Enhancing catalyst effectiveness by increasing catalyst film thickness in coated-wall microreactors: Exploiting heat effects in catalytic methane steam micro-reformers

The potential for increasing endothermic reforming process capacity of a heat-exchanger microreactor without compromising thermal or catalyst efficiency via employing unconventionally-thick catalyst washcoatings is investigated. This is achievable through exploiting the "internal" heating of the catalyst film, i.e. existence of a non-zero heat flux at the wall-catalyst interface at the inner boundary of the film, which is a characteristic of the heat-exchanger microreactor design. Classical one-dimensional analysis of non-isothermal reaction and diffusion in an internally-heated catalyst film identifies minimum values for Prater Temperature and dimensionless activation energy required for internal accumulation of applied heat to be effectively utilized. Under such conditions, analysis confirms the existence of a range of Thiele Moduli, or catalyst film thicknesses, corresponding to complete utilization of internally-supplied heat at catalyst effectiveness greater than unity. Subsequent application of these design rules to a previously validated computational fluid dynamic (CFD) model of an industrial annular micro-channel reformer (AMR) for methane steam reforming confirm that increasing catalyst film thicknesses to values corresponding to Thiele Modulus greater than unity enables intensification of the microreactor performance via increasing reforming capacity while maintaining equivalent thermal efficiency and retaining competitive catalyst effectivenesses.