ,船式环己烷包合物比椅式环己烷包合物稳定4.4kJ·mol-1。因此 ,超分子体系中客体分子的构象平衡不能简单地从其游离态的构象平衡外推得到 。

Synthesis of cerium-doped MCM-48 molecular sieves and its catalytic performance for selective oxidation of cyclohexane

Cerium-doped MCM-48 molecular sieves were synthesized hydrothermally and characterized by X-ray diffraction, nitrogen adsorption, transmission electron microscope, FT-IR spectroscopy, UV-visible spectroscopy, and Raman spectroscopy. The results showed that all the samples held the structure of MCM-48, and Ce could enter the framework of MCM-48. However, when Ce/Si molar ratio in the sampies was high （0.04 or 0.059）, there were CeO2 crystallites as secondary phase in the extraframework of MCM-48. Ce-doped MCM-48 was a very efficient catalyst for the oxidation of cyclohexane in a solvent-free system with oxygen as an oxidant. In the conditions of 0.5 MPa 02 and 413 K for 5 h, the conversion of cyclohexane was 8.1% over Ce-MCM-48-0.02, the total selectivity of cyclohexanol and cyclohaxnone was 98.7%. With an increase of Ce content, the conversion of cyclohexane and the selectivity to cyclohexanol decreased somewhat, but the selectivity to cyclohexanone increased.

A novel approach for one-step forming ε-caprolactam from cyclohexane nitrozation catalyzed by transition metal salt

The nitrozation reaction of cyclohexane in one-step reaction to form ε-caprolactam has been studied using transition metal salt as catalysts in this work. The results indicated that the catalysts play an especially important role. This method is expected to be a novel way to synthesize other lactam by similar reaction. The possible mechanism was suggested.

Highly efficient cobalt-doped carbon nitride polymers for solvent-free selective oxidation of cyclohexane

Selective oxidation of saturated hydrocarbons with molecular oxygen has been of great interest in catalysis, and the development of highly efficient catalysts for this process is a crucial challenge. A new kind of heterogeneous catalyst, cobalt-doped carbon nitride polymer(g-C_3N_4),was harnessed for the selective oxidation of cyclohexane. X-ray diffraction, Fourier transform infrared spectra and high resolution transmission electron microscope revealed that Co species were highly dispersed in g-C_3N_4 matrix and the characteristic structure of polymeric g-C_3N_4 can be retained after Co-doping, although Co-doping caused the incomplete polymerization to some extent. Ultraviolet-visible, Raman and X-ray photoelectron spectroscopy further proved the successful Co doping in g-C_3N_4 matrix as the form of Co(Ⅱ)-N bonds. For the selective oxidation of cyclohexane, Co-doping can markedly promote the catalytic performance of g-C_3N_4 catalyst due to the synergistic effect of Co species and gC_3N_4 hybrid. Furthermore, the content of Co largely affected the activity of Co-doped g-C_3N_4 catalysts, among which the catalyst with 9.0 wt%Co content exhibited the highest yield(9.0%) of cyclohexanone and cyclohexanol, as well as a high stability. Meanwhile, the reaction mechanism over Co-doped g-C_3N_4 catalysts was elaborated.

Quantitative interpretation to the chain mechanism of free radical reactions in cyclohexane pyrolysis

Pyrolysis of cyclohexane was conducted with a plug flow tube reactor in the temperature range of 873-973 K. Based on the experimental data, the mechanism and kinetic model of cyclohexane pyrolysis reaction were proposed. The kinetic analysis shows that overall conversion of cyclohexane is a first order reaction, of which the rate constant increased from 0.0086 to 0.0225 to 0.0623 s-1 with the increase of temperature from 873 to 923 to 973 K, and the apparent activation energy was determined to be 155.0±1.0 kJ mol-1. The mechanism suggests that the cyclohexane is consumed by four processes：the homolysis of C-C bond （Path I）, the homolysis of C-H bond （Path II） in reaction chain initia- tion, the H-abstraction of various radicals from the feed molecules in reaction chain propagation （Path III）, and the process associated with coke formation （Path IV）. The reaction path probability （RPP） ratio of XPath I：XPath II ： XPath III ： XPath IV was 0.5420：0.0045：0.3897：0.0638 at 873 K, and 0.4336 ： 0.0061 ： 0.4885 ： 0.0718 at 973 K, respectively.

One-step Synthesis of ε-Caprolactam by the Liquid Phase Nitrosation of Cyclohexane over the Catalysts Containing CH_3COO^- or —COOH

ε-Caprolactam（CL or CPL） is one of the most important intermediates used in polymer industry for the production of several million tons of nylon-6 every year^[1]. All current commercial processes for the production of caprolactam are based on either benzene or tolueneI21. Caprolactam is synthesized by the Beckmann rearrangement of cyclohexanone oxime with fuming sulfuric acid or sulfuric acid as the reaction medium, and cyclohexanone oxime is produced by the reaction between cyclohexanone and hydro- xylamine（only one exception is the Toray PNC process）.

Oxidation of Cyclohexane Catalyzed by TS-1 in Ionic Liquid with Tert-butyl-hydroperoxide

An efficient and environmentally friendly procedure was described for easy product isolation for the oxidation of cyclohexane with tert-butyl-hydroperoxide catalyzed by titanium silicalite 1 （TS-1） in ambient-temperature ionic liquid [emim]BF4. Good yield and higher selectivity of products were found in the ionic liquid compared with in molecular solvent. The research results showed 13.2% conversion of cyclohexane, 97.6% cyclohexanol and cyclohexanone selectivity were obtained in ionic liquid under mild conditions of 90℃.

Theoretic heat sink simulation and experimental investigation of the pyrolysis of substituted cyclohexanes

Reaxgen program for the pyrolysis mechanism of cycloalkanes was adopted to simulate the heat sink of substituted cyclohexanes. Thermal cracking of cyclohexanes was performed to examine the cracking performance, wherein the substituent effects were detailedly discussed under supercritical condition. It was found that Reaxgen program played a good part in the screening and optimization of cyclohexanes. A good agreement with the experimental data for the mono-substituted and bi-substituted cyclohexanes was demonstrated, however, some deviation for the tri-substituted cyclohexanes were observed. The experiment results indicated that the gaseous product yield increased sharply for mono- substituted cyclohexanes with short substituents containing no more than two carbons. Nevertheless, continuous increase in the alkyl chain depressed the gaseous product yield smoothly. The cyclic substituent dramatically inhibited the pyrolysis of cyclohexanes. All the substituents but cyclohexyl had no obvious effect on the yield of hydrogen and olefins （≤C4）. For bi-substituted cyclohexanes, the more close the distance between the two substituents, the higher the gaseous product yield was obtained. However, opposite result on the selectivity to hydrogen and olefins （≤C4） was generally obtained except 1,3-dimethylcyclohexane. The position of tri-substituents acted little significance on the gaseous product yield, as well as the selectivity to hydrogen and olefins （≤C4）.

Study on Catalytic Cracking of Cyclohexane to Produce Light Olefins

Catalytic cracking of cyclohexane(CHA) over ZSM-5, Beta, and USY zeolite catalysts was examined in a fixed fluidized bed reactor(ACE) at 773 K. The adsorption of cyclohexane in ZSM-5, Beta, and USY catalysts was investigated by IR spectroscopy. The IR results demonstrated that the zeolite structure has a remarkable influence on adsorption. Beta zeolite has stronger adsorption of cyclohexane than ZSM-5 and USY zeolites. During the cracking of cyclohexane, path Ⅰ(cyclohexane →methycyclopentane →light olefins) and path Ⅱ(cyclohexane → cyclohexene → light olefins) were found as two important reaction pathways to produce light olefins. A mixture of ZSM-5 and Beta zeolites is better suited for path Ⅰ, and a combination of ZSM-5 and USY zeolites is suitable for path Ⅱ. When pathway Ⅰ and pathway Ⅱ had the same proportion in cyclohexane conversion, pathway Ⅱ would be a better choice for light olefins production.

New insights for the catalytic oxidation of cyclohexane to K-A oil

Au-based catalysts have been reported to be active in the cyclohexane oxidation to K-A oil, but they showed some limitiations in terms of productivity, selectivity and required reaction conditions. The possibility to overcome some of these limits has been explored coupling Au with Cu, which can be suitable for undergoing the electron-switch in the initial step of the cyclohexane oxidation. Hence, a bimetallic 2 wt% Au Cu/Al_(2)O_(3) catalyst was tested in the oxidation of cyclohexane, working at mild conditions of 120 ℃ and 4 bar of O_(2). The combination of the catalyst with a very small amount of benzaldehyde used as cheaper and non-toxic radical initiator allowed to obtain a very high productivity of cyclohexanol and cyclohexanone(45 mmol*m L/mgmet*h) with a selectivity of 94%. Moreover, comparing the catalysed reaction with the non-catalysed one, the role of the catalyst has been disclosed.

Separation of Benzene and Cyclohexane by Batch Extractive Distillation

Azeotropic liquid mixture cannot be separated by conventional distillation. But extractive distillation or combination of the two can be valid for them. An experiment to separate benzene and cyclohexane by batch extractive distillation was carried out with N, N-dimethylformide （DMF）, dime- thyl sulfoxide （DMSO） and their mixture as extractive solvent. The effect of the operation parameters such as solvent flow rate and reflux ratio on the separation was studied under the same operating conditions. The results show that the separation effect was improved with the increase of solvent flow rate and the reflux ratio; all the three extractive solvents can separate benzene and cyciohexane, with DMF being the most efficient one, the mixture the second, and DMSO the least. In the experiment the best operation conditions are with DMF as extractive solvent, the solvent flow rate being 12.33 mUmin, and the reflux ratio being 6. As a result, we can get cyclohexane from the top of tower with the average product content being 86.98%, and its recovering ratio being 83.10%.

Estimation of Kinetic Parameters for Autocatalytic Oxidation of Cyclohexane Based on a Modified Adaptive Genetic Algorithm

A modified genetic algorithm of multiple selection strategies, crossover strategies and adaptive operator is constructed, and it is used to estimate the kinetic parameters in autocatalytic oxidation of cyclohexane. The influences of selection strategy, crossover strategy and mutation strategy on algorithm performance are discussed. This algorithm with a specially designed adaptive operator avoids the problem of local optimum usually associated with using standard genetic algorithm and simplex method. The kinetic parameters obtained from the modified genetic algorithm are credible and the calculation results using these parameters agree well with experimental data. Furthermore, a new kinetic model of cyclohexane autocatalytic oxidation is established and the kinetic parameters are estimated by using the modified genetic algorithm.

Exploring the Low-Temperature Oxidation Chemistry of Cyclohexane in a Jet-Stirred Reactor:an Experimental and Kinetic Modeling Study

We report the investigation on the low-temperature oxidation of cyclohexane in a jet-stirred reactor over 500-742 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry （SVUV-PIMS） was used for identifying and quantifying the oxidation species. Major products, cyclic olefins, and oxygenated products including reactive hydroperoxides and high oxygen compounds were detected. Compared with n-alkanes, a narrow low-temperature window （-80 K） was observed in the low-temperature oxidation of cyclohexane. Besides, a kinetic model for cyclohexane oxidation was developed based on the CNRS model [Combust. Flame 160, 2319 （2013）], which can better capture the experimental results than previous models. Based on the modeling analysis, the 1,5-H shift dominates the crucial isomerization steps of the first and second O2 addition products in the low-temperature chain branching process of cyclohexane. The negative temperature coefficient behavior of cyclohexane oxidation results from the reduced chain branching due to the competition from chain inhibition and propagation reactions, i.e. the reaction between cyclohexyl radical and O2 and the de- composition of cyclohexylperoxy radical, both producing cyclohexene and HO2 radical, as well as the decomposition of cyclohexylhydroperoxy radical producing hex-5-en-l-al and OH radical.

Diffusion Characteristics and Removal of Cyclohexane in Polyolefin Elastomer Melt

The diffusion coefficient of volatiles in polymer solutions is a crucial parameter to describe the mass transfer efficiency and ability of volatiles.In this research,polyolefin elastomer(POE)was used as a polymer,and cyclohexane was used as a volatile.A gravimetric analysis was applied to measure the diffusion coefficient of cyclohexane in POE.The devolatilization rate of the POE-cyclohexane system under different conditions was measured.The effects of temperature,film sample thickness,and initial concentration of volatiles on the devolatilization rate were discussed.Based on the devolatilization rate data,the average diffusion coefficient of cyclohexane in POE was obtained by fitting with a mathematical model.The experimental results indicate that the devolatilization rate increased with increasing temperature and initial concentration of volatiles,but it decreased with increasing sample thickness.As the thickness increased,the overall diffusion resistance increased.As the temperature increased,the molecular movement increased,resulting in the increase of average diffusion coefficient.The relationship between the diffusion coefficient of the POE-cyclohexane system and temperature follows the Arrhenius law.The diffusion activation energy E=6201.73 J/mol,and the pre-exponential factor of the diffusion coefficient D0=2.64×10^(-10) m^(2)/s.This work can provide basic data for exploring the devolatilization of POE polymers and serves as a useful reference for enhancing the effect of devolatilization.

Solvent-free partial oxidation of cyclohexane to KA oil over hydrotalcitederived Cu-MgAlO mixed metal oxides

A highly efficient and stable hydrotalcite-derived Cu-MgAlO catalyst was developed for the partial oxidation of cyclohexane with molecular oxygen.The physical–chemical properties of Cu-MgAlO catalysts were studied,and the results indicated that the copper component had been successfully introduced into the hydrotalcite unit layer structure.The catalytic reaction results showed that copper as the active species could activate CAH bond and effectively promote the decomposition of cyclohexyl hydroperoxide(CHHP)to the mixture of cyclohexanol and cyclohexanone(KA oil).8.3%of cyclohexane conversion and 82.9%of selectivity for KA oil were obtained over 9%Cu-MgAlO catalyst at 150℃with 0.6 MPa of oxygen pressure for 2 h.Especially,its catalytic performance was still stable after five runs.

Studies on Biomlmetic Oxidation for the Model Compound of Cytochrome P-450(IV)——Studies on Oxygenation of Cyclohexane Catalyzed by μ-Oxo-bis(5,10, 15,20-tetraphenylporphinato)iron(Ⅲ)

Chloro-（5,10,15,20-tetraphenylporphinato）iron（Ⅲ）(TPPFeCl)（A） used as a model compound of cytochrome P-450 to catalyze the monooxyenation of alkane is known, but the oxygenation of alkane catalyzed by μ-oxo-bis（5,10,15,20-tetraphenylporphinato）-iron（Ⅲ）(（TPPFe）;O)（B） has not been reported. The catalytic characteristics of B for the oxygenation of cyclohexane with PhIO in CH;Cl;and cyclohexane medium were studied. We found that B had a fairly good

Studies on the Biomimetic Oxidation Catalyzed by the Model Compound of Cytochrome P-450 (Ⅶ) The Influence of the Axial Ligand X in TPPFe(Ⅲ)X on Its Catalytic Properties for the Oxygenation of Cyclohexane

In the study of cyclohexane monoxygenation with PhIO catalyzed by TPPFe( Ⅲ )X, we found the Influence of different axial ionic ligands X (X = F, Cl, Br, I, SCN, OR, R, CH,3, C2H6, (CH3)2CH, (CH2)3C)in TPPFe( Ⅲ )X on the oxidation products distribution and the yields of cyclohexanol. This paper deals with the linear relationship between the catalytic activity of TPPFe(Ⅲ)X and both the electronic or/ and steric effects of the axial ligands OR in TPPFe(Ⅲ)OR on its catalytic activity.