Mark S. Kleefisch

Dense ceramic membranes for partial oxidation of methane to syngas

Several perovskite-type oxides (ABO3) containing transition metals on the B-site show mixed (electronic/ionic) conductivity. These mixed-conductivity oxides are promising materials for oxygen-permeating membranes that can operate without electrodes or external electrical circuitry. Oxides in the system LaSrFeCoO permeate large amounts of oxygen, and extruded tubes of these materials have been evaluated in a reactor operating at ca. 850°C for direct conversion of methane into syngas (CO + H2) in the presence of a reforming catalyst. Methane conversion efficiencies of > 99% were observed, and some of the reactor tubes have been operated for over 1000 h. Membrane tubes were fabricated from calcined powders by a plastic extrusion technique. Ceramic powders in the LaSrFeCoO system were made by solid-state reaction of the constituent carbonates, oxides, and/or nitrates. The chemical-phase behavior of the ceramic powders with varying stoichiometries were studied by high-temperature in-situ X-ray diffraction (XRD) as a function of oxygen partial pressure. The sintered extruded tubes were also characterized by XRD and scanning electron microscopy.

Gas-phase oxygen oxidations of alkylaromatics over chemical vapor deposited Fe/Mo/borosilicate molecularsieve, Fe/Mo/DBH: I. The selective synthesis of terephthaldehyde from para-xylene

Abstract The Fe/Mo/borosilicate molecular sieve catalyst, Fe/Mo/DBH (Mo/Fe = 1.6–2.0), was prepared from FeCl 3 , MoO 2 Cl 2 and partially deboronated borosilicate molecular sieve (DBH) by the chemical vapor deposition method. The Fe/Mo/DBH catalyst exhibited a stable para -selective oxidation activity to form terephthaldehyde with high selectivity by the gas-phase oxygen oxidation of para -xylene under mild reaction conditions. para -Tolualdehyde was also formed in the reaction, and a molar ratio of terephthaldehyde to para -tolualdehyde in the product was ca. 2–4 to 1. Despite the large surface area of the catalyst, 250–325 m 2 /g, substrate burning was suppressed to less than 10% under controlled conditions. A mechanism featuring two different types of active sites, the “pair” sites for terephthaldehyde and “single” sites for para -tolualdehyde, is postulated.

Gas-phase oxygen oxidation of alkylaromatics over CVD Fe/Mo/borosilicate molecular sieve Fe/Mo/DBH. III: Selective oxidation of p-xylene from a xylene isomer mixture containing ethylbenzene

Abstract In the course of developing a process for selective synthesis of terephthaldehyde by the gas-phase oxygen oxidation of p -xylene over the CVD Fe/Mo/DBH catalyst, it was found that a large reactivity gap exists between p -xylene and o -/ m -xylene isomer due to the para -selective nature of the catalyst. Reactivity of xylene isomers for oxidation is in the order p -xylene > o -xylene > m -xylene. p -Xylene was preferentially oxidized to terephthaldehyde and p -tolualdehyde from the xylene isomer mixture as well as the commercially available xylene isomer feed containing ethylbenzene, while the rest of the components remained almost intact. By coating the CVD Fe/Mo/DBH catalyst with tetramethyl-orthosilicate, the preferential oxidation of p -xylene over its isomers became even more selective.