Oxidation Of N-butane Research Articles

Effects of dimethyl ether on n-butane oxidation

Dimethyl ether (DME) is the simplest ether and it is used as an alternative fuel or fuel additive to reduce toxic emissions from combustion processes. The effects of DME on n-butane oxidation were investigated for two different concentrations of DME in the fuel mixture (i.e., 20% and 50%) and two different fuel-rich equivalence ratios (i.e., 2.6 and 3.0) using detailed chemical kinetic modeling. Reactor model was selected as atmospheric-pressure, adiabatic, tubular reactor, operated under laminar flow conditions. The concentration profiles of major, minor, and trace species were obtained for n-butane/DME/oxygen/argon at six different reactor inlet temperatures, and the results were compared with those attained for pure n-butane oxidation case (n-butane/oxygen/argon). Dimethyl ether addition decreased formations of various toxic species such as carbon monoxide, aromatic species, and polycyclic aromatic hydrocarbons, while it increased the formations of formaldehyde and acetaldehyde. Increasing equivalence ratio increased the formations of carbon monoxide, methane, aromatic species, and polycyclic aromatic hydrocarbons, while its effects on formaldehyde and acetaldehyde were not pronounced under the conditions studied.

Transient Redox Activity of Vanadyl Pyrophosphate at Ambient and Elevated Pressure

Abstract The transient catalytic activity of vanadyl pyrophosphate (VPP) catalyst was studied at ambient and elevated pressure (4.1 bar) and a wide range of operating conditions. The range included the commercial operating conditions typical of fixed bed, fluidized bed and circulating fluidized beds (CFB) for the partial oxidation of n-butane to maleic anhydride (MA). The maleic anhydride yield improved by increasing the feed oxygen molar fraction, temperature and pressure. When the catalyst was cycled between an oxidizing (synthetic air) and a reducing environment; yield increased with an increase in the catalyst residence time in the oxidizing environment. This effect was more pronounced at higher pressure. At ambient pressure, MA selectivity varied between 50-73 % while it decreased to about 48-54 % at a pressure of 4.1 bar. A strong MA selectivity dependency on feed composition was observed when the oxidation time was in the range of actual industrial reactors (< 1 minute). Selectivity data suggested that different oxygen species might be responsible for CO formation compared to other products such as CO2 and MA. Under oxidizing feed conditions (oxygen/n-butane ≥ than 3.7), an increase in n butane conversion was the main contributor to improved MA yield: n-butane conversion increased by about 70 % when the catalyst oxidation time extended from 0.3 to 10 minute. While, under fuel rich feed conditions, typical of industrial CFB operations, both MA selectivity and n-butane conversion contributed to enhancement in MA yield. Depending on the feed composition, MA selectivity increases by about 16-30 % and n butane conversion increases by about 32-55 % by extending the catalyst oxidation time. These results show the critical importance of catalyst oxidation time on reaction yield improvement especially when operating under fuel rich feed conditions. The surface adsorbed or surface lattice oxygen species were suggested to be the main responsible for n butane activation. While, the contribution of catalyst’s sub-surface lattice oxygen was believed to be very limited at fuel rich feed conditions. Under these conditions, catalyst over-reduction cannot be effectively compensated even after excessive catalyst regeneration and presence of gas phase oxygen is critical to maintain a high catalytic activity. As the reactor pressure increased to 4.1 bar, up to 60 % increase in n butane conversion accompanied by 100 % increase in oxygen conversion was observed. MA selectivity decreased by about 20 % on average but the increase in n-butane conversion resulted in an overall yield improvement of up to 30 %. Data show that the catalytic performance could be enhanced at certain combination of reactor pressure and temperature.

The Intimate Relationship between Bulk Electronic Conductivity and Selectivity in the Catalytic Oxidation of n‐Butane

Don't touch! Without electrode contacts, but contact-free with microwaves in a resonant cavity the electronic conductivity of a VPO powder catalyst could be measured under the reaction conditions of the selective oxidation of n-butane to maleic anhydride. As a result, a linear correlation between conductivity and formation rate of maleic anhydride was observed.

Effect of Y-stabilized ZrO2 as support on catalytic performance of Pt for n-butane oxidation

The effect of Y-stabilized ZrO2 as support on the Pt dispersion and catalytic activity for the total oxidation of n-butane was investigated. From XRD, TEM and CO chemisorption measurements, Pt particles were found to be well dispersed with a size of ca. 10nm over the surface of ZrO2 and Y-stabilized ZrO2, when Pt supported catalysts were calcined at 600°C. Although Pt particles supported on ZrO2 were significantly sintered by high temperature calcination above 800°C, no aggregation of Pt particles was observed for Pt/Y–ZrO2. When the catalyst was calcined at higher temperatures, Pt catalysts supported on Y-stabilized ZrO2 showed higher activity than Pt/ZrO2 for the total oxidation of n-butane. The intrinsic activity, expressed in terms of turnover frequency (TOF), increased with the decrease in Pt dispersion, indicating that n-butane oxidation over Pt catalysts supported on Y-stabilized ZrO2 is a structure sensitive reaction. Y2O3 additive plays a role in improving the thermal stability of Pt particles through the metal–support interaction, while it does not alter the catalytic performance of Pt as catalytic active sites.

A Model for the Phosphorus Dynamics of VPO Catalysts during the Selective Oxidation of n‐Butane to Maleic Anhydride in a Tubular Reactor

AbstractA model for the phosphorus dynamics in vanadium‐phosphorus oxide (VPO) catalysts for the oxidation of n‐butane to maleic anhydride was developed. According to the model, reversible sorption processes determine the phosphorus content of the catalyst. Simulations reveal that several phenomena can be successfully described. If no phosphorus is added to the reactant feed, the catalytic activity increases until runaway occurs. With addition of a proper amount of phosphorus, the loss can be compensated while excessive phosphorus addition results in complete catalyst deactivation. Adjusting the model parameters to experimental data may result in a model that can be used to optimize the performance of maleic anhydride reactors.

Improvement of the modeling of the low-temperature oxidation of n-butane: study of the primary reactions.

This paper revisits the primary reactions involved in the oxidation of n-butane from low to intermediate temperatures (550-800 K) including the negative temperature coefficient (NTC) zone. A model that was automatically generated is used as a starting point and a large number of thermochemical and kinetic data are then re-estimated. The kinetic data of the isomerization of alkylperoxy radicals giving (•)QOOH radicals and the subsequent decomposition to give cyclic ethers has been calculated at the CBS-QB3 level of theory. The newly obtained model allows a satisfactory prediction of experimental data recently obtained in a jet-stirred reactor and in rapid compression machines. A considerable improvement of the prediction of the selectivity of cyclic ethers is especially obtained compared to previous models. Linear and global sensitivity analyses have been performed to better understand which reactions are of influence in the NTC zone.

The microwave cavity perturbation technique for contact-free and in situ electrical conductivity measurements in catalysis and materials science

We have developed a noncontact method to probe the electrical conductivity and complex permittivity of single and polycrystalline samples in a flow-through reactor in the temperature range of 20-500 °C and in various gas atmospheres. The method is based on the microwave cavity perturbation technique and allows the simultaneous measurement of microwave conductivity, permittivity and of the catalytic performance of heterogeneous catalysts without any need for contacting the sample with electrodes. The sensitivity of the method towards changes in bulk properties was proven by the investigation of characteristic first-order phase transitions of the ionic conductor rubidium nitrate in the temperature range between 20 and 320 °C, and by studying the temperature dependence of the complex permittivity and conductivity of a niobium(V)-doped vanadium-phosphorous-oxide catalyst for the selective oxidation of n-butane to maleic anhydride. Simultaneously, the catalytic performance was probed by on line GC analysis of evolving product gases making the technique a real in situ method enabling the noninvasive investigation of electronic structure-function relationships.

Effect of tellurium promoter on vanadium phosphate catalyst for partial oxidation of n-butane

Te-promoted (1%) vanadium phosphate catalyst (VPDTe) was prepared via VOPO 4·2H 2O by calcining its precursor VOHPO 4·0.5H 2O in a flow of n-butane/air. VPDTe catalyst has resulted a higher existence of V 5+ phase with V 5+/V 4+ ratio of 0.23. SEM micrographs show that Te addition altered the arrangement of the platelets from “rose-like” clusters to layer with irregular shape. Te addition has also markedly lowered the reduction activation energies of the vanadium phosphate catalyst as revealed by TPR profile. The amount of active oxygen species associated with V 4+ phase of the Te promoted catalyst was significantly higher than those of the unpromoted catalyst. These observations suggest that high mobility and availability of reactive oxygen species contributed to the enhancement of n-butane conversion up to 80% at 673 K, while only 47% over unpromoted catalyst (2400 h −1, 1.7% n-butane in air).

Application of the flowsheet simulation concept to fluidized bed reactor modeling. Part II—Application to the selective oxidation of n-butane to maleic anhydride in a riser/regenerator system

In part I of this paper a new fluidized bed reactor module was presented for the simulation of a bubbling fluidized bed and of the riser of a circulating fluidized bed with the flowsheet simulation tool SolidSim so that several process models can easily be coupled. In the present part II the newly developed fluidized reactor modules are connected to existing cyclone modules to simulate a complex coupled fluidized-bed process, the selective oxidation of n-butane to maleic anhydride in a riser–regenerator system [1,2]. The calculation results for a laboratory setup are found to be in good agreement with experimental data from the literature. The subsequent simulation of an industrial scale sized plant shows that a high solids recirculation rate is needed to achieve satisfying maleic anhydride yield. The usefulness of flowsheet simulation is demonstrated by further process simulation calculations with varied solids recovery systems.

Nanostructured of Vanadium Phosphorus Oxide (Vpo) Catalyst Prepared by Sonochemical Treatment

A series of six nanostructures vanadium phosphorus oxide catalysts were synthesized through the starting material vanadium pentoxide which subjected to high intensity ultrasound irradiation with different duration of time. XRD patterns of all nanostructure vanadium phosphorus oxide catalyst were indexed to (VO)2P2O7 with one additional small peak which corresponds to the present of small amount of V5+ phase except for the catalyst that undergo 120 min of ultrasound irradiation time. The surface morphologies of the catalysts are uniform, well defined shapes and surface structures in nanoscale range but tend to agglomerate with each other to form larger particles. Furthermore, high amount of active oxygen species were released from V4+ phase (O--V4+ pair) for the nanostructures VPO catalyst which were synthesized with 30 min of ultrasound irradiation time and drastic increment in n-butane conversion (9 %) in catalytic evaluation test, suggested that these nanostructure VPO is an active catalyst for partial oxidation of n-butane towards malefic anhydride.

Emissions and photochemistry of oxygenated VOCs in urban plumes in the Northeastern United States

Abstract. Photochemical processes inside urban plumes in the Northeast of the United States have been studied using a highly detailed chemical model, based upon the Master Chemical Mechanism (MCM). The model results have been compared to measurements of oxygenated VOCs (acetone, methyl ethyl ketone, acetaldehyde, acetic acid and methanol) obtained during several flights of the NOAA WP-3D aircraft, which sampled plumes from the New York City area during the ICARTT campaign in 2004. The agreement between the model and the measurements was within 40–60 % for all species, except acetic acid. The model results have been used to study the formation and photochemical evolution of acetone, methyl ethyl ketone and acetaldehyde. Under the conditions encountered during the ICARTT campaign, acetone is produced from the oxidation of propane (24–28 %) and i-propanol (<15 %) and from a number of products of i-pentane oxidation. Methyl ethyl ketone (MEK) is mostly produced from the oxidation of n-butane (20–30 %) and 3-methylpentane (<40 %). Acetaldehyde is formed from several precursors, mostly small alkenes, >C5 alkanes, propanal and MEK. Ethane and ethanol oxidation account, respectively, for 6–23 % and 5–25 % of acetaldehyde photochemical formation. The results highlight the importance of alkanes for the photochemical production of ketones and the role of hydroperoxides in sustaining their formation far from the emission sources.

Synthesis of Nanostructured Vanadium Phosphate Catalysts using Sonochemical Route for Partial Oxidation of n-Butane

In this study, sonochemical treatment is used to synthesize nanostructured vanadium pentoxide, V2O5 with different duration of time andmineralizers. Eight samples of V2O5 have been prepared using KN03 andKCl as mineralizers that undergo sonochemical treatment with different duration i.e., 30, 60, 90 and 120 min, respectively. These samples were denoted as KNO30, KNO60, KNO90, KNO120, KC130, KC160, KC190 and KC1120. Nanostructured V2O5 prepared via ultrasound irradiation for 30 min in KC1 (KC130) was chosen as starting material to synthesis vanadium phosphorus oxide catalyst (denoted VPOS30KC1). All the materials synthesized was characterized by using X-Ray Diffraction (XRD), Brunauer-Emmett-Teller surface area measurement (BET), chemical analysis, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and temperature programmed reduction (H2-TPR). Catalytic properties for n-butane oxidation of the catalyst, VPOS30KC1 was investigated by using a fixed-bed microreactor at 673 K (GHSV = 2400 h1). SEM micrographs show that the morphology of the V2O5 changed from platelet-like particles intonanorods after 90 min of sonochemical treatment. XRD patterns detected that the potassium ion from the mineralizers was incorporated into the V2O5 structure after prolonged sonochemical treatment duration. H j-TPR profiles shown that VPOS30KC1 gave higher amount of reactive oxygen species (0-V4+) removed which will expect to give higher activity. Catalytic evaluation showed that VPOS30KC1 gave higher conversion (19%) while retaining the selectivity towards maleic anhydride (48%) compared to the bulk VPO catalyst prepared in the same organic medium (XC4: 14%).

The mechanism of surface doping in vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride: The role of Au promoter

This paper studies the role of Au as a promoter for vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride. Samples were prepared with a stoichiometric P/V ratio (P/V = 1.0), and then doped with increasing amounts of Au. It was found that the addition of the Au promoter had a profound influence on its catalytic behaviour, as samples containing the greater amount of Au (3 wt%) showed a behaviour that was similar to that of optimal catalysts which were prepared with a slight excess of P. In fact, the presence of Au allowed all the phenomena that typically lead to the worst catalytic behaviour of stoichiometric vanadyl pyrophosphate to be minimised, i.e. both the over-oxidation of vanadium and the development of the very active but poorly selective α I-VOPO 4. This was attributed to the enhanced reducibility of V 5+ that was observed in Au-doped samples, as compared to the undoped ones.

Light alkane oxidation over Ru supported on ZnAl 2O 4, CeO 2 and Al 2O 3

Zinc aluminate, alumina and ceria supported ruthenium catalysts were tested in the total oxidation of propane, n-butane and iso-butane. Structure of the catalysts was characterized by means of XRD, TEM, BET and H 2 chemisorption techniques. The Ru dispersion changes from 0.67 for 5% Ru/CeO 2, 0.56 for 4.5% Ru/ZnAl 2O 4 and to 0.28 for 4.7% Ru/γ-Al 2O 3 catalyst. TEM and XRD results confirmed high dispersion of the samples. All oxidation reactions occur at much lower temperatures over Ru/CeO 2 compared to those over Ru/γ-Al 2O 3 and Ru/ZnAl 2O 4. Also, the site-time yields of all catalysed oxidation reactions follows the order Ru/CeO 2 > Ru/γ-Al 2O 3 > Ru/ZnAl 2O 4. Activity results cannot be explained by the differences in the Ru dispersion. The redox species of ruthenium on CeO 2 oxide, easily reacted with the lattice oxygen of CeO 2, are responsible for the enhanced activity of the Ru/CeO 2 catalyst in the VOCs oxidation.

Detailed product analysis during the low temperature oxidation of n-butane.

The products obtained from the low-temperature oxidation of n-butane in a jet-stirred reactor (JSR) have been analysed using two methods: gas chromatography analysis of the outlet gas and reflectron time-of-flight mass spectrometry. The mass spectrometer was combined with tunable synchrotron vacuum ultraviolet photoionization and coupled with a JSR via a molecular-beam sampling system. Experiments were performed under quasi-atmospheric pressure, for temperatures between 550 and 800 K, at a mean residence time of 6 s and with a stoichiometric n-butane/oxygen/argon mixture (composition = 4/26/70 in mol%). 36 reaction products have been quantified, including in addition to the usual oxidation products, acetic acid, hydrogen peroxide, C(1), C(2) and C(4) alkylhydroperoxides and C(4) ketohydroperoxides. Evidence of the possible formation of products (dihydrofuranes, furanones) derived from cyclic ethers has also been found. The performance of a detailed kinetic model of the literature has been assessed with the simulation of the formation of this extended range of species. These simulations have also allowed the analysis of possible pathways for the formation of some obtained products.

The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory

We have studied the magnetic structure of the high symmetry vanadyl pyrophosphate ((VO)(2)P(2)O(7), VOPO), focusing on the spin exchange couplings, using density functional theory (B3LYP) with the full three-dimensional periodicity. VOPO involves four distinct spin couplings: two larger couplings exist along the chain direction (a-axis), which we predict to be antiferromagnetic, J(OPO) = -156.8 K and J(O) = -68.6 K, and two weaker couplings appear along the c (between two layers) and b directions (between two chains in the same layer), which we calculate to be ferromagnetic, J(layer) = 19.2 K and J(chain) = 2.8 K. Based on the local density of states and the response of spin couplings to varying the cell parameter a, we found that J(OPO) originates from a super-exchange interaction through the bridging -O-P-O- unit. In contrast, J(O) results from a direct overlap of 3d(x(2)-y(2)) orbitals on two vanadium atoms in the same V(2)O(8) motif, making it very sensitive to structural fluctuations. Based on the variations in V-O bond length as a function of strain along a, we found that the V-O bonds of V-(OPO)(2)-V are covalent and rigid, whereas the bonds of V-(O)(2)-V are fragile and dative. These distinctions suggest that compression along the a-axis would have a dramatic impact on J(O), changing the magnetic structure and spin gap of VOPO. This result also suggests that assuming J(O) to be a constant over the range of 2-300 K whilst fitting couplings to the experimental magnetic susceptibility is an invalid method. Regarding its role as a catalyst, the bonding pattern suggests that O(2) can penetrate beyond the top layers of the VOPO surface, converting multiple V atoms from the +4 to +5 oxidation state, which seems crucial to explain the deep oxidation of n-butane to maleic anhydride.

Influence of Milling Media on the Physicochemicals and Catalytic Properties of Mechanochemical Treated Vanadium Phosphate Catalysts

VOHPO4.0.5H2O synthesized via the alcohol reduction of VOPO4.2H2O was mechanochemical treated for 30 min in three different media, i.e. cyclohexane, ethanol and air. XRD results revealed that their structure became less crystalline compared to the unmilled material. SEM showed that the particles for the milled materials become smaller and unique features were observed in the different type of media used. The reactivity of the oxygen species linked to V5? and V4? were also affected by the milling process. The selectivity to maleic anhydride from n-butane oxidation were observed to increase in line with the increase in the oxygen species associated with V5? and the presence of isolated V5? phase. A correlation was observed between the crystallite size of the pyrophosphate phase at (020) plane with the maleic anhydride selectivity.

Mechanism of the oxidation and combustion of normal paraffin hydrocarbons: Transition from C1–C6 to C7H16

Recently, detailed kinetic mechanisms of the oxidation and combustion of higher hydrocarbons, composed of hundreds of components and thousands of elementary reactions, have been proposed. Despite the undoubtful advantages of such detailed mechanisms, their application to simulations of turbulent combustion and gas dynamic phenomena is difficult because of their complexity. At the same time, to some extent limited, they cannot be considered exhaustive. This work applies previously proposed algorithm for constructing an optimal mechanism of the high- and low-temperature oxidation and combustion of normal paraffin hydrocarbons, which takes into account the main processes determining the reaction rate and the formation of key intermediates and final products. The mechanism has the status of a nonempirical detailed mechanism, since all the constituent elementary reactions have a kinetic substantiation. The mechanism has two specific features: (1) it does not include reactions of so-called double oxygen addition (first to the peroxide radical, and then to its isomeric form), i.e., the first addition turns out to be sufficient; (2) it does not include isomeric compounds and their derivatives as intermediates, since this oxidation pathway is slower than the oxidation of molecules and radicals with normal structure. Application of the algorithm makes it possible to compile a compact mechanism, which is important for modeling chemical processes involving paraffin hydrocarbons C n with large n. Previously, based on this algorithm, compact mechanisms of the oxidation and combustion of propane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane have been constructed. In this work, we constructed a nonempirical detailed mechanism of the oxidation and combustion of hydrocarbons from n-undecane to n-hexadecane. The most important feature of the new mechanism is its staged nature, which manifests itself through the emergence of cool and blue flames during low-temperature autoignition. The calculation results are compared with experimental data.

Innovative process for the synthesis of vanadyl pyrophosphate as a highly selective catalyst for n-butane oxidation

Vanadyl pyrophosphate (VPO) catalysts are used for the selective oxidation of light alkanes, which are based on vanadyl hydrogen phosphate hemihydrate (VOHPO 4·0.5H 2O) as the precursor. Catalyst precursor with well-defined crystal size has been successfully synthesized for the first time, using a simple one-step high-pressure autoclave that was surfactant-free and water-free method with significantly lower temperature and shorter reaction time. VOHPO 4·0.5H 2O was prepared from V 2O 5 using an isobutanol, 1-pentanol, 1-heptanol and 1-dectanol as both solvent and reducing agent at elevated temperatures (100, 120, and 150 °C). This new method significantly reduced the preparation time and lowered production temperature (50%) of catalyst precursor (VOHPO 4·0.5H 2O) when compared to conventional hydrothermal synthesis methods. VOHPO 4·0.5H 2O can be obtained at temperature far below 150 °C. It was found that the presence of 1-heptanol and 1-decanol in the reaction mixtures is crucial for obtaining a well-defined crystal size of precursor phase and solely generated impurity [VO(H 2PO 4) 2]. Our findings show that both the phase composition and morphology of vanadium phosphate can be influenced by the use of different reducing agents and temperatures during the preparation process. This new methodology produces catalysts with a much higher surface area ( ca. 23 m 2 g −1) compared with those materials prepared by slow hydrothermal synthesis ( ca. 9.5 m 2 g −1). Finally, the yield of maleic anhydride was significantly increased from 21.3% for conventional catalyst to 37.9% for the new solvothermal catalyst.

Effect of Pt nanoparticle size on the specific catalytic activity of Pt/SiO2 and Pt/TiO2 in the total oxidation of methane and n-butane

The dependence of the specific catalytic activity (Asp) of the catalysts Pt/SiO2 and Pt/TiO2 in the total oxidation of CH4 and n-C4H10 on the Pt nanoparticle size (in the range from 1 to 4 nm) was studied. The specific catalytic activity increases with an increase in the platinum nanoparticle size, indicating that the total oxidation is a structure-sensitive reaction. The structure sensitivity depends on the size of an oxidized molecule: it increases sharply on going from CH4 to n-C4H10. The support also exerts a considerable effect on the Asp value: in the oxidation of both CH4 and C4H10 the specific catalytic activity for the catalysts Pt/TiO2 is 3–4 times that for Pt/SiO2.