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Sodium-tungsten-manganese supported on silica (Na-W-Mn/SiO2) and hydroxyapatite (HAp) are representative catalysts for oxidative coupling of methane (OCM). In this work, the effect of the HAp doping in a Na-W-Mn/SiO2 catalysts on the OCM performance was studied. To enhance the ethylene selectivity of the Na-W-Mn/SiO2 catalyst, silica supports were coated with HAp containing hydroxyl and phosphate groups as oxygen species. A series of Na-W-Mn/xHAp_SiO2 (x=1, 3, 5 and 7) catalysts with the different HAp coating cycles were prepared through the alternative soaking method, and X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that the amount of HAp doping was dependent on the HAp coating cycles. In addition, the change of oxygen species upon HAp doping was examined with X-ray photoelectron spectroscopy (XPS) and oxygen temperature-programmed desorption (O2-TPD) techniques. With HAp doping, the increase of oxygen species assigned to metal oxide responsible for selective oxidation of methane to ethylene was observed in O 1s XPS spectra. In addition, weakly bound oxygen species were observed with the introduction of HAp doping in O2-TPD profiles of prepared catalysts. The influence of these oxygen species on OCM catalytic performance was evaluated at an operating temperature of 775 °C and gas hourly space velocity of 18,000 ml/gcat·h. The amount of HAp doping provided reactive oxygen species for oxidative dehydrogenation of ethane, which resulted in as much as 120% increase in C2H4/C2H6 ratio over the Na-W-Mn/3HAp_SiO2 catalyst compared to the Na-W-Mn/SiO2 catalyst. [ABSTRACT FROM AUTHOR]

A one-dimensional non-isothermal steady state model was developed to simulate the performance of three-reactor configurations for the oxidative dehydrogenation of ethane (ODHE) to ethylene. These configurations consist of side feeding reactor (SFR), conventional fixed bed reactor (CFBR) and membrane reactor (MR). The performance of these reactors was compared in the terms of CH conversion, CH and CO selectivity and temperature profiles. The use of sectional air injections on the wall of SFR with a limited number of injection points showed that the performance of reactor significantly improves and optimum pattern of oxygen consumption is also obtained. Moreover, our SFR with a liquid coolant medium operates in an effectively controlled temperature profile that is comparable with that of the MR, which is cooled by a coolant stream of air. Hence, an enhancement in the level of selectivity is obtained for the SFR configuration. Consequently, the side feeding procedure can decrease the high operating temperature problem and low ethylene selectivity in the ODHE process. According to obtained results, the SFR would be a proper alternative for both the MR and CFBR. [ABSTRACT FROM AUTHOR]