Oxidation Of Isobutane Research Articles

Removal of methyl tert-butyl ether (MTBE) with Nafion

A solid organic polymer, Nafion, is tested for the removal of methyl tert-butyl ether (MTBE) in water. Nafion with perfluorosulfonic acid backbone and terminal sulfonic acid groups has a surface acidity similar to 100% sulfuric acid, and has been commonly used as a strong-acid catalyst in many organic reactions. Sorption and subsequent transformation of MTBE were observed in batch experiments. The transformation of MTBE by porous nanocomposite Nafion SAC-13 to tert-butyl alcohol (TBA), acetone, isobutene and probably methanol was found. Subsequent transformation of TBA to acetone was also observed. Results suggest that transformational pathways may include hydrolysis, dehydrogenation and oxidation. Dissolved oxygen is needed for the oxidation of isobutene to acetone. As Nafion is insoluble in water, chemically stable, and regenerable, its use in packed-bed reactors for MTBE removal looks promising.

The partial oxidation of C4–C6 alkanes to maleic anhydride, 2-methyl maleic anhydride, and acetic acid over MoVO catalysts

Alkanes such as iso-butane, n-pentane, and cyclohexane have been converted effectively to maleic anhydride, 2-methyl maleic anhydride, and acetic acid over MoVO catalysts below 330 °C. In order to explore the possible reaction pathways, the oxidation of iso-butene, cyclohexene, 2-methyl-1-propanol, tert-butanol, and 2-methylacrylic acid were examined over the catalysts. In iso-butene oxidation, acetic acid and 2-methyl maleic anhydride were detected but not maleic anhydride. In cyclohexene oxidation, benzene and phenol were detected as major products but it was not the case in cyclohexane oxidation. The results of our investigation indicate that the oxidation pathway of iso-butane is different from that of iso-butene, 2-methyl-1-propanol, tert-butanol, and 2-methylacrylic acid, whereas the oxidation pathway of cyclohexane is different from that of cyclohexene.

Fine analysis of by-products of the selective oxidation of isobutane into methacrolein and methacrylic acid over Mo–V–P catalyst

The nature of the products of the selective oxidation of isobutane into methacrolein and methacrylic acid over a Mo–V–P Keggin-type-structure catalyst was investigated at 593 K. Gas chromatography/mass spectrometry and 1H and 13C NMR were complementary analytical methods to identify by-products. The quantification was realised by 1H NMR and gas chromatography. Aromatic and linear carbon backbone products detected suggested that an isomerization occurred during the oxidation of isobutane. A better knowledge of the nature of the acid site on which isomerization occurs might design a powerful catalyst.

Selective Oxidation of Isobutane to Methacrolein over Mo–V–Te–Sb Mixed Oxide Catalysts with Different Antimony Contents

A series of MoV0.3Te0.23Sb x (x=0–0.6) mixed oxides were prepared and investigated for the selective oxidation of isobutane. Among them, MoV0.3Te0.23Sb0.5 showed the best methacrolein selectivity (as high as 39%), and the yield to methacrolein reached 7.8% at 20.0% isobutane conversion at 470 °C.

Anaerobic oxidation of isobutane: II. Catalysis by Mg–V complex oxides

Anaerobic oxidation of isobutane was studied using MgV 2O 6, Mg 2V 2O 7 and Mg 3V 2O 8. Isobutene, a small amount of CO x , and trace amount of oxygen containing compounds were formed. CO 2 was formed mainly at the beginning of the reaction and decreased with reaction time. Catalytic activity of Mg 2V 2O 7 was slightly higher than that of MgV 2O 6 but the CO x formation over MgV 2O 6 was more than over Mg 2V 2O 7. Mg 3V 2O 8 was the least active. Therefore, Mg 2V 2O 7 is the most suitable for oxidative hydrogenation of isobutane under the anaerobic reaction conditions. The equilibration between 16O 2 and 18O 2 over MgV 2O 6 was faster than over Mg 2V 2O 7 or Mg 3V 2O 8 at 673 K. The rate of equilibration between 18O 2 and lattice oxygen over MgV 2O 6 was similar to that over Mg 2V 2O 7, which was faster than over Mg 3V 2O 8. Highest yield of isobutene formation over Mg 2V 2O 7 would come from the character of Mg 2V 2O 7, in which mobility of the lattice oxygen is great but surface reaction of isobutane was not so fast. Higher activity for isobutene formation may come from the nature of Mg 2V 2O 7, of which mobility of the lattice oxygen is great but surface reaction of isobutane was not so much fast. Mn, Cr, Fe, Ni and Co can be introduced into Mg 2V 2O 7 to give a single phase. Substitution of Co, Cu and Cr for Mg increased the activity of Mg 2V 2O 7 for isobutane oxidation and substitution of Ni and Mn scarcely affected the activity but substitution of Fe and Zn decreased the activity. Substitution of all the metal ions slightly increased the isobutene selectivity. MgO, MgV 2O 4 and Mg 3V 2O 8 were observed in the sample after the anaerobic oxidation of isobutane. Cu containing catalyst was reduced to give Cu metal.

The “Somersault” Mechanism for the P-450 Hydroxylation of Hydrocarbons. The Intervention of Transient Inverted Metastable Hydroperoxides

A series of model theoretical calculations are described that suggest a new mechanism for the oxidation step in enzymatic cytochrome P450 hydroxylation of saturated hydrocarbons. A new class of metastable metal hydroperoxides is described that involves the rearrangement of the ground-state metal hydroperoxide to its inverted isomeric form with a hydroxyl radical hydrogen bonded to the metal oxide (MO-OH --> MO....HO). The activation energy for this somersault motion of the FeO-OH group is 20.3 kcal/mol for the P450 model porphyrin iron(III) hydroperoxide [Por(SH)Fe(III)-OOH(-)] to produce the isomeric ferryl oxygen hydrogen bonded to an *OH radical [Por(SH)Fe(III)-O....HO(-)]. This isomeric metastable hydroperoxide, the proposed primary oxidant in the P450 hydroxylation reaction, is calculated to be 17.8 kcal/mol higher in energy than the ground-state iron(III) hydroperoxide Cpd 0. The first step of the proposed mechanism for isobutane oxidation is abstraction of a hydrogen atom from the C-H bond of isobutane by the hydrogen-bonded hydroxyl radical to produce a water molecule strongly hydrogen bonded to anionic Cpd II. The hydroxylation step involves a concerted but nonsynchronous transfer of a hydrogen atom from this newly formed, bound, water molecule to the ferryl oxygen with a concomitant rebound of the incipient *OH radical to the carbon radical of isobutane to produce the C-O bond of the final product, tert-butyl alcohol. The TS for the oxygen rebound step is 2 kcal/mol lower in energy than the hydrogen abstraction TS (DeltaE() = 19.5 kcal/mol). The overall proposed new mechanism is consistent with a lot of the ancillary experimental data for this enzymatic hydroxylation reaction.

The partial oxidation of isobutene and propene on TiO 2(110)

General techniques for the partial oxidation of alkenes by molecular oxygen are a goal for surface science and catalysis research as they may lead to more efficient and environmentally friendly industrial processes. To better understand the thermal surface chemistry of metal oxides toward alkene partial oxidation, the interactions of isobutene and propene on TiO 2(110) were studied using temperature-programmed desorption (TPD). Isobutene was found to adsorb and desorb molecularly below 250 K on the clean surface. With exposure to oxygen (>1000 L) and unknown quantities of water (<10 L), isobutene monolayers on TiO 2(110) react to form products that include methacrolein and isobutanal, as well as a third product that has a C 4H 8O stoichiometry. We tentatively assign this species to 2,2-dimethyloxirane (isobutene oxide). Structural conservation within this family of products points to a common surface intermediate that we propose results from the addition of O from a hydrogen peroxo (HOO) species to the C C bond of isobutene. This hydrogen peroxo (HOO) species forms from the reaction of physisorbed water and oxygen, assisted by partial charge transfer from the TiO 2(110) substrate. Initial studies reveal a similar reaction pathway for the partial oxidation of propene on TiO 2(110), yielding acetone and propanal. This work suggests that TiO 2 surface sites on supported Au/TiO 2 catalysts are active for partial oxidation of alkenes.

Preparation of silica-coated Pt metal nanoparticles using microemulsion and their catalytic performance

Pt–SiO2 catalysts were prepared by using water-in-oil type microemulsion. The catalysts were prepared by hydrolysis of tetraethylorthosilicate in the microemulsion containing Pt species, followed by calcination in air and reduction with H2. This preparation method for Pt–SiO2 provided Pt metal nanoparticles with a diameter of ca. 6 nm covered uniformly with silica layers, while a conventional impregnation method formed Pt metal particles supported on the silica surface. The Pt catalysts coated with silica (coat–Pt) showed different catalytic performance for the competitive oxidation of mixed hydrocarbons from Pt catalysts supported on silica (imp–Pt), i.e. in the competitive oxidation of methane and iso-butane, coat–Pt catalysts preferentially oxidized methane, while iso-butane was oxidized selectively over imp–Pt catalysts. The results of the adsorption of Ar on coat-Pt showed that silica in coat-Pt had porous structures of pore diameters < 1 nm. Because the porous structure of silica, which wrapped Pt metal particles, controlled the diffusion rate of reactant molecules, coat-Pt showed a specific catalytic performance for competitive oxidation.

5413 イソブタン冷媒の触媒処理装置の開発(第2報)(G09-3 バイオディーゼル,G09 環境工学)

The proper processing technology of hydrocarbon refrigerant isobutane (R600a) is required to prepare for recycling of the refrigerator. Isobutane extracted from the refrigerator compressor is diluted with air below the flammable range, is oxidized to CO_2 and H_2O by using a palladium catalyst. This paper describes the prototype isobutane oxidation system and its oxidation characteristics. In order to maintain the catalytic conversion efficiency highly, it is required to keep the catalyst inlet gas temperature more than 623K. Exhaust gas recirculation is effective for preheating of gas temperature.

224 炭化水素系冷媒イソブタンの触媒分解装置の開発(安定化・無害化処理,資源循環・廃棄物処理技術)

The proper processing technology of hydrocarbon refrigerant isobutane (R600a) is required to prepare for recycling of the refrigerator. Isobutane extracted from the refrigerator compressor is diluted with air below the flammable range, is oxidized to CO_2 and H_2O by using a palladium catalyst. This paper describes the prototype isobutane oxidation system and its oxidation characteristics. In order to maintain the catalytic conversion efficiency highly, it is required to keep the catalyst inlet gas temperature more than 623K. Exhaust gas recirculation is effective for preheating of gas temperature.

Catalytic Oxidation of Hydrocarbon Refrigerant Isobutane

Hydrocarbon refrigerant isobutane (R600a) began to be carried in household refrigerator. The proper processing technology of isobutane is required in order to prepare for recycling of the refrigerator. Isobutane below the inflammable range is oxidized to CO2 and H2O by usin a palladium catalyst. The catalyst temperature conditions for isobutane completely oxidation were clarified. Oxidation reaction starts at the catalyst temperature of about 570 K, the complete oxidation temperature becomes higher with isobutane concentration and premixture space velocity. The temperature distribution of catalyst showed that 60% or more of isobutane had oxidized near the catalyst inlet. Isobutane oxidation characteristics are mostly in agreement with propane on the condition of the same combustion rate.

Oxidation of isobutene to methacrolein using bismuth molybdate catalysts: Comparison of operation in periodic and continuous feed mode

A series of bismuth molybdate catalysts were compared using a continuous feed of isobutene in air or a cyclic/pulse or gas–gas periodic flow mode, in which the oxide is first treated with air at the reaction temperature, followed by reaction of isobutene in nitrogen or argon in the absence of oxygen. For nonpromoted catalysts, in the continuous-feed mode, relatively low selectivities for methacrolein are observed and significant amounts of byproduct CO 2 are formed. In contrast, in the pulse mode, no CO 2 and almost 100% selectivity to methacrolein can be observed with nonpromoted BiMoO x , especially for the initial reaction period. At realistic reaction temperatures, no carbon or carbon-containing product depositions are observed during the pulse mode, indicating that the very high selectivity observed is realistic for the nonpromoted catalyst under pulse conditions. The effect of Co and Fe as promoters on the catalytic performance was also investigated. The addition of Co and Fe leads to the observation of CO 2 also in the pulse mode along with some carbon deposition, although the selectivity to methacrolein remains significantly higher than that observed in the continuous-feed mode. Investigation of a more complex promoted catalyst representative of a commercial formulation [BiMo 12Fe 2NiCo 7MgSb 0.9Ti 0.1Te 0.02Cs 0.4O x ] also shows that CO 2 is observed in the pulse mode but, at much lower levels than observed with the less complex catalysts. However, in subsequent operation in the gas–gas periodic flow, the catalytic performance for this catalyst is almost identical in the continuous and pulse operations. It is concluded that, for pulse-mode operation, the best results, including almost total selectivity to methacrolein, are observed with the relatively simple nonpromoted binary oxides. In general, the first pulse-mode operation of these catalysts gives the highest yield of methacrolein and subsequent oxidation/reaction cycles gives lower yields. The origin of this effect was investigated using cyclic TPO/TPR and TPR/TPO analysis, revealing that the first TPR/TPO cycles are significantly different than subsequent cycles, likely due to the initial state of the catalyst surface.

Control of Selectivity Based on the Diffusion Rates of the Reactants in the Oxidation of Mixed Hydrocarbons with Molecular Oxygen over Silica-coated Pt Catalysts

Abstract Pt metal catalyst covered with silica layers oxidized methane preferentially in the competitive oxidation of methane and isobutane with gaseous oxygen. Selectivity in the competitive oxidation of mixed hydrocarbons over the catalyst was controlled by the diffusion rates of the reactants in the silica layers which wrapped Pt metal particles.

Thermochemical and Kinetic Analyses on Oxidation of Isobutenyl Radical and 2-Hydroperoxymethyl-2-propenyl Radical

In recognition of the importance of the isobutene oxidation reaction in the preignition chemistry associated with engine knock, the thermochemistry, chemical reaction pathways, and reaction kinetics of the isobutenyl radical oxidation at low to intermediate temperature range were computationally studied, focusing on both the first and the second O2 addition to the isobutenyl radical. The geometries of reactants, important intermediates, transition states, and products in the isobutenyl radical oxidation system were optimized at the B3LYP/6-311G(d,p) and MP2(full)/6-31G(d) levels, and the thermochemical properties were determined on the basis of ab initio, density functional theory, and statistical mechanics. Enthalpies of formation for several important intermediates were calculated using isodesmic reactions at the DFT and the CBS-QB3 levels. The kinetic analysis of the first O2 addition to the isobutenyl radical was performed using enthalpies at the CBS-QB3 and G3(MP2) levels. The reaction forms a chemically activated isobutenyl peroxy adduct which can be stabilized, dissociate back to reactants, cyclize to cyclic peroxide-alkyl radicals, and isomerize to the 2-hydroperoxymethyl-2-propenyl radical that further undergoes another O2 addition. The reaction channels for isomerization and cyclization and further dissociation on this second O2 addition were analyzed using enthalpies at the DFT level with energy corrections based on similar reaction channels for the first O2 addition. The high-pressure limit rate constants for each reaction channel were determined as functions of temperature by the canonical transition state theory for further kinetic model development.

Species active in the selective catalytic reduction of no with iso-butane on iron-exchanged ZSM-5 zeolites

Fe-ZSM-5 catalysts were prepared by ion exchange in aqueous medium or in the solid state and tested in the catalytic reduction of NO with iso-butane. X-ray powder diffraction (XRD), atomic absorption spectroscopy (AAS), electron paramagnetic resonance spectroscopy (EPR), X-ray absorption spectroscopy (XANES, EXAFS), temperature-programmed reduction by H2 (H2-TPR) and Mossbauer spectroscopy (MOS-S) were used for sample characterisation. Irrespective of the method used in catalyst preparation, EPR, XANES and MOS-S showed Fe atoms in the oxidation state of 3+. MOS-S and H2-TPR data on Fe-ZSM-5 prepared by ion exchange in the solid state allowed quantification of a lower hematite (Fe2O3) concentration and a higher proportion of Fe cations than samples prepared in an aqueous medium. In all the catalysts studied these Fe cations were the active sites in the reduction of NO to N2 and in the oxidation of iso-butane. It is further suggested that coordination of Fe species is another important aspect to be considered in their behaviour.

Optimization of MoVSb Oxide Catalyst for Partial Oxidation of Isobutane by Combinatorial Approaches.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Factors limiting selectivity in C3 and C4 amm(oxidation) reactions

An extensive data-mining study of C3 and C4 selective oxidation and ammoxidation reactions occurring in the gas phase over solid catalysts has been conducted. The reactions include the amm(oxidation) of propane, propene, isobutane and isobutene to produce α,β-unsaturated mononitriles and unsaturated carboxylic acids. Selectivity–conversion plots were generated for each reaction from the patent and scientific literature. For each reaction there is a clear upper limit in terms of selectivity–conversion beyond which experimental studies have not advanced. The results show that for some reactions, such as the oxidation of isobutane to methacrylic acid, high product selectivities are never realised due to the production of by-products via parallel oxidation of reaction intermediates, and more importantly, via consecutive oxidation of the unstable product. However, for the reactions of propane amm(oxidation) to produce acrylonitrile and acrylic acid the situation appears to be different. For these reactions, the central problem resides in the inability of conventional catalysts to suppress the propensity of the propene intermediate to desorb and oxidise further to oxides of carbon, rather than the loss in acrylic acid or acrylonitrile selectivity via consecutive oxidation.

Optimization of MoVSb Oxide Catalyst for Partial Oxidation of Isobutane by Combinatorial Approaches

Optimization of the Mo-V-Sb mixed-oxide system for the selective oxidation of isobutane to methacrolein by true combinatorial methods primarily is intended to reduce the number of experiments in a broad parameter space. Therefore, an evolutionary approach based on a genetic algorithm has been chosen to screen three generations of 30 catalysts. With the help of automated sol-gel synthesis techniques, a high-throughput continuous flow reactor (16UPCFR), and appropriate software for experimental design, a new catalyst composition with improved performance has been obtained. Finally, the best catalysts were scaled-up to gram quantities and tested in a continuous-flow reactor unit that was equipped with four parallel reactors (4UPCFR). The final catalyst showed a significantly higher selectivity toward methacrolein at the same isobutane conversion, compared to the initial Mo8V2Sb90O(x) catalyst.

Chemical Behavior of the Biradicaloid (HO···ONO) Singlet States of Peroxynitrous Acid. The Oxidation of Hydrocarbons, Sulfides, and Selenides

Various high levels of theory have been applied to the characterization of two higher lying biradicaloid metastable singlet states of peroxynitrous acid. A singlet minimum (cis-2) was located that had an elongated O-O distance (2.17 A) and was only 12.2 kcal/mol [UB3LYP/6-311+G(3df,2p)+ZPVE] higher in energy than its ground-state precursor. A trans-metastable singlet (trans-2) was 10.9 kcal/mol higher in energy than ground-state HO-ONO. CASSCF(12,10)/6-311+G(d,p) calculations predict the optimized geometries of these cis- and trans-metastable singlets to be close to those obtained with DFT. Optimization of cis- and trans-2 within the COSMO solvent model suggests that both exist as energy minima in polar media. Both cis- and trans-2 exist as hydrogen bonded complexes with several water molecules. These collective data suggest that solvated forms of cis-2.3H(2)O and trans-2.3H(2)O represent the elusive higher lying biradicaloid minima that were recently (J. Am. Chem. Soc. 2003, 125, 16204) advocated as the metastable forms of peroxynitrous acid (HOONO). The involvement of metastable trans-2 in the gas phase oxidation of methane and isobutane is firmly established to take place on the unrestricted [UB3LYP/6-311+G(d,p)] potential energy surface (PES) with classical activations barriers for the hydrogen abstraction step that are 15.7 and 5.9 kcal/mol lower than the corresponding activation energies for producing products methanol and tert-butyl alcohol formed on the restricted PES. The oxidation of dimethyl sulfide and dimethyl selenide, two-electron oxidations, proceeds by an S(N)2-like attack of the heteroatom lone pair on the O-O bond of ground-state peroxynitrous acid. No involvement of metastable forms of HO-ONO was discernible.

Alkane Oxidation by Osmium Tetroxide

Aqueous alkaline OsO4 at 85 degrees C oxidizes saturated alkanes, including primary, secondary, and tertiary C-H bonds. Isobutane affords tert-butanol in quantitative yield based on consumed OsO4. Cyclohexane is oxidized to a mixture of adipate and succinate. Ethane and propane are oxidized to acetate, which itself is further oxidized under the reaction conditions. A few turnovers of isobutane oxidation have been accomplished using NaIO4 as the terminal oxidant. The alkane oxidation is an example of ligand accelerated catalysis, as hydroxide binding to OsO4 is required for reaction. A concerted mechanism involving [3+2] addition of a C-H bond to two oxo groups of OsO4(OH)- is suggested, analogous to the pathways for dihydroxylation of alkenes by OsO4(L) and for addition of H2 to OsO4(L).