Mass transfer effects on the kinetics of methane partial oxidation over Ni/MgO/a-Al2O3 catalyst using spinning basket reactor

Natural gas deposits are abundant and are being continually discovered at a significant rate around the globe. Although natural gas is utilized w idely, production of synthesis gas is important because of the high -value products obtained from it. Synthesis gas is used as a reducing gas in ammonia/urea production, methanol production, Fischer -Tropsch synthesis and in the steel industry. In an effort to reduce the installation and operational cost for synthesis gas production, catalytic partial oxidation is considered to be the most attractive method. In the simulation and design of industrial reactors, the intrinsic kinetic equations have to be combin ed with the formulation of the internal diffusion and surface reaction dependent on the catalyst sizes. This study investigates the mass transfer effect of catalyst sizes on the kinetics of catalyst partial oxidation of methane and proposes the possible ov erall reaction rates for catalytic partial oxidation of methane by using a spinning basket reactor. The catalyst Ni/MgO supporte d on α-Al2O3 was prepared by precipitation method with a Ni/Mg molar ratio of 1/2 and was reduced at 850° for two hours. By changing the reaction temperature and the catalyst size, the effect of the catalyst sizes and the temperatures on reaction rate was investigated. A spinning basket reactor (by assuming a continuous stirred tank reactor) was used for kinetic investigation. The percentage of element components of nickel, magnesium, aluminum, oxygen and carbon were determined by using EDX. The actual percentage nickel loading on the catalyst was obtained by using the AAS analyzer. By using BET the pore sizes and the surface areas were determined. From EDX spectra the desired component ratios were obtained and no impurity was detected. The desired nickel loading (3.5 %) was obtained from AAS reading. The XRD spectra show the similar structures of NiO and MgO, which are completely miscible and form an ideal solid solution. The catalytic partial oxidation of methane on Ni/MgO/α-Al2O3 in the spinning basket rea ctor with GHSV = 14000 and 10000(ml/hr.g cal) is intrinsic kinetic surface -reaction controlled. The sintering effect or mass transfer effect may be more significant in the largest catalyst size of 8 -10 US mesh no (0.00238-0.002 m) and there is no mass transfer limitation with the catalyst pellet particle sizes of less than 20 US mesh no. (\u3c 0.00200 m). It can be said that the rate data are good in agreement even though the experimental rate and theoretical rate fittings are scattered since the catalyst particles used in this study are assumed to be approximately uniform. The rate equations derived for partial oxidation of methane to synthesis gas on Ni/MgO catalyst supported with α-Al2O3 is based on the mechanism that both methane and oxygen are adsorbed o n the catalyst with dissociation of oxygen , assuming that surface -reaction limiting