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Study on Oxidative Dehydrogenation of Isob-Utane to Isobutene Over V-Based MSU-1 Catalysts

Author: HuangQingZe
Tutor: SunGuoSong
School: Guangxi University for Nationalities
Course: Applied Chemistry
Keywords: Support mesoporous materials MSU-1 vanadium oxide oxidative dehydrogenation isobutane carbon dioxide
CLC: O643.32
Type: Master's thesis
Year: 2011
Downloads: 179
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Abstract


The oxidative dehydrogenation of light alkanes into valuable alkenes has become a challenging research area in heterogeneous catalysis. As one of the major greenhouse gases, carbon dioxide can also act as a mild oxidant. Utilization of carbon dioxide in the oxidative dehydrogenation of isobutane reactions can retard greatly coke deposition on the catalysts surface and enhance isobutane conversion and isobutene selectivity. The processes of catalytic conversion of isobutane to isobutene by oxidative dehydrogenation are of increasing importance because of growing demand for isobutene. Thus, The research and development of the effective catalysts for oxidative dehydrogenation of isobutane to isobutene with carbon dioxide plays an important role in catalysis science field.In this paper, the supports, the surface active components and the reacting conditions of the catalysts were studied in dehydrogenation of isobutane to isobutene with CO2. A new catalyst VOx/MSU-1 used in dehydrogenation alkanes to the corresponding alkenes was developed and it had not yet been reported in reaction of dehydrogenation of isobutane to isobutene with CO2. The main contents and results were summarized as follows:1) The effect of support （MSU-1,γ-Al2O3, Cact, MgO or TiO2） on catalytic activity over Cr-based catalysts was investigated for the dehydrogenation of isobutane with CO2. The catalytic activity order was CrOx/MSU-1> CrOx/Al2O3> CrOx/Cact>CrOx/MgO>CrOx/TiO2. The samples were characterized by N2 adsorption-desorption, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and temperature-programmed desorption （TPD）. It was found that the nature of support has significant effect on the catalytic performance. The N2 adsorption-desorption and XRD results show that the order of specific surface area is the same as catalytic activity. Larger surface area resulted in better dispersion of Cr and higher activity. The XPS results reveal Cr6+ is one kinds of the active center. The results of NH3-TPD indicate that catalytic activity of catalysts is proportional to the amount of weak-acid adsorption sites. As a result, a 59.17% conversion of isobutane and 39.51% yield of the isobutene were achieved on the CrOx/MSU-1 catalyst, and MSU-1 was better catalyst in investigative catalysts.2) In this study, the Cr、V、Ga、Fe、Ag and Ni catalysts was prepared by impregnation of MSU-1 with the corresponding nitrate solution and was tested for dehydrogenation of isobutane to isobutene with the mild oxidant CO2. The results showed that VOx/MSU-1 catalyst exhibited highest conversion and selectivity, The conversion of isobutane was 54.83% and the selectivity of isobutene was 40.06%. The VOx/MSU-1 samples were characterized by X-ray diffraction （XRD）, N2 adsorption-desorption and temperature-programmed reduction （TPR）. The XRD results show the VOx active species can be highly dispersed on the surface of MSU-1. The N2 adsorption- desorption results indicate that MSU-1 has a larger surface area and uniform pore size distribution. Furthermore, the catalysts preserve the 3D wormlike pore structure after impregnation. The TPR results suggested that the VOx active species was easier reduced than the V2O5. Because the initial temperature of the reduction peak was lower when the low loading VOx active species was supported. The high surface area and the highly dispersed were the main reason of the high catalyst activity.3) According to the characteristics of the catalyst and the existing process, Linde technology was fit for dehydrogenation of isobutane to isobutene on VOx/MSU-1 with CO2. The fixed bed reactor of the Linde technology was imitated in the laboratory. The temperature, the space velocity and the ratio of CO2/i-C4H10 has played a very important role in the dehydrogenation of isobutane with CO2. The optimum process was determined: reaction temperature 853 K, space velocity 7200 mL/（h·g）, the ratio of CO2/i-C4H10= 3/1, the best conversion of isobutane reached 38.4% and selectivity of isobutene reached 83.2%.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
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