چكيده به لاتين
The desulfurization by the oxidative polymerization desulfurization (OPD) process is considered as a new technology for the maximum removal of the thiophenic compounds (benzothiophene (BT), dibenzothiophene (DBT)) in hydrocarbon fuels. In this regard, development of this process is very important through the optimal design and consideration of the effective parameters on it.
Hence, in this study, first, the oxidative polymerization process was studied to investigate the polymerization reaction, so that the product obtained from BT in the model fuel after the process, was subjected to various types of analysis such as molecular weight (GPC) and thermal analysis (TGA, DSC).
The results showed that the obtained product was a polymer with molecular weight of 183030 and polydispersity of 1.63 and also, it was a highly branched polymer with cross-linked bonded and sticky.
One of the other results, the melting point was 192.5°C. Moreover, in order to investigate the role of the model fuel solvent, three different models fuel with solvents n-decane, tetrahydrofuran and acetonitrile along with BT were used for the structure analysis by H + CNMR, FTIR and CHNSO. The results showed that obtained polymers of the model fuels, including solvents with strong intermolecular force, such as acetonitrile, the solvent is not involved in the polymerization process and the polymer structure is only BT compounds. However, in the model fuels, including solvents with strong intermolecular force (polar), such as n-decane, in the polymer structure, in addition to thiophenic compound, there are also solvent compounds. Then, in the next step, two new catalyst (H5PV2W10O40/SiO2) were prepared, with the replacement of tungsten metal instead of the molybdenum atom in the structure of the catalyst by wet impregnation and sol-gel methods so that to remove the thiophenic compounds (BT and DBT) from the model fuel by the prepared catalysts and along with the H5PV2Mo10O40/SiO2 catalyst, were done. The catalysts were evaluated using analyzes such as FTIR, EDX, XRD, BET and FESEM. In this regard, first, a comparison of the desulfurization strength of the two prepared catalysts (H5PV2Mo10O40/SiO2 and H5PV2W10O40/SiO2) of the model fuel containing DBT was investigated. It was determined that the phosphovanadotungesticacid catalyst (prepared by wet impregnation method) has a greater desulfurization strength than the phosphovanadomolybdicacid catalyst (prepared by wet impregnation method). Then, using the surface-response (BBD method) and the phosphovanadotungesticacid catalyst (prepared by wet impregnation method), effect of more important oxidation parameters; catalyst weight to fuel volume (g/L), agitation rate (rpm) and time of process (h) was studied. The desulfurization results not achieved for more than 70 % which indicated the polymer deposition on the catalyst surface, and caused the catalyst deactivation and a barrier against mass transfer. Therefore, for the purpose of solving the problem, the ultrasound wave irradiation was used during the process of oxidative polymerization in the reactor. In this system, the optimization of the operating parameters such as catalyst weight to fuel volume (11 g/L), POM weight to silica weight (39%) and sonication time (199 min) by the surface-response (BBD method) were done. In this case, the removal of the compounds of DBT, BT and Diesel fuel were 90%, 85% and 83%, respectively. Also, in order to increase the DBT removal rate in the oxidative polymerization process in the presence of ultrasound wave irradiation, the other type of experiment was performed. In the mentioned experiment using the H5PV2W10O40/SiO2 catalyst (prepared by sol-gel method), in the sonoreactor was carried out and 93% of the removal of DBT was achieved.
