2001 TSE: NSF/EPA Partnership for Environmental Research: Source-Based Pollution Prevention through Depolymerization of Poly(ethylene terephthalate) with Carbon Dioxide

超临界二氧化碳解聚聚聚对苯二甲酸乙酯的源头污染防治技术描述：本研究代表了一种通过消除聚对苯二甲酸乙酯（PET）生产过程中产生的废弃聚合物来防治污染的新方法。一步法将研究解聚PET和回收纯化的单体和低聚单元进行再聚合。该工艺的主要特点是：1)使用双螺杆挤出机连续产生解聚剂（甲醇或乙二醇）渗透到聚合物中所需的新表面；2)使用超临界二氧化碳（scCO2）作为加工助剂。熔融聚合物在双螺杆挤出机中与scCO2和甲醇或乙二醇的混合物接触。甲醇或乙二醇使PET在通过挤出机时解聚。scCO2使PET塑化，促进甲醇/乙二醇渗透到聚合物中。scCO2还降低了熔体的粘度，提高了链的迁移率，提高了整体反应速率。最后，scCO2从聚合物中提取有机污染物。含有溶解污染物、未反应的乙二醇或甲醇的scCO2，以及产生的一些单体，在挤出机的排气口中除去。该工艺的潜在优点是：(1)消除了从污染物中分离单体和低聚物所需的溶剂和处理步骤；(2)更高的解聚速率；(3)将多道工序，即解聚和萃取，整合为一个步骤。研究的工艺参数包括解聚剂、解聚剂/聚合物比、压力、温度、CO2/聚合物比以及在挤出机中的平均停留时间。更广泛的意义：美国制造工厂每年产生大约1亿磅的PET废物。虽然其中一些废物被用于填充物等低价值产品，但仍有很大一部分无法使用。这项新技术的成功开发将有助于解决严重的废物处理问题，并提高美国PET制造商的竞争力。对PET解聚的基本理解可以为一些技术的扩展提供基础。首先是对消费后废弃物PET的应用，其年处理量约为厂内废弃物的30倍。其次，这种新工艺应该适用于其他阶梯生长聚合物，如聚双酚A碳酸酯和各种尼龙。

Source-Based Pollution Prevention through Depolymerization of Poly (ethylene terephthalate) with Supercritical Carbon DioxideTechnical Description: This research represents a new approach to pollution prevention through elimination of waste polymer that is generated during the manufacture of poly (ethylene terephthalate) (PET). A one-step process will be investigated to depolymerize PET and recover purified monomeric and oligimeric units for repolymerization. The key features of the process are:1) use of a twin-screw extruder to continuously create the fresh surface that is required for a depolymerizing agent (methanol or ethylene glycol) to penetrate into polymer;2) use of supercritical carbon dioxide (scCO2) as a processing aid.Molten polymer is contacted with a mixture of scCO2 and either methanol or ethylene glycol in a twin-screw extruder. The methanol or ethylene glycol causes the PET to depolymerize as it passes through the extruder. The scCO2 plasticizes the PET, facilitating penetration of the methanol/ethylene glycol into the polymer. The scCO2 also reduces the viscosity of the melt and enhances chain mobility, improving the overall reaction rate. Finally, the scCO2 extracts organic contaminants from the polymer. The scCO2 containing dissolved contaminants,unreacted ethylene glycol or methanol, and some of the monomers produced is removed in a vent on the extruder.The potential advantages of this process are:(1) elimination of the solvents and processing steps that otherwise are required for separation of monomers and oligomers from contaminants;(2) much higher depolymerization rates;(3) integration of multiple processes, i.e., depolymerization and extraction, into a single step.The process parameters will be studied include the depolymerizing gent, the depolymerizing agent/polymer ratio, pressure, temperature, CO2/polymer ratio, and average residence time in the extruder.Broader Significance: Approximately 100 million pounds of waste PET is generated annually in U.S. manufacturing facilities. While some of this waste is used in low-value products such as fillers, a large portion remains unusable. Successful development of this new technology could help to solve a serious waste disposal problem and increase the competitiveness of U.S. PET manufacturers. A fundamental understanding of the depolymerization of PET could provide a basis for several technology extensions. First is the application to post-consumer waste PET, the annual volume of which is about 30 times the volume of in-plant waste. Second, this new process should be applicable to other step-growth polymers such as poly (bisphenol A carbonate) and various nylons.