Showing papers in "Journal of Chemical Engineering of Japan in 1994"

A Novel Combustor Based on Chemical-Looping Reactions and Its Reaction Kinetics

Abstract: A novel combustor based on controlled chemical-looping reactions without flame differs from the traditional combustor, in which the fuel is in direct contact with air. It allows CO2 to be easily recovered and promises advanced-level thermal efficiency for power generation. Promising results of laboratory experiments with the novel combustor are presented here. We found that NiO particles mixed with YSZ (yttria-stabilized zirconia) have very good properties with respect to oxidation rate, conversion, and physical strength. Especially, the rate of oxidation of Ni particles is increased significantly. The effects of YSZ content in the particle, the reaction temperature, the particle size, and the water vapor concentration were examined by studying the kinetic behavior of reactions. These promising results revealed high potential for applying chemical-looping combustion in a power-generation plant.

New PSA Process with Intermediate Feed Inlet Position Operated with Dual Refluxes: Application to Carbon Dioxide Removal and Enrichment

Abstract: A new PSA process was developed and applied to the removal and enrichment of carbon dioxide from air-CO2 mixtures. This PSA process is constituted by a dual reflux policy and admission of the feed gas mixture at an intermediate axial position of the column. The influences of the feed inlet position and reflux ratio on process performance were experimentally investigated. For both parameters there is respectively an optimum value at which the process performance was relatively higher. At the optimal values it was possible to concentrate and remove the CO2 simultaneously beyond a factor of the pressure ratio Pa/Pd, a situation unattainable in the conventional PSA in which the feed gas is supplied at the end of the column.

Carbon Dioxide Reforming of Methane on Supported Nickel Catalysts

Abstract: The reforming of CH4 with CO2 using various Ni catalysts has been investigated. As a result of screening tests, the selection of supports was found to be very important to control the catalytic activity of Ni. Among the various supports, ceramic foam and Al2O3 supports incorporating industrial steam reforming catalysts showed higher activities than SiO2 supports. The kinetic study has shown that the results could be expressed by a simple power-law equation for the three activated catalysts. The effect of the support was also studied. The results showed the importance of the acid-base property of the catalyst.

Preparation of Metal Sulfide Composite Ultrafine Particles in Reverse Micellar Systems and Their Photocatalytic Property

Abstract: CdS, ZnS and their composite ultrafine particles were prepared using nanometer-sized waterpools in AOT/isooctane reverse micellar solutions as reaction media. The size of the ultrafine particles was controlled by changing the water content Wo (=[H2O]/[AOT]) of the reverse micellar solution and this was almost independent of the feed concentrations of Cd2+, Zn2+ and S2–. Stable ultrafine particles, which do not cause excess aggregation and the band gap of which continues to be larger than that of the bulk semiconductor for a long time after formation, could be prepared at a value of Wo less than 8. Mixing a micellar solution containing both Cd2+ and Zn2+ with a solution of S2– gave coprecipitated semiconductor ultrarine particles. Gradual precipitation of ZnS in a micellar solution which had contained CdS particles gave ZnS-coated CdS ultrafine particles. The use of an excess of S2– for precipitation was effective in making the composition of the resulting particles close to that of the initial solution, and also avoided the formation of mixed crystals. The composite ultrafine particles thus prepared could be directly applied to the photocatalytic reduction of water and were found to be improved in their photocatalytic activity compared to CdS particles. The photocatalytic properties of the coprecipitated particles varied according to the particle band gap.

Simultaneous Organic Carbon Removal and Nitrification by Biofilm Formed on Oxygen Enrichment Membrane

Abstract: Biorilm was formed on an oxygen enrichment-type support which consisted of a poly(dimethylsiloxane) hollow fiber membrane and a fibrous support woven around the fiber. Population distribution of nitrifiers and denitrifiers in the biofilm was investigated. Nitrifiers were dominant within the fibrous support while denitrifiers were dominant in the surface biofilm attached to the support. Simultaneous organic carbon removal and nitrification were carried out successfully in single-step treatment of domestic wastewater. The nitrification rate in the present biofilm was about 2.2 g/m2d at an air pressure of 19.6 kPa or 29.4 kPa and was comparable to that in conventional biofilm processes designed especially for nitrification.

Extraction rates of oil from tomato seeds with supercritical carbon dioxide

Abstract: Tomato seed oil was extracted with supercritical carbon dioxide in a semibatch-flow extraction apparatus. The effect of milling of seeds and solvent flow rate on the extraction behavior was studied. The extraction rate increased as solvent flow rate increased. Milling the seeds prior to extraction enhanced the extraction rate. During extraction from milled seeds, the solute from the cells opened by milling was extracted fast, and the solute inside the cell walls was extracted slowly. Mathematical models based on two distinct extraction periods with different extraction rate were applied to analyze the experimental data. The models simulated the extraction behavior satisfactorily.

Size change of very fine silver agglomerates by sintering in a heated flow

Abstract: The size change of silver agglomerate particles with diameters ≤100 mm during sintering is investigated. The growth rate of primary particles due to partial coalescence within an agglomerate is first derived based on a sintering theory. In the experiment, silver agglomerates uniform in electrical mobility-equivalent diameter are introduced into a heating pipe with N2 gas flow. The size changes of the agglomerates are measured using an aerosol technique. Agglomerates heated up to about 500 K (about 0.4 of the melting point) decrease steeply in size with temperature. The agglomerates which have fused into single particles begin to evaporate at a temperature >900 K. The measured change in diameter with temperature agree well with theoretical calculations in which suppression of sintering due to primary particle growth is taken into account.

Global analysis of heat transfer in CZ crystal growth of oxide

Abstract: For the crystal growth of LiNbO3, a global analysis of heat transfer in an inductively heated CZ furnace was carried out by use of the finite element method. The effects of the temperature dependency of physical properties such as viscosity and surface tension of the melt, as well as the effect of processing parameters such as crystal rotation, on the flow and temperature fields in the furnace and on the melt/crystal interface shape were investigated. With the mathematical model developed in the present work, the interface inversion caused by crystal rotation was demonstrated theoretically. It is found that the effect of the temperature dependency of viscosity on CZ crystal growth is not significant under the conditions used here, and that the thermocapillary force strongly affects crystal growth. The critical crystal rotation rate at which the interface inversion occurs becomes much larger, and the RF coil current required to keep the crystal diameter constant becomes smaller, in comparison with those without thermocapillary flow in the melt.

Kinetic studies on the extraction of citric acid from aqueous solutions with tri-n-octylamine

Abstract: Distribution data of citric acid between an aqueous solution and a xylene solution of tri-n-octylamine (TOA) were measured in the 283–323 K temperature range. The complexes formed in the organic phase were determined and the equilibrium constants for the formation of these complexes were evaluated. In addition, the apparent thermodynamic data and the mole fraction of each complex present in the organic phase were calculated. When citric acid was extracted with a mixture of TOA and di(2-ethylhexyl) phosphoric acid (D2EHPA), the synergistic and antagonistic effects, depending on either the excess TOA over D2EHPA or the excess D2EHPA over TOA, were also observed and discussed.

Pressure drop though packed bed

Abstract: We present a more general and more accurate correlation of modified friction coefficient f b with Reynolds number Re and voidage fraction e based on the flow characteristics in a packed bed than that obtained experimentally in a previous paper

Effect of secondary air injection on axial solid holdup distribution in a circulating fluidized bed

Abstract: The effects of secondary air ratio (0–50%), height of injection port (1.5–2.5 m) and injection types (radial and tangential) on the axial solid holdup distribution have been determined in a circulating fluidized bed (0.1 m I.D. × 5.3 m high). As the secondary air ratio is increased, solid holdup increases below the secondary air port, whereas it decreases slightly above the secondary air injection port. The dense bed height increases with increasing height of the secondary air injection port. Different types of secondary air injection system do not produce any significant difference in the overall axial solid holdup distribution. However, solid holdup just above the injection port in a tangential secondary air injection system exhibits somewhat higher values than those of radial secondary air injection system. The effect of secondary air injection on the axial solid holdup distribution in a circulating fluidized bed can be predicted by a modified freeboard-entrainment model with decay constants determined from the proposed correlation.

Extraction of Enzymes and Their Activities in AOT Reverse Micellar Systems Modified with Nonionic Surfactants

Abstract: The extraction of Chromobacterium viscosum lipase and α-chymotrypsin from aqueous solution, and hydrolysis catalyzed by these enzymes were carried out in AOT/Span 60 and in AOT/Tween 85 mixed reverse micellar systems. Span 60 was likely to be solubilized in the water pool of AOT micelles without any change in micellar shape, while Tween 85 brought about an elongation of the micellar shape. The extracted fraction of the α-chymotrypsin at pH 6 was decreased by the addition of Span 60 or Tween 85, owing to the dilution of negative charge density of micelles. However, the extracted fraction of the lipase was increased by the addition of Tween 85, which seemed to act as an affinity ligand. The activity of α-chymotrypsin was improved by the addition of Span 60 or Tween 85, which decreases the electrostatic and hydrophobic interaction with AOT molecules. The activity of the lipase was significantly improved by the addition of Tween 85, especially in the higher range of water content, and the bell-shaped dependence of the activity on the water content disappeared. The lipase activity was maximum when the molar ratio of AOT to Tween 85 was 3:2–4:1.

Hydrodynamic Damage of Cultured Cells of Carthamus tinctorius in a Stirred Tank Reactor

Abstract: The effect of hydrodynamic stress on intracellular factors of plant cells was investigated. Safflower (Carthamus tinctorius) cells were cultivated in a stirred tank reactor. The aggregate size distribution was determined with an image analyzer and it was confirmed that the aggregate size became smaller in a stirred tank. The resultant changes in the cells were evaluated on the basis of cell number, dry cell weight, cell viability, ATP amount and cell membrane fluidity. The viability was estimated by growth potential, membrane integrity and respiration activity of the cells. The cells were damaged by hydrodynamic stress in the respiration activity before the occurrence of the cell lysis and the damage of membrane integrity. ATP amount decreased as the agitation rate increased. The extent of ATP loss was larger than that of viability loss. These results indicated that hydrodynamic stress affected the metabolic system and that the loss of viability was probably due to this metabolic change. The degree of ATP reduction showed a power law dependence on the power dissipation rate per unit mass, e, which is calculated from agitation rates.

Temperature profile and optimal rotation speed of a honeycomb rotor adsorber operated with thermal swing

Abstract: Two-dimensional temperature profiles along the honeycomb axis and rotation angle were monitored by six pairs of thermocouples placed in the rotor at equal intervals in order to measure the extent of regeneration of the rotor. At an optimal rotation speed, the axial part of the rotor near the gas exit is not heated up to the regeneration temperature in the regeneration zone while the exit temperature remains at a characteristic temperature under dynamic equilibrium. Effects of rotation speed n, air velocity U, regeneration temperature Te1 and feed humidity Hs0 on temperature profile in a honeycomb adsorbent rotor were investigated in terms of relative heat capacity Λ = ρbCpcnL/βρgCpgU, number of mass transfer units N = kamL/ρgU and latent heat ratio r = Q′Hs0/Cpg(Te1 – Ts0). Temperature distribution is not much different for various values of N. Regeneration of the rotor becomes incomplete and the cooling stage becomes longer with an increasing value of Λ. Regeneration of the rotor becomes incomplete as the value of r becomes larger.Based on experimental results, optimal rotation speed nopt decreases to some extent at higher humidity and lower regeneration temperature. The final recommendation for the optimal rotation speed is given by a simple relationship Λopt = 0.38(1 – r).

Non-isothermal Adsorption of Nitrogen-Carbon Dioxide Mixture in a Fixed Bed of Zeolite-X

Abstract: The binary adsorption of nitrogen and carbon dioxide on zeolite-X was investigated. The adsorption equilibria of pure and binary systems were measured by static methods. In the binary system the equilibrium Selectivity of CO2 over N2 was very high: about 525 at a CO2 mole fraction of 0.14 and a temperature of 15°C. Consequently, N2 can be considered as inert when its mole fraction is less than 0.8. The ideal adsorbed-solution theory (IAST) predicted quite well the binary equilibrium data, while the extended Langmuir isotherm showed a great deviation. The dynamics of fixed-bed adsorption of CO2-N2 gas mixture (CO2 14.86 mole percent) was analyzed by the cell model under non-isothermal conditions, incorporated with binary adsorption equilibria, mass and heat transfer resistances and variation of gas velocity in the bed. The concentration and temperature history curves were determined and compared with the theoretical results. This cell-model with IAST predicted well the dynamic behavior of the adsorption bed.

Predicting the Minimum Fluidization Velocity of Multicomponent Systems

Abstract: An expression is suggested to appropriately estimate the minimum fluidization velocity of either a perfectly mixed or a completely segregated multicomponent system. Based on experimental data from the literature and our own work it is found that agreement between predictions and experimental results is reasonably good in the context of the inherent limitation of the theory and the accuracy of the data.

Combined Process for Production of Methyl tert-Butyl Ether from tert-Butyl Alcohol and Methanol

Abstract: Reactive distillation for the production of methyl tert-butyl ether (MTBE) from methanol (MeOH) and tert-butyl alcohol (TBA) using two types of catalysts, ion exchange resin and heteropoly acid (HPA), has been studied. The reaction was performed in the liquid phase and at the boiling point of the reactant mixture under atmospheric pressure. The reactive distillation was examined with and without pervaporation. An azeotropic mixture of XTBE and MeOH was obtained as a top product. HPA showed higher selectivity than did ion exchange resin. It was found that the pervaporation might be effective in removing water.

Concentration correlation in a turbulent mixing layer with chemical reactions

Abstract: Instantaneous concentrations of two reacting species were simultaneously measured using a combined laser and electrode-conductivity technique in a turbulent liquid mixing layer with the influence of second-order irreversible chemical reactions. To investigate the effect of turbulent mixing on the mean reaction rate, the concentration correlation was estimated from the instantaneous concentration measurements for three reactions; a very slow reaction, a moderately fast reaction and a rapid reaction, and the results were compared with several closure models. The results show that the segregation parameter increases from –1 towards zero in the downstream region of the mixing layer and it approaches –1 with increasing Damkohler number. The corrected 3E closure model can best predict the concentration correlation for both moderately fast and rapid reactions. The Lagrangian stochastic model can explicitly predict the concentration correlation for all reactions though it underestimates the correlation.

Development of methylal synthesis by reactive distillation

Abstract: The world’s first technology for the commercial production of methylal is the reactive distillation method. Its application to a new formaldehyde process has also been investigated. Whereas the oxidation of methanol yields one mole of water per mole of formaldehyde, methylal oxidation produces only one mole of water for every three moles of formaldehyde. Thus, the output by methylal oxidation is more than 70% formaldehyde compared with 55% by methanol oxidation.For this purpose, basic research on methylal synthesis was conducted and the world’s first commercial production of methylal using reactive distillation was accomplished. Using this methylal, the world’s first methylal oxidation technology for manufacturing highly concentrated aqueous formaldehyde was established.This highly concentrated aqueous formaldehyde is then fed to an acetal homopolyrner and copolymer plant having a combined capacity of 35,000 tons/year.

Axial Distribution of Solid Holdups in Binary Solids Circulating Fluidized Beds

Abstract: The hydrodynamic behavior of binary solids circulating fluidized beds was examined in terms of axial distributions of apparent solid holdup as well as of fine and coarse solid holdups. Experiments were carried out in two circulating fluidized beds of 3 m in height and 97 mm and 150 mm in diameter, using FCC catalysts with a mean diameter of 69.7 μm as the fine particles and 321-μm silica sand and 633-μm activated alumna as coarse particles. The influences of gas velocity, solids circulation rate, loading ratio of coarse particles and bed diameter on the axial distributions of apparent holdup and of fine and coarse particles holdups were investigated. Comparisons were made of the axial distributions of solids holdups both in the presence and absence of coarse particles. It was found that the addition of coarse (or dense) particles results in a significant variation in both the apparent and the fine particles holdups. In addition, the nonuniformity of the axial solid holdup distribution was found to vary with increasing loading ratio of coarse particles.

Equilibrium and kinetics of lithium extraction by a mixture of lix54 and topo

Abstract: The equilibrium and kinetics of Li + extraction in the LIX54-TOPO system were examined on the basis of an extraction mechanism including the parallel reactions of the extractant coordination

Uptake of a few divalent heavy metal ionic species by a fixed bed of hydroxyapatite particles

Abstract: Breakthrough curves were measured for Cd2+, Cu2+ and Pb2+ in their single, binary and ternary nitrate aqueous solution systems using a fixed bed of hydroxyapatite particles in order to obtain volumetric mass transfer coefficients. Breakthrough curves for Pb2+ showed particular profiles depending on the pH of influent solutions in the bed. For the binary and ternary systems containing Pb2+, the curves for each ion showed that Pb2+ displaced not only calcium but also other co-existent ions which were already collected in the substrate. It was considered that Cd2+ and Cu2+ were collected in the vicinity of the internal surface of particles, but the uptake of Pb2+ occurred in the interior as well as at the internal surface of hydroxyapatite particles.

Continuous separation of phenol from an aqueous stream using micellar-enhanced ultrafiltration (meuf)

Abstract: Micellar-enhanced ultrafiltration has been carried out to investigate the separation of phenol from an aqueous stream via hollow fiber membranes. First, phenol is solubilized into the micelles of cationic surfactant such as hexadecyltrimethylammonium chloride (CTAC) and hexadecylpyridinium chloride (CPC), and then the micellar solution is treated continuously through an ultrafiltration membrane module. In the present study we examine the effects of retentate concentration, molecular weight cut-offs, molar ratios of surfactant to phenol and other operating conditions on the rejection efficiency. The results show that the concentration of phenol in the permeate rapidly decreases as the surfactant aggregates to form micelles beyond its critical micelle concentration. Further, the rejection of phenol and surfactant by the membrane is enhanced when the operating condition is favorable to formation of a gel layer at the surface of the membrane which provides the presieving effect. Formation of a gel layer becomes pronounced when either the flux ratio of permeate to retentate or the micelle concentration in the feed increases.

Segregation of particles in binary solids circulating fluidized beds

Abstract: The segregation pattern of particles in circulating fluidized beds, 0.097 m and 0.150 m in diameter and 3 m in height, was investigated by using two groups binary solid particles that are different in diameter and density. The influence of operating conditions on the extent of particle segregation were examined. An empirical correlation for describing the extent of segregation was proposed. For distinguishing the segregation/mixing flow pattern, a theoretical criterion was derived and a segregation diagram was then prepared.

Development of immobilized enzyme entrapped within inorganic matrix and its catalytic activity in organic medium

Abstract: A method for entrapment of enzymes within an inorganic matrix was developed using a sol-gel process. Such entrapping immobilization of biocatalysts within inorganic matrices has some benefits but it is rather difficult to apply in contrast to other types of immobilization and therefore has not been commercialized. The method developed was applied to entrapping lipase within silica beads. The entrapped lipase was six times more active for esterification in an organic medium than lipase immobilized over silica glass with a binding method which has conventionally been used. The high activity may come from the characteristics of the present method. It can entrap the enzyme with less denaturation and provide the matrix with physical properties suited to the reaction, e.g. an abumolance of macro pores.

Evaluation of Dead-End Ultrafiltration Properties by Ultracentrifugation Method

Abstract: In protein ultratiltration, solution environment factors such as pH and solvent density are important in controlling the filtration flux. Also, the properties of the filter cake of macromolecular solutes formed on the membrane surface play a vital role in determining the filtration flux in ultratiltration. On the basis of the sedimentation velocity technique and the high-speed sedimentation equilibrium technique using an analytical ultracentrifuge, the influence of the protein solution pH on the time variation of the filtration flux in unstirred dead-end ultrafiltration was accurately described. It was clearly demonstrated that the low filtration flux around the isoelectric point is mainly due to the build-up of compact filter cake, which causes a large hydraulic flow resistance. Furthermore, it was shown that the solvent density ρ has a large effect on the dynamically balanced filtration rate in upward ultrafiltration just as it does on the sedimentation coefficient in ultracentrifugation.

Isobaric Vapor-Liquid Equilibria for Propyl Methanoate + (n-Alkanes, C7, C8, C9) or n-Alkanols (C2, C3, C4)

Abstract: The compositions of the vapor-liquid equilibria have been obtained in a small capacity recirculating still for the binary mixtures composed of propyl methanoate with n-alkanes (heptane, octane, nonane) and n-alkanots (ethanol, propanol, butanol) at a constant pressure of 101.32 ± 0.02 kPa. Experimental data were thermodynamically verified and then correlated with suitable equations. The mixtures (x1 propyl methanoate + x2 n-heptane, or + x2 ethanol, or + x2 propan-1-ol) have an azeotrope at x1 = 0.786, 0.482 and 0.852, respectively. The predictions made by the ASOG and UNIFAC models can be considered acceptable.