Carbon footprint of CO2-based polypropylene via methanol-to-olefins route

Plastic is one of the most widely used materials today owing to its versatility. However, the rapidly growing plastics industry is largely dependent on fossil fuels and the source of ever-increasing greenhouse gas (GHG) emissions. Decoupling the feedstock from crude oil and natural gas and shifting to renewable sources of carbon is an impactful strategy to reduce these emissions. Power-to-X technology provides routes to convert carbon dioxide (CO2) into renewable plastics. In this thesis, the carbon footprint of CO2-based polypropylene is calculated to provide insight to the following questions: i) does CO2-based polypropylene store more carbon than is emitted during its production; ii) how CO2-based and fossil-based polypropylene compare with respect to global warming potential; and iii) what are the GHG hotspots of CO2-based production? Life cycle assessment methodology is applied in the calculation, which is carried out using Gabi software. CO2-based polypropylene is a net carbon sink at -0.64 kg CO2 equivalents (CO2e) per kg of the polymer and generates 2.27 kg CO2e less emissions than petrochemical polypro¬pylene. Electrolysis of water is identified as the GHG hotspot of this product system due to its high electricity consumption, which is currently a hurdle for power-to-X technology. The results show that the carbon negative production of polyolefins is possible with the current energy mix of Finland, and that CO2-based polypropylene can act as a carbon sink in long-term applications.