The rate of absorption of carbon dioxide from a bubble to a liquid were investigated using a shallow bubble column with a single nozzle. The overall mass transfer rate was classified into three categories depending on the bubble behavior: bubble formation at the nozzle, bubble rising in the bulk liquid and a bubble bursting (often followed by drifting) on the surface of water in the column. Flow properties including bubble diameter, the frequency of bubble formation and the velocity of bubble when rising were measured to determine the interfacial surface area of the bubbles for each region. As a result, it was possible to accurately measure the respective mass transfer coefficients. The contributions of bubble formation and bubble burst were found to be significant for the mass transfer rate in a shallow bubble column. The mass transfer coefficient of bubble formation was much higher than those for bubble burst and bubble rising.
A parallel-competing chemical test reaction was performed in a Higee liquid/liquid system to evaluate the micromixing efficiency. According to the experimental results, it indicated that increasing rotational speed and liquid flow rate could intensify micromixing effectively. The micromixing efficiency in a Higee system was shown to be higher than other reported types of mixing devices, and the centrifugal force was also effective in enhancing micromixing when the liquid viscosity increased. An empirical correlation was then obtained, implying that the characteristic mixing time was proportional to the rotational speed to the power of –0.64. To investigate the relation between micromixing and mass transfer, an experiment of deoxygenation was performed. It is found that mass transfer resistance decreased as the micromixing efficiency increased.
In previous work, we have attempted to apply the singular finite element method (SFEM) developed for Newtonian flow problems to the die-swell simulation of viscoelastic (Giesekus) fluids, and reported that SFEM, with less memory size, gave more accurate results than those obtained by the ordinary decoupled FEM. In this paper, a revised version of above SFEM, i.e. SFEM vpE12, has been presented, where the velocity (v) and stress (E) nodes, as well as the pressure (p) node, are removed from a position of singularity; it implies that asymptotic behaviors of field variables near the singular point (i.e., die-lip) are assumed to be such that v ~ r0.5, E ~ r–0.5 and p ~ r–0.5, where r denotes a radial distance from the singular point. Furthermore, as for the stress substitution for momentum equation, we attempted two methods, i.e., the rearranged substitution (RS) method and the direct substitution (DS) method. It is found that SFEM vpE12 with RS (i.e., SFEM vpE12-RS) extends the upper limit of the Weissenberg number (We) of the die-swell flow simulation up to 150, whereas SFEM vpE12 with DS (i.e., SFEM vpE12-DS) fails to converge beyond 1.8 of We; however, starting from converged results obtained by SFEM vpE12-RS at 130 of We, SFEM vpE12-DS simulation is able to converge at the same We of 130, and gives more smoothed and accurate results than the original SFEM especially in the very vicinity of singularity.
Leaching of nickel from a hydrodesulphurization spent catalyst generated from the sulfur removal process of petroleum refineries was investigated using ammonium sulfate ((NH4)2SO4) solution. The spent catalyst used in the study was composed of vanadium and nickel as sulfides, supported in an alumina matrix. Experiments were carried out in a stirred batch reactor under the temperature range of 298–368 K and the (NH4)2SO4 solution of 1.3–3.3 mol/dm3. As a result, about 94.0% of nickel was leached from the 2.6 mol/dm3 (NH4)2SO4 solution in 90 min at the temperature of 368 K. A shrinking core model was found to be useful in describing the rate of nickel leaching. The rate of nickel leaching is limited by ash layer diffusion. The nickel leaching is of the first order with respect to the (NH4)2SO4 concentration and has an activation energy of 16.2 kJ/mol.
A family of chemical reaction networks, involving heterogeneous catalysis of wet oxidation of acetic acid in an isothermal continuous flow stirred tank reactor (CFSTR), is determined to have the capacity to exhibit steady state multiplicity by implementation of the Deficiency One Algorithm and the Subnetwork Analysis. A set of rate constants and two corresponding steady states are constructed for each case. The phenomena of bistability, hysteresis and bifurcation are discussed. Two sets of signatures of multiple steady states are provided, which can be used to identify the reaction mechanisms as steady states of some species are measured.
Partially carbonized polyimide (CPI) membranes were prepared on a porous alumina support from carbonization of polyimide membranes at 460–500°C. The permeance of O2 through the CPI membrane increased with the increasing carbonization temperature, although the separation factors (O2/N2) reduced from 11 to 4. The highly permeable CPI membranes carbonized at 500°C were silylated with 1,1,1,3,3,3-hexamethyl disilazane (HMDS) at 90°C, 150°C and 180°C before or after carbonization to solve an adverse humidity effect on gas permeation. The molar ratios of C/Si in the cross section of the silylated CPI membranes were analyzed by SEM-EDX measurements. The separation of dry air through the nonsilylated and silylated CPI membranes was performed before and after a steam treatment. Continuous air permeation tests under saturated steam were also performed with prolonged time. The CPI membranes silylated at 180°C had deposition of organosilicate on the outer surface of polyamide layer, resulting in the reduction of the O2 flux. On the other hand, the flux of O2 and the separation factor for the CPI membrane silylated at 150°C before carbonization did not reduce drastically under saturated steam. The results of chemical composition analysis for polyimide and carbonized polyimide suggests that water-resistant CPI membranes with high O2 permeation flux were synthesized by taking advantage of reactive carboxyl groups in the membrane before carbonization.
The equilibria of organic acids (acetic, glycolic, propionic, lactic, butyric, pyruvic, tartaric, succinic, fumaric, L-malic, itaconic and citric, HA) extracted with tri-n-octylamine (TOA) and di-2-ethylhexylphosphoric acid (D2EHPA, HR) were measured. Synergism was observed in the extraction of all acids investigated when a mixed extractant of TOA and D2EHPA was used, while the extraction ability of TOA or D2EHPA alone was negligible under the experimental conditions. In the synergistic system, the distribution ratio of the acids plotted against the D2EHPA concentration showed a bell shape. FT-IR spectrum of the mixed extractant suggested that TOA and D2EHPA interacted. From these results, we estimated that TOA·HR and TOA·(HR)2 were the active and inactive species for the acid extraction, respectively, and that the extracted species was HA·TOA·HR. The calculated distribution ratios of organic acids showed good agreement with the experimental results. The obtained synergistic extraction equilibrium constants roughly correlated with the hydrophobicity of each acid.
In a spouted bed, the gas flow rates cannot be changed independently in either the spout or the annulus. In this study, an experimental spouted bed equipped with a draft-tube was made in such a way that each of the gas flow rates can be changed independently. The effect of the gas flow rate in the spout or in the annulus on the circulation rate of solids was examined for the three types of spouted bed. The relation between the solids circulation rate and the average gas velocity in the annulus differs among these three types of spouted beds. In the spouted bed with a gas inlet nozzle, the solids circulation rate initially sharply decreased with the average gas velocity in the annulus. It was found that an eddy motion of solid particles caused this sharp decrease in the solids circulation rate. The fluid flow that caused this eddy motion in the solids was confirmed by using a two-dimensional water flow model.
It is commonly accepted that one hollow particle is formed from one droplet in conventional spray pyrolysis or drying. Therefore, the particles size distribution is closely related to the droplet size distribution. In this report, however, a new aerosol process was proposed, in which multiple hollow particles were produced from one liquid droplet with the aid of salt and polystyrene (PS) bead. In this process, the particles size and size distribution were determined by the PS beads, not by the droplets. Silica hollow particles of 160 nm in diameter and 10 nm in shell thickness were prepared after washing off the salt with water. Geometric mean dispersion of hollow particles were 1.02, whereas the geometric mean deviation of droplets was 1.3. The role of salt was to keep nano-size hollow particles desegregated while the PS template beads were burnt off at 500°C.
For uniform drying of large particles, a modified fluidized bed with a continuous fluidizing air flow plus one stream of pulsing air, which is termed as a pulsed fluidized bed (PFB), was developed to eliminate some limitations of conventional fluidized beds (FB). The drying kinetics of activated alumina was investigated to assess the advantages of PFB, in comparison with the results obtained in the FB. At the same average air flow rate, the bed is easy to fluidize in the PFB operation and there is little temperature difference along the bed height. Due to the dispersion of particles by pulsing flow, the drying rate for activated alumina is higher to some extent in PFB than that in FB during the constant drying period even at low average superficial air velocity.
The fieldbus control system (FCS) has been increasingly used in the process control area. This paper first shows the timing analysis of the fieldbus control loop by considering both communication and control tasks at the same time. As a result, the fieldbus control loop time was formulated, and the stability condition of the loop operation was represented with the loop time in the FCS. Then a modified PID control algorithm that is suitable for fieldbus devices was proposed to overcome varying communication delays. Finally, a fieldbus control loop was modeled and simulated to validate the timing analysis and the control algorithm. The simulation results showed that the control algorithm works well for the common processes having a first-order model with dead time and the stability of the fieldbus control loop can be assured under the unpredictable and varying time delays caused by the fieldbus.
The operation of a polymerization plant is usually scheduled by being divided into blocks: a production block, a store block, and so on, with the operations of each block usually scheduled by experts. The production block is scheduled to minimize production costs. However, it is difficult to manually schedule the store block, because of the following features. (1) The products must be treated as continuums. (2) The products are concurrently handled by two or more machines for long periods. (3) The capacities of product queues have an upper bound. (4) Operations are not necessarily started when they can be. (5) The store block constitutes a very large system. This paper proposes a scheduling system to concurrently achieve “Just-In-Time” (JIT) production in the store block and to minimize changeover counts in the production block. The proposed system calculates the latest finish times for receiving using a pull type algorithm to achieve JIT production. The latest finish times and all combinations of sequences of orders in the production block are examined by a push type scheduling algorithm under restriction conditions of features (2) and (3). To schedule a very large system, an algorithm based on the branch and bound technique is employed. The effectiveness of the proposed system is assessed via numerical studies.
The present study is concerned with preparation of erythritol–polyalcohols mixtures as PCMs, which may be applicable for heat storage in the temperature range between 80 and 100°C for a hot water supply system. The melting/solidification temperature was adjusted by adding polyalcohols such as trimethylolethane (TME), 2-ethyl-2-methyl-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 1,4-butanediol, 2-amino-1,3-propanediol and trimethylolpropane (TMP), to erythritol. It was found that a new PCM(86) composed of 40% erythritol and 60% TME melted at 86.1 and 97.8°C with a latent heat of 246 kJ/kg. Another PCM(80) composed of 90% PCM(86) and 10% TMP melted at 80.0 and 95.0°C with a latent heat of 231 kJ/kg. These new PCM(86) and PCM(80) derived from erythritol were considered potentially applicable for a hot water supply system, in terms of their relatively large heat storing capacities and specific heats, as well as high thermal conductivities.
This paper has presented some popular methods used to determine the kinetic parameters from nonisothermal thermogravimetric analysis (TGA) data. These methods include the improved Doyle–Ozawa method, and the nonlinear regression method. The above-mentioned methods along with a new method proposed by the present authors are compared with the true thermogravimetric data generated by the synthetic TG/DTG curves. This paper has shown that the proposed E2-function method has the advantages of both reliability in calculation and straightforwardness in formulation.