中空纤维膜促进成核的冷却结晶过程

Cooling crystallization process via hollow fiber membrane promoted nucleation

利用中空纤维膜组件的高单位体积换热面积和优异的传热能力,实现膜界面骤冷促进成核,并利用膜界面流场的综合作用力,完成溶液冷却结晶的自动成核和晶种添加功能.以硫脲水溶液作为研究体系,研究PTFE中空纤维膜促进冷却结晶过程.结果表明,利用膜诱导晶核产生的时间为195 s,无膜参与的自发成核冷却结晶诱导时间为280 s.同时,在相同的温度、原料浓度以及搅拌速度下,由于利用膜促进成核的冷却结晶能够有效调控晶种产生的速率和数量并实现自动输送,制备的晶体产品形貌完整、纯度高(>99.5%)、平均粒径大(>1.35 mm,相比于其他无膜技术提高30%以上)且粒径分布集中.

Cooling crystallization is a widely used separation technology,which has the advantages of low energy consumption and environmental friendliness.At present,the spontaneous nucleation of the solution gradually cooling is difficult to control with high precision;artificial seed addition can improve the quality of the cooling crystallization product;however,it cannot be automated.This paper used the high heat exchange area and excellent heat transfer capacity of hollow fiber membrane modules to achieve rapid cooling at the membrane interface to promote nucleation,thereby completing the automatic nucleation and seed addition functions of cooling crystallization.Thiourea aqueous solution was used as the research system to study the cooling crystallization process of PTFE hollow fiber membranes.The results showed that the time to induce nucleation with membrane was 195 s,and the induction time to cooling crystallization of spontaneous nucleation without membrane participation was 280 s.In addition,at the same temperature,raw material concentration,and stirring speed,the use of the membrane to promote the nucleation of the cooling crystallization can effectively regulate the number and rate of seed production and achieve automatic transportation.Therefore,the quality of the prepared crystal product is excellent,the crystal morphology is complete,the purity is high(>99.5%),the average crystal particle size is large(>1.35 mm),and the particle size distribution is narrower.This novel cooling crystallization method provides a new approach for the optimization and design of the cooling crystallization process.