Miscibility, corrosion and environmental properties of six hexanoate- and sulfonate-based protic ionic liquids.

In this work, six different types of protic ionic liquids (PILs) have been studied. For all these PILs, the bacteria toxicity and environmental biodegradability have been investigated, as well as their corrosive behavior and miscibility in different types of lubricating base oils. The PILs studied showed poor to moderate biodegradability (BOD 5 /COD from 0.072 ± 0.002 to 0.18 ± 0.01) and slight toxicity (TU values between from 1.18 ± 0.04 and 2.7 ± 0.1). However, these environmental properties are much better than those obtained for the reference lubricant additive used in industry (ZDDP). In addition, five of the PILs did not show corrosive activity on steel. Only one of the PILs showed some miscibility in an ester as a base oil and the rest of the mixtures were highly unstable. • The hexanoate-based PILs have higher biodegradability than the sulfonate-based ones. • These PILs show mild toxicity and are environmentally better than ZDDP. • These protic ionic liquids, with the exception of PIL-6, are not corrosive. • With the exception of PIL-3, the rest of PILs were immiscible in different base oils. • Protic ionic liquids could partially replace ZDDP as lubricant additive. [ABSTRACT FROM AUTHOR]