The biological utilization of CO2 in the production of acetic acid in anaerobic fermentations of Acetobacterium woodii was studied in a bubble-column bioreactor. To increase the productivity of acetic acid a repeated-batch culture technique was developed by introducing concentrated cells using a synthetic polymeric flocculant. The effects of the operating conditions of gas flow rate, cell density and medium composition on volumetric productivity of acetic acid were examined. At suboptimal operating conditions the production rates of various cultivation schemes were examined. This approach is especially valuable for simplification of the process and utilization of the energy required for the separation of the cells from the liquid content.
Application of Bayesian dynamic modeling to fault detection is developed for a nonstationary batch process. In the modeling, the observed time series are expressed in several specific components such as local polynomial trend, observation noise and globally stationary autoregressive component. To illustrate the method, detection of a fault in an operation of a stirred vessel with a heater is presented. From the sequential probability ratio test of the model estimation error, the fault can be detected successfully with high sensitivity.
Factors affecting α-tocopherol production using safflower (Carthamus tinctorius) cells were studied from the engineering aspects for plant cell culture. The specific production rate was evaluated as a function of rate-limiting factors. The conditioning factor released from cells, dissolved oxygen (DO) and medium components were considered as the limiting factors responsible for the specific production rate. Increasing the conditioning factor enhanced α-tocopherol production. Increasing DO concentration up to 9 mg-O2/l also caused a linear increase in specific production rate. The specific production rate in batch cultivation decreased, however, at a constant DO concentration with a sufficient amount of the conditioning factor. In repeated batch cultivation, the specific production rate was recovered by the addition of fresh medium. These results showed that an essential component in the medium was exhausted at an early stage of the batch cultivation and that the medium-feeding operation with sufficient CF and DO concentrations was required to maintain high productivity. By repeated batch cultivation, the content of α-tocopherol in the cell was increased to 9 mg/100 g-dry cell, which was considerably higher than that in natural safflower seeds.
Esterification of oleic acid with ethanol in the presence of p-toluenesulfonic acid was carried out at temperatures up to 383 K and initial molar ratios of ethanol to oleic acid, m0, up to 6. A kinetic equation having both a term of rate reduction due to water and a m0-dependent rate constant are presented. The esterification, aided with pervaporation through asymmetric polyimide membranes, was carried out at 348 K and 371 K under atmospheric and elevated pressures respectively. Almost complete conversion was attained for m0 of 2 in a short time with a low concentration of the catalyst at 371 K. Only water and ethanol permeated through the membranes. The permeation flux was expressed by the product of the permeability constant, P, and the permeant concentration of the liquid. P depended on the concentration of oleic acid and ethyl oleate at 371 K, but not at 348 K. A model in which the kinetic equation is combined with the permeation flux equation taking both volume change and sampling loss of the reaction mixture into consideration represented the experimental time course of the reaction sufficiently well. The influence of operating parameters on the reaction time required for a conversion of 98% and on the productivity was investigated by simulation from the model.
To dehydrate a fermented or synthetic crude ethanol using super- and subcritical propane solvent extraction, we previously measured phase equilibrium data for the C3H8-C2H5OH-H2O system9). In this work the applicability of phase equilibrium models was examined using existing well-known PT-EOS, GC-EOS and a NRTL-NRTL solution models. The estimations of binary phase equilibria by these models are relatively accurate, except for PT-EOS, using the random mixing rule. It is found that the solution model NRTL-NRTL is the most practicable one for the C3H8-C2H5OH-H2O ternary system at the extraction stage. At the propane azeotropic distillation stage, GC-EOS gives the most accurate estimation. Although it is a little less practicable, it can be used for design concept. At the propane stripping stage, any equation-of-state method is sufficiently practicable.
Dehydration of a fermented or synthetic crude ethanol using sub- and supercritical C3H8 solvent extraction was studied and developed. A bench-scale plant (maximum feed rate of about 10 kg/h) was constructed, and ethanol was extracted and separated using C3H8 as solvent. The results of bench plant tests and process simulation incorporating phase equilibrium models developed by us were employed in the optimization of process conditions. It can be concluded that ethanol is easily concentrated from 10 wt% to 99.9 wt% with a small energy consumption of approximately 1193 kJ/l of product.
To elucidate the heat transfer phenomena for a package in a refrigerating room with upflow, we considered a vertical-duct model in which one wall was isothermally heated and gas flowed upward through the duct in the laminar-flow range. The velocity profiles, temperature distributions and the local and average heat transfer coefficient were calculated numerically by fundamental equations. The main fluid flow is drawn toward the heated wall in the range of low Re and becomes parallel to the axial coordinate with increasing Re. The higher on the heated wall, the smaller is the local Nusselt number. However, the average Nusselt number does not undergo much change with increasing Re and Gr. A correlated equation for heat transfer was obtained under the operating conditions of this calculation. To check these calculated results, the temperature distributions and heat transfer coefficient were measured experimentally under the same operating conditions as those of the theoretical analysis. The calculated temperature distributions agreed closely with the measured ones. To compare the heat transfer coefficient of the downflow and the upflow, we found that the latter is about twice that of the former.
Minimum deviation control, an advanced technique using a reduced-order dynamic matrix, has been proposed and its performance is investigated through simulation and experiment. Performances of the existing dynamic matrix control technique and the proposed technique are compared in a simulation study by changing set points of top and bottom temperatures and feed flow rate. A control experiment is also conducted with a pilot-scale binary distillation column using the proposed control method. From the simulation result, it is found that the new technique is better than dynamic matrix control in overall performance. The experimental test also shows that the proposed control strategy is suitable for practical application and is better than the existing technique.
Concentration dependency of surface diffusivity of nitrobenzene and benzonitrile was measured at different temperatures for adsorption from aqueous solution onto an activated carbon, by batch kinetic experiments within limited ranges of amount adsorbed. The isotherms obeyed the potential theory of adsorption, and were only partially expressed by Freundlich equations. Eyring’s rate theory was applied to the elemental steps of surface diffusion with the assumption that the rate-controlling step was the hole-making step for the systems under the potential theory. The activation energy was found to be a certain fraction of the sum of the evaporative energy of adsorbate and the adsorption potential. Thus the derived correlation equation had two parameters, and was tested with the measured concentration/temperature dependence of surface diffusivity. Good correlation was obtained, with reasonable values of the parameters from the viewpoint of their definition and/or accord with other research results. The success in the correlation manifested the importance of the hole-making step in surface diffusion.
Gas antisolvent crystallization has the potential for application in the recovery of valuable compounds from liquid solution, and in the separation of solid-solid mixtures. Experimental data are presented for a mixture of anthracene and anthraquinone dissolved in cyclohexanone which was expanded by a gaseous anti solvent, CO2. The pressure range is 0.1 to 12 MPa, and the temperature is 291 to 313 K. The relation of salted-out yield and normalized feed concentration gives an important parameter, the so-called minimum solubility, from which supersaturation can be defined for gas antisolvent crystallization. Effects of initial feed concentrations of solid solutes, temperature, and pressure on the separation of anthracene and anthraquinone have also been studied.
Adsorptive membranes have been recently developed for affinity or chelating separation to reduce diffusion resistance, which is a major factor in broadening of the breakthrough or elution curve. Since the axial distance along the fluid flow is relatively short, the heterogeneity in the membrane is expected to influence the performance of the adsorption. The heterogeneities in membrane structure such as porosity, thickness and pore size are evaluated theoretically by moment analysis. The first, second and third moments are shown as a function of heterogeneity such as porosity distribution. The parameters involved in the system are adsorption equilibrium constant, Peclet number, and adsorption rate constant. The influences of these parameters as well as heterogeneity are evaluated. The heterogeneity produced unfavorable peak broadening and skewness.
A new example of thermal swing adsorption using a honeycomb rotor with a thin sheet of silica gel as adsorbent has been developed for dehumidification of air. Owing to improvement in the dynamic adsorption capacity and rapid thermal response of the rotor, the product humidity was reduced to 10–20% of the feed at an air velocity of 1–2 m/s through a 0.2m-long honeycomb. The existence of an optimal rotation speed of rotor has been observed. It increased in proportion to a single term of velocity of regeneration air, divided by width of the rotor and bulk density of the rotor; the effects of temperature and humidity of the feed and regeneration air were small. A dimensionless formula for the optimal rotation speed was derived on an empirical basis.
For an improved understanding of gas-liquid mass transfer in a stirred-tank reactor and its spatial variation, knowledge of local bubble sizes (mean and distribution), gas holdups and coalescence rate is very important. In this work, bubble sizes at eight positions in an aerated vessel agitated by a 6-blade Rushton turbine were measured for an air-deionized water system by using flash photography. Bubble sizes near the vessel wall (and especially near the baffles) or in the upper levels of the vessel were more than four times those in the impeller region, The number of bubbles was also counted in a given area, and the population density was determined knowing the depth of focus. The coalescence rate during passage of the bubbles from the impeller to the vessel wall was calculated for different gases and liquids by measuring bubble sizes on photographs taken across the annular plane. It was found that coalescence occurs very near the impeller. The calculated values of coalescence rate were almost the same as those reported earlier by other investigators.
The development of phase separation in ternary systems composed of polybutadiene-poly(styrene-co-butadiene)-good solvent was studied by time-resolved light-scattering during the solvent casting process. Double percolated structures with two different periodic distances were observed for the thick film. The structure with the smaller periodic distance was formed at the surface of films and the larger one was formed inside the film. It was found that the periodic distance for the larger percolated structure was proportional to (tP – tS)0.6, where (tP – tS) is the lapse of the time from the start of phase separation to fixation of the structure. The time dependence of the wave number, qm, at which the light-scattering intensity reaches maximum, was correlated by a similar relationship. The intensity of light scattering at qm was proportional to qm3.3 irrespective of the solvent-casting conditions. The development of the percolated structure was qualitatively interpreted by numerical analysis of an equation describing spinodal decomposition and an equation expressing the time dependence of the polymer concentration in the cast solution.
An improved photoelectric capillary method was used to determine the characteristics of the gas dispersion in a stirred tank by disk-turbine impellers with various numbers of blades to examine the effect of the number of blades. The results show that the bubble size distribution in the system has three different characteristics according to the patterns of liquid flow. In the impeller discharge region the sizes of bubbles are dominated by the strength of the trailing vortex and the cavity structure behind the blades. No difference is observed among impellers with various numbers of blades when the region-averaged Sauter mean diameter D32 is correlated with Pg/V and Qg. In the upper circulation region, bubble size is affected by both the cavity structure and the circulating flow. In the lower circulation region, bubble size is controlled mainly by the pumping capacity of the impeller. These transitional rotation speeds, Nc and NR, were obtained from the relationship between D32 and gas flow number Fl, which can serve not only as the turning points of the status of gas dispersion, but also can be used to explain the characteristics of the bubble size distributions for each region.
The formation of CO2 hydrates in both pure and sea waters along the three-phase coexistence of CO2, H2O, and hydrate is measured by use of a convenient temperature-cycle method proposed in the present study. Four kinds of three-phase coexisting curves are investigated in the temperature range from 270 to 283 K and pressures up to 9 MPa. By applying the Langmuir adsorption model based on statistical thermodynamics, the three-phase coexisting pressures obtained are correlated satisfactorily. The enthalpy changes of hydration in both systems are calculated from the Clapeyron equation of the three-phase coexisting curve. The apparent rate constant of hydration is estimated under the assumption of pseudo-first order reaction with respect to CO2 concentration.
The effect of dry mixed grinding of tale, kaolinite and gibbsite using a planetary ball mill on the preparation of cordierite ceramics was investigated by XRD, TG-DTA, SEM, TEM-EDX, EPMA, density and specific surface-area measurements. The structures of talc, kaolinite and gibbsite are easily transformed from crystalline state to amorphous state by grinding within 240 min. This behavior leads to homogeneity in the micro-scale composition of the mixture as well as the aggregation of obtained fine particles. The amount of α-cordierite formed in the sintered body is increased with increase in grinding time for the mixture. In addition, α-cordierite phase in the sintered body obtained from the ground mixture is crystallized at a relatively lower sintering temperature than that of the unground mixture.