(617ds) Oxidative-Extractive Desulfurization of Model Diesel Oil By CTA-Type Dawson Type Emulsion Catalyst

Removal of sulfur containing-compound such as dibenzothiophene (DBT) as a predominant sulfur compound in diesel oil is vital to obey environmental protocols. The catalytic hydrodesulfurization(HDS) as an accepted desulfurization method in the most refineries, has low efficiency in desulfurization of cyclic S-containing compounds such as DBT due to the steric hindrance encountered by these compounds on the surface of the catalyst. In this regard there is a tendency toward catalytic oxidative desulfurization (CODS) as a low temperature, pressure process and one of the most promising alternatives, whereby organic S-containing compounds are selectively oxidized to oxidized compounds and are eliminated in a subsequent extraction process. Among the various available catalysts in the field of CODS, surfactant-type polyoxometalates (POMs) have concerned much attention, because of their acidic and redox properties. The most of researches have been focused on application of Keggin-type POM, while few studies have been paid attention to Dawson type POMs. On the other hand, one of the most significant subclasses of surfactant-type POM is the vanadium substituted types. The vanadium substitution changes the POMâ??s properties from acid-dominated to redox-dominated. The length of alkyl chains of quaternary ammonium cations of surfactant-type tungstate POM catalyst plays an significant role in the catalytic performance of theses catalysts, previous works show that catalysts with longer carbon chain had better activity. Considering mentioned facts, in this study for the first time the cetrimonium-type vanadium substituted Dawson-type emulsion catalysts, [CTA]₁₁P₂W₁₃V₅O₆₂ was successfully synthesized using modified etherate method and ion exchange. Prepared catalyst was characterized by ICP, FT-IR, UV spectroscopy and XPS. The chemical analysis showed that the content of each element in vanadium substituted Dawson-type emulsion catalyst was nearly the same as the calculated values. The finger printing and structural interpretation by FT-IR approved the development and existence of POM in the emulsion catalyst. The XPS analysis demonstrated that the tungstate and vanadium was in the higher level of oxidation level (V⁵⁺, W⁶⁺) in [P₂W₁₃V₅O₆₄]^11-.

The emulsion catalyst along with H₂O₂ (50 wt-%) was used for extractive catalytic oxidative desulfurization (ECODS) of two kinds of model fuel oil (iso-octane and iso-octane containing 20 v% toluene with 500 ppmw total S, DBT was selected as a S-containing component). Three kinds of solvent including deep eutectic solvent (DES, ChCl: EG with mole ratio 3 (EG) to 1(ChCl)), ionic liquid (IL, 1-butyl-3-methyl imidazolium methyl sulfate (BMIM-sulfate)) and ethylene glycol (EG) were utilized under mild conditions for extraction process. Using Taguchi experimental design, effective parameters such as solvent type, volume ratio of solvent to oil, temperature and contact time on the ECODS were studied. All chosen parameters were studied at three levels by means of L₉ orthogonal array (Table 1). The concentration of catalyst in all entries of Table 1 was 7.5 g/L. The efficiency of system containing IL was much better than other systems. The results showed that the EG ECODS system removed DBT better than DES systems.

ANOVA analysis (Table 2) was used to find out the optimized conditions. The result showed that solvent and its volume ratio are the most important parameters. It is found that for the case of paraffinic fuel model (iso-octane) using IL at solvent/oil volume ratio of 1:4 gives the best performance at 50 ^oC after 60 minutes contact time, while in the case of paraffinic-aromatic model fuel (75 % iso-octane, 25 % toluene, volume basis) higher temperature (60 ^oC) was required to meet the same condition. The predicted optimized conditions was not similar to any entry of Table 1 for both model diesel oils. So, the validation test was performed. The results of validation tests approved that the predicted optimized removal of DBT were approximately reputational. The nearly 95 % of DBT was removed under optimized conditions from model diesel oil containing only iso-octane. The existence of toluene reduced the efficiency of system and removal of DBT to ~94 % under determined optimized conditions.