Oxidative Condensation Of Methane Research Articles

In English

Samples of MnOx-Na2WO4/SiO2 based on a mesoporous silica matrix were synthesized using manganese acetate, sodium tungstate, tetraethoxysilane (TEOS) as precursors and cetyltrimethylammonium bromide (CTAB), citric acid and triethanolamine as pore generating agent and characterized by scanning electron microscopy with energy dispersive elemental analysis (SEM/EDS), X-ray diffractometry (XRD), electron magnetic resonance (EMR), N2 adsorption-desorption measurements and tested as a catalyst for the reaction of oxidative condensation of methane (OCM). It is shown that the MnNaW/SiO2 catalyst consists of Mn2O3, MnO2, Na2WO4 and SiO2 phases. The EMR and SEM/EDS data indicate a noticeable effect of the reaction conditions on the surface structure and the distribution of catalytically active components in the catalyst structure. Significant changes in the values of the specific surface area and pore volume of the samples with increasing temperature and duration of the reaction were found (the values of the specific surface area and pore volume, respectively, 116.8 m2/g and 0.590 cm3/g - up to and 46.1 m2/g and 0.232 cm3/g after 15 hours of catalyst operation in the OCM reaction at 800 °C). It has been shown that under the conditions of the OCM reaction, the elemental composition of the surface of the MnOx-Na2WO4/SiO2 catalyst changes, and the degree of change depends on the duration of the OCM reaction. Under the influence of the reaction mixture CH4/O2, the content of Mn and W decreases in the first two hours, and the trend towards a decrease in their amount on the catalyst surface with an increase in the duration of the OCM reaction is generally preserved. A detailed X-ray phase analysis also indicates a change in the phase composition of this catalyst under the influence of the CH4/O2 reaction mixture. It is assumed that under the reaction conditions (700–800 °C) the MnOx-Na2WO4/SiO2 catalyst is silicon dioxide particles basely with the cristabolite structure, the surface of which is coated with molten sodium tungstate containing nanosized particles of MnOx structures activated by sodium ions and WOx.

OXİDATİVE CONVERSİON OF METHANE. EFFECT OF CATALYST AND PERSPECTİVE DİRECTİONS OF REACTİON

The well-known MnNaW catalysts based on SiO2 for oxidative condensation of methane (OCM) were synthesized by various methods, characterized by X-ray diffractometry (XRD), scanning electron microscopy with energy dispersive elemental analysis (SEM/EDX), electron magnetic resonance (EMR) spectroscopy, N2 adsorption-desorption measurements, and tested as OCM catalysts at atmospheric pressure to convert into a mixture of ethylene + carbon oxides for further hydroformylation to propylene. The structural and catalytic features of the synthesized systems are discussed. The necessity of using mainly X-ray diffraction, Raman, and EMR methods for studying catalysts in situ mode in combination with online MS analysis of gasphase reaction products to establish the nature of catalytically active phases, centers, their mechanism of functioning, activation of CH4 with the formation of C-C bond for the synthesis of hydrocarbons C2 and C2+ is considered. Keywords: oxidative conversion of methane, NaMnW/SiO2 catalyst, ethylene-carbon monoxide mixture, magnetic, texture properties

Selection of catalysts for the process of oxidative condensation of methane using the intelligent decision support system

Since most chemical processes are catalytic; the problem of the choice of catalysts is traditionally considered in many publications and is covered on many Internet sites. In this paper; the catalytic process of methane oxidative condensation and intelligent technologies for analysis and decision making for choosing the best catalyst option are considered as an object of research. The authors of the work consider many literature and Internet sources; which highlight the problems of the choice of catalysts in general; and indeed for the methane oxidative condensation. As a result of studying numerous sources; the authors determine that the tasks associated with choosing the best catalyst in each case are often very ambiguous and complex. Therefore; any informational support in solving problems related to the choice of catalysts will be useful. A large amount of information; the attraction of modern computer technology and the knowledge of qualified experts; all this makes the creation of an intelligent decision support system an important and real task.This work is aimed at developing an intelligent decision support system to select the most effective catalyst for the methane oxidative condensation.The methods chosen in the decision-making system are the hierarchy analysis method and data mining based on decision trees. The first of them requires the participation of a human expert; the second performs data mining without the participation of a specialist. It should be noted that the choice of the latter is also due to the fact that methods based on decision trees are among the top ten in terms of their effectiveness for data mining.For computer implementation of the system; object-oriented programming based on Microsoft Visual Studio is used.In the course of the study; in addition to the choice of catalysts using the developed decision-making system; a computer simulation of the methane oxidative condensation using the selected catalysts is carried out and the best version of the scheme is chosen. The obtained results can be useful at the design and implementation stages of the corresponding production; as well as used by process operators to analyze the production process.

Oxidative Condensation of Methane on Sr2 –xLaxTiO4 Catalysts: Effect of the Degree of Substitution of Sr and La

The Sr2 –xLaxTiO4 (x = 0–2.0) catalysts were synthesized based on strontium titanate with a layered perovskite structure. The effect of the degree of substitution of La for Sr on the physicochemical (phase composition and textural characteristics) and catalytic properties of oxides in the oxidative condensation of methane at temperatures of 700–800°C were studied. It was found that multiphase Sr2 – xLaxTiO4 samples with the degree of substitution x = 0.8–1.8 were most active and selective in the test reaction; this was likely related to the presence of lanthanum oxide and strontium oxide impurities in them, their optimum distribution over the surface, and the specific surface area.

A study on the oxidative coupling of methane over La2-xMgxTiO4 catalysts

La2-xMgxTiO5-δ samples with different content of Mg and La were synthesized by the precipitation from a mixed solution of Mg(NO3)2 and La(NO3)3 in the presence of TiO2 suspension. The samples were characterized using X-ray diffractometry, mercury porosimetry, and BET techniques. Specific surface area of the samples ranges from 0.1 to 4.17 m2/g, and pore volume, from 0.005 to 0.023 cm3/g. Activity and selectivity of the samples in the oxidative condensation of methane (OCM) were measured using a fixed catalyst bed flow quartz reactor. It was demonstrated that samples with x ≤ 0.6 showed the highest activity toward OCM reaction. This can be explained by a high content of the main active phase (La,Mg)2TiO5-δ with the layered perovskite structure and a sufficient specific surface area.

Selective Polyoxide Catalysts for Synthesis of Ethylene from Natural Gas

Processing of the methane of natural gas into important hydrocarbons, oxygen-containing products and motor fuels has become one of the major problems of chemistry. The degree of chemical processing of natural gas in valuable products remains at a low level, and a significant portion of associated petroleum gas is burned in flares in the fields. This leads to an irreparable loss of valuable raw materials and generates complex environmental problems in the mining regions. Oxidative condensation of methane, steam and steam-oxygen conversion, dry reforming and tri-reforming of methane attract a great attention in recent years. Catalysts based on Si-W heteropoly compounds supported on carriers were investigated in oxidative condensation of methane to ethylene. Determination of the effect of reaction parameters, the nature of catalyst on composition and distribution of products were carried out. Supporting of Si-W heteropoly compounds on aluminosilicate does not destroy the Keggin molecular structure and increases its thermal stability. Thus, effective catalysts for the production of ethylene from methane have been developed.

Ethylene production by the oxidative condensation of methane in the presence of MnMW/SiO2 catalysts (M = Na, K, and Rb)

The samples of MnMW/SiO2 (M = Na, K, and Rb) were synthesized using various synthesis methods under varied heat treatment conditions and their physicochemical properties and activity in the reaction of the oxidative condensation of methane (OCM) were studied for the development of an effective catalyst for the resource-saving process of natural gas conversion into ethylene. It was found that the preparation method exerts an effect on the textural characteristics of the samples and the reducing properties of the cations of manganese and tungsten. It was determined that the composition of a W-containing phase depends on the alkali metal, and a ratio between the polymorphous modifications of SiO2 is controlled by the method of synthesis and the conditions of catalyst heat treatment. It was established that the yield of C2 hydrocarbons in the OCM reaction increased with the use of incipient wetness impregnation instead of the method of mixing with a suspension for catalyst preparation and with an increase in the catalyst heat treatment temperature from 700 to 1000°C. The optimum composition of the catalyst and the condition of its synthesis were found: 2Mn0.8Na3W/SiO2 obtained by the impregnation method and calcined at 1000°C ensured the yield of target products of ~20% with a CH4 conversion of ~35% at a reaction temperature of 850°C.

Nature of the active sites of ferrospheres in the oxidative condensation of methane

The catalytic properties of ferrospheres containing 76–97 wt % Fe2O3 in the oxidative condensation of methane were compared with their phase composition and the distribution of iron cations over the crystallographic positions of iron-containing phases in a steady state. It was established that the reaction route of methane oxidation changed at a Fe2O3 content of 89 wt %. Deep oxidation was the main reaction route on ferrospheres with a Fe2O3 content of <88.8 wt %. At a Fe2O3 content of ≥89 wt %, the yield of C2 hydrocarbons sharply increased and the contribution of deep oxidation decreased. The yield of C2 hydrocarbons correlated with the amount of defects in the structure of iron spinel, which are iron ions with the tetrahedral cation of Ca2+ and the octahedral cation vacancy among the nearest neighbors.

Oxidative condensation of methane in the presence of modified MnNaW/SiO2 catalysts

The effects of cationic (Ce, Zr, and La) and anionic (S, P, and Cl) admixtures on the activity and physicochemical properties of MnNaW/SiO2 were studied in order to optimize the composition of a catalyst for the oxidative condensation of methane (OCM). It was found that OCM process characteristics can be regulated by varying the type (Ce, Zr, La, S, P, and Cl) and concentration (0.5–5 wt %) of a modifying admixture. For the modified MnNaW/SiO2 catalysts, the yield of the target reaction products increased in the following order of modifying admixtures: S < Zr < P < Ce < La < Cl. The addition of lanthanum, cerium, or phosphorus admixtures insignificantly affected the activity of the MnNaW/SiO2 catalyst, whereas the introduction of sulfur or zirconium led to a decrease in the yield of C2 hydrocarbons. Modification with chlorine improved process characteristics and shifted a maximum yield of C2 hydrocarbons to the low-temperature region. It was established that the introduction of lanthanum considerably improved the stability of catalyst operation. The catalyst composition 2Mn-1.6Na-3.1W-2La/SiO2 was developed to afford a 22% yield of target C2 hydrocarbons at a 54% conversion of methane after a 24-h reaction performed under optimum conditions (reaction temperature, 800°C; reaction mixture flow rate, 117 mL min−1gCat−1 and O2/CH4 molar ratio, 0.5).

Kinetic simulation of the oxidative condensation of methane

The kinetics of the oxidative condensation of methane (OCM) over a mixed-oxide lithium-manganese-tungsten-silicate catalyst has been simulated, and systems of stoichiometric chemical equations possible under the OCM conditions have thereby been discriminated. A phenomenological kinetic model has been developed to fit the observed rates of formation and disappearance of the compounds involved in OCM.

Oxidative condensation of methane in the presence of lanthanum—cerium catalysts: fundamental character of the effect of nonadditivity

Oxidative condensation of methane (OCM) was conducted for the first time in the presence of new mesoporous amorphous catalysts containing lanthanum ions, cerium ions, and mixed lanthanum and cerium ions. It was shown that the previously discovered effect of the nonadditive action of lanthanum and cerium ions in OCM is a fundamental feature which is characteristic of both a mixture of these rare-earth element (REE) oxides and of the ions of these elements incorporated in a nanostructured silicate matrix.

Kinetic limit of the ethane and ethylene yield in the gas phase condensation of methane

A kinetic simulation of the initiated oxidative condensation of methane in the gas phase showed that the additional generation of methyl radicalsvia the reaction CH4 + O2 → CH3 + HO2 causes a nearly tenfold increase in the C2 hydrocarbon yield. However, a kinetic limit of the yield exists that is close to that determined in experiments on the catalytic oxidative condensation of methane.

Intermediate oxygen-containing compounds in oxidative condensation of methane over sodium-manganese catalysts

CH2O conversion over sodium-manganese oxide and oxychloride catalysts in methane dehydrodimerization have been studied under unsteady-state conditions at high temperatures (600–750 °C). It has been established that formaldehyde conversions produce deep oxidation (CO, CO2), condensation (C2H4, C2H6) and methanation products through CH3O− formation and decomposition.

Oxidative conversion of methane on lanthanum-containing hydroxychloride catalysts

The activity of lanthanum-containing oxide and hydroxychloride catalysts in oxidative condensation of methane has been studied. It has been established that modification of La 2O 3 with sodium (NaCl) and application on Al 2O 3 leads to high selectivity of the process. Selectivity with respect to C 2 hydrocarbons at 760°C amounts to 84% with 20·4% methane conversion. Catalyst NaClLaO/Al 2O 3 is multiphase, and NaCl, LaOCl and LaAlO 3 phases coexist in reaction conditions. As the reaction progresses there is a change in the phase composition and selectivity of the catalyst.

Oxidative condensation of methane on modified natural mordenites

Modified samples of natural mordenites have been found to catalyze the oxidative condensation of methane to yield ethane and ethylene. The selectivity towards C2 hydrocarbons increases, whereas the acidity of zeolites falls.

ChemInform Abstract: Electrophilic Methane Conversion

Conversion of methane into substituted derivatives and higher hydrocarbons is a most desirable goal. If we survey the literature and current textbooks of organic chemistry,' they report pyrolytic and free -radical reactions (such as combustion , hydrogenation, nitration, sulfochlorination).2 These reactions show little selectivity , characteristic of radical reactions . The chlorination of methane , for example , gives all four possible chloromethanes . Recently, catalytic oxidative condensation of methane to ethane with metal oxides3 gained significance . Conversion to ethylene and acetylene via high-temperature conversion with chlorine4 was also explored . It should be noted that the long-known high-temperature production of acetylene from methane is a related radical process . In many of these processes, however, a significant portion of methane is lost to further oxidation and soot formation. A new approach to the possible chemical conversion of methane involves organometallic insertion reactions.5 Pioneering work with iridium complexes and other transition-metal systems (rhodium , osmium , rhenium, etc.) was carried out. However , until now these were noncatalytic , stoichiometric reactions taking place in the coordination sphere of the metal complexes and therefore limited in their practical application. In the present Account an additional alternative, i.e., the-electrophilic conversion reactions of methane to condensed and substituted products , will be discussed, a field where the research interest of my group centered in recent years. Scheme I summarizes the presently existing alternative possibilities of methane conversion . Biological conversion of methane to higher hydrocarbons or to methyl alcohol may also be significant for the future.6

Manganese catalysts for the oxidative condensation of methane with alkali and alkaline-earth metal salt additives

1. The addition of acetates of alkali (Li, Na, K, and Cs) and alkaline-earth (Mg and Ca) metals affects the catalytic properties of Mn/SiO2 catalysts in the oxidation condensation of methane to give C2-hydrocarbons. 2. The promotion effect of sodium salts depends on the nature of the salt anion. Greatest efficiency is found for the (Mn + NaCl)/SiO2 catalyst. At 800°C and methane/air mole ratio equal to 0.55, C2-hydrocarbons are formed on this catalyst with 25.8% yield and 77.5% selectivity; the ethylene content in the methane condensation products is 95%.

Oxidative condensation of methane into ethane and ethylene on manganese catalysts

The dependence of the activity and selectivity of Mn catalysts on the nature of the carrier and conditions of oxidative condensation of CH/sub 4/ was investigated. Manganese catalysts based on zeolites and silica gel are found to be efficient in oxidative condensation of methane into ethylene and ethane. Conversion of CH/sub 4/ attains 25.6% with 51.9% selectivity for C/sub 2/ hydrocarbons on the most active catalyst, 10% Mn/HNaHSZ at 750/sup 0/C.ivatives

Catalysts for the oxidative condensation of methane to form C2 hydrocarbons

The oxidative condensation of CH/sub 4/ has been accomplished under catalysis conditions. The best results were obtained for a lead system at 700-750 C with CH/sub 4/:O/sub 2/:N/sub 2/ = 10:1:2.3 (mole ratio). The conversion was 2-10% with selectivity for C/sub 2/ hydrocarbons equal to 30-70%. Manganese catalysts prepared using SiO/sub 2/ and zeolites were also found to be active in this reactions. The experiments were carried out at atmospheric pressure in a quartz flow reactor, in which methane conversion at 750 C without catalyst is not observed. The reaction products were analyzed by chromatography. Only extensive oxidation of CH/sub 4/ was observed on the supports without manganese; C/sub 2/H/sub 6/, C/sub 2/H/sub 4/, CO/sub 2/, CO, H/sub 2/O, and traces of C/sub 3/ hydrocarbons were found among the reaction products. The results demonstrate the possibility of expanding the scope of the catalytic systems used for methane oxidative condensation.