An Algorithm to estimate the effectiveness factor in catalytic pellets

S. D. KEEGAN; S. BRESSA; N. J. MARIANI ; G. D. MAZZA

Praga, República Checa

Congreso; 15th. International Congress of Chemical and Process Engineering (CHISA 2002); 2002

Czech Society of Chemical Engineering (631st. Event of de European Federation of Chemical Engineering)

&lt;!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --&gt; Abstract  The 1D model proposed by Burghardt and Kubaczka (1996) to approximate the behavior of 3D catalytic pellets has been recently found able to provide accurate results for evaluating effective reaction rates when its parameter σ is suitable adjusted (Mariani et al., 2002). This parameter represents the concentration of the cross section available for diffusion. The well known 1D geometries result for some specific values: slab (σ =0), infinitely long circular cylinder (σ =1) , sphere (σ =2). In general the range of interest is -1/5< σ< 5 (Mariani et al., 2002). A formulation coupling a first order Galerkin approximation with a truncated asymptotic expansion is proposed here to evaluate the effectiveness factor of single reactions in the range  -1/5< σ< 5. The formulation provides a  3 % level of precision for essentially all normal kinetics af practical interest and a large range of abnormal kinetics. In particular, this conclusion includes reaction rates approaching a zero order reaction, for which large deviations arise from the use of previous approximations proposed in the literature. On the other hand, the extent of abnormal kinetics being accurately approximated is significantly enlarged.