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Selective production of polymorphs and pseudomorphs using supercritical fluid crystallization from aqueous solutions

机译：使用超临界流体从水溶液中结晶选择性生产多晶型物和假晶型物

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摘要

A number of supercritical fluid technologies are known to enable the selective production of polymorphs, only by changing the process conditions. These techniques use either supercritical CO2 or organics as solvent. In this work, the precipitation of small organic molecules from aqueous solution was studied using a mixture of supercritical CO2 and ethanol as drying medium and as anti-solvent. Glycine, which has three polymorphs, was precipitated by a direct spraying process. By simple manipulation of the flow rates, the process could be tuned to selectively precipitate either pure alpha- or beta-glycine. When increasing the ethanol concentration in the system, the precipitation of the metastable beta-glycine was preferred over the precipitation of alpha-glycine. Small portions of gamma-glycine could be found when choosing slow drying conditions. The same process route was applicable to selectively precipitate pseudomorphs as well. Increasing the ethanol concentration in the extractant phase favored the precipitation of phenylalanine anhydrate over the monohydrate form. The study shows that the supercritical fluid crystallization process has significant potential for the selective production of polymorphs and pseudomorphs of water soluble compounds into small particles in a single step.
机译：已知许多超临界流体技术仅通过改变工艺条件就能选择性生产多晶型物。这些技术使用超临界CO2或有机物作为溶剂。在这项工作中，研究了使用超临界CO2和乙醇的混合物作为干燥介质和抗溶剂，从水溶液中沉淀出小的有机分子的方法。具有三个多晶型物的甘氨酸通过直接喷涂过程沉淀。通过简单地控制流速，可以调节该过程以选择性地沉淀出纯的α-或β-甘氨酸。当增加系统中乙醇的浓度时，亚稳态β-甘氨酸的沉淀优于α-甘氨酸的沉淀。选择慢速干燥条件时，会发现少量的γ-甘氨酸。相同的工艺路线也适用于选择性沉淀假晶。与一水合物形式相比，萃取相中乙醇浓度的增加有利于苯丙氨酸无水物的沉淀。研究表明，超临界流体结晶过程具有巨大的潜力，可以一步一步将水溶性化合物的多晶型物和假晶型选择性地生产成小颗粒。

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