Abstract

Heterogeneous Catalytic Hydrogenations in Flow – Obstacles, Methods, and Scale-Up Considerations

Joshua Trenchard, Chemical Engineer, AM Technology

Continuous flow manufacturing offers several benefits to the chemical industry such as: reducing carbon footprint by reducing process energy requirements and waste generation; re-shoring production to strengthen supply chains; and increasing existing process plant productive capacity. Across the industry, there is a high prevalence of heterogeneous catalytic hydrogenations with 10% of all chemical processes falling into this reaction category. It is therefore vital that a continuous flow solution at scale has the ability to perform such reactions in order to be industrially relevant. Solids handling in continuous flow reactors, however, poses significant challenges at low volume scales, hindering process development of heterogenous reactions in flow despite relative ease in higher throughput systems. A key parameter in slurry handling is the fluid velocity at which the slurry travels through the system. At higher throughputs when handling slurries, fluid velocities can be maintained far above sedimentation velocities whilst maintaining multiple orders of magnitude between particle size and line size. As throughput decreases, slurry and suspension dosing becomes a balancing act between sedimentation, where fluid velocity is no longer sufficient to maintain a homogenous mixture, and bridging, where particles in small bore lines accumulate into a cross-sectional layer rapidly leading to a blockage. An alternative option to continuous addition of catalyst is immobilisation within a flow reactor. This option allows the user to overcome the handling issues observed with heterogenous chemistry in flow, but presents fresh technical challenges, for example decreasing catalyst activity over time, and operational disturbances from catalyst changeover becoming increasingly complex with scale up. AM Technology has designed, developed, and tested multiphase handling solutions for both low flowrate slurry handling alongside immobilisation methods for application within the Coflore reactor range, ensuring a viable process irrespective of solids properties and throughput. Here we outline examples of both slurry feed and immobilisation in the Coflore ACR, exploring the benefits and drawbacks when applied to the behaviour of a continuous reactor. Also discussed are the consequential effects on upstream and downstream processing, equipment requirements, and unit operations. As no two slurries behave the same, and no two reactions are identical, we will discuss the importance of continuous flow equipment versatility, enabling process intensification through multiphase processing as well as process reliability through immobilisation.