We have already reported that the microemulsion system composed of sodium dioleylphosphate (SDOLP) and sodium bis(2-ethylhexyl) sulfosuccinate mixtures has peculiar dynamic properties, i.e., slow solute-exchange between the bulk aqueous phase and microemulsion droplets with increasing SDOLP content in total surfactants, and fast exchange between microemulsion droplets. In this work, as a supplement to that report, we present the full data concerned with the interdroplet solute-exchange process with the aid of time-resolved fluorescence. The specific rate of the interdroplet quencher-exchange is 108 dm3mol–1s–1 in order of magnitude, and is insensitive to the SDOLP-content. The quenching process between the fluorescence probe and the quencher in a droplet was markedly decreased with increasing SDOLP-content. The droplet concentration determined from this quenching process approximately agrees with those evaluated from a geometric model.
Knowledge of heat transfer during melting and freezing in enclosures is important in the design of heat exchangers using phase change materials (PCMs) for thermal energy storage. While freezing heat transfer is governed mainly by conduction, melting of a PCM generally invokes free convective currents in the melt phase depending on the orientation and geometry of the heat transfer surfaces. In this paper, a finite element simulation is carried out to predict the flow and temperature fields as well as the rate of heat storage during melting of a PCM in a horizontal cylindrical annulus heated from an isothermal inside surface. A novel yet simple method is suggested and validated numerically to enhance the heat storage rate in a PCM. The technique involves simply “flipping” the horizontal cylinder, i.e., turning it through 180° about its own axis, at an optimum time during the melting process. It is found that up to 18% enhancement in the energy storage rate can be achieved with this simple technique.
In this work, deposition of TiO2 was performed as a typical case study to demonstrate the concept of area-controlled CVD process. As the reactant gases, TiCl4, H2 and CO2 were used. In this reaction system, TiO2 is deposited by the reaction of TiCl4 with H2O which is formed by the reverse water gas shift reaction. Hence, the formation and deposition zone of TiO2 was controlled by regulating the position of the catalyst of the reverse water gas shift reaction and the concentration of reactant gases. At 443–473 K, TiO2 was deposited on a inner surface of tetrafluoroethylene tube, where a certain amount of catalyst pieces were set at the close end. The deposition profile was measured with SEM. The deposition area depended on the length of the Teflon tube, the reaction temperature, the number of catalyst pieces and the concentration of reactant gases. The relationship between the deposition area and the above parameters could be interpreted by a model, which is based on an assumption that the rate-limiting step in the CVD process is TiCl4 diffusion process. It was found to be possible to control the deposition area by the proposed CVD method.
The partial oxidation of methane (POM) reaction is conducted using several nickel catalysts which show high activities in carbon dioxide reforming of methane. Temperature programmed reaction and thermogravimetric analysis show that a reduced state of nickel is required to start the POM reaction, and that carbonaceous deposition occurs on alumina with high nickel contents. The temperature profile of the catalyst bed during the POM reaction suggests that this reaction consists of two consecutive reactions; methane combustion, following by reforming reactions (with steam and carbon dioxide). The heat caused from methane combustion keeps the temperature high enough to progress the reforming reactions. To suppress the carbonaceous deposition which causes catalytic deactivation and plugging of the reactor, carbon deposition-removal (D-R) treatment is applied in the POM reaction. On the basis of the hypothesis that active cores forming carbon whiskers are different from surface active sites for the main reaction, this treatment has been proposed to only remove or deactivate the former core nickel. It was concluded that this treatment makes the catalyst inactive for carbonaceous deposition with only a small influence on the main reaction activity.
Reactive distillation, a configuration in which the reaction section is located inside the column, is employed to continuously synthesize ethyl tert-butyl ether (abbreviated as ETBE) from bioethanol (2.5 mol% ethanol in aqueous solution) and tert-butyl alcohol (TBA) using Amberlyst 15 in pellet form as a catalyst. Results under standard operating conditions indicate that ETBE at about 60 mol% can be obtained in the distillate, and almost pure water in the residue. The conversion of TBA and the selectivity of ETBE are 99.9 and 35.9%, respectively. The effects of operating conditions on conversion and selectivity are also investigated. Further purification of the distillate using the residue results in 95 mol% ETBE. The experimental results are compared with the results calculated by using an ASPEN PLUS simulator.
We propose a new technique, “position-controlled CVD using catalytic reaction, ” to modify pore structure. By loading the catalyst for the reverse water gas shift reaction on a support that is to be modified, we can confine the hydrolysis reaction zone to a narrow region surrounding the catalyst where H2O is generated. An anodic alumina membrane with pore size of 26 nm was used as the support. Reactant gases, H2, CO2 and TiCl4 were fed into the same side of the membrane. The effects of reaction conditions on pore modification are investigated on the basis of FE-SEM observations and permeation tests. The pore size and permeance through the membrane gradually decrease with reaction time. Deposition morphology changes with reaction conditions, such as temperature, and H2, CO2 and TiCl4 feed rates. In some cases, particles with 0.1–1 μm diameter are formed on the outer surface of membrane.
A statistical approach is still the most effective tool for handling coupled absorbing and scattering phenomena in a heterogeneous system for the assessment of light energy absorption in a photoreactor. A Monte Carlo simulation model has been developed for the prediction of light intensity distribution in a photoreactor. The model has three parameters, an attenuation coefficient, a probability of light ray absorption, and a scattering parameter which specifies the mode of isotropic and/or anisotropic scattering. Experimental measurements of light transmittance and reflectance through solid particle suspensions bounded by two infinite plates were carried out using a newly designed integrating sphere device attached to a spectrophotometer. Light intensity distributions in a rectangular photoreactor with the suspension irradiated by a laser beam were also measured with a photo-probe. These data are compared with simulation results and model parameters are determined to satisfy the experiments. Light absorption fractions measured in the suspensions with different optical lengths show satisfactory agreement with those estimated by the simulation. Thus, the model developed is verified to be effective for the assessment of light absorption rates in a heterogeneous photoreactor.
Fitting kinetic data with kinetic rate expressions has been a challenge for many years. In hopes of providing some guidelines for tackling this problem, kinetic parameter estimation is revisited, covering such topics as data transformations, nonlinear single and multi-response techniques, optimization techniques, and parameter confidence measures. Among the optimization techniques discussed are direct and indirect methods, use of higher-order derivatives, and global optimization. New perspectives on statistical tests for model and parameter confidence are discussed, paying particular attention to exact, nonlinear methods and pointing out the distinct lack of these tests throughout the kinetics literature. In each section, either a single-site or a dual-site Langmuir-Hinshelwood (L-H) example model is shown for illustration of the aforementioned concepts.
Organic materials such as porphyrin are decomposed by ultrasonic irradiation. In this study, the effect of liquid mixing on the performance of porphyrin decomposition by ultrasonic irradiation is experimentally investigated. The ultrasonic frequency used was 22.8 kHz. In order to create the various liquid mixing conditions, the rotation speed of the stirrer or liquid circulation flow rate is changed. Decomposition conversion increases with increasing rotation speed of the stirrer or liquid circulation flow rate. Under both mixing methods, the ratio of decomposition conversion, which is defined as the ratio of decomposition conversion with liquid mixing to that without liquid mixing, is found to be correlated by the liquid mixing time.
Chemical enhancement factors for CO2 absorption into partially carbonated NH3 solutions in a stirred-cell absorber were experimentally determined over a wide range of carbonation ratio in this work. The results reveal that the one-reaction promotion mechanism, which is traditionally used in the literature, has shortcomings in describing the effects of initial total ammonia concentration and carbonation ratio on absorption enhancement. A shuttle mechanism, by which NH3 and CO2 undergo an irreversible second-order reaction in the interface region while the chemical equilibrium of multiple reactions prevails in the bulk region to liberate free NH3, is then proposed for the absorption enhancement. The calculation of the bulk-liquid compositions is made by using the rigorous thermodynamic package in ASPEN PLUS simulator. The chemical enhancement factors predicted by the present promotion mechanism are in good agreement with the experimental data available.
An improvement of the productivity of the preparation process for ultrafine ZnS and CdS particles using sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/isooctane reverse micellar systems is studied. Sufficient quantities of reactants are provided to the reverse micelles by using H2S gas and the functionalyzed surfactants, Zn(AOT)2 and Cd(AOT)2. Bis(2-ethylhexyl) sulfosuccinic acid formed as by-product restrains the formation of ZnS particles, and destabilizes the CdS particles. Neutralization of the acid by addition of an alkaline reagent, triisooctylamine, improves the conversion for ZnS particles and the stability for CdS particles. Ultrafine ZnS and CdS particles containing about 0.02 M of constituting ions are successfully prepared in the presence of the amine. The particles can be recovered from the reverse micelles and redispersed in non-micellar solvent via the surface capping of the particles with thiols. The proposed route using reverse micelles is applicable for the practical production of ultrafine particles.
A Zn(II)-imprinted microsphere is prepared by surface template polymerization with W/O/W emulsions. Dioleyl phosphoric acid, which has two long alkyl chains in the hydrophobic moiety, and divinylbenzene were employed as a functional host and a cross-linking agent, respectively. In order to create a spherical imprinted polymer, composition of the external aqueous phase in the W/O/W emulsion is a key factor: the value of the ionic strength to prevent shrinking of emulsions during polymerization and the choice of the water-soluble surfactant for stabilizing the spherical W/O emulsion are important. The metal-imprinted beads exhibit a high selectivity towards target zinc ions over copper ions. The novel preparation technique is very useful for an industrial application because it can easily control the particle size between 10 and 100 μm.
A simulation model for heterogeneous distillation proposed by Saito et al. (1998) is modified by taking account of mass transfer resistance in the aqueous and organic liquid phases. In the present model, the heat and mass transfer rates between the vapor and each liquid are calculated separately. The simulation results are compared with the experimental data obtained previously by a wetted-wall column for an ethanol-benzene-water system. The predicted reflux flow rate is improved compared with the previous simulation model where mass transfer resistance in the liquid phase is ignored, and the prediction accuracy is less than 10% of the observed values.
The operational power of a co-axial double rotating cylinders mill with blades is estimated on the basis of the balls motion simulated by the Particle Element Method (PEM). The boundary condition on the rotating blades is introduced to simulate the balls motion. The estimated mill power is calculated from the balls motion in the divided working space to save simulating time. The actual and estimated power data tend to increase as rotational speed becomes high, while they remain at a low value and are independent of the speed of the inner cylinder when the speed of the outer cylinder is low. Both power data decrease at high rotational speed due to the rolling motion of the media balls, and the estimated power is in fairly good agreement with the actual one. It is confirmed that the boundary condition introduced in the present paper is suitable and applicable for estimating the operational power, as well as the balls motion in a rotational media mill with complex configuration in the working space.
Silica microcapsules comprising methylene blue (MB-SiO2) of mean diameter 4.0 μm were prepared by sol-gel and water-in-oil emulsion techniques where water pools are used as microreactors in which methylene blue is dissolved at a high water to surfactant molar ratio. It is confirmed that the cationic methylene blue is incorporated in the silica microcapsule wall during hydrolysis and condensation of tetraethoxysilane. Fixation of methylene blue in the silica wall is examined by passing water or acetic acid aq. soln. (pH 2–4) through a cartridge in which MB-SiO2 is packed and then measuring the fractions using UV-VIS analysis. The elution behavior is affected drastically by the pH value of the eluent. Methylene blue tends to stay in the wall when the pH value of eluent is above the isoelectoric point (IEP) of the silica microcapsules. However, release of methylene blue cation occurs when it is below the IEP. These results reveal that coulomb interaction has an important role to fix methylene blue in the silica microcapsule.
A Powder-Particle Fluidized Bed (PPFB) is applied to the calcination of small limestone particles 2–64 μm in mean diameter. The effects of reaction temperature, size of limestone particles, superficial gas velocity, static bed height of medium particles, and inlet CO2 concentration upon the calcination conversion are investigated. Under conditions where the average residence time of gas in the bed is 0.4 s, more than 95% calcination is achieved in the case of 5 μm limestone at temperatures higher than 1173 K. The dependence of calcination conversion on 20 vol% CO2 in fluidizing gas becomes small at temperatures higher than 1123 K.
In this paper, we propose an identification method to estimate the second order plus time delay (SOPTD) model parameters. The proposed method obtains the parameters of the SOPTD model directly using a time weighted integral transform and a least square method, so model reduction steps can be avoided to tune the PID controller. It can also be applied regardless of the initial states while almost all previous identification methods require the assumption of zero initial states. Through extensive simulations, it is proved clearly that the proposed method gives acceptable estimation performances whether initial states are zero or not. Moreover, it shows an acceptable robustness to the disturbances and measurement noise.
This work used Candida rugosa lipase to resolve racemic Naproxen by esterification with ethanol, n-butanol, n-hexanol or n-decanol in supercritical CO2. It was found that the lipase enantioselectively esterified (S)-Naproxen within all systems. The enantiomeric ratio increased four folds by slightly decreasing the alcohol concentration. The effect of the alcohol concentration on the enantioselectivity was greater than that of changing acyl acceptors.
Lipase was immobilized with adsorption or covalent binding on silica particles, being comparatively assayed for esterification in an organic medium. The results show that adsorption, when compared with covalent binding, immobilizes lipase as larger pores are left on the particles, i.e. the extent of plugging of larger pores is less. This dependency suggests that the former proceeds within only larger pores on the particles, while the latter proceeds within all pores. Correspondingly, the former immobilizes lipase in quantities half that of the latter. Nevertheless the former is able to produce more active preparations than the latter. Both kinds of preparations vary their activities with an increase in their water contents with similar convex functions, having respective maximum activities at water contents equivalent to their pore volumes.
Red beet hairy roots are cultivated in a single column reactor to investigate the influence of superficial velocity of medium on formation of betanin (a major pigment component in red beet hairy roots). The betanin content in the cells increases with increasing superficial velocity in the range of 13 to 40 m/h. In the cultures at superficial velocities of 15 and 40 m/h for 166 h, the betanin content increases with elapsed time of cultures. The growth of the hairy roots is responsible for an increase in shear stress on the root surfaces by means of lowered void fraction of hairy root bed, and the estimated values of shear stress range from 0.22 to 188 N/m2 during both the cultures. The activity of monophenol monooxygenase in the cells, which is a key enzyme involved in the biosynthesis of betanin, can be correlated with the value of shear stress in such a manner as to approach plateaus gradually with increasing shear stress.
The behavior of Datong coal particles in a flotation column was investigated in a batchwise operation using a gas distributor evolving uniform bubbles by varying the superficial gas velocity and column height. The value of superficial gas velocity was controlled at 0.66 or 1.99 cm s–1. The time course of ash content in floats was measured when column height was 1.85 m. The ash content in clean coal was larger for higher superficial gas velocity. The hydrophobicity of coal particles recovered from the top of the column was evaluated by means of a film flotation method. Hydrophilic particles having the critical wetting surface tension of particles, γc, greater than 60 mN m–1 floated well for higher superficial gas velocity. The weight percent of fractions having γc above 60 mN m–1 was 29.5, 31.9 and 40.5% for 0.25, 2.00 and 4.25 min, respectively. These values increased with sampling time, and were much greater than those for the lower superficial gas velocity. At lower superficial gas velocity, the hydrophobic coal particles seem to be selectively floated by colliding and attaching to the bubble surfaces. On the other hand, at higher superficial gas velocity, hydrophilic particles that are difficult to attach to bubbles seem to be entrained in the turbulent wake of bubble swarms and float. The grade of clean coal was better for the lower superficial gas velocity, however, carbonaceous materials recovery was lower than that for higher superficial gas velocity. Carbonaceous materials recovery was improved by increasing the recovery zone height.
A new method was proposed to assess the surface properties of coal by adsorption of metanil yellow using a continuous feed system. The area fraction of the hydrophobic site on the exterior surface, αm, was measured for Datong, Tyanfu, Shanxi No. 1, Illinois No. 6 and Blair Athol. Except for Tyanfu coal, the order of the values of αm is consistent with that of carbonaceous materials recovery. The metanil yellow adsorption experiment requires no specific preparation, and can be applied to powder samples.
A series of ignition experiments using electric sparks are made to investigate the explosion characteristics of gaseous ozone with a concentration up to 60 vol%. The results show that the lower explosion limit of ozone diluted in oxygen at room temperature and atmospheric pressure is about 10 vol%. Partial decomposition of ozone in the ignition vessel is observed in the range from 10 to 12 vol%, and ozone with a concentration of more than 12 vol% can cause an explosive chain decomposition and convert to oxygen completely. The lower explosion limit shifts to higher concentration with decreasing initial pressure. For instance, at 100 Torr the lower limit is 25 vol%. Explosion pressure ratio is proportional to ozone concentration. For 40 vol% ozone, the ratio is 8. Besides, detonation was observed at ozone concentration above 40 vol% in our experiment. Moreover, we have proved that carbon dioxide has a weak restraint effect on ozone explosion. As a result, adding carbon dioxide to 70 vol% into an ozone-oxygen mixture can raise the lower explosion limit to 12 vol%.
Extraction equilibrium data is obtained for distribution of indium(III) between bis(2-ethylhexyl) phosphinic acid dissolved in toluene and acidic aqueous nitrate media. The stoichometry of the extracted species is determined on the basis of slope analysis and IR spectra. The extraction of indium(III) proceeds by a cation exchange mechanism and the extracted species is InR3·3HR. Temperature dependence of the extraction equilibrium is examined by temperature variation method to estimate apparent thermodynamic functions (ΔH, ΔS and ΔG). The extraction process is exothermic in nature and an increase in temperature is not favorable.