Tracking Diffusion Limitations During Liquid-Phase Hydrogenation Reactions in Real Time

What is it about?

Hydrogenation reactions often involve gas, liquid, and solid phases and are widely used in industrial chemistry. However, it's difficult to measure how much hydrogen actually dissolves into the liquid where the reaction happens — a key factor in understanding how fast and efficiently the process works. In this study, a new type of permeation probe was used to directly measure the amount of hydrogen dissolved in the liquid during a typical hydrogenation reaction. By doing this in real time, the researchers were able to determine whether the reaction was limited by how quickly hydrogen moved from the gas into the liquid (known as gas–liquid mass transfer). They found that at high stirring speeds, hydrogen was plentiful in the liquid and the reaction rate depended mainly on the chemistry at the catalyst surface. At lower stirring speeds, however, not enough hydrogen could enter the liquid quickly enough, and this slowed down the reaction. This method provides a simple, effective way to monitor and improve three-phase reactions in the lab and in industry.

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Photo by Kurniawan Eka Saputra on Unsplash

Photo by Kurniawan Eka Saputra on Unsplash

Why is it important?

This work demonstrates the first real-time use of a commercial permeation probe to measure hydrogen concentrations directly in a working hydrogenation reactor. It enables a fast and reliable distinction between kinetic and mass transfer control in gas–liquid–solid systems, which is critical for catalyst testing, scale-up, and reactor design. Understanding when and how diffusion limitations affect reaction rates can significantly improve the efficiency and safety of hydrogenation processes in chemical manufacturing. The approach also lays the groundwork for broader applications of in situ gas sensing in multiphase catalysis and process optimization.

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