Promoting sustainability in chemical process design using process modelling, environmental assessment and decision making
Creators: name: Rodriguez Vallejo, Daniel
Publisher: name: Imperial College London
Year: 2021

description: This dissertation explores the integration of life-cycle assessment (LCA), monetization of environmental impacts and process system engineering, aimed to contribute to the adoption of practices and tools supporting decision-makers into the transition towards a more sustainable design of chemical processes. The key contributions of this thesis are twofold: the first dealing with the development of methodologies derived from the powerful combination of process design, decision-making and environmental assessment; the other involving the practical implementation of the proposed approaches to several case studies within the chemical industry. In this regard, several key technical achievements have been acknowledged in this dissertation. Firstly, the combination of LCA, monetization and input-output process models applied to multiple production pathways for OME3-5-an alternative fuel-and benchmarked against conventional diesel fuel. Secondly, the integration of detailed process simulation, monetization and environmental assessment under uncertainty in the design of chemical processes. Here, the production of propylene from methanol (derived from different sources), is used as a case study. Finally, the development of a methodological framework combining data envelopment analysis (DEA)-a mathematical programming tool-and process synthesis aimed to improve the sustainability of chemical processes. We demonstrate the capabilities of this framework through a case study involving the production of a methanol-based fuel from captured CO2 and H2, in comparison with ten other fuels. Our results highlight how important it has become to include holistic sustainability indicators beyond specific impacts in the design of chemical processes. Specifically, accounting for the damage to the end protection areas of human health, ecosystems quality and resources scarcity, not only provide a more realistic picture about the sustainability level associated to chemical processes, but also assistance in identifying the raw materials, emissions, wastes and process stages that contribute the most to the damage of these protection areas. The results also show how relevant it is to account for negative externalities and uncertainty in the economic and environmental assessment of chemical processes, as it can completely change the outcome of the analysis. Furthermore, the conversion of the environmental impacts to a common monetary base and its posterior addition to the economic indicator, enables the comparison between process alternatives based on a single score, which simplifies the analysis and allows decision-makers to estimate the real cost associated to chemical processes. In our methodology combining DEA with process synthesis, given a set of chemical processes, each one characterized by inputs and outputs, the framework discriminates between efficient and inefficient chemical processes according to sustainability indicators, and for those inefficient units, it identifies and estimates realistic targets that in case of being achieved, would allow them to become sustainable. We prevent those targets to be unrealistic by taking into account thermodynamic limitations represented as mass and energy flow constraints. The capabilities of the approaches and tools developed in this dissertation have been extensively explored through a series of case studies aligned with the sustainability development goals defined by the United Nations. These successful implementations have demonstrated the feasibility and practicality of the methods and approaches proposed. They have also illustrated the potentials that, the synergistic combination between process modelling, decision-making and environmental assessment, offers to decision-makers in the transition towards a more sustainable chemical industry.