Falling film crystallization kinetics of paraxylene
(2.Changzhou Ruihua Chemical Eng. & Tech. Co., Ltd., Changzhou, Jiangsu, China 213000)
【Abstract】Falling film crystallization is an important production method of paraxylene in industry. The falling film crystallization kinetics of paraxylene was studied based on the fractal and porous media theory. The experimental conditions were optimized by kinetic modeling. The crystallization conditions were feeding speed of 60 mL·min−1, crystallization temperature of −15 °C and raw material precooling temperature of 25 °C, and sweating conditions were heating rate 1 °C·min−1, and sweating end temperature of 5 °C. Under the optimized experimental conditions, the crystal growth rate equation and the liquid entrapment rate equation were built by measuring the amounts of paraxylene crystallization and liquid entrapment, and the correlation coefficients were 0.967 and 0.977. The results show that the liquid entrapment rate increases faster, and the volume fraction of the liquid entrapment in the crystal layer increases with the augment of supersaturation, resulting in the increase of porosity in the crystal layer. The establishment of crystal growth rate equation and liquid entrapment rate equation has important significance for the control of the crystal layer growth by adjusting the liquid film supersaturation in the industrial paraxylene production by falling film crystallization.
【Keywords】 paraxylene; crystallization; kinetics; optimization; supersaturation; porosity;
(Translated by SUN Z)
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