Recycling of Plastics in the United States: Plastic Material Flows and Polyethylene Terephthalate (PET) Recycling Processes

As efforts are made toward establishing a circular economy that engages in activities that maintain resources at their highest values for as long as possible, an important aspect is understanding the systems which allow recycling to occur. In this article a common plastic, polyethylene terephthalate, i.e., PET or plastic #1, has been studied because it is recycled at relatively high rates in the U.S. as compared to other plastics. A material flow analysis is described for PET resin showing materials collected, reclaimed for flake, and converted into items with recycled content. Imports/exports, reclaimer residue, and disposal with mismanaged waste are all shown for U.S. flows of PET. Barriers to recycling PET exist in the collecting, sorting, reclaiming, and converting steps, and this article describes them, offers some solutions, and suggests some research that chemists and engineers could focus on to improve the systems. This effort also models sorting at material recovery facilities (MRF) and reclaimers, with detailed descriptions of the material streams involved, to characterize the resource use and emissions from these operations that are key processes in the recycling system. Example results include greenhouse gas intensities of 8.58 kg CO2 equiv per ton of MRF feed and 103.7 kg CO2 equiv per ton of reclaimer PET bale feed. The results can be used in system analyses for various scenarios and as inputs in economic input-output and life cycle assessments.随着全球致力于构建循环经济，通过各类活动尽可能长久地维持资源的最高价值，厘清支撑回收利用的系统机制便成为一项关键议题。本文聚焦于常见塑料聚对苯二甲酸乙二酯（polyethylene terephthalate，简称PET，即塑料#1）的相关研究：相较于其他塑料品类，美国境内PET的回收利用率相对较高。本文针对PET树脂开展物质流分析，涵盖物料收集、造粒回收以及加工为含回收成分制品的全流程，并完整呈现了美国PET物料流中的进出口、回收残渣以及未规范处置的废弃物情况。PET回收在收集、分拣、再生加工与制品转化各环节均存在瓶颈，本文针对这些瓶颈展开分析并提出应对方案，同时建议化学家与工程师可聚焦相关研究方向以优化回收系统。本研究同时针对物料回收设施（material recovery facilities，MRF）与再生加工厂的分拣环节建立模型，详细阐述所涉及的物料流，以表征回收系统核心环节——上述作业的资源消耗与碳排放情况。示例结果包括：每处理1吨物料回收设施进料的温室气体强度为8.58千克二氧化碳当量，每处理1吨再生厂PET打包进料的温室气体强度为103.7千克二氧化碳当量。本研究结果可用于多场景下的系统分析，亦可作为经济投入产出分析与生命周期评价的输入参数。