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A generalized isothermal effectiveness factor correlation has been proposed for catalytic reactions whose intrinsic kinetics are based on the redox model. In this correlation which is exact for asymptotic values of the Thiele parameter the effect of the parameters appearing in the model, the order of the reaction and particle geometry are incorporated in a modified form of Thiele parameter. The relationship takes the usual form: and predicts effectiveness factor with an error of less than 2% in a range of Thiele parameter that accommodates both the kinetic and diffusion control regimes.

Based on the generalized treatment of isothermal mean effectiveness factor presented by Aris, an experimental factor Φ exp has been obtained, the numerical value of which could be ascertained from experimental measurements of reaction rate and other pertinent properties of the fluid-particle system. It is shown that if Φ exp ⩽ 0·03, the experimental data reflect solely the influence of intrinsic kinetics of the system. Based on available kinetic information pertaining to a phthalic anhydride process, the variation of Φ exp with temperature, catalyst activity and external diffusion has been presented. Finally a plot of Φ exp against generalized Thiele parameter for low orders of reaction, has been used to check the consistency and absence or otherwise of pore diffusion limitation in experimental data reported in existing literature.

The kinetics of decomposition of iron pyrites, according to the stoichiometric relation: 2FeS2 → 2FeS + S2 ΔHr=20,400 cal/g mol have been investigated using well compacted cylinders decomposing in a turbulent stream of nitrogen. The zeroth-order reaction rate constant has been obtained as: k1 = 12.57 exp(−22,58O/RTp) By correlating the ratio of reaction times to achieve a predetermined conversion of 0.80 for two pellet sizes with reaction temperature in a range of 770° to 1120°K, it is found that below 770°K the decomposition process is reaction-controlled and above 850°K, diffusion-controlled. For temperatures higher than 770°K, evidence of progressive influence of diffusional processes is marked. The problem of predicting temperature gradients inside the pellet, for the non-isothermal case, has been solved by adopting a graphical marching technique based on pseudo steady state analysis. Analysis of computed data indicates negligible influence of Sherwood number of product layer in affecting temperature gradients. It is the Nusselt number which is significant. Finally, it is proposed that unless the heat of reaction is considerable, all endothermic reactions proceed under practically isothermal conditions. bl

The process of thermal decomposition of calcium carbonate has been treated as one governed by simultaneous heat and mass transfer, under quasi steady state conditions, to the decomposition interface. It is believed that the surface chemical reaction is very fast and as such does not interfere in the determination of the overall decomposition rate. Rigorous expressions, based on heat transfer rate, have been derived, based on the system properties, for the prediction of decomposition times for definite geometric shapes such as spheres and cylinders. The good agreement observed between the actual and predicted values bears out the soundness of the decomposition scheme assumed for the process. The expression derived are: Based on an analysis of simultaneous heat and mass transfer rates the following correlation is obtaiend: This equation bears very close resemblance to the theoretical expression for the evaporation of small spheres into quiet air. This equation may be rearranged to provide: which is a modified form of the usual correlation for simultaneous heat and mass transfer based on Chilton-Colburn analogy. The mathematical treatment has been extended to a two-phase solid system (Mg CO 3 -Ca CO 3 ) characterized by finite but different equilibrium decomposition temperatures. The mathematical analysis involves the solution of simultaneous differential equations. This has been done numerically by the modified Runge-Kutta method with the help of an IRM computer. The confirmation of the proposed equation must await future experimental data for the two-phase system.

The cell model developed by Amundson and co-worker has been applied to compute the bulk and particle temperatures and partial pressure along the length of a packed bed reactor where an exothermic non-catalytic solid-gas reaction, viz. proceeds under adiabatic conditions. The kinetic data previously obtained have been used in the numerical computation procedure adopted in programming on a CDC 3200 computer. By linearizing the transient equations around the steadystate, the stability problem has been investigated by examination of the Lienard-Chipart criterion. The condition of sectional stability has been obtained as: which is a more conservative condition that the usual van Heerden's slope conditions, at the specified cell. An approximate but safe stability condition applicable over the entire bed at any stage of conversion has been obtained as Experimental work is in progress.