Process Safety and Environmental Protection, Vol.139, 191-200, 2020
Regeneration of different extractive solvents for the oxidative desulfurization process: An experimental investigation
In this study, gasoil with sulfur content of 1550 ppm was oxidized employing an ultrasound-assisted oxidative desulfurization system followed by an extraction stage. The results indicated that desulfurization efficiency of the oxidation stage was 20 %. Then, the oxidized gasoil was extracted by either DMF or acetonitrile or 50-50 vol.% solution of DMF - acetonitrile or 50-50 vol.% solution of DMF - n-propanol. Fresh DMF was found to be the best solvent in terms of desulfurization efficiency (92 %), though acetonitrile resulted in the best fuel recovery (95 %). In addition, 50-50 vol.% solution of DMF - acetonitrile and 50-50 vol.% solution of DMF - n-propanol showed better performance to extract the sulfur compounds compared to pure acetonitrile. Regeneration of the solvents was investigated in various aspects such as regeneration efficiency, solvent ability to extract the sulfone compounds by once, twice and three times regenerated solvents as well as in a multistage extraction procedure. The results indicated that acetonitrile had the highest regeneration efficiency (85 %) since its boiling point is not close to the boiling points of the sulfur containing compounds. In addition, the results showed the desulfurization efficiency of DMF, 50-50 vol. % solution of DMF - acetonitrile, and 50-50 vol.% solution of DMF - n-propanol decreased from 92 %, 84 %, and 83 % in the fresh solvents to 63 %, 78 %, and 75 %, respectively, after three times regeneration. However, the desulfurization efficiency of acetonitrile was almost constant even after three times regeneration. Desulfurization efficiency using the regenerated acetonitrile in a three stage extraction was almost equal to the fresh DMF in a single stage extraction. Finally, the oxidized gasoil, desulfurized gasoil, and separated sulfur compounds were studied in detail using FTIR. The FTIR spectra results indicated that ODS was successful in removing the heavy sulfur compounds such as thiophenes. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.