用石蜡-CO_2超临界流体快速膨胀在流化床中进行细颗粒包覆

对超临界流体快速膨胀技术在流化床中进行细颗粒的表面包覆进行了研究 ,以实现细颗粒中关键成分的有效控制释放 .实验研究了含有包覆剂———石蜡的超临界二氧化碳流体通过微细喷嘴快速膨胀到装有细颗粒的流化床中 ,膨胀射流中所产生的微核在细颗粒表面均匀沉积 ,形成细颗粒表面薄层包覆 .结果分析表明 ,超临界流体快速膨胀前的温度是包覆过程的关键参数 ,通过控制操作过程参数可以获得良好的包覆结果

FINE PARTICLE COATING FOR RELEASE CONTROL BYUSING RESS PROCESS IN FLUIDIZED BED

Fine particle coating was conducted by the rapid expansion of supercritical fluid solution (RESS) in a fluidized bed for release control of some key component in core particles. The supercritical carbon dioxide solution of paraffin was jetted into the fluidized bed of the core particles. The rapid phase change of the fluid solution from supercritical state to gas results in a solute at high supersaturating state in the solvent, which forms a huge number of superfine nuclei in the jetting flow. The deposition of the superfine nuclei on the surface of the core particles leads to a thin layer coating of paraffin. The size of the superfine nuclei is in the order of 40 nm. A porous spherical particle was selected as the core particle, which carried a tracer component of a kind of dye. Coating level was examined by the tracer's release concentration in a solvent over a certain time. The state of coating was analyzed by measuring the average mass of coated particles and a SEM observation on the surface of coated particles. The rapid expansion of the supercritical fluid solution causes a big temperature drop at the nozzle outlet. The low temperature of the nozzle outlet affects the phase of carbon dioxide and the properties of the superfine nuclei in the jetting flow, therefore it affects the particle coating process. The effect of temperature at nozzle inlet, an important parameter, on surface coating was investigated. Seal coating was formed on the core particle surface at higher temperature. Porous coating was formed on the core particle surface at lower temperature. The temperature of the nozzle inlet affects the nucleus size significantly. Higher temperature results in a bigger size of the superfine nuclei. By controlling the operation parameters, a satisfactory quality of coated particles was achieved.