Ionic liquid long-term stability assessment and its contribution to toxicity and biodegradation study of untreated and altered ionic liquids

Abstract

In contrast to well understood degradation mechanisms in conventional lubricants generally promoted by thermo-oxidative stress, the degradation of ionic liquids is widely unknown although they are considered as promising novel types of lubricants. Hence, the ionic liquid long-term stability has been evaluated by small scale artificial alteration experiments under thermo-oxidative conditions. The ionic liquid selection was based on non-functionalized and functionalized ammonium type cations with three different counter anions. The identification of ionic liquid degradation products accomplished by high end mass spectrometric methods, namely time-of-flight/reflectron time-of-flight mass spectrometry and linear quadrupole trap-orbitrap-mass spectrometry, revealed that ionic liquids which were composed of functionalized cation moieties were prone to degradation. Furthermore, the amounts of the most abundant degradation product formed under various artificial alteration conditions have been quantified by ultra high pressure liquid chromatography coupled to electrospray ionization linear quadrupole ion trap orbitrap mass spectrometry, suggesting that the ionic liquid degradation preferably takes place at higher temperatures after a longer period of time. The proposed degradation mechanism requires the presence of nucleophilic species such as methanesulphonate anion. The (eco)toxicological impact of the selected ionic liquids have been evaluated by comprehensive toxicity studies and biodegradation experiments. As the evaluation of selected ionic liquids revealed contrary assessments from stability and (eco)toxicological studies, the need for mutual and complementary consideration of the ionic liquids for a successful implementation of ionic liquid lubricants has been disclosed.

Persistence of selected ammonium- and phosphonium-based ionic liquids in urban park soil microcosms

“…These findings from a long-term soil microcosm experiment are not in disagreement with findings from biodegradation tests performed in aquatic systems for structurally similar ILs. In a manometric respiratory test with activated sludge, Pisarova et al (2012) showed that one (i.e., (2-hydroxyethyl)-trimethylammonium methanesulphonate) out of three ammonium-based ILs reached 74% of ultimate biodegradation within 28 days. The two other ILs (i.e., tributyl-methylammonium methanesulphonate and butyltrimethylammonium methanesulphonate) reached 7 and 4%, respectively.…”

The ecotoxicity and tribological properties of choline monocarboxylate ionic liquid lubricants

“…Among the [Ch][MA] ILs, the [Ch][Ethylhex] exhibits the largest toxicity, with, however, low LC 50 value of 6590 mg/L and EC 50 of 1670 mg/L, as compared with 116 and 34 mg/L, respectively, for L‐B104. This indicates that the toxicity of L‐B104 is much higher than that of the as‐synthesized ILs, which can be ascribed to the presence of the imidazolium ring and the halogen containing anion . According to the acute toxicity assessment level HR, [Ch][MA] ILs are graded as “relatively harmless.”…”

Ionic liquid biodegradability depends on specific wastewater microbial consortia

“…While they are a useful starting point, standard biodegradability assays preclude many industrial and environmental conditions that will determine chemical degradability beyond microbial community composition. For example, IL stability can become altered through wear at high temperatures when used as lubricants (Pisarova et al, 2012;Stolte et al, 2012), or through hydrolysis as a result of altered pH and temperature , which may alter, or possibly promote, subsequent biodegradability by microorganisms and their potential toxicity. Once in the aeration tank, presence or absence of nutrients and cofactors , adaptation of aeration tank microbial communities to operating conditions (e.g.…”