Chemical and Biological Engineering, Northwestern University, Evanston, IL, USA.
Institute of Sustainability and Energy at Northwestern, Northwestern University, Evanston, IL, USA.
Waste Manag. 2022 Nov;153:81-88. doi: 10.1016/j.wasman.2022.08.015. Epub 2022 Aug 30.
Pyrolysis is a leading technology to convert non-recyclable plastic waste to fuels or chemicals. As interest in the circular economy grows, the latter option has seemingly become more attractive. Once waste plastic is pyrolyzed to, for example, naphtha, however, additional steps are required to produce a polymer product. These steps consume additional energy and water and emit greenhouse gases (GHG). It is unclear whether this more circular option of non-recyclable plastics to virgin plastics offers environmental benefits, compared to their conversion to fuels. We therefore examine whether it is possible to determine the best use of pyrolyzing non-recyclable plastic - fuels or chemicals (low-density polyethylene (LDPE) as product)- from a life cycle perspective. We use recently published life cycle assessments of non-recycled plastics pyrolysis and consider two functional units: per unit mass of non-recyclable plastics and per unit product - MJ of naphtha or kg of LDPE. In the U.S., on a cradle-to-gate, per unit mass waste basis, producing fuel is lower-emitting than producing LDPE from pyrolysis. The opposite is true in the EU. But expanding the system boundary to the grave results in LDPE as the lower-emitting product in both regions. Naphtha and LDPE produced from non-recyclable plastics are less GHG-intensive than conventional routes to these products. Fossil fuel and water consumption and waste generation are all lower in the P2F case. Our results highlight that prioritization of P2P and P2F may depend on regional characteristics such as conventional waste management techniques and water scarcity.
热解是将不可回收塑料废物转化为燃料或化学品的主要技术。随着循环经济兴趣的增长，后者似乎变得更具吸引力。然而，一旦废塑料热解为例如石脑油，就需要额外的步骤来生产聚合物产品。这些步骤消耗额外的能源和水，并排放温室气体（GHG）。目前尚不清楚与将不可回收塑料转化为燃料相比，不可回收塑料转化为原生塑料的这种更循环的选择是否具有环境效益。因此，我们从生命周期的角度研究了不可回收塑料热解为燃料或化学品（低密度聚乙烯（LDPE）为产品）的最佳用途是否可行。我们使用最近发表的不可回收塑料热解生命周期评估，并考虑了两个功能单位：每单位质量的不可回收塑料和每单位产品 - 每单位质量的石脑油或千克 LDPE。在美国，基于摇篮到大门，每单位质量的废物基础上，生产燃料的排放量低于从热解生产 LDPE 的排放量。在欧盟则相反。但是，将系统边界扩展到坟墓会导致 LDPE 在两个地区都是排放量较低的产品。不可回收塑料生产的石脑油和 LDPE 的温室气体排放强度低于这些产品的传统路线。在 P2F 情况下，化石燃料和水的消耗以及废物的产生都较低。我们的结果表明，P2P 和 P2F 的优先级可能取决于区域特征，例如常规废物管理技术和水资源短缺。
