A novel methodology for assessing the environmental sustainability of ionic liquids used for CO₂ capture

Abstract

Ionic liquids (ILs) have been proposed as suitable sorbents for CO capture because of their high CO absorption capacity, thermal stability, negligible vapour pressure and physico-chemical tunability. However, the environmental implications of ILs are currently largely unknown because of a lack of data. The issue is further complicated by their complex chemical structures and numerous precursors for which environmental data are scarce or non-existent. In an attempt to address this issue, this paper presents a new methodology for estimating life cycle environmental impacts of novel ILs, with the aim of aiding synthesis and selection of more sustainable CO sorbents. The methodology consists of four main steps: (1) selection of an appropriate IL and synthesis route; (2) construction of a life cycle tree; (3) life cycle assessment; and (4) recommendations for improvements. The application of the methodology is illustrated using trihexyltetradecylphosphonium 1,2,4-triazolide ([P][124Triz]), a promising IL for CO capture currently under development. Following the above steps, the paper demonstrates how the data obtained from laboratory synthesis of the IL can be scaled up to industrial production to estimate life cycle impacts and identify environmental hotspots. In this particular case, the main hotspots are the precursors used in the synthesis of the IL. Comparison of impacts with monoethanolamine (MEA), currently the most widely-used CO sorbent, suggests that [P][124Triz] has much higher impacts than MEA, including global warming potential. However, human toxicity potential is significantly higher for MEA. Therefore, the proposed methodology can be used to optimise the design of ILs and to guide selection of more sustainable CO sorbents. Although the focus is on ILs, the methodology is generic and can be applied to other chemicals under development.

Environmental sustainability of cellulose-supported solid ionic liquids for CO2 capture

“…Furthermore, most ILs have complex chemical structures and numerous precursors are used in their production, for which environmental data are often lacking. To address this issue, a new LCA methodology was developed by Cuéllar-Franca et al 24 which is applied in this study. This methodology helps to fill in data gaps and scale up laboratory data to industrial production, thus aiding the design of ILs under development and identification of more sustainable CO 2 sorbents.…”

“…A life cycle assessment (LCA) methodology has been used for these purposes, developed specifically to guide the sustainable development of novel ILs. 24 This is described in the next section, followed by the results in section 3 and the conclusions and recommendations for future work in section 4.…”

Using Life Cycle Thinking to Assess the Sustainability Benefits of Complex Valorization Pathways for Bauxite Residue

“…For example, electricity is used in all branches, and was therefore assigned to all avoided products, however, boric oxide was only used in branches producing iron (which is assumed to displace iron) and inorganic polymers (which are assumed to displace cement), and was therefore assigned to the 'iron' and 'cement' analyses. LCI data from the ecoinvent 3 database and literature sources [47,48] were then used to assess the environmental impact of each item in this list, with LCIA results for climate change, acidification, freshwater eutrophication and freshwater ecotoxicity calculated.…”

Green solvents in urban mining

“…LCA methods for ILs are hard to implement [14] because of several unknowns but it is clear that their synthesis protocols are not green and ILs are, most of the time, harmful to the environment [15]. ILs non-flammability and non-volatility are not enough to stamp them as green solvents.…”