Technology
From Nanobits
Nanobits leading edge microreactor technology was developed by the Micro Products Breakthrough Institute (MBI) which is a collaboration between Pacific Northwest National Lab and Oregon State University. The continued development of the technology has been supported by ONAMI (Oregon Nanoscience and Microtechnologies Institute).
In an effort to bring microreaction technology to nearer term markets, Nanobits has begun to work with Oregon State University and the MBI in specialty chemical market. Specialty chemical manufacturing is based almost exclusively on batch or semi batch operation of chemical processes. The concept is simple and involves the sequential charging of raw materials and reagents into large stirred tank reactors. The reactions are then processed by stirring and heating until complete as judged suitable in process analyses. The reaction products are finally isolated following a series of work up steps (addition of water, solvent extraction, distillations, crystallization, filtration etc).
The limitations of batch processing are essentially those associated with:
- reaction selectivity (poor mixing in relation to prevailing reaction kinetics and local concentration gradients) and -
- management of highly exothermic reactions (thermal hazards), where the heat transfer limitations of large volume reactors allow for heat accumulation (poor surface area : volume ratio). In the latter case, it is possible for specific reactions to reach self heating where secondary exothermic processes propel the batch to catastrophic failure (explosion)
- use of exceptionally toxic materials such as phosgene.
A further drawback to batch processing is the time and effort needed for process development, where the reaction performance changes from one vessel size to another. This often leads to unpredictable performance going from lab to pilot to full scale operation. This inherent variability stems from changes in agitation, mixing characteristics, vessel geometry, heat flow etc.
In most specialty chemical organizations, many useful chemical reactions are simply not carried out due to the safety concerns of batch scale up. Typically these are highly exothermic reactions or reactions which produce very unstable intermediates. The basic problem is that, for such reactions, operation in batch mode will inevitably involve a large inventory (several tens or hundreds of kilos) of potentially explosive mixtures or intermediates.
Microreaction technology is based on the concept of carrying out reactions using very small specially designed mixing chambers with only a few milliliters of capacity. The reactions are carried out continuously so that space time yields can approach traditional batch operation once enough micro reactor modules are placed in parallel and the throughput rates adjusted accordingly. The benefits are however:
- excellent heat transfer / dissipation and
- extremely thorough mixing.
As a result of these benefits, highly exothermic or otherwise hazardous reactions can be carried out safely. At no time will there be a significant inventory of hazardous intermediates due to continuous quenching in downstream micromixers.
Installation of microreactor technology within a specialty chemical organization will allow operation of a range of chemistries otherwise off limits (or accessible only at very high cost due to the need for expensive multiple redundancy safety equipment and protocols).
In order to extend our capabilities we have identified microreactor technology as the key approach to help us add a number of useful reaction chemistries to our toolkit. These reactions include:-
- Phosgenation (toxicity)
- Ozonolysis (versatile oxidation technology)
- Azide chemistry (versatile introduction of nitrogen synthons and assembly of special heterocycles)
- Nitromethane chemistry.
In addition, many standard reactions have been shown to run at higher yields under the continuous conditions associated with microreactors. This is thought to be a result of much more efficient and consistent mixing profiles.
Oxidation is an important class of chemical reactions for industrial production of chemicals. Oxidation with ozone, ozonolysis, is a clean and selective way for oxidative cleavage of double bonds. There are many challenges to implementing ozonolysis for industrial scale production. The fast reaction and low solubility of ozone indicated that this reaction is limited by slow mass transport of ozone into the solution. Multichannel microreactors, due to their high heat- and mass-transfer rates, can mitigate the risks resulting from the reaction process or the products and increase the reaction efficiency.