Recent studies focusing on greenhouse gas emission reduction strategies indicate that material recycling has a significant impact on energy consumption and greenhouse gas emissions. The question arises how these effects can be quantified. Material recycling is not at all or insufficiently considered in energy system models, which are used today to derive climate gas mitigation strategies. To better assess and quantify the effects one option would be to couple energy system models and material flow models. The barriers and challenges of a successful coupling are addressed in this article. The greatest obstacles are diverging temporal horizons, the mismatching of system boundaries, data quality and availability, and the underrepresentation of industrial processes. A coupled model would enable access to more robust and significant results, a response to a greater variety of research questions and useful analyses. Further to this, collaborative models developed jointly by the energy system and material analysis communities are required for more cohesive and interdisciplinary assessments.

Within the European Green Deal, the European industry is summoned to transform towards a green and circular economy to reduce CO₂ -emissions and reach climate goals. Special focus is on the chemical industry to boost recycling processes for plastics, exploit resource efficiency potentials, and switch to a completely renewable feedstock (defossilization). Despite common understanding that drastic changes have to take place it is yet unknown how the industrial transformation should be accomplished. This work explains how a cost-optimal defossilization of the chemical industry in the context of national greenhouse gas (GHG) mitigation strategies look like. The central part of this investigation is based on a national energy system model to optimize the future energy system design of Germany , as a case study for a highly industrialized country. A replacement of fossil-based feedstocks by renewable feedstocks leads to a significant increase in hydrogen demand by +40% compared to a reference scenario. The resulting demand of hydrogen-based energy carriers, including the demand for renewable raw materials, must be produced domestically or imported. This leads to cumulative additional costs of the transformation that are 32% higher than those of a reference scenario without defossilization of the industry. Fischer-Tropsch synthesis and the methanol-to-olefins route can be identified as key technologies for the defossilization of the chemical industry.