Applications And Molecular Simulation Studies Of Ionic Liquids And Zeolites In Deep Desulfurization Of Diesel Fuel

Deep desulfurization of fuels has drawn extensively attention worldwide due to the increasingly stringent regulations for environment and fuel specifications in many countries. Many previous studies on deep desulfurization of diesel fuel were reviewed in detail, and the following originally innovative researches applying ionic liquids and zeolites in the desulfurization were carried out:1. Six ionic liquids synthesized by our team,which is stable in air and water, were firstly applied in extractive desulfurization from model diesel (500μg/g sulfur) and real hydrotreated diesel (438μg/g sulfur). Under same conditions, the desulfurization with different ionic liquids was investigated, and the desulfurization capability increased in the order: quarternary ammonium types﹤ones with pyridine ring﹤ones with imidazole ring for the cations, and [HSO4-]﹤[Tos-] for anions of ionic liquids. The acidic ionic liquid [(CH₂)4SO3Hmim] [Tos] has the best extraction capability to hydrotreated diesel, and its sulfur content can be reduced from 438μg/g to 45μg/g after extracting for 5 times. The ionic liquid can be easily recycled without obvious change in extraction capability.2. Oxidative desulfurization from model diesel and hydrotreated diesel was firstly carried out in acidic ionic liquids [(CH₂)4SO₃Hmim][Tos](one with best extraction capability) With Na₂WO₄·2H₂O as a catalyst and H₂O₂ as an oxidant. The results show that good selectivity would be found to dibenzothiophene as compared with aromatics, and dual function of both oxidation and extraction were combined in one step for the desulfurization of model diesel. When the reaction is completed, model diesel can be separated from the catalyst by simple decantation,with its sulfur content from initial 500μg/g to 3μg/g. The ionic liquid phase separated can be recycled by extraction by 1,4-butyrolactone after vacuum drying. As for the desulfurization from real hydrotreated diesel, the oil should be finally extracted by N-methyl-2-pyrrolidone (NMP) once after separating from the catalyst by simple decantation, good desulfurization capability would be obtained with sulfur content reducing from 200μg/g to 20μg/g. The catalytic system, i.e. the ionic liquid phase, can be recycled directly after vacuum drying. So the catalytic system offer advantages of simple separation of catalyst from diesel, and ease of recycling of catalyst.3. In order to improve the ionic liquid catalytic system without adding solid catalyst of Na₂WO₄·2H₂O, the carboxylic group with catalytic oxidation function was introduced in ionic liquid. Five new task-specific acidic ionic liquids(including [(CH₂)₂COOHmim] Cl ,[CH₂COOHmim] [HSO₄],[(CH₂)₂COOHmim] [HSO₄],[CH₂COOHmim] [H₂PO₄] and [(CH₂)₂COOHmim] [H₂PO₄]), which contain carboxylic group in cations, were firstly synthesized and characterized by IR, 1H NMR, 13C NMR, TG and Elemental Analysis. Oxidative desulfurization experiments from model diesel and hydrotreated diesel were carried out with one of task-specified ionic liquids as a catalyst and H₂O2 as an oxidant, and the results show that the acidic ionic liquid [(CH₂)₂COOHmim] [HSO₄] has the best desulfurization capability to model diesel with dual function of both oxidation and extraction, so one-step desulfurization can be carried out, the model oil and catalyst can be separated by simple decantation. As for hydrotreated diesel with sulfur content 200μg/g, due to its complex ingredient, Extraction by NMP once should be finally carried out for the diesel, which is separated from the catalyst by simple decantation after the reaction. Ultra–clean diesel with the sulfur content about 20μg/g would be obtained. The ionic liquid can be recycled directly after vacuum drying. Meanwhile, the mechanisms of oxidative desulfurization reaction were further investigated。This catalytic oxidation system in ionic liquid offer advantages such as low reaction temperature (298K), better selectivity for sulfur-compounds than aromatics, ease of separating diesel from the catalyst, ease of recycling, etc., and resolve the problems existing in other catalytic systemsDensity functional study was also used to study the structures of the newly synthesized task-specific ionic liquids from the atomic level. The relationship of structures, equilibrium existing modes of cations and anions, and acidity of ionic liquid was investigated, leading to a good understanding of the effect of the structures and acidity to their catalytic oxidation desulfurization capabilities.4. Density functional theory has been used to investigate the adsorptive desulfurization with Cu(I)Y zeolite as an adsorbent, various possible adsorption structures of five model thiophenic sulfur compounds were firstly calculated, and find thatη² adsorption mode through the C=C bond of the thiophenic ring on the zeolite has been found to be energetically preferred for the BTs, abundant in gasoline, while for the DBTs, mainly available in diesel fuel, theη¹S adsorption mode is the most preferential one, implying that the competitive adsorption of aromatics over S-compounds is stronger in gasoline than that in diesel fuels. This gives a good theoretical demonstration of the mechanisms of selective adsorption desulfurization. At the same time, the effects of the refractory nitrogen compounds in diesel and the Br(?)nsted acid site of zeolites on the desulfurization capabilities were also investigated.5. In order to design a selective adsorbent, which can be interacted with thiophenic compounds through direct Metal-Sulfur interaction rather thanÏ€complexation. The effect of different metal ions on the adsorptive desulfurization is investigated with DFT methods, and their interactions with thiophene molecule increases in the following order: Ag(I)﹤Cu(I)﹤Au(I). On Au(I) modified zeolites, the major adsorption modes isη¹S, i. e., Au is directly bonded with S atom, while on Cu(I) and Ag(I) modified ones,η²adsorption mode through the C=C bond of the thiophenic ring is found to be the energetic one, so Au(I) modified zeolites is the best one among the three. Au/SBA-15 is used for the experiments of static desulfurization and the results shows that Au/SBA-15 is a good adsorbent.