Crystallization in Chemical Industry
所属分类:Technical Documents
发布日期:2013-03-07
浏览量:118
收藏:

Contrary to many people’s beliefs, mixing and crystallization have a strong interaction. A study of calcium oxalate crystallization showed that the particle size distribution was affected significantly by impeller speed and other mixing variables. Mixing affects crystal nucleation, growth and slurry maintenance in different ways, which makes crystallization the most difficult operation to scale-up successfully [3, 9, 22].

General problems are:
• control of crystal size to ease filtration wash and drying.
• excess nucleation and/or crystal fracture.
• occlusion of impurities and unacceptable physical properties.

Equipment. The crystallizers employed in the fine chemical and pharmaceutical industries are generally multipurpose vessels with a pitched blade turbine, which have good circulation and relatively low shear to reduce secondary nucleation and crystal breakage. Another good impeller choice in some crystallization processes is Intermig by Ekato. Baffles are necessary to prevent poor mixing. Other crystallization vessels could also be a batch crystallizer, fluidized bed crystallizer or draft tube baffle (DTB) crystallizer [22]. Fluidized beds are optimized for crystal growth by providing low shear, low energy and minimum impact between crystals, while impinging jets do the opposite by promoting nucleation with extreme mixing, high shear and large energy input.

Mixing and Crystal Growth. Mixing minimizes the supersaturation gradient in the film around a growing crystal by maintaining high mass transfer rates. Additionally, mixing improves heat transfer, bulk turnover, dispersion of additives like an antisolvent, uniformity of crystal suspension, avoidance of settling, minimization of wall scale and reduction of impurity concentration at the crystallizing surface. Over-mixing results in crystal breakage and shredding of nuclei promoting secondary nucleation.

上一页:Mixing of Bulk Chemicals
下一页:Scale-up in the Chemical Industry

联系我们


全国服务热线
86-20-39900130

总部地址: 广州市番禺区东环街番禺大道北555号天安总部中心14号楼410房

工厂地址:广东省肇庆国家高新区(大旺)康泰街3号
电话:86-758-3623881
  • 官方微信
  • 官方微博
咨询反馈
扫码关注

微信公众号

返回顶部