The Guerbet Reaction Network - a Ball-in-a-Maze-Game or: Why Ru-MACHO-BH is Poor in Coupling two Ethanol to n-Butanol

The Guerbet reaction from two alcohols to a long-chain alcohol and water requires a redox catalyst and a strong base in homogeneous liquid systems. Especially, the reaction from ethanol to n-butanol is a challenging example of the reaction that suffers from low yields and selectivities in comparison with reactions of higher alcohols. The most important side reactions are the polymerization of acetaldehyde to C6+-components and the saponification of ethyl acetate under consumption of the base. This work pursues the systematic kinetic investigation of the Guerbet reaction network by experiments with isolated subsystems of the network. In-situ-infrared spectroscopy is applied to determine time-resolved concentration profiles. Adapted kinetic models of the single steps are integrated into a microkinetic model of the whole network. The simulation of the reaction network reveals dependencies between temperature, hydrogen pressure, initial concentrations and the yield and selectivity of n-butanol. Finally, it is shown that Ru-MACHO does not lead to high yields in the reaction, because the dehydrogenation to ethyl acetate exhibits a too low activation barrier.

Automated summary

The Guébert reaction involves the conversion of two alcohols to a long-chain alcohol and water, with factors such as temperature, hydrogen pressure, and initial concentrations influencing the yield and selectivity of n-butanol. Side reactions involving the polymerization of acetaldehyde and saponification of ethyl acetate contribute to lower efficiency in the conversion of ethanol to n-butanol. Ru-MACHO catalyst is found to have low yields due to the low activation barrier in the dehydrogenation process.