Catalyst Development Strategies

A successful catalyst development strategy must take the chemical and physical conditions into account, from the outer shape of the catalyst to the pore structure to the active center, and from the chemical composition to the various crystalline phases to the influence of promoters. The reactor type must also be included in an overall view of the process [10]. 

The different routes to these intermediates were outlined in the previous section. In this example we present the catalyst development strategy (Ratnasamy and Sivasankar, 1996) for a process based on the use of extrudates of TS-1 to produce catechol and hydroquinone in a continuous fixed-bed reactor. 

The strategy of the catalyst development was to use a rhodium complex similar to those of the Wilkinson hydrogenation but containing bulky chiral ligands in an attempt to direct the stereochemistry of the catalytic reaction to favor the desired L isomer of the product (17). Active and stereoselective catalysts have been found and used in commercial practice, although there is now a more economical route to L-dopa than through hydrogenation of the prochiral precursor. 

There are many good reasons for using multiphasic methods to carry out reactions that employ homogeneous catalysts. In general, the catalyst is immobilized in one phase and the reactants and products are supported in other phases. Ideally, once the reaction is complete the products can be removed without contamination by the catalyst and the catalyst phase is ready for immediate reuse. However, a perfect system is extremely difficult to obtain in practice, although many solvent combinations and catalyst design strategies have been developed which come close to the ideal situation. 

We first studied group 4 metals (titanium, zirconium and hafnium) supported on a silica dehydroxylated especially at 700 °C (Table 3.8). Following the laboratory-developed strategy, surface-species have been well-characterized by classical techniques (IR, solid-state NMR gas evolvement, reactivity, etc.). Catalysis results show that titanium is the most active even if its activity is far less than that of homogeneous catalysts. In addition, an important amount of metal was lost by lixiviation even if this phenomenon seemed to stop after a certain time. 

A model which is consistent with the chemistry described previously has been developed to predict the performance of ZSM-5 in an FGG unit. Application of this model allows the user to take full advantage of ZSM-5 s flexibility for specific applications. The model has been used in many commercial applications to determine the catalyst makeup rate required to achieve a given octane boost. It has also been used to tailor the catalyst makeup strategy to obtain a desired octane boost in a given period of time. 

All of these applications use fixed-bed reactors, and, very importantly, all were scaled up from bench-scale pilot plant data. This successful scale-up experience with the ZSM-5 catalyst was an important consideration in formulating the MTG development strategy. 

From this work, the analysis developed clearly shows how to optimize the catalyst to feed ratio to minimize catalyst inventory but maximize the feed conversion as well as the product selectivity. Although at the present stage, this cannot be directly applied to the commercial operation without further pilot plant substantiation. Since this is a continuous research program, further work will be undertaken using the typical FCC feed contmning metal and sulphur fouling precursors to refine the developed strategy. This will be, finally adopted to run in a MAT for FCC catalyst evaluation. 

Stell, J. Catalyst developments driven by clean fuel strategies. Oil Gas J. 2003, Oct 6, 42. 

This strategy is mostly technology-driven and the emphasis is on the development of the catalyst and new catalytic process technology usually the domain of fine chemicals companies who want to apply their own technology and who can choose the molecules for which to develop a new process. Important issues are most often the search for the catalyst, development of the process and the technical catalyst synthesis. 

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