# Application of Polymers as a Tool in Crystallization--A Review  
[PERSON]  
1 Department of Chemical Engineering and Process Design, Faculty of Chemistry,  
Silesian University of Technology, 44-100 Gliwice, Poland; [EMAIL_ADDRESS] (T.W. ); [EMAIL_ADDRESS] (M.K. ); [PERSON]A.G.)  
2 Department of Physical Chemistry and Technology of Polymers, Faculty of Chemistry,  
Silesian University of Technology, 44-100 Gliwice, Poland  
Correspondence: [PERSON].L. ); [PERSON] (A.M.); Tel. : +48-32-237-28-32 (M.L. ); +48-32-237-15-73 (A.M.); Fax: +48-32-237-14-61 (M.L. ); +48-32-237-15-09 (A.M.)  
[PERSON]  
2 Department of Chemical Engineering and Process Design, Faculty of Chemistry,  
Silesian University of Technology, 44-100 Gliwice, Poland; [EMAIL_ADDRESS] (T.W. ); [EMAIL_ADDRESS] (M.K. ); [PERSON]A.G.)  
[PERSON]  
1 Department of Chemical Engineering and Process Design, Faculty of Chemistry,  
Silesian University of Technology, 44-100 Gliwice, Poland; [EMAIL_ADDRESS] (T.W. ); [EMAIL_ADDRESS] (M.K. ); [PERSON]A.G.)  
[PERSON]  
1 Department of Chemical Engineering and Process Design, Faculty of Chemistry,  
Silesian University of Technology, 44-100 Gliwice, Poland; [EMAIL_ADDRESS] (T.W. ); [EMAIL_ADDRESS] (M.K. ); [PERSON]A.G.)  
and [PERSON]  
1 Department of Chemical Engineering and Process Design, Faculty of Chemistry,  
Silesian University of Technology, 44-100 Gliwice, Poland; [EMAIL_ADDRESS] (T.W. ); [EMAIL_ADDRESS] (M.K. ); [PERSON]
in 2008 [6]. These examples prove that the quality of crystalline products is of great importance both at the stage of manufacturing and storage. At the present moment, two basic methods of crystallization are used in industry; namely, crystallization from solution and crystallization from melt. However, the later method will not be discussed here since it is out of scope of this paper. The basic parameters describing the crystallization process are supersaturation (supercooling), hydrodynamic conditions (mixing power), and crystal growth time. The condition of supercooling and supersaturation may be achieved by the cooling of the solution or by the evaporation of the solvent, respectively. Another aspect of crystallization is precipitation, in which the crystal nuclei are created due to a chemical reaction. In this case the hydrodynamic conditions play the dominant role in the control of the process. The first stage of the crystallization process is named nucleation--a phenomenon leading to the creation of a stable cluster of molecules or ions, a nucleus which will later form the crystal [9]. Generally speaking, it may be divided into primary and secondary nucleation, whereas the primary nucleation may be considered as homogeneous and heterogeneous. The first case refers to the pure solutions in which no crystals are present. The population of clusters is created--some of them are short-lived entities which will eventually break, but some of these clusters will create the critical nucleus leading to the formation of crystals. Simultaneously it is worth emphasizing that homogeneous nucleation is rare and hard to accomplish. On the other hand, the second case refers to the solutions in which impurities are present. Importantly, the foreign substance which inhibits the nucleation in one system may induce this process in another one. This is a principle that will be broadly used in the research presented in this paper. The term secondary nucleation is used for description of the nucleation which takes place in a solution in which the crystals of solute are already present. Such a phenomenon occurs more readily compared to the primary, homogeneous nucleation. Therefore, often in industrial practice the seeding process is used during which the crystals are added deliberately to the system. In the case of crystallization realized in agitated vessels, the secondary nucleation may occur due to the attrition and breakage of already formed crystals due to the hydrodynamic conditions [9]. The second stage of the crystallization process is crystal growth.