Abstract
In this study, the recovery of base oils from waste
lithium based lubricating grease was investigated using a novel
combination of thermal degradation in an aqueous caustic solution
and solvent extraction. Lubricating grease is an important resource
that cannot be disposed of randomly due to the presence of pollutants.
In response to economic challenges and environmental protection,
there is a growing trend to regenerate and reuse waste lubricant.
Waste grease was initially dissolved in a 20 w/w% KOH solution at
80oC while being agitated for a period of 15 min. Two distinct layers
were observed after 10 min of settling time. The top layer being of
dark brown oil and the bottom layer was a heterogeneous mixture.
The two layers were separated by decantation. The bottom layer was
cooled to 45oC followed by slow addition of n-hexane while agitating
to prevent the settling of solids. Two distinct layers were also formed,
the top homogeneous mixture of light brown oil–toluene mixture and
the bottom sludge layer. This research has further optimized the
process by studying the effect of KOH concentration to enhance
flocculation and recovery of oil. Oil recovery increased from 5% to
30%. The recovery also increased with an increase of solvent-togrease
ratio up to 1:6. A solvent recovery of 82.6% to 88% by mass
was obtained through fractional distillation. The overall oil recovery
from waste grease using the combined extraction processes was 75
w/w% .