What variables affect how fast a reaction proceeds, how pure the product is, and for how long you can reuse your solid phase (e.g., catalyst or adsorbent)? Many variables are easily controlled in a rotating bed reactor, and it is a good idea to experiment with them on a smaller scale.
Many studies report faster processes at increasing stirring speeds. The flow through the rotating bed reactor is strengthened, increasing the mass transfer rate. For example, the activity of an immobilized lipase for ammonolysis increased when going from 100 to 400 rpm. A plateau was reached above 400 rpm. This indicated that enzyme kinetics limited this reaction at higher speeds, and it wouldn't be necessary to further increase the stirring speed.
Similarily, an esterification performed on lab scale ran faster at higher stirring speed. Beyond 500 rpm the reaction rate was nearly independent of stirring speed, indicating that the external mass transfer limitation had been eliminated.
Even slightly different catalysts or adsorbents can yield very different results when creating or capturing a molecule. This was demonstrated at Zurich University of Applied Sciences (ZHAW) for the case of adsorption by different types of activated carbon.
The differences are perhaps even greater when comparing similar biocatalysts (all lipases) for a reaction at a screening stage.
The effect of temperature on a reaction is complex. It affects the solubility of reagents and products, the reaction kinetics, and greatly impacts catalyst activity and lifetime.
Immobilized enzymes are typically more thermostable than free enzymes. Common immobilized lipases may tolerate temperatures up to 70-80°C.
Generally speaking, lower viscosity yields higher flow rate and in turn faster reactions. The viscosity of most liquids will decrease at higher temperatures, so try and heat your reaction if conditions allow.
In the case of a lipase-catalyzed acetylation the temperature, stirring speed and the ratios of substrate to solvent and catalyst were optimized on gram scale and then kept constant during scale up. The yield [%] after 90 min was practically identical in all rotating bed reactor models tested (RBR S2, S3, and S4).
This behaviour is frequently observed for many applications, including:
Scaling up a process with an RBR from lab to production is often as simple as linearly increasing all quantities of materials and the solids in the RBR by the same factor. It is wise to consider what conditions are feasible on large scale, then downscale that to the size of a Complete starter kit S2 and optimize.
Use a rotating bed reactor to screen for optimal reaction conditions, then use the same technology to manufacture on industrial scale. - Ask us how!
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