Jessica Juweriah Ibrahim,Shurong Gao,Ahmed A. Abdeltawab,Salem S. Al-Deyab,Liang Yu,Guangren Yu,Xiaochun Chen,Xingyue Yong
The inability of traditional hydrodesulfurization (HDS) to effectively remove aromatic sulfur compounds such as thiophene (TS) and dibenzothiophene (DBT) has called for alternative methods to be studied, among which extractive desulfurization using ionic liquids (ILs) has attracted increasing interest. In this work, we prepared a new IL, 1-butyl-3-methylimidazolium dicyano(nitroso)methanide ([C4mim][dcnm]), and investigated its extractive desulfurization for both model oils and real FCC gasoline, where model diesel fuel was composed of n-hexane and droplets of DBT and model gasoline was composed of n-hexane, toluene and droplets of TS. Other three [dcnm]-based ILs, 1-ethyl-3-methylimidazolium dicyano(nitroso)methanide ([C2min][dcnm]), N-ethyl-N-methylpyrrolidinium dicyano(nitroso)methanide ([C2mpyr][dcnm]), and N-butyl-N-methylpyrrolidinium dicyano(nitroso)methanide ([C4mpyr][dcnm]), were also comparatively investigated. These [dcnm]-based ILs have low viscosity which favors the mass transfer and reduces the extractive equilibrium time, also are fluorine-free which avoids the corrosion by hydrogen fluoride from anion decomposition that occurs generally in fluorine-containing ILs. The desulfurization ability follows the order [C4min][dcnm] > [C4mpyr][dcnm] > [C2min][dcnm] > [C2mpyr][dcnm]. Typically, [C4min][dcnm] is capable of removing 66% DBT and 53% TS from their respective model oils after one cycle (initial 500 ppm S, 25°C, 15 min, mass ratio of IL:oil 1:1), and < 10 ppm S-content can be obtained after 4 cycles. It was observed interestingly that the S-content in real FCC gasoline can be reduced from initial 250 ppm to < 30 ppm after 6 cycles using [C4min][dcnm] as extractive reagent, which is better than some previous results for real feedstocks. Mutual solubility, extractive temperature, IL:oil mass ratio, multiple extraction, initial S-content, and regeneration were also studied. These dcnm-based ILs are competitive extractive reagents compared with some other ILs to remove those aromatic S-compounds from fuel oils.
Separation of olefin from fluid catalytic cracking (FCC) naphtha is a high way to protect the research octane number (RON) from a loss during hydrodesulfurization . Solvent extraction is a promising way to separate olefin and extract sulfides simultaneously. In order to realize effective separation of olefin from FCC naphtha, this paper focused on the development of a kind of high efficient solvent and optimization of corresponding operation conditions for olefin separation. The results showed the combined solvents consisted of sulfolane (95 v%) and N -methyl-2-pyrrolidone (5 v%) exhibited high separation capability for olefin, and the best solvent to oil ratio was 3:1. Based on the combined solvent and optimal solvent to oil ratio, the best olefin enrichment coefficient could be up to 97.63 indicating lots of olefin enriched in raffinate . The desulfurization efficiency exceeded 90% after 3-stage extraction by the combined solvents, which was close to and even prior to some kinds of ionic liquids . Moreover, the combined solvents exhibited remarkable stability, and variation of desulfurization efficiency of the combined solvents was only around 1% after recycled 8 times. These studies gave a high efficient way to upgrade clean gasoline by separating olefin and enriching sulfides from FCC naphtha.
NiSO4/ZnO-Al2O3-SiO2 adsorbent, as a novel reactive adsorption desulfurization (RADS)adsorbent, has self-sulfidation ability and high desulfurization performance when treating model fuel. However, the RADS performance of the adsorbent under FCC gasoline feedstock is not well understood. Here, we compare the performance of the adsorbent under FCC gasoline with model fuel to test the effect of the hydrocarbon composition of the feedstock. The complex composition of FCC gasoline makes it sensitive to the nickel loading amount of the adsorbent. Under the influence of specific surface area and pore structure, the adsorbent loaded with 3 wt% nickel shows better desulfurization activity when treating FCC gasoline. As hydrocarbons in FCC gasoline compete with sulfur compounds for active Ni sites, the reaction conditions have been tested and optimized to achieve deep desulfurization while maintaining low olefin loss to ensure the octane number of the product. By experimental tests and characterization, it has been proved that NiSx and NiO acted as active Ni sites of the adsorbent. Based on these observations, the mechanism of RADS of FCC gasoline over NiSO4/ZnO-Al2O3-SiO2 adsorbent has been proposed, which provides theoretical support for the development of new adsorbents and the optimization of RADS process.
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