A μVT-ensemble Orientational-Bias Monte Carlo technique has been utilized to simulate adsorption isotherms of pure and mixed propane/propylene in NaX zeolite at 303 K. Propylene is adsorbed more strongly than propane, and the adsorption energy of propylene is found to be about 5 kJ/mol larger than that of propane mainly through the Coulomb interactions between molecules and zeolite atoms/Na ions. The adsorption isotherms of pure gases are correlated with four theoretical models: Langmuir, multi-site occupancy, two-dimensional van der Waals fluid and Ruthven+U models. The latter three models are found to fit much better than the Langmuir model. The simulation isotherms of propane/propylene mixtures, calculated at 100 kPa in total pressure, are qualitatively well predicted by the latter three models.
Mixing behaviors in a conical Taylor–Couette flow system were investigated at low Reynolds numbers using flow-visualization and salt-solution tracer techniques. Owing to sensitivity during the start-up procedure, the acceleration rate of the inner conical cylinder was precisely controlled by computer. Two different flow modes were observed in the laminar flow regime. When the inner conical cylinder was accelerated at a low rate (0.05 rad/s2), the whole fluid column was filled with helical vortices. In the case of a high acceleration rate (0.5 rad/s2), an upward traveling motion of the Taylor vortices was observed. The vortices started to display a global upward motion due to the strong meridional circulation. These two flow modes showed quite different mixing behaviors even at nearly equal Reynolds numbers. In the case of the upward traveling motion, the tracer substance was convected with the traveling vortices in the main flow cross-section and with the meridional flow at the outer-edge cell boundaries. In the helical motion, on the other hand, the tracer was transported by diffusion-like motion along the helical vortex filament and by convection along the secondary flow streamlines at outer-edge cell boundaries.
The purpose of the present work is to investigate time-dependent flow properties in doubly periodic and weakly turbulent wavy vortex flows in a Taylor–Couette flow system with the aid of a wavelet analysis. Time series data of fluctuating tangential velocity were obtained with a fiberoptic laser-Doppler velocimeter. To clarify the dependence of time-fluctuation flow properties on spatial location, the velocity was measured at many positions within each vortex. In order to estimate wavelet correlation patterns, logarithmic expectation and information entropy were calculated at each time scale. The wavelet patterns revealed that the time-fluctuation properties depend not only on the spatial location but also on time. The continuous wavelet transform analysis can provide a promising technique to reveal the fractal structure of a chaotic wavy vortex flow.
In order to ensure the practical application of a titanium dioxide-based photocatalytic system, it is essential that reactors capable of being scaled up be designed. This has been difficult due to the issue of light distribution and irradiation of the photocatalytic surface. In this paper, a novel design utilizing a mixture of glass granules and titanium-dioxide coated particles are used in a packed bed configuration. A detailed phenomenological model to predict degradation rates of gas phase organic species (toluene) is developed. The parameters of the model are evaluated by experiments performed in differential bed reactors. These are then used in the model and the predictions are compared to the measured values, and reasonable agreement is obtained. The surface area utilization factor is approximately 0.66, indicating that a large fraction of the surface is being irradiated. These configurations can therefore be scaled up for use in larger scale applications.
The concept to immobilize homogeneous catalyst to a solid support has received considerable attention, as it simplifies the separation of catalyst from products and also it solves the loss of expensive metal complexes such as rhodium in the separation area. Since a rhodium carbonyl iodide complex as a methanol carbonylation catalyst is an anion, the ionic bond immobilization to a pyridinium cation resin support was studied. Virtually all rhodium was immobilized, because the ion exchange equilibrium is understood to favor extremely the pyridinium cation resin. The reaction mechanism was exactly the same as that by homogeneous catalyst and the activity per rhodium was rather increased equivalent to that promoted by addition of iodide additives under low water condition. Therefore, the rhodium complex anion is ionically immobilized as the same formula in the liquid phase and also promoted with surrounding pyridinium iodide back bones. Reaction time or catalyst concentration did not directly affect the rhodium leaching, but the water concentration of the product controlled the rhodium leaching through iodide anions to be exchanged with rhodium complex anions. The catalyst stability for 2,000 hours operation was confirmed using CSTR and no rhodium leaching was demonstrated with 0.3 wt-ppm of co-feed of equilibrium rhodium concentration.
The effects of coexistent compounds, such as H2O and CO2, contained in hydrocarbon reformed gas on CO preferential oxidation over a Ru catalyst were investigated for residential polymer electrolyte fuel cell (PEFC) systems using the natural gas steam reforming process. The presence of either or both H2O and CO2 decreased the CO preferential oxidation removal performance of the Ru catalyst over all temperature ranges. Consequently, the temperature window of the catalyst for reducing CO to less than 10 ppm was narrowed by those compounds.
Rotating membrane filtration is a means of dynamic filtration that incorporates both high shear and flow instabilities to reduce membrane fouling. The device consists of a cylindrical membrane filter rotating within an outer cylindrical shell. The superior performance of rotating membrane filtration appears to be a consequence of the high shear in the annulus, which is enhanced by the redistribution of azimuthal momentum by the appearance of Taylor vortices in the annulus. The anti-fouling characteristics of rotating filtration can be utilized for reverse osmosis in addition to microfiltration. In this paper, we review the physics underlying rotating filtration, examine the anti-fouling mechanisms in rotating filtration, and describe recent efforts to apply rotating filtration to reverse osmosis.
To elucidate the kinetic characteristics of the adsorption of organic solvents dissolved in water onto a solid adsorbent, the authors proposed an elaborated experimental scheme where the adsorptive components can be batchwisely taken up from the aqueous medium, being well stirred in a vessel without dead space. The present study deals with chloroform (CH)–water and/or 1,2-dichloropropane (DCP)–water systems. It can be concluded from the observed isotherms that DCP can adsorb more strongly than the other over the whole concentration range examined. On the basis of the measured transient concentration decay curves and the mathematically simulated ones for single component systems, it can be concluded that the predominant mass transfer resistance would be confined within the solid phase, and the simulated effective diffusion coefficients for CH and DCP increased linearly with an increasing adsorption amount for each component, which does not contradict the previous results of other investigators. To predict the adsorption amount of each component in a binary mixture system, the authors employed a widely acknowledged Ideal Adsorbed Solution Model (IAS) and concluded that the model is successfully applicable to the present mixture system. Some transient decay curves were also measured for the binary systems. Incorporating the IAS model into the mass transfer governing equations, the authors simulated the observed decay curves in terms of the effective diffusion coefficients. As a result, the coefficient of DCP for the binary system is compatible with that for the single component system, while the coefficient for CH is larger than that for the single component system.
For precise control of the release rate for fertilizers, pharmaceuticals, etc., the release characteristics were investigated by preparing active core particles coated with multiple layers of insoluble but permeable particles dispersed inside impermeable wax. The release profiles were described by a mathematical model which was successfully verified with experimental data. The two release stages were taken into account; the initial stage corresponds to a constant concentration of the inner solution during the existence of the solid core, and the final stage to a decreasing inner concentration with the elapse of time without the core. As a result, the low release rate was attained by involving the layer of a low volume fraction of permeable particles most closely to the core or by a thicker layer. Also, the effect of the layer thickness was verified to be lower than that of the volume fraction. Thus, the present results confirmed the potentiality of the multiple layer coating to achieve the desired release rate characteristics by choosing the proper combination of the volume fraction of permeable particles, the layer thickness and the position of the layer.
This paper proposes a novel approach to sensor fault detection and isolation for chemical processes. Based on the improved PCA (principal component analysis), faulty variables are projected onto PRV (principal component related variables) sub-space and OV (other variables) sub-space, respectively according to the correlation between variables and PCs (principal components). Then, by defining the NOR (normal region) and the ANSR (abnormal sub-region), the variables in the two spaces will be classified as normal variables or possibly abnormal variables. This procedure is recursively carried out, and the possibly abnormal variables are finally projected onto the NOR and the ANSR, the only variable retained in the ANSR is considered to be faulty, which completes the fault isolation. This is only used for sensor fault detection and isolation. Application results on a PVC (polyvinylchloride) making process illustrate the effectiveness of the proposed approach.
The artificial neural network (ANN) or fuzzy neural network (FNN) is one of the superior modeling methods that can be used to estimate the relationship between input and output with excellent accuracy. When an FNN model is constructed, reverse calculation is often carried out using this model. However, solutions estimated by reverse calculation may not necessarily have low estimation errors. In this paper, we propose a reverse calculation method that can be used to search input values with high reliability. For estimating the reliability of an arbitrary point in the input, many equations were tested in our study using the distance between the point of interest and the nearest learning point, and the estimation error of the nearest learning point. As a result, we selected the following equation to calculate the reliability index value (RI).
RI = (1/n)Σi = 1n(–log ei/li)
where l, e, and n represent the distance between the point of interest and the nearest learning point, the estimation error of each nearest learning point, and the number of input variables, respectively. The larger the RI value is, the smaller the estimation error for the point of interest is. The reverse calculations using the genetic algorithm (GA) combined with the RI (referred to as RIGA henceforth), and the conventional GA, were conducted in the study using the FNN learned by the learning data with three or six inputs and one output. The relative error for the target value of GA searching was 1.9% to 32%, whereas that of the RIGA was only 0.1% to 2.6%.
A macroporous HAp culture substratum was formed by hydrothermal treatment of gypsum. The macropores derived from poly(methylmetacrylate) (PMMA) beads had diameters of 150–200 μm, and a porosity of 28% that was dependent on the PMMA beads quolity. The maximum CHO-K1 cell density of the macroporous HAp microcarrier was 7.3 × 107 cells·ml–1-HAp. This value is similar to most existing suitable porous microcarriers. A macroporous HAp plate packed-bed type bioreactor was designed. The density of CHO-K1 cells in the bioreactor was seven times higher than that from a stationary culture. These results suggest that the HAp synthesized from gypsum by hydrothermal treatment is a suitable animal cell culture substratum.
The silica gel/water adsorption heat pump (AHP) with an adsorber consisted of fin-type silica gel tube (FST) modules was proposed for producing cold heat energy with temperature below 288 K. Considering the performance of such a silica gel/water AHP, the heat and mass transfer characteristics in the FST module were studied by the proposed model, and the optimal sizes (fin pitch and fin length) of the FST module for obtaining maximum cold heat output were decided. It is found that an AHP using the optimized FST module in the adsorber can produce 2 times cold heat output as much as the AHP using the previous FST module (Fujisawa et al., 2002).
Nickel Oxide-Yttria Stabilized Zirconia (YSZ) composite powders for the fabrication of the cermet anode of solid oxide fuel cell (SOFC) was produced by an advanced dry mechanical process. The morphology of the Ni-YSZ cermet anode fabricated from NiO-YSZ composite powder could be controlled by the operating conditions of the mechanical process. Highly homogeneous cermet anode with very fine Ni and YSZ grains was obtained by applying the mechanical process. As a result, the Ni-YSZ cermet anode showed exceptional performance at low operating temperatures (≤800°C) for the SOFC. It is evident that the homogeneous Ni and YSZ grain structure in the size of less than several hundred nano-meters has increased the Three Phase Boundary (TPB) length for the electrochemical reaction, which contributed to the performance improvement of the cermet anode.
Effect of the cationic polyelectrolytes on sodium perborate crystallization in the presence of 2.5% excess sodium metaborate concentration has been studied in an MSMPR type reaction crystallizer. Polyelectrolytes, which are in various charge densities but in the same chemical composition, have been used in the experiments. Cationic polyelectrolytes affected the SPT crystallization by its non-ionic adsorption mechanism. It has proven that the polyelectrolyte having 2% cationicity has affected the quality of sodium perborate tetrahydrate (SPT) crystallization positively. Increasing the cationicity leads to reversing the effect on a product quality change with the cationicity of polyelectrolytes. Polyelectrolytes having 2% cationicity can be used to smooth the shape of crystals and to increase the mechanical strength, the bulk density and the average particle size in SPT crystallization.