(85c) A Multiscale Model for Determination of Kinetic Rate Constants for Hydrotalcite Catalyzed Biodiesel Synthesis

Biodiesel is a renewable, environmentally friendly fuel. Commercially most biodiesel is produced from the esterification reaction of vegetable oil with methanol in the presence of a homogeneous catalyst 1. Heterogeneous catalysis however lowers the cost of production by reducing the number of downstream processes. There have been some experimental studies on hydrotalcite as a heterogeneous catalyst2, but little work has been done on the modelling of the process. To evaluate the industrial applicability of the heterogeneous catalyzed process, we have developed a multiscale model for hydrotalcite catalyzed transesterification using a hybrid Monte Carlo/mean field approach. The spatial distribution of species on the catalyst surface is an important factor in determining the reaction rate and this can be taken into account by the application of Kinetic Monte Carlo3. An Eley-Rideal type mechanism is used to model the reactions on the catalyst surface. The overall reaction rate expressions have been derived based on the assumption of quasi steady state conditions for the surface species. We have used a novel hybrid model based on elementary reaction steps to increase the accuracy and robustness of the overall reaction kinetic expression and hence the design of the reactor. This model can be further extended to determine optimum catalyst properties and bulk conditions.

1. MacLeod CS, Harvey AP, Lee AF, Wilson K. Evaluation of the activity and stability of alkali-doped metal oxide catalysts for application to an intensified method of biodiesel production. Chemical Engineering Journal. 2008;135(1-2):63-70.

2. Cantrell DG, Gillie LJ, Lee AF, Wilson K. Structure-reactivity correlations in MgAl hydrotalcite catalysts for biodiesel synthesis. Applied Catalysis a-General. 2005;287(2):183-190.

3. Reese JS, Raimondeau S, Vlachos DG. Monte Carlo Algorithms for Complex Surface Reaction Mechanisms: Efficiency and Accuracy. Journal of Computational Physics. 2001;173(1):302-321.