Monolithic stirrer reactor

The use of a monolithic stirred reactor for carrying out enzyme-catalyzed reactions is presented. Enzyme-loaded monoliths were employed as stirrer blades. The ceramic monoliths were functionalized with conventional carrier materials carbon, chitosan, and polyethylenimine (PEI). The different nature of the carriers with respect to porosity and surface chemistry allows tuning of the support for different enzymes and for use under specific conditions. The model reactions performed in this study demonstrate the benefits of tuning the carrier material to both enzyme and reaction conditions. This is a must to successfully intensify biocatalytic processes. The results show that the monolithic stirrer reactor can be effectively employed in both mass transfer limited and kinetically limited regimes. 

The monolithic stirrer reactor (MSR, Figure 2), in which monoliths are used as stirrer blades, is a new reactor type for heterogeneously catalyzed liquid and gas-liquid reactions (6). This reactor is thought to be especially useful in the production of fine chemicals and in biochemistry and biotechnology. In this work, we use cordierite monoliths as stirrer blades for enzyme-catalyzed reactions. Conventional enzyme carriers, including chitosan, polyethylenimine and different are used to functionalize the monoliths. Lipase was... 

In summary, it can be concluded that the monolithic stirrer reactor is a convenient reactor type both for the laboratory and the production plant. It is user-friendly and can be used to compare different catalysts in the kinetically limited regime or hydrodynamic behavior in the mass transfer controlled regime. Stirrers or monolith samples can be easily exchanged and reloaded to suit the desired enzyme and/or reaction conditions. 

Monoliths allow the efficient use of small catalyst particles, such as zeolites, and are remarkably flexible with respect to their catalyst inventory. Multifunctional reactor operations such as reactive stripping and distillation are challenging applications that are not far away. They have several potential applications in oil refineries, in fhe chemical process industry, and for consumers. The industrial application of the monolithic stirrer reactor as alternatives to many slurry-t)q5e reactors in fine chemisfry has the greatest potential as a new practice involving monolithic catalysts. 

In this example, lipase is immobilized on different carbon monoliths and applied in a transesterification reaction in toluene. The biocatalysts are compared in terms of carrier preparation, enzyme immobilization, and performance. A commercially available immobilized lipase is used as a comparison. A convenient tool to compare monolithic biocatalysts is the monolithic stirrer reactor (MSR), consisting of two monoliths that have the catalyst immobilized on the wall of their channels. These monoliths work as stirrer blades that can easily be removed from the reaction medium, thereby eliminating the need for a filtration step after reaction [37]. 

Catalytic tests with the lipase-monolithic catalysts were performed in a monolithic stirrer reactor consisting of a glass vessel equipped with a stirrer motor (V = 2.5 dm ). 1-Butanol and vinyl acetate concentrations were 0.6 M and 1 M, respectively. Activity tests with immobilized lipase Candida antarctica) were performed at varying stirrer rates and temperatures. Carbon monoliths (Westvaco integral carbon monoliths, with a loading of 30 wt% of microporous activated carbon, wall thickness 0.3 mm) were used as a reference material. 

Hydrogenation of 3-methyl-l-pentyn-3-ol was performed in a monolithic stirrer reactor in which pieces of monolith were used instead of blades (Scheme 9.9). The excellent performance of ca. 90% yield in the desired 3-methyl-l-penten-3-ol is, however, comparable to that of a conventional slurry reactor [35]. 

A monolith reactor that might be particularly useful in fine chemicals manufacfure and biofechnology was developed at Delft Technical University (45,46). Monolithic structures in this reactor are moimted on the stirrer shaft, replacing conventional impeller blades (Figure 18). The monolithic stirrers can be mounted on a vertical or on a horizontal shaft, and more than one set of stirrers can be placed on the shaft. Compared to conventional stirrers, the monolith impellers have a much higher geometric catalytic surface area. 

For the experiments with increased water content or suppressed water removal, a 5 cm-long piece of coated monolith was mounted in a 500-mL autoclave. All liquid concentrations, operation conditions and catalyst hold-up were the same as in the pilot-scale plant. To maintain a gradient-less operation, a turbine-type stirrer recirculated the liquid very rapidly through the monolith channels. During the experiments, liquid samples were taken from the reactor and analyzed as described above. 

Mass transfer-limited processes favor SRs over monoliths as far as the overall process rates are concerned. Moreover, SRs are more versatile and less sensitive to gas flow rates. However, the productivity per unit volume is not necessarily higher for SRs because of the low concentration of catalyst in such reactors. There is also no simple answer to the selectivity problem, and again each process should be compared in detail for both reactors. For a kinetic regime, monoliths can be more advantageous due to their easier operation. The catalyst does not disintegrate due to the stirrer action, and catalyst separation is avoided. Catalysts are often pyrophoric materials, handling of which is usually a hazardous operation. The benefits of MRs can be achieved only for stable catalysts. For quickly deactivating catalysts, SRs are easier to operate, since replacement of decayed catalysts is simpler. 

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