The Guerbet Reaction Network – a Ball‐in‐a‐Maze‐Game or: Why Ru‐MACHO‐BH is Poor in Coupling two Ethanol to n‐Butanol. Issue 4 (24th February 2021)

• Record Type: Journal Article
• Authors: Ohligschläger, Andreas; van Staalduinen, Nils; Cormann, Carsten; Mühlhans, Jan; Wurm, Jan; Liauw, Marcel A.
• Is Part Of: Chemistry methods. Volume 1:Issue 4(2020)
• Page Start: 181
• Page End: 191
• Publication Date: 2021-02-24
• Subjects: homogeneous catalysis -- solvent effects -- sustainable chemistry -- reaction kinetics -- time-resolved spectroscopy; Chemistry, Analytic -- Periodicals; 543
• DOI: 10.1002/cmtd.202000056
• Languages: English
• ISSNs: 2628-9725

Abstract

Abstract: 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. Abstract : The Guerbet Reaction Network from ethanol to n ‐butanol is systematically divided into isolated subsystems that are investigated with in‐situ IR spectroscopy. The kinetic models of all single steps are compounded to a microkinetic simulation. The n ‐butanol yield follows a saddle shape in a plot versus temperature and hydrogen pressure, but no parameter combination enables a satisfying yield using Ru‐MACHO as the redox catalyst. A too low activation barrier for the dehydrogenation of acetaldehyde is identified as a central issue.