This study developed a membrane separation process for biogas using a DDR-type Zeolite membrane with high CO2/CH4 selectivity. Biogas produced in a sewage plant was separated and purified by using the DDR-type Zeolite membrane, and the performance and durability of the membrane was estimated. We first analyzed the membrane performance required for a simple, one-stage separation process through a mathematical model and experimentation, and then decided upon the appropriate flow rate through DDR type Zeolite pattern usage. Next, in order to conduct actual biogas separation and purification, we set up a pilot plant within the sewage treatment facility. The purification tests showed that purification was possible with our objective purity of CH4 concentration of 90% and emission CO2 concentration of over 97%. Separation factor of CO2/CH4 and permeation of the DDR-type Zeolite membrane changed little even after 40 h of ventilation. These results demonstrate that the membrane separation process developed is fully applicable to the separation and purification of biogas. Finally, we examined the influence of impurities in the biogas on membrane separation performance by supplying the biogas without pre-treatment for 1600 h. From the results, we believe that membrane performance is reduced by long periods of ventilation and high boiling compounds such as higher hydrocarbons and siloxane, which are present as impurities in the biogas.
In order to produce sulfites from SO2 contained in flue gases, an SO2 absorption experiment was conducted using a gas mixture, containing oxygen that emulates industrial flue gases. Concentrations of sulfite and sulfate produced by SO2 absorption were measured by HPLC, and their production ratios were assessed at temperatures between 288 K and 333 K. As a result, the absorption product was mostly sulfate irrespective of temperature when SO2 was absorbed using a liquid absorbent with a pH of over 6; however, sulfite ions were produced when the pH was around 4. When SO2 absorption was carried out using an absorbent with a pH of under 4, sulfate was produced at a temperature of 333 K, but sulfite was produced at temperatures below 303 K.
The occurrence of secondary atomization in emulsified fuel is widely accepted to explain a decrease in NOx and soot emissions. Although it is known that secondary atomization, such as puffing and micro-explosion, occurs in heating process, little detailed information is available on the secondary atomization behavior of emulsified fuel droplets. In this paper, the effect of surfactant on secondary atomization was investigated. A method was proposed to visualize the internal behavior in emulsified fuel droplets using colored water. Emulsified fuel droplets prepared using various surfactants and colored water were suspended by use of a thermocouple, and the secondary atomization behavior of the droplets was observed using a hi-speed video camera. In the case of O/W emulsified fuel droplets, reaggregation of dispersed water droplets and micro-explosion were observed after aggregation of dispersed oil droplets and phase inversion from O/W type to W/O type. Although the probability of micro-explosion occurring decreased with an increase in HLB value in the case of W/O emulsified fuel droplets, little difference was observed in the probability as a function of HLB value in the case of O/W emulsified fuel droplets.
The reaction rate constant of carbonyl sulfide over a titanium oxide-based catalyst, CRS 31 (Axens), was measured using a fixed-bed reactor at temperatures from 393 to 473 K. The conversion of carbonyl sulfide by hyrolysis over CRS 31 was 0.9 at 393 K, 2.6% H2O. The hydrolysis of carbonyl sulfide over CRS 31 was a first-order reaction with a rate constant of 3.3 s−1 at 433 K, 2.6% H2O. The resistance to HCl of CRS 31 was superior to that of aluminum oxide-based catalysts. In experimental apparatus consisting of a gasfier operating under atmospheric pressure, a water scrubber, and COS converters, the performance of CRS 31 was evaluated by use of syngas. The conversion of carbonyl sulfide by hydrolysis over CRS 31 was 0.98 at above 453 K with a residence time of 1 s.
Direct decomposition of PCBs-containing insulation oil as a model of persistent liquid waste was attempted by use of microwave non-thermal plasma. The decomposition ratio of insulation oil was found to be about 80%, and the dechloridation ratio of trichlorobenzene was 78–87%. In the case of PCBs, although about 5.2×10−4% of PCBs were converted to PCDFs and the decomposition ratio of non-ortho Co-PCBs was 3.0–46%, the total decomposition ratio was 77%. As a result, PCBs-containing insulation oil in a liquid state could be decomposed by use of microwave non-thermal plasma.
Event correlation analysis for alarm data at the ethylene plant in Japan was applied to reduce the number of plant alarms. This is a data-mining method that detects statistical similarities among discrete events of alarms or operations. By grouping correlated events based on the degree of similarity, countermeasures for reducing alarms can be considered more easily than by analyzing individual events of alarms and operations. By using the event correlation analysis, event data of alarms or operations of the ethylene plant was divided into a limited number of groups. The result of the analysis was helpful for estimating the effect of each countermeasure to reduce unnecessary alarms such as sequential alarms buried in the noisy plant data.
The importance of plant alarm systems has grown with increases in the scale of plants and the sophistication of plant monitoring and control systems. In this paper, a two-layer cause-effect model is proposed that represents the cause-and-effect relationship between state variables. Using the proposed model, a derivation algorithm of sets of pairs of alarm variables and signs is proposed. The signs indicate the upper or lower limits of alarm variables. The derived sets of pairs are theoretically guaranteed to be able to qualitatively identify all assumed malfunctions. The proposed method using the two-layer cause-effect model was applied to a simple process, and the simulation results illustrated the usefulness of the method.
Removal of negative-tone novolak chemical amplification resist by use of ethylene carbonate (EC) and propylene carbonate (PC) was investigated. Unlike positive-tone resist, the removal rate of negative-tone resist by these chemicals was found to be easily measurable. The removal rate of resist by both EC and PC decreased with increasing exposure dose because of the increasing degree of crosslinking of the resist. The removal rate by EC was faster than that by PC at the same temperature. EC more readily penetrates the exposed resist than PC because of its smaller molecular size. From Arrhenius plots of removal rate, we found that both high exposure dose and large molecular size of the chemicals lead to high activation energy in the resist removal reaction.
Structural analysis of a self-assembled layer with lattice-like structures composed of cubic hematite particles with the side length of approximately 0.9 μm were carried out by means of radial distribution functions (RDFs). The cubic particles were synthesized by aging a solution of FeCl3 for 8 days at 373 K. The RDFs were determined by a digital image analysis method from the direct optical microscope observation of the particles. Two-dimensional Monte Carlo simulations of the cubic hematite particles were also carried out in order to clarify the influences of a weak magnetic field and magnetic interactions between particles on the lattice structure. In the case of very weak geomagnetic fields, chain-like and square lattice structures were formed on a glass plate through the sedimentation process of the particles. The simulation results revealed that the square lattice structures are stabilized by the zigzag orientation of the magnetic moments of the particles. In the case of relatively strong magnetic fields, a broad shoulder appeared at a slightly longer distance from the first peak position in the experimental RDF. This corresponds to the three small peaks that appeared in the simulated RDF for an ideal monodisperse system. This suggests that energetically stable oblique lattice structures are formed with magnetic moments aligned to the field direction.
To develop a direct methanol fuel cell (DMFC) which can directly use high concentration of methanol, a novel passive DMFC employing a perforated metal sheet, of which the open ratio and the pore diameter were regularly controlled, between the anode electrode and methanol tank were proposed. The effect of the open ratio and the pore diameter of the perforated metal sheet on the power generation characteristics of the passive DMFC were investigated on the basis of the power generation experiment at several methanol concentrations. Methanol crossover was controlled by decreasing the open ratio to less than 1%, therefore, a high concentration of methanol could be used effectively. The methanol transfer coefficient through the metal sheet increased with increasing the open ratio up to 1%. However, when the open ratio was over 3%, the methanol transfer coefficient was nearly constant, and the control of the methanol crossover was incapable. Such effect of the open ratio on the methanol transfer coefficient could be explained by spreading the methanol solution on the surface of the metal sheet from the pore with a certain distance. The pore diameter was hardly affected the transfer coefficient.
By bubbling air or nitrogen gas, 1,4-dioxane in waste water was vaporized at 298–357 K. The vaporization behavior could be explained by means of the Henry constant. By UV irradiation of the gaseous phase containing 1,4-dioxane, a constant amount of 1,4-dioxane was decomposed per unit time regardless the mean residence time in an UV irradiation vessel. By appyling the gas bubbling-UV irradiation treatment to the waste water eluted from solid-waste reclaimed land, it was verified that 1,4-dioxane in the solution was sufficiently decomposed. As UV irradiation products, acetic acid, acetol, ethylene glycol monoformate and ethylene glycol diformate were detected. These products were presumed to be formed by oxidative cleavage of the 1,4-dioxane ring.