In the previous studies, it has been found that there is a significant influence of the solids on the liquid phase mixing time at high solid concentrations. This is due to appearing a clear liquid layer above the cloud solid layer at a certain specific power input. The state of solids suspension and the mixing time affect the purity, productivity and selectivity of the reaction and the size distribution and morphology of the precipitation and crystallisation. Consequently, more information in these conditions is necessary in order to operate properly the reactor handling particle suspensions. In this study, the effect of D/T ratio (the ratio of impeller to tank diameter) on solid suspension and mixing time has been investigated in a stirred tank equipped with Chemineer HE-3 impeller, which is typically used for solid–liquid mixing at high solid concentrations. The maximum mixing time for the largest D/T employed in this study is the longest despite almost the same specific power input and height of interface. However, to use the large D/T has led a high degree of homogeneous suspension and fast mixing time with a small increase in power input. On the contrary, large power input is necessary to disappear the cloud layer when the small D/T is used.
A simple technique has been developed to directly produce fine ceramics powders from liquid solution by drip pyrolysis in a fluidized bed reactor. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium ion battery, has been carried out for various superficial gas velocities U0 = 0.30–0.91 m/s, concentrations of precursor solution C0 = 0.45–4.50 mol/dm3 and static bed heights Ls = 50–150 mm. The as-prepared samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns, and the chemical composition of as-prepared powders showed in a good agreement with the one of precursor solution. The as-prepared sample was used as cathode active materials for lithium-ion battery and their charge/discharge properties have been investigated. Test experiments in the electrochemical cell Li|1M LiClO4 in PC|LiMn2O4 demonstrated that the sample, prepared by the drip pyrolysis method and then calciend at 750°C for 4 h in the air, was a promising cathode material for 4 V lithium-ion batteries.
The processing and characterization of a novel membrane system for CO2 separation is described. The membrane was made of lithium zirconate (Li2ZrO3), which has a potential to react reversibly with CO2 molecules at high temperatures. The reaction of Li2ZrO3 with CO2 essentially produced two electrolyte materials in situ. One of them, Li2CO3, is capable of carrying CO2, and the other, ZrO2, is a well-known O2 ion conductor. This combination of selective reaction and electrolyte conduction permitted the design of a membrane system capable of selective CO2 steady-state permeation across the membrane. Using the membrane, a separation factor of 4.9 was measured between CO2 and CH4 gas molecules at a temperature of 600°C. The measured separation value of 4.9 is very high compared with the Knudsen diffusion limit of 0.6 and therefore clearly supports the use of the membrane system for selective separation of CO2.
A new HPLC recycling system for binary separation is proposed. This system uses the interference of broadening by recycling the residual components on both sides of the introduced feed. By using this system, the high purity, high concentration, and high yield of both components are achieved. Furthermore, reduction of the eluent consumption is achieved. In this paper, simulations and experiments are performed for the separation of optical isomers.
Porous silica, silica-zirconia and silica-titania membranes were prepared by the sol-gel techniques for separation of aqueous solutions of organic acids (acetic acid and propionic acid) by pervaporation at 50–100°C and at normal boiling points. Applying the hot coating procedures with the colloidal sols prepared in different concentrations (different particle sizes), a quite thin porous silica layer active for separation was formed on a porous α-alumina cylindrical substrate. A fresh porous silica membrane showed a long time-dependency of several hours in the pervaporation performance before reaching a steady state due to the formation of silanol groups on the pore surface. Because of its small thickness less than about 0.5 μm quite large water fluxes of about 300 mol·m–2·h–1 were observed with a separation factor higher than several hundreds at around 73 mol% of acetic acid (10 wt% water) at 100°C, for example. Stability tests of the porous ceramic membranes were performed in aqueous organic acid solutions to find that silica and silica-titania membranes were quite stable in an aqueous solution of organic acid of concentration higher than about 20 mol% acid. Silica-zirconia membranes, on the other hand, were not stable in aqueous organic acid solutions of high concentration. The membrane stability is discussed on the observed solubility of inorganic membrane materials. Furthermore, separation and permeation mechanisms were discussed based on a simple pore model for pervaporation proposed previously to give good coincidence between observed and simulated results.
This paper proposes a PID controller design method for the second order systems to satisfy the design specifications in time domain via an LQR design technique. The optimal tuning method of the PID controller is developed by establishing relationships between the exploited design parameters and the weighting factors Q and ρ. Then the weighting factors are determined to meet the design requirement. And an extension to the time delay systems is made.
Several shapes of BaSO4 particles were synthesized by the reaction of Ba(AOT)2 microemulsion with NaAOT microemulsion containing SO42– at differing [Ba2+]/[SO42–] mole ratios. BaSO4 nanofilaments were obtained under an excess of Ba2+ with the same mole ratio to that of Li and Mann (2000). A plasma replica SEM revealed that the nanofilaments were formed exactly in the microemulsion. Further excess Ba2+ resulted in the formation of short rags and thick spirals rather than nanofilaments. In contrast, fine particles were formed under a shortage of Ba2+. By addition of excess Ba2+ to the microemulsion after the generation of the fine particles under a shortage of Ba2+, whisker-like rods were obtained. These results suggest a new mechanism for formation of the whisker-like rods through an anisotropic aggregation of the fine particles.
We investigated a combined process for remediating dioxins-contaminated soil (i.e., initial concentration ≈ 9100 pg-TEQ/g) involving solvent washing followed by UV irradiation. More than 95.1% of TEQ was removed from the soil under a pseudo-first order by performing ethanol washing seven times, and the resulting TEQ removal efficiency of ethanol washing solution (i.e., initial concentration ≈ 2468.5 pg-TEQ/mL) after 16 h of UV irradiation was 99.8%. In addition, most of the PCDDs/DFs peaks disappeared based on HRGC-MS chromatography. These results indicate that the proposed ethanol washing-UV irradiation treatment can be effectively applied in remediating dioxins-contaminated soil.
Adsorption properties of wood charcoal prepared by a traditional method are investigated by using CO2 adsorption at 195 K and N2 adsorption at 77 K, focusing on the effects of the treatment temperature. The amount of CO2 adsorbed at 195 K and N2 adsorbed at 77 K increases with treatment temperature. The shape of the N2 adsorption isotherm indicates that the charcoal is predominantly characterized by micropores with the presences of mesopores, when high treatment temperature is applied. At a low treatment temperature, the ratio of nCO2 to nN2 is high, whereas, it approaches to unity at the higher treatment temperature than 773 K. The adsorption of CO2 at 195 K can be used for surface area measurement, in place of N2 adsorption at 77 K, for the charcoal treated higher temperature.
In order to develop a gasifier of municipal solid waste (MSW), the basic characteristics of pyrolysis and thermal degradation of its gases derived from each component of MSW were examined. Tea leaf, cotton, paper, wood and fish meat decomposed rapidly in the temperature range of 550–650 K. For PE, PP and PS, the maximum rate of weight loss occurred in the temperature range of 600–750 K. For PVC, on the other hand, there existed two distinct steps of weight loss, which represented a lower (550–620 K) and a higher temperature (700–770 K) of decomposition. The gases derived in pyrolysis process at 770 K were further degraded during thermal degradation at 1020–1220 K for 5–15 s. Comparing between the amount of resultant tar before degradation at 1220 K for 15 s and after, average content of tar with molar fraction of 0.36 reduces to 0.03.
Immobilization of heavy metals contained in fly ash was conducted by mixing fly ash with asphalt, sulfur and sodium hydroxide in a bi-axial kneader heated at 403 K. From XRD analysis of the products after treatment of a mixture of CuCl, CuCl2·2H2O, CuO, CdCl2·2.5H2O, HgCl2 and HgO with sulfur and sodium hydroxide, it was confirmed that all heavy metal compounds were sulfurated to form metal sulfides at 403 K. On the other hand, zinc compounds (ZnCl2 and ZnO) were not converted to zinc sulfide, but were converted into water insoluble compounds. In this treatment, chromium(IV) oxide (CrO3) was reduced to chromium(III) oxide (Cr2O3). The amount of sulfur and sodium hydroxide necessary for complete immobilization of the heavy metals was estimated by the total metal content in fly ash, on the assumption that all heavy metals reacted with sulfur and sodium hydroxide in accordance with the following relations: