2 research outputs found
Oxygen flux through unmodified and modified La0.6Sr0.4Co0.2Fe0.8O3-8 hollow fibre membranes and application to methane oxidation
PhD ThesisImproved catalytic routes could help to transform the exploitation of the large worldwide
natural gas reserves, whose principal component is methane. They transform methane into
more valuable chemicals and fuels through carbon dioxide reforming of methane (CDRM),
steam reforming of methane (SRM) and partial oxidation of methane (POM). These
reactions facilitate the formation of syngas, which is subsequently converted to fuels through
the Fischer-Tröpsch synthesis. Mixed Ionic and Electronic Conducting (MIEC) membrane
reactors are of interest because they have the potential to produce high purity oxygen from air
at lower costs and provide a continuous oxygen supply to reactions or/and industrial
processes, and hence avoid sourcing the pure oxygen from air by conventional cryogenic
separation technology. In addition, the MIEC ceramic membrane shows the ability to carry
out simultaneous oxygen permeation and hydrocarbons oxidation into single compact
ceramic membrane reactor at high temperature. This can reduce the capital investment for
gas-to-liquid (GTL) plants and for distributing hydrogen.
This study compares the oxygen release and oxygen uptake obtained through a
LaSrCoFeO hollow fibre membrane (referred as LSCF6428-HFM) under an 0.60.40.20.83-δ
Air/He gradient at 850°C and 900°C. The separation and quantification of these two
processes permitted the determination of the oxygen incorporated into LSCF6428 structure
and the development of a model for apparent overall rate constant using the molar flow of the
oxygen at the inlet and outlet in different side of membrane (i.e. shell side and lumen side).
The results show that the oxygen flux is enhanced by rising helium flow rates, this is due to
an increased driving force for oxygen migration across the membrane and also the air flow
determines the oxygen amount that permeates across the membrane. In addition, the oxygen
flux improves at higher temperatures, due to its dependence on bulk oxygen diffusion and the
oxygen surface reaction rates. The temperature increase improves the mobility of the lattice
oxygen vacancies and also the concentration of lattice oxygen vacancies in the perovskite.
The impact of surface modification was also studied by coating CoO and 5%Ni-LSCF6428 34
catalysts on the shell side surface of the LSCF6428 hollow fibre membrane for oxygen
permeation. It was found that the oxygen flux significantly improved under Air/He gradient
for catalyst-coated LSCF6428-HFM. However, under continuous operation conditions over a
long time both the unmodified and the modified perovskite LSCF6428-HFM reactors
suffered segregation of metal oxides or redistribution of metal composition at the surface
membrane, although the bulk LSCF6428 membrane stoichiometry did not change.
The apparent overall rate constants for oxygen permeation of the CoO/LSCF6428-HFM and 34
5%Ni/LSCF6428-HFM were enhanced 3-4 fold compared to unmodified LSCF6428-HFM.
Comparison of both modified HFM reactors revealed that the apparent overall rate constants
for CoO/LSCF6428-HFM were 2 fold higher than those obtained for 5%Ni- 34
LSCF6428/HFM. According to the distribution of total oxygen permeation residence for
unmodified and modified LSCF6428-HFM reactor, the oxygen permeation rate is limited by
surface exchange on the oxygen lean side or lumen side (R) at 850°C and 900°C and the
ex
contribution of bulk diffusion on the oxygen permeation rate increased with a rise in the
temperature (900°C).
The methane oxidation reaction was studied in unmodified and modified 5%Ni-
LSCF6428/LSCF6428 hollow fibre membrane in reactors at 850°C. The results suggest that
catalytic pathways in methane oxidation depended upon flow operation modes, oxygen
concentration, Htreatment and on the type of catalyst.
The performances in methane conversion of LSCF6428-HFM and 5%Ni/LSCF6428-HFM
modules facilitated the formation of SrCO3 because of the reaction of CO2 with segregated
strontium oxide.University of Newcastle upon Tyne (EPSRC
Synthesis of light alkenes on manganese promoted.
Synthesis of light alkenes on manganese promoted.
(González Cortés, Sergio Luis; Rodulfo Baechler, Serbia M. A.; Oliveros Bastidas, Alberto; Orozco, José; Fontal, Bernardo; Mora, Asiloé J.; Delgado, Gerzon)
Abstract
The light alkenes formation capacity and the interaction of Mn with Fe and Fe-Co
of Fischer-Tropsch catalysts have been studied. The samples were characterized
by X-ray diffraction and temperature-programmed reduction. It was found that Fe-
Co-Mn has a better catalytic stability than the Fe-Mn catalyst. It is proposed that
iron particle size and its interaction with oxide and carbide phases produced
during the catalytic reaction are mainly responsible for the high activity and light
alkene selectivity.
This article was jointly published by Akadémiai Kiadó, Budapest and Kluwer Academic Publishers, Dordrecht React.Kinet.Catal.Lett. Vol. 75, No. 1, 3-12 (2002)[email protected]@[email protected]@ula.veNivel monográfic