Coating Granulation by Rapid Expansion of Supercritical Fluid Solutions in a Fluidized Bed

在流化床中，利用黏结剂（石蜡）的超临界CO_2溶液快速膨胀进行包覆造粒，在芯粒（玻璃微珠）表面包覆细硅颗粒。超临界CO_2溶液快速膨胀沉积石蜡，使细小的二氧化硅颗粒进入岩心颗粒周围的层中。最初，单个细颗粒由于附着力附着在核心颗粒上，然后由于粘合剂的沉积而被固体桥接所包围。获得了稳定的涂层造粒，没有过量的结块。在低气速下，粘结剂材料沉积在粘接芯粒的细颗粒涂层上。这导致均匀的涂层造粒层细颗粒。另一方面，在高气速下，发现小团聚体和细颗粒层状分布在核心颗粒上。此外，还对多孔颗粒进行了膜掩膜处理，以控制超临界CO_2溶液在流化床中的快速膨胀释放。通过红色素释放率测定和扫描电镜观察，考察了涂层的特性。结果表明，通过控制操作条件可以控制其释放速度。包衣过程中所有颗粒均呈单分散状态，无颗粒团聚现象。实验中对其释放速率和涂层表面形貌进行了分析。

The coating granulation by the rapid expansion of supercritical CO_2 solutions of binder (paraffin) was performed to coat the surface of core particles (glass beads) with fine silica particles in a fluidized bed. The deposition of paraffin by rapid expansion of supercritical CO_2 solutions incorporated fine silica particles into the layers around core particles. Initially individual fine particles are attached to the core particles due to the adhesion force and then are bounded by solid bridging due to the deposition of binder. A stable coating granulation was achieved without the excess agglomeration. At low gas velocity the binder material was deposited on the coating layer of fine particles adhered to the core particle. This leads to the uniform coating granulation by layering fine particles. On the other hand, at high gas velocity small agglomerates and fine particles are found to be layered on the core particles.In addition, porous particles were coated with film masking for releasing control by the rapid expansion of supercritical CO_2 solution in a fluidized bed. The coating characteristics was examined by the measurements of releasing rate of red pigment and SEM observation. It was found that the releasing rate can be controlled by controlling the operation condition. All the particles in mono-dispersion in the coating process with out agglomeration in granules. The releasing rate and the coating surface analysis was analyzed in the experiment.