Chemical Engineering Science, Dec 24, 2012, Vol.84, p.120(14)
To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ces.2012.08.026 Byline: Xiaobin Jiang (a)(b), Baohong Hou (a), Gaohong He (b), Jingkang Wang (a) Keywords: Crystal Layer Growth; Diffusion; Melt Crystallization; Parameter identification; Separations; Simulation Abstract: This paper was concerned with the model development and experimental validation of the detailed crystal layer growth and multi-ions impurity distribution process in the falling film melt crystallization (FFMC) model. The phosphoric acid (PA) was separated and purified by FFMC to obtain a hyperpure phosphoric acid (HPA), which was a vital electronic chemical in IT industry. To establish a valid model, which offered an easy and convenient path of the simulation, dynamic heat and mass balance, approaches were adopted to describe the variation of crystal layer growth rate along the crystallizer. An impurity balance approach was adopted to describe the change of distribution coefficient for multi-ion impurity. A criterion was proposed to determine the formation of branched-porous (B-P) structure. The model was validated by experimental results with various equipments and operational conditions and a good agreement was obtained. The effective distribution coefficient K.sub.eff for multi-ion impurities were less than 0.2 (Na.sup.+), 0.25 (Fe.sup.3+) and 0.35 (Ca.sup.2+) with proper operation conditions. The resulting model was directly exploited to understand crystal layer growth and impurity distribution behaviors in FFMC from laboratory to industrial scale. More significantly, the model proposed a method for the separation effect evaluation and the key operational conditions (feed rate and cooling rate) determination which could readily develop optimal crystal layer growth route during industrial crystallization. In addition, the model was a vital base to describe the subsequent purification step of FFMC: sweating process. Author Affiliation: (a) School of Chemical Engineering and Technology, State Research Center of Industrialization for Crystallization Technology, Tianjin University, No.97 Weijin Road, Nankai Distrct, Tianjin 300072, China (b) State Key Laboratory of Fine Chemicals, The R&D Center of Membrane Science and Technology, Dalian University of Technology, Dalian, China, 116012 Article History: Received 18 June 2012; Revised 1 August 2012; Accepted 12 August 2012
Phosphoric Acid -- Analysis ; Phosphoric Acid -- Models ; Phosphates -- Analysis ; Phosphates -- Models
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