NO dissociation on Cu-based catalyst is investigated using density functional theory based calculations. NO dissociation on Cu-terminated Cu₂O(111) surface is comparable with its dissociation on Rh(111) which is characterized by a transition state lying below the reference level (surface and NO_gas). This finding is associated to the modified electronic and geometric structure of the surface Cu atoms in comparison to the Cu atoms of Cu(111). The local density of states profile of the d orbital of the Cu atoms in Cu₂O(111) shows that the states are shifted to the Fermi level region which explains the good adsorption and easy dissociation of NO. In Cu(111), the dissociation is accompanied by a large amount of activation barrier and NO desorption is more likely to happen. Coadsorbed N and O atoms are unstable on O-terminated Cu₂O(111) and is due to the repulsive effect of the surface and subsurface O atoms. This work is made through the initiative of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of the Japanese government through the Elements Science and Technology Project and is a collaboration among various research groups to realize functional materials that are free from precious and hazardous substances.

View full abstract

Local structure and acidic properties of catalytic active sites on metal oxides and zeolites were studied using molecular simulation methods, DFT (density functional theory) and ONIOM. Strong acidity of sulfate modified ZrO₂ surface could be explained by local structure incorporating co-adsorbed SO₃ and H₂O molecules on the surface. The structure around Ti ion in MFI zeolite framework was studied. Relative stability of Ti atom at each T site was investigated using a large cluster model. The local structure of Brønsted acid sites on beta (BEA) zeolite was studied in detail. It has been revealed that the proton in a 6-oxygen ring interacts with two oxygen atoms to form hydrogen bond. These hydrogen bonds stabilize the proton in the framework, so that the proton shows very weak acidity. Finally, the acidity of OH group ensemble on a pure quartz surface was studied. Interestingly, the proton in the OH group ensemble shows strong acidity, suggesting that addition of atoms such as Al is not necessary to induce acid site in a silicate structure.

View full abstract

Screening, synthesis, and testing of metal-modified carbon catalysts for fast pyrolysis of Jatropha waste were carried out using Pyro-GCMS (Py-GC/MS) and a quartz reactor. Our results suggest that activated carbon-based catalysts, especially those impregnated with Ni, are effective catalysts. The selectivity for aromatic and aliphatic hydrocarbons was 79.4 %, with relatively low amounts of oxygenated compounds or other unfavorable components. Using Ni/C catalyst in a quartz reactor, the selectivity for aromatic and aliphatic hydrocarbons was 64.1 %. Successive reaction through hydrogen migration over the metal-modified activated carbon catalyst surface could occur at 600 °C. Further improvements of catalyst activity and the reactor configuration may be required to produce liquid fuel commercially.

View full abstract

To enhance the acidity of cobalt oxide, sulfation was carried out using aqueous solution of cobalt sulfate impregnated on cobalt oxide and the product calcined at high temperatures. Conventional sulfation of oxides by sulfuric acid could not avoid dissolution of cobalt oxide in the sulfuric acid. The activity of cobalt oxide for acid-catalyzed ethanol dehydration reaction was greatly enhanced by sulfation using cobalt sulfate. The activity of the prepared sulfated cobalt oxide was comparable to that of conventional SiO₂–Al₂O₃ acid catalyst. The sulfated cobalt oxide did not show activity for pentane isomerization, which was catalyzed by sulfated zirconia prepared by the same methodology of sulfate salt impregnation, using zirconium sulfate solution was impregnated onto zirconia. The highest activity was obtained by heat treatment at 1073 K. This treatment temperature is the highest among solid acid catalysts reported so far.

View full abstract

Conversion of heavy oil to added-value lighter fractions is very important. One conversion method is hydrotreatment of heavier residues in the hydroprocessing unit followed by cracking in the FCC or RFCC unit. However, if heavier residues are treated with the same catalyst under the same process conditions, the sulfur contents in the product oil will increase, so higher temperatures will be required to maintain constant sulfur in the product oil. This higher temperature also results in shorter catalyst life. This study developed zinc and phosphorus modified NiMo/Al₂O₃ catalyst which is resistant to deactivation by coke deposition. The effect of zinc on the suppression of deactivation rate was remarkable in the catalyst containing phosphorus in this study. IR spectroscopy showed that the coexistence of zinc with phosphorus inhibited the increase of acidic hydroxyls and the addition of phosphorus increased acidic alumina hydroxyls, leading to lower coke deposition on the zinc and phosphorus modified NiMo/Al₂O₃ catalyst. Zinc and phosphorus modified NiMo/Al₂O₃ catalyst also showed less deactivation and higher hydrodesulfurization activity in the middle period of the bench plant test. These results were well-consistent with catalyst performance in the commercial plant.

View full abstract

Synthetic natural gas (SNG) production using biomass gasification has recently become important as SNG has been suggested as an alternative to fossil fuels. In the process, CH₄ synthesis (methanation) must be considered in addition to biomass gasification. By integrating exothermic methanation and endothermic gasification, the required heat energy can be lowered in an autothermal process. In this study, the performances of autothermal SNG production were estimated from process simulations. In this process, CO₂ separation after methanation is inevitably energy-intensive. Therefore, feasibility analysis was conducted on the autothermal SNG production process with CO₂/CH₄ membrane separation, which is expected to achieve drastically lower energy consumption. These assessments can determine whether membrane separation has the potential as an alternative to the conventional separation unit. Using a membrane process, CH₄ loss can become less than 2 %, if the separation factor of CO₂ over CH₄ exceeds 50. Therefore, we conclude that this value should be set as the minimal target value for the CO₂/CH₄ separation factor. Achievement of this goal will probably facilitate widespread use of SNG production by biomass gasification.

View full abstract

Three types of oil-mist traps were evaluated for the efficient collection of bio-oil (tar) aerosol produced in a fast pyrolysis reaction at the laboratory scale. The oil-mist traps employed a cooling method, a solvent method, or an electrostatic precipitator (ESP) for collecting the oil mist. If the ESP electrode was energized at 9 kV, almost all of the bio-oil mist was collected by the ESP. The liquid yield of the bio-oil obtained using the three methods decreased in the order: ESP method>solvent method>cooling method. For these experiments, biomass samples of Jatropha cake and cedar, sieved to yield a powder (300-500 μm), were pyrolyzed at 500 °C in a fluidized-bed reactor. Although the solvent method showed a relatively high collection efficiency, it was necessary to separate the bio-oil from the solvent. Therefore, the ESP method is the most effective method for collecting bio-oil.

View full abstract

During the oil production process, oily waste water is coproduced at a rate several times that of oil. This water is known as produced water. Treatment levels and technologies are selected based on disposal method or reutilization objectives, environmental impacts, economics, and other such factors. A 50 m³/day capacity pilot plant was designed, fabricated, and utilized to conduct produced water treatment trials. Pilot treatment trials of produced water from three different oilfields in Oman were carried out by nitrogen microbubble flotation in conjunction with coagulation/flocculation. Filtration and adsorption treatment processes were tested as well. Oil concentration in one of the produced waters was reduced to below the Omani standard for re-use, through flotation combined with flocculation/coagulation. Oil concentrations in the other two produced waters, which had higher-initial concentrations, were reduced to below the Omani standard for marine discharge. With additional adsorption treatment, these concentrations were further reduced of the level of the re-use standard as well. Additionally, aeration treatment was effective for removal of sulfur compounds such as sulfide from produced water.

View full abstract

Bioethanol has recently become an important resource for chemical industries. The chemical compositions of 17 different types of bioethanol were investigated with a focus on impurities that could affect catalytic performances in the downstream chemical processes. Lignocellulosic ethanol contained higher concentrations and a greater variety of organic impurities compared to sugar- or starch-derived bioethanol. Twenty-nine impurities were identified in lignocellulosic ethanol, whereas 16 impurities were in sugar- or starch-derived bioethanol. Lignocellulosic ethanol contained high concentrations of acetic acid, acetaldehyde, methanol, and furan-related compounds such as furfural. In contrast, with the exception of molasses-derived bioethanol obtained by crude distillation, the concentrations of these components were lower in sugar- or starch-derived bioethanol samples. Lignocellulosic ethanol contained dimethyl disulfide and thiazole, whereas the only organosulfur compounds found in sugar- or starch-derived bioethanol were dimethyl sulfide and dimethyl sulfoxide. These sulfur-containing impurities can cause catalyst deactivation in the bioethanol transformation processes. In lignocellulosic ethanol, more than 0.1 μg/mL of Si was detected.

View full abstract