Evaluating the profitability and global warming potential of manufacturing styrene-butadiene rubber with chemicals synthesised from bulk waste plastic and CO2 emissions

Abstract

Conventional mechanical recycling of waste plastics is limited in its scale and ability to deliver quality materials to reproduce plastic products like tyres. While plastic waste is often combusted as fuel for energy production, other thermochemical processes such as gasification, combined with methanol synthesis, and methanol to olefins (MTO) or methanol-to-aromatics (MTA) technologies, may offer a better solution to reproduce plastic products from olefin and aromatic chemicals. To explore these possibilities, this study focused on ascertaining the economic feasibility and carbon footprint of a refinery's large scale conversion of waste plastic methanol (MeOH) into ethylene (ET) via MTO, its capture and conversion of on-site CO2 emissions for the production of benzene (plan A), the outsourcing of bio-benzene produced via the wood methanol-to-aromatics (MTA) process (plan B), and the conversion of benzene and ET into styrene-butadiene rubber (SBR). The material and energy inputs and outputs for these chemicals processes, were simulated in the bio-chemical engineering software SuperPro Designer (SPD). A Microsoft Excel Green SBR Refinery (MSE-Ref._Green-SBR) template tool file was designed and uploaded with the simulation's process flows, financial data, and global warming potential (GWP) factors in kg CO2eq. to complete the pre-scripted formulas for techno-economic analysis (TEA) and life cycle analysis (LCA). The results concluded that the SBR refinery could achieve maximum profitability if it allocates roughly 25.0 % of its plastic MeOH for SBR production, with the remainder sold as ET on the market, and converts a maximum of 25.0 % of its CO2 emissions for SBR production. However, profitability depends on a financial grant covering at least 60.0 % of the total fixed capital investment (TFCI) cost. Switching to plan B reduced the grant needed by 30.0 %. The SBR products in both plan A and plan B had a lower CO2eq. footprint compared to other examples sampled, with the SBR product in plan A offering a slightly better carbon neutrality at 0.38 kg CO2eq./kgSBR, than plan B at 0.39 kg CO2eq./kgSBR. While the waste plastic MeOH feedstock accounted for the highest operational cost and most of the plant's carbon emissions (41.1 %), with future technical developments the cost and carbon footprint of upcycling plastic MeOH into SBR could be improved, or with bio-MeOH. By granting the public free access to the resources, data, and tools (e.g., MSE-Ref._Green-SBR file) utilised, this study's objective is to provide a template and methodology for the reader to modify or update the data, assumptions, and calculations it contains for their own academic or professional purposes. Thereby helping promote research and development in plastic waste and CO2 upcycling.