Butane Oxidation Research Articles

Butane oxidation process development in a circulating fluidized bed

DuPont designed and operated a circulating fluidized bed reactor (CFB) to produce maleic anhydride from n-butane using a vanadium pyrophosphate catalyst (VPP) encapsulated in a silica shell. A fraction of the pyrophosphate was oxidized to the V 5+ state from the V 4+ state in an air fed fluidized bed regenerator. The oxidized VPP was shuttled to a transport bed reactor with a high concentration of butane and oxygen. The gas carried the catalyst up through the bed at velocities of 0.8 m/s and, in the commercial plant, solids circulation rates exceeding 7 kt/h. Early development work was conducted on an experimental scale facility containing 1 kg of catalyst. The pilot plant catalyst inventory exceeded 2000 kg and there was 175 t in the commercial reactor. Throughout the program, significant advances in catalyst manufacture and process design were achieved. The CFB reactor configuration is being considered for several unrelated processes including chemical looping combustion, methanol-to-olefins and hot gas desulphurization. Improvements in spray drying technology reduced attrition losses by an order of magnitude versus expectation based on the pilot plant. Together with the low attrition losses and good stability, catalyst consumption was reduced by successfully re-spray drying used/attrited catalyst. By modifying the solids entrance and exit configurations, we were able to double initial plant capacity. Operability of the plant was excellent with a turn-down ratio of 5 demonstrated. At a production rate of 65,000 t/year of maleic acid – one of the largest single train reactors for a partial oxidation of an alkane – the maximum temperature difference within the bed was less than 20 °C. Heat transfer had been a major design consideration but even at this rate, only 1/3 of the total coil surface for cooling was activated.

Structural evolution and catalytic performance of DuPont V-P-O/SiO 2 materials designed for fluidized bed applications

An industrial V-P-O catalyst (DuPont), comprising vanadyl pyrophosphate crystallites encapsulated by a silica shell, has been investigated. Reaction evaluation for butane oxidation was conducted over (i) the catalyst precursor, (ii) the calcined precursor and (iii) equilibrated material (2 years on-line) in a fixed-bed reactor. Characterization was conducted on these three samples by XRD, SEM, TEM and XPS. The core–shell particles have also been examined with a novel X-ray ultramicroscopy (XuM) technique which reveals the internal structure without having to section the material. The microstructural and surface compositional changes that have occurred over the course of its industrial lifespan in a fluidized bed reactor are correlated with the catalytic activity measurements.

Regeneration studies of redox catalysts

Cited advantages of circulating fluidized bed reactors (CFB) include higher selectivity and conversion together with the ability to optimize the process conditions of each vessel independently—temperature, gas partial pressure and residence time. DuPont commercialized a CFB process to produce maleic anhydride in which a vanadium pyrophosphate (VPO) was cycled between a fast bed riser and an air fed regenerator. Together with VPO, we examined two other redox catalyst systems—MoVSb (acrylic acid from propane) and FeMoO (methanol to formaldehyde). The lattice oxygen capacity of the FeMoO catalyst was about five times higher than either the VPO or MoVSb with little adsorbed carbon but a significant quantity of chemisorbed water. Above 350 °C, carbon deposition was detected and increased with increasing temperature. Carbon deposition decreased with increasing temperature for the MoVSb system and its lattice oxygen capacity was slightly higher than for VPO. The carbon deposition pattern for VPO was the opposite of the MoVSb and increased with temperature. Based on a hydrogen and carbon mass balance during the catalyst re-oxidation treatment, the molecular composition of the adsorbed species were C 4H 6 and C 3H 3—like for the VPO and MoVSb, respectively. Based on the high lattice oxygen capacity, the formaldehyde reaction appears to be ideally suited for development in a CFB. Whereas the lattice oxygen contribution of the MoVSb is equivalent to VPO, less oxygen is required to produce acrylic acid (compared to maleic anhydride) so the incentive of developing a CFB process should be greater than for butane oxidation to maleic anhydride.

Differential aerobic and anaerobic oxidation of hydrocarbon gases discharged at mud volcanoes in the Nile deep-sea fan

The present study investigates hydrocarbon oxidation processes at Isis and Amon mud volcanoes (MV’s), in the eastern Nile deep-sea fan. In the water column, molecular and carbon isotopic signatures of light hydrocarbons indicate that gases rapidly dissolve in seawater and are partially oxidized. In the upper sediments, anaerobic oxidation of the light hydrocarbons takes place, as clearly shown by their molecular and isotopic composition. These processes lead to the presence of a distinct Sulfate–Hydrocarbon Interface at 120–145 cm and 20–50 cm below the seafloor, for Isis and Amon MV’s, respectively. In contrast to processes occurring in the water column, a clear preferential oxidation of methane, propane and n-butane over ethane and i-butane is observed in the anoxic sediments. Furthermore, for the first time, fractionation factors have been determined for the anaerobic oxidation of propane and butane, being respectively −4.80‰ and −0.7‰ for δ 13C, and −43.3‰ for δ 2H of propane.

Physicochemical properties of catalysts based on aqueous solutions of Mo–V–phosphoric heteropoly acids

Various organic substrates can be selectively oxidized with O 2 in two stages using aqueous solutions of Mo–V–phosphoric heteropoly acids (HPA) as catalysts. In stage (1), a substrate is oxidized with a HPA solution to the desired product that is separated from the reduced form of HPA. The latter is oxidized with O 2 in stage (2) closing a catalytic cycle. All physicochemical properties of the homogeneous catalysts based on HPA solutions continuously alter during these redox processes. Using as an example a solution of the modified high-vanadium HPA having gross composition H 16P 3Mo 17V 7O 84 (HPA-7′), it was shown that viscosity and pH of this solution reach their maxima after reaction (1) and attain their minima after reaction (2). The reverse situation is observed for redox potential of the HPA-7′ solution. Many-cycled testing of 1-butene oxidation in stages (1) + (2) in the presence of the Pd + HPA-7′ catalyst confirms that the alterations of physicochemical properties of the catalyst are completely reversible.

Heterogeneous catalysts—discovery and design

Heterogeneous catalysis plays a key role in the manufacture of essential products in key areas of agriculture and pharmaceuticals, but also in the production of polymers and numerous essential materials. Our understanding of heterogeneous catalysts is advancing rapidly, especially by using the latest characterisation methods on these relatively complex effect materials. At the heart of these catalytic processes, both selective oxidation and hydrogenation play a key role. Both oxidation and hydrogenation exhibit similar requirements since often a partial reaction product is required, rather than the products of total hydrogenation or oxidation, in the latter case this being typically carbon dioxide and water. This Feature Article considers the approaches available for catalyst discovery and design for heterogeneous catalysts. Three catalysts are considered in detail, two exemplifying oxidation and the other selective hydrogenation. The design of vanadium phosphates for the selective oxidation of butane to maleic anhydride is described in terms of the search for advanced materials with superior activity. This is achieved through the synthesis of wholly amorphous vanadium phosphates. The design of supported gold and gold palladium alloy catalysts for the oxidation of carbon monoxide and the direct hydrogenation of oxygen to form hydrogen peroxide is described and the problems concerning selectivity control are discussed.

Catalytic combustion of butane on Ru/γ-Al2O3 catalysts

Ru/γ-Al2O3 catalysts were prepared by incipient wetness method from RuCl3 precursor and their performance in oxidation of iso- and n-butane was investigated. The catalytic activity was examined on the calcined–reduced and on the directly reduced catalysts, with and after removing Cl ions, as well as after the oxidation at 250°C. All catalysts have been characterized by various methods such as BET, XRD, TEM, XPS, H2 chemisorption and O2 uptake in order to correlate their performance with their physiochemical properties. It was found that pre-treatment procedure has a significant influence on activity of the Ru/γ-Al2O3 catalysts. The considerable contamination of Ru particles by chlorine ions results in lowering activity of the Ru/γ-Al2O3 catalysts. It was established that reduced nearly Cl-free Ru/γ-Al2O3 catalysts exhibited higher activity than catalysts oxidized at 250°C. It was shown by XRD, TEM and O2 uptake data that at this temperature, very small Ru particles were transformed completely into RuO2, while the large Ru particles were partly covered by a thin RuO2 film (1.6nm). Catalytic and characterization results revealed that the most active sites in the butane oxidation reaction, consist probably of a few layers of thick surface oxide on the large Ru particles and small RuxOy clusters without well-defined stoichiometry. Such surface species were formed at 100–200°C in all catalysts and in the most active reduced Cl-free 4.6% Ru catalyst which reached 100% butane conversion below 200°C. The catalytic performance of Ru declined as the catalysts were oxidized at higher temperature. The activity loss was attributed to the formation of crystalline RuO2 phase and to some sintering of the active phase. In the used catalysts, small Ru particles were oxidized to RuO2 while the large Ru particles were covered with RuO2 layer, with a thickness of 2–3nm, as shown by TEM and XRD.

In Vivo Evolution of Butane Oxidation by Terminal Alkane Hydroxylases AlkB and CYP153A6

Enzymes of the AlkB and CYP153 families catalyze the first step in the catabolism of medium-chain-length alkanes, selective oxidation of the alkane to the 1-alkanol, and enable their host organisms to utilize alkanes as carbon sources. Small, gaseous alkanes, however, are converted to alkanols by evolutionarily unrelated methane monooxygenases. Propane and butane can be oxidized by CYP enzymes engineered in the laboratory, but these produce predominantly the 2-alkanols. Here we report the in vivo-directed evolution of two medium-chain-length terminal alkane hydroxylases, the integral membrane di-iron enzyme AlkB from Pseudomonas putida GPo1 and the class II-type soluble CYP153A6 from Mycobacterium sp. strain HXN-1500, to enhance their activity on small alkanes. We established a P. putida evolution system that enables selection for terminal alkane hydroxylase activity and used it to select propane- and butane-oxidizing enzymes based on enhanced growth complementation of an adapted P. putida GPo12(pGEc47 Delta B) strain. The resulting enzymes exhibited higher rates of 1-butanol production from butane and maintained their preference for terminal hydroxylation. This in vivo evolution system could be useful for directed evolution of enzymes that function efficiently to hydroxylate small alkanes in engineered hosts.

A Proton‐Conducting Fuel Cell Operating with Hydrocarbon Fuels

Low temperature, high voltage! Direct oxidation of hydrocarbon fuels, including methane, ethane, propane, and butane, occurs over Pt-free anodes in a proton-conducting fuel cell in the temperature range 100–300 °C. A Mo2C–ZrO2/C anode (30 mg Mo2C–ZrO2 per cm2) yields power densities equal to those obtained from Pt/C anodes (1–7 mg Pt per cm2) and generates higher open-circuit voltages than the Pt/C anodes.

Modulating the Selectivity for CO and Butane Oxidation over Heterogeneous Catalysis through Amorphous Catalyst Coatings

The preparation of porous films directly deposited onto the surface of catalyst particles is attracting increasing attention. We report here for the first time a method that can be carried out at ambient pressure for the preparation of porous films deposited over 3 mm diameter catalyst particles of silica-supported Pt−Fe. Characterization of the sample prepared at ambient pressure (i.e., open air, OA) and its main structural differences as compared with a Na−A (LTA) coated catalyst made using an autoclave-based method are presented. The OA-coated material predominantly exhibited an amorphous film over the catalyst surface with between 4 and 13% of crystallinity as compared with fully crystallized LTA zeolite crystals. This coated sample was highly selective for CO oxidation in the presence of butane with no butane oxidation observed up to 350 °C. This indicates, for the first time, that the presence of a crystalline membrane is not necessary for the difference in light off temperature between CO and butane to be achieved and that amorphous films may also produce this effect. An examination of the space velocity dependence and adsorption of Na+ on the catalysts indicates that the variation in CO and butane oxidation activity is not caused by site blocking predominantly, although the Pt activity was lowered by contact with this alkali.

Techniques for Fabricating Nanoscale Catalytic Circuits

This paper describes the development of a new technique, atomic beam deposition (ABD), for the fabrication of catalysts with different active sites capable of catalyzing different chemical reactions. Using ABD, submonolayer amounts of Te and Cu atoms were deposited on vanadyl pyrophosphate (VPO) catalyst particles, and precise non-steady-state kinetic characterization was performed using the temporal analysis of products (TAP) reactor immediately following deposition. Results from TAP Knudsen pulse response experiments determine if small changes in the metal surface composition would produce detectable changes in catalytic properties. Partial oxidation of 1-butene to furan was used as the test reaction. Furthermore, this paper also demonstrates the sensitivity of the TAP reactor by measuring oxygen uptake on a single 350 μm diameter polycrystalline Pt particle packed in a bed with 100,000 inert quartz particles of similar dimensions. The Pt experiments demonstrate the precise manipulation of surface oxygen content.

Fast and exergy efficient start-up of micro-solid oxide fuel cell systems by using the reformer or the post-combustor for start-up heating

The start-up process of a micro-solid oxide fuel cell system strongly influences its overall efficiency, especially for portable applications where a frequent switch-on and switch-off is required. We present herein a novel start-up process for such systems that exploits existing units, such as the post-combustor or the reformer, as a heat source to reach the operation temperature of the cell at 600 °C. Our experimental results show that the employment of platinum catalysts in the post-combustor or rhodium catalysts in the reformer for total oxidation of butane by air combined with an electrically heated wire led to a faster and more efficient start-up than conventional start-up methods using only electrical energy. By using the post-combustor as heat source, the start-up time could be reduced by 79% and the exergy cost by 86%. The latter includes the cost of the stand-alone fuel cell system to produce electrical energy for the joule heating of the wire (i.e. the system efficiency is accounted for). There are several advantages to use the reformer as heat source during start-up, such as prevention of coking of the fuel cell or improved heat transfer by internal heating of the other components. The start-up performance, however, was lower than that of the post-combustor: the start-up time could be reduced by 65% and the exergy cost by 68% compared to a conventional start-up.

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.

Characterization of new catalysts based on uranium oxides

Catalysts based on uranium oxides were systematically studied for the first time. Catalysts containing various amounts of uranium oxides (5 and 15%) supported on alumina and mixed Ni-U/Al2O3 catalysts were synthesized. The uranium oxide catalysts were characterized using the thermal desorption of argon, the low-temperature adsorption of nitrogen, X-ray diffraction analysis, and temperature-programmed reduction with hydrogen and CO. The effects of composition, preparation conditions, and thermal treatment on physicochemical properties and catalytic activity in the reactions of methane and butane oxidation, the steam and carbon dioxide reforming of methane, and the partial oxidation of methane were studied. It was found that a catalyst containing 5% U on alumina calcined at 1000°C was most active in the reaction of high-temperature methane oxidation. For the Ni-U/Al2O3 catalysts containing various uranium amounts (from 0 to 30%), the introduction of uranium as a catalyst constituent considerably increased the catalytic activity in methane steam reforming and partial oxidation.

Oxidation of butane to butanol coupled to electrochemical redox reaction of NAD+/NADH

A crude cell extract from a butane-utilizing bacterium, Alcaligenes sp., catalyzed the oxidation of butane to butanol coupled to NADH. A graphite electrode modified with Neutral Red (NR-electrode) catalyzed the reduction of NAD(+) to NADH. About 4.9 mM butanol was produced from 50% n-butane/O(2) mixture through the combined reactions of the crude enzyme and the NR-electrode in 250 ml reactor for 3 h.

Pressure Calcination of VPO Catalyst

Calcination and activation are critical steps in the transformation of vanadyl hydrogen phosphate hemihydrate (VPO precursorVOHPO4·0.5H2O) to vanadyl pyrophosphate (VPO catalyst(VO)2P2O7). Whereas many published kinetics studies for butane oxidation over VPO demonstrate the relationship between catalytic activity and reaction conditions, the relationship between calcination conditions and activity has only received superficial attention in the open literature. This study delineates the operating boundaries in which to optimize catalytic performance. The control variables included temperature, pressure, time, and gas-phase composition (principally, oxygen and water vapor partial pressures), and their effects on surface area, oxidation state, and catalytic activity were measured. The experimental plan included several hundred calcination experiments. The commercial-design operating conditions were chosen as the base-case conditions: temperatures from 330 to 460 °C, pressures up to 6 atm, and oxygen and water concentrations between 0 and 20% and 0−3%, respectively. The optimal temperature was found to be about 390 °C. Catalyst performance declines with increasing pressure, but the pressure−time relationship allows a range of conditions: optimal catalytic performance was achieved within 20 h of calcination at atmospheric pressure, but it took less than 4 h to achieve this high level of performance when precursor was calcined at 3.5 atm (at longer times, the catalytic performance deteriorated). Co-feeding steam (in the presence of oxygen) generally had a deleterious affect on catalyst performance and, in particular, maleic anhydride yield. Moreover, oxidation states higher than 4.5 were achieved with steam/oxygen mixtures in as little as 20 h. Catalyst performance declined linearly with oxidation state for precursor calcined to vanadium oxidation states exceeding 4.5.

Evidence for Modified Mechanisms of Chloroethene Oxidation in Pseudomonas butanovora Mutants Containing Single Amino Acid Substitutions in the Hydroxylase α-Subunit of Butane Monooxygenase

The properties of oxidation of dichloroethene (DCE) and trichloroethylene (TCE) by three mutant strains of Pseudomonas butanovora containing single amino acid substitutions in the alpha-subunit of butane monooxygenase hydroxylase (BMOH-alpha) were compared to the properties of the wild-type strain (Rev WT). The rates of oxidation of three chloroethenes (CEs) were reduced in mutant strain G113N and corresponded with a lower maximum rate of butane oxidation. The rate of TCE degradation was reduced by one-half in mutant strain L279F, whereas the rates of DCE oxidation were the same as those in Rev WT. Evidence was obtained that the composition of products of CE oxidation differed between Rev WT and some of the mutant strains. For example, while Rev WT released nearly all available chlorine stoichiometrically during CE oxidation, strain F321Y released about 40% of the chlorine during 1,2-cis-DCE and TCE oxidation, and strain G113N released between 14 and 25% of the available chlorine during oxidation of DCE and 56% of the available chlorine during oxidation of TCE. Whereas Rev WT, strain L279F, and strain F321Y formed stoichiometric amounts of 1,2-cis-DCE epoxide during oxidation of 1,2-cis-DCE, only about 50% of the 1,2-cis-DCE oxidized by strain G113N was detected as the epoxide. Evidence was obtained that 1,2-cis-DCE epoxide was a substrate for butane monooxygenase (BMO) that was oxidized after the parent compound was consumed. Yet all of the mutant strains released less than 40% of the available 1,2-cis-DCE chlorine, suggesting that they have altered activity towards the epoxide. In addition, strain G113N was unable to degrade the epoxide. TCE epoxide was detected during exposure of Rev WT and strain F321Y to TCE but was not detected with strains L279F and G113N. Lactate-dependent O(2) uptake rates were differentially affected by DCE degradation in the mutant strains, providing evidence that some products released by the altered BMOs reduced the impact of CE on cellular toxicity. The use of CEs as substrates in combination with P. butanovora BMOH-alpha mutants might allow insights into the catalytic mechanism of BMO to be obtained.

Partial differentiation of neural network for the analysis of factors controlling catalytic activity

In order to examine the possibility for identifying the factors controlling catalytic activity by neural network, the numerical partial differentiation of trained neural network was applied to several examples of experimentally established correlations of catalytic activities with primary factors: oxidation of propene on oxide catalysts, oxidation of butane on lanthanide oxides, decomposition of formic acid on metal catalysts, oxidation of methane on lanthanide oxides, and support and additive effects on low temperature combustion of propane over Pt catalyst. The relative importance of the given factors including dummy parameters were estimated from the numerical differentiation of trained artificial neural network, and they were compared with those obtained by previously proposed methods using the weightings of connecting links of trained neural network. In all the examples, the primary factors that had been proposed in experimental studies were successfully identified by the numerical differentiation of trained neural network. As for the connecting weight-methods examined for the comparison, only the method proposed by Olden et al. and us gave satisfactory results to identify the primary factors. Further, it was demonstrated that the partial differentiation method could be used to obtain local information, that is, the partial derivatives for individual catalyst, which would enable us to know the method how each catalyst can be improved.

Analysis of catalytic performance by partial differentiation of neural network pattern

Numerical partial differentiation of trained neural network pattern was proposed as a tool for identification of primary factors controlling catalytic activity. The validity of the method was demonstrated by applying it to experimentally established correlations between catalytic activity and catalyst properties: the oxidations of butane and methane on lanthanide oxides were taken as examples, because good correlations had been established between catalytic activity and fourth ionization potential of lanthanide ion.

Variation of the vanadium oxidation state within a VPO catalyst layer in a membrane reactor: XPS mapping and modelling

Recently, the feasibility of butane oxidation in an electrochemical membrane reactor (EMR) using a vanadium phosphorus oxide (VPO) catalyst layer on a tubular anodic electrode has been reported. This novel application of EMR gives rise to questions about the vanadium oxidation state (V ox) under working conditions and about its spatial distribution in the catalyst layer. It has now been determined by means of position-resolved XPS measurements. In addition, model calculations on the spatial V ox distribution have been performed for the first time. The simulations reveal a non-uniform 3D distribution of V ox due to the relative rate of reduction and re-oxidation processes in the catalyst layer, in good agreement with the experimental XPS data.