Continuous flow synthesis in academia and industry: quo vadis?
Continuous flow synthesis is a currently rediscovered technique with roots tracing back to the petrochemical industry in the beginning of the last century. At the same time and not without a reason, the pharmaceutical, fine chemical and specialty chemical industries remain solely a batch process domain. The batch-to-flow transition is a difficult step to make due to a plethora of unresolved issues such as the lack of proper equipment at reasonable price, experienced personnel and the low flexibility of a flow process. Flow synthesis has the potential to establish itself in niche applications in the pharmaceutical, fine chemical and specialty chemical industries, however a broad replacement of established batch processes appear to be out of reach anytime soon.
The development of the assembly line by Ransom Olds in 1903 and its adoption by Henry Ford in 1913 (delivering a fully operational Ford Model T at the end of the line every 93 minutes) has inevitably changed today’s industry. In parallel, continuous processing became the most frequently used approach for the large-scale production of commodity chemicals. Driven by the demand for nitrates and ammonia, the Haber-Bosch ammonia synthesis (developed about 1909 by Fritz Haber and operational as of 1913 at BASF-Oppau, Figure 1) arguably landmarks the first high-temperature (400-500 °C), high-pressure continuous synthesis (150-250 bar) to be performed on a 20 tonnes/year scale in the chemical industry (1). Apart from processes at high pressures and temperatures, particularly the domain of (very) hazardous syntheses has become an early playground for industrial applications of continuous processing. The continuous synthesis of nitroglycerine, allowing 120 kg/h uninterrupted nitration of glycerine (Figure 1), was developed by Mario Biazzi in 1936 to pave the way for what later became BIAZZI SA, a leading company in nitration chemistry (2). Througho ...