DESULFURIZATION OF CRUDE OIL USING IMIDAZOLIUM-BASED-PHOSPHATE IONIC LIQUIDS

Because of the dramatic environmental impact of sulphur oxides contained in engines
emissions, sulphur content specification in fuels are becoming more and more
stringent worldwide. In the petroleum refining industry, hydrodesulphurization (HDS)
is the conventional process to reduce the sulphur levels of the fuels. However, HDS is
cost consuming, besides requiring high temperature and high hydrogen pressure in
order to eliminate the aliphatic and alicyclic sulphur compounds. Refractory sulphur
compounds such as dibenzothiophene, methyl dibenzothiophene and 4,6-methyl
dibenzothiophene are less reactive to this process. Due to this reason, alternative
sulphur removal techniques are being explored. In the past years, due to its unique
properties both as extractant and also as catalyst, ionic liquids have gained increasing
interest. In this project, eight imidazolium-based-phosphate ionic liquids were
successfully synthesized, namely, 1-methyl-3-methylimidazolium dimethylphosphate
(MMIM[DMP]), 1-methyl-3-ethylimidazolium diethylphosphate (EMIM[DEP]), 1-
methyl-3-butyllimidazolium dibuylphosphate (BMIM[DBP]), 1-ethyl-3-
methylimidazolium dimethylphosphate (EMIM[DMP]), 1-ethyl-3-ethylimidazolium
diethylphosphate (EEIM[DEP]), 1-butyl-3-methylimidazolium dimethylphosphate
(BMIM[DMP]), 1-butyl-3-ethylimidazolium diethylphosphate (BEIM[DEP]), 1-
butyl-3-butylimidazolium dibutylphosphate (BBIM[DBP]). These ionic liquids were
characterized using Differential Scanning Calorimeter (DSC), CHNS Analyzer,
Density and Viscosity meter and Coulometric Karl-Fisher. The ionic liquids were then screened for sulphur removal from dodecane model oil. The sulphur containing
compound used in preparing the model oil, were dibenzothiophene (DBT),
benzothiophene (BT), and 3-methylthiophene (3-MT). Ionic liquid 1-butyl-3-butyl
imidazolium dibutylphosphate (BBIM[DBP]), 1-butyl-3-ethyl imidazolium
diethylphosphate (BEIM[DEP]), and 1-ethyl-3-ethyl imidazolium diethylphosphate
(EEIM[DEP]) showed the best sulphur removal with a percentage of 74%, 75% and
81% respectively, and were used for further study. A combination of catalytic
oxidation and simple liquid-liquid extraction was employed for desulphurization
(ECODS) utilizing molybdic catalyst, hydrogen peroxide (H2O2) and imidazoliumbased-
phosphate ionic liquids, namely, 1-butyl-3-butyl imidazolium dibutylphosphate
(BBIM[DBP]), 1-butyl-3-ethyl imidazolium diethylphosphate (BEIM[DEP]), and 1-
ethyl-3-ethyl imidazolium diethylphosphate (EEIM[DEP]). The precatalyst of
molybdic compounds was oxidized with H2O2 to form peroxomolybdic compounds,
which is soluble in ionic liquid and dissolved in oil. The sulphur containing
compounds in the model oil were extracted into ionic liquid phase and oxidized to
their corresponding sulfones by peroxomolybdic compounds. Further studies were
conducted for research parameters such as the temperature, amount of H2O2, amount
of catalyst, type of sulphur species and initial concentration of sulphur on the sulphur
removal from the model oil. From the experiments, the optimum conditions for
ECODS process were 70oC, ratio of H2O2 to sulphur compound used was 4
([n(H2O2)/n(S)]=4), and ratio of sulphur compounds to catalyst was 20
([n(S)/n(Cat)]=20), giving 85.2% sulphur removal for ionic liquid BBIM[DBP]. Other
desulphurization methods; extraction (EDS) and oxidation (ODS) were also
compared. It was found that imidazolium base phosphate ionic liquids with longer
alkyl chain displayed better sulphur removal efficiency. BBIM[DBP] was found to
display the best performance in sulphur removal showing a removal of 85.2 % for
ECODS process, 68.4% for EDS process and 65.8% for ODS
process