Scale-Up of Heterogenous Catalysts

The scale-up of heterogeneous catalysts presents unique challenges to researchers in the chemical industry, as critical technical know-how is not widely available in the open literature.

Process scale-up is the art and science of translating laboratory discoveries into a commercially viable means of producing chemicals for the benefit of society. The entire discipline of chemical engineering, at its heart, exists to leverage a fundamental understanding of chemical and physical phenomena to that end, and practicing professionals have numerous tools at their disposal in service to that goal.

Catalysts are an integral component of many chemical processes, and heterogeneous catalysts are among the most commonly encountered in the chemical industry, owing to their durability and facile separation from the reaction products. However, the study and development of heterogeneous catalysts is complicated by the interplay between chemical kinetics and transport phenomena, which can make it difficult to translate discoveries into profit-generating engines.

Successful process development using heterogeneous catalysts requires selecting the right reactor for the right use: materials screening, kinetic analysis, or commercial implementation (Figure 1). The catalyst itself is also a chemical product — developed and tested in the laboratory. Catalyst scale-up is crucial to commercialization but presents unique challenges. First, catalyst scale-up for manufacture is a narrow specialty infrequently encountered in chemical engineering curricula. Second, it exists at the intersection of multiple disciplines: synthetic chemistry, materials science, and chemical reaction engineering. Finally, its execution is primarily an industrial activity. Consequently, much of the technical know-how and experience resides within companies. Since companies must protect intellectual property to maintain a competitive advantage, most catalyst scale-up knowledge exists as trade secrets or in patent literature.

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▲Figure 1. Selecting and properly sizing an appropriate reactor must be commensurate with objectives: screening, kinetic measurements, or production. A laboratory plug flow reactor (PFR, left) is an excellent tool for screening catalyst formulations in powdered form. The continuous stirred-tank reactor (CSTR, center) allows kinetic analysis of the formed catalysts without temperature and concentration gradients. The commercial reactor (right) dispenses with these concerns in pursuit of the economical, safe, and reliable generation of large quantities of products.

Practitioners, particularly outside of industry, may struggle to find suitable references for study, though some examples can be found in peer-reviewed journals (1–6). As patents are hybrid legal-scientific documentation geared toward protecting intellectual property rather than open exchange of scientific ideas, and trade secrets are confidential by definition, it can be challenging to know how to proceed. Additionally, for many industrial researchers, while their employers are catalyst users, they are not necessarily catalyst producers, which means that they must collaborate with other companies to commercialize discoveries.

These barriers and challenges create perceptions that catalyst development is entirely empirical. Though experimentation is the cornerstone of all scientific work, the catalysis researcher need not proceed blindly. This article provides some guidelines for interacting effectively with catalyst vendors, addressing potential pitfalls in catalyst scale-up, and rigorously applying chemical and chemical engineering principles to achieve successful scale-up. The considerations discussed herein are specific to catalysts used in gas-solid fixed bed reactors, but they may be generalized to other types of heterogeneous reactions (liquid phase, fluidized beds, etc.), although the details might vary...