Thermal chemical vapor deposition (CVD) is a fundamental technique that is used to process thin films and fine powders in various industries. However, there are few ways to model the thermal CVD reaction process. Consequently, many industrial resources have been expended to determine empirically the optimum conditions for film growth. To resolve this problem it is necessary to analyze and model thermal CVD based on reaction engineering. The distribution of the growth rate in a tubular reactor provides much information on the reaction processes and chemical kinetics in the gas phase. The shapes of films grown at microsize roughness can give information on the surface reaction process. This paper presents, and explains the ways to determine the kinetic constants involved in, simplified reaction schemes for some thermal CVD systems. The growth rate and composition distribution of the film grown in a small tubular reactor and the shape of film grown at microscale roughness were well explained by the computational simulations. This method of analyzing and modeling CVD systems requires small experiments and simulations. It proved useful for finding the optimum operating conditions for synthesizing a film, because growth rate and distribution in any shaped reactor and at microscale roughness can be predicted under various conditions using computer simulations.
Suppression of the cross-linking reaction at low temperature is a key factor to increase total volatiles during the pyrolysis of brown coals. To do so, it is essential to clarify the mechanism and kinetics of such cross-linking reactions. We prepared coal samples having similar monomer units but different macro-molecular structures through liquid phase oxidation of an Australian brown coal. The oxidized coal samples were heated from 303 to 1173 K at the rate of 20 K/min in a TG-MS analyzer and were pyrolyzed. It was found that the formation rates of inorganic gases, H2O, CO and CO2, were significantly dependent on the amount of oxygen functional groups in the coals. Oxidized coals having a large amount of COOH groups decomposed at lower temperatures and distinct peaks of the formation rates of inorganic gases appeared at around 673 K. We proposed six kinds of cross-linking reactions based on the types of hydrogen bonding formed between the functional groups, and estimated the change in the extent of each reaction with increasing temperature from the formation rates of the inorganic gases measured. The hydrogen bonded COOH–COOH and COOH–OH decomposed at 500–600 K and 600–700 K, respectively, to form the inorganic gases and cross-linked products such as anhydrides, ether, and ester. These cross-linked products decomposed further into CO and CO2 at temperatures above 800 K. Based on the above analysis and the 13C-NMR measurement of the pyrolyzed chars, it was clarified that the number of cross-links was equal to the number of H2O molecules formed and that the CO and CO2 formation rates were closely related to the H2O formation rate.
The drying characteristics of porous materials immersed in a fluidized bed were examined. The glass bead (0.12 mm in diameter) was used as the fluidizing particle. A brick ball and a sintered glass ball were used as the samples, mainly. The sample was fixed or unfixed in the fluidized bed. The mass velocity and temperature of drying gas were changed. In the case of unfixing, the brick ball floats on the bed and the sintered glass ball sinks at the bottom of the bed. The drying time for unfixing is shorter than that for fixing in the fluidized bed when the sample exists on the bed surface. The fluidization behavior of bed has a large effect on the drying characteristics of the unfixed sample. There is the period when the temperature of sample center is constant, and the temperature becomes higher with an increase in the drying gas temperature.
Using enzymatic hydrolysate of corn gluten as a model solution, we measured the ultrafiltration permeate flux for periodically oscillating transmembrane pressure gradient. The objective was to evaluate the potential flux enhancement of the square-wave pressure oscillation, not pressure reversal. It was expected to instabilize the solute layer deposited on the membrane surface by repeatedly inducing its compression and relaxation. The oscillation was applied in the later part when the instantaneous flux dropped to a half of the initial flux. It was observed that the solute layer was more readily relaxed than compressed, which indicated that the time constant for the compression at higher pressure was larger than that of the relaxation. As a result, the time-averaged overall flux of the oscillatory-pressure filtration increased slightly (approx. 11%) over the constant-pressure filtration.
The bubble sizes and distribution were measured in a horizontally two-dimensional vibro-fluidized bed. Glass bead of group B particles was fluidized at varying gas velocities, while the bed was vibrated at different frequencies and amplitudes to study the effect on the bubble behavior. Experimental results show that the local average bubble sizes under the vibration field are generally smaller than those without vibration. The local average bubble sizes are hardly affected with the change of vibration frequency, but increase with an increase in the vibration amplitude. Few bubbles were observed in the both side-well of a bed in the experiment at a gas velocity of 0.0907 m/s. Due to horizontal vibration, bubbles were too small to measure the bubble size in the lower area (H < 50 mm). The ratio of the maximum diameter to the minimum diameter of a bubble is not correlated well with vibration, superficial gas velocity and bed height.
A new bipolar charger for nanometer aerosols using soft X-ray photoionization was developed. The concentrations and mobility distributions of the positive and negative ions generated by the X-ray charger were investigated, and then the charging probability of nanoparticles was evaluated experimentally and theoretically. All experimental data of the X-ray charger were compared with those of a 241Am α-ray bipolar charger. It was found that the X-ray bipolar charger could produce at least about 3.5 times as high concentration of gaseous ions as the α-ray charger and thus could have particles attain the equilibrium bipolar charging state in shorter residence time than the α-ray charger. The charging state of particles attained by the X-ray charger was explained by theoretical calculations as well as α-ray bipolar charging. It was concluded that the X-ray charger would be a useful instrument for charging high number concentration nanoparticles in the electrical aerosol measurements.
A transport phenomena based process model is a prerequisite for supervisory level online process optimization. For real time applications it is necessary to have an efficient and robust solution procedure for the model equations. A method for the reduction in the number of model equations for a crude petroleum distillation unit is reported here. The predictions from the rigorous, and several reduced order models were compared with the experimental data from an operating refinery. The results of the reduced order model not only compared favorably with those of the rigorous model but the former was also found to be more flexible to tuning with the plant data and showed greater tolerance to noisy measurements as compared to the latter. Use of empirical thermodynamic relations for VLE (vapor-liquid equilibrium) data, and analytical derivatives, choice of independent variables and numbering of stages were found to further reduce computation time significantly.
This article deals with output regulation of an exothermic tubular reactor system. Based on model order reduction and a specified coil apparatus for heat removal, a finite difference-based nonlinear model with single manipulated input can be developed. Under the difference-based feedback linearization strategy associated with Lyapunov stability analysis, the developed low-order state/output feedback controllers can induce asymptotic output regulation. Moreover, the output feedback control scheme together with anti-windup compensation can reduce the controller saturation and provide satisfactory control performance. Simulations clearly demonstrate that the proposed control methodologies with a fast coil flow rate condition can recover the desired temperature performance, and that they are also robust against the presence of unstructured modeling errors.
This article addresses the complete identification of stable, integrating, and unstable processes. Despite the stability of the process, a biased relay experiment can be performed to provide abundant process input-output data in stable operation. Based on a time-weighted integral filter, an effective method is developed to estimate the orders and time delay as well as the model parameters from the relay-induced data in a straightforward fashion. The method utilizes a small amount of experimental data and is robust with respect to measurement noise and model structure mismatch. Furthermore, it can easily be applied as a model reduction technique by estimating an apparent delay with user-specified orders.
To pursue sustainable technology as a key responsibility for chemical engineers, we have presented an infrastructure for integrating element technologies of life cycle engineering (LCE). By that, we can evaluate and make a rational decision on LCE in chemical industries. With this point of view, we attempt to integrate a product life cycle model developed earlier together with various data bases, simulators and applications on G2 that is known as a development environment of intelligent systems. We also aim at facilitating a collaborative research accessible from global horizon through the Internet. Finally, through implementation associated with the management of plastic wastes, we have shown that more elaborate concerns on LCE is possible through our idea.
The model drug, 17-β-Estradiol (E2) was dissolved in an acrylic pressure-sensitive adhesive (PSA) DURO-TAK® 87-2516 to manufacture the DURO-TAK matrix (DTM). Eight loading doses of E2 from 0.25% to 12% (w/w) were prepared. The in vitro penetration flux of E2 across hairless mouse skin from the DTM increased proportionally to E2 concentrations of up to 6% (w/w) and decreased thereafter. When the DTM with more than 2% E2 (w/w) was stored for a period of 140 and 360 days, the in vitro penetration flux of E2 decreased gradually. CCD microscope observations revealed that this phenomenon was attributed to induction and growth of E2 crystal in the DTM. By segmenting the CCD micrograph, the volume ratio of crystal occupied in the DTM was determined and the concentration of E2 dissolved in the DTM was estimated. The E2 flux calculated from the estimated concentration agreed with the value gathered from the in vitro penetration experiments. These results showed that the in vitro flux at steady-state (dQ/dt)ss of E2 was mainly dependent on the concentration of E2 dissolved in the supersaturated DTM rather than loading dose. Furthermore, we obtained a simple method for predicting the effect of crystallization on the in vitro flux (dQ/dt)ss by using a differential scanning calorimeter (DSC).
Implementation of polychlorinated biphenyls detoxification is being accelerated globally. We have developed an environmentally sound chemical polychlorinated biphenyls detoxification plant (codenamed: HM1), using the Ultraviolet ray (UV)/Catalyst Method. Safety analysis greatly facilitates communication on the subject of risk between the entity wishing to construct and operate the plant and the local residents. In the UV/Catalyst Method, PCB is mixed with sodium hydroxide (NaOH) and isopropyl alcohol (IPA: solvent) to realize PCB concentration in IPA of 1 wt% and subsequently PCB is dechlorinated by two independent process steps. The first step is the UV irradiating process (UV process), and the second step is the catalyst reaction process. As a result, biphenyl, NaOH, acetone, and water are generated after PCB is dechlorinated. A distilling column is designed in order to separate IPA from the solution, and IPA can be recycled many times as a solvent of PCB. IPA and acetone may form an inflammable mixture after leakage. Concerning HM1, first, hazardous events which produce severe accidents were identified by Failure Mode and Effect Analysis (FMEA); and secondly, leak of isopropyl alcohol (IPA), that causes fire/explosion, is defined as the most serious event. Based on this result, numerical safety analyses were carried out and the following findings were obtained. • Thermal runaway experiment of residual liquid in the bottom of a distilling column: It was confirmed experimentally that no possibility of thermal runaway exists. • Stress analysis of the distilling column after fire/explosion: The strength of the distilling column was proved. • Impact evaluation concerning the surrounding facilities and residents after fire/explosion: It was confirmed that impact would be slight. • Impact evaluation concerning exposure of residents to PCB: Exposure of residents to PCB would be negligibly small. In conclusion, the standardized methodologies for both safety evaluations and procedures concerning PCB plants were proposed and their validity verified.
We present an extension of our recent work on the existence of low dimensional chaotic attractors in the rheology of dilute periodically forced suspensions to the semi-dilute limit. We present some approximations that reduce the computation time significantly and make it possible to generate sufficient data for analysis using the tools of nonlinear dynamics and chaos theory, even on a Pentium P-III PC. These results indicate that the simulation technique outlined in the present paper can be used in simpler situations to provide a rough basis for design calculations. We also discuss the effects of hydrodynamic interactions on the simulations.