Continuous processes – sustainable manufacturing
Continuous processes are considered to support sustainability in many ways. In general, continuous processes require less energy, less materials and less solvents. The heat exchange is better than in batch reactions and therefore reactions can run in a more precise and steady manner which may improve yield and selectivity: whereas batch processes involve a continuous variation of temperature, pressure and other parameters. In addition, the smaller reaction volumes, compared to batch processes, can be conducted in a safer way and some processes are only possible as continuous processes.
In this article, different continuous processes are presented which support sustainability and which are based mostly on conventional multi-purpose equipment. Examples are given for sustainable processes with a complete continuous production process from raw material uptake until final distilled product described.
The term "flow chemistry" or "continuous flow chemistry" - although not limited in general to a certain volume - is usually associated with microreactor technology and refers to relatively small volumes in continuous flow reactions. The principle benefits of microreactor technology are: the possibility to perform critical reactions in a safe way, the ease of scalability from lab up to commercial volumes and the possibility of using several microreactors in parallel in order to obtain more product in a shorter time.
Characteristics of microreactor chemistry are: the excellent heat exchange; the closed system; the possibility to pressurise the microreactor and the easy automation. This leads to efficient and reproducible mixing and very precise reaction control. Reactions in microreactors therefore are often cleaner with better yields and less by-products compared to batch reactions (1). However there are limitations of microreactor technology when using multi-phase systems, e.g. suspensions.
Most of the benefits apply to continuous processes in general - independent from the reactor size, as long as the critical reactor size ...