【摘 要】
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When crystallization is in progress,one substance may stack in more than two types of lattice structure and the resulting crystal types are called polymorphic forms.L-glutamic acid (LGA) has two polym
【机 构】
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Dept.of Chem.& Biol.Eng.,Korea Univ.,Seoul 136-713,Korea
【出 处】
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第七届国际分离科学与技术会议(Proceedings of the 7th International Conferen
论文部分内容阅读
When crystallization is in progress,one substance may stack in more than two types of lattice structure and the resulting crystal types are called polymorphic forms.L-glutamic acid (LGA) has two polymorphic forms,metastable α form and stable β form.The α-form crystals are easier to be handled thanks to its granular shape [1].In a solution,the metastable form is spontaneously transformed into the stable form as β-form crystal grows on the surface of α-form crystal while α-crystal is dissolved [2].This so-called solution-mediated polymorphic transformation is an obstacle to growth of pure α-crystals.Mathematical modeling and simulation of polymorphic transformation was used to find the optimal operating conditions.Model equations for birth and growth of both polymorphs are excerpted from Scholl et al.Solubility data for α- and β-form in Hermanto et al.were used [3].For metastable limit,data points from Kee et al.are fitted as exponential curve [4].Based on the case study,cooling strategy composed of initial cooling,heating,and final cooling can be suggested.Initial cooling step plays a role of inducing appropriate nucleation of α-crystals.Heating pushes the degree of saturation of solution into the metastable zone.Final cooling profile is programmed in order to operate within metastable zone width where only growth of crystals is allowed and excess nucleation is suppressed.Temperature in final cooling step is controlled for solute concentration to be in the range of 95-100 % of metastable zone width when α-saturation limit is 0 % and metastable limit is 100 %.Cooling rate is set not to exceed 1.00 K/min.Objective function is set for optimization of producing α-LGA by cooling-heating-cooling crystallization.
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