Two-dimensional (2D) transition metal oxide nanosheets have useful characteristics such as high surface areas, and defined and controllable surface acidity, with potential for applications in solid acid catalysts and photocatalysts. The most common synthesis method to obtain 2D metal oxide nanosheets is the "exfoliation method" from the corresponding bulk layered oxide by the top-down approach. However, fragmentation and re-aggregation of nanosheets are some of the problems. In addition, this method requires calcination processes for the synthesis of layered compounds at high temperature and prolonged exfoliation treatment of the 2D crystal layer. In this study, layered titanate nanosheets and single layer niobate nanosheets were formed by the bottom-up approach utilizing hydrolysis and condensation of metal alkoxides in the presence of surfactants. Formation processes of the metal oxide nanosheets and effects of surface modification by the surfactants on their properties were studied. In addition, these nanosheets were evaluated for photocatalytic reactions such as photodegradation of organic dyes and hydrogen evolution from water decomposition. Composites of niobate nanosheets with other types of 2D nanosheets (graphene oxide and MoS2) achieved effective photocatalytic activities. Furthermore, stacked nanosheet membranes can be formed by assembling nanosheets. The nanosheet membranes have stable structures in water and high separation performance against aniomic dyes and salts, suggesting high potential as separation membranes.
It has been proven that activated carbon with certain physical properties has capability for removal of sulfur compounds, especially the refractory sulfur species, such as 4,6-dimethyldibenzothiophene in diesel fuel. Also, it has been confirmed that the spent activated carbon of sulfur breakthrough can be regenerated by washing with a warm aromatic solvent. Based on these characteristics of activated carbon, this paper proposes a new flow scheme with high energy and capital efficiency for clean diesel fuel production. The use of this new process in refineries enables existing diesel HDS units to produce diesel fuel with a lower sulfur content without increasing the severity in HDS reaction or reducing the throughput. Therefore, this process is applicable to existing diesel HDS units requiring modification to comply with the new, severer regulations on sulfur level. The present study technically and economically justifies applying this new process to refineries with FCC or coker facilities.
Methylcyclohexane (MCH) is a candidate liquid organic hydrogen carrier for the storage of renewable energy. The by-products were examined in dehydrogenation and hydrogenation of the MCH/toluene (TOL) pair that forms an energy storage and release system. Pt catalyst was used for the dehydrogenation of MCH, and Ni catalysts were used for the hydrogenation of TOL, and 10 cycles of dehydrogenation/hydrogenation were conducted. Conversion of TOL to MCH greater than 97 % across all cycles, and conversion of MCH to TOL decreased from 90 to 84 %, with increasing cycle number. The original MCH feed contained 0.6 % impurities, and the concentration of by-products ranged from 0.7-0.9 %. More than 70 by-products were identified in the liquid product, and were categorized as the products of six types of side reactions: demethylation, ring-opening, isomerization to form 5- or 6-membered ring compounds, dimerization, and polycyclic compound formation. Demethylation compounds showed remarkable accumulation after 10 cycles.
Changes in asphaltene content in heavy oils after thermal visbreaking at different cracking temperatures and reaction times were studied by various techniques, including elemental analysis, X-ray diffraction, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The yield of asphaltene decreased at the beginning of thermal visbreaking, but further increased with deep thermal visbreaking. The aromaticity of asphaltene increased with higher cracking severity. In addition, the effect of asphaltene on viscosity was investigated before and after thermal visbreaking. There was a close relationship between asphaltene content and viscosity, and the viscosity increased dramatically with higher asphaltene content. The viscosities were also different at the same asphaltene content due to the differences in chemical composition and macrostructure of the asphaltene molecules. Therefore, both the contents and structures of asphaltene had significant influences on the viscosity of heavy oils. However, the changes in the content and structure of asphaltene were not major causes for the decrease in viscosity after thermal visbreaking.
The energy-saving performances of membrane separation and hybrid membrane separation/distillation processes for a propylene/propane binary system were investigated using a process simulator, and the effect of stage-cut was assessed on product composition and propylene recovery ratio for one-stage and two-stage membrane separation processes as well as hybrid processes comprising a membrane separation unit and a distillation column. The propylene contents in the feed were 30, 60, 90, and 98 mol%. The optimum separation process based on the propylene content in the feed was based on the simulation results. A hybrid process was suitable for 30 mol% propylene, with the permeate and retentate streams fed into a distillation column after membrane separation of the mixture. High energy-saving performances were achieved for both the hybrid process and the membrane separation process for propylene contents of 60, 90, and 98 mol%.