2.2. Flocculation, solvent extraction and filtration process
Several weighed portions of potassium hydroxide (KOH) ranging
from 1.0 to 3.0 g were carefully added to a specified volume
of solvent in a beaker. The mixture was strongly mixed until all
the KOH dissolved into the solvent solution and was ready for
solvent extraction. Then, the used oil sample was weighed (Woil)
and mixed with the solvent/KOH mixture in a beaker with solvent
to oil ratios of 1:1–3:1 for 15 min under continuous stirring
(stirring speed set at 350–400 rpm). This is to ensure perfect
mixing and at the same time preventing any losses of oil to
the sludge. After strong agitation, it was then left under a controlled
temperature of 30 C for 24 h to allow extraction–flocculation.
After that, solvent-oil solution was separated from
sludge by filtration. The sludge was dispersed twice with the
same solvent to extract any remaining oil. The sludge was then
dried till constant weight at 105 C (WDry). The washing solvent
was mixed with solvent–oil solution. The solvent was recovered
by vacuum distillation. The percent sludge removal represents
the quality of dry waste oil (additives and impurities) removed
from the used oil after mixing with solvent according to the
experiment above. The percentage sludge removal (PSR) can be
calculated as shown: