Catalytic Partial Oxidation Reactor Research Articles

Optimal integration modeling of Co – Electrolysis in a power-to-liquid industrial process

High temperature co-electrolysis using solid-oxide electrolysis cells is a highly efficient pathway for green syngas production owing to the possibility of heat integration with other processes. Therefore, this study described and evaluates a flexible and efficient configuration for producing sustainable synthetic fuels using electricity from renewables and captured CO2 by integrating co-electrolysis in a power-to-liquid industrial plant. Thereafter, novel and efficient technologies were implemented for green syngas production and its subsequent purification, increasing the overall process efficiency and achieving a significant reduction in the carbon footprint compared to mature synthetic crude production processes. Catalytic partial oxidation and dual pressure swing adsorption were integrated with co-electrolysis and Fischer–Tropsch synthesis in a scaled industrial plant, using residual streams from the complex or those of renewable origin as feed, which allowed the continuous operation of the process independent of renewable power generation. The mass and energy balance, performance, and efficiency estimations were also included in this study. A solid-oxide electrolytic cell (SOEC) plant using renewable electricity and heat input from thermal integration with the outlet syngas stream of the catalytic partial oxidation reactor was selected as a case study. Both the performance and efficiency analyses of the co-electrolysis unit demonstrated the benefits of such thermal integration in comparison with current solutions. In this study, both the thermal integration of the process streams, as well as the energy and heat consumed by the syngas purification process were considered.

Carbonate dimorphism, and the reinterpretation of rates of lattice and excess oxygen-driven catalytic cycles

Catalytic implications of local deviations from nominal oxide stoichiometry remain critical to consider yet challenging to elucidate in the context of bulk oxide-mediated light alkane oxidation reactions, in part due to a lack of a priori knowledge of surface active oxygen site counts. Carbonate dimorphism, i.e., differences in carbonate speciation resulting from CO2 adsorption onto unsupported nickel oxide surfaces, can be exploited toward quantifying the surface density of lattice and excess oxygens, and to further deconvolute their respective contributions toward specific steps within the ethane oxidation reaction network. Density functional theory, volumetric gas sorption, in situ titration, in situ spectroscopy, and transient kinetic data interpreted in light of quantitative estimates of surface excess oxygen density confirm the involvement of excess oxygen in partial oxidative turnovers producing ethene from ethane and O2. These collective studies cast a more nuanced interpretation of site requirements pertaining to nickel oxide-mediated alkane oxidation. Our findings reveal that excess oxygen atoms can be titrated under reaction conditions, and that these sites are (on average) more selective to ethene than lattice oxygens. Tools and methodologies employed herein connect seemingly disparate elements of bulk oxide catalysis research – the need for quantitative estimates of oxide surface non-stoichiometry on the one hand, and the propensity of unsupported oxides toward carbonate formation on the other – and provide a template for the possible broader application of quantitative analyses of probe-molecule binding characteristics toward elucidation of active site density and speciation in catalytic partial oxidation reaction systems of commercial relevance.

Techno economic analysis of a micro Gas-to-Liquid unit for associated natural gas conversion

Flared and vented natural gas in remote regions of the world contribute ¿1% of the total CO2 emissions. High investment costs to build facilities to treat this gas and labor costs to operate the infrastructure are deterrents to addressing this environmental burden. Here we report a techno-economic analysis of a commercial mobile manufacturing plant that processes 2400 m3 d-1 of methane via a tandem short contact time catalytic partial oxidation (CPOX) and a single-pass Fischer–Tropsch fluidized bed to produce 7 bbl d-1. Starting from methane and air, a thermodynamic analysis identified the optimized operating conditions considering both carbon yield, CO/H2 ratio and adiabatic conditions. We studied the flammability limits of the mixture at operating pressures and temperatures. The economic analysis itemizes costs for all equipment rather than applying scale-up power law or factors. The greatest contributors to direct costs are the compressors and the CPOX reactor. Operating CPOX at 2.0 MPa reduces reactor volumes but to achieve 90% conversion and selectivity requires operating this unit above 900 °C. Avoiding syngas compression and upstream syngas conditioning reduces capital costs. The capital cost (CAPEX) reaches 570 000 USD when the whole process operates at 2.0 MPa. Considering numbering-up, the price of the 100th unit approaches 360 000 USD thus the MRU increases profitability. We demonstrate how thermodynamics constrains methane conversion and syngas selectivity. A large part of achieving low CAPEX is operating a single pass process, building multiple units, and replacing the methane to heat the treater at the oil tank battery with the incondensable gas leaving the three phases separator downstream the Fischer–Tropsch reactor.

Gas Turbine/Solid Oxide Fuel Cell Hybrids for Aircraft Propulsion and Power

The impact on range and endurance of increasing electrical loads on aircraft and burgeoning interest in all-electric aircraft are driving a need for more efficient replacements for engine-driven mechanical generators. This Paper presents a model of a synergistic gas turbine/solid oxide fuel cell system for combined propulsion and electrical power on aircraft. It is developed using Numerical Propulsion System Simulation and features realistic representations of the engine, reformer (a catalytic partial oxidation reactor), solid oxide fuel cell, and external aerodynamic losses. The results show that incorporating the reformer and fuel cell directly into the engine’s flowpath reduces vehicle-level fuel consumption of a high-altitude long-endurance aircraft at cruise by at least 8% when the engine is mounted inside the fuselage and at least 4% when the engine is installed within a nacelle. It also increases electrical generation capability by factors of 2 or more versus engine-driven mechanical generators in several aircraft applications. The main limitation in nacelle-mounted applications is increased external aerodynamic drag associated with the protrusion of the fuel cell into the flow around the engine, but it is shown that this can be mitigated through tight integration with high-pressure-ratio engines and careful flowpath design.

Scaling Relations for Autothermal Operation of Catalytic Reactors

Autothermal operation (AO) has several advantages for carrying out highly exothermic catalytic partial oxidation (CPO) and/or oxidative dehydrogenation (ODH) reactions compared to traditional cooled multitubular reactors. In steady-state autothermal operation (AO), there is no heat addition to the reactor or intentional heat removal by cooling through reactor walls; the heat of reaction is removed mainly by convective flow of the cold feed. The existence of an ignited high temperature (and conversion) state at the lowest possible feed temperature and/or space time is essential. This work examines the impact of various design and operating variables on the feasibility and economic scale-up of shallow packed-bed catalytic reactors for autothermal operation. Specifically, we present scaling relations that can be used to examine the impact of effective bed thermal conductivity, bed length, particle size, catalyst activity, reaction kinetics, and operating pressure on the extinction (blow-out) flow rate or feed temperature for large scale autothermal CPO and ODH reactors operated close to the adiabatic limit. The scale-up relations derived for a single-step CPO/ODH reaction are verified by numerical simulations. They are also validated using the highly complex oxidative coupling of methane (OCM) as an example.

Oxidative dehydrogenation of ethane over mixed metal oxide catalysts: Autothermal or cooled tubular reactor design?

AbstractA kinetic model consistent with experimentally measured reaction orders for the oxidative dehydrogenation of ethane (ODHE) over a MoVTeNbO catalyst is developed and applied to compare autothermal and multi‐tubular reactor designs for the same. The results suggest that autothermal reactor configurations are more favorable compared to multi‐tubular ones for this highly exothermic reaction, and become even more so with increasing active site density. A bifurcation analysis based on ignition and extinction behavior is presented as a function of adiabatic temperature rise (varied by altering the feed ethane to oxygen molar ratio) and catalyst active site density (varied by altering the pre‐exponential factor), thereby providing additional insights into strategies for successful scale‐up of ODHE reactors. These strategies for the design of viable reactor configurations may be more broadly applicable to high temperature catalytic partial oxidation reactions currently in practice or under consideration in the context of large‐scale processes for chemical production.

A non-premixed reactive volatilization reactor for catalytic partial oxidation of low volatility fuels at a short contact time

This work presents a novel non-premixed opposed-flow reactive volatilization reactor that simultaneously vaporizes and partially oxidizes low volatility liquid hydrocarbons at a short contact time (<12 ms).

A combined heat, hydrogen and power tri-generation system based on the use of catalytic membrane reactors with a dual-loop organic Rankine cycle

A dual-loop organic Rankine cycle (D-ORC) was used to recover waste heat from a biomass gasification process, for combined heat, hydrogen, and power (CHHP) generation. The process is based on the integration of biomass gasification with catalytic partial oxidation (CPO) and water-gas shift catalytic membrane reactors (WGS CMRs) for the simultaneous production and separation of hydrogen. The high temperature loop of the ORC was used to cool the CPO reactor effluent, while the low temperature loop was used to cool the WGS CMR retentate. Energy and exergy analyses were carried out to select the optima working fluids for this application. Hydrocarbons, siloxanes, hydrofluorocarbons (HFCs), and hydrofluoroolefins (HFOs) were examined as potential candidates in this analysis. Results indicate that the highest efficiency was obtained when n-heptane and n-pentane were used as working fluids for the high and low temperature loops, respectively. Using this combination, electric and exergy efficiencies of 13.93% and 36.41% were computed, receptively. The process generates 1.37 kW of power, and produces 1.41 kg/hr of hydrogen at 773 K and 91.32 kg/hr of hot water at 363 K. The exergy analysis has also showed that the high temperature loop turbine and condenser have contributed the most, by around 32%, to the overall system irreversibility.

Hetero-/homogeneous chemistry interactions and flame formation during methane catalytic partial oxidation in rhodium-coated channels

The hetero-/homogeneous chemistry interactions during the catalytic partial oxidation (CPO) of methane were investigated numerically in rhodium-coated cylindrical channels using axisymmetric simulations with detailed catalytic and gas-phase chemistries, conjugate heat transfer in the solid wall and detailed transport. Simulated conditions spanned pressures 1–25 bar, methane-to-air equivalence ratios 2.5–4.0, inlet temperatures 300–900 K and channel diameters 0.5–2.0 mm. The formation of vigorous flames in the oxidation zone of the CPO reactor was promoted as the pressure, inlet temperature and channel diameter increased. The catalytic pathway induced a strong radial stratification of the reactant and temperature distributions over the homogeneous combustion zones. This in turn resulted in flames spatially confined to the channel core, such that the catalytic wall temperature was only modestly affected by the flames (∼25 K wall temperature rise due to the flame presence), a result highly desirable for the reactor thermal management and for the catalyst thermal stability. Even when strong flames were formed, combined hetero-/homogeneous combustion persisted over the entire axial extent of the flames. The deficient oxygen reactant leaked through the flame zones and was subsequently converted catalytically on the channel walls, with the oxygen leakage increasing as the channel diameter, pressure, and inlet temperature decreased. Extensive parametric simulations delineated the regimes of operating conditions and geometrical parameters (pressure, inlet temperature, equivalence ratio and channel diameter) for which gas-phase combustion could not be ignored during methane CPO over rhodium. It was shown that for practical power generation systems (pressures and inlet temperatures above 15 bar and 600 K, respectively) gaseous chemistry could not be neglected and offered the benefit of reducing the extent of the oxidation zone and hence the overall reactor length.

Surface Alloy Composition Controlled O2 Activation on Pd–Au Bimetallic Model Catalysts

Oxygen is an important reactant in several catalytic conversions and partial oxidation reactions on Pd–Au alloy surfaces; however, adsorption and dissociation are not fully understood, especially as a function of the surface alloy composition. In this study, we probe the influence of the atomic makeup of the surface of Pd–Au catalysts regarding control of the catalytic activity toward O2 dissociation and the reactivity of the resulting oxygen adatoms. To experimentally investigate this, we prepared various bimetallic surfaces under ultrahigh vacuum via evaporation of Pd onto a Au(111) surface. Hydrogen molecules were used to characterize the composition of the Pd–Au surfaces, which we simplistically group into two categories: (i) Pd–Au interface sites and (ii) Pd(111)-like island sites. When the Pd coverage is 1.0 ML, which predominantly indicates Pd–Au interface sites, no dissociative adsorption of O2 at 300 K is observed, but dissociation begins to be measurable on the surfaces with larger Pd loadings (...

Prediction of morphological changes of catalyst materials under reaction conditions by combined ab initio thermodynamics and microkinetic modelling.

In this article, we couple microkinetic modelling, ab initio thermodynamics and Wulff-Kaishew construction to describe the structural variation of catalyst materials as a function of the chemical potential in the reactor. We focus specifically on experiments of catalytic partial oxidation (CPO) of methane on Rh/α-Al2O3. We employ a detailed structureless microkinetic model to calculate the profiles of the gaseous species molar fractions along the reactor coordinate and to select the most abundant reaction intermediates (MARIs) populating the catalyst surfaces in different zones of the reactor. Then, we calculate the most stable bulk and surface structures of the catalyst under different conditions of the reaction environment with density functional theory (DFT) calculations and ab initio thermodynamics, considering the presence of the MARIs on the catalyst surface in thermodynamic equilibrium with the partial pressures of their reservoirs in the gas phase surrounding the catalyst. Finally, we exploit the Wulff-Kaishew construction method to estimate the three-dimensional shape of the catalyst nanoparticles and the distribution of the active sites along the reactor coordinate. We find that the catalyst drastically modifies its morphology during CPO reaction by undergoing phase transition, in agreement with spectroscopy studies reported in the literature. The framework is also successfully applied for the analysis and interpretation of chemisorption experiments for catalyst characterization. These results demonstrate the crucial importance of rigorously accounting for the structural effect in microkinetic modeling simulations and pave the way towards the development of structure-dependent microkinetic analysis of catalytic processes.

Thin PdCu membrane for hydrogen purification from in-situ produced methane reforming complex mixtures containing H2S

A 0.9 µm PdCu (69 wt% Pd) membrane prepared by an electroless plating method on a ceramic tubular support was tested in hydrogen sulfide containing streams. H2S/H2 mixtures with 40 and 100 ppmv of H2S were tested in order to observe the reversibility of sulfur addition. The membrane permselectivity operating in H2S/complex mixtures with around 32 ppmv of H2S in CH4, CO, CO2 and H2 was also tested. The streams were in-situ produced by Methane Steam Reforming and Methane Catalytic Partial Oxidation reactions. Prior to the tests with H2S, the hydrogen flux of the membrane at 773 K and 2 bar of pressure difference was 0.92 mol m−2 s−1. Membrane hydrogen flux decreased by around 50–80% in the tests with H2S/H2 mixture, but it recovered to the original values after removing H2S. In H2S/complex mixtures operation, the flux decrease was smaller due to concentration polarization phenomena. Although no sulfide compounds where detected on the membrane by SEM−EDX, XRD or XPS, the H2S or the employed temperatures seem to induce Cu segregation to the membrane surface.

A computational fluid dynamic evaluation of a new microreactor design for catalytic partial oxidation of methane

A novel microreactor with embedded mixing elements that result in flow splitting and recombination is proposed and was numerically tested for its capability to enhance the catalytic partial oxidation reaction of methane. The effects of various geometrical parameters and inlet reactant Reynolds number on the transport phenomena within and reaction effectiveness of the microreactor were investigated. Optimal design of the microreactor was then selected via the use of the response surface methodology, with the reaction product selectivity and pumping power requirement as the criteria. Performance of the optimal microreactor design was compared with that of a conventional straight-channel microreactor. Methane conversion within the optimized microreactor was noted to be higher than that within the straight-channel microreactor due to the presence of secondary flow, especially at a higher Reynolds number, while CO/CO2 ratio was noted to be slightly lower.

Hierarchical Vanadia Model Catalysts for Ammonia Selective Catalytic Reduction

There is an ongoing debate on the structure of titania supported vanadia used for catalytic partial oxidation reactions as well as for abatement of nitrogen oxide (NOx) by ammonia selective catalytic reduction (NH3-SCR). To gain further insight into the essential features of the catalyst composition of the surface we introduce a new class of vanadia model catalysts based on monodispersed silica particles as a platform. The evaluation of the influence of different catalyst components (TiO2, WO3) and different vanadia synthesis approaches (incipient wetness, ion-exchange) is facilitated by the hierarchical structure of the catalysts as well as the controlled synthesis approach. Catalysts tested under industrial ammonia SCR conditions show a strong dependence on the catalyst composition. In particular, the presence of crystalline titania and tungsta leads to a strong increase in NO conversion. Detailed catalyst characterization by X-ray diffraction and by visible Raman, UV Raman, UV–Vis and X-ray photoelectron spectroscopies provides insight into the bulk structure, the surface composition as well as the vanadia surface structure of the catalysts. The potential of UV resonance Raman spectroscopy for structural analysis of vanadia model catalysts for SCR is highlighted. Differences in catalytic activity are discussed in light of the structural results and the available literature.

Synthesis gas production by catalytic partial oxidation of natural gas using ceramic foam catalyst

Catalytic partial oxidation (CPOX) of natural gas was investigated over granule and ceramic foam Rh/CeO2+ZrO2+MgO catalysts under high throughput (GHSV of 180,000–1,600,000h−1) conditions at various pressures from 0.1 to 2.1MPaA. The application of ceramic foam as the substrate of Rh/CeO2+ZrO2+MgO catalyst improved the stability of the catalytic performance. It was found that the catalyst deactivation occurred when Reynolds number for flow through the catalyst bed exceeded around 20 and flow in the void of the catalyst bed changed from laminar flow regime to transitional flow regime. This change of fluid flow causes the acceleration of the mass transfer of the reactants from the gas phase to the catalyst surface and a rapid increase of the exothermic surface reaction rates over the catalyst, leading to hot spot formation. Due to larger void and smaller strut diameter of the ceramic foam, the configuration of the foam catalyst can make linear velocity lower in the catalyst bed and maintain laminar flow regime up to higher GHSV conditions than the granule catalyst, resulting in higher stability of the foam catalyst by suppression of hot spot formation. Chemical species measurements in the ceramic foam catalysts by means of a capillary sampling method revealed that the consumption rates of CH4 and O2 over Rh/CeO2+ZrO2+MgO were much lower than those over Rh/MgO and mild exothermic oxidation reaction over Rh/CeO2+ZrO2+MgO proceeds in wide region of the catalyst bed. High resistance to oxidation of Rh surface over CeO2+ZrO2+MgO even in the presence of O2 during CPOX reaction is considered to change the rates of both complete combustion reaction and reforming reaction, and to increase a contribution of another way to produce syngas.

In-situ XANES and XPD studies of NiO/Ce0.9Zr0.1O2 IT-SOFCs anode nanomaterial as catalyst in the CPOM reaction

The aim of this paper is to study the oxidation states of metal cations and the changes in the crystalline phases in NiO/Ce0.9Zr0.1O2 nanocatalysts under typical conditions of methane catalytic partial oxidation reaction by in-situ X ray absorption near edge spectroscopy (XANES) and X-ray powder diffraction (XPD) studies. The Ce0.9Zr0.1O2 mixed oxide was obtained by glycine-nitrate-combustion method, being the nickel incorporated by incipient wetness impregnation. The evolution of the crystalline structure with temperature and operating conditions was followed by in-situ XPD experiments and the oxidation states of Ce and Ni cations by in-situ XANES experiments at the Ce-LIII and Ni-K absorption edges. It was observed that NiO is completely reduced to Ni° at temperatures above 650°C while Ce0.9Zr0.1O2 fluorite-like phase showed changes in lattice parameter due to cerium reduction and crystallite growth, but no phase transformations or segregations were observed. It was confirmed that Ni° is the active centre to activate methane molecule while Ce4+/Ce3+ ratio is strongly related with CO/CO2 concentration in the exhaust gas flow.

A comparative experimental and numerical investigation of the heterogeneous and homogeneous combustion characteristics of fuel-rich methane mixtures over rhodium and platinum

The heterogeneous and homogeneous combustion of fuel-rich CH4/O2/N2/CO2 mixtures (equivalence ratios φ=1.8–3.5) was investigated experimentally and numerically at 5bar. Experiments were carried out in an optically accessible channel-flow reactor, which was coated with either rhodium or platinum, and involved in situ spatially-resolved Raman measurements of major gas-phase species concentrations for the evaluation of the heterogeneous processes and planar laser induced fluorescence (LIF) of formaldehyde for the assessment of homogeneous combustion. Simulations were performed with an elliptic 2-D code that included detailed heterogeneous and homogeneous chemical reaction mechanisms. The surface reaction mechanism for Rh modestly overpredicted the formation of partial oxidation products (H2/CO) and underpredicted the total oxidation products (H2O/CO2) at φ≥3.0. Rhodium was shown superior to platinum in syngas production and, furthermore, it maintained a good catalytic partial oxidation (CPO) capacity even at the low φ=1.8 where Pt showed minimal H2/CO yields. The higher syngas production in Rh, and in particular of the highly reactive hydrogen, had a drastic impact on the ensuing gas-phase combustion characteristics. While vigorous homogeneous combustion was always established in Rh, it was altogether suppressed in Pt despite the higher attained surface temperatures in Pt. The agreement between LIF-measured and predicted flame anchoring positions and flame lengths in Rh was particularly good. The strong gaseous combustion in Rh had profound implications, as it considerably reduced the length of the oxidation zone in CPO reactors such that the reforming zone could be initiated farther upstream. It was also shown that homogeneous combustion did not affect the reactor thermal management and that it promoted the syngas yields at the reactor outlet.

Effect of active thermal insulation on methane and carbon dioxide concentrations in the effluent of a catalytic partial oxidation reactor for natural gas conversion to synthesis gas

Two reactor designs with either passive or active thermal insulation were tested to produce synthesis gas from natural gas using catalytic partial oxidation on a system that exceeded laboratory scale. Preheating the working mixture significantly improves the conversion parameters. Preheating levels are limited by two factors: mixture ignition in the heater and overheating at the catalyst bed inlet area. The use of hot conversion products to provide active thermal insulation significantly improves the quality of the conversion. Because the same amount of identical catalyst was used in both reactors, the observed effect supports the hypothesis that the product composition depends primarily on the heat transfer process.

Engine-integrated solid oxide fuel cells for efficient electrical power generation on aircraft

This work investigates the use of engine-integrated catalytic partial oxidation (CPOx) reactors and solid oxide fuel cells (SOFCs) to reduce fuel burn in vehicles with large electrical loads like sensor-laden unmanned air vehicles. Thermodynamic models of SOFCs, CPOx reactors, and three gas turbine (GT) engine types (turbojet, combined exhaust turbofan, separate exhaust turbofan) are developed and checked against relevant data and source material. Fuel efficiency is increased by 4% and 8% in the 50 kW and 90 kW separate exhaust turbofan systems respectively at only modest cost in specific power (8% and 13% reductions respectively). Similar results are achieved in other engine types. An additional benefit of hybridization is the ability to provide more electric power (factors of 3 or more in some cases) than generator-based systems before encountering turbine inlet temperature limits. A sensitivity analysis shows that the most important parameters affecting the system's performance are operating voltage, percent fuel oxidation, and SOFC assembly air flows. Taken together, this study shows that it is possible to create a GT-SOFC hybrid where the GT mitigates balance of plant losses and the SOFC raises overall system efficiency. The result is a synergistic system with better overall performance than stand-alone components.

Catalytic partial oxidation of a biodiesel surrogate over molybdenum dioxide

The generation of synthesis gas by catalytic partial oxidation (CPO) from renewable liquid fuels for solid oxide fuel cell applications has been the target of several studies. Typically, noble metals or nickel are employed as the active catalyst for fuel reforming, but they present drawbacks in terms of high cost and deactivation due to carbon deposition, respectively. Thermodynamically, the CPO of the model biodiesel compound, methyl oleate (C19H36O2), was found to be favorable at temperatures>800°C. Under these conditions, we report a high catalytic activity of molybdenum dioxide (MoO2) toward the reformation of methyl oleate into synthesis gas, while overcoming the disadvantages of coking and methane formation. For an O2/C molar ratio between 0.60 and 0.70 and a WHSV up to 10h−1, the CPO reaction shows a fuel carbon conversion above 80%, relatively good H2 and CO yields, and the catalyst exhibits high redox stability. It is proposed that the lattice oxygen present in the oxide promotes the CPO reaction via the Mars–van Krevelen mechanism.