| Ionic liquid, a species of green solvent, has been highly paid more and more attention by both industrial and scientific community, especially being a novel reaction medium and functional material since twenty-first century. In this paper, in order to realize the industrialization of deep desulfurization on fuel oil with ionic liquid fleetly, we focus the primary coverage of research on this field. First of all, a review about the characteristics of the domestic fuel oil product has been done, and it is highlighted that the product of clean fuel oil with stringent specification is going to be imperative under the situation. Then the hydrogenation as well as non-hydrogenation technology of sulfur-removal in fuel oil, involving application condition and trend of development, have been also analyzed. It was majorly studied about the application of ionic liquids in desulfurization of transportation fuels through comparing some kind of non-hydrodesulfurization technology, which was on the basis of our team’s research foundations. And also the desulfurization of ionic liquid, which could be designed, on transportation fuels can be expected to produce clean fuel oil in order to relieve the increasingly severe environmental pollution such as haze weather.We have designed and synthesized many different kind of ionic liquids (ILs) applied in the field of desulfurization of catalytic cracking gasoline, also called FCC gasoline. From these ionic liquids,1-alkyl-3-methyl-imidazolium hydrogen sulfur acid ([CnMIM]HSO4(n=2,3,4,5,6))?1-alkyl-3-methyl-imidazolium tetrafluoboric acid ([CnMIM]BF4(n=2,3,4,5,6)) and1-alkyl-3-methyl-imidazolium trifluoroacetic acid ([CnMIM]TFA(n=2,3,4,5,6)) were screened based on the desulfurization efficiency, experimental conditions and other properties of physics or chemistry. Then, characterization of these three ionic liquids including of1H NMR,19F NMR, IR and ESI-MS spectroscopy were conducted. The experiments showed the optimized conditions which included the volume ratio of ILs/oil, the molar ratio of O/S, reaction time, reaction temperature and structure of ILs. When these three ILs were applied in the desulfurization of modle oil and real oil sample, FCC gasoline produced in Fushun Petrochemical Branch Company No.2Petroleum Factory of PetroChina Company Limited, as extractants with H2O2as oxidant, the promising effects of sulfur-removal were observed. Meanwhile, the performance indexes of gasoline were not almost varied under the guarantee of oil yield. The experiment conclusions are:(1) With [CnMIM]HSO4(n=2,3,4,5,6) as catalytic extractant and H2O2as oxidant, over95%of the desulfurization efficiency in n-octane as model oil(200μg/g) was obtained under the optimal conditions of volume ratio of ILs/oil of1:20, molar ratio of H2O2to sulfur of6, reaction time of90minutes, reaction temperature of60℃, and the desulfurization efficiency of [C3MIM]HSO4was the best in this series ionic liquids. The desulfurization efficiency of FCC gasoline (63.2μg/g) was up to94.7%under the optimal conditions. We can accept the promising sulfur removal performance, but not the quite long reaction time and the a little high ratio ILs to oil.(2) When using [CnMIM]BF4(n=2,3,4,5,6) as extractant, H2O2as oxidant and methyl rhenium trioxide(MTO)as catalyst,95.03%of the desulfurization efficiency in model oil(200p,g/g) was received under the optimal conditions of volume ratio of ILs/oil of1:5, molar ratio of H2O2to sulfur of8, the dosage of MTO catalyst of20mol%to sulfur, reaction time of60minutes, reaction temperature of60℃, and [C5MIM]HSO4of this series ionic liquids gave the best desulfurization efficiency. The desulfurization efficiency of FCC gasoline (63.2μg/g) was also over93.58%under the optimal conditions. This type of ILs can be recycled easier than others,. Nevertheless, the high desulfurization efficiency can be obtained only by additional using MTO, a kind of expensive material, as catalyst. So, it is the key to synthesize a cheap oxidative catalyst using with ILs together.(3) The optimal conditions of [CnMIM]TFA (n=2,3,4,5,6) in desulfurization of model oil(200μg/g) were volume ratio of ILs/oil of1:20, molar ratio of H2O2to sulfur of6, reaction time of90minutes, reaction temperature of60℃, and that the desulfurization efficiency of [C4MIM]HSO4was the best in this series ionic liquids,95.02%for the model oil and93.80%for the FCC gasoline, which displayed superior desulfurization application prospects because of its ability of continuous use, large extraction saturation capacity, low ratio of ILs to oil, short reaction time and without obvious influence to the gasoline.(4) More investigations were employed on [CnMIM]TFA (n=2,3,4,5,6) ILs. The ability of removing different sulfides such as thiophene, benzothiophene and dibenzothiophene contained in FCC gasoline and diesel largely decreased in the following order:4,6-DMDBT> DBT>BT, which showed its good sulfur removal selectivity to the heavy sulfides. Even though4,6-DMDBT was highly contained in diesel, the access point to the ILs industrialized is still gasoline in view of operational conditions.(5) Through the comparison of three kinds of ILs’ desulfurization, we can conclude that the desulfurization efficiency decreased in the order:TFA>HSO>4>BF4without any catalysts or oxidants; When oxidant H2O2was added, the order became HSO4>TFA>BF4, the desulfurization efficiency of both HSO4and TFA is much higher than BF4’, which showed us that desulfurization effect is dependent on the polarity and acid of ILs. As the catalyst MTO was used with BF4ILs, the desulfurization effect was improved obviously, almost being the highest. But involving of the dosage, reaction time, reaction temperature and other operational conditions, TFA ILs is better than the other two. Also, the ILs’ corrosion brought from strong acid to equipment should be taken into account.(6) Considering desulfurization efficiency, cost, operation conditions such as reaction time, reaction temperature and ratio of IL/oil, trifluoroacetic acid showed better application prospect, but it does not affect the performance indexes of oil, and ensures the production of clean gasoline. At present, understanding the structural properties of ILs from a deeper level, the physical and chemical properties, and their relationship have become an important direction of ILs research, but also are the necessary step in the course of industrialization. This paper focused on the1-alkyl-3-methyl-imidazolium trifluoroacetic acid ([CnMIM]TFA(n=2,3,4,5,6)) ILs, and kept studying their physical and chemical properties, thermodynamics as well as dynamics for explaining desulfuration mechanism. The conclusions are as follows:(1) At the range of temperature from293.15k to343.15k, the surface tension of five kinds of trifluoroacetic acid imidazolium ILs was determined using the maximum bubble method, and the density was measured by Westphal balance method. The numerical linear of density and surface tension, as well as the standard deviation are acceptable.(2) According to the research about the volume and surface properties, the molecular volume, standard entropy, surface entropy, surface energy and crystal lattice energy of five ILs are received by calculation, and the crystal lattice energy is low.(3) Utilizing the gap model theory, the average void volume, thermal expansion coefficient of five ILs are gained, which are in good agreement with the experimental data, so that which could prove the correctness of space model theory about ILs.(4) Based on the method of Kabo and Rebelo about ILs, normal boiling point and enthalpy of vaporization are estimated.(5) In order to test the heat of dissolution of ILs, a dissolution reaction calorimeter of constant temperature environment is assembled. Because the calibration is the basic method to detect the reliability and accuracy of calorimeter, we calibrated the calorimeter by standard KC1. Very good agreement with the literature values were observed in the range of error, which shows that the precision of our assembling online isoperibol reaction calorimeter can meet the testing requirements. (6) On the basis of the Pitzer electrolyte solution theory and using the calorimeter which has been calibrated, We can determined the molar dissolved heat, the infinite dilution molar heat of solution, Pitzer enthalpy parameters, apparent relative molar enthalpy, hydration heat of cation and anion of different concentrations in water.(7) The infinite dilution molar heat of solution,△sHm0, of five ILs are all negative, which shows the dissolution process was an exothermic reaction, and we can also get the conclusion that the infinite dilution heat of solution increases with the number of carbon chain on the imidazolium. In addition, the linears of the heat of solution curve fitting of five ILs are increasing with the number of carbon chain on the imidazolium. The [C5MIM]TFA and [C3MIM]TFA have been basically composite linear fitting rules, which tells us that the volume of the cation of the last two Ils are large, and the cation and anion are asymmetry with weak interaction each other resulting to no effect of the three item and low influence of two item in the Pitzer parameters.(8) We acquired the apparent activation energy Ea for15.98kJ/mol of the reaction of extraction-oxidation desulfurization using ionic liquid by dynamics. The small activation energy Ea tells us that a few relative energy can accelerate the reaction to positive direction, which also interpreted why this type of reaction complete so fast.It is worth of studying the physical and chemical property of ionic liquids either theory or application. The data of thermodynamics and dynamics is an important parameter for the industrialization, which is the basis of process design, and the lack of them can become a big obstacle of ionic liquid industrialization. Through the research of this paper, I hope to solve the barriers of ionic liquid in the fields of desulfurization of fuel oil partly, and to promote the process of industrialization of ionic liquids. |
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