Continuous Crystallization of Bulk and Fine Chemicals
Continuous operation is common for most industrial large scale productions of bulk chemicals. Such productions are continuous because of the need to optimize energy efficiency and investment cost. In such continuous production processes the solids formation step (crystallization, precipitation) is also continuous. In addition to their economic optimum, such continuously operated plants have further advantages: They are operated at quasi-steady state and therefore produce products of rather constant quality. Furthermore, they may be operated for very long periods of time (days to weeks) without cleaning and removing of incrustations. In addition, the product quality may be adjusted in a wide range of particle sizes from a few microns to a few millimetres. In contrast to the continuous operation of large scale production of bulk chemicals most processes for fine chemicals are batch- or semi-batch-wise and are carried out in multi-purpose/multi-product plants. Here, the priority lies with the variability and flexibility of the plant. Characteristic is the rather low tonnage of fine chemical products. Nevertheless, the advantages for continuous processes in the bulk chemicals production are valid also for the fine chemicals production, and hence, there is a number of reasons why continuous crystallization may be seen more often in the future.