Oxidation Of N-butane Research Articles

The mechanisms of oxidation and combustion of normal alkane hydrocarbons: The transition from C1–C3 to C4H10

The known detailed mechanisms of oxidation of the higher hydrocarbons include hundreds of particles and thousands of reactions. In spite of their merits, the use of such mechanisms for solving applied problems of the gas dynamics of combustion is impeded at present because of great computational expenditures. We suggest a compact kinetic mechanism of the oxidation of n-butane including the main processes and intermediate and final reaction products. The mechanism can be classified as a nonempirical detailed mechanism, because all its elementary reactions are kinetically substantiated. The mechanism does not contain reactions of the double addition of oxygen and intermediate species in the form of isomeric compounds and their derivatives. The calculation results are compared with the experimental data on the oxidation, self-ignition, and combustion of n-butane.

N-Butane Oxidation over γ-Al 2O 3 Supported Vanadium Phosphate Catalysts

Four vanadium phosphate catalysts supported on γ-Al 2O 3 (20 wt%) were synthesized via wetness impregnation of VOHPO 4·0.5H 2O precursor and calcined for different durations (6, 10, 30 and 75 h) at 673 K in a reaction flow of n-butane/air mixture. The samples calcined for 6 and 10 h produced only a single phase of (VO) 2P 2O 7. However, the VOPO 4 phase (β-VOPO 4) was detected and became more prominent with only a minor pyrophosphate peaks were found after 30 h of calcination. All these pyrophosphate peaks disappeared after 75 h of calcination. The formation of V 5+ phase was also observed in the SEM micrographs. The redox properties and the nature of oxidants of the catalysts employed in this study were investigated by H 2-TPR analysis. Selective oxidation of n-butane to maleic anhydride (MA) over these catalysts shows that the percentage of n-butane conversion decreases with the transformation of the catalysts from V 4+ to V 5+ phases. An appropriate ratio of V 5+/V 4+ can enhance the performance of the VPO catalyst. However, a higher amount of V 5+ and its associated oxygen species are responsible to promote the MA selectivity.

Selective oxidation of n-butane over nanosized crystallites of (VO) 2P 2O 7 synthesized by an exfoliation–reduction process of VOPO 4⋅2H 2O in a mixture of 2-butanol and ethanol

Intercalation, exfoliation, and reduction of VOPO 4⋅2H 2O were conducted in 2-butanol alone and in a mixed-alcohol solvent (2-butanol and ethanol). Whereas both processes produced crystallites of pure VOHPO 4⋅0.5H 2O, much smaller and thinner crystallites (average size, 340 × 35 nm) were formed in the mixed alcohol compared with 2-butanol alone (average size 950 × 200 nm). The small, thin crystallites of precursor VOHPO 4⋅0.5H 2O could be transformed into sharply angular nanosized crystallites (60 nm long and 31 nm thick) of highly crystalline (VO) 2P 2O 7, without mesopores. When used as a catalyst, this compound exhibited higher activity and selectivity to maleic anhydride (75% at 80% conversion) for selective oxidation of n-butane compared with that derived from the precursor prepared in 2-butanol alone. The high activity of the nanosized crystallites of (VO) 2P 2O 7 is attributed to their large surface area (40 m 2 g −1), which is due to their smaller dimensions, and their high selectivity may be attributed to the lack of mesopores as well as their highly crystalline state.

VIIIVIV3O3(PO4)3: A Novel Vanadium Phosphate for Selective Oxidation of Light Hydrocarbons

A novel vanadium(IV) phosphate VIIIVIV3O3(PO4)3 has been synthesized and crystallized (1073 K, sealed silica tube, a few milligrams of PtCl2 as mineralizer). According to the single-crystal structure analysis [orthorhombic, F2dd (No. 63), Z = 24, a = 7.2596(8) A, b = 21.786(2) A, c = 38.904(4) A (lattice parameters from Guinier photographs), R1 = 0.032, wR2 = 0.067, κ-CCD diffractometer, 83 949 reflections measured, 6836 independent, 5986 with I > 2σ(I), 299 variables], VIIIVIV3O3(PO4)3 belongs to the Lipscombite/Lazulite structure family. At 1073 K VIIIVIV3O3(PO4)3 is in thermodynamic equilibrium with (VO)2P2O7, VO2, and VPO4. Substitution of V3+ in VIIIVIV3O3(PO4)3 by Cr3+ and Fe3+ is possible. Like vanadylpyrophosphate the oxide phosphates MIIIVIV3O3(PO4)3 (MIII: V, Cr, Fe) show significant catalytic activity in selective oxidation of n-butane and 1-butene to maleic acid anhydride.

Preparation of Vanadium Phosphate Catalysts from VOPO4 · 2H2O: Effect of Microwave Irradiation on Morphology and Catalytic Property

The present work addresses the influence of microwave irradiation on undoped and doped vanadium phosphate catalysts. These catalysts were prepared via VOPO4 · 2H2O. The catalyst’s precursors‚ VOHPO4 · 0.5H2O were subjected to microwave irradiation and comparison was made with the conventional heating. The interaction of these complex materials with microwave and the addition of several doponts (Nb, Bi, Co, Mo) provide interesting improvements in catalyst preparation found to be a faster, develop higher surface area, higher activity and selectivity for the oxidation of n-butane to maleic anhydride. All the catalysts were characterized by using a combination of powder XRD, H2-TPR, BET surface area and SEM.

Oxidation of organic compounds in a microstructured catalytic reactor

A microstructured catalytic reactor for the oxidation of organic compounds has been fabricated from aluminum alloy AlMgSiCu1 (6082 series, Al51st). The catalyst section was assembled of 63 microstructured plates with catalytic coating. In each plate of 416m thickness, 45 semicylindrical microchannels of 208m in radius with a distance in between of 150m were electrodischarge machined. A porous alumina layer of 29 ± 1m thickness was produced on the plates by anodic oxidation. The resulting coatings were impregnated with an aqueous solution of copper dichromate followed by drying and calcination at 450 ◦ C to produce active catalysts. Kinetics of deep oxidation of organic compounds n-butane, ethanol, and isopropanol was studied in the reactor at 150–360 ◦ C and of 1,1-dimethylhydrazine (unsymmetrical dimethylhydrazine, UDMH) at 200–375 ◦ C. Intermediate reaction products in the reactions of alcohols and UDMH oxidation were identified. For UDMH, these are methane, dimethylamine, formaldehyde 1,1-dimethylhydrazone, and 1,2-dimethyldiazene. Nitrogen atoms from the UDMH and N-containing intermediates were shown to convert mainly to N2. Kinetic parameters of the reactions of n-butane and alcohols (rate constants and apparent activation energies) were calculated using kinetic modeling based on a modified method of quickest descent. © 2007 Elsevier B.V. All rights reserved.

Selective oxidation of n-butane over MoV-containing oxidic bronze catalysts

MoV-containing oxidic bronze catalysts were synthesized, characterized, and tested in the selective oxidation of n-butane. For comparison, an activated V–P–O catalyst was also studied. The catalytic behavior of MoV-containing catalysts was found to be dependent on both the catalyst composition and the nature of crystalline phases. In this way, the M1 phase (i.e., Te 2M 20O 57 and (SbO) 2M 20O 56 in Te- and Sb-containing catalysts, respectively) is proposed as an active and selective crystalline phase for n-butane oxidation on these catalysts. The selectivity to maleic anhydride/acid obtained on MoV-catalysts follows the order: MoVTeNbO > MoVTeO = MoVSbNbO > MoVSbO > MoVNbO. Although less selective than a vanadium phosphorous catalyst, a higher productivity to MA is obtained over a MoVTeNbO mixed oxide catalyst as a consequence of its remarkably superior catalytic activity. Moreover, the amount of maleic anhydride obtained on oxidic bronze catalysts strongly depends on the composition of the feed. In addition, the nature of active sites, the reaction network for n-butane oxidation, and a comparison of their catalytic performance in the oxidation of C 2–C 4 alkanes are discussed.

Real‐Time Control of a Catalytic Solid in a Fixed‐Bed Reactor Based on In Situ Spectroscopy

A reality check: Reactor control by online spectroscopy is illustrated for a Cr/Al2O3 alkane dehydrogenation catalyst and a vanadium phosphorus oxide catalyst used in the selective oxidation of n-butane to maleic anhydride. Rather than testing the product composition alone, the methodology monitors the state of the catalyst in the reactor, and changes the reaction conditions to keep the catalyst in its optimal state (see picture).

Modeling of n-butane ignition, combustion, and preflame oxidation in the 20-l vessel

The objective of the study reported herein is to simulate various physical and chemical phenomena accompanying fuel-rich n-butane–oxygen mixture preparation, ignition, preflame oxidation, and combustion in the standard 20-l explosion vessel, by applying mathematical models. Based on the computational fluid dynamics (CFD) simulations of the mixing process and natural convection of the ignition kernel, as well as on the analysis of the detailed reaction mechanism of n-butane oxidation, laminar flame propagation, and self-ignition, possible explanations for the phenomena observed experimentally have been suggested. The results of the study indicate that seemingly inflammable mixtures can become hazardous depending on the mixture preparation procedure and forced ignition timing.

VPO catalysts supported on H 3PO 4-treated ZrO 2 highly active for n-butane oxidation

VPO catalysts supported on ZrO 2 and H 3PO 4-treated ZrO 2 were prepared for the first time by means of precipitation–deposition in an organic medium. The physicochemical properties of the catalysts were investigated by the BET, XRD, TEM, Raman, XPS, and H 2-TPR techniques. It was found that the way of H 3PO 4 treatment conducted on ZrO 2 has a significant effect on the nature of the support, as well as on the state and structure of the VPO component loaded on it. The discrepancies in the synergistic interaction between VPO and the different supports induce variation in catalytic performance. The change in VPO loading is found to have an effect on catalyst efficiency. At 673 K, the MA yield is 61 mol% over the 36%VPO/(H 3PO 4)- p-ZrO 2 catalyst, the best performance achieved so far among the supported VPOs.

Reaction induced current generation by butane oxidation in high temperature electrochemical membrane reactor

The electrocatalytic n-butane oxidation has been investigated in an electrochemical membrane reactor with yttria-stabilized zirconia as a solid electrolyte and Pt as cathodic and Au as anodic electrode material, respectively. Vanadyl pyrophosphate (VPO) catalyst layer was deposited on the anode. The investigations of butane partial oxidation were carried out at temperatures between 823 and 873 K in semi-batch and continuous operating mode. The desired product maleic anhydride was detected in the product stream simultaneously as electrical current was generated in the system. The catalyst performance and the induced current level were stable over some hours of operation, after which the catalyst activity gradually reduced due to the insufficient oxygen supply. The reduced catalyst was rejuvenated easily by re-oxidation. In the semi-batch operation mode, pulses of the induced current were observed depending on the hydrocarbon concentration and the oxidation reactions, which were occurring in the anodic compartment.

Promotional Effect of Bismuth as Dopant in Bi-Doped Vanadyl Pyrophosphate Catalysts for Selective Oxidation of n-Butane to Maleic Anhydride

Bismuth-promoted (1% and 3%) vanadyl pyrophosphate catalysts were prepared by refluxing Bi(NO 3) 3· 5H 2O and VOPO 4· 2H 2O in isobutanol. The incorporation of Bi into the catalysts lattice increased the surface area and lowered the overall V oxidation state. Profiles of temperature programmed reduction (TPR) in H 2 show a significant shift of the maxima of major reduction peaks to lower temperatures for the Bi-promoted catalysts. A new peak was also observed at the low temperature region for the catalyst with 3% of Bi dopant. The addition of Bi also increased the total amount of oxygen removed from the catalysts. The reduction pattern and reactivity information provide fundamental insight into the catalytic properties of the catalysts. Bi-promoted catalysts were found to be highly active (71% and 81% conversion for 1% and 3% Bi promoted catalysts, respectively, at 703 K), as compared to the unpromoted material (47% conversion). The higher activity of the Bi-promoted catalysts is due to that these catalysts possess highly active and labile lattice oxygen. The better catalytic performance can also be attributed to the larger surface area.

Mechanism of phthalic anhydride formation in the oxidation of n-pentane on a vanadium-phosphorus oxide catalyst

The reaction paths of product formation in the partial oxidation of n-pentane on vanadium-phosphorus oxide (VPO) and VPO-Bi catalysts are considered. The condensed products of n-pentane oxidation were analyzed by chromatography-mass spectrometry, and the presence of C4 rather than C5 unsaturated hydrocarbons was detected. It was found that the concentration of phthalic anhydride in the products increased upon the addition of C4 olefins and butadiene to the n-pentane-air reaction mixture. With the use of a system with two in-series reactors, it was found that the addition of butadiene to a flow of n-butane oxidation products (maleic anhydride, CO, and CO2) resulted in the formation of phthalic anhydride. The oxidation of 1-butanol was studied, and butene and butadiene were found to be the primary products of reaction; at a higher temperature, maleic anhydride and then phthalic anhydride were formed. The experimental results supported the reaction scheme according to which the activation of n-pentane occurred with the elimination of a methyl group and the formation of C4 unsaturated hydrocarbons. The oxidation of these latter led to the formation of maleic anhydride. The Diels-Alder reaction between maleic anhydride and C4 unsaturated hydrocarbons is the main path of phthalic anhydride formation.

Nano-sized crystallites of vanadyl pyrophosphate as a highly selective catalyst for n-butane oxidation

Exfoliation-reduction of VOPO4 · 2H2O in a mixed alcohol consisting of 2-butanol and ethanol, followed by the thermal treatment in the presence of n-butane, O2, and He at 663 K for 300 h, produces novel nano-sized crystallites (~ 50 nm) of (VO)2P2O7. The nano-sized (VO)2P2O7 crystallites exhibit a high selectivity to maleic anhydride (~ 84%) for the selective oxidation of n-butane.

Effects of mechanochemical treatment to the vanadium phosphate catalysts derived from VOPO 4·2H 2O

Modification by using mechanochemical treatment of vanadium phosphate catalysts on the microstructure, morphology, oxygen nature and catalytic performance for n-butane oxidation is described and discussed. In this work, the precursor, VOHPO 4·0.5H 2O prepared by reduction of VOPO 4·2H 2O by isobutyl alcohol was subjected to a high energy planetary ball mill for 30, 60 and 120 min in ethanol. The ball milling process reduced the crystallite size of the catalysts and consequently increased their surface area. The morphologies of the milled catalysts are dependent on milling time. The highest reactivity and mobility of the lattice oxygen species has been achieved by the catalyst milled for 60 min with lower reduction peak temperature and higher amount of oxygen atoms removed. The oxygen species removed from the active V 4+ phase was shown to be correlated with the rate of reaction. A good relationship was also found between the oxygen species associated with V 5+ and maleic anhydride selectivity. However, a larger amount of this oxygen species will give a deleterious effect on the conversion rate. The present study demonstrate that the mechanochemical method (with an appropriate duration) effectively enhanced the catalytic activity by increasing the surface area and controlling the reactivity, and that the amount of oxygen species contributed to the partial oxidation of n-butane to maleic anhydride.

The dilution of vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride, with aluminum phosphate: unexpected reactivity due to the contribution of the diluting agent

This paper describes the preparation, characterization and reactivity in n-butane oxidation of catalysts made of vanadyl pyrophosphate (VPP) diluted in aluminum phosphate. Catalysts were prepared by synthesizing at the same time the VPP precursor and AlPO4, in order to develop mixed systems, suitable for the conglomeration into fluidizable particles by spray-drying. Al phosphate was chosen due to its presumed chemical inertness towards the active phase and towards n-butane. No evidence was obtained for the formation of mixed V/Al phosphates; an homogeneous reciprocal dispersion of the two compounds developed. However, Al phosphate showed an unexpected activity in n-butane oxidation; specifically, in the temperature range comprised between 340 and 400 °C, the hydrocarbon was converted to formaldehyde and carbon monoxide by radical-like reactions. The activity of Al phosphate became negligible above 400 °C, in the temperature range where instead VPP was active in hydrocarbon oxidation and selective to maleic anhydride. Moreover, Al phosphate was also responsible for the consecutive oxidative degradation of maleic anhydride, at high temperature.

Carbon nanotube-induced preparation of vanadium oxide nanorods: Application as a catalyst for the partial oxidation of n-butane

A vanadium oxide-carbon nanotube composite was prepared by solution-based hydrolysis of NH 4VO 3 in the presence of carbon nanotubes. The carbon nanotubes induce the nucleation of the 1D vanadium oxide nanostructures, with the nuclei growing into long freestanding nanorods. The vanadium oxide nanorods with the lengths up to 20 μm and the widths of 5–15 nm exhibit a well-ordered crystalline structure. Catalytic tests show that the composite with nanostructured vanadium oxide is active for the partial oxidation of n-butane to maleic anhydride at 300 °C.

Oxidation of saturated hydrocarbons under the effect of nanosecond pulsed space discharge

Slow oxidation of n-butane and n-decane in lean mixtures with oxygen under the action of a nanosecond pulsed discharge has been experimentally investigated. The discharge was excited by 25 ns pulses with an amplitude of 22 kV on high-voltage electrode and repetition frequency of 40 Hz in a 20 cm long quartz tube. The initial pressure of the mixtures was varied within the range from 0.8 to 10 Torr. The energy input in the discharge has been measured. The radiation intensities of the following molecular bands have been measured in time-resolved and integral modes:,, OH(A2 Σ, v′ = 0 → X2 Π, v″ = 0), CO(B1 Σ, v′ = 0 → A1 Π, v″ = 2). It has been demonstrated that, under the same experimental conditions in lean mixtures with oxygen, the times for the n–decane and n–butane oxidation are equal.

Non-steady catalytic performance as a tool for the identification of the active surface in VPO, catalyst for n-butane oxidation to maleic anhydride

The reactivity of equilibrated VPO catalysts with different P/V ratio was investigated under steady and unsteady conditions, with the aim of gaining information on the status of the active surface in reaction conditions. Specific treatments were applied, and then the unsteady performance was followed along with the reaction time, until the steady behaviour was recovered. These transient states made possible to infer that the nature of the true active surface is a function of the VPO characteristics and of the reaction conditions. With the catalyst having P/V ratio >1.0, the hydrolysis of the VPP surface under working conditions at temperatures higher than 340–350 °C, followed by the oxidation of vanadium, generates an active layer made of vanadium oxide and of P 2O 5/H 2O. When instead the P/V ratio is close to 1.0, the VPP surface is oxidized to VOPO 4 already at mild temperature under working conditions, with development of an active layer which is very active but unselective to maleic anhydride at 380 °C. Higher temperatures then lead to the hydrolysis of VOPO 4, with generation of an active layer which is similar, and behaves similarly, to that one which develops with the catalyst having P/V ratio >1.0.

Spin–spin exchange in vanadium-containing catalysts studied by in situ-EPR: a sensitive monitor for disorder-related activity

In unsupported V-containing catalysts, V4+ sites are frequently present in amorphous oxidic clusters and/or crystalline paramagnetic bulk phases in which they are coupled by effective spin–spin exchange interactions. This work presents two EPR procedures for evaluating these interactions and relating their strength to the degree of disorder and catalytic performance, namely (1) evaluating permanent structural disorder by calculating exchange energies and integrals and (2) monitoring transient electronic disorder caused by catalyst–reactant interaction in working catalysts using the ratio of the fourth and the square of the second moment of the EPR signal. Selected application examples comprise VPO catalysts such as (i) (VO)2P2O7, in which a certain degree of structural disorder revealed to be essential for high catalytic performance in the selective oxidation of n-butane to maleic anhydride, (ii) (NH4)2(VO)3(P2O7)2 in which transient perturbation of spin–spin exchange sensitively reflects the strength of reactant adsorption during ammoxidation of toluene and (iii) (NH4)2VOP2O7 in which an amorphous VO2+-containing phase could be identified as active component besides inactive crystalline phases. Based on operando-EPR measurements, reasons for activity differences in MoVTeNb oxide catalysts could be suggested.