Utilising CO2 as a feedstock for chemicals and fuels could help mitigate climate change and reduce dependence on fossil fuels.

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.

Biogas from anaerobic digestion of sewage sludge is a renewable resource with high energy content, which is composed mainly of CH 4 (40−75 vol %) and CO 2 (15−60 vol %). Other components, such as water (H 2 O, 5−10 vol %) and trace amounts of hydrogen sulfide and siloxanes, can also be present. A CH 4 -rich stream can be produced by removing the CO 2 and other impurities so that the upgraded biomethane can be injected into the natural gas grid or used as a vehicle fuel. The main objective of this paper is to assess the technical and economic performance of biogas upgrading processes using ionic liquids that physically absorb CO 2 . The simulation methodology is based on the COSMO-SAC model as implemented in Aspen Plus. Three different ionic liquids, namely, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, 1-hexyl-3methylimidazoliumbis[(trifluoromethyl)sulfonyl]imide, and trihexyl(tetradecyl)phosphonium bis[(trifluoromethyl)sulfonyl]imide, are considered for CO 2 capture in a pressure-swing regenerative absorption process. The simulation software Aspen Plus and Aspen Process Economic Analyzer is used to account for mass and energy balances as well as equipment cost. In all cases, the biogas upgrading plant consists of a multistage compressor for biogas compression, a packed absorption column for CO 2 absorption, a flash evaporator for solvent regeneration, a centrifugal pump for solvent recirculation, a preabsorber solvent cooler, and a gas turbine for electricity recovery. The evaluated processes are compared in terms of energy efficiency, capital investment, and biomethane production costs. The overall plant efficiency ranges from 71 to 86%, and the biomethane production cost ranges from $9.18−11.32 per GJ (LHV). A sensitivity analysis is also performed to determine how several technical and economic parameters affect the biomethane production costs. The results of this study show that the simulation methodology developed can predict plant efficiencies and production costs of large scale CO 2 capture processes using ionic liquids without having to rely on gas solubility experimental data.

Purpose A circular (bio)economy is sustained through use of secondary raw material and biomass feedstock. In life cycle assessment (LCA), the approach applied to address the impact of these feedstocks is often unclear, in respect to both handling of the recycled content and End-of-Life recyclability and disposal. Further, the modelling approach adopted to account for land use change (LUC) and biogenic C effects is crucial to defining the impact of biobased commodities on global warming. Method We depart from state-of-the-art approaches proposed in literature and apply them to the case of non-biodegradable plastic products manufactured from alternative feedstock, focusing on selected polymers that can be made entirely from secondary raw material or biomass. We focus on global warming and the differences incurred by recycled content, recyclability, LUC, and carbon dynamics (effects of delayed emission of fossil C and temporary storage of biogenic C). To address the recycled content and recyclability, three formulas recently proposed are compared and discussed. Temporary storage of biogenic C is handled applying methods for dynamic accounting. LUC impacts are addressed by applying and comparing a biophysical, global equilibrium and a normative-based approach. These methods are applied to two case studies (rigid plastic for packaging and automotive applications) involving eight polymers. Results and discussion Drawing upon the results, secondary raw material is the feedstock with the lowest global warming impact overall. The results for biobased polymers, while promising in some cases (polybutylene succinate), are significantly affected by the formulas proposed to handle the recycled content and recyclability. We observe that some of the proposed formulas in their current form do not fully capture the effects associated with the biogenic nature of the material when this undergoes recycling and substitutes fossil materials. Furthermore, the way in which the recycled content is modelled is important for wastes already in-use. LUC factors derived with models providing a combined direct and indirect impact contribute with 15–30% of the overall life cycle impact, which in magnitude is comparable to the savings from temporary storage of biogenic C, when included. Conclusion End-of-Life formulas can be improved by addition of corrective terms accounting for the relative difference in disposal impacts between the recycled and market-substituted product. This affects the assessment of biobased materials. Inclusion of LUCs effects using economic/biophysical models in addition to (direct) LUC already embedded in commercial datasets may result in double-counting and should be done carefully. Dynamic assessment allows for detailed modelling of the carbon cycle, providing useful insights into the impact associated with biogenic C storage.

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CO2 capture and storage is widely anticipated to play a key role in combatting climate change, however the solvents proposed for use have embedded environmental concerns.

The life cycle environmental impacts of cellulose-supported solid ionic liquids are estimated in comparison with a range of other CO2 sorbents.