摘要
微颗粒的研制已成为当今高新技术中的一个热门领域。超临界流体结晶技术拥有一些传统技术不具备的优点，可以不造成或减少环境污染，是一种新的、很有发展前景的绿色微颗粒制备技术。国内外有许多学者对此进行了大量的实验研究，但因缺乏定量描述过程的模型，对有些实验现象尚难给出满意的解释，操作条件与产物粒径和形态间的比较准确的关系也尚未建立，距放大到工业规模形成生产力尚有相当大的差距。
论文通过超临界流体抗溶剂过程(SAS)的理论研究和实验，探讨了SAS过程制备聚合物微颗粒的原理和实验参数对颗粒形态的影响；计算了高压下相平衡性质，回归二元相互作用参数；建立了SAS过程的传质模型，用于溶剂在喷嘴出口瞬间的传质速率及液滴在下降过程中扩散消失时间的计算；在自行设计和搭建的SAS实验装置上成功地制备了聚苯乙烯微颗粒；并考察了过程参数对实验结果的影响。
研究表明，回归得到的(CH_3)_2SO-CO_2、CH_2Cl_2-CO_2两个体系MPR方程中的二元相互作用参数，计算相平衡值与文献值的平均误差约为1.5％；根据建立的SAS过程的传质模型，预测了液滴消失时间t与CO_2密度ρ_B、液滴下降速度ν_t、喷嘴直径d、摩尔分数x_A的关系，部分结果与一些文献实验结果相符。通过预测釜中流体的相态变化，结合抗溶剂原理较好地解释了抗溶剂与溶剂流量比对颗粒形成的影响。表明长时间制备聚合物微颗粒时，该流量比存在最小值，此比值应维持釜中的甲苯含量小于或略高于甲苯在二氧化碳中的溶解度。通过釜中甲苯含量变化与清洗时间关系的计算和实验表明，清洗时间决定了甲苯残留量，而甲苯残留量对颗粒形态有较大影响。实验表明，CO_2密度从446kg／m~3到719kg／m~3变化时，生成聚苯乙烯粒径变化不大；降低温度有利于聚合物结晶生成离散微颗粒，而较高的温度会使聚合物塑化，25℃时聚苯乙烯无团聚现象发生；溶液浓度的增加，不利于聚合物结晶形成微颗粒，当溶液浓度5％时，生成熔融状聚苯乙烯，无颗粒生成；搅拌不利于聚合物结晶；在超临界状态下CO_2所含杂质不利于对聚合物结晶；在超临界点以下时，CO_2所含杂质对聚合物结晶影响不大。甲苯中少量的杂质对实验结果影响不大。这些结论为进一步研究SAS过程奠定了一定的基础。
The study on the micro-particle has already become a hot field in current new and high technology. Supercritical Fluids (SCF) crystallization technique has some great advantages that some traditional ones do not have. The technique is a new prospective micro-particles manufacturing technique with little environmental pollution. Many scholars have carried on a number of experiments to study it. But some experimental phenomena are still too difficult to explain. The relationship between particle size, morphology and operating conditions has not been exactly correlated yet. Models are correlative rather than predictive. The inherent relationship among unit dimension, construction of equipment, process parameters, particle size and morphology has not been established because the dominant controlling factors are not thoroughly understood.
The object of this paper was to find out the effect of process parameters on polymeric micro-particles produced by Supercritical Antisolvent Solution (SAS) techniques. In the experiments, the system of polymer-toluene-carbon dioxide was chosen.
In the first chapter of this paper, the technique of micro-particles formation by Supercritical Fluids (SCF) was introduced. And then, the paper reviewed the methods of producing compound particle techniques by SCF. The methods included Rapid Expansion of Supercritical Solution, Supercritical Anti-solvent (SAS), Immersion, Chemical Reaction, Gas Saturated Solutions.
In the second chapter, a computer program was designed, which was used to regress binary acting parameters and calculate phase equilibrium property. The calculating results were precise in comparison with the experimental values of the references. The paper also built a model to simulate the SAS process. The model can well describe the effects of density of carbon dioxide, diameters of jets, and solubility of solvent in anti-solvent on droplet dispersion time.
The third chapter introduced experimental process, materials and SAS experimental apparatus which was designed and made by ourselves.
At the final part of the paper, the experimental results were listed and effects of process parameters on these results were discussed. The experiments found flow rate had an important influence on particle formation. In a long-time and continuous process, the content of toluene in the high pressure vessel should be smaller or a little bigger than the solubility of toluene in supercritical carbon dioxide. Finally, the paper suggested how to choose proper time of washing and analysed the effect of flow rate, washing time, density of carbon dioxide, temperature, solute concentration, et al on the experimental results.
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