Continuously monitored lactose crystallization in a vibrated bed

Abstract The aim of this work was to evaluate the crystal size distribution (CSD) and microscopy of the crystalline phase in isothermal lactose crystallization, using a high seeding concentration (dense phase). In-line monitoring was carried out using Focused Beam Reflectance Measurement (FBRM) and Particle Vision Measurement (PVM) probes in a stainless steel trunk-conical shaped jacketed crystallizer. The vibratory shaking system consisted of two perforated discs coupled to a movable axle. A conventional crystallization unit, with a three-blade propeller attached to a stainless steel shaft, was used for comparison. Concentrated cheese whey, purified with an organic coagulant, and commercial lactose solutions were used. Crystallization was improved in the high-purity solutions. Microparticles and/or aggregates appeared before seeding, mainly in the purified cheese whey solution, in which there are impurities. Secondary nucleation was present in both the vibratory agitation and conventional rotary agitation systems, being intensified by increases in agitation. Crystallization in a vibratory system should be carried out with a vibration frequency of 250 rpm, since an increase to 400 rpm reduced the amount of larger crystals.摘要 本研究旨在采用高晶种浓度（致密相），对等温乳糖结晶过程中的晶体尺寸分布（CSD）及结晶相显微特征进行评估。实验在不锈钢筒锥型夹套结晶器中开展，采用聚焦光束反射测量法（FBRM）与粒子视觉测量法（PVM）探头进行在线监测。振动搅拌系统由两块连接于活动轴的多孔圆盘构成。本研究设置常规结晶装置作为对照，该装置采用固定于不锈钢轴的三叶桨搅拌器。实验原料包括经有机凝结剂提纯的浓缩乳清，以及商用乳糖溶液。高纯度溶液中的结晶过程更为优异。晶种添加前便已出现微粒与/或聚集体，该现象主要出现于含杂质的提纯浓缩乳清溶液中。振动搅拌与常规旋转搅拌体系中均存在二次成核现象，且搅拌强度提升会加剧该过程。振动搅拌体系的结晶过程宜采用250 rpm的振动频率，当频率提升至400 rpm时，大尺寸晶体的占比会出现下降。