Deep desulfurization of model diesel by extraction with N,N-dimethylformamide: Optimization by Box-Behnken design

The extractive desulfurization (EDS) of thiophene, dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in model diesel was studied using polar solvent, N,N-dimethylformamide. The effects of operational conditions on desulfurization percentage such as solvent to diesel ratio, stirring speed, extraction time and extraction temperature were explored. The influence of inorganic solvents on the extraction process was also studied. Experimental results showed that the pertinent extraction conditions were; DMF/model diesel ratio of 1.0, stirring speed of 1000 rpm, extraction time of 30 min and extraction temperature of 29 °C (ambient temperature). Maximum sulfur removal of thiophene, DBT and 4,6-DMDBT were obtained at 90.2%, 97.2% and 77.0%, respectively. Furthermore, the desulfurization of thiophenic compounds was hampered using inorganic solvent. The DMF extractant was recycled five times without significant decrease in extractive activity. The impact of three critical parameters (DMF ratio, temperature and time) was investigated using Box-Behnken experimental design and their optimum values were found to be 30 °C, 34 min and 1.4 of extraction temperature, extraction time and DMF ratio, respectively.