Modelling and sustainability assessment of industrial ionic liquid production and applications using life cycle thinking

Abstract

The main goal of this dissertation is to build on the current state-of-the-art research regarding ionic liquid (IL) sustainability assessment to help answer the research question, "how sustainable are ILs as alternatives to conventional technologies?" This is accomplished by developing a systematic computer-aided framework that integrates life cycle assessment (LCA) and life cycle costing (LCC) with process modelling and simulation for the consistent and complete economic and environmental assessment of ILs. The work further explores the use of monetization and an advanced framework that couples uncertainty analysis and global sensitivity analysis to enhance decision-making. The main novelties of the thesis are the methodological components and the case studies, in which the production of different ILs are evaluated in the context of relevant applications including their use. This thesis has contributed to the existing body of research by developing the following aspects. First, an integrated framework that combines LCA, LCC with process modelling and simulation was applied to evaluate the production of 1-butyl-3-methylimidazolium tetrafluoroborate using two synthesis routes and compare them with two conventional solvents in terms of their application in fuel desulfurization. Second, the developed framework was enhanced by incorporating factors of monetization, and this was applied to a case study involving hydrogen sulfate-based ILs to quantify their externalities and compare the true cost of these ILs with that of conventional solvents in biomass pretreatment applications. Finally, LCA uncertainty and global sensitivity analysis (GSA) was included in the framework to improve uncertainty analysis by accounting for process model uncertainties and identifying key parameters in non-linear systems, which was demonstrated in a case study involving the production of dialkylimidazolium ILs. The results show that the use of data from detailed process models, as highlighted in the holistic framework, makes a big difference compared to the use of simplified methods. Unlike short-cut methods, the framework accounts for process efficiency, emissions, and waste and covers a wide range of environmental impact categories for a more consistent and complete assessment. Additionally, coupling monetization with LCA can improve the assessment by turning a multi-objective problem into a single-objective problem, and hence, facilitating decision-making. The environmental externalities quantified through monetization reveal hidden costs that are usually overlooked when conducting a conventional economic assessment. Moreover, the importance of including foreground uncertainties in the uncertainty analysis was demonstrated by the results obtained from applying uncertainty-GSA analysis. In particular, foreground uncertainties can significantly overlap with the background uncertainties because of the multiplicative effect, which impacts decision-making. Furthermore, using GSA can help correctly identify uncertain parameters by accounting for collaborative effects in non-linear systems. Finally, case studies were used to test the efficiency of the developed framework and its methodological components. The contributions of this thesis build on the state-of-the-art economic assessment and LCA for ILs and support research on evaluating the sustainability of ILs and similar novel chemicals. This in turn will help us better understand the potential of such chemicals in terms of their sustainability performance as decision-making in most industries today is driven by policies pursuing sustainable development.