Faster, safer, cleaner heating
Microwave chemistry has been used for many years, especially for the synthesis of small quantities of compounds for the pharmaceutical and fine chemical industries. The benefits of flow chemistry have been outlined above and when combined with microwave heating these benefits can be further enhanced.
- Microwave heating can produce substantially faster reactions than conventional heating, due to selective heating, very rapid temperature rise, the removal of wall effects or simply the ease of operating at high temperatures and pressures
- The rapid temperature rise and the absence of hot heat transfer surfaces can mean fewer undesired side reactions, resulting in higher yields and lower impurity levels.
- Microwave heating is a direct heating method with no need for heating jackets or heat exchangers with large thermal mass. This means that turning off the power immediately stops energy input to the system and the temperature can be lowered quickly.
C-Tech has developed a continuous flow microwave reactor that is capable of producing >100 kg of product/working day and has been trialled using a range of reactions that are applicable to a variety of industrial sectors, with significant reductions in reaction times and increases in yields. Examples include the reduction in reaction time of a Suzuki coupling from two hours to one minute with no loss of yield, and a dihydropyrimidine synthesis which gave a two-fold increase in yield and a reduction in reaction time from eight hours to four minutes.
C-Tech has shown the ability to quantify the energy-saving potential of microwave chemistry due to the shortened reaction times and reduced downstream work up as a result of the higher yields and purity that are often achieved. In all cases such reactions showed significant savings in energy and reduction in CO2 emissions, on average 58%. In some cases, the switch gave a 90% saving in energy consumption. This energy saving was brought about by the faster reaction times possible, enabling larger volumes of material to be processed per hour. These sizable increases in yield observed when using the reactor also gave a downstream energy saving as it reduced the amount of purification required (reducing solvents required) and also decreased the amount of starting materials necessary for the reaction.
This innovation enables the transfer of technology directly from the lab to plant without the need for a time consuming and costly process development step and can also result in considerable energy savings if implemented.