Reverse Flow Reactor for Catalytic Oxidation of Lean Methane

Manipulation of the catalyst surface coverage for improved conversion and selectivity substantially requires more frequent flow reversals than the classical reverse flow operation for energy saving does (Chapter 1). 2.A reverse flow reactor should be operated at comparable switching time and residence time in order to manipulate the reactor's selectivity (Chapter 3).3. The concept of reverse flow operation with concentration programming provides an engineering tool to control conversion and selectivity, with three benefits: ammonia feedstock savings, increased ammonia conversion, and increased selectivity to NO; a drawback is the decrease of production rate (Chapter 4).4. The concept of reverse flow operation with reactor side feeding shows a fourfold superior performance: higher conversion of ammonia, higher selectivity to NO, no dead gas volume, and high production rate (Chapter 5).5. Intensification of a university study program must assure that the students' residence time distribution for completing their study follows a plug flow model.6.The concept of periodic reactor operation is natural.7. So called relaxation oscillation occurs when the cycling time period is much less than the system's time constant.However, this is not the case during reverse flow operation when operating the reactor at extremely short cycling time.8. The porosity of a fixed bed can be determined elegantly by a combination of reverse flow operation and cycling of the feed concentration.9. Joint bachelor-master-doctor programs improve the selectivity to master and doctor degrees as well as the productivity of a university.10. Assalamu'alaikum is a time-independent greeting.

Energy storage technologies to overcome the intermittent nature of renewable power sources are essential for economic and environmental security. The conversion of energy from solar to fuel follows the blueprint of evolution, which has demonstrated sustainability over a three billion year timescale and inspired researchers for over one hundred years. There are major challenges to efficient solar fuel synthesis leading to it being described as a Holy Grail of science. The synthesis of a fuel occurs via the endothermic reduction of a suitable reactant (e.g., H+, CO2, N2), thus an an electron source is required with H2O the ideal molecule to be oxidised due to its abundance and innocuous nature. However, the oxidation of water (the oxygen evolution reaction, OER) is kinetically complex and active catalysts are required for it to proceed in an energy efficient manner. An objective of global scale artificial photosynthesis also necessitates that the catalysts and all other components are composed of Earth abundant elements. First row transition metal oxides (i.e. Mn, Co, Ni) have demonstrated high catalytic activity towards the OER and have been studied in detail as electrocatalysts. The focus herein is on metal oxides prepared through oxidative electrodeposition, specifically non-stoichiometric Co-oxide (CoOx). CoOx electrosynthesised from neutral and near-neutral, pH buffered electrolyte solutions has been demonstrated as an active water oxidation catalyst and received tremendous attention within the literature, including integration into devices. Herein, ultra-thin and transparent CoOx films are described, with cobalt complexes used as precursors to allow conformal catalyst coatings. This facilitates integration of CoOx films onto photoanodes via photo-electrodeposition and addresses previously identified limitations from opaque CoOx layers. Systematically varying the stability of the precursor allows control of the deposition rate at po- tentials more positive than the OER. The precursor can thus be tailored to the photopotential of an n-type light harvester. Furthermore, the films with lower Co loadings demonstrated higher activity per metal amount at high positive poten-tials, which is due to proton transport becoming the limiting step in thick catalyst films. The mechanism of electrocatalysis and quantification of parameters was then herein examined using large amplitude Fourier transformed alternating current (ac) voltammetry. In contrast to typical direct current (dc) voltammetry, ac voltam- metry filtered out water oxidation dc current and allowed the resolution of redox transformations of CoOx, MnOx and NiOx coupled to catalytic water oxidation. A general water oxidation model was then developed for these surface confined redox transformations coupled to a catalytic reaction with a substrate in solution. The model emphasises the role of the Bronsted base in proton abstraction within a proton coupled electron transfer mechanism. Comprehensive comparisons be- tween experimental and theoretical data revealed comparable effective reversible potentials of 1.9-2.1 V vs the reversible hydrogen electrode for each type of catalyst, i.e. for the formation of the species that undergoes catalytic turnover accompanied by the evolution of O2. The pseudo-first order forward rate constants for these species were also determined to be between 2 ·103 to5 ·104 s–1 for all three metal oxides, which is higher than any previously reported OER catalyst. Retaining a focus on CoOx, the relationship between structural disorder and catalytic activity was examined with samples synthesised in systematic steps through a bulk chemical oxidation. Electrochemical testing revealed the more disordered cobalt oxides were less active for OER catalysis but stronger oxidants, viz. they were more readily involved in non-catalytic chemical reactions. This supports more disordered CoOx being less thermodynamically stable, but challenges previously proposed correlations about disorder in metal oxide OER catalysts being beneficial to catalytic activity. Finally, effective pairing of Ni electrodes to a III/V type photovoltaic (PV) allowed overall water splitting at 22% solar to fuel power conversion efficiency (SFE) using commercially available components, while avoiding the use of Pt group metals and eclipsing the 12% SFE demonstrated in the previous year. The approach was defined with PV-electrolyser pairing parameters that demonstrate the point of power loss from photon to current through to SFE and identify the directions for improvement. Additionally, the parameters allow the maximum SFE of a system to be determined from characterisation of the PV.

In this study, nickel catalysts supported on mesoporous nanocrystalline gamma alumina promoted by various strontium contents were prepared by the impregnation method and employed in dry reforming of methane (DRM). The prepared catalysts were characterized using N2 adsorption (BET), temperature-programmed reduction and oxidation (TPR,) and oxidation (TPDTPO), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. TPR analysis revealed that the increases in Sr content enhanced the reducibility of the catalysts. The obtained results indicated that increasing Sr content increased both the methane and carbon dioxide conversions. In addition, the CO2 conversion was higher than the CH4 conversion due to the occurrence of the reverse water gas shift reaction. Among the studied catalysts, Ni/10% Sr-Al2O3 exhibited the highest catalytic activity and the lowest carbon formation. This catalyst showed high stability without any decrease in methane conversion up to 12 h of reaction. The results of this study could be employed in developing an industrial catalyst for the dry reforming reaction.

The oxidative coupling of methane is the catalytic conversion of methane into ethene. Carbon dioxide is generated as a reaction by-product and must be removed from the gaseous stream. In this paper, the application of a hybrid carbon dioxide removal process including absorption with amines and gas separation membranes is investigated through simulations and cost estimations.

The feedstocks of natural gas exceed the resources of crude oil by far. Therefore, there is a strong interest in the utilisation of natural gas with its main component methane for the production of more useful chemicals. This leads to a strong demand for compact and low-capital-cost reactors for the conversion of natural gas to methanol and liquid hydrocarbons and the production of H2. The combustion of natural gas is also considered for power generation in catalytic devices, because the flameless catalytic process results in lower emissions of NOx. Noble metals such as Pt, Pd, and Rh are very active catalysts for the conversion of CH4. However, the processes occurring during the partial and complete oxidation of CH4 on these catalysts are not completely understood. A detailed understanding of the reactor behaviour at all possible conditions is crucial for the technical realisation of these catalytic processes, because explosive mixtures are handled. In particular it is necessary to control the operation of the reactors at transient conditions such as light-off and shut-down. The objective of this work is to study total and partial oxidation of methane over Pt, Pd, and Rh catalysts for a wide range of operating conditions. Therefore, an experimental setup, which is easily applicable for modelling and numerical simulation, has to be developed. The experiment and analysis has to be arranged in a way that allows studies of transient processes such as light-off. Based on the experimentally derived conversion and selectivity surface-reaction schemes, available in literature, have to be evaluated. Available computational tools have to be used for numerically predicted reactor performance and compare these results with the experimental data. Crucial conditions, at which the reaction models need improvement, have to be found, and if necessary and possible improved. A flow reactor with associated analysis is designed to meet these requirements. In order to facilitate the simulation of the system catalysts exhibiting a simple geometry such as monolithic structures are used. The reactor consists of a 40 cm long quartz tube with varying inner diameters. Honeycomb catalysts coated with Rh, Pd, or Pt are placed inside. The gas temperature at the exit of the catalytic monolith and outside the quartz tube is. The reaction is ignited by heating up the reactor by a furnace, in which the flow system is integrated. After ignition, in the case of autothermal operation, the furnace can be switched off. The gases are premixed at room temperature and flow into the quartz tube at atmospheric pressure. The product composition is quantitatively analysed by a quadrupole mass spectrometer (QMS) in order to study transient phenomena. For the evaluation of reaction mechanisms, detailed numerical simulations of the physical and chemical processes using the computer program package DETCHEM and the commercially available CFD code FLUENT are applied. The numerical codes take into account detailed mechanisms of surface and gas-phase reactions as well as mass and heat transport processes in the channels and heat transport in the solid monolithic structure. The channels are simulated under steady-state conditions in a 3D elliptic approach using FLUENT and in two dimensions by a parabolic approach using DETCHEMCHANNEL. Transient phenomena are simulated by DETCHEMMONOLITH with 2D parabolic flow field simulations of a representative number of single channels including transient heat balances of the monolithic structure. First, the ignition of catalytic combustion of CH4 on a Pt loaded monolith is investigated. The conversions of CH4 and O2 as well as the product selectivities are experimentally determined and the results numerically simulated. The influence of H2 addition on the combustion is investigated. Reaction-rate oscillations of the catalytic combustion of methane on a Pd based catalyst are found experimentally at lean conditions in Pd coated monoliths and simulated with a surface-reaction mechanism. The second set of experimental focuses on CPO of CH4 over Rh coated monoliths. The experimentally derived conversion and selectivities are used to improve a detailed reaction mechanism. Next, the influence of the support material on the ignition process is investigated. In the experiment, either -alumina or cordierite as support material is applied and coated with Rh. The models are able to describe the light-off behaviour and are applied for catalyst design: The ignition behaviour of a set of virtual catalytic monoliths exhibiting varying physical properties is modelled. In addition, catalysts coated with Rh-nanopowder produced by laser ablation is experimentally examined and compared with wet coated catalysts. Finally, the CPO of methane is carried in a Pt, presenting an even more well-defined configuration for modelling. At CH4/O2 ratios above 1.9 complex patterns of oscillation in conversion and selectivity occur.

The catalytic oxidation of methane for abating the emission vented from coal mine or natural gas transportation has been known as most reliable method. A reverse flow reactor operation has been widely used to oxidize this methane emission due to its capability for autothermal operation and heat production. The design of the reverse flow reactor requires a proper kinetic rate expression, which should be developed based on the operating condition. The kinetic rate obtained in the steady state condition cannot be applied for designing the reactor operated under unsteady state condition. Therefore, new approach to develop the dynamic kinetic rate expression becomes indispensable, particularly for periodic operation such as reverse flow reactor. This paper presents a novel method to develop the kinetic rate expression applied for unsteady state operation. The model reaction of the catalytic methane oxidation over Pt/-Al2O3 catalyst was used with kinetic parameter determined from laboratory experiments. The reactor used was a fixed bed, once-through operation, with a composition modulation in the feed gas. The switching time was set at 3 min by varying the feed concentration, feed flow rate, and reaction temperature. The concentrations of methane in the feed and product were measured and analysed using gas chromatography. The steady state condition for obtaining the kinetic rate expression was taken as a base case and as a way to judge its appropriateness to be applied for dynamic system. A Langmuir-Hinshelwood reaction rate model was developed. The time period during one cycle was divided into some segments, depending on the ratio of CH4/O2. The experimental result shows that there were kinetic regimes occur during one cycle: kinetic regime controlled by intrinsic surface reaction and kinetic regime controlled by external diffusion. The kinetic rate obtained in the steady state operation was not appropriate when applied for unsteady state operation. On the other hand, the kinetic rate expression obtained in the unsteady state operation fitted quite well. It was proven that in one cycle period the kinetic rate would always shift according to the ratio of CH4/O2.

This thesis focuses on different aspects of the synthesis of renewable methane and methanol from carbon dioxide. By modeling, a general overview about limitations of the two reactions is given. Different reactor concepts were established to overcome these limitations. Modeling showed that sorption-enhancement helps to increase the conversion of CO2 to CH3OH, a prin-ciple that has already been proven to be successful in CO2 methanation. For understanding the fundamental reaction mechanism of the CO2 methanation, a commercial nickel catalyst was investigated by inelastic neutron scattering and diffuse reflectance infrared Fourier transform spectroscopy. We found that the byproduct water is a persistent adsorbate on the catalyst thereby impeding the catalyzed CO2 methanation. The kinetics of water removal on a microscopic scale in sorption-enhanced methanation catalysts were investigated by neutron imaging. Measurements highlight the importance of nanostructured catalysts rather than mac-roscopic mixtures of sorbent and catalytic moiety. The promising outcome of the modeling of sorption-enhancement in CO2 reduction to CH3OH triggered us to apply the recipes of catalysts developed for the CO2 methanation on sorption-enhanced methanol production. Despite various similarities, there are specific challenges asso-ciated with this reaction. With the CO2 reduction to methanol being less exothermic than that of CO2 methanation, the formation of methane has to be avoided which asks for other catalysts than nickel. As an educated guess, we started with copper exchanged zeolites in order to proof the positive influence of sorption-enhanced CO2 reduction to CH3OH. Already the first attempt demonstrated the general feasibility of the concept, though the catalytic performance lied much below commercial catalysts. Careful analyses including the investigation of different catalysts and sorbent materials paved the way to sorption catalysts with enhanced activities by increasing the active copper surface and stabilizing the zeolite used. However, despite the positive influ-ence of zinc doping, the role of this element is still under debate. For unravelling the promotional effect of zinc, we studied a commercial Cu/ZnO/Al2O3 catalyst by operando neutron imaging. Measurements revealed that ZnO interacts with hydrogen and is therefore not a pure spectator but actively participates in the reaction.

Simulation of reverse flow operation for manipulation of catalyst surface coverage in the selective oxidation of ammonia

Surface ozone (SOZ) can be very harmful if it exceeds the threshold limit. It can accumulate over sea and can return back to the land along with the breeze. Rural and vegetation rich areas often record elevated levels of surface ozone because of the variations in Volatile Organic Compound (VOC) levels, wind velocity and direction. Similarly methane is also an important greenhouse gas and plays a vital role in the atmospheric budget. In this work, ozone and methane levels measured during daytime in a mangrove estuary near Manakudy(8.0911 N, 77.477 E),kanyakumari, South India for a period of ten months from March 2014 to December 2014 are analyzed.SOZ showed an imprecise diurnal pattern with an early morning peak whereas methane recorded an apparent diurnality. The maximum value of SOZ was around 50 ppb. Summer months recorded high levels of SOZ followed by Southwest monsoon (SWM) and Northeast monsoon (NEM).High levels of methane were found in SWM followed by NEM and low concentration during summer. The correlation between SOZ and methane was found as r = -0.257, p

The world is steadily moving toward greener alternatives of established chemical production processes. Process modeling and simulation play a vital role in conceiving, designing and optimizing these greener processes. In many cases, these simulation tools are limited to a few project design stages, thus limiting their true potential. This thesis presents the benefits of process modeling and simulation at different levels of process development. The work focuses on ammonia production, which sustains global agricultural and mining activities. Ammonia production has traditionally been based on large-scale plants. The thrust toward large-scale production in order to gain economic advantages has overshadowed the benefits that could be derived from small-scale production plants. Additionally, the ammonia industry is a major consumer of global fossil fuels, and in the process of providing ammonia, also burdens the planet with greenhouse gases. In order to ensure sustainable ammonia production, this thesis highlights the techno-economic advantages that result from small-scale ammonia plants based on biomass feedstock. The use of biomass as a potential feedstock can help neutralize the carbon footprint of ammonia production. To establish the feasibility of such a process, this thesis presents the application of process simulations at different modeling levels.<br> <br> A Computational Fluid Dynamics (CFD) model was used to understand the flow patterns inside a dual fluidized bed gasifier. This elevated the understanding of the hydrodynamics of the gasifier freeboard, which is neglected by the conventional two-phase methodology. The CFD simulation was utilized to perform a Residence Time Distribution (RTD) analysis of the reactor. Four different tracer approaches namely the frozen velocity approach, the snapshot approach, the data sampling approach and the transient approach, were compared. The RTD analysis formed the basis of a steady-state compartment model that was developed in ASPEN Plus simulation software. The ASPEN Plus gasifier model decoupled the pyrolysis, gasification, and combustion sections of the gasifier to affect a better comprehension of the process and the results. The model predicated satisfactory results upon validation. Additionally, the model could also be used to predict the output for different biomass feedstocks.<br> <br> ASPEN Plus is used to simulate the biomass gasification process as well as downstream gas conditioning that leads to ammonia production. Apart from major constituent gases, the model accounted for tar production in the gasifier process as well as for its subsequent removal. Three different configurations of the biomass-to-ammonia process, namely, Autothermal Reforming (ATR), Steam Methane Reforming (SMR), and CO₂ Reforming (CR) have been modeled and compared. The configurations differ on the basis of the reforming of the methane and tars, which are present in the syngas. The output of the ASPEN Plus simulation is fed into an MS Excel-based framework, which performs Life Cycle Costing (LCC) and Life Cycle Assessment (LCA) for the simulated flowsheet. Finally, these outputs are utilized by an MS Excel-/VB-based Multi-Objective Optimization (MOO) framework in order to optimize both LCC and LCA for changing process parameters.<br> <br> Three biomass feedstocks, namely, wood, straw pellets, and bagasse, which are available in Australia, India, and Brazil, respectively, have been compared in order to understand the effect of biomass composition, the supply chain, and the national economic and environmental scenario on the viability of the biomass-to-ammonia process. The MOO results that were derived for changing flowsheet configurations as well as for different biomass feedstocks that were grown at different locations worldwide are expected to highlight a more rigorous analysis of the biomass-to-ammonia process. Such an analysis will provide decision makers with consistent and comparable data to objectively judge the viability of the proposed process. This analysis distinguishes this thesis from past studies that focused on ammonia production from biomass, and presented their LCC and LCA results for a single process configuration and for a single feedstock. The results predicted that different biomass feedstocks, process configurations, and geographical regions have their own advantages. The results provide a benchmark for comparison of other biomass-to-ammonia processes on a techno-enviro-economic scale. The methodology can be employed as an example in the development of different sustainable chemical production processes.

Pubic Compliance with New Collection Procedures at Rutgers

Reverse flow reactors are regarded as an appropriate tool for removing gaseous pollutants from industrial effluents. This paper presents the results of an experimental study on a particular reverse flow reactor with periodic variations in inlet concentration; these experimental results are compared with those obtained by numerical simulation studies. Catalytic oxidation of methane is chosen as model reaction. When the inlet concentration is low (i.e., close to extinction limits) and periodically varied, the interaction between the feeding cycle period and the flow-reversal cycle period may lead to reactor instability; adjusting the period of flow reversal is one way to maintain thermal stability in such situations. Results of numerical investigations reveal that if the flow-reversal cycle time is an odd multiple of the inlet variation cycle time, a harmonic response will occur, with sharply increased variation of the maximum temperature. Basically, it is the inequality of total methane input during the two half-cycles during flow-reversal operations that cause reactor instability. Adjusting the phase between the two cycle periods may ease the inequality of the inlet concentration values, which procures a second strategy to enhance reactor stability. The temperature maximum is very sensitive to the heat-transfer parameters, when periodic inlet variations are introduced.

The goal of this review was to analyze published data related to mitigation of enteric methane (CH4) emissions from ruminant animals to document the most effective and sustainable strategies. Increasing forage digestibility and digestible forage intake was one of the major recommended CH4 mitigation practices. Although responses vary, CH4 emissions can be reduced when corn silage replaces grass silage in the diet. Feeding legume silages could also lower CH4 emissions compared to grass silage due to their lower fiber concentration. Dietary lipids can be effective in reducing CH4 emissions, but their applicability will depend on effects on feed intake, fiber digestibility, production, and milk composition. Inclusion of concentrate feeds in the diet of ruminants will likely decrease CH4 emission intensity (Ei; CH4 per unit animal product), particularly when inclusion is above 40% of dietary dry matter and rumen function is not impaired. Supplementation of diets containing medium to poor quality forages with small amounts of concentrate feed will typically decrease CH4 Ei. Nitrates show promise as CH4 mitigation agents, but more studies are needed to fully understand their impact on whole-farm greenhouse gas emissions, animal productivity, and animal health. Through their effect on feed efficiency and rumen stoichiometry, ionophores are likely to have a moderate CH4 mitigating effect in ruminants fed high-grain or mixed grain-forage diets. Tannins may also reduce CH4 emissions although in some situations intake and milk production may be compromised. Some direct-fed microbials, such as yeast-based products, might have a moderate CH4-mitigating effect through increasing animal productivity and feed efficiency, but the effect is likely to be inconsistent. Vaccines against rumen archaea may offer mitigation opportunities in the future although the extent of CH4 reduction is likely to be small and adaptation by ruminal microbes and persistence of the effect is unknown. Overall, improving forage quality and the overall efficiency of dietary nutrient use is an effective way of decreasing CH4 Ei. Several feed supplements have a potential to reduce CH4 emission from ruminants although their long-term effect has not been well established and some are toxic or may not be economically feasible. © 2013 American Society of Animal Science. All rights reserved.

This study demonstrates the use of a selective and sensitive voltammetric sensor for determination of acetaminophen (AC). This was performed by modifying a glassy carbon electrode with composite film of poly(4-vinylpyridine) and graphene sheet (P4VP/GR-GCE). The redox peak currents of AC increased significantly at P4VP/GR-GCE. The result was achieved by the synergistic effect of combined electron mediator property of P4VP along with remarkable physical properties of GR which improved the kinetics of the catalytic oxidation of AC. The P4VP/GR-GCE exhibited excellent sensitivity, good reproducibilityand long-termstability for measuring AC with detection limits of 3.2 nM in the linear range of 0.04-300 µM. The novel developed sensor was not interfered by physiologically common interference, viz. ascorbic acid (AA) and uric acid (UA). The P4VP/GR-GCE was also successfully applied for detection of AC in tablets and urine samples, so it is reasonable to expect its broad use as AC sensor.

Catalytic oxidation emerges as a highly promising and cost‐effective approach for eliminating gaseous pollutants, greenhouse gases, and volatile organic compounds (VOCs) from industrial exhaust streams. However, achieving the simultaneous activation of O 2 and substrate molecules at low temperatures using non‐precious metal catalysts remains a significant challenge. In this study, we introduce gradient oxidative Cu─O─Ti/Cu─O─Cu dual sites that enhance bimolecular activation for catalytic oxidation reactions. The catalyst, Ti‐doped CuO, is synthesized on a TiO 2 support through the immobilization of Cu 2⁺ on NO 3 ⁻‐grafted TiO 2 , followed by thermal treatment. The resulting gradient oxidative Cu─O─Ti/Cu─O─Cu sites exhibit exceptional catalytic oxidation activity for NH 3 and various VOCs at low temperatures, matching the performance of precious metal‐based catalysts. Notably, during NH₃ oxidation, Cu─O─Ti sites enhance the activation of both O₂ and NH₃. HNO intermediates formed on Cu─O─Ti sites react with NH intermediates on neighboring Cu─O─Cu sites—producing N₂ and H₂O via an imide mechanism—which effectively lowers the reaction barrier for catalytic NH₃ oxidation. As such, dual sites in non‐precious metal catalysts show promising results for advancing future catalytic oxidation technologies.