Influence of a reaction mixture streamline on partial oxidation of methane in an asymmetric microchannel reactor

Partial oxidation of methane (POM) has been tested in an asymmetric microchannel reactor with different inlet configurations. One inlet of the reactor provided successive splitting of an inlet flow into parallel channels, whereas the opposite inlet allowed the inlet flow to enter the parallel channels simultaneously. It was found that concentrations of carbon monoxide and carbon dioxide changed by 20–30% and the conversion of methane changed by 5–20%, depending on the rate and direction of the inlet flow. The hydrogen production rate practically did not depend on the inlet configuration and equaled 15 l/h at the inlet flow rates from 600 to 1400 cm³/min and at the methane conversion of 80%. The data obtained demonstrated that the use of different operating modes of the asymmetric microreactor allows changing the composition of produced syngas.     

A two-step process for hydrogen production from vacuum residue

A two-step process has been developed for the conversion of vacuum residue to hydrogen. The first step involves oxidation of the vacuum residue in liquid phase at 373-423 K using ozone. The partially oxygenated products are utilized for hydrogen production by catalytic oxidative steam reforming over 2 wt% Pt/Al₂O₃-La₂O₃-CeO₂ catalyst. This two-step process reduces the formation of coke on the catalyst surface. Results show that it is a viable and technically feasible method for production of hydrogen from vacuum residue.     

Partial oxidation of methane over CeO2 loaded hydrotalcite (MgNiAl) catalyst for the production of hydrogen rich syngas (H2, CO)

In this work, partial oxidation of methane (POM) was investigated using Mg-Ni-Al (MNA) hydrotalcite promoted CeO₂ catalyst in a fixed bed reactor. MNA hydrotalcite was synthesized using the co-precipitation process, while CeO₂ was incorporated via the wetness impregnation technique. The CeO₂@MNA samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) technique. The catalytic activity of CeO₂ promoted MNA (CeO₂@MNA) for POM reaction was evaluated for various CeO₂ loading kept the feed ratio CH₄/O₂ = 2 at 850 °C. The catalyst containing 10 wt% cerium loading (10%CeO₂@MNA) showed 94% CH₄ conversion with H₂/CO ratio above 2.0, that is more suitable for FT synthesis. The performance of catalyst is attributed to highly crystalline stable CeO₂@MNA with better Ce-MNA interactions withstand for 35 h time on stream. Furthermore, the spent catalyst was examined by TGA, SEM-EDS, and XRD to evaluate the carbon formation and structural changes during the span of reaction time.     

The effect of gold on the copper-zinc oxides catalyst during the partial oxidation of methanol reaction

Hydrogen production resulting from the partial oxidation of methanol (POM) was investigated using copper-zinc-supported gold catalysts. The influence of oxygen concentration on activity and initiation temperature (T_i) over Au_4.3CZ (ca. 4.3 wt.% Au, 32.3 wt.% Cu and 63.4 wt.% Zn) catalysts was compared with CZ (ca. 31.7 wt.% Cu and 68.3 wt.% Zn) catalysts. The Au_4.3CZ catalyst was able to react at temperatures lower than 195 °C, while CZ catalyst could not be initiated without pre-activation. In addition, Au_4.3CZ performed higher hydrogen selectivity and lower carbon monoxide selectivity than CZ catalyst. The addition of gold might induce a change in the reducibility of copper species and result in the more active species, Cu⁰ and Cu⁺, on the catalytic surface and, especially, enhance the adsorption of oxygen and methoxy group at low temperature. These adsorbed oxygen atoms could be removed as CO₂, which speed up the rate-determining step of POM. It might influence initiation temperature and catalytic performance, i.e. the POM reaction can be initiated at T_i: 120 °C, with catalytic performance at 95% methanol conversion, 97% hydrogen selectivity, and 5.5% carbon monoxide selectivity at 190 °C over Au_4.3CZ without pre-activation.     

Calcium silicate-based catalytic filters for partial oxidation of methane and biogas mixtures: Preliminary results

Development and testing of catalytic filters for partial oxidation of methane to increase hydrogen production in a biomass gasification process constitute the subject of the present study. Nickel, iron and lanthanum were coated on calcium silicate filters via co-impregnation technique, and catalytic filters were characterized by ICP-MS, XPS, XRD, TEM, TGA, TPR and BET techniques. The influences of varying reaction temperature and addition of Fe or La to Ni-based catalytic filters on methane conversion, and hydrogen selectivity have been investigated in view of preliminary results obtained from reactions with 6% methane-nitrogen mixture, and catalytic filters were tested with model biogas mixtures at optimum reaction temperature of each filter which were 750 °C or 850 °C. Approximately 93% methane conversion was observed with nearly 6% methane-nitrogen mixture, and 97.5% methane conversion was obtained with model biogas containing CH₄ which is 6%, CO₂, CO, and N₂ at 750 °C. These results indicate that calcium silicate provides a suitable base material for catalytic filters for partial oxidation of methane and biogas containing methane.     

Numerical simulation on non-catalytic thermal process of methane reformation for hydrogen productions

The reformer that produces hydrogen from hydrocarbon is very important part of fuel cell system. One of the promising solutions has been recently considered as direct partial oxidation of hydrocarbon by excess enthalpy flame under rich and ultra-rich condition without a platinum catalyst. In this paper, excess enthalpy flame reforming process in the perforated silicon carbide tube reformer using a two dimensional approached with GRI mechanism 1.2 was investigated. The result shows that the stable excess enthalpy flame with temperature spike was observed in a perforated silicon carbide tube reformer under condition of higher equivalence ratio than rich flammability limit of methane. It is found that hydrogen rich gases could be produced through partial oxidation at very rich equivalence ratio by formation of excess enthalpy flame. The peak flame temperature of excess enthalpy flame was higher than the adiabatic flame temperature for a free laminar flame at identical conditions and excess enthalpy flame at ultra-rich equivalence ratio could become effective way to produce hydrogen rich gases from hydrocarbon. The conversion efficiency of hydrogen and carbon monoxide by partial oxidation of excess enthalpy flame was calculated as 37.64% and 60.62%, respectively at equivalence ratio of 2.0 and inlet velocity of 80 cm/s.     

Effective hydrogen production from partial oxidation of propane over composite Ni/Al2O3SiC catalyst

In this work, hydrogen production from partial oxidation (POX) of propane over composite Ni/Al₂O₃SiC catalyst was investigated. In order to utilize the high thermal conductivity and chemical stability of SiC, the composite Al₂O₃SiC support of the catalyst was synthesized by precipitation technique, then Ni component was loaded using impregnation method. The as-prepared samples were characterized by X-ray diffraction, BET, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. As observed, stacking porous structures were appeared after calcination process by doping SiC with certain ratios. According to the stiochiometric ratio, a C₃H₈O₂ (1:1.5) gas mixture was used to study the catalytic activity for hydrogen production from POX of propane. From the results, local overheat of the catalyst bed generated by the exothermic reactions was relieved by doping SiC and Ni/Al₂O₃SiC (30 wt%) catalyst performed a higher hydrogen production. Aggregation and carbon deposition of Ni/Al₂O₃SiC (30 wt%) catalyst were reduced compared to Ni/Al₂O₃ from the observation of SEM and TEM with H₂ production up to around 236 μmol/g_cat·s and kept stable for 26 h at 600 °C. By means of TGA, non-isothermal oxidative decarburizations of the spent catalysts were studied. It was found that less carbon deposit and lower activation energy for oxidative decarburization were found by doping SiC to Ni/Al₂O₃.     

Support effects on the properties of Co and Ni catalysts for the hydrogen production from bio-ethanol partial oxidation

Partial oxidation of bio-ethanol over Co- and Ni-based catalysts supported on Al₂O₃, ZnO and AlZn binary mixed oxide was studied in a temperature range between 300 and 600 °C. Substantial difference in catalytic behavior of the materials was related to variation in metal dispersion and to metal-support interaction realized on different supports. Hence, the state of active metallic phase and reducibility of the catalysts were investigated. Among the presented systems, Ni supported on AlZn mixed oxide prepared by sol–gel method afforded the most active catalyst producing a H₂ and CO rich fuel gas. It is proposed that ZnAl₂O₄ spinel phase determines the reaction pathway and Ni promote the hydrogen generation. High hydrogen selectivity of around 90% at complete ethanol conversion was achieved at 600 °C, whereas CO, CO₂ and insignificant amounts of CH₄ were the only carbon-containing products. This high catalytic performance combined with the low cost metals and the supports used in this study makes the materials prepared herein attractive as candidates for hydrogen generation by catalytic partial oxidation of bio-ethanol.     

High-temperature reactor for hydrogen production by partial oxidation of hydrocarbons

Today, conversion of hydrocarbons is one of the most common hydrogen production technologies. This paper presents a design of a high-temperature reactor — the main component of a hydrogen production unit using partial oxidation of hydrocarbons — as well as a physical model of gas generation. It also presents a schematic diagram of an experimental setup as well as results of experimental studies on steady-state modes of partial oxidation in the combustion chamber of a high-temperature reactor for various hydrocarbon feed/oxidant combinations. In the course of the study, we identified patterns that describe how the excess oxidant ratio affects the composition of products of incomplete combustion of hydrocarbons to obtain hydrogen-containing gas of the required composition and parameters for hydrogen production. We propose a method to calculate nominal geometric dimensions of a high-temperature reactor, which makes it possible to estimate its weight and size at the design stage. The paper presents results of experimental studies confirming the adequacy of the proposed method.     

Metal oxides as combustion catalysts for a stratified,dual bed partial oxidation catalyst

Bimetallic, dual bed catalysts made up of metal oxides were investigated in the millisecond catalytic partial oxidation of methane to synthesis gas. A metal oxide combustion catalyst containing manganese, chromium, or copper was coupled with a nickel reforming catalyst to carry out the partial oxidation of methane. These catalysts produce hydrogen yields that compare to a platinum/nickel dual bed catalyst at a fraction of the cost. The high space velocity of the millisecond reactor improves performance by giving high rates of heat convection from the exothermic, upstream combustion catalyst to the downstream, endothermic reforming catalyst. Additionally, over a 10 h experiment, the catalyst activity did not decrease.     

Low-temperature catalytic partial oxidation of hydrocarbons (C1–C10) for hydrogen production

The catalytic partial oxidation of hydrocarbons to provide hydrogen for fuel cells, mobile or stationary, requires high temperatures (900°C), multireactors and incurs the highest incremental costs for the gasoline fuel processor. New experimental data between 500°C and 600°C, supported by equilibrium calculations, show that hydrogen with low carbon monoxide concentrations can be produced from liquid and gaseous hydrocarbons, thus simplifying the reactor chain. Low sulphur refinery feeds (C₄–C₆, C₄–C₁₀), simulated natural gas (C₁–C₃) and single compounds are used and safety procedures discussed. Results from laboratory reactors with 1 wt% rhodium on mixed oxide catalysts show that hydrogen rates of 43,000 lH₂/h/l reactor (power density 129 kWth/l reactor) are produced with RON=95 feeds. However, the cost and availability of rhodium limit the catalyst rhodium content to 0.1 wt% when 31,100 lH₂/h/l reactor were measured. Optimisation and reactor scale-up for heat management is in progress.     

A new catalyst based on a nickel(II) complex of diiminodiphosphine for hydrogen evolution and oxidation

Based on that hydrogen energy is widely used in fuel cells, we focus our interests on the design and research of new complexes that catalyze the reaction in both directions, such as hydrogen evolution reactions (HERs) and hydrogen oxidation reactions (HORs). A highly efficient catalyst for both hydrogen evolution and oxidation, based on a nickel(II) complex, [Ni-en-P₂](ClO₄)₂, has been designed and provided by the reaction of Ni(ClO₄)₂ with N,N′-bis[o-(diphenylphosphino)benzylidene]ethylenediamine (en-P₂) in our group. Its structure has been determined by X-ray diffraction. [Ni-en-P₂](ClO₄)₂ can electro-catalyze hydrogen evolution both from acetic acid and a neutral buffer (pH 7.0) with a turnover frequency (TOF) of 204 and 1327 mol of hydrogen per mole of catalyst per hour (H₂/mol catalyst/h) under an overpotential (OP) of 914.6 mV and 836.6 mV, respectively. [Ni-en-P₂](ClO₄)₂ also can electro-catalyze hydrogen oxidation with a TOF of 111.7 s⁻¹ under an OP of 330 mV. The results can be attributed to that [Ni^II-en-P₂](ClO₄)₂ has three good reversible redox waves at 1.01 (Ni^III/II), −0.79 (Ni^II/I) and −1.38 V (Ni^I/0) versus Fc^+/0, respectively. We hope these findings can afford a new method for the design of electrocatalysts for both H₂ evolution and H₂ oxidation.     

A comparative study of molybdenum phosphide catalyst for partial oxidation and dry reforming of methane

Molybdenum phosphide (MoP) was firstly used as a catalyst for partial oxidation of methane (POM) and its catalytic performance for POM was compared with that for dry reforming of methane (DRM). It was found that the MoP phase was the dominant active site in POM and DRM reactions, and the activity would gradually decrease when more and more MoP was converted to Mo₂C phase (non-dominant active site) and then rapid deactivation would occur due to bulk oxidation of catalyst. The redox type mechanism over MoP catalyst was vitally important to keep its structure reasonably well during methane reforming reactions. The MoP catalyst revealed a higher catalytic stability in POM than in DRM, attributing to the higher H₂ yield obtained in POM, which can promote and maintain the redox cycle of catalyst.     

Syngas production via partial oxidation of dimethyl ether over Rh/Ce0.75Zr0.25O2 catalyst and its application for SOFC feeding

Dimethyl ether (DME) partial oxidation (PO) was studied over 1 wt% Rh/Ce_0.75Zr_0.25O₂ catalyst at temperatures 300–700 °C, O₂:C molar ratio of 0.25 and GHSV 10000 h⁻¹. The catalyst was active and stable under reaction conditions. Complete conversion of DME was reached at 500 °C, but equilibrium product distribution was observed only at T ≥ 650 °C. High concentration of CH₄ and low contents of CO and H₂ were observed at 500–625 °C 75 cm³ of composite catalyst 0.24 wt% Rh/Ce_0.75Zr_0.25O₂/Al₂O₃/FeCrAl showed excellent catalytic performance in DME PO at O₂:C molar ratio of 0.29 and inlet temperature 840 °C which corresponded to carbon-free region. 100% DME conversion was reached at GHSV of 45,000 h⁻¹. The produced syngas contained (vol. %): 33.4 H₂, 34.8 N₂, 22.7 CO, 3.6 CO₂ and 1.6 CH₄. Composite catalyst demonstrated the specific syngas productivity (based on CO and H₂) in DME PO of 42.8 m³·L_cat⁻¹·h⁻¹ (STP) and the syngas productivity of more than 3 m³·h⁻¹ (STP) that was sufficient for 3 kW_e SOFC feeding. PO of natural gas and liquified petroleum gas can be carried out over the same catalyst with similar productivity, realizing the concept of multifuel hydrogen generation. The syngas composition obtained via DME PO was shown to be sufficient for YSZ-based SOFC feeding.     

Synthesis of cubic and hexagonal ZnTiO3 as catalyst support in steam reforming of methanol: Study of physical and chemical properties of copper catalysts on the H2 and CO selectivity and coke formation

Performance of cubic and hexagonal phases of ZnTiO₃ as catalyst supports were studied in steam reforming of methanol and the obtained data were compared with TiO₂ and ZnO supports. The ZnTiO₃ phases were synthesized with the sol-gel method in low temperature and copper (as the active metal) was deposited on the surface of the ZnTiO₃ nanoparticles with incipient wetness impregnation method. The Cu/cubic-ZnTiO₃ catalyst exhibits high activity, selectivity and low coke formation in this reaction. This high activity is associated with the development of low-moderate acid sites in the cubic sample. Also, inappropriate byproducts such as carbon monoxide were not detected in the Cu/cubic-ZnTiO₃ catalyst, which are related to the oxygen vacancy defects and acid sites on the cubic-ZnTiO₃ surface. Consequently, our findings prove that the Cu/cubic-ZnTiO₃ catalyst has commercial (inexpensive raw materials) and industrial (high conversion and selectivity) advantages.     

Partial oxidation of methane on neodymium and lanthanium chromate based perovskites for hydrogen production

Perovskite-type mixed oxides LaCrO₃ and Nd_0.95CrO₃ were synthesized by the polymerization complex method. The perovskites were characterized by different techniques aiming to evaluate the influence of the non-stoichiometry and the nature of site A on the catalytic properties for the POM reaction. The non-stoichiometry and A sites did not affect the methane conversion, but the selectivity. The methane conversion with the neodymium catalyst Nd_0.95CrO₃ (N95) was 34%, and of the mixed La_0.95CrO₃ (L95) catalyst 38%, under these conditions. The rate of the Nd_0.95CrO₃ (N95) perovskite was equal to 3.50 mol.g⁻¹.h⁻¹ at 700 °C, which suggests higher activity compared to cobaltate perovskites. Although the hydrogen selectivity was similar the selectivity to CO and CO₂ were different. Catalysts did not suffer structure changes during the POM reaction and negligible deactivation.     

Sorption-enhanced reaction process for glycerol-to-hydrogen conversion over cobalt catalyst supported on promoted hydrotalcites

New bi-functional materials comprising the reforming catalyst, cobalt, and the CO₂-sorbent, hydrotalcite were used to produce pure hydrogen (H₂) from sorption-enhanced steam glycerol reforming (SESGR). Three promoters, calcium, copper and zinc, were used for modifying the properties of hydrotalcites. All materials were characterized using X-ray diffraction, nitrogen physisorption and electron microscopy techniques. They were found to be very proficient for glycerol-to-H₂ conversion in a fixed-bed reactor, even at low temperature (623–823 K). Copper-promoted materials were especially promising, due to longest duration of the pre-breakthrough stage (40 min) and highest H₂ content of the reformed gas (93.1%) at T = 823 K. Besides, their sorption capacity was the highest (1.1 mol CO₂/kg sorbent) at T = 823 K. The effects of temperature, steam-to-carbon ratio in feed (S/C ratio) and gas hourly space velocity (GHSV) on the SESGR process were investigated. Durability tests over 20 cycles of adsorption and regeneration showed that materials promoted with calcium, copper and zinc were stable up to 8 (at 773 K), 11 and 5 cycles (at 823 K) correspondingly. The role of cobalt metal and cationic hydrotalcite promoters in the reforming pathway was elucidated. This insightful study will assist in improved H₂ production from renewably producible glycerol.     

Experimental investigation on the partial oxidation of methane with the effect of shrunk structure

Hydrogen energy is an ideal clean energy to solve the expanding energy demand and environmental problems caused by fossil fuels. In order to produce hydrogen, a double-layer porous media burner with shrunk structure was designed to explore the partial oxidation (POX) of methane. And the combustion temperature, species concentration and reforming efficiency were studied under different shrunk parameters and operating conditions. The results indicated that the shrunk structure greatly influenced the flame position and temperature distribution. The flame moved to the downstream section with the decreasing of the inner shrunk diameter and the increasing of the shrunk height. When the diameter of the filled Al₂O₃ pellets was 8 mm, the hydrogen yield reached the highest value of 43.8%. With the increasing of equivalence ratio, the reforming efficiency increased first and then decreased, and the maximum value of 53.0% was reached at φ = 1.5. However, the reforming efficiency and axial temperature kept increasing when the inlet velocity increased from 10 to 18 cm/s. The corresponding results provided theoretical reference for the control of flame position and species production by the design of shrunk structure in porous media burner.     

Partial oxidation of ethanol in a membrane reactor for high purity hydrogen production

Partial oxidation of ethanol was performed in a dense Pd–Ag membrane reactor over Rh/Al₂O₃ catalyst in order to produce a pure or, at least, CO_x-free hydrogen stream for supplying a PEM fuel cell. The membrane reactor performances have been evaluated in terms of ethanol conversion, hydrogen yield, CO_x-free hydrogen recovery and gas selectivity working at 450 °C, GHSV ∼ 1300 h⁻¹, O₂:C₂H₅OH feed molar ratio varying between 0.33:1 and 0.62:1 and in a reaction pressure range from 1.0 to 3.0 bar. As a result, complete ethanol conversion was achieved in all the experimental tests. A small amount of C₂H₄ and C₂H₄O formation was observed during reaction. At low pressure and feed molar ratio, H₂ and CO are mainly produced, while at stronger operating conditions CH₄, CO₂ and H₂O are prevalent compounds. However, in all the experimental tests no carbon formation was detected. As best results of this work, complete ethanol conversion and more than 40.0% CO_x-free hydrogen recovery were achieved.     

Experimental and numerical study of detailed reaction mechanism optimization for syngas (H2 + CO) production by non-catalytic partial oxidation of methane in a flow reactor

The National Institute of Standards and Technology (NIST) detailed reaction mechanism of methane combustion was optimized based on a flow reactor experiment to obtain syngas (H₂ + CO). The experimental methane partial oxidation was conducted with pre-mixed gas in a flow reactor. Specifically, 0.2% methane and 0.1% oxygen were diluted with 99.7% argon, restraining the exothermic effect. The experiment was conducted from 1223 K to 1523 K under pressure. Through a comparison of the experimental results with calculated values, the NIST mechanism was selected as a starting point. Rate coefficients of O + OH = O₂ + H, CH₃ + O₂ = CH₃O + O, and C₂H₂ + O₂ = HCCO + OH were replaced with results from other studies. The replaced rate coefficient for CH₃ + O₂ = CH₃O + O was again optimized, within its reported uncertainty of 3.16, based on the experimental results of this study. The revised value of the rate coefficient for CH₃ + O₂ = CH₃O + O was k₃₇ = 7.92 × 10¹³ × e^{(−31400/RT)}. The optimized mechanism showed better performance in predicting the results of other studies, as well as this study. The optimization reduced the RMS error for the results of this study from 6.7 to 1.18.