Crystallizers are devices used to separate and purify polymers solutions and emulsions by crystallization. They remove polymers from solution and emulsion by accelerating the crystallization process, thus enabling the polymers to be collected as a pure solid for use in further processing.
Crystallizers are mainly divided into two categories: batch and continuous-flow. Batch crystallizers comprise of a vessel and a return line that recycles the solution from the crystal and the solution is cooled externally. Heat transfer from the bath, to the solution, results in a transition from a liquid to a solid state. On the other hand, continuous-flow crystallizers are designed to move material from inlet to out, through convention and radiation heat transfer, where crystalline particles are collected as effluent.
Crystallizers can be further classified by the type of heat-removal device used. For instance, a forced convection crystallizer utilises external heating and cooling to adjust the temperature of the circulating liquid, while a non-forced convection crystallizer uses magnetic levitation to provide the cooling effect. Other types of crystallizers, such as bubble-column and drum crystallizers, also utilise different variants of heat-removal methods, depending on the nature and size of the polymer.
A number of advantages are associated with the usage of crystallizers. In comparison with traditional precipitation, crystallizers tend to result in the formation of larger, cleaner particles with higher purity. This is because, during the crystallization process, insoluble impurities are removed, along with volatile products, thereby resulting in higher purity and larger crystal size. Also, crystallizers are capable of producing crystals of uniform size which can be easily separated by filtration, sedimentation or centrifugation.
More importantly, crystallizers are capable of producing large amounts of product and are highly efficient in terms of time, space and energy-usage. Owing to their flexibility and large production capacity, they are suitable for industrial batch-processing applications.
In addition, crystallizers are highly versatile in terms of their ability to perform different functions. For instance, continuous-flow crystallizers are capable of performing multi-step crystallization processes, involving the separation of fine, uniform crystals from solution containing both small and large crystalline fractions. Furthermore, bubble-column, drum and forced convection crystallizers are capable of performing specialised functions such as size-separation, concentration and recrystallization, in addition to carrying out a wide range of preparatory processes.
In conclusion, crystallizers are highly efficient devices used to separate and purify polymers from solution and emulsion. They are primarily employed for industrial batch process applications due to their ability to produce large amounts of product in a short time frame. Moreover, they also have the capability of performing a variety of tasks such as size-separation and concentration. As a result, they are becoming increasingly popular amongst the scientific and industrial community.
