Vapor Phase Beckmann Rearrangement Research Articles

Modulating the Microenvironment of Silanols in Pure-Silicon Zeolites for Boosting Vapor-phase Beckmann Rearrangement of Cyclohexanone Oxime.

Vapor-phase Beckmann rearrangement of cyclohexanone oxime (CHO) to ε-caprolactam (CPL) is still difficult to commercialize at the industrial scale due to its relatively low catalytic activity and poor lifetime. Herein, we synthesized a series of pure-silicon zeolites (including MFI, MEL, and -SVR) with three-dimensional 10-member-ring topolgies, diverse silanol status, and hierarchical porosity to investigate the synergistic effects of inner diffusivity and reactivity. S-1 zeolite of MFI-type topology with plentiful silanol nests exhibits a more preferable catalytic performance in terms of CHO conversion (99.7%) and CPL selectivity (89.7%), much higher than those of MEL- and -SVR-type zeolites mainly due to their diverse silanol distribution. With the construction of hierarchical porosity, S-1-P shows improved CPL selectivity of 94.1% owing to the enhanced diffusivity to shorten the retention time of the reactant and product molecules. The reaction mechanism and network have been further revealed by density functional theory (DFT) calculations and experimental designs, which indicate that silanol nests are major active sites due to their suitable interaction with CHO rather than terminal silanols. Particularly, the microenvironments of silanols can be modulated by alcohol solvents, ascribed to their different charge transfer and steric hindrance. Consequently, S-1-P shows superior CPL selectivity of 97.3% in ethonal solvents, which have higher adsorb energy of -0.627 eV with silanol nests than other alcohols. The present study not only provides a fundamental guide for the design of zeolite catalysts but also provides a reference for modulating the microenvironment of active sites according to the catalytic mechanism.

Rational construction of multiple hollow silicalite-1 zeolite with enhanced quasi acidity for robust vapor-phase Beckmann rearrangement

Rational construction of multiple hollow silicalite-1 zeolite with enhanced quasi acidity for robust vapor-phase Beckmann rearrangement

Deactivation kinetic study on vapor phase Beckmann rearrangement of cyclohexanone oxime and design of the multi-layer inclined channel bionic reactor

The optimal design of the reaction system of a large-scale industrial vapor phase Beckmann rearrangement of cyclohexanone oxime to caprolactam process requires both deactivation kinetics and reactor optimization. The deactivation kinetics was study in a micro fluidized bed reactor with online catalyst particle sampling system. An empirical coke formation rate equation was obtained based on time evolution of coke amounts. A Langmuir-Hinshelwood kinetics with deactivation factor based on coke amount was developed. Based on the obtained deactivation kinetics, a Multi-layer Inclined Channel Bionic Reactor was designed as a substitute of the conventional fixed-bed reactor. The hierarchical structure has four levels with inclined channel implementation in the third and fourth level to reduce the pressure drop and improve the flow distribution uniformity. The optimized massive structure of the Multi-layer Inclined Channel Bionic Reactor designed for 200 thousand tons of CPL productivity has a total pressure drop lower than 2kPa, and the maximal relative difference of the bed infiltration velocity is about 11 %.

Preparation of Silicalite-1 Nanosheets and its Application in Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime

Silicalite-1 nanosheets catalyst with a hierarchical architecture was hydrothermally synthesized using [C18H37-N+(CH3)2-C6H12-N+(CH3)2-C6H13](Br)−2 as template. It has been studied systematically by investigating the influence of different synthesis parameters and crystallization kinetics under tumbling conditions. Highly crystalline silicalite-1 nanosheets with large external surface was obtained by regulating the crystallization time and the amount of water, template and the alkalinity. It was examined as catalyst for vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam and exhibited an excellent catalytic performance and long catalytic lifetime. This can be attributed to nest silanol groups located on the large external surface of the nanosheets. Furthermore, the high mesoporosity of nanosheets shorten the diffusion path length and reduce coking deposition, which remarkably improve catalyst stability.

Controllable Synthesis and Structure-Performance Relationship of Silicalite-1 Nanosheets in Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime

Bulky silicalite-1 shows high catalytic activity for vapor phase Beckmann rearrangement of cyclohexanone oxime. However, it often deactivates rapidly and the structure-performance relationship is unclear. Here, a series of well-crystallized silicalite-1 catalysts from three-dimensional micron particles (n < 10) to two-dimensional nanosheets (10 ≤ n ≤ 18) were controllably synthesized using diquaternary ammoniums [CnH2n+1-N+(CH3)2-C6H12-N+(CH3)2-C6H13](Br−)2 (n = 6–18) as the structure directing agent. The influence of morphology of catalysts on active sites distribution and the pore confinement effect on caprolactam selectivity and the catalytic stability were studied by XRD, SEM, TEM, In situ vacuum IR, 29Si MAS NMR and N2 adsorption/desorption isotherms. The silicalite-1 nanosheets with relatively high crystallinity exhibited superior catalytic activity to almost 100% and remarkably high caprolactam selectivity (92%). The catalytic lifetime of silicalite-1 nanosheets could be increased by 28 times in comparison to bulky silicalite-1 zeolite. The external surface area and mesopore volume of the synthesized catalyst dramatically increase with increasing the tail length of surfactant from C6 to C18, leading to high active sites and coke tolerance capacity. It was found the lifetime of the catalysts is almost linearly related to the product of area of silanol nest and volume of mesopore (Asilanol·nest*Vmeso) with correlation coefficient of 0.97, which strongly supports the excellent performance of nanosheets results from the synergetic effect of its high active sites and high coke tolerance capacity. This provides a theoretic guide for designing new catalysts with high catalytic activity. Silicalite-1 nanosheets were controllable synthesized through adjusting alkyl tail length of diquaternary ammoniums, resulting in large mesoporous volume and external surface area, which effectively improve high coke tolerance capacity and active sites of catalysts and exhibit much longer catalytic lifetime and high selectivity.

Synthesis of mesoporous silicalite-1 zeolite for the vapor phase Beckmann rearrangement of cyclohexanone oxime

Abstract Mesoporous silicalite-1 zeolites with large mesopore volume have been synthesized with the assisting of CO2 solvent. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images show that mesoporous silicalite-1 zeolites have good crystallinity. N2 sorption isotherm and transmission electron microscopy (TEM) images indicate the mesoporous silicalite-1 zeolites have mesopores. Catalytic tests for the vapor phase Beckmann rearrangement of cyclohexanone oxime show that mesoporous silicalite-1 zeolites have high conversion of cyclohexanone oxime and selectivity of e-caprolactam compared with conventional silicalite-1 zeolites.

Hierarchical zeolites comprising orthogonally stacked bundles of zeolite nanosheets for catalytic and adsorption applications

The synthesis of hierarchical MFI zeolites comprising orthogonally stacked bundles of zeolite nanosheets using a new type of triblock structure-directing agents (SDAs) was reported. The textural properties, including the degree of nanosheet branching and the spacing between adjacent nanosheets, could be controlled by changing the length of the linkers in the triblock SDAs. The hierarchical pure-silica silicalite-1 materials exhibited high and stable catalytic activity for the vapor-phase Beckmann rearrangement of cyclohexanone oxime with high selectivity of ε-caprolactam. On the other hand, the hierarchical ZSM-5 materials showed high adsorption capacity of Pb2+ ion following a Langmuir-type adsorption behavior. After being deposited with Pd nanoparticles, the hierarchical Pd/ZSM-5 nanocomposites exhibited high activity in the aqueous-phase hydrogenation of phenol to cyclohexanone at room temperature. The results show promise of the disclosed hierarchical zeolites for catalytic and adsorption applications.

Kinetic study of vapor-phase Beckmann rearrangement of cyclohexanone oxime over silicalite-1

The intrinsic kinetics for vapor-phase Beckmann rearrangement of cyclohexanone oxime (CHO) to caprolactam (CPL) over fresh silicalite-1 was studied at atmospheric pressure by an improved approach that combines the differential and the integral methods. To keep the reaction zone temperature constant at high flow rate and obtain homogeneous mixture of CHO and methanol largely different in boiling point, a special fixed-bed tubular reactor was designed. The relationship of deactivation rate with weight hourly space velocity (WHSV) was investigated in a wide range of CHO concentrations under high gas superficial velocity. The rate equation was directly deduced by the differential method on the basis of the dependence of CHO disappearance rate on CHO and CPL partial pressures. The reaction mechanism and rate-limiting step were determined by in situ infrared spectroscopy and comparison of the catalytic results of fresh and partially poisoned silicalite-1. The kinetic parameters were estimated and statistically tested by the integral method. It is shown that the vapor-phase Beckmann rearrangement of CHO to CPL occurs via a single-site surface reaction route with activation energy of 94.69kJ/mol, and desorption of CPL is the rate-limiting step.

Hierarchical silicalite-1 octahedra comprising highly-branched orthogonally-stacked nanoplates as efficient catalysts for vapor-phase Beckmann rearrangement

A triblock structure-directing agent was designed to synthesize hierarchical silicalite-1 octahedra comprising highly-branched, orthogonally-stacked and self-pillared nanoplates that exhibited excellent and stable activity for the vapor-phase Beckmann rearrangement of cyclic oximes and high lactam selectivity.

Bismuth supported SBA-15 catalyst for vapour phase Beckmann rearrangement reaction of cyclohexanone oxime to ɛ-caprolactam

Development of environmental benign as well as low cost metal precursor based catalyst is a challenge for chemical industry. In this work we report Bi promoted SBA-15 catalyst for vapour phase Beckmann rearrangement reaction of cyclohexanone oxime. The three different Bi loaded SBA-15 catalysts are prepared and characterized by BET surface area and porosity measurement, small angle X-ray scattering, wide angle X-ray diffraction, field emission scanning electron microscope, high resolution transmission electron microscope, ultraviolet–visible spectroscope, Fourier transform infrared spectroscopy and temperature programmed desorption techniques. Further, catalytic activity is optimized by changing reaction temperature, pre-treatment temperature and pre-treatment time so that 100% cyclohexanone oxime conversion and 100% ɛ-caprolactam selectivity has been achieved. Role of solvent, silylation and time on stream has also been examined. The TPD profiles of all three bismuth loaded samples are mainly characterized by weak acidic sites or surface silanol groups. The FTIR profile shows hydroxyl rich surface in the vicinity of bismuth at Bi-SBA-15 (Bi/Si=1/100). Based on catalyst characterization and activity data correlation, it can be suggested that protonation at oxime oxygen can be triggered by surface silanol in the vicinity of a Lewis acid centre bismuth. The high space-time-yield of caprolactum was 114.3molgcat−1h−1 was obtained.

Synthesis of hierarchical porous silicalite-1 and its catalytic performance in Beckmann rearrangement

Hierarchical porous silicalite-1 with micropores and mesopores was successfully synthesized via dry gel conversion route using tetrapropylammonium hydroxide (TPAOH) and polyvinyl alcohol (PVA) as microporous and mesoporous templates, respectively. The obtained hierarchical porous silicalite-1 was characterized by X-ray diffraction (XRD), nitrogen adsorption and desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The characteristics of the samples are comparable with conventional silicalite-1. The influence of the PVA on the hierarchical porous properties of the samples was investigated. The hierarchical porous silicalite-1 showed higher activity and selectivity than conventional silicalite-1 in vapor phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam under reaction condition.

Niobium doped hexagonal mesoporous silica (HMS-X) catalyst for vapor phase Beckmann rearrangement reaction

The synthesis of e-caprolactam, a demanding monomer, through a heterogeneous catalytic pathway has remained a key area of research in the last decade. The Beckmann rearrangement reaction in the vapor phase using a solid acid catalyst was found to be very effective for producing e-caprolactam. It is observed that niobium incorporated into mesoporous silica serves as a good catalyst for the Beckmann rearrangement reaction. Recently developed mesoporous silica, having an ordered honeycomb structure, is very useful as it can lead to effective diffusion of reactants and products for several reactions. In this study, Nb-doped mesoporous HMS-X nanocomposite materials with different Nb loadings were prepared by a one step hydrothermal synthesis and characterized by BET surface area and porosity measurements, wide and small angle XRD, SEM, HR-TEM, elemental mapping, FTIR, 29Si-NMR and NH3-TPD techniques. The activity of the Nb–HMS-X catalyst was evaluated for the vapour phase Beckmann rearrangement reaction. The catalyst characterization study shows that Nb is highly dispersed on the HMS-X matrix at lower Nb loadings. At higher Nb loadings it is present in the extra-framework position as revealed from XRD, HR-TEM and 29Si-NMR studies. The NH3-TPD result shows the presence of acidic sites on the catalyst surface, which are active sites for the Beckmann rearrangement reaction. Using the Nb–HMS-X catalyst (Si/Nb = 13) under vapour-phase reaction conditions [temperature = 350 °C, weight hourly space velocity (WHSV) = 15 h−1, cyclohexanone oxime in benzene, cyclohexanone oxime : benzene weight ratio of 1 : 11] gave 100% cyclohexanone oxime conversion with 100% e-caprolactam selectivity, with a space time yield of 1.4–1.6 × 10−3 mol h−1 gcat−1. The catalyst was highly recyclable up to 9 times without significant loss of catalytic activity.

Synthesis of TS-1 submicrocrystals from inorganic reactants by a seed method for the vapor Beckmann rearrangement of cyclohexanone oxime

The size of molecular sieve crystals will significantly affect their catalytic performances. In this paper, TS-1 submicrocrystals (SMCs) have been size-controllably synthesized using S-1 and TS-1 seeds in a tetrapropylammonium bromide (TPABr)–ammonia system. The sizes of TS-1 were effectively controlled by the seeds. For the same type of seeds, the smaller one provided smaller TS-1 SMCs. The TS-1 SMCs using S-1 seeds was smaller than those using similar size TS-1 seeds. The crystallinity behavior, microstructure, morphology of the TS-1 SMCs and coordination states of Ti were affected by S-1 or TS-1 seeds. The TS-1 SMCs were examined as catalysts in the vapor phase Beckmann rearrangement of cyclohexanone oxime. The highest catalytic performances including conversion of cyclohexanone oxime and selectivity to ε-caprolactam were obtained over the TS-1 SMCs synthesized with nano S-1 seed.

Coking and deactivation of boron modified Al-MCM-41 for vapor-phase Beckmann rearrangement reaction

The influences of different parameters such as boron content, reaction temperature, and calcined temperature on carbonaceous compounds deposited on the boron modified Al-MCM-41 catalyst have been investigated. The carbonaceous compounds were characterized using FT-IR, N2 adsorption, TGA, SEM, XPS, NH3-TPD, and a solvent extraction analysis. The coke deposited on the catalyst was majorly amorphous. The filamentous carbon and graphitic-like carbon were not formed on the catalyst during the vapor-phase Beckmann rearrangement over boron modified Al-MCM-41 catalyst. The coke was preferably deposited on the acid sites. Neither the high nor the low reaction temperate was beneficial to decrease the amount of coke. The uniform dispersion of boron in the catalyst was good at reducing the formation of coke. The catalyst deactivation was attributed to blockade of the pore and active sites by the excessive dehydrogenated carbon species, except the aliphatic carbon (B.E.=284.6eV).

Preparation of Nanosized Silicalite-1 and Its Application in Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime

Series of silicalite-1 catalysts with particle size varying from 50 to 450 nm were synthesized by hydrothermal method using tetrapropylammonium hydroxide as a template and l-lysine as an additive. The crystal size of silicalite-1 could be easily controlled by regulating the amount of l-lysine. The series of silicalite-1 and their NaOH-modified derivatives were examined as catalysts for vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam in the 330–390 °C range. It was found that the crystal size of silicalite-1 has an effect on catalytic activity, ε-caprolactam selectivity, and catalyst stability. With a decline in crystal size, there was improvement of catalytic activity and catalyst stability. It is deduced that silicalite-1, of a smaller crystal size, is less inclined to pore blocking by coke and hence has better resistance to deactivation.

Preparation of tantalum-pillared magadiite and its catalytic performance in Beckmann rearrangement

Vapor phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam has been carried out using tantalum-pillared magadiites (Ta-magadiites) with different surface areas as catalysts. The Ta-magadiite catalysts of relatively large surface areas showed high catalytic activities, due to a large number of active sites. For the Ta-magadiite catalyst of the largest surface area, the oxime conversion reached 99.1%, with 97.5% of lactam selectivity. FT-IR and NH3-TPD results demonstrated that the new hydroxyl groups and a large amount of acidic sites generated by Ta pillaring into the magadiite interlayer were responsible for the high catalytic performance of Ta-magadiite catalyst.

Influence of Na+ on the synthesis of silicalite-1 catalysts for use in the vapor phase Beckmann rearrangement of cyclohexanone oxime

Silicalite-1 was hydrothermally synthesized in the presence of different concentrations of Na+ using tetrapropylammonium hydroxide (TPAOH) as a template. The synthesis was followed by a base treatment. The silicalite-1samples were characterized using X-ray diffraction, scanning electron microscopy, N2 adsorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and NH3 temperature-programmed desorption. The samples were used as catalysts for the vapor phase Beckmann rearrangement of cyclohexanone oxime. During the synthesis, the sodium ions were incorporated onto the silicalite-1 crystals, but were then removed by the base treatment. All the catalysts exhibited nearly complete conversion of cyclohexanone oxime to ɛ-caprolactam with selectivities grater than 95%. Addition of less than 2.5 mol-% Na+ (relative to TPAOH) did not influence the catalytic properties. However, for Na+ concentrations ⩽5 mol-%, the particle sizes of silicalite-1 increased and the catalytic activities decreased, which can be attributed to carbon deposition. The results in this work are of great importance for the polymer industry.

Influence of Br − and Na + in synthesis of Silicalite-1 on catalytic performance in vapor phase Beckmann rearrangement of cyclohexanone oxime

Silicalite-1 was hydrothermally synthesized with tetrapropylammonium hydroxide (TPAOH) as the template in the presence of various Br − and Na + concentrations, characterized by XRD, SEM, BET, XPS, FT-IR and NH 3-TPD and studied in the vapor phase Beckmann rearrangement of cyclohexanone oxime. The characterization results show that the crystal sizes of Silicalite-1 increase with the increase of Na + concentrations in the synthesis; Na + is combined in the Silicalite-1 crystals, but removed by a base treatment. The base treated catalysts exhibit nearly complete conversion of cyclohexanone oxime with above 95% selectivity to ɛ-caprolactam. Catalysts with the addition of up to 20 mol% Br − relative to TPAOH without Na + in the synthesis do not influence the physical and chemical as well as the catalytic properties. The addition of Na + below 2.5 mol% of TPAOH do not influence the catalytic properties either. However, at the concentrations of Na + ≥ 5 mol% of TPAOH in the synthesis, the catalysts deactivate faster with the increase of Na + contents, which is attributed to more carbon deposition in the larger Silicalite-1 particles, determined by TGA. The results of this work are of great importance for the industry.

Beckmann rearrangement of cyclohexanone oxime over Al-MCM-41 and P modified Al-MCM-41 molecular sieves

Abstract P modified Al-MCM-41 molecular sieves were prepared via impregnating method and applied to vapor-phase Beckmann rearrangement reaction. The catalysts were characterized by XRD, N2 adsorption, ICP-OES, NH3-TPD and 27Al and 31P MAS NMR spectroscopy. NH3-TPD results reveal that P modification of Al-MCM-41 can increase the number as well as the strength of weak acid sites, whereas the introduction of P decreases the number of intermediate acid sites. 27Al and 31P MAS NMR results indicate that formation of Si-O-P-O-Al seems to be favored in P modified Al-MCM-41 catalysts. Overall, these results indicate that P modified Al-MCM-41 catalysts can improve their selectivity for caprolactam. In addition, more abound weak acid sites with certain acid strength are favorable to Beckmann rearrangement.

Vapor-phase Beckmann rearrangement of cyclohexanone oxime over phosphorus modified Si-MCM-41

A series of phosphorus modified Si-MCM-41 catalysts prepared via the impregnation method were used for the vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam. The catalysts were characterized by XRD, N2 adsorption, FT-IR, and NH3-TPD. The results indicated that weak acid sites increased with P content, leading to enhanced catalytic activity. The catalyst with Si/P mol ratio of 25 showed best performance at 633 K. The conversion of cyclohexanone oxime and the selectivity for caprolactam were 92.7 and 64.2%, respectively. The P–OH groups are main active sites for the Beckmann rearrangement. Grafting acid hydroxyl groups to cover the Si–OH groups may be a good way to improve the selectivity for this reaction.