An investigation of the comparative reactivities of ethane and ethylene in the presence of oxygen over Li/MgO and Ca/Sm2O3 catalysts in relation to the oxidative coupling of methane

In order to examine the importance of the further oxidation of the desired C2 products in the oxidative coupling of methane, ethylene and ethane have been added to the feed (containing methane and oxygen) to a Li/MgO or Ca/Sm2O3 catalyst. The results of these measurements show that neither of these C2 molecules is stable under these conditions with either of the catalysts. Additionally, the rates of the oxidation of ethane and of ethylene alone have been measured using a gradientless reactor for both catalysts as well as for a quartz bed. It was found that the Ca/Sm2O3 material had higher activities for the oxidation of C2H6 and C2H4 (and also of CH4) than had the Li/MgO material. These higher activities result in a lower optimal reaction temperature for the oxidative coupling of methane and are (at least partially) responsible for the lower selectivity to C2 products observed with the Ca/Sm2O3 catalyst compared to that with the Li/MgO catalyst

Kinetic studies of oxidative coupling of methane on samarium oxide

Kinetic behaviour of three samples of samarium oxide (cubic (Sm-1 ), monoclinic (Sm-3) and mixed cubic-monoclinic (Sm 2) ) were studied in the oxidative coupling of methane using a gradientless flow circulation system. The specific rate of C2- product formation differed by a factor of 6-8 for Sm-1 and Sm-3. The specific activity for CO formation did not depend upon the crystal structure of samarium oxide while the rate of formation of CO2 was different for the samples studied. It is proposed that formation of CO and CO2 occurs via different reaction routes. The rate of CO2 formation at high CHJO2 ratio is limited by oxidant activation or surface CO2-complex decomposition

Oxidative Coupling of Methane to Ethylene

This report details the design of a plant using the oxidative coupling of methane (OCM) to produce one billion pounds of ethylene and 534 million pounds of ethane per year. The ethylene and ethane produced are produced for sale to an olefins plant for further refining into polymers and plastics. The OCM process consumes a total feed of 9.10 billion pounds of methane and 4.62 billion pounds of oxygen per year. The methane and oxygen will be converted in four isothermal fixed-bed catalytic reactors operating at 1292°F and 96 psi. The catalyst is LiMgO in the form of 50 mm diameter spherical pellets. The remainder of the process encompasses an intricate separations train involving condensation, pressure swing adsorption, and cryogenic distillation. The unconverted methane is combusted to produce steam that is fed to a turbine to provide power to the plant with a residual 108 MW of electricity sent into the grid. The plant will be located in Baytown, Texas where access to feedstock and the olefin plants buying the products are easily attainable. After conducting an analysis of the sensitivity of the plant’s Internal Rate of Return with variable pricing and ethylene prices, it was determined that the plant is profitable exhibiting a Return on Investment of 25.61% and a Net Present Value of $517.2 million. Further research into catalysts increasing conversion of methane coupled with increased selectivity to C2 hydrocarbons will offer more attractive returns

The effect of Nb2O5 and ZrO2 additions on the behaviour of Li/MgO and Li/Na/MgO catalysts for the oxidative coupling of methane

Incorporation of Nb2O5 or ZrO2 into both Li/MgO and Li/Na/MgO systems produced ternary and quaternary catalysts, respectively, capable of attaining optimal C2 yields and selectivities at lower temperatures relative to the unpromoted materials. The degree of enhancement effected by these metal oxide additives was compared to that produced by Li/MgO and Li/Na/MgO catalysts promoted with SnO2 or Co3O4. At reaction temperatures < 700°C, the Li/Co/MgO ternary system showed marked differences in behaviour compared to the other ternary catalysts tested. This was particularly evident in the variation in C2 selectivity with time on stream during ageing studies of (i) untreated materials, (ii) materials pretreated in CO2, and (iii) materials dosed periodically with CHCI3

Oxidative coupling of methane in a mixed-conducting perovskite membrane reactor

Ionic-electronic mixed-conducting perovskite-type oxide La0.6Sr0.4Co0.8Fe0.2O3 was applied as a dense membrane for oxygen supply in a reactor for methane coupling. The oxygen permeation properties were studied in the pO2-range of 10¿3¿1 bar at 1073¿1273 K, using helium as a sweeping gas at the permeate side of the membrane. The oxygen semi-permeability has a value close to 1 mmol m¿2 s¿1 at 1173 K with a corresponding activation energy of 130¿140 kJ/mol. The oxygen flux is limited by a surface process at the permeate side of the membrane. It was found that the oxygen flux is only slightly enhanced if methane is admixed with helium. Methane is converted to ethane and ethene with selectivities up to 70%, albeit that conversions are low, typically 1¿3% at 1073¿1173 K. When oxygen was admixed with methane rather than supplied through the membrane, selectivities obtained were found to be in the range 30¿35%. Segregation of strontium was found at both sides of the membrane, being seriously affected by the presence of an oxygen pressure gradient across it. The importance of a surface limited oxygen flux for application of perovskite membranes for methane coupling is emphasized

Oxidative coupling of methane over Ba/CaO catalysts: a comparison with Li/MgO

A comparison has been made of the behaviour in the oxidative coupling of methane of a Ba/CaO catalyst with that of a Li/MgO material. Doping of CaO with BaCO3 resulted in a catalyst which is more active at lower reaction temperatures than is BaCO3. The active oxygen entity in the case of Ba/CaO is probably an O2−2 species. Ba/CaO is more stable but less selective than is Li/MgO. The effect of residence time was studied for both Ba/CaO and Li/MgO. The direct oxidation of methyl radicals to give carbon monoxide and carbon dioxide plays a more important role in the case of Ba/CaO than is the case with Li /MgO

Reaction path of the oxidative coupling of methane over a lithium-doped magnesium oxide catalyst:Factors affecting the Rate of Total Oxidation of Ethane and Ethylene

Experiments using gas mixtures of O2, C2H6 or C2H4 and CH4 or He have been carried out with a Li/MgO catalyst using a well-mixed reaction system which show that the total oxidation products, CO and CO2, are formed predominantly from ethylene, formed in the oxidative coupling of methane. It is therefore concluded that the network of reactions taking place during oxidative coupling of methane over a Li-doped MgO catalyst can be simplified to a serial reaction scheme: CH4→C2H6→C2H4→COx. Additional experiments have shown that the rates of gas-phase oxidation reaction of C2H6 and C2H4 are lowered by the presence of excess CH4 or by alkali metal carbonates