Recently, biomass has attracted much attention as a renewable energy resource. Microalgae are particularly promising biomass species because of the high growth rate and high CO2 fixation ability compared to plants. Effective liquid fuel production from microalgae was studied using Botryococcus braunii and Dunaliella tertiolecta, which accumulated terpenoid hydrocarbon and glycerol, respectively. B. braunii could remove nitrogen and phosphorus from secondarily treated sewage (STS) in a batch system and a continuous bioreactor system with hydrocarbon production. The intracellular glycerol content could be controlled by post-translational modifications in D. tertiolecta. B. braunii is more profitable for liquid fuel production than D. tertiolecta based on calculating the energy balance.
The movement characteristics of aggregates in asphalt mixtures were investigated with wheel tracking tests under the following loading conditions: reciprocating motion, one-way motion, and one-way motion with braking. The outside wheel tracking tests used fine and gap graded (13F) asphalt mixtures. The tests showed that the amount of rutting in one-way motion was larger than that in reciprocating motion. In the case of reciprocating motion, the surface heaved up at the right load end. In the case of one-way motion, the surface heaved up at the point 50 mm from both contact ends of the tire. Consolidation caused the rutting phenomenon during reciprocating motion, and flow caused the rutting phenomenon during one-way motion, based on the movement of aggregates as viewed from the right-angle direction to the loading. Therefore, the rutting phenomenon including the deformation in the transverse direction can be analyzed by wheel tracking tests based on one-way motion, or reciprocating motion, using the conventional wheel tracking test. However, in the case of rutting during one-way motion with braking, the movement of aggregates in the wheel direction caused by tire friction was larger than movement in the depth direction. The inside of the asphalt mixture was dragged by tire friction in the wheel direction. Therefore, at locations where brake operation is frequently needed, the rutting phenomenon caused by flow and abrasion will be greater.
Hydrothermal decomposition of thiophene derivatives in subcritical and supercritical water with alkali was studied to enhance desulfurization using a new on-site upgrading technology. Benzothiophene, dibenzothiophene, and derivatives (BTs and DBTs) can be decomposed by hydrothermal reaction with alkali in a temperature region where thermal decomposition is difficult. The ease of decomposition is influenced by the type and concentration of the alkali solution. Decomposition in KOH solution is the most complete, and occurs at a certain alkali concentration. The reaction is sensitive to the pressure in supercritical water. Moreover, the reaction products of hydrothermal decomposition obtained in the present study differ to those by the hydrodesulfurization method (HDS) previously reported by other researchers. These results suggest that the mechanisms of decomposition are different and hydrothermal decomposition is preceded by ionic reaction. The ease of decomposition of BTs and DBTs is influenced by the molecular structure, similar to the trends seen in HDS.
Model hydrodesulfurization catalysts (Co2.75Mo11, Ni2.75Mo11 and Ni0.9Co1.85Mo11 wt%/γ-Al2O3) prepared by impregnation of similar supports with similar starting materials were used in the following test reactions: hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene, with and without addition of H2S or NH3. The presence of H2S or NH3 has a profound effect on the catalyst ranking and the activities of various reaction pathways, e.g., the hydrogenation (HYD) route and the direct desulfurization (DDS) route. In the case of the HDS of DBT and 4,6-DMDBT, hydrogen sulfide only weakly poisoned CoMo and NiCoMo catalyst, whereas a NiMo catalyst is poisoned more strongly. On the other hand, ammonia strongly poisoned HYD route of CoMo catalyst, whereas DDS route of NiMo catalyst is not at all poisoned in the case of the HDS of DBT. The trimetallic NiCoMo catalyst exhibited the best performance in the conversion of DBT. A comparison of the HYD and DDS rate constants among CoMo, NiMo and NiCoMo catalysts shows that in the presence of rich H2S, the activity of HYD and DDS of the NiCoMo catalyst equals the sum of the activity of the HYD of NiMo catalyst and of the DDS of CoMo catalyst. On the other hand, in the presence of rich NH3, the activity of the NiCoMo catalyst equals the sum of the HYD and DDS of NiMo catalyst, which each in turn are higher than those of CoMo catalyst. This dual promoting effect of NiCoMo catalyst causes higher activity than either NiMo or CoMo catalyst in the presence of either rich H2S or rich NH3.
Characterization of nickel and cobalt catalysts supported on oxidized diamond (O-dia) in the partial oxidation of methane to synthesis gas was carried out by X-ray photoelectron spectroscopy (XPS) and the transient response pulse technique. Carbon deposition occurred on nickel/O-dia, but not on cobalt/O-dia catalyst at 873 K throughout prolonged reaction. XPS analyses observed partially reduced nickel oxides on nickel/O-dia catalyst after reaction with methane/oxygen (5/1) at 873 K. Co(0), partially reduced cobalt oxide, and Co(III) oxide phases were found on cobalt/O-dia catalyst after reaction at 873 K. Transient response methane/oxygen (2/1) pulse studies found a large amount of hydrogen production occurred immediately at 873 K over the nickel/O-dia catalyst. However, a very small amount of hydrogen production was seen over the cobalt/O-dia catalyst, indicating that nickel and cobalt species supported on O-dia exhibited different behavior. Transient response of the catalyst bed temperature found that endothermic reaction occurred on the nickel/O-dia catalyst at 873 K, but exothermic reaction proceeded on the cobalt/O-dia catalyst. These results suggest that methane decomposition to hydrogen is the primary reaction path over nickel/O-dia catalyst, whereas complete oxidation is the primary reaction followed by steam and carbon dioxide reforming to produce synthesis gas over the cobalt/O-dia catalyst.
Nickel-catalyzed decomposition of methane into carbon and hydrogen was examined using a thermogravimetric apparatus. The Ni catalyst supported on zirconia synthesized by the glycothermal method gave hydrogen and a high yield of multi-walled carbon nanotubes. The initial rate of methane decomposition increased with increasing reaction temperature at 400-680°C, but decreased with reaction temperature > 700°C. Raman spectroscopy suggested that carbon nanotubes formed at higher temperatures had more graphite like structure than those obtained at lower temperatures. Feed gas containing methane and hydrogen caused slow deactivation of the catalyst. As a result, carbon yield increased with increasing partial pressure of hydrogen in the feed gas. Mechanisms for the deactivation of the catalysts are discussed.
Any fractures present in a porous medium have a greater influence on the flow of fluid than the porosity of the bulk material because the fractures are much more permeable. The tracer test, one method for detecting fractures, can estimate the properties of fractures by inverse analysis of effluent-tracer concentration data. This study simulated tracer tests for a porous medium containing a single fracture and tried to identify the properties of the fracture by inverse analysis of the effluent-tracer concentration curve. The complex variable boundary element method (CVBEM), which precisely describes the flow around a fracture, was utilized for the simulation and the genetic algorithm (GA) was used for the inverse analysis. Several model studies showed that accurate identification of the fracture was difficult by inverse analysis using only one series of effluent-tracer concentration data, whereas two series of concentration data obtained in different well arrangements could identify the fracture more accurately. The crucial parameters that determine the shape of the tracer concentration curve were identified from the convergence behavior in the GA.
The most commonly used and cost effective method of transmission pipeline non destructive testing (NDT) utilizes the magnetic flux leakage (MFL) technique. The corrosion pits occur in many and complex shapes, so it is very difficult to research variety rules in MFL testing using experimental methods. Finite element analysis (FEA) has been used to study MFL signals. We used three-dimensional FEA to simulate the effect of complex corrosion on MFL signals from a steel plate in the absence of a geometrical defect. We derived the complex corrosion patterns from finite-element structural modeling of simulated defects. MFL for four complex corrosions was described and calculated using FEA. The results show that the relative position of the complex corrosion pits affects the magnitude of the MFL signal significantly. Better understanding of these effects will be helpful for interpreting the MFL signals in transmission pipeline NDT.
Special precautions for evaluating ultra deep gas oil hydrodesulfurization catalysts in the pilot plant were investigated. Analysis using gas chromatograph atomic emission detector (GC-AED) and GC-MS showed free sulfur was formed in the hydrodesulfurized product gas oil, if H2S dissolved in the product oil contacted air. Although the precise mechanism of free sulfur formation is not clear, direct oxidation of H2S, Claus reaction or the oxidation of ammonium polysulfide are possible routes. Once free sulfur forms in the product gas oil, it is difficult to remove by stripping with nitrogen gas. To prevent the formation of free sulfur compound completely, H2S should be separated before contacting air in a pilot plant or in a sampling chamber sealed with nitrogen gas. On the other hand, no free sulfur compound was observed in commercial gas oil, as no contact with air occurs before H2S stripping.