Environmental properties of phosphonium, imidazolium and ammonium cation-based ionic liquids as potential lubricant additives

Abstract

This research compares the environmental properties (bacterial toxicity and biodegradability) of 12 ionic liquids-ILs-(7 phosphonium, 2 imidazolium and 3 ammonium cation-based ones), potentially applicable as lubricant additive, with two types of the traditional lubricant additive ZDDP. Aquatic toxicity was determined by means of Vibrio fischeri and Escherichia coli bacteria, while biodegradability was evaluated through biological oxygen demand (BOD 5) and chemical oxygen demand (COD) measurements. Regarding toxicity results, [P 4442 ][DEP] was the least toxic IL (acute 3 according to GHS) for both bacteria, whereas ZDDP fell into the acute 1 category (very toxic). All samples tested turned out to be poorly biodegradable, showing BOD 5 /COD values below 0.1. Two ILs showed better combined tribological and environmental properties than ZDDP.

Physicochemical, traction and tribofilm formation properties of three octanoate-, laurate- and palmitate-anion based ionic liquids

“…Considering TU data, all these three [N8881] cation-based ILs can be classified as toxic (TU values from 1 to 10). It should be noted that, although it is included in the same category, the [N8881][TFSI] IL showed a value of TU around 4 times higher than those obtained for the ILs here studied [28]. A C C E P T E D M A N U S C R I P T a EC50 classification for aquatic life: non-toxic: EC50 > 100 mg/L; harmful (acute 3): EC50: 10 -100 mg/L; toxic (acute 2): EC50: 1 -10 mg/L; and very toxic (acute 1): EC50 < 1 mg/L.…”

“…The values of toxicity, expressed as EC50, for the ILs tested are shown in Table 5. Various authors have reported that the cationic part is the one which principally controlled toxicity [28,43,44]. Nevertheless, on viewing these data, it should be noted that the anionic part also had a considerable effect on toxicity.…”

“…corrosion products, reduce toxicity and improve biodegradability. Despite the importance of these issues, there are only few works focused on the environmental properties of ionic liquids with lubricant potential [26][27][28]. Some ionic liquids with potential improved environmental properties were obtained via a metathesis reaction using fatty acids as anion precursors, but environmental properties of them were not reported [29][30].…”

“…The aqueous solutions were prepared according to Oulego et al [28]. The minority phase (additive) was discarded and the main phase (aqueous) was employed to prepare the stock solutions used in the measurements of toxicity and biodegradability.…”

“…These concentrations were obtained based on the equation 1 found in Oulego et al [28]. by the dichromate methodology at 600 nm, using a Hach DR/2500 spectrophotometer [31].…”