|Credit: Morschhäuser et al., Green Process Synth.|
For example, Kappe has been engaged in determining how to translate the benefits of the high temperature and pressure of batch microwave reactions to microwave-assisted continuous flow.
In collaboration with scientists at specialty chemical firm Clariant, Kappe recently used his model benzimidazole synthesis and carried out what he believes is the first reported description of microwave-assisted continuous-flow chemistry at the production scale (Green Process Synth., DOI: 10.1515/gps-2012-0032). The researchers used a flow reactor capable of operating at up to 310 °C and 60 atm pressure and at flow rates as high as 20 L per hour, which works out to about 1,000 metric tons per year. The reactants need to spend only about 30 seconds in the microwave-irradiated zone for the reaction to be complete.
“For many researchers in the lab, microwaves have become the first choice and not a last resort,” Kappe says. “Now, in moving to microwave flow chemistry, we may be seeing a new game-changer in sustainable process chemistry.”Looks interesting to me. Obviously, capital costs and maintenance would be an issue, as well as the broad applicability of the specific setup.
[The concerns about safety and microwave leakage become really real -- does anyone remember the "Microwave Oven in Use" signs from the early 80's?]
[You can click through to the actual Green Process Synthesis article and download the PDF, stunningly.]