Jungho Cho

Optimization study of pressure-swing distillation for the separation process of a maximum-boiling azeotropic system of water-ethylenediamine

The separation of ethylenediamine (EDA) from aqueous solution is a challenging problem because its mixture forms an azeotrope. Pressure-swing distillation (PSD) as a method of separating azeotropic mixture were investingated. For a maximum-boiling azeotropic system, pressure change does not greatly affect the azeotropic composition of the system. However, the feasibility of using PSD was still analyzed through process simulation. Experimental vaporliquid equilibrium data of water-EDA system was studied to predict the suitability of thermodynamic model to be applied. This study performed an optimization of design parameters for each distillation column. Different combinations of operating pressures for the low- and high-pressure columns were used for each PSD simulation case. After the most efficient operating pressures were identified, two column configurations, low-high (LP+HP) and high-low (HP+ LP) pressure column configuration, were further compared. Heat integration was applied to PSD system to reduce low and high temperature utility consumption.

Optimization study on the azeotropic distillation process for isopropyl alcohol dehydration

Modeling and optimization work was performed using benzene as an entrainer to obtain a nearly pure anhydrous isopropyl alcohol product from dilute aqueous IPA mixture through an azeotropic distillation process. NRTL liquid activity coefficient model and PRO/II with PROVISION 6.01, a commercial process simulator, were used to simulate the overall azeotropic distillation process. We determined the total reboiler heat duties as an objective function and the concentration of IPA at concentrator top as a manipulated variable. As a result, 38.7 mole percent of IPA at concentrator top gave the optimum value that minimized the total reboiler heat duties of the three distillation columns.

Reactor sizing for butane steam reforming over Ni and Ru catalysts

We obtained kinetics data on steam reforming of butane and calculated the appropriate reactor size based on the kinetics data. Using commercial Ni and Ru catalysts, steam reforming reactions of butane were performed while changing the reaction temperature and partial pressure of reactants. After comparing the power law model and the Langmuir-Hinshelwood model by using the kinetics data obtained from the experiment, it is revealed that the reaction rate could be determined by both models in the reforming reaction of butane over commercial Ni and Ru catalysts. Also, calculation of the steam reforming reactor size using a PRO/II simulation with a kinetic model equation showed that the reactor size using the Ni catalyst is smaller than that with the Ru catalyst to obtain the same conversion.

First-Order Mass Transfer in a Diffusion-Dominated (Immobile) Zone of an Axisymmetric Pore: Semi-Analytic Solution and Its Limitations

Comparison of the classical mobile-immobile zone (MIM) model to the derived model led to several conclusions. If the MIM model is to be applied, the initial concentration in the immobile zone has to be down-scaled by a correction factor that is a function of pore geometry. The MIM model was valid only after sufficiently long time has passed, i.e., only after the diffusion front reaches the deepest pore wall in the immobile zone. The MIM mass-transfer coefficient , was inversely proportional to the square of the pore depth. Also it did not depend on the mobile-zone flow velocity, contrary to the number of laboratory and field observations. The classical MIM model displayed a rapid exponential decay of immobile-zone concentration. Meanwhile at large times, the newly derived model displayed similar exponential decay. This was contrary to the mounting evidence of power-law BTC tails observed in laboratory and field settings.

Separation of triethoxysilane from tetraethoxysilane by batch distillation in a packed column

A batch distillation of a crude tetraethoxysilane containing 8mol% triethoxysilane was performed in a glass packed column, 2.54 cm in diameter and 1m in height. Two distillate rates, 3.0mL/min and 6.0mL/min, were used and the reflux ratio was varied up to 3.0. Experimental data were compared with predicted values by Pro/II, a process simulator widely used in the chemical industry. The differential condensation of the vapor in the packed column due to heat losses from the vapor to the column internals and to the surroundings affected the separation efficiency seriously so that a considerable discrepancy was observed between experimental data and prediction by Pro/II in which such heat-loss effects are unaccountable. A model was developed to explain the effect of the differential condensation. For a larger distillation unit scaled up by 100 times where the heat-loss effect is regarded to be minimal, Pro/II simulations were performed to produce 99.9% TEOS with varying reflux ratio, number of stage, and feed composition.

Comparative Study on the Estimation of CO 2 absorption Equilibrium in Methanol using PC-SAFT equation of state and Two-model approach.

The thermodynamic models, PC-SAFT (Perturbed-Chain Statistical Associated Fluid Theory) state equation and the Two-model approach liquid activity coefficient model NRTL (Non Random Two Liquid) + Henry + Peng-Robinson, for modeling the Rectisol process using methanol aqueous solution as the CO2 removal solvent were compared. In addition, to determine the new binary interaction parameters of the PC-SAFT state equations and the Henrys constant of the two-model approach, absorption equilibrium experiments between carbon dioxide and methanol at 273.25K and 262.35K were carried out and regression analysis was performed. The accuracy of the newly determined parameters was verified through the regression results of the experimental data. These model equations and validated parameters were used to model the carbon dioxide removal process.In the case of using the two-model approach, the methanol solvent flow rate required to remove 99.00% of CO2 was estimated to be approximately 43.72% higher, the cooling water consumption in the distillation tower was 39.22% higher,and the steam consumption was 43.09% higher than that using PC-SAFT EOS. In conclusion, the Rectisol process operating under high pressure was designed to be larger than that using the PC-SAFT state equation when modeled using the liquid activity coefficient model equation with Henrys relation. For this reason, if the quantity of low-solubility gas components dissolved in a liquid at a constant temperature is proportional to the partial pressure of the gas phase, the carbon dioxide with high solubility in methanol does not predict the absorption characteristics between methanol and carbon dioxide.

Profit maximization of the normal hexane recovery process through a thermal integration method

We developed a separation process that can minimize utility consumption in order to obtain normal hexane from crude raffinates for electronic-grade reagents. For the separation of normal hexane from the crude raffinate mixtures, a two-column configuration was selected. The first distillation column removes lighter constituents than normal hexane as a column top product, after which heavier constituents containing normal hexane are put into the middle of the second distillation column. This allows normal hexane with a purity of 95.5 wt% to be obtained from the top of the second distillation column by removing the constituents that are heavier than normal hexane as a second column bottom product. When both distillation columns are operated at approximately atmospheric pressure, it requires about 5.2 tons of steam per hour both for the reboiling heating source. However, when the operating pressure of the second distillation column is increased, the vapor stream coming out of the top of the second distillation column can be used as a heating medium for the reboiling source of the first distillation column. In this way, steam of only 3.1 tons per hour is required, potentially reducing the amount of steam used to 59.6% of the original amount.

Simulation of the Mixed Propane Refrigeration Cycle Using a Commercial Chemical Process Simulator

Abstract In this study, a computer simulation has been performed for the refrigeration cycle using mixed refrigerants in order to decrease the process stream temperature to -20 o C. Refrigerant supply temperature was assumed to be -30 o C considering the temperature difference as 10 o C with process stream. Peng-Robinson equation of state model was selected for the computer simulation. A new alpha function proposed by Twu et al was used for an accurate prediction of pure component vapor pressure experimental data. One fluid mixing rules were used for the estimation of mixture vapor-liquid equilibria calculations. A commercial process simulator, PRO/II with PROVISION was utilized for the simulation of the overall refrigeration process. In order to minimize the compressor power consumption, we have optimized the two-stage compression system by varying the first stage compressor outlet pressure. Finally, we could obtain the minimum total power 755.7kW at the first stage compressor outlet pressure, 6 bar.Key Words : Refrigeration cycle, Simulation, Mixed refrigerants, Equation of state, Two-stage Compression