In the past decade, both Monte Carlo (MC) and molecular dynamics (MD) calculations have been extensively used in the field of chemical engineering thermodynamics for the purpose of obtaining general features of dynamic and equilibrium properties of simple model fluids at the molecular level. The most frequently used model is pure and mixed fluids interacting with Lernnard-Jones (LJ) potential. In this review article, some representative results are presented and discussed with particular emphasis on structure (local composition), PVT relation, excess properties and phase equilibria of LJ fluid. The possibility of utilizing these results for physical property prediction is discussed. The present status of application of quantum chemistry-based potential models has also been given.
Computer simulation of granulation in a fluidized bed process was carried out using a two-dimensional random coalescence model, In this contribution, seed circles of two sizes were granulated by circular spray mist with radii obeying log-normal distribution on the basis of adhesion probability, in which the adhesion force of spray mist was taken into consideration. This simulation was then applied to fluidized bed granulation, in which a 7:3 weight ratio mixture of lactose and corn starch was granulated by an aqueous solution of hydroxypropylcellulose of several concentrations. Effects of moisture content and spray mist size on geometric median diameter of granules were investigated experimentally and analytically. It was found that granulation phenomena, in which granule growth progressed with an increase in moisture content and spray mist size, were very well simulated by the model proposed, thereafter, the mechanism of particle adhesion in fluidized bed granulation was elucidated.
The cross-flow ultrafiltration of reverse micelles was investigated to examine the applicability of a membrane reactor for continuous enzymatic reaction. An ultrafiltration ceramic membrane module of tubular type was used to separate the Aerosol OT reverse micelles from the continuous phase of iso-octane. The rejection of reverse micelles as well as the permeation flux were measured at different concentrations of surfactant, water, enzyme and molar ratio of water to surfactant ωo. The permeation flux decreased and the rejection of water increased with increase in the concentration of lipase, probably as a result of the higher enzyme mass adsorbed on the membrane. The rejection of reverse micelles also increased with increase in ωo, which influences the diameter of reverse micelle. The permeation flux, however, could not be correlated solely with the parameter ωo, and it depended on the concentration of surfactant itself when ωo was less than rive. This direct influence of surfactant is supposed to be due to the adsorption of surfactant in the membrane which can change the hydrophobic property of the membrane.
Adsorption/desorption behavior and simultaneous heat and mass transfer in a honeycomb adsorber were investigated using a humidity chart. It was found that the dehumidifying performance is sometimes decreased remarkably owing to the mass/heat balance limitation when the feed humidity is high or regeneration temperature is low. A prediction method is proposed for the design principle of honeycomb adsorbers by taking into account the optimal rotation speed and the regeneration air velocity obtained from the graphical solution using a humidity chart. The method is simple to use, without complicated computation and it is useful to avoid the serious influence of by the mass/heat balance limitation. At a process air velocity of 1 m/s, by considering the relation between the optimal rotation speed and the moderate regeneration air velocity obtained using a graphical method, the product air humidity decreases to a value near to the thermodynamic limit.
A model has been developed for fluidized bed electrodes based on an operative bipolar mechanism and the concept of two bipolar aggregates of particles in the direction of current flow. Extensive measurements of local overpotential frequency distribution and time-averaged overpotentials using a probe electrode technique have been made in both monopolar and bipolar packed bed electrodes, and in both monopolar and bipolar fluidized bed electrodes. Validation of the probe for overpotential measurement is claimed; and good agreement between fluidized bed electrode measurements and the model has been shown. This validation of a reasonable model for bipolarity in fluidized bed electrodes should permit application in design and scale-up of such electrodes.
The NVT and μVT ensemble MC techniques have been used for simulations of adsorptions in a slitpore from a binary mixture of benzene diluted in supercritical CO2. The LJ potential function is used for representing intermolecular interactions between CO2, benzene and surface carbon. A typical curve for adsorption of benzene shows a maximum at a pressure below the critical pressure of CO2 and then decreases with increasing pressure. The magnitude of maximum adsorption increases with increasing interaction energy between benzene and surface carbon. It has been shown that this adsorption behavior is attributable mainly to enhanced solubility in the supercritical CO2 and partly to the competitive adsorption of CO2. The adsorption of carbon dioxide increases linearly with pressure and the slit pore becomes full of CO2 molecules under supercritical fluid conditions. The local density profile of benzene in a pore is scarcely affected by CO2; however, the profile of CO2 is strongly affected by benzene molecules when they occupy the first monolayer near the wall.
Transfer of hydrocarbons in an O/W emulsion drop was simulated by the dimensionless multi-layer liquid membrane model in order to find a way of improving the separation selectivity of an emulsion liquid membrane, which will be of practical use. The results suggested that the selectivity of the emulsion membrane, lowered by the unfavorable concentration profile which appeared in an emulsion drop, would be improved by decreasing the number of inner oil droplets in the emulsion drop. A series of batch permeation experiments were conducted with a one-dimensional supported liquid membrane and an emulsion liquid membrane. The separation selectivity of the supported membrane was equivalent to that of the mono-layer liquid membrane and that of the emulsion membrane was lower. Selectivity of the emulsion membrane could be improved by decreasing the number of inner droplets in the emulsion drop as suggested by the simulation. These experimental confirmations of the suggested model led to a simple way of improving the separation selectivity of this separation technique.
Poly(Acrylamide-co-N,N′-methylene bisacrylamide) microspheres were prepared and the sustained release of Fe3+ via ion exchange was investigated in response to the hydrochloric acid concentration. The experimental results revealed that the adsorption/desorption of Fe3+ with microspheres proceeds via ion exchange between Fe3+ and proton. The release rates of Fe3+ from microspheres were found to be moderate under proton concentrations below 10–1 mol·dm–3. However, an abrupt increase in the release rate was observed above 10–1 mol·dm–3. The permeability coefficient was proportional to the hydrochloric acid concentration and had a discontinuity at around 10–1 mol·dm–3. A on-off release mechanism from microspheres was demonstrated in response to a small change in the hydrochloric acid concentration between 10–1 mol·dm–3 and 10–3 mol·dm–3. The permeability coefficients were independent of the stirring speed, and the activation energy for sustained release was 63.9 kJ·mol–1, indicating that sustained release was controlled by ion exchange of Fe3+ and proton.
A fly ash of low calcium content (1.67 wt% CaO) was ground (to particle sizes ofunder 5 μm) and treated with slaked lime (Ca(OH)2) to produce an improved sorbent for high-temperature dry sorbent injection. Four samples were treated at 350 K for 8 hours with different Ca(OH)2 concentrations (6.6–28.6 wt%). The specific pore surface area and pore volume were extensively characterized before and after treatment. Sulfation tests were performed by exposing the treated samples to a 0.31 vol% SO2 containing atmosphere at 1123 K in a thermo-gravimetric analyzer (TGA). The TGA experimental conditions were carefully controlled to closely simulate those encountered in an atmospheric fluidized bed combustor (AFBC). The treated fly ash sorbents showed higher SO2 sorptivity compared to untreated sorbents. The sorption capacity was found to increase as the Ca(OH)2 concentration increased in the range of interest. Up to 92% CaO conversion could be achieved when the 28.6% Ca(OH)2 fly ash sorbent was sulfated for 1 hour. Treatment of fly ash with Ca(OH)2 enhanced the specific surface area (by about 5 to 8 times), which was principally responsible for the high SO2 capture.
A kinetic study of the solvent extraction of palladium (II) with 3,3-Diethylthietane (DETE) from aqueous chloride media was conducted at 303 K using a hollow fiber membrane extractor, together with a study of the interfacial adsorption and distribution equilibria of DETE between the organic and aqueous phases. From the equilibrium studies, it was found that DETE was not interfacially active but was highly soluble in the aqueous phase. From the kinetic study, the apparent reaction orders of the extraction rate were determined experimentally from the concentration dependencies of the extraction rate on hydrogen ion, palladium (II), chloride ion and DETE, respectively. From both the equilibrium and kinetic studies, the extraction rates could be reasonably explained by a combination of a diffusion model and the homogeneous reaction kinetics in the aqueous phase, taking into account the velocity distributions of the aqueous and organic phases through the inner and outer sides of a hollow fiber. The diffusional effect of each species on the extraction rates in the hollow fiber membrane extractor was determined. Furthermore, we confirmed the utility of the membrane extractor as an experimental apparatus for studying kinetics as well as of the proposed diffusion model for developing membrane extractors using hollow fiber modules.
T-x-y data for binary systems containing methyl ethanoate + n-butyl alcohol and methyl ethanoate + iso-butyl alcohol were measured at 74.66 and 127.99 kPa using a dynamic method. No azeotrope was found and the mixtures studied exhibited positive deviations from ideality. All data, p-T-x-y were found to be thermodynamically consistent and application of the group contribution models ASOG and UNIFAC gave good predictions.
The dynamics and control of two complex column configurations (sidestream column with stripper and prefractionater/sidestream column configuration) which are multivariable, interacting and nonlinear, have been studied. A new control scheme developed by Han and Park (1993) to deal with the nonlinear and multivariable nature of distillation processes has been applied to these complex distillation configurations. The control scheme incorporates a nonlinear wave model into a generic model control framework. An observer based on the nonlinear wave model is used to determine the profile positions of distillation column sections. The control scheme enables tight control of the profile position of each column section that leads to fast stabilization of product compositions.
Divinylbenzene homopolyineric microcapsules with porous membranes, where pores act as channels for extraction, were prepared using various solvents in the dispersed phase such as toluene, benzene, 4-methyl-2-pentanone and Exxsol D-80. Experimental evidence suggested that addition of volatile solvents resulted in the formation of divinylbenzene homopolymeric microcapsules with highly porous membranes by in situ polymerization accompanied by a solvent evaporation process. Solvent type was found to be a significant factor to change the surface morphology of the microcapsules. A membrane structure with macropores could be prepared by using volatile solvents. However, for a system of microcapsules with non-volatile solvents or without any solvent, only mesopores were formed in the microcapsule membrane. Using microcapsules with macroporous membranes, hydrochloric acid can be sufficiently extracted from aqueous solution. This infers that macropores formed by solvent evaporation function as efficient channels for extraction. The influence of preparation conditions such as solvent type and monomer concentration on extraction properties was also discussed.
The extraction of molybdenum and vanadium from weak-acidic sulfate and chloride media by bis(2-ethylhexyl)monothiophosphoric acid (D2EHTPA) and bis(2-ethylhexyl)phosphoric acid (D2EHPA) was investigated. The cationic species of the metals, such as MoO22+, were extracted by both extractants. In the case of vanadium, the supplied VO3– was reduced to VO2+ by contact with the organic phase containing D2EHTPA, and this extractant was partially oxidized to disulfide. While molybdenum was found to be more extractable than vanadium by both extractants, the separation factor of the metals by using D2EHTPA was greater than in the case using D2EHPA, especially when VO3– was used as feed. The oxidized D2EHTPA containing disulfide enhanced the extractability of molybdenum and vanadium. However, the separation factor of the metals decreased with the formation of disulfide. It is important to reduce V(V) to VO2+ prior to extraction in order to minimize the oxidation of D2EHTPA for separation and repeated use of the extractant.
The extraction of Ce(III) from aqueous solutions containing Al(NO3)3 was examined by using styrene-divinylbenzene copolymer (SDB) gels swollen with dihexyl-N,N-diethylearbamoylmethylphosphonate (CMP), octyl(phenyl)-N,N-diisobutylcarbanoylmethylphosphine oxide (CMEPO) and an equimolar mixture of CMP and CMPO. The extraction constants (Kex) for the gels with CMIP and CMPO were evaluated. The distribution ratio of Ce(III) for the gel with an equimolar mixture of CMP and CMFO was described as Kd = (KexCMP[CMP]3 +KexCMPO[CMPO] 3)[NO3–]3) by using these extraction constants. The extraction rate was found to be controlled by diffusion of Ce-complex [Ce(NO3)3(CMFO)3 or Ce(NO3)3(CMP)3] through the gel. The diffusion coefficient (Ds) was inversely proportional to the viscosity of extractant (η) and represented by an expression similar to the Stokes-Einstein equation, Dsη/T = constant. A decrease in the viscosity of extractant was effective for increasing the extraction rate.
Quantitative correlation between the variation of surface net and local hydrophobicities and the conformational change of cytochrome c induced by added acid and salts was investigated by using aqueous two-phase partitioning systems (ATPS). Cytochrome c is unfolded at pH 2 under conditions of low ionic strength, but it is refolded to the molten-globule state by further addition of acid. By addition of salts, a conformational change from the unfolded to the molten-globule state by the anion binding to the positive charge of a protein was also observed. Surface net and local hydrophobicities observed by using the ATPS method clearly show significant differences in these three conformational states, in contrast to the conventional CD measurement. The local hydrophobicity, which can be evaluated by the increment of partition coefficient by the binding of Triton added to the ATPS, is greatest for the molten-globule state, whereas its surface net hydrophobicity is intermediate between the unfolded and native states.
The selective separation of amino acids, glutamic acid, methionine and lysine, from their solution mixture was examined by electrodialysis with ion-exchange membranes, SELEMION-CMV and SELEMION-AMV, under conditions of pH 1 to 12 and current densities of 0 to 15 A/m2. The amino acids were almost completely separated from each other under the conditions studied: Only glutamic acid is transported across the anion-exchange membrane; only lysine across the cation-exchange membrane; and methionine is not transported at all. Their fluxes across the membranes have maxima in the neutral pH range, increasing almost linearly with current density. A model for explanation of the experimental results has been proposed considering solution equilibrium, ion-exchange equilibrium and diffusion in the membranes. Successful simulation has confirmed the amino acid transport mechanism which was proposed in the model. The diffusivities of ionic species, model parameters, have been determined. Moreover the role of each ionic species in carrying current and the effect of water splitting are also discussed.
A Monte Carlo procedure is used to examine the structure of equilibrium, colloidal aggregates governed by hard-disk (or hard-sphere) or square-well interparticle interactions. The resulting aggregates consist of a core with a liquid-like topological structure embedded in a fractal. The core extends over three to four particle diameters and its structure and range are determined by the interaction forces. The sheath surrounding the core has a fractal dimension of 1.93, corresponding to that of continuum percolation clusters, in the case of two-dimensional aggregates and a dimension of about 2.9 in the case of three dimensions. The occurrence of liquid-like cores and fractal sheaths is consistent with recently reported results (based on small-angle neutron-scattering studies) on silica dispersions flocculated by weakly charged or uncharged polymers of large molecular weight. The procedure outlined here can be readily extended to other interaction potentials through importance-sampling techniques and can be used for interpreting small-angle radiation-scattering data on colloidal, biological and other dispersions.