Preparation Of Cellular Oxygen Carrier And Its Partial Oxidation Of Methane Performance Studies

Partial oxidation of methane to syngas using the lattice oxygen of solid oxides (oxygen carrier) is a new process for natural gas conversion. Syngas with a H2/CO ratio of 2.0 can be obtained through gas-solid reactions between methane and an oxygen carrier. The reduced oxygen carrier is then be reoxidized by air (rather than pure oxygen) to restore its initial state. Since air can be used instead of pure oxygen, this technology can significantly reduce the production cost of syngas for no requiring expensive oxygen separation plantThe design and elaboration of a suitable oxygen carrier which can satisfy the redox cycle is a prerequisite for the application of this process. In addition, the preparation of a honeycomb monolithic oxygen carrieris is an important step for the further utilization of the technology.In this thesis, a series of oxygen carriers with Ce-Fe-Zr-O oxides (n(Ce):n(Fe):n(Zr)=7:3:0.5) as active components and Al2O3, MgO or SiO2 oxides as support, were prepared by co-precipitation method. The prepared oxygen carriers were characterized by XRD, BET, TG. SEM and H2-TPR techniques and the performance of their partial oxidation of the methane to syngas was investigated through temperature-programmed reduction and isothermal reaction at 850℃. The results showed that Ce-Fe-Zr-O(x)/Al2O3 oxygen carriers represent relatively high methane conversion at the early stage of the reaction but with a rapid decrease thereafter. The Ce-Fe-Zr-O(20%)/SiO2 oxygen carriers showed relative low activity due to the sintering seriously of material in the reaction. By contrast, the Ce-Fe-Zr-O(x)/MgO oxygen carriers showed high methane conversion (ca.70%) and selectivity (about 90%) with the n(H2)/n(CO) of syngas remaining at about 2.0 during the fifty minutes reaction. Moreover, the specific surface area of this kind of oxygen carrier is almost invariable after the reaction, indicating high stability. The redox cycling test showed that the oxygen carrier after several cycles still represented good catalytic performance, and both the methane conversion and syngas selectivity maintained at a high level.With the Ce-Fe-Zr-O(20%)/MgO oxides as active component, carboxymethyl cellulose(CMC) as binder, glycerol as plasticizer solution, oleic acied as glue, ethanol as wetting agent and defoamer and, soybean oil as lubricant, the Ce-Fe-Zr-O(20%)/MgO honeycomb monolithic oxygen carriers were prepared by using a extrusion method.. The characterizations of the honeycomb monolithic oxygen carriers by XRD, BET, TG, SEM and H2-TPR techniques showed that the structure of the honeycomb monolithic oxygen carriers are similar with the Ce-Fe-Zr-O(20%)/MgO oxygen carriers prepared by co-precipitation method. The catalytic performance tests appeared that the methane conversion was high up to to 50% and the selectivity CO and H2 is maintained at high level above 95% as well as the ratio of n(H2)/n(CO) keeping at around 2 for 60 minutes. The redox cycle test showed there is a slight decline (about 10%) in the methane conversion owing to the sintering of oxygen carrier, but the syngas selectivity remained at a high level.