A Preliminary Assessment of the ‘Greenness’ of Halide-Free Ionic Liquids—An MCDA Based Approach

Kranthi Kumar Maniam,Shiladitya Paul

doi:10.3390/pr9091524

Kranthi Kumar Maniam, Shiladitya Paul

Open Access

https://doi.org/10.3390/pr9091524

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Abstract

With the growing interests in non-aqueous media for diversified applications, ionic liquids (ILs) are frequently considered as green solvents. While the environmental, health, and safety assessments of the commercially developed ILs and their ‘greenness’ status are in debate, research focus is shifting towards the application of halide-free ILs for diversified applications. To clarify the situation on their greenness, and to understand if they really possess safe characteristics, we performed an initial assessment of 193 halide free ionic liquids composed of four groups of cations (imidazolium, pyridinium, pyrrodilinium, piperidinum) and 5 groups of anions (acetate, propionate, butyrate, alkanesulfonates, alkylsulfates). The ‘Technique for Order of Preference by Similarity to Ideal Solutions’ (TOPSIS), a multi-criteria decision analysis (MCDA) tool that allows ranking many alternatives is applied by carrying out the assessment against 14 criteria that includes hazard statements, precautionary statements, biodegradability, and toxicity towards different organisms. The ranking results obtained against the set of criteria considered show that the halide free ILs placed between recommended polar solvents: methanol and ethanol can be considered to be safer alternatives in terms of ‘greenness’. The study in this work provides an initial assessment of the halide-free ionic liquids evaluated against 14 criteria in terms of their safety characteristics (“green character”) using the MCDA-TOPSIS approach.

Highlights

Ionic liquids (ILs) are a class of compounds with melting temperatures below 100 ◦ C that are made up of large asymmetric organic cations and either organic or inorganic anions.ionic liquids (ILs) have changed dramatically since their discovery in 1912, and their unusual physiochemical features have attracted a lot of attention in recent decades [1,2]
To understand the greenness of the halide-free ILs (HF-ILs), the greenness of the raw materials that are used for the synthesis are evaluated initially by assessing against 14 criteria, as mentioned in Section 2 and in the Supplementary Information
It is important to note that certain halide containing ILs are used for the synthesis of HF-ILs and as a result, these ILs are assessed along with the raw materials used for the synthesis of HF- ILs

Summary

Introduction

Ionic liquids (ILs) are a class of compounds with melting temperatures below 100 ◦ C that are made up of large asymmetric organic cations and either organic or inorganic anions.ILs have changed dramatically since their discovery in 1912, and their unusual physiochemical features have attracted a lot of attention in recent decades [1,2]. Superior chemical and thermal stability, low flammability, high ionic conductivity, wide electrochemical window, and excellent solvation ability of a wide spectrum of chemicals are examples of such properties. They are commonly used as designer solvents for a wide range of applications, including chemical unit operations and processes, renewables, and electrochemical engineering [3]. Certain complexing agents present in the aqueous plating/deposition solution are subjected to anodic oxidation and tend to form breakdown products during the electrolysis Such products may impact the plating process and pose an environmental hazard [5,6]

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