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Study on Deep Desulfurization of Fuel Oil with the Heteropolyacid Anion as Functional Building Block in Host-Guest Type Composite Catalyst

Author: YuFengLi
Tutor: WangZuo
School: Shandong University
Course: Environmental Engineering
Keywords: oxidative desulfurization heteropolyacid compounds catalyst fuel oil
CLC: X701.3
Type: PhD thesis
Year: 2013
Downloads: 32
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Abstract

A great deal of sulfur oxide has been emitted from fuel oil combustion, and has been found to contribute to acid rain and aerosol, even to endanger people’s health. Due to the danger of sulfur compounds in fuel oil, the limitation of S content in fuel oil becomes more critical in the world. The aim of researchers is to find out the production technology of ultra-low sulfur fuel oil. Oxidative desulfurization (ODS) is considered to be one of the most promising desulfurization methods for its mild reaction condition, high efficiency, simple technology, low cost, low carbon and environment-friendly. Heteropoly compounds have the advantage of mild reaction conditions, high catalysis, high stability and high selectivity. Heteropoly compounds, as a new environment-friendly catalyst for ODS, have attracted the attention of worldwide researchers during the past years.In this paper, four heteropoly compounds with the heteropolyacid anion as subject and the change of object were prepared as catalyst, including supported for heteropolyacid cesium, heteropolyacids pillared hydrotalcite like compounds, organic-inorganic heteropolyacids, and immobilization of heteropolyacids on amino group functionalized MCM-41moleculars sieves. And we studied the catalysis of four catalysts in the ODS process.Supported for heteropolyacids cesium was synthesized, which keeps the catalytic performance by the subject of heteropolyacid and was achieved fixation by the object. The catalyst can be recovered by filtration after reaction. The operation of catalyst regeneration is simple. And it shows excellent catalytic performance on ODS. Three heteropolyacids cesium were prepared by coprecipitation, including CS2.5H0.5PW12O40, Cs2.5H0.5PMo12O40and Cs2.5H1.5SiW12O40. Compared the catalysis of them on ODS in simulated fuel oil, Cs2.5H0.5PW12O40showed the best catalytic performance. The catalysis of Cs2.5H0.5PW12O40in an ODS process was studied with H2O2as oxidant and acetonitrile as extractant. The main factors affecting the desulfurization process were investigated, including temperature, the amount of catalyst and oxidizing agent, and the pre-reaction time, obtaining finally the optimum experimental conditions. Then, Cs2.5H0.5PW12O40was supported to CNT, AC and silica column respectively to prepared CsPW/CNT, CsPW/AC and CsPW/SiO2.Compared the catalysis of them on ODS in simulated fuel oil by the same loading level. Experiment results show the catalysis of CsPW/CNT is the best. Compared the different loading level of CsPW/CNT, it shows the catalysis of30%loading level of CsPW/CNT is the best. With30%CsPW/CNT as catalyst, H2O2as oxidant and acetonitrile as extractant, the main factors affecting the desulfurization process were investigated, including temperature, the amount of catalyst and oxidizing agent, and the pre-reaction time, obtaining finally the optimum experimental conditions. Under the optimal conditions(catalyst dosage,1%the mass of normal octane; O/S molar ratio,20; pre-reaction time,20min; temperature,60℃; acetonitrile dosage,100%the volume of normal octane), compared the desulfurization efficiency of different sulfur compounds with the catalyst of30%CsPW/CNT on the same S-content simulated fuel oil. It shows that the oxidation reactivity of different sulfur compounds was in the order of DBT>4.6-DMDBT> BT> TH. The result shows the electron density of sulfur compounds on the sulfur atoms and the space steric hindrance were two important factors in the ODS. By filtration, recycling and roasting regeneration, the catalysis of the fifth recycling30%CsPW/CNT was down slightly. It shows the supporter was high stability. And the catalyst can be reused. Under the optimal conditions, the desulfurization efficiency of diesel was investigated. It shows that S-content in diesel decreased from507ppmw to48.1ppmw, the desulfurization efficiency90.5%and the recovery rate97.1%.Heteropolyacids pillared hydrotalcite like compounds were prepared by ion exchange. Heteropolyacid anions insert hydrotalcite like compounds, the chemical attachment between the heteropolyacid anions and the interlaminar metal ions, which keeps the catalytic performance by the subject of heteropolyacid and achieves the characteristic of insoluble in water or fuel oil the object of hydrotalcite like compounds oxidative desulfurization. The catalyst can be recovered by filtration after reaction. The catalysis in an ODS process of DBT in simulated fuel oil was studied, which were prepared by the different heteropolyacids anion pillared bimetal (or trimetal) hydrotalcite like compounds. At first, when the catalyst were prepared by the different subject of heteropolyacids anion and the same object of bimetal (or trimetal) hydrotalcite like compounds, the catalytic activity of them was related to the kind and amount of heteropolyacids. Their catalytic activity decreased according to the order: phosphomolybdic acid pillared hydrotalcite like compounds> phosphotungstic acid pillared hydrotalcite like compounds> silicotungstic acid pillared hydrotalcite like compounds. Secondly, when the catalyst were prepared by the same subject of heteropolyacids anion and the different object of bimetal (or trimetal) hydrotalcite like compounds, the catalytic activity of them was related to the ionic radius comparison similar principles. When the rate of divalent metal ionic radius and trivalent metal ionic radius is near one in hydrotalcite like compounds, its layer board structure is close to the typical structure of octahedral coordination. It shows that when the same subject of heteropolyacids anion and the different object of bimetal hydrotalcite like compounds in the catalysts, their catalytic activity decreased according to the order: NiAl hydrotalcite like compounds> MgAl hydrotalcite like compounds> ZnAl hydrotalcite like compounds. When the same subject of heteropolyacids anion and the different object of trimetal hydrotalcite like compounds in the catalysts, their catalytic activity decreased according to the order:NiMgAl hydrotalcite like compounds> NiMgAl hydrotalcite like compounds> MgZnAl hydrotalcite like compounds. With NiAl-PMo or NiMgAl-PMo as catalyst, H2O2as oxidant and acetonitrile as extractant, the main factors affecting the desulfurization process were investigated, including temperature, the amount of catalyst and oxidizing agent, and the pre-reaction time, obtaining finally the optimum experimental conditions. And the catalysis activity of NiAl-PMo is better than NiMgAL-PMo. Under the optimum experimental conditions, we compared the desulfurization efficiency of different sulfur compounds with the catalyst of NiAl-PMo on the same S-content simulated fuel oil. It shows that the oxidation reactivity of different sulfur compounds was in the order of DBT> 4.6-DMDBT> BT> TH. The result shows the electron density of sulfur compounds on the sulfur atoms and the space steric hindrance were two important factors in the ODS. The catalysis of the fifth recycling NiAl-PMo was never down. It exhibits excellent catalyzed active properties and utilization. Under the optimal conditions(catalyst dosage,1%the mass of normal octane; O/S molar ratio,15; pre-reaction time,5min; temperature,60℃; acetonitrile dosage,100%the volume of diesel), we investigated the desulfurization efficiency of diesel. It shows that S-content in diesel was decreased from492ppmw to44.3ppmw, the desulfurization efficiency90.4%and the recovery rate96.8%.In this paper, organic-inorganic heteropolyacids were prepared, including [π-C5H5NC16H33]3[PW4O16],[π-C5H5NC16H33]3[PMO4O16],[π-C5H5NC12H25]3[PW4O16] and [π-C5H5NC12H25]3[PMo4O16].During the reaction process, the phase state of catalyst changed in "solid-liquid-solid". The results show that organic-inorganic heteropolyacids are phase transfer catalyst and oxidative desulfurization system belongs to the phase transfer catalysis system controlled by reaction. The efficiency of oxidative desulfurization was investigated on the four kinds of catalysts under same conditions using the simulated oil prepared by dissolving organo-sulfur in normal octane. The results show that the catalytic activity of [π-C5H5NC16H33]3[PW4O16] is the best. With [π-C5H5NC16H33]3[PW4O16]as catalyst, H2O2as oxidant and acetonitrile as extractant, the main factors affecting the desulfurization process were investigated, including temperature, the amount of catalyst and oxidizing agent, and the pre-reaction time, obtaining finally the optimum experimental conditions. It shows that the phase state of organic-inorganic heteropolyacids is solid under normal pressure and temperature and it is insoluble in water or oil. When it reacted with H2O2, the production of peroxide heteropolyacid is soluble in acetonitrile and it react with sulfur compounds. When [π-C5HsNC16H33]3[PW4O16] reacted with H2O2, the organic part of the production of peroxide heteropolyacid is lipophilicity, which can promoted the oxidative reaction. The catalyst [π-C5H5NC16H33]3[PW4O16] can be reclaimed by auto precipitation due to the exhausting of H2O2.It shows that the catalyst has the characteristics of homogeneous catalysis, the phase state of which changes in the precipitation from the reaction system after the reaction. It realized the automatic separation and recycling of the catalyst. On the similar conditions, the catalyst of the3th recovered [π-C5H5N C16H33]3[PW4O16], the DBT conversion was nearly98%after120min, which was quite close to the result of fresh catalyst. The catalytic activity of the recycled [π-C5H5NC16H33]3[PW4O16] is almost the same as the fresh. We investigated the desulfurization efficiency of diesel with [π-C5H5NC16H33]3[PW4O16] as catalyst. It shows that S-content in diesel was decreased from515ppmw to44.8ppmw, the desulfurization efficiency91.3%and the recovery rate96.2%.The heteropolyacids have been immobilized on the inner surface of amino group functionalized MCM-41moleculars sieves. A new kind of catalyst were prepared, which keeps the catalytic performance mesoporous and avoids the loss of heteropolyacids in the traditional MCM-41supported heteropolyacids. And it can be recycled by filtration. EDTA-2Na was involved in the ODS as H2O2decomposition reaction inhibitors for the first time. The catalysts were prepared on the different heteropolyacids immobilization on amino group functionalized MCM-41moleculars sieves, including MCM41-NH-PW, MCM41-NH-PMo, MCM41-NH-V1, MCM41-NH-V2and MCM41-NH-V3. The five catalysts were synthesized and characterized by FT-IR, X-ray diffraction and SEM. The results show that they have the Keggin-type heteropolyacids and the structure of mesoporous. Compared with the above catalysts, the desulfurization efficiency of DBT in simulated fuel oil was investigated.It showed that the catalysis activity of MCM41-NH-PW was the best. With MCM41-NH-PW as catalyst, H2O2as oxidant and acetonitrile as extractant, the main factors affecting the desulfurization process were investigated, including temperature, the amount of catalyst and oxidizing agent, and the pre-reaction time, obtaining finally the optimum experimental conditions (catalyst dosage,1%the mass of normal octane; O/S molar ratio,15; pre-reaction time,5min; temperature,60℃; acetonitrile dosage,100%the volume of normal octane).It shows that the oxidation reactivity of different sulfur compounds was in the order of DBT>4.6-DMDBT> BT> TH. The result shows the electron density of sulfur compounds on the sulfur atoms and the space steric hindrance were two important factors in the ODS. Under the optimum experimental conditions, we studied the desulfurization efficiency of DBT in simulated fuel oil with EDTA-2Na as inhibitors. It showed that when10mL of EDTA-2Na were added to the reaction system, the desulfurization efficiency was obviously increased from96.8%to100%after180min. EDTA-2Na and trace metal ions can react to product the stable circular metal chelate. So there were no metal ions to catalyze the decomposition of hydrogen peroxide. The main reason is the production of the stable circular metal chelate. On the similar conditions, the catalyst of the1st and2nd recovered MCM41-NH-PW, the DBT conversion was obviously decreased. The catalyst of3rd and more time recovered MCM41-NH-PW, the DBT conversion was unchanged. When the MCM41-NH-PW was reused, the phosphotungstic acid was shedding, which were adsorbed on the surface of the catalyst, and the percent of unit mass heteropolyacids anion were reduced. Under the optimum experiment conditions and EDTA-2Na as inhibitors, we investigated the desulfurization efficiency of diesel with MCM41-NH-PW as catalyst. It shows that S-content in diesel decreased from496ppmw to49.2ppmw, the desulfurization efficiency90.1%and the recovery rate96.2%.Kinetics of the process catalyzed by four kinds of heteropolyacid compounds were studied, from which the reaction order were found to be1to DBT and the activation energy of reaction was found to be from45.2to49.4kJ/mol. It was found that heteropolyacids anion were be oxidized by H2O2, and the production of them were peracetic heteropolyacids anion by FTIR. Then, the peracetic heteropolyacids oxidized the sulfur atom in the sulfur compounds. And the oxidation of sulfur atoms were determined by the electron density of sulfur compounds on the sulfur atoms and the space steric hindrance. It was found that the DBT sulfone was only production on ODS and it was soluble in acetonitrile to achieve desulfurization.

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