External Mass Transfer Coefficients for Monolith Catalysts

Abstract

Monolith catalyst reactors are used for controlling emissions of automotive and industrial pollutants. Various external mass transfer correlations are available for small-pitch catalysts typical of automotive applications; however, little information is available for catalysts having larger pitch and length that are more typical of power plant applications. The present paper proposes a new correlation Sh = 2.696[1 + 0.139ScRe(d/L)]0.81 based on data for the mass transfer limited performance for the CO oxidation reaction in square-channeled titania−silica honeycomb catalysts. The correlation is suitable for describing the performance of square-channeled honeycomb catalysts used for the selective catalytic removal of nitric oxide from power plant effluents. The differences between the present correlation and other literature correlations are discussed.

Monolithic Supports with Unique Geometries and Enhanced Mass Transfer

“…bulk mass transfer control). In section 4.4, it will be shown using the Sherwood number that the experimental results presented in this section detailing the mass transfer limit for honeycomb monoliths are consistent with those found in the literature 12,15,19 . The honeycomb sample will serve as the basis for judging the performance of novel monoliths with alternate geometries.…”

“…Finally, a plot of Sherwood versus Graetz numbers (for each sample) was generated. The results from this analysis are presented in Figure 14, along with the three empirical curves 12,15,19 detailed previously (equations 12, 16, and 17) for mass transfer in straight-channel monoliths. This quantitative analysis (N SH vs. N GZ ) is a useful method for directly comparing the structural impact on bulk mass transfer for different monolith samples, as all important system parameters are included in the calculations, and differences in surface area, porosity, etc, are, in effect, "normalized" out.…”

“…A point can be reached for which surface kinetics (which may be adjusted for pore diffusion using an effectiveness factor approach [12][13][14] ) exceeds the rate for bulk mass transfer, causing the overall reaction rate to become mass transfer limited. In this regime, transfer of reactants from the fluid flow to the catalytic surface is the rate-limiting step.…”

“…A predominant method to quantify mass transfer found in the literature 1,11,12,14,15,[18][19][20][21] is the use of the Sherwood number, N SH . The Sherwood number is defined as:…”

Removal of Low-Concentration Formaldehyde by a Fiber Optic Illuminated Honeycomb Monolith Photocatalytic Reactor

“…Conversely, the surface-reaction limit occurs when C interface ≈ C and hence kK << k g (1 + KC). The mass transfer coefficient of formaldehyde k g can be estimated by the following correlation (Uberoi and Pereira, 1996): 0.81 2.696 1 0.139 Re…”