Liquid-phase Oxidation Of Hydrocarbons Research Articles

Liquid Phase Oxidation of Hydrocarbons to High-Value Chemicals in Microfluidic Reactors - Prospects and Challenges.

Liquid phase oxidation (LPO) of hydrocarbon is an industrially important process to produce petrochemicals and pharmaceuticals. It follows a free radical path having initiation, propagation and termination. The initiation step is slow while the propagation and termination steps are fast. The main challenge of such process is to control product selectivity at an appreciable conversion level. With the advancement of microfluidic reactor technology, it is possible to control the free radical steps. The present contribution critically reviewed the reaction engineering aspects of LPO of hydrocarbon, the influence of microfluidic reactor design and operation on reaction mechanism, conversion and product selectivity. It also outlines the challenges associated with microfluidic reactor operation, and prospects to apply the understanding from microfluidic reactors in few sectors. The understanding from the free radical oxidation process can also be applied to any other free radical processes.

Amorphous Porous Chromium‐Zirconium Bimetallic Phosphate: Synthesis, Characterization and Application in Liquid Phase Oxidation of Hydrocarbons by Different Oxygen Sources

AbstractCr−Zr bimetallic phosphates catalysts were prepared by sol‐gel method and used in the oxidation of cyclohexane, ethylbenzene and cyclohexene, respectively. The catalysts were characterized by a variety of analytical techniques. The results show that chromium ions enter the framework of mesoporous zirconium phosphate, Cr−Zr phosphates catalysts with molar ratio of Cr: Zr=2 (CrZr2P) or Cr: Zr=1 (CrZrP) still retain the mesoporous structure and form composite metal phosphates. Two active centers‐ redox (Cr6+) and acidic sites in these bimetallic phosphates play a synergistic catalytic role in the oxidation of C−H bond. Catalytic activity is closely related to the amount of acid or acid strength, the C=O product selectivity depends on the amount and high dispersion of Cr6+ species. Acidic sites and redox sites are affected by different molar ratios of chromium/ zirconium. Among the Cr−Zr phosphates catalysts, CrZr2P and CrZrP catalysts show excellent activity, just because the formation of mesoporous structure leads to the uniform dispersion of acidic and redox sites.

Carbon nanotubes catalysis in liquid-phase aerobic oxidation of hydrocarbons: Influence of nanotube impurities

Pure carbon nanotubes (CNTs) have a high electron affinity and as such are able to actively absorb free radicals. This functional feature of CNTs leads to a linear chain breakage with the formation of inert spin adducts and effective inhibition of the oxidation process. However, there is a clear contradiction in this issue in the literature with the analysis of research results indicating that CNTs exhibit antioxidant activity mainly in polymeric materials, under conditions of diffusional restrictions for oxygen access. While, in the liquid-phase oxidation of hydrocarbons by CNTs (CNTs synthesised by the thermal catalytic pyrolysis of carbon-containing raw materials (CVD-process)), the CNTs enhance catalytic processes. In this study the aerobic liquid phase oxidation of cumene and initiated (by azobisisobutyronitrile) at low-temperature (333 K) in the presence of multi-walled carbon nanotubes (MWCNTs) obtained by thermal catalytic pyrolysis of cyclohexane (catalyst-ferrocene) has been undertaken. Kinetic analysis establishes that the catalysis of the oxidation process is associated with the presence of metal compounds in the structure of the MWCNTs. These metals are residues of metal catalysts remaining in the synthesis and in the process of pyrolysis. The metals are converted, as a rule, into metal carbides and are not easily removable by treatment with mineral acids. Thus, in the presence of metals in the composition of MWCNTs, interfering parallel reactions are observed with two processes running in parallel — MWCNTs + R• (RO2 •) → •MWCNTs-R (RO2) and ROOH + M @ MWCNTs → RO• radicals (RO2•). The branching of the chain processes involving hydroperoxides suppresses the route of attachment of alkyl and peroxide radicals to the carbon cage structure of the nanotubes and the reaction proceeds in an autocatalytic mode. Contradictory conclusions regarding the effect of CNTs on the chain processes in the oxidation of organic substances (hydrocarbons, polymers) that exist in the literature are attributed to the lack of control over the presence and nature of the metal containing impurities in the CNTs.

Liquid Phase Oxidation and the Use of Heterogeneous Catalysts – A Critical Overview

AbstractNumerous homogeneous catalyst‐initiator systems are known and utilized in industrial scale to conduct various autoxidation processes. The reaction mechanism and kinetic details of homogeneous liquid phase autoxidation have been extensively investigated. This article presents an overview on the state of the art of heterogeneous catalyst‐initiator systems in the liquid phase oxidation of hydrocarbons. Mechanistic insights and limitations of the heterogeneous catalyst‐initiator systems are discussed. The potentials and challenges towards an industrial application are evaluated.

Antioxidant activity of humic acids in radical-chain oxidation processes

The behavior of humic acids in radical-chain oxidation processes was examined by the gas-volumetric method using model hydrocarbons (cumene and ethylbenzene). It was shown that the liquid-phase oxidation of hydrocarbons is inhibited in the presence of humic acids. The hydrocarbon oxidation rate depends on the humic acid concentration. Owing to pronounced inhibitory properties, humic acids can be considered as promising natural antioxidants for biomedical and technical (antioxidants for liquid fuels and oils) applications.

The stability of autocatalytic processes. The kinetics of oxidation of hydrocarbons

The use of the theory of stability in an analysis of complex chemical systems was illustrated for the example of particular chemical reactions. Stability for the known models of chain reactions, nonchain autocatalytic processes, and the kinetics of liquid-phase oxidation of hydrocarbons was considered using a unified approach.

Some peculiarities of the photocatalytic oxidation of hydrocarbons by hydrogen peroxide on a heterogeneous catalyst: Titanium silicalite

Data on the effect of the type and intensity of irradiation on the basic characteristics of the process and distribution of products of catalytic liquid-phase oxidation of hydrocarbons were obtained using as an example the oxidation of n-dodecane by hydrogen peroxide aqueous solutions on the heterogeneous catalyst: titanium silicalite.

Effect of Template Removal Methods on Physical Properties and Catalytic Performance of Co-HMS

With Co(OAc)2 as Co source and hexadecylamine (HDA) as template, cobalt-containing hexagonal mesoporous silicas (Co-HMS) was successfully synthesized by a one-step co-condensation route at ambient temperature. Two different methods (calcination and solvent extraction) were separately utilized to remove the template molecules, and the effects on physical properties and application performance were studied in detail using the characterization of XRD, N2 adsorption-desorption, TEM, FT-IR, UV-vis diffuse reflectance techniques and catalytic activity measurement, respectively. The results showed that solvent extraction was more favorable for mesoporous structure maintaining. And in the liquid-phase oxidation of hydrocarbons, higher activities were obtained with Co-HMS-E being used.

Effect of surfactants on liquid-phase oxidation of hydrocarbons and lipids

A review is presented compiling new data on liquid-phase oxidation of hydrocarbons and plant oils in microheterogeneous environment formed by the addition of surfactants. Cationic surfactants catalyze the decomposition of the primary oxidation products, hydroperoxides, into free radicals thus accelerating the oxidation process. Anionic surfactants catalyze the heterolystic decomposition of hydroperoxides and therefore are excellent antioxidants for ethylbenzene, cumene, and other alkylaromatic hydrocarbons.

05/00889 Modeling the liquid-phase oxidation of hydrocarbons over a range of temperatures and dissolved oxygen concentrations with pseudo-detailed chemical kinetics

05/00889 Modeling the liquid-phase oxidation of hydrocarbons over a range of temperatures and dissolved oxygen concentrations with pseudo-detailed chemical kinetics

Polyfunctional Activity of Metal Complexes Containing 2,6‐Di‐tert‐butylphenol in Catalytic Oxidation

AbstractFor Abstract see ChemInform Abstract in Full Text.

BiO x clusters occluded in a ZSM-5 matrix: preparation, characterization, and catalytic behavior in liquid-phase oxidation of hydrocarbons

A series of Bi-ZSM-5 containing 4.26, 5.54, and 6.64 wt% bismuth oxide was prepared by introducing Bi during ZSM-5 synthesis. For comparison, 5 wt% Bi (expressed as bismuth oxide)-impregnated ZSM-5 samples were also prepared. These samples were characterized by N 2 adsorption–desorption isotherms at 77 K, XRD, XPS, IR spectroscopy in the lattice vibration range and in the presence of chemisorbed pyridine and CO 2 and EXAFS. The characterization data confirmed the occlusion of bismuth oxide clusters in the zeolite pores. An intrinsic acidity due to bismuth oxide clusters was evidenced. This consisted, on one hand, in weak Lewis acid sites, ascribed to coordinatively unsaturated bismuth cations, and, on the other hand, in strong Brönsted acid sites, attributed to boundary Bi⋯OSi linkages. These catalysts were tested in the liquid-phase oxidation of benzene, toluene, and cyclohexane using hydrogen peroxide as oxidizing agent. The results showed that Bi-ZSM-5 catalysts are more active than the reported titanium silicalites, but the efficiency of H 2O 2 use was quite small, an important part of this being nonselectively decomposed. A good selectivity was observed in cyclohexane oxidation.

Investigation of the catalytic behavior of ion-pair complexes of vanadium(V) in the liquid-phase oxidation of hydrocarbons with molecular O 2

Ion-pair complexes of decavanadate were prepared with different cationic phase-transfer catalysts (PTCs) and their catalytic behavior was investigated in the oxidations of tetralin and cyclohexene with molecular O 2. It was found that both the PTCs themselves and their ion-pair complexes enhanced the rate of oxidation. The catalytic activities of both the PTCs and their ion-pair complexes depend strongly on their concentrations. At low concentrations (<10 −3 M), the PTCs themselves (in the form of spherical inverse micelles) proved to be the more active but at higher concentrations where the growing micelles are transformed into a more open layer structure, the ion-pair complexes exerted the higher catalytic activities. At concentrations near 0.1 M the efficiencies of both types of catalysts decreased because the layers start to transform into a more closed micellar structure. The structure of the micelles is also influenced by the pH of the aqueous phase used during the preparation of the catalyst solutions.

Selective and efficient hydrocarbon oxidation in a packed bed membrane reactor

The liquid phase hydrocarbon oxidation is studied in a packed bed membrane reactor. A mathematical model is developed, reaction simulations are performed and interpreted using the conversion, organic peroxide efficiency and oxidation product separation factor. The influence of several process parameters, such as space time, overall membrane mass transfer coefficient and aqueous-organic phase distribution coefficient is investigated. A substantial increase in organic peroxide efficiency was observed in the packed bed membrane reactor configuration as compared to a conventional packed bed reactor.

Macrokinetics of initial stages of liquid-phase oxidation of hydrocarbons by nitric acid

The influence of mass transfer on the rates of initial stages of liquid-phase oxidation of hydrocarbons by nitric acid was analyzed. The parameters of the diffusion-controlled nearsurface regime were determined.

Clean catalytic technology for liquid phase hydrocarbon oxidation

Liquid phase hydrocarbon oxidation is one of the principal routes towards industrial organic chemicals. However, low product selectivity and associated by-product formation are major problems in several oxidation processes. As a result of the increasingly stringent environmental regulations, the development of oxidation catalysts has been a major challenge in the last decade. An overview of novel selective and clean oxidation catalysts and processes is presented.

Vanadium(IV) complexes with picolinic acids in NaY zeolite cages Synthesis, characterization and catalytic behaviour

Encapsulated vanadium picolinic complexes have been synthesized by treatment of a dehydrated form of VO2+-NaY zeolite with molten picolinic acids and characterized by X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), EPR, FTIR and UV–VIS spectroscopies, and XRD. It was suggested by XRD and XPS that the complexes were located in the zeolite cavities. Differences in the spectroscopic properties of encapsulated and impregnated samples were explained in terms of coordination of vanadium complexes with zeolite –OH groups. The stability of VO(pic)2 and its adduct with pyridine depended strongly on the complex location. The encapsulated vanadium picolinate complex retained solution-like activity in the liquid-phase oxidation of hydrocarbons and alcohols with hydrogen peroxide.

Catalytic Oxidation of Ethylbenzene to Acetophenone Using Alumina-Supported Dichromate: Process Optimisation and Development of a Continuous Process

Potassium dichromate supported on neutral alumina is a heterogeneous catalyst for the liquid phase oxidation of hydrocarbons. The material has been used to catalyse the oxidation of ethylbenzene to acetophenone using air as the consumable oxidant with high selectivity and is truly catalytic in the metal, unlike homogeneous Cr(VI) systems. Optimisation of reaction conditions has been achieved in terms of air flow rate, agitator speed, and catalyst quantity. An induction period prior to achievement of maximum catalytic turnover, which is proportional to both temperature and the concentration of catalyst, may be reduced by doping the substrate with 5−15% acetophenone (w/w) and eliminated by doping with 30% (w/w) acetophenone. A rate of conversion of ca. 3.8% h-1 (0.39 turnover s-1) may be achieved at a reaction temperature of 130 °C for a period of ca. 10 h before catalyst deactivation occurs. However, this rate may be maintained for periods in excess of 24 h by continuous addition of substrate to the reacti...

Liquid-phase oxidation of hydrocarbons in the presence of different types of phase-transfer reagents

The autoxidation of cyclohexene, tetralin and cumene was investigated in the presence of non-ionic, anionic and cationic surfactants and it was found that all three types of phase-transfer reagents are able to influence the rate of oxidation. If their HLB values are not too low (> 3) or not too high (< 15) all the non-ionic surfactants increase the rate of oxidation, otherwise they exert a slight inhibitory effect. If present in acid form, anionic surfactants all increase the rate of oxidation, while their Na-salts slightly inhibit the oxidation. Cationic surfactants all increase the autoxidation rate, but their catalytic efficiencies depend strongly on the experimental conditions. It was shown that the phosphonium ion-type surfactants are quickly oxidized by hydroperoxide present, but their catalytic and phase-transfer capabilities are not detectably reduced. In biphasic systems, the catalytic activities of cationic surfactants are strongly reduced by the presence of water as a separate phase. Light scattering measurements demonstrated that all three types of surfactants are prone to self-association when their concentrations are increased, and this limits their influence on the rate of oxidation. The oxidation rate is strongly reduced when non-ionizing but strongly solvating solvents are simultaneously applied in the reaction mixture. The rate-diminishing effect seems to correlate with the sequence of solvating ability of the solvents. It was pointed out that the presence of hydroperoxide is essential for the PTC-catalyzed oxidation of hydrocarbons. It is thought that the cationic and the anionic surfactants interact with the more nucleophilic (the inner one) and the more electrophilic (the outer one) O-atom of hydroperoxide, respectively, whereby homolysis of the OO bond is facilitated. The non-ionic surfactants exert their rate-influencing effects through H-bond formation. In the PTC-catalyzed oxidation of hydrocarbons, the rate changes linearly only in a narrow range of PTC, hydroperoxide and substrate concentrations, and consequently the turnover number is not suitable to characterize the oxidation.

Catalysis and Inhibition by Water during the Liquid-Phase Oxidation of Hydrocarbons

In the abundant literature on the liquid-phase of hydrocarbons by dioxygen, many references can be found to the rate-influencing role of water (formed or added during the oxidation). Most of them relate to the inhibitory effect of water then present in high excess. For example, it has been reported that the autoxidation of different alkylbenzenes and [alpha]-phenylcarbinols is entirely prevented by an excess of water. On the other hand, it has also been stated that, of the polar molecules, water is able to form H-bonds with inhibitors such as phenols and aromatic amines; the inhibiting group is then blocked and the H-bonded inhibitor molecules do not react with the peroxy radicals. The inhibitory activity is therefore diminished, and the overall rate of the inhibited reaction will be increased by the presence of water. No references are in the literature with respect to real catalysis by water in the liquid-phase oxidation of hydrocarbons in the absence of metal ions. In the presence of metal ions, however, water may exert a rate-influencing effect, but this is always connected with the formation of aquo and hydroxo complexes, i.e., the catalytic species is modified. In this paper, the authors present examples to show thatmore » water is a real catalyst when applied in small quantities during the oxidation of hydrocarbons with dioxygen. 8 refs., 1 fig., 2 tabs.« less