Transport Reagents through the Pore Structure of a Membrane Catalyst under Isothermal and Non-Isothermal Conditions

Abstract

The article presents the results of an experimental comparison of methane transport in the pore structure of a membrane catalyst under isothermal and non-isothermal Knudsen diffusion conditions. It is shown that under the conditions of non-isothermal Knudsen diffusion in the pore structure of the membrane catalyst, there is a coupling of dry reforming of the methane (DRM) and gas transport, which leads to the intensification of this process. The reasons for the intensification are changes in the mechanism of gas transport, an increase in the rate of mass transfer, and changes in the mechanism of some stages of the DRM. The specific rate constant of the methane dissociation reaction on a membrane catalyst turned out to be an order of magnitude (40 times) higher than this value on a traditional (powder) catalyst.

Intensification of Dry Reforming of Methane on Membrane Catalyst: Confirmation and Development of the Hypothesis

“…The rate constants (extrapolated at contact time = 0) of reaction (R2) in both modes of the membrane reactor are close at all temperatures and significantly exceed the constants on a traditional catalyst. The activation energy (Table 1) in a traditional reactor is higher than in the membrane type, and its value corresponds to the values that we observed earlier [18,32] on such catalysts. The E a values for the membrane catalyst, although different, are insignificant.…”

“…If we consider the material presented in this article as the first attempt to explain the effect of the intensification of catalytic processes in a reactor with a membrane catalyst (described in [Alexandrov et al [32], Gavrilova et al [17,18]], a hypothesis based on a new approach to catalysis utilizing the phenomenon of thermal transpiration, it seems appropriate to us to note that it is difficult to consider all aspects of the proposed approach to the membrane reactor. The article considers only one of the many possible modes of a reactor with a membrane catalyst-the contactor mode.…”

“…The hypothesis on the causes and mechanism of intensification of dry reforming of methane (DRM) in a reactor with a membrane catalyst (RMC) in the publication [17], was substantiated by a kinetic experiment in traditional and membrane reactors. Comparison of the rate constants of the rate-limiting reaction (methane dissociation) in the DRM process in membrane and conventional reactors was explained by the intensification of the mass transfer stages of the process, which was confirmed [18] by the appearance in the porous wall of the membrane catalyst (MC) of one of the types of non-isothermal Knudsen diffusion-the phenomenon of thermal slip (other names for this phenomenon are thermal transpiration or thermal creep).…”

“…In work [18], the analogy between a membrane reactor and a Knudsen compressor is analyzed in detail. In this work, it is shown that the intensification of the DRM process under no isothermal conditions of Knudsen diffusion is primarily due to a change in the mechanism of mass transfer in the channels of the pore structure of the membrane catalyst, which can be accompanied by a change in the type of reaction involved in this process.…”