Thermal separation processes are of great importance, because they usually cause the greatest part of costs (investment, operating) of a chemical process. For the synthesis, design and optimization of separation processes, in particular, a reliable knowledge of the real phase equilibrium behavior is necessary. If no experimental data are available, group contributions methods can be used to predict the required phase equilibria and excess properties. In recent years, Modified UNIFAC (Dortmund) has become very popular because of its reliable results obtained for different thermodynamic properties such as vapor-liquid equilibria (VLE), solid-liquid equilibria (SLE), azeotropic data, activity coefficients at infinite dilution (γ∞) and excess enthalpies (hE) in a wide temperature range. This paper gives an idea about the large range of applicability and the potential of Modified UNIFAC (Dortmund) for the synthesis, design and optimization of thermal separation processes and other applications of industrial interest. Furthermore, the results of an extensive model comparison for azeotropic data and excess enthalpies are presented.
Microwave enhanced combustion of methane-air mixture in a ceramic burner is studied and the results suggest perturbation of the assumed Boltzmann distribution of molecular energy levels. A small signal gain, which represents the level of amplification of an incident beam in a medium, was detected using a CO2 laser. An increase in the signal ratio of two MCT photodetectors when the combustion zone was irradiated by microwaves (2.45 GHz) indicates amplification of infrared radiation (10.6 μm), hence the possibility of using the system for laser applications. However, statistical analysis reveals that varying levels of microwave power are not significantly different.
A two-dimensional mathematical model has been developed to describe annular electrochemical reactor performance. Multiple electrochemical reactions of copper electrowinning from a chloride solution were evaluated to illustrate the usage of the model. The simulation includes the mass transport of ionic species and the associated electrochemical kinetics under the laminar fluid flow condition. The model predicts current distributions on the electrodes, conversion per pass (CPP), selectivity of copper as a function of the applied potential, residence time, and anode to cathode diameter ratio.
An approximate analytical solution of the Caram-Amundson model of combustion of carbon has been obtained based on a cubic polynomial for the homogenous reaction rate in the “film” surrounding a flat carbon slab. The film has been defined as the region where both the homogenous reaction rate and its gradient vanish at its edge. The agreement between the present solution and the numerical solution of Caram and Amundson is very good.
Nano-sized zinc oxide (ZnO) colloids were prepared by hydrolyzing zinc acetate solution with ammonia (NH3) gas as a volatile catalyst, instead of metal hydroxides such as NaOH and LiOH, which have been used previously. The procedure consists of two major steps: (1) preparing the precursor by reacting zinc acetate with ethanol, and (2) hydrolyzing the precursor to form the colloid. Hydrolysis was performed by bubbling the desired composition of NH3-N2 gas mixture into the precursor for the desired time in an ultrasonic bath. The hydrolysis conditions required for forming ZnO colloids such as the composition of the NH3-N2 gas mixture and bubbling times are examined. In addition, optical properties such as luminescence and absorption of these ZnO colloids produced via this basic hydrolysis procedure, and the effect of the residual NH3 in the suspension on colloidal stability are examined. It is found that a critical amount of dissolved NH3 to form nano-sized ZnO particles is existent, and that the luminescence intensity largely depends on the gas composition and the bubbling time. Residual NH3 remaining in the suspension greatly affects colloidal stability. But, it could be easily removed by evaporating ethanol of the solvent under reduced pressure. The resulting ZnO powder could be re-dispersed quickly and completely into ethanol. The luminescence and absorption properties of the re-dispersed colloidal suspension were almost the same as those of the original suspension. Moreover, the re-dispersed ZnO suspension was absolutely transparent for more than one month at room temperature. In other words, the colloidal stability is remarkably improved.
Cross-linked microcapsules entrapping ascorbic acid magnesium salt as a core material are prepared by in-situ copolymerization of styrene and divinylbenzene in a (W/O/W) emulsion system. The effects of the preparation conditions of the microcapsules on the capsule morphologies, the entrapment efficiency and release profiles of the core material are investigated. The entrapment efficiency of the core material is improved by lowering the volume fraction of the dispersion phase in the (W/O) emulsion and adding the salt to the outer aqueous phase when tricalcium phosphate is used as the dispersion stabilizer. Both the entrapment efficiency of the core material and the internal morphologies of the microcapsules affect the release profiles of the core material.
Sesame oil bleaching by acid-activated rice hull ash is examined. Lovibond color indices of sesame oils before and after bleaching by activated rice hull ash were determined to calculate the bleaching efficiency of the ash. Surface area meter and inductively coupled plasma-mass spectroscopy were employed to determine specific surface areas and average pore diameters as well as metallic contents of the rice hull ashes before and after acid activation, respectively. Effects of the following factors on bleaching efficiency have been studied; acid type, acid concentration, activation time, ashing temperature and ashing time. Experimental results indicate that rice hull ash activated by H2SO4 has relatively higher bleaching efficiency than that activated by H3PO4 or HCl. The increase in acid concentration or activation time did promote bleaching efficiency, though mildly. Acid activation might increase bleaching efficiency of rice hull ash from 0% to 43%. The effect of activation is found to be most significant when the ashing temperature is in the range of 673-773 K or the ashing time is over 1,800 s. The increase in bleaching efficiency by acid activation might be due to the increase of number of active site available for adsorption on the pore surface of the rice hull ash. Replacement of activated clay as an adsorbent to bleach sesame oil by acid activated rice hull ash is found to be promising.
A process simulator for prediction of separation performance of a cryogenic air separation plant by packed columns with structured packing is developed by use of our heat and mass transfer model. The basic equations for the simulation are mass transfer correlations which were proposed in our previous work (Egoshi et al., 2000). Comparison of observed data from a pilot-scale cryogenic air separation plant, which consisted of a 710 mm-diameter high pressure sieve plate column for feed to low pressure column, a 500 mm-diameter low pressure packed column with structured packing for production of pure grade nitrogen and oxygen, and a 380 mm-diameter argon column with structured packing for production of crude argon is made. Predicted concentration profiles in the low pressure column and the ones in the argon column show good agreement with observed data. The effect of liquid feed location, side-cut location, vapor-liquid ratio of the feeds to the low pressure column on purity of the product nitrogen, oxygen and crude argon are also discussed.
Parallel transport of acetic acid and lactic acid by the solid-phase, and macropore diffusion within a highly porous polyaminated chitosan bead is studied by measuring equilibrium isotherms and uptake curves. The experimental adsorption isotherms of acetic acid and lactic acid are correlated by isotherm equations considering the adsorption on four different fixed functional groups. These equations were derived by simplifying the accurate isotherm equation which we have presented elsewhere. Intraparticle effective diffusivities Deff are determined from the homogeneous Fickian diffusion model. As Deff for acetic acid is about 4 times larger than those for lactic acid, these acids can be separated by the difference of the diffusion rate. The theoretical equations for the parallel diffusion model are derived from the mass balance equation based on the macropore and solid-phase diffusion and the theoretical isotherm equation mentioned above. The solid-phase diffusivity (Ds) and macropore diffusivity (Dp) are determined using Deff. Ds and Dp are independent of the bulk concentration. This parallel diffusion model correlates the experimental uptake curve well. The solid phase diffusion is the rate controlling step in β (= the ratio of the solid-phase diffusion to macropore diffusion) ≥ 3, while the macropore diffusion is the rate controlling step in β ≤ 0.3, and parallel diffusion should be considered in 0.3 ≤ β ≤ 3.
Experiments have been carried out on the extraction of nickel from ammonium sulphate aqueous solutions using LIX 54 as extractant. Nickel extraction decreases with increasing ammonium sulphate concentration of the aqueous solution. This decrease can be attributable to the formation of nickel ammine complexes in the aqueous phase thus decreasing the free nickel ion concentration. From the slopes of log DNi versus equilibrium pH plots, the extracting species has been found to be NiR2, further, numerical analysis of experimental data confirmed the proposed stoichiometry and the corresponding log Kext are given. The extraction of free metal ion by LIX 54 was also confirmed by IR studies of nickel loaded organic solutions.
Liposome immune lysis assay (LILA), which depends on immune lysis of artificial phospholipid vesicles by the activation of complement, is a homogeneous immunoassay method and much better than ELISA in respects of simplicity and rapidity in measurements. Fluorescent agents have been used as markers encapsulated in liposomes, but they need an expensive apparatus for detection. In this work, we measure the concentration of polyclonal and monoclonal antibodies by LILA by use of antigen-bound liposomes encapsulating coenzyme β-NAD+. Conjugated redox reactions involving β-NAD+ can accumulate a colored material and attain a high sensitivity similar to fluorescent agents in detection of released marker. We also analyze the characteristics of immune lysis of liposomes in LILA depending on the equilibrium relationship between antigen and antibody. The marker release depends on the concentration of the antibodies, and the decrease in the concentration of liposomes raises the sensitivity. The marker release is proportional to the concentration of antigen-antibody complex formed on liposomes. Polyclonal antibody can sensitively be detected even at a lower average association constant than monoclonal antibody.
Magnetoliposomes (MLs) were conjugated with an antibody fragment to give specificity to a tumor. The antibody fragment was cross-linked to N-(6-maleimidocaproyloxy)-dipalmitoyl phosphatidylethanolamine (EMC-DPPE) in liposomal membrane. The immobilization of the antibody fragment was optimal when the content of EMC-DPPE was 10-wt% and the reaction time for immobilization was 18 h. The Fab' fragment-conjugating MLs (FMLs) were 2.4 times higher molar immobilization density compared with the method using the whole antibody. The targetability of the FMLs to the glioma cells, U251-SP, was then investigated. The amount of FMLs uptake reached 85 pg/cell in an in vitro experiment using plastic dishes. In an in vivo experiment using glioma-harboring mice, 260 μg of the FMLs per 1 g of tumor tissue accumulated (tumor sizes was 0.1 cm3), which corresponded to approximately 60% of the total injection. This value was 7 times higher than that of the MLs. After injection of the FMLs, mice were exposed to intracellular hyperthermia using the alternating magnetic field irradiation. The temperature of tumor tissue increased to 43°C and the growth of the tumor was found to be arrested over 2 weeks. These results indicate the FMLs could target the glioma cells in vitro and in vivo, and are efficiently applicable to the hyperthermia of tumor.
A statistical method for short-term prediction is investigated to predict the ozone concentration in Seoul, Korea. Parameter estimation method and an artificial neural network (ANN) method were used to achieve real-time short-term prediction. Ozone concentrations often exceed air quality standards in cities around the world, and thus reliable prediction methods of ozone levels are needed. In this work, 1-6 hours and 16-21 hours prediction was performed. To verify the effectiveness of the prediction methods proposed in this work, the prediction results of ozone concentration were compared to the actual data. It appears that the methods proposed are a reasonable means of developing real-time short-term prediction for an ozone warning system.
RDF pyrolysis behavior over a temperature range of 773 to 1173K is experimentally investigated by measuring released gas composition and accumulative gas volume in a pyrolysis process for three kinds of RDF. The major combustible components in the released gas were CO, H2, CH4, C2H6, C2H4, C3H8 and C3H6. A rise in pyrolysis temperature resulted in improved content of combustible gas components, particularly H2 and CH4. The total heating value of the released gas is dependent upon the temperature and the type of RDF, and higher temperature improves the recycle energy efficiency converted into inflammable gas from RDF, but reduces the volumetric heating value of the gas. The amount of total gas yields can be expressed by a function of temperature and volatile matter content in raw materials regardless of the type of RDF.