Sustainable Design and Synthesis of Waste High-Density Polyethylene Recycling Process

Abstract

Global optimization in sustainable waste high-density polyethylene (HDPE) chemical recycling process is addressed under economic and environmental criteria. In this work, by far the most comprehensive superstructure of the HDPE recycling process with 867 processing routes is developed to produce valuable products from waste HDPE. Using the methodologies of life cycle assessment and techno-economic assessment, the superstructure optimization problem is then formulated as a multi-objective mixed-integer nonlinear fractional programming (MINFP) problem to address the sustainable waste HDPE recycling process with maximum unit net present value (NPV) and minimum levelized ReCiPe end-point score. A tailored parametric algorithm is utilized to efficiently convexify the fractional objective functions. With the help of the piecewise linearization method, nonlinear economic constraints can be linearized and effectively solved. This research proposes to use the ‘e-constraints’ method to obtain the Pareto-optimal curve. Results show that the optimal unit NPV ranges from -65 USD/t HDPE to 170 USD/t HDPE, and the levelized ReCiPe point of the most environmentally friendly design is 0.6 times of that of the most economically competitive design.