Ammoximation Of Cyclohexanone Research Articles

Ammoximation of Cyclohexanone to Cyclohexanone Oxime Catalyzed by Titanium Silicalite-1 Zeolite in Three-phase System

An innovative green process of producing ɛ-caprolactam was proposed by integrating ammoximation and Beckmann rearrangement effectively. As a first part of the new process, TS-1 molecular sieve-catalyzed synthesis of cyclohexanone oxime from cyclohexanone, ammonia and hydrogen peroxide was carried out in a batch plant. Cyclohexane was used as the solvent in the three-phase reaction system. The influences of essential process parameters on ammoximation were investigated. Under the reaction conditions as catalyst content of 2.5% (by mass); H2O2/yclohexanone molar ratio of 1.10; NH3/cyclohexanone molar ratio of 2.20; reaction temperature of 343 K; reaction time of 5 h, high conversion of cyclohexanone and selectivity to oxime (both>99%) were obtained. Thus, the three-phase ammoximation process showed equal catalytic activity as TS-1 but much more convenient and simpler for the separation of catalyst in comparison to the industrial two-phase system with t-butanol used as solvent.

Synthesis of Zeolite/Mesoporous Silica Composite Microspheres by Microemulsion Method

Zeolite/mesoporous silica composite microspheres (ZMMS) have been prepared by self-assembling mesoporous silica phase with Y or Ti-MWW zeolites crystallites in a simple microemulsion system. The synthesis process involved the formation of a stable O/W microemulsion from silica precursor of tetrabutyl orthosilicate and cationic quaternary ammonium surfactants as well as a simultaneous assembling of zeolite into the oil phase by their hydrophobic interaction, in which mesoporous silica was formed by self-assembling of surfactant and silica source. Through optimizing synthesis conditions, the ZMMS materials were prepared to possess controllable mass ratio of zeolite to mesoporous silica (0—2.3) and sphere diameter (186—965 μm). The mesopore sizes of the ZMMSs were 3.75 (zeolite-Y/MMSs) and 3.98 nm (Ti-MWW/MMSs). In the liquid-phase ammoximation of cyclohexanone, Ti-MWW/mesoporous silica microspheres showed a high mechanical stability and a catalytic activity comparable to the parent Ti-MWW powders. Keywords zeolite microsphere; micro/mesoporous composite; microemulsion; zeolite-Y; Ti-MWW

Formulation of Reaction Kinetics for Cyclohexanone Ammoximation Catalyzed by a Clay-Based Titanium Silicalite-1 Composite in a Semibatch Process

This article focuses on the kinetic modeling of cyclohexanone ammoximation catalyzed by the clay-based titanium silicalite-1 (TS-1) composite. With the use of computational tools, modeling was carried out systematically, and a rational interpretation of the reaction mechanism was successfully achieved. By fitting the experimental and calculated data, it was found that cyclohexanone ammoximation over the clay-based TS-1 composite follows the Eley–Rideal mechanism in which the reaction takes place between adsorbed H2O2 and other reactants in the free state. It is concluded that a full understanding of the mechanism and kinetics of the reaction allows one to engineer the overall cyclohexanone ammoximation process by influencing elementary steps. The pre-exponential factor and activation energy of the reaction were also determined as a reference for industrial reactor design.

Postsynthesis of mesoporous MOR-type titanosilicate and its unique catalytic properties in liquid-phase oxidations

Mesoporous titanosilicate with the MOR topology, denoted as Ti-Meso-MOR, was postsynthesized from commercially available mordenite by sequential acid, alkaline, acid, and TiCl 4 vapor treatments, and its catalytic oxidation properties were investigated in detail in liquid-phase oxidation reactions with hydrogen peroxide as an oxidant. A controllable acid leaching was first carried out on H-mordenite (Si/Al = 7.8) to induce a partial dealumination to Si/Al = 80, which was suitable for constructing secondary mesopores by subsequent alkaline treatment. Alkaline treatment-induced desilication introduced a large number of intracrystal mesopores. Tetracoordinated Ti species were then inserted into the resultant mesoporous mordenite with a high dealumination degree (Si/Al = 145) through the gas–solid reaction with TiCl 4 vapor at elevated temperatures. In comparison with conventional Ti-MOR and TS-1, Ti-Meso-MOR thus prepared exhibited an improved catalytic activity in the hydroxylation of toluene and the ammoximation of cyclohexanone as well. Moreover, Ti-Meso-MOR proved to be a robust catalyst for continuous ammoximation since the mesopores minimized diffusion limitation and suppressed coke formation efficiently.

Preparation and evaluation of titanium silicalite-1 utilizing pretreated titanium dioxide as a titanium source

In this paper, TS-1 powder was prepared by utilizing pretreated titanium dioxide as titanium source. The structure and activity of the prepared catalysts were investigated by XRD, FT-IR, UV–vis and semicontinuous reaction of cyclohexanone ammoximation. The results showed that the prepared catalyst with pretreated titanium dioxide as a titanium source containing less Brönsted acidic sites than that of the standard sample using TBOT as titanium source. After the post-treatment by 0.5 M hydrochloric acid aqueous solution for removing the extra-framework Ti species, the obtained catalysts displayed almost the same catalytic activity under optimal condition as the titanium source of TBOT.

An investigation into cyclohexanone ammoximation over Ti-MWW in a continuous slurry reactor

In the present study, the liquid-phase ammoximation of cyclohexanone with ammonia and hydrogen peroxide was studied using a MWW-type titanosilicate (Ti-MWW) catalyst in a continuous slurry reactor to develop a clean process for producing cyclohexanone oxime. The reaction parameters, which governed the cyclohexanone conversion, oxime selectivity and catalyst deactivation, were investigated by simulating the operating conditions of an industrial process. Under optimized reaction conditions, Ti-MWW produced a cyclohexanone conversion and oxime selectivity over 96% and 99%, respectively. Moreover, Ti-MWW was extremely robust and showed a longer lifetime than the conventional titanium silicalite-1 catalyst. The causes of deactivation were elucidated to be the coke deposition and partial dissolution of the zeolite framework of Ti-MWW during ammoximation. The deactivated Ti-MWW catalyst was regenerated effectively by a combination of acid treatment and cyclic amine-assisted structural rearrangement.

Ethanol-assistant synthesis of TS-1 containing no extra-framework Ti species

Titanium silicate-1 (TS-1) was synthesized via three different procedures, respectively, using tetraethylorthosilicate (TEOS) and tetrabutyl orthotitanate (TBOT) as Si and Ti sources and tetrapropylammonium hydroxide (TPAOH) as template. In the procedures A and B, ethanol and isopropanol were respectively employed as the solvents of TBOT and were remained all through the hydrothermal crystallization of TS-1. In the procedure C, isopropanol was also employed as the solvent of TBOT but was evaporated before the crystallization step. The TS-1 specimens synthesized via the three procedures were characterized by means of XRD, FT-IR, DRS UV–vis, SEM, N 2-physisorption and NH 3-TPD. It was shown that, the contents of framework Ti species in the TS-1 basing on the procedures A and C were comparable, being both larger than that basing on the procedure B. Extra-framework Ti, anatase, was absent in the TS-1 basing on the procedure A but present in the TS-1 basing on the procedures B and C, with its content being larger for the procedure B than for the procedure C. The extra-framework Ti might disperse highly both on the surfaces and in the micropores of TS-1. The framework Ti contributed the weak acid sites and the extra-framework Ti the strong acid sites of TS-1. The catalytic performance for the ammoximation of cyclohexanone over the TS-1 synthesized via various procedures was evaluated and the yield of cyclohexanone–oxime was found to follow an order procedure A > procedure C > procedure B. It was concluded that the TS-1 with a large content of framework Ti but without anatase, exhibiting high catalytic performance, could be effectively synthesized by the employment of ethanol.

Hydrophobic Modification of Ti-Containing Zeolite (TS-1) and Their Applications in Liquid-Phase Selective Catalytic Reactions

Abstract Hydrophobic modification of Ti-containing zeolite (TS-1) was performed by using triethoxyfluorosilane (TEFS). TS-1 after modification with TEFS (w = 1%) showed higher catalytic activity for the ammoximation of cyclohexanone than those on unmodified and modified TS-1 with TEFS (w = 5%) due to effective modification without covering the underlying catalytically active Ti-oxide species.

Studies on the liquid-phase ammoximation of cyclohexanone over a titanium silicate sieve using on-line ATR–FTIR spectroscopy

The liquid-phase ammoximation of cyclohexanone over a titanium silicate sieve is followed in real time using on-line ATR–FTIR spectroscopy. We have discovered the formation and the vanishment of an intermediate during the reaction with the aid of on-line ATR–FTIR spectroscopy. A new possible reaction mechanism is proposed according to the experimental results. Hydrogen peroxide is firstly adsorbed on titanium silicate sieves, forming a complex peroxidic species of titanium, which can react with cyclohexanone to form an intermediate. Then the intermediate reacts with ammonia to give cyclohexanone oxime. The infrared spectra indicate that the intermediate has strong absorption of C–O bond.

Hyperplane Intercept Vector Calibration Method in Grey Analytical Systems

A novel vector calibration method, hyperplane intercept, is proposed for grey analytical systems to resolve the concentrations of the chemical components from the multi-component data gained from attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. This method is capable of quantifying a particular component known to be present in the mixture without having to know the identity of the rest of the components. Through the target factor analysis (TFA), a section of the IR spectrum of the interested component is chosen to calculate the concentration by the proposed hyperplane intercept method. Results calculated from on-line ATR-FTIR spectroscopy data of cyclohexanone ammoximation process are used to illustrate the simplicity and efficiency of this proposed method.

Catalytic Activity of Clay-Based Titanium Silicalite-1 Composite in Cyclohexanone Ammoximation

Following the recent report on the synthesis of a clay-based titanium silicalite-1 (TS-1) composite, this work provided important information on the catalytic activity of the catalyst developed for cyclohexanone ammoximation. Experimental works showed that the optimum molar ratio of cyclohexanone:H2O2:NH3 was 1:1.6:2.5. It was found that the cyclohexanone ammoximation over the clay-based catalytic composite gave the highest oxime yield when H2O2 and NH3 was continuously added and was evenly distributed in 5 doses, respectively, to the reaction mixture. The external and internal diffusions can be eliminated by using a water:t-butanol mixture as a solvent, with sufficiently fast agitation speed and having TS-1 crystal with size smaller than 500 nm. On the basis of the adsorption studies and the spectroscopic evidence, the mechanism of the cyclohexanone ammoximation over the catalyst developed are suggested to follow Langmuir−Hinshelwood and Eley−Rideal kinetics. The data acquired in this study is particular...

Adding Microsized Silica Particles to the Catalysis/Ultrafiltration System: Catalyst Dissolution Inhibition and Flux Enhancement

A system combining catalytic reaction with crossflow ultrafiltration (UF) was used to catalytic ammoximation of cyclohexanone to the oxime over titanium silicalite-1 (TS-1) catalysts. The effect of...

The Fouling Mechanism of Ceramic Membranes Used for Recovering TS-1 Catalysts

Ceramic ultrafiltration membranes were used to separate titanium silicalite-1 (TS-1) catalysts from theslurry of catalytic ammoximation of cyclohexanone to oxime. Silica was shown to have a great effect on membrane fouling in the alkaline environment of this system. In the ammoximation system, there are three main silica sources, which are residual silica on the catalyst particles surface during preparation, silica dissolved from TS-1 catalyst particles by ammonia solvent, and silica sol added into the reaction slurry to inhibit the dissolution erosion of the TS-1catalyst. The silica dissolved by ammonia has been proved to influence membrane fouling most among the three silica sources. This was because the amount of silica dissolved by ammonia was the largest, and the polymerizationof silica monomers at high concentration caused colloid particles formation, which led to a dense cake layer depositing on the membrane surface. Meanwhile, the size reduction of catalyst particles caused by alkaline dissolution also increased specific resistances of cake layers.

A heterostructured titanium silicalite-1 catalytic composite for cyclohexanone ammoximation

Submicron-sized titanium silicalite-1 is difficult to recover in industrial process because of their fineness and rapid decrease in catalytic activity due to particle agglomeration. To solve these problems, we present a heterostructured titanium silicalite-1 (TS-1) catalytic composite using bentonite clay as the catalyst support. The catalytic composite is synthesized by hydrothermal treatment which directly crystallizes TS-1 on the bentonite clay surface. The synthesized composite has been characterized using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TS-1 crystals have been found on and between the layers of the bentonite with strong attachment. Characterizations suggest that crystallization temperature of 175 °C is the optimum hydrothermal temperature to produce TS-1 on the bentonite support with characteristics necessary to promote selective catalytic reactions. It is found that prolonged crystallization duration does not necessarily increase the crystallinity of TS-1 on the bentonite surface. The heterostructured composite is able to maintain high conversion of cyclohexanone (97%) and oxime selectivity (83%) after three reaction cycles which is contrary to the unsupported TS-1 that shows apparent decrease in activity (>10%), especially in the selectivity to oxime. The synthesized composite also has significant improvement in separation efficiency with respect to the unsupported catalytic system. Therefore, we conclude that the heterostructured TS-1 composite is a promising catalytic material for cyclohexanone ammoximation and potentially for other TS-1 related processes where catalyst recovery and reuse are required.

Vanadium resin as an efficient catalyst for the liquid phase ammoximation of cyclic ketones

A new vanadium resin catalyst has been prepared through ion exchange at the cationic sites of Amberlite IR 120 resin. This vanadium-loaded resin is characterized by using AAS, UV–vis, FTIR and EPR spectroscopic tools. Ammoximation of cyclic ketones e.g. cyclohexanone, cyclooctanone and cyclododecanone in the presence of aqueous hydrogen peroxide and ammonia have been carried out under eco-friendly liquid phase conditions over this vanadium resin at 333 K. Interestingly, for ammoximation of cyclohexanone the progress of the reaction could be visually monitored from the change in color of the catalyst during the reactions; after the consumption of H 2O 2 the orange catalyst returns back to its original green color. For all the cyclic ketones corresponding oximes are obtained as major products with moderately high yields. The new catalytic system described herein is an efficient and eco-friendly method for the ammoximation of bulky cyclic ketones, with the advantages of good conversion and selectivity, devoid of hazardous solvents and byproducts.

Enhancement in microporosity and catalytic activity on grafting silica and organosilica moieties in lamellar titanium phosphate framework

New silica-grafted analogs of lamellar semicrystalline titanium phosphate (sc-TiOP), silicotitanium phosphate (STP) and organic–inorganic hybrid silicotitanium phosphate (HSTP) have been synthesized under hydrothermal condition without the assistance of any template or structure-directing agent under acidic pH conditions. These materials were characterized by elemental analysis, powder XRD, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), N2 sorption and spectroscopic studies. N2 adsorption studies revealed that the surface area increased significantly when the Si atoms were incorporated into the layered titanium phosphate framework. The surface area improves further with the grafting of organosilane moiety in HSTP material. Fourier-transformed infrared (FT IR), UV–vis and X-ray photoelectron spectroscopic (XPS) results suggested the presence of Si–O–P, Ti–O–Si bonds and octahedral coordination of Ti(IV) in these novel microporous materials. Si- and Si–CH2CH2–Si-grafted materials showed considerable enhancement in catalytic activity towards the liquid phase partial oxidation of styrene, α-methyl styrene, cyclohexene and acrylic acid using dilute H2O2 as an oxidant. These materials also showed excellent catalytic activity and selectivity in ammoximation of cyclohexanone to cyclohexanone oxime in the presence of aqueous ammonia and dilute aqueous H2O2 with reference to the silica-free sc-TiOP analogue.

Green catalysis by microwave synthesized nanostructured materials

MFI type zeolite with incorporated titanium and/or aluminum was successfully prepared by microwave method. MFI type zeolite with incorporated titanium (NSTS-1) which was prepared by microwave had the stacking morphology whereas MFI type zeolite incorporated with titanium and aluminum (NSAlTS-1) gave stacked morphology with arrayed structure. UV–vis spectra and 27Al-MAS-NMR revealed that Ti and/or Al species were incorporated in tetrahedral position. The NSTS-1 catalyst exhibited an enhanced catalytic activity in the epoxidation of 1-dodecene compared with the conventional TS-1 catalyst. The NSAlTS-1 had two catalytic active sites which could carry out both ammoximation of cyclohexanone and Beckmann rearrangement of cyclohexanone oxime, simultaneously.

Fouling and regeneration of ceramic membranes used in recovering titanium silicalite-1 catalysts

Ceramic ultrafiltration (UF) membranes were used to separate titanium silicalite-1 (TS-1) catalysts from slurry in catalytic ammoximation of cyclohexanone to the oxime. Both the fouling mechanisms and the regeneration of fouled membranes were studied. The fouling was mainly caused by TS-1 particles deposition, silica additive adsorption and iron precipitation. The interaction between the two solutes in the system, silica additive and TS-1 catalysts, played a significant role in the formation of dense cake layers at the membrane surface, leading to a greater flux decline during ultrafiltration of TS-1 particles. Estimation of hydrodynamic forces acting on a single particle shows crossflow velocity (CFV) has an important effect on the deposition of TS-1 particles. However, after particles have deposited, increasing CFV will not resuspend them due to the strong and dense cake layer formation. The cleaning of a fouled membrane can be achieved by sequential use of strongly basic and acidic solutions. In addition, a particle-cleaning method was applied. Micro-sized alumina particles were used for their scouring effect to remove the cake layer from the membrane surface effectively. The particle cleaning combined with acid cleaning was effective to fully restore membrane flux.

Ammoximation of cyclohexanone over nanoporous TS-1 using UHP as an oxidant

Abstract Ammoximation of cyclohexanone to cyclohexanone oxime has been carried out using ammonia and urea hydrogen peroxide adducts as the oximation reagents. Effect of catalyst concentration, temperature, and molar ratio of reactants and effect of doping TS-1 with Fe has been studied to obtain the optimum conversion of cyclohexanone (CH) and selectivity to cyclohexanone oxime. The catalyst has been characterized employing the techniques of XRD, FT-IR, EDAX, SEM, AAS and Mossbauer spectroscopy with a view to confirm phase purity, stoichiometry, particle size distribution and oxidation state of Fe. The BET surface area of TS-1 catalyst was found to be 680 m2/g. A maximum conversion of about 70% of cyclohexanone with cyclohexanone oxime selectivity of 99.72% was obtained over TS-1 doped with Fe at a temperature of 40 °C and cyclohexanone to UHP molar ratio of 1:1. Reaction seems to proceed through a redox mechanism and follow hydroxylamine as well as imine routes. According to hydroxylamine route ammonia and UHP react within the TS-1 pores and produce hydroxylamine. The hydroxylamine thus formed reacts with cyclohexanone outside the pores to produce cyclohexanone oxime. In the imine route cyclohexanone and ammonia react to produce cyclohexanone imine, which is oxidized to cyclohexanone oxime. A tentative mechanism for the process has been proposed.

Coke deposition and characterization on titanium silicalite-1 catalyst in cyclohexanone ammoximation

In this work, the changes of catalytic activity, as well as the main deactivation mode were investigated on a commercial titanium silicalite-1 (TS-1) catalyst under simulated industrial conditions in continuous tank slurry reactor. The conclusions about deactivation behavior have been achieved based on the changes of activity, conversion and selectivity. XRD and FTIR analyses indicate the MFI framework structure of zeolite cannot be changed evidently during the reaction. It is found by comparative experiments that the main reason for catalyst deactivation is coke formation on the surface of TS-1. Results from TGA-DTA, N 2 adsorption and pyridine TPD analyses of used catalysts demonstrate there are two types of coke deposited mainly on micropores. Soft coke is located near Ti sites and can be removed by oxidation under 350 °C, while refractory coke can be oxidized by air until 700 °C. Analysis results of GC–MS for soluble coke and NMR, FTIR spectra for insoluble coke indicate that N-containing polycyclic aromatic and/or polyalkene species are the main components of coke deposits.