Analytical Methods
Content of crude oil in each sample was analyzed by referring to GB/T
14488.1-2008 (Chinese National Standard). After each sample (containing
< 10% water) was extracted by using petroleum ether for 4
hours in a Bolton-Williams direct drop extractor, the sample-containing
filter cartridge was taken out and the absorbed solvent was removed by
an evaporator. The first extracted sample was poured out from the filter
cartridge and crushed for 7 minutes. The crushed sample was
quantitatively transferred to the filter cartridge and then extracted
for 4 hours. This step was repeated once. Finally, the sample was
weighed after the complete removal of solvent and crude oil content was
calculated.
Acid value (AV) of each sample was analyzed by referring to GB/T
5530-2005 (Chinese National Standard). Each sample was dissolved in
neutralized solvent and then titrated by using KOH solution.
Peroxide value (PV) of each sample was analyzed by referring to GB/T
5538-2005 (Chinese National Standard). Each sample in acetic isooctane
reacted with potassium iodide. The iodine formed was titrated by using
sodium thiosulfate solution. PV was finally calculated.