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Performance of fouled catalyst pellets
Author(s) -
Masamune Shinobu,
Smith J. M.
Publication year - 1966
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690120232
Subject(s) - thiele modulus , fouling , pellets , diffusion , pellet , chemistry , isothermal process , thermal diffusivity , catalysis , thermodynamics , chemical engineering , materials science , composite material , organic chemistry , engineering , physics , biochemistry , membrane
Equations are developed for the bulk rate of a gaseous reaction on a porous catalyst whose activity changes with time due to a decrease in active surface. The performance is evaluated in terms of a pellet effectiveness factor which is a function of time and a Thiele (diffusion‐reaction) modulus. By a stepwise numerical technique, the equations can be solved without resort to assumptions regarding the distribution of fouled surface within the pellet. The method is applicable at isothermal conditions for any form of the rate equations for the main and fouling reactions and for any diffusivity‐concentration relationship. To illustrate the method, results are given for first‐order isothermal reactions for three types of fouling processes. For a series form of self‐fouling, a catalyst with the lowest intraparticle diffusion resistance gives the maximum activity for any process time. In contrast, for parallel self‐fouling a catalyst with an intermediate diffusion resistance is less easily deactivated and can give a higher conversion to desirable product, particularly at long process times. A simpler solution is possible by supposing that the shell model represents the disposition of fouling material in the pellet. It is shown that for parallel self‐fouling and independent fouling this model gives reasonably good results, even when the reaction resistance for the main reaction is important. However, the shell concept does not appear suitable over a range of conditions when the fouling is of the series type. The single‐pellet effectiveness factors can be used to determine the effect of fouling on the conversion in a fixed‐bed reactor. To illustrate the method of approach curves of conversion as a function of time and position in the bed are presented for a parallel, self‐fouling reaction system. The results show the influence of intraparticle diffusion on the overall effects of fouling.