Abstract: The objective of this study was to investigate the effect of N-(β-ethyl sulfonate) aminoethyl sulfonate (SA), an inevitable impurity during the taurine production using the ethylene oxide synthetic route, on the morphology of taurine crystals (TCs). Crystal morphology was investigated under different SA concentrations and cooling rates, and the length-diameter ratio of TCs were statistically analyzed. The molecular dynamics simulation method was used to investigate the attachment of the SA molecules on TC faces and the reason for SA changing crystal morphology. The results showed that the average length-diameter ratio of TCs increased as the SA concentration and cooling rate increased. The dosage of 0.04 mol SA per kg H2O could bring in an more than 100% increase of the TCs average length-diameter ratio when the cooling rate was 30 K/h. An increase of approximately 3.8 times in the average length-diameter ratio was observed when the cooling rate increased from 6 K/h to 36 K/h with 0.02 mol SA per kg H2O added. The cooling rate in the crystallization process should be controlled to less than 12 K/h to obtain taurine products with an average length-diameter ratio less than 3. The simulation results showed that the presence of SA increased the attachment energy barrier of taurine molecules on all stable crystal faces and the crystal habit simulated by the modified attachment energy model was consistent with the experimental morphology. The reduction of (111 ?) face area ratio and the expansion of (102) and (102 ?) face area ratios were the fundamental reasons for high length-diameter ratio needle-like morphology of TCs in the presence of SA. In conclusion, this study provides insights into the role of SA in shaping the morphology of TCs and offers recommendations for optimizing the taurine production process.

Key words: taurine, crystallization, impurity, crystal morphology, molecular simulation

摘要： 在环氧乙烷法合成牛磺酸的工艺路线中，杂质亚氨基二乙磺酸单钠(SA)会不可避免地进入结晶工序，杂质的存在会对牛磺酸产品的性质产生显著影响。本工作考察了SA浓度和降温速率对牛磺酸晶体形貌的影响，采用分子动力学模拟方法分析了SA在牛磺酸晶面上的附着情况以及SA改变牛磺酸晶体形貌的原因。结果表明，牛磺酸长径比随着SA浓度增加和降温速率加快而增大；降温速率为30 K/h时，添加浓度为0.04 mol/kg的SA会使牛磺酸晶体的平均长径比增加1倍以上；SA浓度为0.02 mol/kg时，随着结晶冷却速率从6 K/h升至36 K/h，晶体的平均长径比增大约3.8倍。结晶过程的降温速率应控制在12 K/h以下，以获得平均长径比小于3的牛磺酸晶体产品。模拟结果表明，基于修正的附着能模型模拟得到的晶习和实验晶习一致；(111 ?)晶面的面积占比缩小，(102)和(102 ?)晶面的面积占比扩大，这是SA水溶液中牛磺酸晶体生长成针状形貌的根本原因。本研究有助于理解SA改变牛磺酸晶习的作用机理和指导牛磺酸结晶工艺的优化。

关键词: 牛磺酸, 结晶, 杂质, 晶体形貌, 分子模拟