Integrating Gas Permeation with Gas-Consuming Reactions in Slug-Flow Capillaries: Continuous and Selective Hydrogenation of Biodiesel

The catalytic and selective hydrogenation of biodiesel is employed here as a model reaction to demonstrate, for the first time, the integration of gas permeation with a gas-consuming process in a capillary slug-flow. In such systems, gas consumption during the reaction leads to bubble shrinkage and ultimately destabilizes the flow regime, which counteracts the benefits of intensified mass transport and mixing. By continuously replenishing hydrogen through the permeable capillary wall, a stable slug flow under reactive conditions can be maintained. Compared to batch operation, the model reaction illustrates more than a 9-fold increase in reaction rate while preserving high selectivity. This proof-of-concept highlights how permeation enables continuous operation of reactive slug-flow systems without a loss of stability. Beyond the chosen example of biodiesel upgrading, the approach establishes a generalizable method for conducting gas-limited multiphase reactions in a continuous flow. The concept combines reactor engineering and catalysis to support sustainable process intensification and opens new opportunities for multiphase transformations requiring precise gas management.