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Partial oxidation of CH4, CO2 reforming of CH4, and oxidative CO2 reforming of CH4 to produce synthesis gas at 700°C over supported Ni catalysts have been studied. A Ni/Mg-Al catalyst was prepared by the solid phase crystallization (spc-) method starting from a hydrotalcite-type (HT) anionic precursor. From XRD analysis, only Ni0.5Mg2.5Al catalyst consists of the layered hydrotalcite-type structure; not Ni0.5Ca2.5Al and Ni/Al2O3 catalysts. By TPR test, the Ni0.5Mg2.5Al-HT catalyst requires a high reduction temperature than the Ni0.5Ca2.5Al catalyst. It implies that the Ni0.5Mg2.5Al-HT which has a layered structure shows the stronger interaction strength between the molecules. It might increase the resistance of coke formation on the surface of the catalyst. For the reaction tests, the Ni0.5Ca2.5Al showed the highest initial activity for synthesis gas production for all reactions; but, its activity was decreased quickly due to coke formation except during the partial oxidation of CH4. The Ni0.5Mg2.5Al-HT showed a relatively higher reactivity compared to the equilibrium level than Ni/Al2O3 catalyst; and it shows very stable reactivity than other catalysts. By TPO test, the Ni0.5Mg2.5Al-HT has the lower amount of coke formed during the reaction than the Ni0.5Ca2.5Al catalyst. It confirms that the Ni0.5Mg2.5Al-HT catalyst has stronger resistance to coke formation; and it leads to provide stable reactivity in any reforming conditions at high temperature. Therefore, the Ni0.5Mg2.5Al-HT catalyst was the most promising catalyst in terms of activity and stability for partial oxidation, CO2 reforming, and oxidative CO2 reforming of CH4. The Ni0.5Mg2.5Al-HT catalyst was used to investigate the CO2 reforming of CH4 kinetics. With increasing CH4 partial pressures at constant CO2 partial pressure, the rates of CH4 consumption were increased. However, with increasing CO2 partial pressure at constant CH4 partial pressure, CH4 consumption rates was increased at lower CO2 partial pressure, but turned to independent at higher CO2 partial pressure. When the partial pressure of H2 was increased, the CO formation rate was decreased; it confirmed that the reverse water-gas shift (RWGS) reaction was occurring during the CO2 reforming of CH4 reaction. In addition, the reaction kinetic expression was proposed when the CH4 dissociation step was considered as a rate-limiting step.

Partial oxidation of CH4, CO2 reforming of CH4, and oxidative CO2 reforming of CH4 to produce synthesis gas at 700°C over supported Ni catalysts have been studied. A Ni/Mg-Al catalyst was prepared by the solid phase crystallization (spc-) method starting from a hydrotalcite-type (HT) anionic precursor. From XRD analysis, only Ni0.5Mg2.5Al catalyst consists of the layered hydrotalcite-type structure; not Ni0.5Ca2.5Al and Ni/Al2O3 catalysts. By TPR test, the Ni0.5Mg2.5Al-HT catalyst requires a high reduction temperature than the Ni0.5Ca2.5Al catalyst. It implies that the Ni0.5Mg2.5Al-HT which has a layered structure shows the stronger interaction strength between the molecules. It might increase the resistance of coke formation on the surface of the catalyst. For the reaction tests, the Ni0.5Ca2.5Al showed the highest initial activity for synthesis gas production for all reactions; but, its activity was decreased quickly due to coke formation except during the partial oxidation of CH4. The Ni0.5Mg2.5Al-HT showed a relatively higher reactivity compared to the equilibrium level than Ni/Al2O3 catalyst; and it shows very stable reactivity than other catalysts. By TPO test, the Ni0.5Mg2.5Al-HT has the lower amount of coke formed during the reaction than the Ni0.5Ca2.5Al catalyst. It confirms that the Ni0.5Mg2.5Al-HT catalyst has stronger resistance to coke formation; and it leads to provide stable reactivity in any reforming conditions at high temperature. Therefore, the Ni0.5Mg2.5Al-HT catalyst was the most promising catalyst in terms of activity and stability for partial oxidation, CO2 reforming, and oxidative CO2 reforming of CH4. The Ni0.5Mg2.5Al-HT catalyst was used to investigate the CO2 reforming of CH4 kinetics. With increasing CH4 partial pressures at constant CO2 partial pressure, the rates of CH4 consumption were increased. However, with increasing CO2 partial pressure at constant CH4 partial pressure, CH4 consumption rates was increased at lower CO2 partial pressure, but turned to independent at higher CO2 partial pressure. When the partial pressure of H2 was increased, the CO formation rate was decreased; it confirmed that the reverse water-gas shift (RWGS) reaction was occurring during the CO2 reforming of CH4 reaction. In addition, the reaction kinetic expression was proposed when the CH4 dissociation step was considered as a rate-limiting step.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20389号 / 工博第4326号 / 新制||工||1670(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 陰山 洋, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Production of high-quality syngas from biomass gasification in a dual fluidised bed gasifier (DFBG) has made a significant progress in R&D and Technology demonstration. An S&M scale bio-automotive fuel plant close to the feedstock resources is preferable as biomass feedstock is widely sparse and has relatively low density, low heating value and high moisture content. This requires simple, reliable and cost-effective production of clean and good syngas. Indirect DFBGs, with steam as the gasification agent, produce a syngas of high content H2 and CO with 12-20 MJ/mn3 heating value. The Mid Sweden University (MIUN) gasifier, built for research on synthetic fuel production, is a dual fluidised bed gasifier. Reforming of tars and CH4 (except for methanation application) in the syngas is a major challenge for commercialization of biomass fluidised-bed gasification technology towards automotive fuel production. A good syngas from DFBGs can be obtained by optimised design and operation of the gasifier, by the use of active catalytic bed material and internal reforming. This thesis presents a series of experimental tests with different operation parameters, reforming of tar and CH4 with catalytic bed material and reforming of tar and CH4 with catalytic internal reformer.   The first test was carried out to evaluate the optimal operation and performance of the MIUN gasifier. The test provides basic information for temperature control in the combustor and the gasifier by the bed material circulation rate.    After proven operation and performance of the MIUN gasifier, an experimental study on in-bed material catalytic reforming of tar/CH4 is performed to evaluate the catalytic effects of the olivine and Fe-impregnated olivine (10%wtFe/olivine Catalyst) bed materials, with reference to non-catalytic silica sand operated in the mode of dual fluidised beds (DFB). A comparative experimental test is then carried out with the same operation condition and bed-materials but when the gasifier was operated in the mode of single bubbling fluidised bed (BFB). The behaviour of catalytic and non-catalytic bed materials differs when they are used in the DFB and the BFB. Fe/olivine and olivine in the BFB mode give lower tar and CH4 content together with higher H2+CO concentration, and higher H2/CO ratio, compared to DFB mode. It is hard to show a clear advantage of Fe/olivine over olivine regarding tar/CH4 catalytic reforming.    In order to significantly reduce the tar/CH4 contents, an internal reformer, referred to as the FreeRef reformer, is developed for in-situ catalytic reforming of tar and CH4 using Ni-catalyst in an environment of good gas-solids contact at high temperature.  A study on the internal reformer filled with and without Ni-catalytic pellets was carried out by evaluation of the syngas composition and tar/CH4 content. It can be concluded that the reformer with Ni-catalytic pellets clearly gives a higher H2 content together with lower CH4 and tar contents in the syngas than the reformer without Ni-catalytic pellets. The gravimetric tar content decreases from 25 g/m3 down to 5 g/m3 and the CH4 content from 11% down below 6% in the syngas.   The MIUN gasifier has a unique design suitable for in-bed tar/CH4 catalytic reforming and continuously internal regeneration of the reactive bed material. The novel design in the MIUN gasifier increases the gasification efficiency, suppresses the tar generation and upgrades the syngas composition. / Gasification-based Biorefinery for Mechanical Pulp Mills