(2.常州瑞华化工工程技术有限公司, 江苏常州 213000)
【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。
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;
 LIN Z, NIKOLAKIS V, IERAPETRITOU M G. Life cycle assessment of biobased p-xylene production [J]. Industrial & Engineering Chemistry Research, 2015, 54 (8): 2366–2378.
 CHEN L, XIAO J, XIE Z K, et al. Suspension melt crystallization kinetics of p-xylene [J]. CIESC Journal, 2009, 60 (11): 2787–2791 (in Chinese).
 SONG S H. The crystallization purification process and mathematical model of paraxylene [D]. Xiangtan: Xiangtan University, 2016 (in Chinese).
 SHEN S, LI S Y. Purification of p-xylene by melt crystallization [J]. Chemical Industry and Engineering Progress, 2017, 36 (5): 1605–1611 (in Chinese).
 BLANKS R F. In-line measurement of crystallization kinetics for paraxylene recovery by continuous melt crystallization slurry process industrial crystallization [J]. Symposium on Industrial Crystallization, 2001, 2: 5-063-5-068.
 CHEN L, XIAO J, XIE Z K, et al. Advances in p-xylene separation by crystallization [J]. Modern Chemical Industry, 2009, 29 (2): 10–14 (in Chinese).
 ZHU J, DING X F, LI T X, et al. Application of falling film crystallization process in preparation of high-purity sulfuric acid [J]. Inorganic Chemical Industry, 2014, 46 (6): 38–41 (in Chinese).
 ZHU Z. The purification of β-methylnaphthalene by melt crystallization [D]. Tianjin: Tianjin University, 2007 (in Chinese).
 KASYMBEKOV B A, MYASNIKOV S K, MALYUSOV V A. Separation of substances by fractional crystallization from outflowing liquid films [J]. Theoretical Foundations of Chemical Engineering, 1985, 19 (1): 15–21.
 JIANG J J. Study on the crystallization process of liquid film [D]. Tianjin: Tianjin University, 1988 (in Chinese).
 BEIERLING T, MICOVIC J, LUTZE P, et al. Using complex layer melt crystallization models for the optimization of hybrid distillation/melt crystallization processes [J]. Chemical Engineering & Processing Process Intensification, 2014, 85: 10–23.
 ZHANG Z, ZHANG J W. Numerical modeling of coupled momentum heat and mass transport in falling crystallization process (Ⅰ): Continuum model [J]. Journal of Chemical Industry and Engineering (China), 2001, 52 (7): 580–586 (in Chinese).
 ZHANG J W, ZHANG Z. Numerical modeling of coupled momentum heat and mass transport in falling film crystallization process (Ⅱ): Simulation [J]. Journal of Chemical Industry and Engineering (China), 2001, 52 (7): 587–592 (in Chinese).
 LIU A. Numerical simulation of double falling film melt crystallization process [D]. Tianjin: Tianjin University, 2009 (in Chinese).
 BENNON W D, INCROPERA F P. A continuum model for momentum heat and species transport in binary solid–liquid phase change systems (Ⅰ): Model formulation [J]. International Journal of Heat & Mass Transfer, 1987, 30 (10): 2161–2170.
 BENNON W D, INCROPERA F P. A continuum model for momentum heat and species transport in binary solid–liquid phase change systems (Ⅱ): Application to solidification in a rectangular cavity [J]. International Journal of Heat & Mass Transfer, 1987, 30 (10): 2171–2187.
 BENNON W D, INCROPERA F P. Numerical analysis of binary solidliquid phase change using a continuum model [J]. Numerical Heat Transfer, 1988, 13 (3): 277–296.
 JIANG X, HOU B, ZHAO Y, et al. Kinetics study on the liquid entrapment and melt transport of static and falling-film melt crystallization [J]. Industrial & Engineering Chemistry Research, 2012, 51 (13): 5037–5044.
 ZHANG B, YU B M, WANG H X, et al. A fractal analysis of permeability for power-law fluids in porous media [J]. Fractalscomplex Geometry Patterns & Scaling in Nature & Society, 2006, 14 (3): 171–177.
 CAI J, YU B, ZOU M, et al. Fractal analysis of invasion depth of extraneous fluids in porous media [J]. Chemical Engineering Science, 2010, 65 (18): 5178–5186.
 JIANG X, HOU B, HE G, et al. Falling film melt crystallization (Ⅱ): Model to simulate the dynamic sweating using fractal porous media theory [J]. Chemical Engineering Science, 2013, 91 (2): 111–121.
 JIANG X, HOU B, WANG J, et al. Model to simulate the structure of a crystal pillar and optimize the separation efficiency in melt crystallization by fractal theory and technique [J]. Industrial & Engineering Chemistry Research, 2011, 50 (17): 10229–10245.
 SCHOLZ R, WANGNICK K, ULRICH J. On the distribution and movement of impurities in crystalline layers in melt crystallization processes [J]. Journal of Physics D Applied Physics, 1993, 26 (8B): B156.
 BEAR J. Dynamics of Fluids in Porous Media [M]. America: Elsevier Pub. Co., 1972.
 HADDON W F, JOHNSON J F. Solubility data for p-xylene [J]. J. Chem. Eng. Data, 1964, 9 (1): 158–159.
 CHE G Q, GU X L. Solid–liquid equilibrium of system of m-xylene and p-xylene [J]. Chemistry, 1995, (6): 50–52 (in Chinese).
 JAKOB A, JOH R, ROSE C, et al. Solid–liquid equilibria in binary mixtures of organic compounds [J]. Fluid Phase Equilibria, 1995, 113 (1): 117–126.
 PORTER R S, JOHNSON J F. Extended xylene solubility studies [J]. Journal of Chemical & Engineering Data, 2002, 12 (3): 392–394.
 GUO Y Z. Study on the solid–liquid equilibrium of xylene isomer binary systems [D]. Shanghai: Tongji University, 2006 (in Chinese).
 CHEN L, XIAO J, XIE Z K, et al. Solid–liquid equilibrium study of p-xylene crystallization process [J]. Polyester Industry, 2009, 22 (1): 7–11 (in Chinese).
 GUO S S. Study on the solid–liquid equilibrium of xylene isomer ternary systems [D]. Shanghai: Tongji University, 2008 (in Chinese).