Partial Oxidation Of N-butane Research Articles

Dependences of catalyst layer thickness and pellet grading mode on partial oxidation of n-butane

An industrial-scale reactor-pellet coupled model incorporating realistic radial bed voidage is established for n-butane partial oxidation to maleic anhydride (MA) process. Simulation results demonstrate that the reactor packed with CLT-2.75 cylindrical pellets exhibits intense exothermic behavior at the front end of reactor, resulting in the over-oxidation of n-butane within the interior zone of the pellet. Although reducing the thickness of catalyst layers effectively mitigates heat release and prevents n-butane over-oxidation within the pellets’ interior zone, pellets with excessively thin catalyst layers would lead to lower n-butane conversion, making the reactor packed with CLT-0.825 pellets exhibiting improved MA selectivity and reduced hot spot temperature. The ultimate optimization of pellet grading with CLT-0.275/1.10 pellets indicates that implementing a temperature sequence characterized by lower temperature at the front end and higher temperature at the back end of the reactor could further notably reduce the hot spot temperature while maintaining a high MA yield.

Modeling the selective oxidation of n-butane to maleic anhydride: From active site to industrial reactor

In this contribution to the Special Issue honoring 100 very successful years of Casale S.A., we review and critically discuss the current status of modeling the most demanding selective partial oxidation reaction industrially applied: the partial oxidation of n-butane to maleic anhydride. We examine theoretical model descriptions of this partial oxidation reaction covering all relevant length scales: from modeling the active site and elementary steps, microkinetic and macrokinetic models, to reactor models on all length scales from laboratory reactors up to industrial-size production reactors. We also include in our manuscript the latest CFD developments aiming at a better understanding of heat and mass transfer in industrial catalyst beds as well as effects of the local bed structure. The contribution also covers relevant experimental findings with respect to the catalytically active species or sites on the catalyst surface, the reaction mechanism as well as microkinetic considerations. 60 years of research have greatly improved our understanding of the selective partial oxidation reaction. However, a critical review of the different aspects of the n-butane oxidation and its industrially used catalyst reveals on all length scales that there still remain unanswered questions, and that there are still some inconsistencies in our fundamental understanding. This situation arises from the fact that the catalyst for n-butane partial oxidation is a highly complex and dynamic system and its performance depends on all details of its generation and its operational history.

Characterization and reactivity of VMgO catalysts prepared by wet impregnation and sol–gel methods

ABSTRACTThis paper reports the study of physicochemical, surface, and catalytic properties of two series of VMgO catalysts prepared by two different methods: wet impregnation and sol–gel. The characterizations of the elaborated materials were performed using N2-sorption (Brunauer, Emmett and Teller (BET)), X-ray diffraction, Raman, transmission electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analyses. The catalytic properties of the elaborated materials were investigated in the isopropanol decomposition reaction to determine their acid–base character and in the selective oxidation of n-butane to evaluate their dehydrogenation properties. The preparation method and vanadium content strongly affected the properties of our materials. The sol–gel method leads to smaller crystallite size, higher specific surface area, and uniform particle distribution compared to the impregnation one. Both impregnation and SG solids promote the formation of acetone, which is related to the presence of strong basic sites (O2− species) on the catalytic exposed surface. The more pronounced basic character was obtained through the SG samples. The sol–gel samples exhibited the highest catalytic activity and C4-olefin selectivity in the partial oxidation of n-butane. Whatever the preparation procedure, the nature of surface oxygen species plays an important role in the orientation of catalytic performances.

Simulation of an industrial turbulent fluidized bed reactor for n-butane partial oxidation to maleic anhydride

A fluid-dynamic and chemical model of an industrial-scale turbulent fluidized-bed reactor, which performs n-butane partial oxidation to maleic anhydride (MA) catalyzed by (VO)2P2O7 solid particles, is proposed. Main assumptions are: gas plug-flow in the dense bed because gas back-mixing is minimized by internals; perfectly mixed particulate phase in the dense bed due to high recirculation rate of entrained particles at the bottom of the reactor, after separation by cyclones; plug-flow of both gas and solids in the freeboard. Literature kinetic models are considered to simulate reactions, slightly modified to allow careful prediction of industrial performance. The model is organized in ordinary differential and algebraic equations describing mass and energy balances and constitutive expressions for reaction rates, heat and mass transport phenomena, and implemented in MATLAB®. Numerical results simulate accurately temperature along the reactor, MA yield and by-products selectivity in the outlet stream, and allow to estimate the solid circulation rate. Inlet gas flow rate and n-butane/air feeding ratio are varied within a ±10% range around industrial operating conditions, to test the parametric sensitivity of the model: corresponding dense bed height, n-butane conversion, products selectivity in the outlet stream vary within ±5% of the experimental performances, depicting stable conditions.

Partial Oxidation of n-Butane over a Sol-Gel Prepared Vanadium Phosphorous Oxide

Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO4∙0.5H2O (the precursor) followed by in situ activation to produce (VO)2P2O7 (the active phase). This paper discusses an alternative synthesis method based on sol-gel techniques. Vanadium (V) triisopropoxide oxide was reacted with ortho-phosphoric acid in an aprotic solvent. The products were dried at high pressure in an autoclave with a controlled excess of solvent. This procedure produced a gel of VOPO4 with interlayer entrapped molecules. The surface area of the obtained materials was between 50 and 120 m2/g. Alcohol produced by the alkoxide hydrolysis reduced the vanadium during the drying step, thus VOPO4 was converted to the precursor. This procedure yielded non-agglomerated platelets, which were dehydrated and evaluated in a butane-air mixture. Catalysts were significantly more selective than the traditionally prepared materials with similar intrinsic activity. It is suggested that the small crystallite size obtained increased their selectivity towards maleic anhydride.

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.

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.

Effect of feed nozzle configuration on n-butane to maleic anhydride yield: From lab scale to commercial

In the process to produce maleic anhydride via the partial oxidation of n-butane, selectivity is sensitive to feed gas configuration of both oxygen and n-butane. Based on laboratory scale fluidized bed experiments, selectivity was superior when the n-butane was co-fed together with oxygen. When the oxygen and n-butane were fed separately through a distributor and a sparger, selectivity was highest when the sparger was closest to the distributor (independent of whether the n-butane was fed through the sparger and the oxygen through the distributor or vice versa). Various feed gas configurations were tested in a 4.2 m diameter commercial circulating fluidized bed reactor equipped with 926 spargers at three different levels. Maleic acid production rate increased by about 15% when oxygen was fed to a lower sparger 0.45 m above the distributor compared to when it was fed at a height of 1.9 m. These observations indicate that maintaining the catalyst in an atmosphere containing oxygen is important for overall n-butane conversion and maleic anhydride selectivity.

“ALL FREE” — a novel design concept of applying partial oxidation process to vehicle engine

With the rapid expansion of the global motor vehicle population, the transportation sector has taken up a growing proportion among all the carbon dioxide emission-related sectors. To contribute to solutions of the carbon dioxide-oriented problem in transportation, this paper proposes the “ALL FREE” concept that applies partial oxidation process instead of the conventional complete oxidation to vehicle engines. In such an engine, the fuels are partially oxidized into corresponding chemical products, which, as a result, enable the process to be theoretically free of CO2, while the heat output of the partial oxidation could drive the vehicle. On the other hand, the resulting products are of great value, which could decrease or even counteract the cost of fuels in transportation. In this paper, the thermodynamic and kinetic data (e.g., the heat output and heat release rate) of five selected partial oxidation reactions were calculated at length to demonstrate and exemplify the theoretical feasibility of the “ALL FREE” concept. It turned out that the partial oxidation of n-butane to maleic anhydride has the most potential to meet the basic requirements of this concept. To sum up, this design concept is of significant application potential for the reduction of CO2 emissions in the transportation industry, although there remain many technical challenges.

Influence of thermal conditions on partial oxidation of n-butane over supported Rh catalysts

Abstract Short residence time catalytic reactors for partial oxidation of alkanes are effective for production of H 2 -rich syngas. In this study, partial oxidation of n -butane in O 2 /Ar mixtures at ratios of 1/3.76 have been investigated over Rh catalysts impregnated in γ-Al 2 O 3 washcoat supports coated onto α-Al 2 O 3 ceramic foam monoliths (1.0 cm in length). Experiments in non-adiabatic reactors show that n -butane conversion and H 2 and CO selectivity depend strongly upon the reactor temperature and thereby upon heat lost through external walls of the reactor. For a baseline condition with a C/O atomic ratio of 1.0, inlet flow temperature of 300 °C, and catalyst-contact time of approximately 50 ms, improving reactor adiabaticity dramatically increases n -butane conversion and H 2 and CO selectivity. Raising inlet-flow temperature increases fuel conversion but does not improve H 2 selectivity. However, higher flow rates (with catalyst-contact times below 40 ms) show further increases in fuel conversion and syngas selectivity. These results suggest that under conditions with adequate heat release, partial oxidation occurs rapidly within the first few mm of the reactor. Improved heat confinement in the reactor increases catalyst temperature and thereby results in higher conversion and syngas selectivity. Under these conditions, the reactor effluent has much higher H 2 and CO selectivities than predicted by equilibrium at the exit temperature, which implies that higher internal temperatures determine the effluent composition. These results provide critical insight into the role of thermal processes and indicate a need for detailed mechanisms to model how competitive reaction pathways impact performance in catalytic partial oxidation reactions.

Partial oxidation of n-butane over ceria-promoted nickel/calcium hydroxyapatite

LPG has good infrastructure and is anticipated to be used for production of hydrogen, and n-butane which constitutes a main component of LPG for vehicles. Partial oxidation (POX) of n-butane is investigated in this research by employing ceria-promoted Ni/calcium hydroxyapatite catalysts (Ce x Ni2.5/Ca10(OH)2(PO4)6 x=0.1–0.3) which have recently been reported to exhibit good catalytic performance in POX of methane and propane. The experiments were carried out with changing ceria content, O2/n-C4H10 ratio and reaction temperature. As the O2/n-C4H10 ratio increased up to 2.75, the n-C4H10 conversion and H2 yield increased and the selectivity of methane and other hydrocarbons decreased. But with O2/n-C4H10=3.0, the n-C4H10 conversion and H2 yield decreased. Ce0.1Ni2.5/Ca10(OH)2(PO4)6 showed the highest n-C4H10 conversion and H2 yield on the whole. In durability tests, higher hydrogen yield and better catalyst stability were obtained with the O2/n-C4H10 ratio of 2.75 than with the ratio of 2.5.

Partial Oxidation of n-Butane in a Solid Electrolyte Membrane Reactor: Influence of Electrochemical Oxygen Pumping

The partial oxidation of -butane to maleic anhydride (MA) in a solid electrolyte membrane reactor was studied in three different operation modes: electrochemical membrane reactor (EMR), cofeed membrane reactor (CR), and mixed-feed membrane reactor (MMR). The EMR operation exhibited lower selectivity to MA but higher conversion of oxygen than the CR operation. The electrochemical oxygen pumping in the MMR operation led to decrease in the MA selectivity compared to the CR operation. By means of comparing the three operation modes, the electrochemically pumped oxygen was found to be more reactive but less selective to MA than gas-phase oxygen, which is directly related to the different reaction mechanisms between the CR and EMR operations. The butane oxidation occurred in the EMR involved not only the same catalytic reaction mechanism as in the CR but also an electrocatalytic reaction. A simplified catalytic and electrocatalytic reaction-mechanism scheme was proposed for the butane oxidation carried out in the EMR.

VPO transient lattice oxygen contribution

n-Butane partial oxidation to maleic anhydride is practiced commercially in several reactor types with vanadium phosphorous oxide (VPO) catalyst. DuPont operated a Circulating Fluidized Bed facility in which catalyst was shuttled between a net reducing zone (a transport bed) to a net oxidizing zone (air regenerator). Several advantages have been cited for this technology but the role of oxygen is hotly debated and different models have been proposed to characterize the complicated 14e − exchange. To examine the role of surface lattice oxygen, we carried out transient experiments in which catalyst was subjected to high concentrations of butane followed by an extensive re-oxidation treatment. Carbon accumulates on the surface lattice surface thereby contributing to a reduction in reaction rates and the quantity increases with the butane/oxygen ratio. This carbon reacts in the presence of molecular O 2 during the regeneration step. The surface lattice is capable of storing significant amounts of oxygen and when the catalyst is highly oxidized, both selectivity and activity are higher.

Feasibility of an Electrochemical Membrane Reactor for the Partial Oxidation of n-Butane to Maleic Anhydride

The feasibility of n-butane partial oxidation to maleic anhydride (MA) over vanadium phosphorus oxide catalysts in an electrochemical membrane reactor in which an oxygen-ion-conducting electrolyte was used as the membrane was studied. Butane oxidation and oxygen separation were carried out simultaneously on the opposite surfaces of the membrane, and the oxygen flux transferred across the membrane was controlled by the external current between the two electrodes. At 751 K and with a current of 40 mA, the conversion of butane was 15−16%, and the selectivity to MA was about 39%. The selectivity and yield of MA increased with increasing applied current. The optimal reaction temperature was 750 ± 5 K, as a compromise among the ionic conductivity of the membrane, the polarization resistances of the electrodes, and the selectivity and the yield of MA.

Microstructural differences between the catalyst and the standard V5+ phases of VPO

Vanadium phosphorus oxides, (VPO) are commercially used as catalysts for the synthesis of maleic anhydride, (MA) from the partial oxidation of n-butane. The phase constitution and the morphology of the catalyst are found to be dependent on the preparation routes and the applied solvent. The final catalyst consists of the main V phase, (VO)2P2O7 and a mixture of pentavalent phases: αI-VOPO4, αII-VOPO4, γ-VOPO4 [1]. These phases are crucial for the conversion and selectivity rate of the final catalyst. It is believed that only a specific combination of Vand V phase leads to the high catalytic performance [2]. In this work we present a comprehensive characterisation of the standard V phases: αI-VOPO4, αII-VOPO4, β-VOPO4 and γ-VOPO4 and the real VPO catalyst.

New insight into the role of gas phase reactions in the partial oxidation of butane

The partial oxidation of n-butane at high alkane to oxygen ratio was studied in the presence of a Pt–Rh gauze and in an empty tubular reactor under identical conditions. Temperature-programmed reaction (TPR) experiments with the metal gauze showed dramatic changes in the product distribution in the range 25–500 °C. Total oxidation of butane at low temperature is followed by selective conversion to olefins and oxygenates around 400 °C; a further increase in the oven temperature enhances selectively olefins formation. In situ infrared and visible imaging of the reacting gauze revealed remarkable ignition/extinction phenomena of the surface reactions. Fast ignition on the metal catalyst was observed around 200 °C; upon further raising the oven temperature, suppression of these reactions occurred at a temperature level corresponding to the transition to high selectivity conditions. These results indicate a shift from heterogeneous to homogeneous reaction mechanism, the latter being responsible for high selectivity to partial oxidation products (84% olefins+oxygenates). With the empty reactor, conversion and selectivity were similar to those obtained in the presence of the catalyst. The study shows that the gauze plays no significant role in butane partial oxidation, as reactions take place in the void upstream of the catalyst, presumably via an alkylperoxy intermediate.

Development of fluidized‐bed catalyst for partial oxidation of n‐butane

AbstractOptimization experiments were carried out for preparation of a catalyst precursor. Results show that the acid concentration and reaction temperature in precursor preparation exhibit strong effects on the catalyst behavior. For the catalysts prepared at higher concentrations of acid, the quantity of the V4+ phase (VO)2P2O7 is large, and the n‐butane conversions are all quite high. When decreasing the acid concentration in precursor preparation, the relative amount of the V5+ phase δ‐VOPO4 and the n‐butane conversion increase continuously; at the same time, the selectivity to maleic anhydride increases at the beginning, and then decreases after reaching a maximum value. The catalyst prepared at an acid concentration of 102.3% gave a maximum yield of maleic anhydride of 48.10% at an inlet n‐butane concentration of 4.0% and a space velocity of 500 h−1. The fine particle catalyst in this study offers great flexibility of operation.

A Study on VPO Specimen Supported on Aluminum-Containing MCM-41 for Partial Oxidation of n-Butane to MA

Dispersed vanadium–phosphorus oxide species supported on Al-MCM-41 with different vanadium loadings have been synthesized for the first time for partial oxidation of butane to MA. It was found that the VPO species was dispersed over the Al-MCM-41 support material, both in the internal channel and on the external surface. With increasing vanadium loading, n-butane conversion increased but MA selectivity decreased considerably under the same reaction conditions. At lower conversions (<30%), rather high MA selectivity (ca. 70%) can be achieved on the low loading sample. Compared with the amorphous structure of large pore SiO2 support, the unique structure of the MCM-41 and the incorporated Al3+ in the framework do have an impact on the reaction behavior of the supported VPO specimen. The chemical nature of the supported VPO species and the interaction between the applied VPO species and the support was found to vary notably with the content of vanadium in the sample and likewise affected the related physico-chemical characteristics and their reaction behaviors.

Transport modelling of packed-tube reactors — IV: Steady-state modelling with intraparticle gradients

A data-based model of surface states in packed tubes is joined with an intraparticle diffusion–reaction model to describe reactors with significant intraparticle gradients. This modelling approach is demonstrated with steady-state simulations of the partial oxidation of n-butane to maleic anhydride in a packed-tube reactor with spherical particles and a tube/particle diameter ratio of 2.02. The simulation is based on a correlation of heat transport experiments performed in a unique packed-tube gas flow apparatus, and on a kinetic model taken from the literature. An orthogonal collocation scheme, using rounded Hahn polynomial zeros as axial nodes and Jacobi zeros as intraparticle nodes, allows efficient solution of the resulting detailed reactor model.

Oxygenate Formation from n-Butane Oxidation at Short Contact Times: Different Gauze Sizes and Multiple Steady States

The production of olefins and oxygenates by partial oxidation of n-butane over a single layer of Pt–10% Rh gauze has been examined at atmospheric pressure in the fuel rich regime and in the space velocity range of 3.3×106to 1.6×107h−1(contact times of ∼1000 to 200 μs) using a single gauze reactor. We show that there is an optimum regime of space velocities to maximize the oxygenate selectivity and that at least 75% selectivity to olefins and oxygenates can be obtained. Nitrogen diluent in the feed lowers the production of oxygenates, and coarser mesh gauze gives higher oxygenate yield than finer mesh. In addition, at a specific range of fuel/oxygen feed ratios, multiple steady states are observed on the more open gauze. Analysis of the product distribution of these steady states indicates that initially the exothermic complete combustion of the butane on the gauze surface to CO2and H2O provides most of the necessary heat for this process. Oxygenates and olefins are then produced by homogeneous reaction in the quench zone downstream of the gauze. A detailed model of homogeneous chemistry confirms that oxygenates are produced by homogeneous reactions.