Paper Information

Journal:   IRANIAN JOURNAL OF CHEMICAL ENGINEERING   SPRING 2012 , Volume 9 , Number 2; Page(s) 3 To 13.
 
Paper:  APPLICATION OF A KINETIC MODEL FOR STUDYING IMPURITIES EFFECT ON CRYSTALLIZATION OF NACL, KBR, ADP AND SUCROSE SOLUTIONS
 
Author(s):  SODEIFIAN GH.*, NIKNAM M.H.
 
* DEPARTMENT OF CHEMICAL ENG., FACULTY OF ENG., UNIVERSITY OF KASHAN, KASHAN,I. R. IRAN
 
Abstract: 
Addition of impurities has an important role on the kinetic crystallization. Therefore, influence of impurities on the crystallization kinetics of NaCl, KBr, ADP and Sucrose solutions was investigated in a fluidized bed crystallizer. The growth and dissolution rates were related to the super saturation and impurity concentration. A strong mathematical model is applied to describe crystal growth rates within aqueous solutions as a function of impurity concentration. The model tries to relate the step velocity to the useful parameters such as the surface coverage (qeq), as well as the effectiveness factor of impurity, a. When a>1, the step velocity is stopped at qeq<1 (incomplete coverage of the active sites for adsorption). In the case of q=1, the velocity reaches zero just at qeq=1 (complete coverage) but approaches a limiting value. The value of q is changed by stereo chemical factors and decreases as the super saturation is increased. The Langmuir adsorption isotherm is used to relate the relative step velocity with the impurity concentration in solution. Experimental results show that increasing the amount of impurity concentration leads to a decrease in the step velocity.
Experimental data and model predictions have been compared to show that the agreement between them is very good. The obtained results are suitable for designing and quality control of the crystallization processes in chemical industries.
 
Keyword(s): CRYSTAL GROWTH RATE, IMPURITY EFFECTIVENESS FACTOR, SUPER SATURATION, STEP VELOCITY
 
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