Falling film crystallization kinetics of paraxylene

doi:10.11949/j.issn.0438-1157.20180134

Abstract

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℃ and raw material precooling temperature of 25℃, and sweating conditions were heating rate 1℃·min^-1, and sweating end temperature of 5℃. Under the optimized experimental conditions, the crystal growth rate equation and the liquid entrapment rate equation were built by measuring the amount 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.

Key words: paraxylene, crystallization, kinetics, optimization, supersaturation, porosity

摘要：

降膜结晶是工业生产对二甲苯的重要方法。以多孔介质分形理论为基础开展对二甲苯降膜结晶动力学的研究。通过动力学模型优化实验条件，结晶条件为进料速度为60 ml·min^-1、结晶温度-15℃、原料预冷温度25℃，发汗条件为升温速率1℃·min^-1、发汗终温5℃。在此条件下测定降膜结晶过程中对二甲苯结晶量以及液相夹带量，建立了晶体生长速率方程和液相夹带速率方程，相关系数分别为0.967和0.977，模型可靠。结果表明随着过饱和度的增加，液相夹带速率增长更快，晶层中夹带液相体积分数越大，晶层孔隙率越大。晶体生长速率方程和液相夹带速率方程的建立对工业降膜结晶生产对二甲苯过程中，通过调节液膜过饱和度控制晶层生长具有重要参考意义。

关键词: 对二甲苯, 结晶, 动力学, 优化, 过饱和度, 孔隙率

CLC Number:

WANG Rui, XU Yanxia, SONG Xingfu, XU Zhigang, YU Jianguo. Falling film crystallization kinetics of paraxylene[J]. CIESC Journal, 2018, 69(8): 3460-3468.

王瑞, 许妍霞, 宋兴福, 徐志刚, 于建国. 对二甲苯降膜结晶动力学[J]. 化工学报, 2018, 69(8): 3460-3468.

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