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首页> 外文期刊>Crystal growth & design >An Examination of the Crystallization of Urea from Supersaturated Aqueous and Aqueous-Methanol Solutions as Monitored In-Process Using ATR FTIR Spectroscopy
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An Examination of the Crystallization of Urea from Supersaturated Aqueous and Aqueous-Methanol Solutions as Monitored In-Process Using ATR FTIR Spectroscopy

机译：使用ATR FTIR光谱监测过程中尿素从过饱和水溶液和甲醇水溶液中的结晶化

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In-process ATR FTIR spectroscopy combined with optical turbidometry is applied to the measurement of reactant supersaturation during temperature-programmed studies of the batch crystallization of urea from aqueous and mixed aqueous/methanolic solvent systems at the 400 mL scale size (pitched blade impeller) for solute compositions in the 35-65 w/w% range.The metastable zone widths were found to be in the range 3-12degC and critical supersaturations in the 1.05-1.18 range,respectively,inversely dependent upon solute concentration.Only a slight dependency of the metastable zone width with reactor heating/cooling rates,indicative of fairly matched rates of nucleation and solubility change,is found.Cross-correlation between FTIR and turbidometic measurements reveal,as expected,the former technique to be more sensitive to the detection of the crystallization onset.No evidence was found for phase separation (oiling-out) prior to nucleation,in contrast to previous studies of citric acid (Groen,H.;Roberts,K.J.J.Phys.Chem.B 2001,105,10723-10730).Crystallization enthalpic release at the onset point is found to affect transient crystal dissolution and regrowth following nucleation.Good FTIR calibration,with excellent correlation to known solubility data,using a univariant IR transmittance (peak intensity) model is achieved for both single and mixed solvent systems,this despite slight variation in the IR peak positions with temperature and concentration.Attempts to use the calibration data at higher solute concentrations beyond the calibration range were not successful,this being associated with a significant underestimation of the solution supersaturation.A forward look to improvements in FTIR calibration using multivariant chemometric approaches is highlighted.
机译：过程ATR FTIR光谱技术与光学浊度法相结合，用于在程序升温研究中，以400 mL规模（桨叶式叶轮）从含水和混合水/甲醇溶剂系统中分批结晶尿素的程序升温过程中，测量反应物过饱和度。溶质组成在35-65 w / w％的范围内。发现亚稳区域宽度在3-12degC范围内，临界过饱和度分别在1.05-1.18范围内，与溶质浓度成反比。发现了具有反应器加热/冷却速率的亚稳区域宽度，表明成核速率和溶解度变化相当匹配。FTIR和比浊法测量值之间的互相关性表明，正如所料，前一种技术对检测氢原子的敏感性更高。与以前的柠檬酸（Groe）研究相反，成核前没有相分离（析出）的证据n; H.; Roberts，KJJPhys.Chem.B 2001,105,10723-10730）。在起始点的结晶焓释放影响成核后的瞬时晶体溶解和再生长。良好的FTIR校准，与已知的相关性极佳尽管单峰和混合溶剂系统的IR峰位置均随温度和浓度略有变化，但仍使用单变量IR透射率（峰值强度）模型获得了溶解度数据。尝试在高于校准的较高溶质浓度下使用校准数据范围未成功，这与溶液过饱和度的明显低估有关。着重指出了使用多变量化学计量学方法改进FTIR校准的前瞻性观点。

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