Bubble columns with and without solid suspensions have been used widely as chemical reactors and bioreactors. This paper summarizes research on the design parameters of bubble columns with and without solid suspensions, and introduces new trends in research activities such as applications of computational fluid dynamics and of newly developed experimental techniques to bubble columns, and research on high pressure bubble columns.
The constrained generalized predictive control is extended for multivariable system and applied to a binary distillation column. Also, the property of tuning parameters of the control is analyzed to show tuning guideline. The performance of the generalized predictive control is examined through simulation using a rigorous process model. Set-point tracking and regulatory performances of the proposed control scheme are compared with those of the quadratic dynamic matrix control. The comparison indicates that the generalized predictive control gives improvement over the existing quadratic dynamic matrix control.
The effect of salt (NaCl, MgCl2, LiCl, NH4Cl, Na2SO4, MgSO4, (NH4)2SO4) on the adsorption properties of thermosensitive N-isopropylacrylamide hydrogel was studied using hydrophobic organic molecules as adsorbate. The effect of salt on the adsorption properties of the gel was evaluated in terms of the phase transition temperature Tp of the gel and the structure of water in the solution. The addition of salt increased the amount of adsorption of organic molecules onto the gel, while decreasing the phase transition temperature Tp of the gel. The addition of salt containing Cl– ions gave the gel larger adsorption capacity without decreasing the Tp of the gel significantly. On the contrary, the addition of salt containing SO42– ions increased the amount of adsorption, while decreasing the Tp of the gel substantially. The addition of salt affected enormously the structure of water in the salt solution. The amount of adsorption was enhanced with increasing fraction of bound water in the salt solution. The fraction of bound water in the solution containing Cl– ions was larger than that in the solution containing SO42– ions so that the amount of adsorption increased effectively in the solution containing Cl– ions. The effect of salt on the adsorption properties of thermosensitive polymer hydrogel is determined by both the Tp of the gel and the structure of water in the salt solution.
A mathematical model of iron deposition on the rotating disk electrode (RDE) in the presence of surface inhibitor is presented. The model describes the plating process by incorporating the mass transport of participating ionic species, homogeneous chemical reactions within the diffusion layer, adsorption phenomena of hydroxyl ion and surface agent, and the associated electrochemical kinetics. Iron deposition rate can be predicted as a function of disk rotation speed, solution pH, bulk concentrations of participating ionic species. It is shown that iron deposition rate is inhibited in the presence of surface additive due to the less available electroactive area. Model results indicate that higher ferrous ion concentration can be preserved at the interface in the presence of additive so that higher potential can be applied without concentration depletion within the diffusion layer.
A new thermodynamic model has been developed for solvent extraction equilibria using the K-value method. In this model, the activity coefficients of all solutes in both phases were caluculated by Edwards’ equation. The model provides a means for calculating the equilibrium constant of the extraction reaction from a few experimental measurements. Based on the calculated equilibrium constant, the model can predict the distribution coefficient at any pH, metal concentration and extractant concentration. The calculated values were insensitive to the values of the phase equilibrium constant of the extractant between the aqueous and the organic phases or the formation constant of the extracted metal species and the extractant in the aqueous phase. The calculated distribution coefficients of zinc in the ZnSO4-H2SO4-H2O-D2EHPA-kerosene system were in good agreement with those obtained experimentally. The calculated values for copper in the CuSO4-H2SO4-H2O-LIX65N-toluene system and nickel in the NiSO4-CH3COOH-NaOH-Kelex 100-xylene system were also found to be in very good agreement with those obtained from the literature. A simillar procedure is expected to be applicable for other solvent extraction systems involving alkaline solutions or anionic extractants.
The adsorption behavior of organic substances onto bubble surface in nonfoaming bubble separation was investigated. Experiments were conducted with a bubble column equipped with a droplet collector or a trap at its top. Crystal violet (CV) and humic acid (HA) were used as examples of surface-active substances. The amount adsorbed onto the bubble surface was calculated through the mass balance in the bubble column. Two adsorption parameters, equilibrium constant, K, and saturated surface density on bubble surface, γ, were determined for CV and HA, respectively, by flitting of the experimental results to a Langmuir-type isotherm. Using the value of K, γ and the intrinsic volumetric flow rate of droplets at the liquid-atmosphere interface, the variation of enriching ratio, E, with concentration of the solution was estimated and compared to the experimental results. The calculated E was in good accordance with the experimental ones for both CV and HA.
Local gas holdup was measured throughout an aerated vessel equipped with a Rushton turbine impeller by means of an electrical probe. Integration of the data of local gas holdup gave a good correlation for the overall gas holdup. The gas recirculation rate, which influences cavity formation and the related power consumption and mass transfer, was also determined by integrating the data of local gas holdup for regions lower than the height of impeller. By taking into account the gas recirculation rates, a more precise correlation for overall gas holdup could be obtained.
To overcome the limitation of linear feedfoforward controllers in nonlinear chemical processes, Lee and Park proposed the feedforward control scheme using a neural network and a dynamic matrix control (DMC). The neural feedforward controller (NFFC) using a neutral network and a general linear controller is proposed to extend Lee and Park’s control scheme. The generalized disturbance error learning method using the pseudo desired output is also proposed to train the neural network in the NFFC. Results are given for the implementation of the NFFC on a pilot-scale distillation column. The control performance of the NFFC is compared with conventional linear feedforward-feedback and feedback-only controllers such as the PI and the DMC controllers through various experiments. The trained NFFC shows excellent control performance compared with the linear controllers. The results indicate that the NFFC copes well with high nonlinearities and interactions, and may by useful in practice.
Ultrasound frequency of 1.0 MHz was applied with an ultrasound probe to a piece of excised hairless mouse skin for enhancing the rate of prednisolone (PN) transfer across the skin in vitro. The results showed that the rate of PN transfer through the intact skin was greatly enhanced according to the application time of ultrasound. Although ultrasound increases the temperature adjacent to the probe, its effect on enhancing the rate of PN transfer through the intact skin was found to be insignificant. Pretreatment experiments in which ultrasound was applied before performing normal permeation experiments were also performed. Although ultrasound was not applied in the normal permeation experiments following the pretreatment, the results showed that pretreatment also enhanced the rate of PN transfer through the intact skin in proportion to the period of pretreatment time. This implied that the ultrasound might have changed some structures of the skin. Pretreatment of 1800 s or more made the rate of PN transfer through the intact skin close to that through tape-stripped skin. This was caused either by a morphology change of the skin or by enlargement of the diameters of some follicles, or by both.