چكيده به لاتين
Abstract:
The major impurities in deep desulfurization processes are thiophene and thiophene derivative compounds. Thiophene compounds often would not be removable by hydrogen desulfurization process or operating conditions are very hard for their removal. Various new methods have been developed to extract and remove them. One of these methods is the use of ionic liquids. The unique properties of ionic liquids compared to other salts is created by the combination of certain anions and cations and provides the possibility for their use instead of the usual solvents.
In current work, the separation of thiophene derivatives (thiophene, benzothiophene and dibenzothiophene) from fuel (n-hexane, n-octane, n-decane, naphtha model and kerosene) by using ionic liquids based on imidazolium and pyridinium and environmentally friendly anions including nitrate [NO3] and thiocyanate [SCN] has been studied. The experimental data of Liquid-liquid equilibrium for twenty-one of ternary system (ILs + model fuel +S component) have been obtained. These new data have been reported for the first time. Selectivity and distribution coefficients were calculated using the experimental results and the results have been compared with other works. Research shows that regardless of the type of cations and anions, decreasing the alkane chain length on IL cation, increases selectivity and decreases distribution coefficients. Since ionic liquids have the capability of being recovered through too many recovery processes the selectivity compared to distribution coefficient is more important and ionic liquids with shorter alkyl chain length are preferable. In addition, these results show that as the length of the alkane chain increases, the solubility value decreases while the selectivity increases and the process will be more economical.
The results showed that temperature has a little effect on desulfurization process and ambient temperature is the optimum condition for desulfurization process in terms of savings the energy consumption. Then, the experimental data have been correlated using NRTL model and had reasonable accuracies for all of the systems. The best results have been obtained for [BMIM][SCN] and the n-decane for the ionic liquid and fuel, respectively.
After determination of superior ionic liquid and with using the process method, the removal amounts of thiophene compounds in the fuel model were obtained as following order: thiophene < benzothiophene < dibenzothiophene. In extractive desulfurization with the superior ionic liquid, changing the composition of non-sulfur components in the model fuel was minimum and the desired selectivity has been shown. Tests for real fuel kerosene have been repeated and showed similar results. The optimum weight ratio of ionic liquid to fuel has been determined as 1:1 and with three stage separation process, 90% of the most difficult to extract sulfur compound; (thiophene) has been removed. Extractive - oxidative desulfurization process was evaluated with the superior ionic liquid and an inappropriateness to this process has been indicated.
Keywords: ionic liquids, extractive desulfurization, fuel, thiophene derivatives and
thermodynamic models.