超声强化复合溶剂洗涤聚丙烯脱灰分工艺参数优化

Optimization of Process Parameters for Ultrasound-Enhanced Composite Solvent Washing in Polypropylene Ash Removal

摘要

在电池隔膜材料、电容器膜料等介电材料领域的高端市场中，对灰分含量在50×10^-6 以下的低灰分聚丙烯的需求强劲．这些高端应用领域对聚丙烯的纯度、电绝缘性能以及化学稳定性提出了极高的要求，而灰分的存在会显著降低材料的介电性能和机械性能，限制其在高端领域的应用．因此，如何高效率脱除聚丙烯颗粒的灰分，拓展其在高要求、高标准的新兴行业中的应用，具有重要的科学意义和工业价值．本文针对已有的“正己烷+异丙醇”复合溶剂脱灰分工艺传质效率低的问题，引入超声强化促进传质，获得优化的工艺参数揭示超声强化机理．采用自主设计的正八棱柱超声反应器，系统研究了超声换能器数量及排布方式、复合溶剂液位高度、复合溶剂组分配比、液固比例及超声处理时间等工艺参数对聚丙烯洗涤脱灰分效果的影响规律．结果表明，在换能器个数为 4、复合溶剂液位高度为80 mm、复合溶剂正己烷和异丙醇体积比为21∶4、复合溶剂与聚丙烯颗粒液固比例为10 mL∶1 g以及超声处理时间为30 min的优化工艺参数条件下，聚丙烯颗粒的灰分含量降低至50×10^-6 以下．通过正交分析，获得了各参数对聚丙烯洗涤脱灰分结果的影响顺序从大到小依次为：超声处理时间，复合溶剂组分配比，复合溶剂液位高度，液固比例．本文通过测量洗涤前后的聚丙烯颗粒粒度分布，揭示了超声强化复合溶剂洗涤聚丙烯脱灰分的作用机理：空化效应产生的微射流使固体颗粒破碎，破坏颗粒表面的致密结构，辅助复合溶剂更好地进入颗粒内部达到洗涤脱灰的效果．相关结果能为超声强化复合溶剂洗涤聚丙烯脱灰分技术及装备开发提供指导．

Abstract

In high-end markets for dielectric materials, such as battery separator films and capacitor membranes, there is a growing demand for low-ash polypropylene with an ash content below 50×10^-6. These premium applications require exceptional purity, electrical insulation, and chemical stability of polypropylene. Residual ash significantly impairs the dielectric and mechanical properties of the material, limiting its use in advanced applications. Therefore, developing efficient ash removal methods for polypropylene particles is critical to expanding their applications in emerging industries with stringent requirements, offering substantial scientific and industrial value. To address these limitations, this study integrated an “n-hexane＋isopropanol” composite solvent ash removal system with ultrasound-enhanced technology to improve efficiency. Using a self-designed octagonal prism ultrasonic reactor, this study systematically investigated the influence of various process parameters on ash removal efficiency during polypropylene washing, including the number and arrangement of ultrasonic transducers, composite solvent liquid level height, solvent composition ratio, liquid-to-solid ratio, and ultrasonic treatment duration. The experimental results showed that, under optimized conditions, i.e., four transducers, 80 mm composite solvent liquid level height, 21∶4 volume ratio of n-hexane to isopropanol, 10 mL∶1 g liquid-to-solid ratio, and 30 min ultrasonic treatment duration, the ash content in polypropylene particles could be reduced to less than 50×10^-6. Orthogonal analysis revealed the following decreasing order of parameter influence on ash removal effectiveness, i.e., ultrasonic treatment duration, solvent composition ratio, composite solvent liquid level height and liquid-to-solid ratio. Particle size distribution measurements before and after washing polypropylene particles clarified the ultrasound-enhanced mechanism:cavitation-induced micro-jets crush the granules and disrupt their dense surface layer, facilitating deeper penetration of the mixed solvent and thus more effective ash removal. These findings provide valuable guidance for the development of ultrasound-enhanced composite solvent washing technologies and equipment for polypropylene ash removal.

关键词

超声强化 / 聚丙烯脱灰分 / 复合溶剂洗涤 / 正八棱柱超声反应器

Key words

ultrasound enhancement / polypropylene ash removal / composite solvent washing / octagonal prism ultrasonic reactor

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基金资助

国家自然科学基金资助项目(22178250)