(732a) Dense Ceramic Membrane Reactor for CH4 and CO2 Utilization

Methane (CH4), the main component of natural gas, can be converted to liquid fuels, hydrogen, and other value-added chemicals through a syngas intermediate. Currently, partial oxidation of methane (POM) with pure oxygen in the presence of a catalyst is established to be the most potential process for CH4 conversion because of its greater selectivity to syngas, its exothermicity, and more desirable CO/H2 ratio. Meantime, thermal decomposition of carbon dioxide (TDCD) to CO and O2 is an alternative process for the consumption and utilization of Carbon dioxide (CO2). However, this reaction is limited by the thermodynamic equilibrium and not easy to be realized in conventional fixed-bed reactors.

In our work, an important advance in using CO2 as a feedstock for POM process is resulted from the application of a mixed-conducting membrane reactor, which integrated the TDCD and POM processes in a single unit. [1, 2] TDCD takes place in one side of the membrane and the POM occurs simultaneously in the other side, or more clearly, methane reacts with oxygen, which is permeated through the membrane from the CO2 decomposition, to produce H2 and CO over supported transition metal catalysts. At 900 ˚C, the CO2 conversion reached about 11.1%. Then, we developed an innovative catalyst process to decompose CO2 in an oxygen-permeable membrane reactor packed with a mixed-conducting oxide supported noble metal catalyst, or Pd/SrCo0.4Fe0.5Zr0.1O3-delta (Pd/SCFZ), which is of high activity in the decomposition of CO2 into CO and O2.[3] The catalytic activity was expected to be self-regenerated by removing the oxygen from the TDCD reaction by the oxygen permeable membrane. At 900 ˚C, this catalytic process attains 100% of CO selectivity at 15.8% of CO2 conversions. Recently, the TDCD reaction was also realized in a thin tubular oxygen-permeable membrane reactor. [4] At 950˚C, the CO2 conversion reached 17.2%, which is higher than the best values reported in literatures so far. The proposed catalytic process can also be extended to the decomposition of other oxygen-containing molecules (such as NOx and H2O) and the oxidation of light alkanes (such as ethane and propane). However, we found that the stability of the mixed-conducting membrane reactor was not more than 60h, and the membrane significantly broke due to the erosion of the CO2 and reducing atmospheres on the surface of the membrane. Recently, we developed a new kind of La0.85Ce0.1Ga0.3Fe0.65Al0.05O3-delta(LCGFA) mixed conducting oxide [5], which showed high thermal and chemical stability, low thermal expansion coefficient (TEC), and promising oxygen permeability. Our work indicated that mixed-conducting membrane may play an important role in effective utilization of fossil energy and greenhouse gases.

Acknowledgements This work is supported by the National Basic Research Program of China (No. 2009CB623406); National Natural Science Foundation of China (No. 20990222) and China Postdoctoral Science Foundation funded project (No. 20090461105).

Reference [1] Jin, W. Q.; Zhang, C.; Zhang, P.; Fan, Y. Q.; Xu, N. P. AIChE J. 2006, 52, 2545?2550. [2] Zhang, C.; Chang, X. F.; Fan, Y. Q.; Jin, W. Q.; Xu, N. P. Ind. Eng. Chem. Res. 2007, 46, 2000?2005. [3] Jin, W. Q.; Zhang, C.; Chang, X. F.; Fan, Y. Q.; Xing, W. H.; Xu, N. P. Environ. Sci. Technol. 2008, 42, 3064?3068. [4] Zhang, C.; Jin, W. Q.; Yang, C.; Xu, N. P. Catal.Today 2009, 148, 298?302. [5] Dong, X. L.; Zhang, G.R.; Liu, Z. K.; Zhong, Z. X.; Jin W. Q.; Xu, N. P. J. Membr. Sci. 2009, 340, 141?147.