Circular use of plastics-transformation of existing petrochemical clusters into thermochemical recycling plants with 100% plastics recovery

Abstract

Plastics represent a serious waste-handling problem, with only 10% of the plastic waste (PW) generated world-wide being recycled. The remainder follows a linear economy model, involving disposal or incineration. Thermochemical recycling provides an opportunity to close the material cycle, and this work shows how this can be achieved using the existing petrochemical infrastructure. The transformation of a generic petrochemical cluster based on virgin fossil feedstocks into a cluster that is based on PW has the following proposed sequence: (1) the feedstock is partially replaced (45% on carbon basis) by PW; (2) the feedstock is totally replaced by PW; (3) the process undergoes electrification; and (4) oxy-combustion and carbon capture and storage are introduced to achieve 100% carbon recovery in the form of monomers or permanent storage. An alternative transformation pathway that includes the introduction of biomass is also considered. The energy and carbon balances of the proposed implementation steps are resolved, and cost estimates of the savings related to the feedstock and required investments are presented. The main conclusion drawn is that switching the feedstock from virgin fossil fuels to PW (Implementation steps 1 and 2) confers economic advantages. However, the subsequent transformation steps (Implementation steps 3 and 4) can only be justified if a value is assigned to the environmental benefits, e.g., CO2 savings, increased share of biogenic carbon in plastic products, increasing recycling quotas, and/or the potential of the process to compensate for the intermittency of renewable power. It is also discussed how utilisation of the diverse compositions of PW streams by additional processes can meet the other demands of a chemical cluster.