Nowadays, computing systems with extremely high computational power, well-known as High performance computing (HPC), has popularly replaced the pilot plant. Consequently catalyst evaluation, screening, testing and research in laboratory through pilot plant have shrunk in size. However, decreasing of sizes may promote negative effects such as

• Deviation from Plug-flow behavior
• Wall effect and bypassing
• Catalyst wetting
• Liquid hold-up

In order to minimize above problems, inert bed dilution is popularly used in many activities of heterogeneous catalysis. The use of inert bed diluent is not only able to minimize undesirable effects but also improve isothermality of catalyst bed (reduce the radial and axial temperature gradients on reactor scale except the temperature gradients around the catalyst particles), especially in exothermic and endothermic reaction.

Conversely, improper use of inert bed diluent may negatively promote unreliable information during catalyst testing as

• Local bypassing of catalyst (inhomogeneous dilution)
• The difference of measured reaction rate and conversion between with or without inert bed diluent

Tips:

• Ensure homogenous mixing of catalyst and diluent during loading step
• Avoid using excessive diluent in high conversion
• Use inertness and good heat transfer properties

Picture ref: https://www.indiamart.com/proddetail/inert-ceramic-ball-4949736288.html

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