The volumetric liquid-phase mass transfer coefficients kLa were measured by an optical probe in a 0.102-m (inner diameter) bubble column operated under both ambient (0.1 MPa) and high pressures (0.2, 0.5, 1.0, 2.0 and 4.0 MPa). The measurement was performed during desorption of oxygen from gasoline and toluene by nitrogen. The superficial gas velocity was varied in the range 0.01–0.2 m·s–1. The classical penetration theory was used for the sake of prediction of the experimental data. The theory was corrected, however, due to the ellipsoidal shape of the bubbles formed in the bed. By applying the new correction factor which is a function only of bubble size, the deviation between experimental kLa coefficients and calculated ones for both liquids was 8.8%.
The flow characteristics in the bubble column, in the case of highly viscous liquid, were experimentally examined. Carboxymethyl cellulose (CMC) aqueous solution was used as the liquid phase, and the liquid height, column diameter, gas velocity and CMC concentration were changed. The flow pattern was observed, and the gas holdup and volumetric mass transfer coefficient were measured. When a large bubble, or slug, flowed out of the liquid surface, the liquid surface was violently disturbed and small bubbles were entrained into the liquid. The entrained small bubbles had a significant influence on the flow characteristics. The gas holdup and volumetric mass transfer coefficient decreased with increasing liquid height and were unchanged beyond a certain liquid height. The critical aspect ratio of the column was about 8, independently of the column diameter, gas velocity and liquid viscosity. Experimental equations on the volumetric coefficient were obtained.
A membrane reactor is a reaction system that provides higher productivity and separation cost reduction in chemical reaction processes. In this research, we developed a numerical simulator, taking into account the mass transfer and heat transfer in the axial and radial directions, and analyzed characteristics for temperature distribution and hydrogen permeation in a membrane reactor with Pd-Ag membrane for dehydrogenation of ethylbenzene, with highly endothermic reaction heat. The simulation results exhibited that the temperature distribution in the reactor has considerably changed in the axial and radial directions, and the hydrogen permeability through the membrane has varied from position to position in the reactor. In membrane reactor analysis for the reaction with highly reaction heat, consideration of the temperature gradient in the reactor is believed to lead to the precise estimation of performance characteristics of the membrane reactor. Furthermore, on the basis of the analyzed results, some knowledge for the effects of the tube radius, sweep gas rate, operating pressure of reaction and thickness of membrane on the performance of the membrane reactor, was accumulated to design a membrane reactor system.
The use of a double-spiral heat exchanger/catalytic reactor is proposed to decompose nitrous oxide (N2O) gas, which is widely used as anesthetic in the operating rooms of hospitals. Air contaminated with N2O enters one spiral passage with a rectangular cross-section at the periphery of the reactor, is heated by exchange with the outflowing stream of air, and passes through an Rh/Al2O3 or Pd/Al2O3 catalyst layer in which N2O is decomposed to N2 and O2. The purified air is then heated electrically in the central core and finally passes through the other spiral passage to the periphery where it is exhausted into the surroundings. With this device, a sufficiently high temperature is produced in the layer of catalyst to attain an essentially complete conversion of N2O with a minimal electrical input and a minimal elevation of the temperature of the exiting air. The characteristics of heat transfer and the decomposition of N2O in a double-spiral heat exchanger/catalytic reactor for this service were investigated experimentally and computationally. As an example, with an electrical heat input of 130 watts at the core and a volumetric rate of flow of 20 L/min of air plus 60 ppm of N2O, the device produced a heat refluxing rate of over 200%, a temperature of 973 K for the air in the core, a temperature of 333 K in the exiting air, and a greater than 90% decomposition of N2O.
This study is a starting point for creating a new plastic recycling process. The process consists of two spouted bed reactors. In the first reactor, plastic chips are fed and instantaneously thermally decomposed into lower hydrocarbons (gas or vapor). In the second reactor, the hydrocarbons are further decomposed into carbon and hydrogen. Carbon can be utilized as carbon black, activated carbon and so forth. Hydrogen is a useful and clean fuel (no carbon dioxide evolution) and a raw chemical material. In this study, the decomposition of hydrocarbons (methane, ethane, propane, ethene and propene) was investigated to obtain basic data for the second reactor of the process. The hydrocarbons were decomposed in a fixed bed flow reactor packed with 1-mm-diameter α-alumina balls or 1-mm-diameter nickel-plated α-alumina balls, which were used as a decomposition catalyst. Carbon and hydrogen were the main products. The nickel-plated α-alumina balls gave a higher hydrogen production rate than the unplated α-alumina balls. This is caused by the dehydrogenation activity of nickel. For alkanes, the higher the carbon number, the greater the hydrogen production rate. For alkenes, a similar tendency was observed. The hydrogen production rate showed positive temperature dependency and positive hydrocarbon partial pressure dependency. The results obtained in this study showed that production of hydrogen and carbon is possible using the second reactor of the process we proposed.
Solvent effects on the selective hydrogenation of unsaturated aldehyde were studied by using three kinds of catalysts, Pd/C, Pt/C and Co/Al2O3. Many kinds of organic solvents, whose polarities were different, were used. Non-polar solvents had high selectivity to saturated aldehyde while polar solvents had high selectivity to unsaturated alcohol. The addition of water decreased the selectivity to saturated aldehyde.
A method has been developed for preparing the gel emulsions highly concentrated by filtration-consolidation of oil-in-water emulsions. The cake is highly consolidated without the cake cracking or the coalescence of droplets by applying the pressure further after filtration of the whole emulsion was completed. The compressed cake formed by this method has a porosity that is much smaller than that of hexagonal close packing of undistorted spheres. In consideration of the compressibility of the cake, the properties of the filtration period were analyzed on the basis of the Ruth filtration rate equation. It was revealed that the highly compressible filter cake forms on the membrane surface during filtration. Also, the properties of the consolidation period were analyzed using the modified Terzaghi model. The variations over time of the average consolidation ratio and the average porosity in the compressed cake during the consolidation process were well described by the theory. In addition, the properties of the filter cake in filtration were related to those of the compressed cake in consolidation.
Partially carbonized polyimide (CPI) membranes were prepared from a solution of 30 wt% polyamic acid in N, N-dimethylacetamide. The polymer membranes formed on an alumina support were thermally treated, involving imidization in air at 180°C and carbonization in N2 at relatively low temperature (400–500°C). The cross-sectional views of the supported CPI membranes show that the membranes consist of a top layer (thickness, 10 μm) on the support and a CPI/alumina thin layer in the support. The CPI membranes carbonized at 500°C showed high permeability for O2 of 1000–30000 barrer and permselectivity for O2/N2 of 3–6. The permeability of the CPI membranes was much higher than that of the reported polymer membranes and the carbon membranes. The pores formed under carbonization at 500°C and 400°C were effective for separating O2/N2 and CO2/CH4 mixtures, respectively. TG analysis indicated that the carbonization proceeds even at a constant temperature of 500°C. The successive generation of flexible pores before the formation of graphite structure with rigid pores seems to contribute to the higher permeability of the CPI membranes.
The relationship between the pore size distribution and the separation characteristics of metallic filter media is investigated and a method for estimating the partial separation efficiency is proposed. First, the pore size distribution of metallic filter media is measured via the bubble point method. The broadness of the distribution depends on the type of filter media, but the distribution is found to be in accordance with a normal distribution. In addition, pore size obtained by the bubble point method and separation particle size in actual filtering operations are not consistent due to the variety of pore shapes. Thus, the correlation between the pore size and the separation particle size is determined for individual types of filter media by performing a filtration test. Then, a method for estimating partial separation efficiency based on the sieving theory is proposed and its validity is confirmed. This method can estimate the partial separation efficiency of metallic filter media via the non-destructive measurement of the pore size distribution, and so gives valuable information when selecting a suitable filter medium for filtering operations.
The ever increasing number of variables measured in chemical and biological plants has led to increased emphasis on monitoring performance and fault detection in process system engineering. However, conventional T2 and squared prediction error (SPE) charts based on principal component analysis (PCA) and partial least squares (PLS) are ill-suited to detecting small disturbances resulting from process faults because these monitoring techniques only use information from the most recent samples. In this paper, a new statistical process monitoring algorithm is proposed for detecting process changes resulting from small shifts in process variables. This new algorithm is based on the multivariate exponentially weighted moving average (MEWMA) monitoring concept combined with independent component analysis (ICA) and kernel density estimation. ICA is a recently developed statistical technique for revealing hidden, statistically independent factors that underlie sets of measurements. In this research, three monitoring charts (I2, Ie2 and SPE) obtained using a combination of ICA and MEWMA are developed to better monitor processes undergoing small mean shifts with autocorrelation, where the control limits for these statistics are obtained by kernel density estimation. The proposed monitoring method is applied to fault detection in both a simple multivariate process and the simulation benchmark of the biological wastewater treatment process (WWTP). For a small shift in these processes, the simulation results illustrated the monitoring power of MEWMA-ICA and ICA-MEWMA versus various existing methods (conventional PCA, ICA, MEWMA-PCA and PCA-MEWMA monitoring).
Activity of free Candida rugosa lipase (CRL) in hydrolysis reaction of tuna oil was reduced significantly under high pressure carbon dioxide (CO2). A lot of factors, such as water content, pressure, temperature, pH, phase behavior and the kind of atmospheric gas affect the activity of CRL in the hydrolysis reaction under high pressure CO2 and the effect of them was investigated. The hydrolysis activity was affected mainly by the water content, pressure and temperature. Besides, pH was not a key factor for the hydrolysis activity of CRL under high pressure CO2. The dilution effect by a great amount of CO2 dissolved in the oil phase was suggested to be the most possible cause to the reduction of hydrolysis reaction activity of CRL under high pressure CO2.
Mixotrophic culture of Euglena gracilis was carried out using a fed-batch culture system. Glucose and L-glutamic acid were added every 24 hours for 6 days to make the concentrations in the culture medium return to their initial values. We proposed a mixotrophic growth kinetics model to correlate a specific growth rate with a specific rate of energy consumption. In the model, the specific growth rate was proportional to the (1/n)th power of the specific energy consumption rate, and a corresponding yield parameter and a maintenance factor depended on light intensity. The specific growth rate in mixotrophic culture was correlated with incident light intensity by an equation that combined pseudo-photoautotrophic growth rate comparable to that of the modified Aiba model with heterotrophic growth rate. The optimum light intensity that produced the attainable maximum growth rate in mixotrophic culture could be estimated by the equation.
A multi Adsorption Heat Pump (AHP) system, which can successfully produce high level cold heat energy (253 K) by using waste heat with temperature below 373 K, was proposed in the present study. It consists of an active carbon/ammonia AHP and another AHP such as a silica gel/water AHP, which generates cold heat energy and provides heat sink energy for the active carbon/ammonia AHP, respectively. Considering the performance of ammonia AHP, the adsorption equilibria and adsorption rates of ammonia vapor on several adsorbents were experimentally investigated under 268–303 K. It is found that, (1) compared with other adsorbents, both super active carbon (SAC) and active carbon (AC) have larger reversible adsorptivity at low relative pressure of ammonia vapor; (2) the adsorption rates of ammonia vapor on SAC and AC are much higher than that of water vapor on silica gel; (3) the AHP combined by AC/ammonia as the adsorbent/adsorbate pair can be driven by low temperature heat sources (≤373 K) with high COP when the heat sink temperature TM is lower than 283 K.
In order to understand the crystallization conditions of zeolite A, induction periods for nucleation from clear aluminosilicate solutions were measured and correlated with operating variables. The induction periods were found to decrease with supersaturation of reactant solutions and were represented by two lines when they were plotted against the supersaturation on a semilog ordinate system at given temperature and given NaOH concentration. At higher supersaturations, amorphous phases precipitated, while zeolite A crystals were obtained at lower supersaturations. For precipitation of zeolite A, the induction periods decreased with the NaOH concentrations, indicating that the crystallization rate of zeolite A was accelerated by the presence of NaOH. The boundary between the precipitation of zeolite A and that of amorphous phases was found to depend on the NaOH concentration and the ratio of [Al3+] to [NaOH] as well as saturation ratios. Finally, an attempt was made to determine the activation energy for nucleation and the surface energy of zeolite A on the basis of measured induction periods.
Experiments on transformation rates of zeolite A from amorphous phases at different feed rates to alter the particle size of the amorphous phases were carried out to analyze the kinetics of the transformation, and were analyzed by performing simulation of the transformation. A clear dependence of the induction time for nucleation of zeolite A crystals on the surface area of the amorphous phase was recognized, indicating that the nucleation of zeolite A was heterogeneous and the nucleation rate was almost proportional to the size of the amorphous particles. From the simulation, the mechanism of the transformation was found to be heterogeneous nucleation of zeolite A crystals on the surface of amorphous particles followed by solution mediated phase transformation, and the transformation kinetics were well reproduced at different feed rates.