Partial Oxidation Process Research Articles

Methane conversion in a mixture of enriched air and water vapor

On the basis of thermodynamic analysis of the methane partial oxidation (conversion) process in a mixture of enriched air and water vapor, the conditions of practical implementation of such a process are determined for the integrated energotechnological use of natural gas with coproduction of electricity and synthetic liquid fuels. Considerable attention is paid to the conditions of formation of solid carbon (carbon black) in partial oxidation, and the means to reduce its yield are discussed.

Partial oxidation of methane in a temperature-controlled dielectric barrier discharge reactor

We studied the relative importance of the reduced field intensity and the background reaction temperature in the partial oxidation of methane in a temperature-controlled dielectric barrier discharge reactor. We obtained important mechanistic insight from studying high-temperature and low-pressure conditions with similar reduced field intensities. In the tested range of background temperatures (297<T<773K), we found that the conversion of methane and oxygen depended on both the electron-induced chemistry and the thermo-chemistry, whereas the chemical pathways to the products were overall controlled by the thermo-chemistry at a given temperature. We also found that the thermo-chemistry enhanced the plasma-assisted partial oxidation process. Our findings expand our understanding of the plasma-assisted partial oxidation process and may be helpful in the design of cost-effective plasma reformers.

Crude glycerol as a raw material for the liquid phase oxidation reaction

In the present work, crude and partially purified glycerol fractions received from large biodiesel production plant were used as a raw material in the catalytic partial oxidation process. Before using, each fractions were carefully characterized in order to identify and quantify the major contaminants. Depending on the purification degree, the weight concentration of glycerol in the different fractions varied from 40.3% to 98.2%, the methanol content did not exceed 29.1%, mineral salts (determined as ash) varied from 0.03% 6.6%, while the residual organic matter (non-glycerol and non-methanol, named here MONG-NM) was between 0.7% and 22.1%. The reaction of glycerol oxidation was carried out in the liquid phase over a commercial 1wt.% Pt/Al2O3 catalyst. The effect of each identified impurity type was independently studied, both in the presence and absence of base in the reaction mixture. The results indicated that MONG-NM is the most problematic compound, as it strongly hinders the reaction. As the post-reaction analysis of spent catalyst (Elemental Analysis and XPS) showed practically negligible leaching of platinum and lack of important changes in its oxidation state, the most probable explanation for observed decrease in glycerol conversion is blocking of glycerol access to the catalyst active sites by adsorbed heavy-weight components of MONG-NM. An attempt of regeneration and reusing of spent catalyst proved that such poisoning can be reversed by simple washing of catalyst with organic solvent enable to dissolve hydrophobic fatty acid derivatives. The mineral salts also have a detrimental effect on the glycerol oxidation process, but much tinier than that of MONG-NM. In contrast, the presence of methanol in the feed promoted the process reactivity, which was attributed to improved oxygen solubility in the methanol–water solutions (at least in the analysed range of methanol concentrations ≤5wt.%).

Mo-V-Te-Nb oxide catalysts: Reactivity of different oxygen species in partial and deep oxidation

Isotopic oxygen exchange on the surface of Mo-V-Te-Nb oxide catalysts was studied. Catalyst samples contained more than 95% of (i) orthorhombic phase M1, (ii) pseudo hexagonal phase M2, or (iii) layered phase with structure Me5O14 (Me – Mo, V, Nb). Two forms of exchangeable oxygen were found on the surface, i.e. strongly bonded lattice oxygen and relatively weakly bonded adsorbed oxygen. According to in situ studies with isotope 18O adsorbed oxygen leads to deep oxidation products, while lattice oxygen participates mainly in the partial oxidation processes. Weakly bonded oxygen concentration decreases in series: Me5O14>M2>M1 and thus selectivity towards partial oxidation increases.

The effect of interstitial nitrogen in the activity of the VOx/N-TiO2 catalytic system for ethanol partial oxidation

Interstitial nitrogen (N) doped titanium dioxide was prepared and used as support for vanadium oxide to test the nitrogen effect on vanadia-catalyzed partial oxidation processes. Ethanol partial oxidation catalytic studies and surface studies on the structure of the N doped support before and after vanadia loading indicate that nitrogen acts as a promoter of catalytic activity. Samples were characterized by X-ray diffraction, electron dispersive X-ray, and surface area measurements to evaluate their crystallinity, surface chemical composition and surface area. Diffuse reflectance UV–visible and Fourier transform intra-red spectroscopy, together with X-ray photoelectron spectroscopy were used to probe the effect of nitrogen on the vanadia-titanium dioxide interaction. The band gap edge energies obtained for the vanadium oxide species suggest that the size of the vanadia cluster is larger on the nitrogen doped catalysts compared to the ones observed in the N-free support, pointing to a weaker interaction between vanadia and TiO2 when nitrogen is present. At the same time and in-situ Fourier transform infra-red spectroscopy studies indicate that interstitial N exists in the catalyst surface in forms of hyponitrite or nitrite-like species. A model in which nitrogen affects vanadia dispersion and ethanol adsorption capacity is proposed to explain all these observations.

An Efficient Oxygen Activation Route for Improved Ammonia Oxidation through an Oxygen‐Permeable Catalytic Membrane

AbstractUpon using a reactant/oxygen mixture as co‐feed in partial oxidation, adsorbed surface molecular oxygen species can cause low selectivity. We propose a concept different from the conventional co‐feed partial oxidation process in packed‐bed reactors. In this new configuration, the activation of oxygen is separated from the catalytic oxidation by using an oxygen‐permeable membrane to suppress the formation of nonselective surface molecular oxygen species. A continuous flux of lattice oxygen through the membrane allows highly selective partial oxidation. In the oxidation of ammonia to NO, the NO selectivity was improved from 77 to 95 % if a La0.6Sr0.4Co0.2Fe0.8O3–δ oxygen‐permeable catalytically active membrane was used at 850 °C instead of a co‐feed fixed bed reactor.

Thermodynamic analysis for syngas production from volatiles released in waste tire pyrolysis

This paper shows the maximum limit on syngas composition obtained from volatiles released in waste tire pyrolysis when they are submitted to an air–steam partial oxidation process. Thus, from mass and energy balances and a stoichiometric equilibrium model, syngas composition and reaction temperature as well as some process parameters were predicted by varying both the equivalence ratio (ER) and the steam to fuel ratio (SF). In addition, pyrolysis experiments were performed using a continuous auger reactor, and the influence of pyrolysis temperature on composition of both volatiles and char was studied. Consequently, the resulting syngas characteristics were correlated with the pyrolysis temperature. The stoichiometric equilibrium model showed that an ER down to 0.4 is a practical limit to perform the air–steam partial oxidation process. When the process is carried out only with air, volatiles obtained at high pyrolysis temperature lead to lower reaction temperature and higher LHV of syngas in comparison with those found at low pyrolysis temperature. The H2 production is favored between 0.20 and 0.40 of ER and seems to be more influenced by the H/C ratio than by the water gas-shift reaction. On the other hand, the steam addition shows a more notable effect on the H2 production for volatiles obtained at the highest pyrolysis temperature (600°C) in agreement with the lower reaction temperature under these experimental conditions. This thermodynamic analysis provides essential data on the optimization of syngas production from volatiles released in waste tire pyrolysis prior to run any test.

A low temperature, isothermal gas-phase system for conversion of methane to methanol over Cu-ZSM-5.

A low temperature, isothermal, gas-phase, recyclable process is described for the partial oxidation of methane to methanol over Cu-ZSM-5. Activation in NO at 150 °C followed by methane reaction and steam extraction (both at 150 °C) allowed direct observation of methanol at the reactor outlet.

Chemical looping beyond combustion: production of synthesis gas via chemical looping partial oxidation of methane

Systematic development of Fe–Ni bimetallic carrier results in efficient and safe chemical looping process for methane partial oxidation to syngas.

Conversion of Methane to Hydrogen in a Reversible Flow Reactor in the Process of Filtration Combustion of Fuel Mixtures Enriched with Oxygen

This paper considers the process of partial oxidation of methane to syngas in a reversible flow reactor in the process of filtration combustion of fuel mixtures enriched with oxygen in an inert porous medium. Experimental studies have been made of the influence of the volume concentration of oxygen in the initial fuel mixture on the basic parameters of the conversion process — the maximum temperature in the combustion wave and the composition of reaction products. Investigations have been carried out for fuel mixtures having different calorific values under the same filtration conditions. It has been shown that the addition of oxygen to the initial methane–air mixture permits increasing considerably the efficiency of the conversion process.

Partial oxidation of ethanol to acetaldehyde over surface-modified single-walled carbon nanotubes

The catalytic activity of surface-modified single-walled carbon nanotubes (SWCNTs) for partial oxidation processes was tested. A battery of characterization techniques including temperature programmed desorption (TPD) Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to probe the degree and type of oxygen bearing functional groups introduced on the nanotube surface and responsible for catalytic activity. Raman and optical absorption spectroscopy and temperature programmed oxidation (TPO), were used to probe the SWCNTs structure before and after reaction to monitor structural changes that take place during partial oxidation of ethanol to acetaldehyde. The results indicate a strong link between ketonic surface groups (CO) on the SWCNTs surface and its catalytic activity for partial oxidation processes.

Plasma-Assisted Combustion Technology for NOx Reduction in Industrial Burners

Stronger regulations on nitrogen oxide (NOx) production have recently promoted the creation of a diverse array of technologies for NOx reduction, particularly within the combustion process, where reduction is least expensive. In this paper, we discuss a new combustion technology that can reduce NOx emissions within industrial burners to single-digit parts per million levels without employing exhaust gas recirculation or other NOx reduction mechanisms. This new technology uses a simple modification of commercial burners, such that they are able to perform plasma-assisted staged combustion without altering the outer configuration of the commercial reference burner. We embedded the first-stage combustor within the head of the commercial reference burner, where it operated as a reformer that could host a partial oxidation process, producing hydrogen-rich reformate or synthesis gas product. The resulting hydrogen-rich flow then ignited and stabilized the combustion flame apart from the burner rim. Ultimately, the enhanced mixing and removal of hot spots with a widened flame area acted as the main mechanisms of NOx reduction. Because this plasma burner acted as a low NOx burner and was able to reduce NOx by more than half compared to the commercial reference burner, this methodology offers important cost-effective possibilities for NOx reduction in industrial applications.

Methane-to-hydrogen conversion in a reversible flow filtration combustion reactor at a high pressure

The noncatalytic process of partial oxidation of methane to syngas in a reversible flow filtration combustion reactor at high pressures has been considered. The influence of the operating pressure in the reactor on the main parameters of the conversion process — the maximum temperature in the combustion wave and the composition of reaction products — has been investigated experimentally. Investigations were carried out for fuel mixtures of different calorific powers at pressures of up to 6.0 bars. It has been shown that at a fixed value of the specific mass flow of the fuel mixture the efficiency of the process of methane-to-syngas conversion decreases with increasing pressure in the reactor.

Partial oxidation of butane to syngas using nano-structure Ni/zeolite catalysts

In this study, performance of nano-structure Ni over different zeolite supports in partial oxidation of butane was investigated. First, partial oxidation process was performed without catalyst to evaluation of optimal conditions. For in situ reduction of catalysts, H2 produced from homogenous reaction was used. Catalytic partial oxidation was carried out using nano-structure nickel catalysts supported by ZSM5, mordenite and Y. Each catalyst was synthesized through reverse microemulsion method. The catalysts were characterized by BET surface area, XRD, SEM and TGA. Highest butane conversion (≈89%) observed in the presence of Ni/Y catalyst. Also Ni/Y shows the highest overall selectivity to CO and H2 as the most desired partial oxidation products. Results from TGA showed that the minimum quantity of formatted coke was related to Ni/Y, which confirmed the stability of butane conversion versus time for this catalyst.

ChemInform Abstract: Gas‐Phase Oxypyrolysis of Light Alkanes

AbstractReview: 95 refs.

Co-Gasification of Mesquite and Coal Blend in an Updraft Fixed Bed Gasifier

In order to reduce the emission of NOx, SOx, and CO2 and mitigate the dependence on the fossil fuel, the use of renewable energy, especially the biomass energy, has been explored. Since most biomass fuels are hard to grind to the very fine size, gasification is the preferred technology of energy conversion. Updraft fixed bed gasification using partial oxidation process is adopted where air less than the stoichiometric quantity is admitted to oxidize the char to CO. The temperature profile within the bed reveals a characteristic temperature peak. The results reveal a correlation between the higher heating value (HHV) of producer gas and the peak gasification temperature (Tpeak). Coal with higher char content (~45%) is blended with biomass of low char content (~20%) in order to produce high quality gas. In this study, the Texas-based mesquite fuel was blended with Wyoming Power River Basin (PRB) coal with mass ratios of 100:0, 90:10, and 80:20 and fired downward into the gasifier. It was found that at a given mesquite to the coal mass ratio, the peak gasification temperature decreased with the increase in ER. With the increase of the coal ratio in the mesquite: coal blend and the peak temperature increased significantly; more combustible gases such as CO, CH4 were generated at the end of product gas, and the HHV of the product gas increased by 10%-20%.

Factors for Improvements of Catalytic Activity of Zirconium Oxide-Based Oxygen-Reduction Electrocatalysts

Partially oxidized zirconium carbonitrides (Zr-CNO) were evaluated as a non-precious-metal cathode used for polymer electrolyte fuel cells. The zirconium-oxide-based catalysts were prepared from zirconium carbonitrides under controlled oxygen partial pressures from 10−2 to 10−18 atm at 1000°C. The ORR activity of Zr-CNO showed a volcano-like tendency against the degree of oxidation (DOO). We found a significant lattice-parameter decrease for highly active Zr-CNOs, and this could be ascribed for the formation of oxygen- and zirconium-vacancies in monoclinic ZrO2. On the other hand, carbon originated from starting materials was deposited on the surface of Zr-CNOs during the partial oxidation process. We also found that the oxygen content on the surface of highly active Zr-CNOs was drastically decreased when the amount of carbon significantly decreased during partial oxidation processes. This result indicates that the deposited carbon acted as a strong reduction agency. From XPS and XRD analyzes, there is a linear relationship between the ORR current and amount of oxygen vacancy formed in monoclinic phase. Therefore, we believe that oxygen vacancy formed in monoclinic phase could act as active sites for the ORR.

Flamelet-Modeling of Inverse Rich Diffusion Flames

An experimental and numerical investigation of a confined laminar inverse diffusion flame (IDF) with pure oxygen as oxidizer and carbon dioxide diluted methane as fuel with a global stoichiometry of partial oxidation processes (equivalence ratio of 2.5) is presented. The present burner setup allows studying both the flame and the post-flame zone in a simplified geometry considering typical operating conditions as found in large-scale gasifiers. This partial oxidation flame setup is characterized by very high temperatures close to the stoichiometric oxidation zone due to oxy-fuel combustion, whereas lower temperatures and slow endothermic post-flame conversion reactions with long residence times are found in the fuel rich post-flame region. The scope of this paper is to investigate different modeling approaches suitable for both regimes by comparing the simulation results to detailed experimental data. Planar OH laser-induced fluorescence (OH-LIF) was performed for measuring the hydroxyl radical in the reaction zone and the results are compared to CFD calculations. Based on this comparison, the necessary level of detail of diffusion flux modeling, which includes Soret and Dufour effects, is analyzed and established. Finally, steady and unsteady non-premixed flamelet approaches based on a single mixture fraction are used in order to study their applicability for both the oxidation and post-flame zone. Significantly different time scales are obtained using different flamelet paths. Their influence on the results is investigated in the steady flamelet and the Lagrangian flamelet approach.

The influence of partial oxidation mechanisms on tar destruction in TwoStage biomass gasification

TwoStage gasification of biomass results in almost tar free producer gas suitable for multiple end-use purposes. In the present study, it is investigated to what extent the partial oxidation process of the pyrolysis gas from the first stage is involved in direct and in-direct tar destruction and conversion. The study identifies the following major impact factors regarding tar content in the producer gas: oxidation temperature, excess air ratio and biomass moisture content. In a experimental setup, wood pellets were pyrolyzed and the resulting pyrolysis gas was transferred in a heated partial oxidation reactor and oxidized between 800 and 1050°C with excess air rations between 0 and 0.7 and fuel moisture content between 8% and 30%. The gas composition was analyzed before and after oxidation by means of gas chromatography and mass spectrometry. The tar compounds were sampled by solid phase adsorption and determined by stable isotope dilution analysis. The results have shown that partial oxidation reduces and converts primary tars into low molecular weight, polycyclic aromatic hydrocarbons (PAHs), primarily naphthalene. At temperatures above 950°C practically all phenol is converted. The resulting PAH tar compounds are readily converted in the subsequent char-bed of the TwoStage gasification process and the partial oxidation process thus contributes directly as well as in-directly to the overall tar destruction. A high temperature and excess air ratios contribute positively to the direct tar destruction and a high moisture content of the biomass enhances the decomposition of phenol and inhibits the formation of naphthalene. This enhances tar conversion and gasification in the char-bed, and thus contributes in-directly to the tar destruction.

Experimental and numerical study of rich inverse diffusion flame structure

An experimental and numerical investigation of a laminar confined and inverse diffusion flame (IDF) with pure oxygen as oxidizer considering global stoichiometry of partial oxidation processes is presented. The present burner setup allows studying the structure of the high temperature oxidation zone and the subsequent reforming region in a simplified geometry considering typical operating conditions as found in large scale gasifiers for the production of synthesis gas out of different hydrocarbon feedstocks. The use of pure O2 as oxidizer leads to extremely high temperatures and higher concentrations of radiating species, i.e. H2O and CO2, compared to a partial oxidation process with air as oxidizer. Hence the flame structure is strongly influenced by radiation and diffusion effects. The scope of this paper is to determine how the Soret effect and the radiative heat transfer at high temperatures in combination with low strain rates in the downstream region influences the flame structure. In this respect the radiation model and potential self-absorption of radiating species become of major importance for the numerical predictions. In the experimental part the flame structure was studied with a planar OH-laser-induced fluorescence (LIF) setup, while the temperature was determined by a two-line LIF approach using the rotational temperature of the OH radical. The correlation between OH concentration and temperature was used as an indicator for comparison purposes. In the numerical part two-dimensional laminar CFD calculations with detailed chemistry and transport were performed and the numerical results show the importance of the Soret effect. The optically thin radiation model yields good agreement with the experiments at high strain rates close to the nozzle, but the radiation model underpredicts the temperature further downstream at low strain rates with potentially significant self-absorption of the radiating species.