Development and lifecycle assessment of various low- and high-density polyethylene production processes based on CO2 capture and utilization

Abstract

This work focuses on the design and analysis of innovative environmentally friendly pathways to produce low-density polyethylene and high-density polyethylene, as the main feedstock of petrochemical industries, based on CO2 capture and utilization. For each polymer, the process development and simulation of the proposed pathways are performed using Aspen Plus. Each pathway includes the following units: CO2 capture from flue gas, hydrogen production via electrolysis of water, methanol production, olefin production, and polymerization of ethylene. Moreover, the greenhouse gas emissions of the proposed pathways are compared to those of the conventional method i.e., steam cracking. The midpoint and endpoint lifecycle assessment of each pathway are conducted using TRACI 2.1 and ReCiPe Endpoint (H, A) lifecycle impact assessment methods in the OpenLCA software, respectively, for various geographical locations, electricity sources and assessment scenarios for the incorporation of the by-products. The lifecycle assessment results show that the new pathway is an environmentally attractive option, particularly in regions where renewable (low-carbon) electricity is more prominent, such as Quebec and Ontario provinces in Canada. In such regions, negative CO2 emissions, as low as −6.1 kg CO2eq/kg polymer, can be achieved. However, in locations where coal or natural gas are the main sources of electricity generation, such as Alberta, lifecycle emissions increase to 20 times the emissions of the conventional method. Furthermore, the impact of incorporating alternative methanol production processes is evaluated. Results show that using the tri-reforming of methane as an effective syngas production technology from CO2 and natural gas can reduce the lifecycle greenhouse gas emissions by up to 94% and 62%, compared to the conventional high- and low-density polyethylene production pathways.