This indicates that the solvent precipitates out
the non-metallic polymeric material which improves the viscosity.
1-butanol has the best performances to remove these additives.
Ash content value shows the presence of metallic impurities which has been reduced by 46% in the extracted oil. The total base number
of the oil extracted by 1-butanol has been reduced by 72%
showing the removal of basic character constituents (amino compounds,
salts of weak acids, basic salts of polyacidic bases, and salts
of heavy metals