Selectivity Of C2 Hydrocarbons Research Articles

Direct synthesis of dimethyl ether from syngas over Cu-based catalysts: Enhanced selectivity in the presence of MgO

Direct synthesis of dimethyl ether (DME) from syngas was investigated over a series of hybrid catalytic systems containing a Cu-based methanol synthesis component with varying amounts of ZnO and MgO, and γ-Al2O3 as a methanol dehydration component. Methanol synthesis and methanol dehydration components were homogeneously mixed in a 2:1 weight ratio to prepare the hybrid catalysts, which were characterized by transmission electron microscopy, scanning electron microscopy, BET surface area analysis, powder X-ray diffraction, NH3 temperature-programmed desorption, and H2 temperature-programmed reduction methods. The syngas-to-DME (STD) reaction was studied in an isothermal fixed bed reactor at 30bar and 260°C. The catalysis results revealed improved effectiveness of the catalyst in the presence of 20mol% MgO, enabling a significant enhancement in CO conversion from 19% to 37% and in DME selectivity from 36% to 83%, as compared with the activity of a catalyst without MgO. By-product CO2 and C1 and C2 hydrocarbon selectivity was also decreased from 48% to 14% for CO2 and from 8% to 2.5% for hydrocarbons. Catalyst performance, CO conversions and DME selectivity were evaluated by varying the reaction temperature, pressure, space velocity and H2/CO ratio in syngas. XRD data revealed the formation of a good crystalline malachite structure for the catalysts containing up to 20mol% MgO, but the crystallinity in the structure was lost when 30% MgO was added, resulting in decreased catalytic activity.

Synthesis of Na2WO4-Mn Supported YSZ as a Potential Anode Catalyst for Oxidative Coupling of Methane in SOFC Reactor

The oxidative coupling of methane (OCM) over a 5%Na2WO4-2%Mn on YSZ, has been investigated in a fixed bed reactor (FBR) and a solid oxide fuel cell reactor (SOFC). A 60% C2 selectivity and a 26% CH4 conversion have been obtained in a FBR at 800 o C and CH4/O2 of 4:1. Importantly, an addition of Na2WO4-Mn to YSZ support can significantly enhance the performance of the catalyst especially C2 hydrocarbons selectivity and CH4 conversion. A maximum power density of 7.8 mW cm −2 was achieved at 800°C with CH4 in the SOFC reactor having a 50 μm thick YSZ electrolyte. The CH4 conversion and C2 selectivity at 800°C were 1.1% and 85.2%, respectively.

Mathematical Modelling of the Methane Conversion to Heavier Hydrocarbons in a Plasma Reactor

In this study, mathematical modeling of fixed-bed plasma reactor operated under isothermal condition was investigated. In this process, methane and acetylene were the inputted feed and ethane, ethylene, propylene, propane, i-butane, and n-butane were the output products. The amount of methane conversion obtained was 12.7% for the former feed, however, if pure methane was inputted this conversion rose to 13.8%. Furthermore, the plasma process enhanced the conversion as well as the selectivity toward the desired product and yield. In the present study, when methane and acetylene were fed at a molar ratio of CH4/C2H2 = 10 to the reactor, the selectivity of C2, C3, and C4 hydrocarbons was determined to be 30%, 24%, and 44%; respectively. A comparison between the thermal and the plasma process showed that the methane conversion and production yield in the plasma process were higher than in the thermal process under the same operating conditions. On the other hand, product selectivity in the plasma process was determined to be lower than that of the thermal process. Finally, results of the methane conversion processes in the plasma phase were compared with those available in the open literature.

Hydrogen production from methane by DC spark discharge: Effect of current and voltage

Effects of current and voltage of consumed power on plasma reactor with rotating electrode at different feed flow rates is investigated for the non thermal decomposition of methane using a system of direct current (DC) discharge. Experimental results showed that designed reactor increases not only the concentration of the produced hydrogen in continues condition but also guarantees stable plasma. It is demonstrated that decreasing both electrical voltage and electrical current results in decreasing of methane conversion but on the other hand C2 hydrocarbons selectivity will increase. After the break down voltage, increasing the input power results in increasing electrical current more intensively than increasing electrical voltage.

Ce-Doped La2O3 based catalyst for the oxidative coupling of methane

The effect of ceria was studied on the oxidative coupling of methane (OCM) with Ce-doped La2O3 in a La:Ce molar ratio of 75:25 using two preparation methods. The characterisation techniques used were XRD and XPS. The results revealed high concentration of oxygen vacancies. Different types of ions (Ce3++Ce4+) were detected. More surface Ce3+ and higher ratio [(O22―+O—)/ O2―] were obtained in the oxide synthesised by the solvothermal method, affecting the OCM reaction in terms of higher C2 hydrocarbons selectivity. This was ascribed to the higher relative amount of O― species on the catalyst surface.

Conversion of Methane to C2 Hydrocarbons and Hydrogen Using a Gliding Arc Reactor

Methane conversion has been studied using gliding arc plasma in the presence of argon. The process was conducted at atmospheric pressure and ambient temperature. The focus of this research was to develop a process of converting methane to C2 hydrocarbons and hydrogen. The main parameters, including the CH4/Ar mole ratio, the CH4 flow rate, the input voltage, and the minimum electrode gap, were varied to investigate their effects on methane conversion rate, product distribution, energy consumption, carbon deposit, and reaction stability. The specific energy requirement (SER) was used to express the energy utilization efficiency of the process and provided a practical guidance for optimizing reaction conditions for improving energy efficiency. It was found that the carbon deposition was not conducive to methane conversion, and the gliding arc plasma discharge reached a stable state twelve minutes later. Optimum conditions for methane conversion were suggested. The maximum methane conversion rate of 43.39% was obtained under the optimum conditions. Also, C2 hydrocarbons selectivity, C2 hydrocarbons yield, H2 selectivity, H2 yield and SER were 87.20%, 37.83%, 81.28%, 35.27%, and 2.09 MJ/mol, respectively.

Methane conversion under cold plasma over Pd-containing ionic liquids immobilized on γ-Al2O3

Pd-containing ionic liquid (IL) l-hexyl-3-methylimidazolium tetrafluoroborate (C6MIMBF4) immobilized on γ-Al2O3 (Pd-IL/γ-Al2O3) was prepared and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The influences of C6MIMBF4 loading and Pd on methane conversion to C2 hydrocarbons under cold plasma were investigated. FTIR and SEM analyses indicated that C6MIMBF4 had been successfully immobilized on γ-Al2O3 and the C6MIMBF4 showed excellent stability under cold plasma. The results of BET and methane conversion showed that with the increase in immobilization amount of C6MIMBF4 onto γ-Al2O3, the specific surface area and pore volume of IL/γ-Al2O3 decreased, while the selectivity and yield of C2 hydrocarbons increased. The selectivity of C2 hydrocarbons was 94.6% when the loading of C6MIMBF4 was 40%, and the percentage of C2H4 in C2 hydrocarbons was as high as 64% when using Pd-IL/γ-Al2O3 as a catalyst with no conventional thermal reduction treatment. Optical emission spectra (OES) from the cold plasma reactor during methane conversion were also studied. The results indicated that the intensity of the C2, CH, H, and C active species from methane and hydrogen decomposition increased when IL/γ-Al2O3 or Pd-IL/γ-Al2O3 was introduced into the plasma system. Based on the analyses of the gas product and OES spectra, it can be concluded that the surface catalyzed reactions between plasma and ionic liquid were very important for the reduction of Pd2+ and the formation of C2H4

Exploiting shape effects of La2O3 nanocatalysts for oxidative coupling of methane reaction

High activity towards oxidative coupling of methane and high selectivity for C2 hydrocarbons could be achieved over La2O3 nanorods with a large surface area, strong surface basic sites, electron deficient surface oxygen species and defined surface structure compared with La2O3 nanoparticles at low temperature.

Ionic liquids as novel catalysts for methane conversion under a DC discharge plasma

Nine imidazolium-based ionic liquids were investigated as novel catalysts for methane conversion in a direct current (DC) discharge plasma reactor. The conversion of methane increased from 21.2% to 43.6% in the plasma system when the C6MIMHSO4 IL was used as a catalyst, C6MIMBF4 successfully achieved 91.0% selectivity for C2 hydrocarbons. The results of the optical emission spectroscopy indicate that the intensity of the C2, CH, H, C+, and C active species from methane decomposition increased when C6MIMHSO4, C6MIMCF3COO, and C6MIMBF4 were introduced into the plasma system. FTIR analysis indicates that C6MIMBF4 is steady in the DC discharge plasma.

Theoretical Investigations of Methane Conversion to Heavier Hydrocarbons in a Plasma Reactor

In this study, mathematical modeling of Oxidative Coupling of Methane (OCM) to C2 hydrocarbons (C2H6 and C2H4) over La2O3/CaO catalyst in a fixed-bed reactor operated under isothermal and non-isothermal conditions was investigated. The kinetic model proposed for OCM process consisted of 10 elementary reactions and 8 chemical species. In this process, methane and acetylene were the inputted feed and ethane, ethylene, propylene, propane, i- butane and n-butane were the output products. The amount of methane conversion obtained was 12.7% for the former feed, however, if pure methane was inputted this conversion rose to 13.8%. Furthermore, the plasma process would enhance the conversion, selectivity towards desired product and yield. In the present study, when methane and acetylene were fed at a molar ratio of CH4/C2H2=10 to the reactor, the selectivity of C2, C3 and C4 hydrocarbons was determined to be 30, 24 and 44% respectively. Concurrently, a higher yield was obtained for n-butane at about 3.9% and the minimum yield achieved for propylene was approximately 0.7%. A comparison between the thermal and the plasma process showed that the methane conversion and yield production in the plasma were higher than in the thermal process under the same operating conditions. On the other hand, product selectivity in the plasma process was determined to be lower than that of the thermal process. Finally, the results of the catalytic OCM and methane conversion processes in the plasma phase were compared with one another.

Study on Natural Gas Converted to C<sub>2</sub> Hydrocarbons in Plasma State

This paper presents the methane coupling with a new developed rotary multidentate helix electrode under plasmas at atmospheric pressure and in the presence of hydrogen to investigate the effects of peak voltage input the electric fields and feed flow rate on CH4 conversion and C2 yield and selectivity. The best result without remarkable amount of coke is 69.85% of single pass yield of C2 hydrocarbons with 70.46% of CH4 conversion and 99.14% of selectivity of C2 hydrocarbons. The emission of excited species such as excited radicals and atoms (C,CH,C2,H and H2) were detected in the spectra range of 300 nm～700 nm.

Activation of Methane over Perovskite Catalysts

Perovskite-type catalysts group one Ln0.6Sr0.4FexCo1−xO3 (Ln = Nd, Pr, Gd, Sm, La, 0 < x < 1), (La0.8Sr0.2)0.9MnO3 and La0.8Sr0.2CrO3, and group two sodium-doped ACoO3 (Na:A = 1:4) and A0.8Na0.2MnO3 (A = La, Gd, Sm) were synthesized, and their properties for activation of methane were evaluated in a quartz reactor first. Catalysts group one presented much higher activity than catalysts group two at temperatures below 740 °C, and the main product was, however, carbon dioxide. Group two showed much higher selectivity to C2 hydrocarbons than group one. Electrochemical measurements were conducted in a solid oxide membrane reactor with sodium-doped LaCoO3 as the catalyst electrode. It was found that electrochemical supply of O2− to the catalyst film can significantly change the rate of methane consumption and C2 hydrocarbon selectivity. The total selectivity to C2 hydrocarbon exceeded 80% in the case of the electrochemical supply of oxygen. On the basis of the experimental results, a kinetic model was suggeste...

Conversion of methane through dielectric-barrier discharge plasma

Methane coupling to produce C2 hydrocarbons through a dielectric-barrier discharge (DBD) plasma reaction was studied in four DBD reactors. The effects of high voltage electrode position, different discharge gap, types of inner electrode, volume ratio of hydrogen to methane and air cooling method on the conversion of methane and distribution of products were investigated. Conversion of methane is obviously lower when a high voltage electrode acts as an outer electrode than when it acts as an inner electrode. The lifting of reaction temperature becomes slow due to cooling of outer electrode and the temperature can be controlled in the expected range of 60°C–150°C for ensuring better methane conversion and safe operation. The parameters of reactors have obvious effects on methane conversion, but it only slightly affects distribution of the products. The main products are ethylene, ethane and propane. The selectivity of C2 hydrocarbons can reach 74.50% when volume ratio of hydrogen to methane is 1.50.

Effect of Cooling Methods on Methane Conversion via Dielectric-Barrier Discharges

Effects of cooling methods on stability and methane conversion rate using dielectric-barrier discharges (DBD) were systematically investigated in this article. The results showed that the methane conversion rate was as high as 44.43% in a pure methane system at a flow rate of 100 mL ± min−1 and an input power of 234.2 W with air cooling. A dark greenish and soft film-like carbon was deposited on the outer surface of quartz tube when the outer electrode was water-cooled, which decreased the methane conversion. With air cooling of inner electrode the selectivity of C2 hydrocarbons was higher than that with other cooling methods, while the C3 hydrocarbons had higher selectivity with flowing water cooling. Cooling the inner electrode could restrain the carbon deposition, but would decrease the methane conversion rate. The stability of both reaction and plasma operation can be improved through cooling the reactor. From thermodynamic analysis, it was found that the effective collisions frequency among the reactant molecules and free electrons (e−) increased with temperature, which in turn led to a higher methane conversion rate and a change in the distribution of products.

La-promoted Na2WO4/Mn/SiO2 catalysts for the oxidative conversion of methane simultaneously to ethylene and carbon monoxide

Abstract A series of La-promoted 5 wt% Na2WO4/2 wt% Mn/SiO2 catalysts were prepared by varying the impregnation sequence and the concentration of La promoter, and their catalytic performance for the oxidative conversion of methane was investigated in a micro-quartz-tube reactor. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the existence of Mn ions was in favor of the dispersion of La species on the catalyst, and the addition of La promoter could increase the dispersion of Na2WO4, which enriched the amount of surface oxygen species connected with the metal atoms. This oxygen species was found to be active for the oxidative coupling of methane to C2 hydrocarbons. The selectivity and yield of C2 hydrocarbons with a C2H4/CO ratio of 1/1 reached the optimized value of about 56% and 25%, respectively, at 800 °C, over the 5 wt% Na2WO4/2 wt% La–2 wt% Mn/SiO2 catalyst prepared by co-impregnation of La and Mn.

Study of the Effect of Gas Space Time on the Combination of Methane Gas-Phase Oxidation and Catalytic Oxidative Coupling over Mn/Na2WO4/SiO2 Catalyst

The effects of gas space time on the product distribution in noncatalytic gas-phase methane oxidation and in the combination reaction of noncatalytic and catalytic oxidative coupling of methane (OCM) over Mn/Na2WO4/SiO2 catalyst were studied. For the gas-phase reaction, methane and oxygen conversions and syngas selectivity increase drastically with increasing gas space time (tg) from 6.2 to 7.7 s; however, the selectivity of C2 hydrocarbons decreases sharply in this range and the concentration of C2H4 in the producing mixture is much lower than that of CO and H2. For the combination reaction, there is a minimum of methane conversion and C2 hydrocarbon selectivity with tg increasing from 3 to 5 s resulting from the variation of the mixture composition reaching the catalyst bed. The dilution of the catalyst bed with silica chips in the combination reaction partially restricts the sequential oxidation of products and raises the selectivities of ethylene and hydrogen. Surface enrichment of Na, W, and Mn speci...

APLICATION OF CATALYTIC DIELECTRIC BARRIER DISCHARGE PLASMA REACTOR FOR CO-GENERATION OF SYNTHESIS GAS AND HIGHER HYDROCARBONS

This paper deals with potential application of hybrid catalytic DBD plasma reaktor for the co-generation of C2 hydrocarbons and synthesis gases from methane and carbon dioxide. The synergism of the catalyst, feed ratio and the plasma discharge affect the products, distribution, particularly C2 hydrocarbons selectivity . The CH,CO2 feed ratio total feed flow rate, and the discharge voltage incatalytic BDB plasma reactor systems shoe significant effects on the reactor performances. However increasing the reactor wall temperature has no apparent influence on the selectivity to C2 hydrocarbons and hydrogen within the investigated range. The hybrid catalytic DBD plasma rectorwas more suitable for CO2OCM process than the conventional catalytic reactor over CaO-MnO/CeO2catalyst

Tin-Containing Catalysts, Modified with Alkaline Earth Metals in the Oxidative Dimerization of Methane

The effect of addition alkaline earth metals on the physico-chemical properties of M-Sn-O/α-Al2O3 and M-Pb-Sn-O/α-Al2O3 catalysts is studied. The formation of metal metastannates in the M-Sn-O/α-Al2O3 system facilitated the growth of selectivity of the catalysts. Addition of alkaline earth metals into the Pb-Sn-O/α-Al2O3 composition resulted in stabilization of lead in the 4-valent state with formation of metal ortho-plumbates and a decrease in the selectivity for C2 hydrocarbons. The linkage between the basicity of the surface and the catalytic properties of the samples was established.

Non-equilibrium Plasma Dehydrogenation Coupling of Methane

A few factors effecting the reaction of plasma dehydrocoupling of methane have been investigated. The experiment shows that plasma power load, i.e. the ratio of methane flow to plasma power, is the most important factor effecting methane dehydrocoupling. The products of the reaction are mainly acetylene, ethylene, ethane and unreacted methane etc. If oxygen with a suitable molar ratio is introduced into plasma region at a reasonable position, the selectivity of C2 hydrocarbons can be increased greatly.

Chemical and Physical Modification of a Ceramic Membrane Reactor and the Performance Changein the Oxidative Coupling of Methane

The smaller pore size of a ceramic membrane contributed to an increase in the selectivity of C2 hydrocarbons in the oxidative coupling of methane, with keeping high CH4 conversions about 50 %.