Partial Oxidation Process Research Articles

Methane partial oxidation over Pt–Ru catalyst: An investigation on the mechanism

The mechanism of the partial oxidation of methane has been investigated over a bimetallic Pt–Ru catalyst. Dedicated experiments aimed to separate and quantify the relative contribution of single reactions included in the so-called “combustion and reforming” mechanism using the same catalyst. The catalyst is 0.5% Ru and 0.5% Pt (w/w) supported on mixture of alumina, ceria and zirconia (75/4.4/20.6%, w/w), washcoated on a ceramic monolith. Steam reforming, dry reforming, direct and reverse water-gas shift reactions were investigated. The temperature range investigated is 300 < T < 800 °C, while the space velocity range is 25,000 < GHSV < 100,000 h −1. Conditions at which single side reactions are expected to occur during the partial oxidation process, were approximated by tuning the reactant composition. The experimental results are also compared with thermodynamic equilibrium calculations. The CO and H 2 yields of partial oxidation have been quantitatively connected with steam and dry reforming, while the persistent water-gas shift reaction always rearranges the products and intermediates.

Guidance on Safety/Health for Process Intensification including MS Design; Part II: Explosion Hazards

AbstractThe implementation of process intensification by multiscale equipment will have a profound impact on the way chemicals are produced. The shift to higher space‐time yields for partial oxidation processes using micro‐designed reactors comprises the risk of having a permanent explosive atmosphere in the reaction section. In Part I, it was concluded that spontaneous reaction with hot spots can be presumed if highly exothermic reactions were performed and may cause ignition of an explosive atmosphere. The risk analysis of the situation, based on public information in the literature, leads to the conclusion that microreactors are inherently safe regarding the initiation and propagation of an explosion inside a microchannel by an uncontrolled reaction. The situation is the opposite when a propagating explosion enters the same micro‐designed reactor from one of the outside openings. The external explosion may enter the micro‐designed equipment and destroy it when the same starting conditions are present.

Numerical simulation of methane partial oxidation in the burner and combustion chamber of autothermal reformer

This study aims to model the methane partial oxidation process in the burner and combustion chamber of autothermal reactor. The numerical simulation based on this model offers a powerful tool that can assist in reactor design and optimization and scale up of the process saving expensive pilot work. The steady-state governing equations were solved using the SIMPLE algorithm and the effect of turbulence on the mean flow field was accounted for using the RNG k– ε model. A two-step reaction mechanism was used for the gas combustion with CO as the intermediate species. The reaction rates were modeled using an Eddy-Dissipation Model. In terms of the geometrical model, a 3D model for burner was developed while an axis-symmetric model for the combustion chamber was implemented to reduce the computational costs. The model formulated was validated against a currently operating autothermal reactor and then has been used to investigate different aspects of these reactors. Results show that effect of oxygen to methane ratio is more than that of feed temperature. It is demonstrated that a 60% increase in O 2/CH 4 ratio causes a 15.4% decrease and 42.7% increase in H 2/CO ratio and methane conversion, respectively. In contrast, a 60% increase in feed temperature does not have a significant effect on the process.

“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.

Temperature profile in a two-stage fixed bed reactor for catalytic partial oxidation of methane to syngas

Detailed axial temperature distribution has been studied in a two-stage process for catalytic partial oxidation of methane to syngas, which consists of two consecutive fixed bed reactors with oxygen or air separately introduced. The first stage of the reactor, packed with a combustion catalyst, is used for catalytic combustion of methane at low initial temperature. While the second stage, filled with a partial oxidation catalyst, is used for the partial oxidation of methane to syngas. A pilot-scale reactor packed with up to 80 g combustion catalyst and 80 g partial oxidation catalyst was employed. The effects of oxygen distribution in the two sections, and gas hourly space velocity ( GHSV) on the catalyst bed temperature profile, as well as conversion of methane and selectivities to syngas were investigated under atmospheric pressure. It is found that both oxygen splitting ratio and GHSV have significant influence on the temperature profile in the reactor, which can be explained by the synergetic effects of the fast exothermic oxidation reactions and the slow endothermic (steam and CO 2) reforming reactions. Almost no change in activity and selectivity was observed after a stability experiment for 300 h.

Evaluation of reactor and catalyst performance in methane partial oxidation over modified nickel catalysts

The process of catalytic partial oxidation (CPO) of methane was investigated at moderate furnace temperatures (500–973 K) and 1 atm over a series of modified Ni catalysts. By exposing the catalysts to different GHSV (15–600 N l CH 4/g h), the conditions ranged from approaching equilibrium at bed exit gas temperatures to oxygen break-through with associated effects on methane conversion and product composition. By modifying Ni catalysts we illustrate that the expected availability of reducible oxygen species influence the combustion activity of the catalyst. This is reasoned from observations of stronger temperature gradients and a higher maximum gas temperature with modifiers such as Co, Mo, Pt, Pd, Rh and to some degree Cr, as compared to a pure Ni catalyst. Modifiers which are generally difficult to reduce, such as oxides of W, Fe and Mn did not increase combustion activity at the bed entrance. At conditions where oxygen break-through was observed, the formation of coupled products, in particular ethane was promoted. It is reasoned that hetero-homogeneous coupling may be involved. The pure Pt and Pt-modified Ni catalysts were found to promote ethane formation even at 100% oxygen conversion. Interestingly, we here report results suggesting a direct route to synthesis gas over Rh, most likely working in parallel to a combustion reforming mechanism at high GHSV. This is argued based on an evaluation of water-gas-shift and the H 2/CO ratio at low bed exit gas temperatures. The conclusion appears reasonable even when accounting for a potentially higher surface temperature than gas temperature.

Investigation of the intermediate oxidation regime of Diesel fuel

A very high temperature fuel–air mixture is necessary for the thermal partial oxidation process of hydrocarbon fuels in order to have a high reaction temperature which accelerate the reaction kinetics. For Diesel fuel and due to the ignition delay time behavior, different oxidation behavior can be realized at different preheating temperatures. In this work, the intermediate oxidation region of Diesel fuel is investigated. By making use of the ignition delay time behavior, an vaporizer like tube reactor is constructed in order to enable a very high preheating temperature without the risk of self-ignition in a time-independent experiment. The oxidation behavior of Diesel fuel in air is investigated numerically and experimentally. In the numerical part, the ignition delay time was estimated using CHEMIKIN tools for different air–fuel mixtures at different temperatures. The evaporation behavior of the Diesel fuel–air mixtures are investigated at relatively high air preheating temperatures ranging from 500 °C up to 680 °C. The amount of the process air was varied from an air ratio λ = 0.35 to λ = 0.6. The experiments are also performed with N 2 as an evaporation media and compared with those performed with air to detect any temperature increase in the case of Diesel–air mixtures. The amount of heat release in the low chemistry region as well as in the intermediate region is calculated for the case of Diesel/air mixtures. The experiments show that four different oxidation region of Diesel fuel can be distinguished depending on air inlet temperatures and on the air ratio. At a temperature lower than 723 K (450 °C), no chemical reaction takes place. The cool flame reactions start at temperatures above 723 K (450 °C). However, no stable cool flame can be achieved unless the air preheating temperature reached about 753 K (480 °C). The cool flame region is extended up to about 873 K (600 °C), at which the intermediate regime started. This regime stabilized to a short range up to about 923 K (650 °C) after which ignition takes place.

Hydrogen production by thermal partial oxidation of hydrocarbon fuels in porous media based reformer

The thermal partial oxidation process of methane was investigated numerically and experimentally. Thermodynamic calculations and kinetic simulation were performed using CHEMKIN tools to determine the practical operating conditions. Experimentally, a porous material-based reactor was built to perform the partial oxidation process. Temperature profiles along the reactor central axis and concentration profiles of CO, H 2, CO 2, C 2H 2 and CH 4 were measured. Two different porous structures were installed in the reaction zone: Al 2O 3 fiber static mixer structures and SiC foams. The effects of air preheating temperature, thermal load and air ratio on the reforming process were investigated for both structures. The numerical calculation showed that an air ratio down to 0.4 is a practical limit to perform the partial oxidation process. Experimentally, it was found that the air preheating temperature has no significant influence on the syngas composition; however, it does affect the soot point ( λ c). Higher heat recuperation was detected in the case of SiC foam based reformer than in the case of the Al 2O 3 mixer one. The SiC foam based reactor showed also a better performance than the Al 2O 3 regarding the soot point. For air preheating temperature of 700 °C, the current soot point for the SiC foam based reformer was 0.42, while it was 0.45 for the Al 2O 3 mixer one.

Effects of Ethanol Addition on n-Heptane Decomposition in Premixed Flames

The goal of this paper is to explain the effects of ethanol addition on n-heptane decomposition and partial oxidation processes. An experimental study of the oxidation of n-heptane in the absence and presence of ethanol has been performed. The specific flames were low-pressure (25 Torr), laminar, premixed flames at an equivalence ratio of 1.0. The experiment was performed with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry. Major species on the centerline of each flame were identified by measurements of the photoionization mass spectrum and photoionization efficiency (PIE) spectra. Mole fraction profiles of these species were derived at the selected photon energies near the ionization thresholds. With the addition of ethanol, the partial oxidation of n-heptane into ketones was enhanced and 1-butene mainly decomposed to 1,3-butadiyne instead of 1,3-butadiene. Propargyl radicals were more important than butenynyl and butadienyl radicals in benzene formation.

Process analysis of syngas production by non-catalytic POX of oven gas

A non-catalytic POX of oven gas is proposed to solve the problem of secondary pollution due to solid wastes produced from the great amount of organic sulfur contained in oven gas in the traditional catalytic partial oxidation (POX) process. A study of the measurement of flow field and a thermodynamic analysis of the process characteristics were conducted. Results show that there exist a jet-flow region, a recirculation-flow region, a tube-flow region, and three corresponding reaction zones in the non-catalytic POX reformer. The combustion of oven gas occurs mainly in the jet-flow region, while the reformation of oven gas occurs mainly in the other two regions. Soot would not be formed by CH4 cracking at above 1200°C. Since there are very little C2 + hydrocarbons in oven gas, the soot produced would be very tiny, even if they underwent cracking reaction. The integrated model for entrained bed gasification process was applied to simulate a non-catalytic POX reformer. It indicated that the proper oxygen-to-oven gas ratio is 0.22–0.28 at different pressures in the oven gas reformation process.

Investigation of H2O and CO2 Reforming and Partial Oxidation of Methane: Catalytic Effects of Coal Char and Coal Ash

Methane reforming and partial oxidation was studied to evaluate the catalytic effects of coal chars and coal ashes on methane (CH4) conversion, sum selectivity (the sum of H2 and CO), and ratio selectivity (the ratio of H2/CO) in an atmospheric fluidized bed. The kinetics study presented the possibility of CH4 reforming and partial oxidation with a favorable H2/CO ratio, greater than 5. The higher H2/CO ratio in CH4 reforming and the partial-oxidation process can reduce the consumption of CH4 needed to adjust the H2/CO ratio during combined coal gasification and methane reforming. Coal ashes failed to be good candidates of catalysts on CH4 reforming and partial oxidation because of their very low specific surface area available for catalytic reactions. However, coal chars presented very promising catalytic performance on CH4 reforming and partial oxidation because of their larger specific surface area. In this study, no other constituents in coal fly ash or special surface properties of coal chars were correlated with the enhanced methane-conversion efficiency. It seems that the specific surface area is only variable in controlling methane-conversion efficiency.

Modeling electrochemical partial oxidation of methane for cogeneration of electricity and syngas in solid-oxide fuel cells

This paper uses computational models to evaluate strategies for scaling electrochemical partial oxidation (EPOX) processes from the laboratory scale to practical application. In addition to producing electrical energy alone, solid-oxide fuel cells (SOFC) can be operated with hydrocarbon fuel streams to produce synthesis gas (H 2 and CO) as well. SOFC systems are usually operated to consume most of the fuel and produce electricity. However, by operating with a hydrocarbon fuel at relatively high flow rates, the exhaust-gas composition can be predominantly syngas. In this case the steam (and CO 2), produced from electrochemical and thermal reactions, reacts to reform the hydrocarbon fuel within the catalytic anode support structure. A practical limitation of electrochemical partial oxidation operation is the fact that carbon tends to deposit on Ni-based anode catalysts. The present paper explores the use of barrier layers to prevent carbon deposits. The results show that a tubular cell can be designed to deliver syngas and electricity using methane as the primary fuel.

Biomass as an energy source: Thermodynamic constraints on the performance of the conversion process

In the present work an equilibrium model (gas–solid), based on the minimization of the Gibbs energy, has been used in order to estimate the theoretical yield and the equilibrium composition of the reaction products (syngas and char) of biomass thermochemical conversion processes (pyrolysis and gasification). The data obtained from this model have also been used to calculate the heating value of the fuel gas, in order to evaluate the overall energy efficiency of the thermal conversion stage. The proposed model has been applied both to partial oxidation and steam gasification processes with varying air to biomass (ER) and steam to carbon (SC) ratio values and using different feedstocks; the obtained results have been compared with experimental data and with other model predictions obtaining a satisfactory agreement.

Nickel catalyst prepared via glycine nitrate process for partial oxidation of methane to syngas

Nickel/alumina catalyst promoted by Li2O and La2O3 was prepared via glycine nitrate process (GNP) for the first time. The catalyst was characterized by BET specific surface area measurement, powder X-ray diffraction (XRD), H2 temperature programmed reduction (H2-TPR), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and catalytic performance measurements for partial oxidation of methane, comparison between the catalysts with the same composition while prepared via different methods and initial catalyst stability were also investigated. The results indicated that there was a strong interaction between the NiO and Al2O3 phase in the catalyst prepared via GNP. Alumina existed in mainly in a γ form, while spinel phase of nickel aluminate also occurred. The catalyst showed superior catalytic performances, e.g. higher methane conversion and selectivity to CO under similar working conditions over the one with same composition prepared by sol–gel and incipient-to-wetness impregnation method. Thus, an alternative method for preparing catalyst for methane partial oxidation was developed, which may find application to develop composite anodes for direct hydrocarbon fuelled solid oxide fuel cells.

Electron Transfer Mechanisms upon Lithium Deintercalation from LiCoO2 to CoO2 Investigated by XPS

Lithium deintercalation of LixCoO2 from x = 1 to x ≈ 0 has been carried out electrochemically. The changes in the electronic structure from LiCoO2 to CoO2 have been investigated by X-ray photoelectron spectroscopy (XPS) to bring some new developments about the electron transfer mechanisms upon lithium deintercalation. All available XPS core peaks (Co 2p, Co 3p, Co 3s, O 1s, F 1s, P 2p, C 1s) and valence spectra have been analyzed. The contributions of the electrode material and of the electrode/electrolyte interface have been clearly distinguished. We show that cobalt and oxygen simultaneously undergo a partial oxidation process and that the sole participation of oxygen atoms to the charge transfer process, as it is sometimes assumed, can be excluded. The surface film consists of organic and inorganic species resulting from degradation of the electrolyte.

Nickel Complexes with N2O Donor Ligands: Syntheses, Structures, Catalysis and Magnetic Studies (Eur. J. Inorg. Chem. 32/2007)

AbstractThe cover picture shows how a novel tetranuclear NiII complex [Ni4L41(μ‐tp‐κ4‐O)(H2O)2(μ‐tp‐κ2‐O)]·2C2H5OH·CH3OH·3H2O [L1 = N‐(3‐aminopropyl)‐5‐bromosalicylaldimine] acts as an active catalyst for the partial oxidation of cyclohexene into its epoxide product when it is immobilized over a network of hexagonal mesoporous silica. Herein the catalytic sites allow the formation of epoxide over their surfaces. tert‐Butyl hydroperoxide acts as an oxidant for the partial oxidation process. A dinuclear unit is formed, in which the NiII is bridged by a phenolato group, and two such units are connected through a terephthalate moiety to form a tetranuclear nickel(II) complex. The tetranuclear units are connected to each other by another terephthalate moiety in its bis(monodentate) mode to form one‐dimensional networks. Details are described in the article by P. Banerjee et al. on p. 5033 ff. The artwork was designed by Mr. Jishnunil Chakraborty and Mr. Gopal Das.

Chemical behaviour of metallic inclusions in glass melts

Inclusions of all kinds cannot be accepted in glass articles. Most of them are non-metallic stones, silicon spheres, cords, bubbles, and sometimes metallic inclusions. Identification of every appearance is not possible, since body structure and chemical composition do not compare. Laboratory experiments regarding the behaviour of the metals copper, brass and iron and their dissolution mechanisms in glass melts at technological relevant temperatures were analysed. Besides partial oxidation processes, sulphidic species were found. The experiments have been compared with thermodynamic calculations of several reaction mechanisms.

Micro Process Technology as a Means of Process Intensification

AbstractDifferent implications and possible applications of the process intensification (PI) approach in the chemical industry are shown. Whereas in its pioneer days PI was defined as a pure reduction in plant size by a factor of 10–100, the PI idea has developed towards a multidisciplinary approach for process and plant. This tendency is driven by the challenges the chemicals business is facing today in terms of cost and innovation pressure. This study describes how micro process technology could provide the opportunity to realize chemical processes and plant designs faster, resulting in lower investment and operating costs. In this context, it is shown that microstructured catalytic wall reactors can boost partial oxidation processes operated in multitubular reactors by increasing chemical conversion by a factor greater than 2, though only adding 20 % of nominal capacity enhancement.

Ni–Fe Competition in the Catalysis of Carbon Nanotube Growth

The paper presents the results of competitive catalysis investigation of the carbon nanotube growth in situ of the partial oxidation process of methane. The competition between Ni and Fe results in suppression of Ni catalytic activity and the growth of Fe‐capped carbon nanotubes. The discrimination is so strong that iron is segregated from Ni–Fe based stainless steel alloy leaving characteristic Ni‐enriched corrosion caverns. The process strongly depends on temperature. Depending on particular catalyst bed composition, the nanotubes of various morphology may occur. In particular, the use of perovskite‐type catalyst leads to formation of “olive‐branch”‐like peculiar carbon nanostructures.

Novel application of aluminum salt for cost-effective fabrication of a highly creep-resistant nickel–aluminum anode for a molten carbonate fuel cell

A one-step sintering process using aluminum acetate as an aluminum source is used to fabricate a nickel-based anode for a molten carbonate fuel cell (MCFC). The process is designed to replace existing partial or full oxidation and reduction processes, which are quite complicated and expensive. The aim is to simplify the fabrication process of a highly creep-resistant Ni–Al anode and eventually to contribute to the commercialization of a MCFC. Considering the solubility limit of Al in Ni, two types of anodes, Ni–2.5 wt.%Al and Ni–5 wt.%Al, are fabricated by sintering at either 1000 or 1100 °C for 2 h in a 99.5% H 2 atmosphere. After characterizing the resulting material by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, it is confirmed that among the anodes fabricated, the Ni–5 wt.%Al sample sintered at 1100 °C contained the most suitable Al 2O 3 in a dispersed form. A 100-h creep test reveals that the creep strain of the anode has the lowest value of 1.3% compared with the other anodes. This value is superior to the creep strain of 2.3% obtained from a Ni–5 wt.%Al anode using Al powder as a fine Al 2O 3 dispersion source in a Ni-base anode matrix. A single cell using the Ni–5 wt.%Al anode fabricated in this study shows a stable closed-circuit voltage of 0.795 V for 1000 h at 150 mA cm −2.