Developing circularity, renewability and efficiency indicators for sustainable resource management : propanol production as a showcase

Resource efficiency analysis is an important tool in the chemical sector to evaluate the performance of new process concepts. However, such analysis does not account for the renewability and circularity of resources. Therefore, a resource efficiency and use analysis, including those two aspects, is proposed in this paper. A renewability indicator and recovery indicator were calculated as a measure for renewability and circularity, respectively. In addition, the resource efficiency was determined at different levels. At the life cycle level, the cumulative exergy extraction of the natural environment method was applied and the cumulative degree of perfection, including waste-as-resources, was calculated. Exergy calculations were used to determine the exer-getic efficiency at process chain and plant level and to identify inefficiencies. A new propanol production concept, using biogas (scenario BG), marginal gas (scenario MG) and associated gas (scenario AG), was selected as a case study. Exergetic efficiencies are high at the individual process level (between 90 and 100%). However, the preceding biogas production in scenario BG is inefficient (exergetic efficiency of 12%). The exergetic effi-ciency at the process chain level amounts to 45-68% due to the high exergy content of the recycling stream and the low conversion of methane into propanol per pass. Scenario AG has the highest cumulative degree of perfection (including waste-as-resources) compared to the other scenarios (28% against 6 and 14% in scenario BG and MG). In contrast, when looking at both renewability, circularity and efficiency, scenario BG is identified as the most promising scenario. Thus, this study shows that it is important to include those three aspects in resource efficiency analysis. Finally, implementing renewable electricity production and heat integration in the process concept may increase the resource efficiency.