Trickle-bed reactors modeling

Using the evaluated intrinsic reaction coefficient, compare the predictions made by using the simple trickle-bed reactor model for this type of reaction. Explain the differences. 

A number of attempts in interpreting trickle-bed performance appeared in the open literature (6-14). These studies did not demonstrate the predictive ability of the proposed reactor models. Some used the reaction data in trickle-beds to evaluate unknown model parameters in order to match calculated and experimental results (7-11). Other studies left certain observed phenomena unexplained (6-12). The objective of this paper is to develop a model for a gas reactant limited reaction in an isothermal trickle-bed reactor. Model parameters are evaluated by independent means and model s predictive ability is tested. 

Crine and co-workers (32—33) have developed a trickle-bed reactor model based upon percolation theory which more closely approximates the physiochemical processes on a particle and reactor-scale than previous models. Details which explain the model development have not been given by these authors so it has not gained wide applicability. 

The present investigation has the overall objective of testing the predictive ability for a trickle-bed reactor model in which the gaseous reactant is limiting. First, a model is presented which contains particle-scale incomplete contacting as one of the key parameters. Second, model predictions for various limiting cases are compared to experimental results obtained in a laboratory scale trickle-bed reactor using independently measured model parameters and available literature mass transfer correlations. 

A review of previous reaction studies used to support the development of trickle-bed reactor models is presented. This review suggests that these previous models have neglected the effect of incomplete liquid-solid contacting even though it was experimentally observed in a number of cases. For the few cases where it was included, it was used as an adjustable parameter to match the measured conversion versus liquid mass velocity data to the model. 

One can develop governing equations for the two cases mentioned and compare their performances with the conventional trickle-bed reactor modeled as a string of suspended spherical pellets contacted by cocurrent flow of gas and liquid. Based on such a comparison, the following observations can be made (Harold and Cini, 1989 Harold et al., 1989 Cini et al., 1991) ... 

Examples of several models and their numerical solutions were given by Attou et al. [30], whose model is limited to the descriptions of hydrodynamics, and by Khadilkar et al. [31] as well as Jiang et al. [32], who present general trickle-bed reactor models. The two latter papers originate from the well-known Dudukovic research group and show the latest state-of-the-art modeling of trickle-bed reactors in stationary operation. 

The dynamic trickle-bed reactor model consists of the following set of coupled second order partial differential equations (PDEs). 

Khadilkar, M. R., Mills, P. L., Dudukovic, M. P., Trickle-bed reactor models for systems with a volatile liquid phase. Chemical Engineering Science, 1999, 54, 2421-2431... 

A trickle bed reactor model was developed for the Esterification reactions studied. This model incorporates the contribution of intraparticle mass transfer resistances. The kinetic equations already developed were used for the respective esterification reactions. Experimental data were obtained in a 25 mm diameter glass trickle bed reactor at different concentrations of reactants, flow rates and temperatures. The performance of the reactor was measured in terms of the conversions of the acids obtained at the exit of the reactor. The model predictions were compared with experimental data at different operating conditions. This model would be useful in predicting the performance of a trickle bed reactor for esterification reactions in general. 

Trickle-bed reactors, wherein gas and liquid reactants are contacted in a co-current down flow mode in the presence of heterogeneous catalysts, are used in a large number of industrial chemical processes. Being a multiphase catalytic reactor with complex hydrodynamics and mass transfer characteristics, the development of a generalized model for predicting the performance of such reactors is still a difficult task. However, due to its direct relevance to industrial-scale processes, several important aspects with respect to the influence of external and intraparticle mass transfer effects, partial wetting of catalyst particles and heat effects have been studied previously (Satterfield and Way (1972) Hanika et. al., (1975,1977,1981) Herskowitz and Mosseri (1983)). The previous work has mainly addressed the question of catalyst effectiveness under isothermal conditions and for simple kinetics. It is well known that most of the industrially important reactions represent complex reaction kinetics and very often multistep reactions. Very few attempts have been made on experimental verification of trickle-bed reactor models for multistep catalytic reactions in the previous work. 

For the purpose of developing a trickle-bed reactor model for esterification reactions the approach used by Rajshekharam et. al. (1998) was used. They have... 

Chowdhury, R., Pedemera, E., Reimert, R. 2002. Trickle-bed reactor model for desulfurization and dearomatization of diesel. AIChE J. 48(1) 126-135. 

---