(100f) An Integrated Process for Desulfurization (HDS-Extractive-Oxidative)

Mokhtarian, M.R. Dehghani, F. Banisharif

Chemical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, Iran

Abstract:

Available sulfur compounds in the fuels such as thiophens are considered as one of the main source of air pollution. They converted to SOx and released to the atmosphere as a harmful chemical for human health. Hence, removal fuel desulfurization is mandatory from environmental point of view as well as public health issues. Nowadays, in many countries, stringent regulations are being enacted to reduce the sulfur content to lower than 10 ppm for both diesel and gas oil. During recent years many attentions have been paid to extractive-oxidative desulfurization (EDS-ODS) while economic evaluations show that they are not economically feasible compared to the hydro desulfurization (HDS) process. On the other hand, HDS process is considered as an energy insensitive process and needs to be operated at High pressure and temperatures. To present an economic process, in this work an integrated process of HDS and EDS-ODS were modeled. The HDS section was modeled based on operational data from Tehran refinery and extractive- catalytic oxidative desulfurization (ECODS) part were modeled based on our novel pilot experimental data. Gas oil as the feedstock with total sulfur content of 22600 ppmw was fed to the process. Optimal conditions were obtained using the response surface methodology and box-behnken design (BBD), based on experimental design results, hydro desulfurization from the 22600 ppmw to 1930 ppmw level was done under the following conditions: hydrodesulfurization temperature: 311 ℃, hydrodesulfurization pressure: 24 bar and hydrogen purity of 35 wt%. Then gas oil with the total sulfur content of 1930 ppmw was entered into the oxidative-extractive desulfurization unit. The effects of different operating parameters such as temperature, oxidant to sulfur molar ratio and the type of solvent in the extraction stage were investigated. The best performance was obtained at oxidant to sulfur molar ratio of 4:1 and acid to oxidant volumetric ratio of 1:1. It must be mentioned that hydrogen peroxide (30%) and acetic acid (95%) were used as oxidant. Finally, a liquid-liquid extraction process was utilized for deep desulfurization step. Acetonitrile used as solvent at 1:1 ratio towards gas oil. It was found that the proposed process has lower costs and also is inherently safer than that of conventional HDS, ODS and EDS.

Keywords: Optimization, Hydrodesulfurization, Extractive- Catalytic oxidative desulfurization, Ultra-low Sulfur Fuel