A Life Cycle Assessment (LCA) of methanol production via gasification of mixed plastic waste

One of the most promising technologies for plastic waste valorization in the frame of a circular economy is gasification. Gasification of plastic waste allows to produce a syngas which can be further processed to produce chemicals. In this thesis, a plastic waste-to-methanol route is investigated. After evaluating the plastic waste mass potential available in the Netherlands for gasification through Material Flow Analysis, a waste-to-methanol process is modeled based on literature review and Aspen Plus simulations. Finally, a Life Cycle Assessment (LCA) is performed with the aid of the software SimaPro and specifically focusing on global warming potential (GWP) and cumulative fossil energy demand (CFED). The obtained results are compared with the environmental performance of a traditional natural gas-to-methanol route. This case study shows that 270 kt of plastic waste would be available for gasification in the Netherlands in an optimistic scenario. The modeling of the plastic waste-to-methanol process proves the feasibility of synthesizing pure methanol from a waste-sourced syngas. The results from the LCA indicate that the plastic waste-to-methanol process is associated to a global warming potential equal to almost 3.75 tonnes of CO2 equivalent and responsible for the consumption of about 37.41 GJ of primary energy derived from fossil resources. The waste-to-methanol process is responsible for six times greater GHG emissions than methanol produced from steam reforming of natural gas, and it consumes an additional 11.0% of primary fossil energy. Different sensitivity analyses were carried out to test the robustness of the results. All scenarios confirmed a higher GWP associated to the waste-to-methanol process, which therefore has, for the foreseeable future, rather limited practical relevance since there is no environmental convenience relative to a standard fossil-based methanol production.