Dae-Ki Choi

Adsorption and reaction behavior for the simultaneous adsorption of NO–NO2 and SO2 on activated carbon impregnated with KOH

Abstract This study examined the individual and simultaneous adsorption of NOx (NO–NO2) and SO2 on activated carbon impregnated with KOH (KOH-IAC). For individual component adsorption, KOH-IAC showed a higher adsorption capacity in NO–NO2 rich air than in SO2–air. In the simultaneous adsorption of NO–NO2–SO2, SO2 showed a greater adsorption affinity than NO–NO2. The smaller the amount of NO–NO2 adsorbed, the more SO2 was adsorbed. XPS analysis of the adsorption of NO–NO2 rich SO2–air on KOH-IAC revealed that the adsorbed SO2 was predominantly found on the external surface, producing mainly K2SO4 and, additionally, H2SO4 and K2SO3. Depth profile analysis showed that the amount of SO2 adsorbed decreased regularly away from the surface, while the amount of adsorbed NO–NO2 increased irregularly. We confirmed that the presence of the impregnant in KOH-IAC is a determining factor in the adsorption of NO–NO2 and SO2 by chemical reaction, clarifying the surface chemical behavior.

Benzene adsorption and hot purge regeneration in activated carbon beds

Experimental and theoretical studies were performed on adsorption of benzene from nitrogen gas stream and thermal regeneration by hot nitrogen purge, in fixed beds charged with activated carbon. System temperature and effluent concentration data were collected during adsorption-regeneration runs. A mathematical model was developed to simulate temperature and concentration data of adsorption and regeneration. The model developed was based on non-equilibrium, non-isothermal and non-adiabatic conditions. Three heat transfer resistances were considered in interfaces of gas–solid, gas–wall, and wall–atmosphere. A linear driving force mass transfer model with a variable lumped-resistances coefficient was found to provide an acceptable fit to the experimental data. Experimental and modelling results were used to study the effects of adiabatic and non-adiabatic operations, contact time, gas velocity, regeneration temperature and initial bed loading on the regeneration efficiency. Besides, the specific energy requirement and purge gas consumption were evaluated to discuss the process efficiency.

Performance of fixed-bed KOH impregnated activated carbon adsorber for NO and NO2 removal in the presence of oxygen

Abstract KOH-impregnated activated carbon (K–IAC) was used in this study. This paper contains observation the adsorption behavior of NO and NO2 with/without oxygen and with different bed depths of adsorbent. The paper also defines surface chemical changes due to NOx adsorption. By using a simple design of adsorber, the packed amount of adsorbent for NOx abatement for 6 months on a pilot scale was calculated. When oxygen was present, NO and NO2 had a great improvement in adsorptivity. Adsorption of NO2 forms a oxide crystal on the surface of the K–IAC and at the same time produces NO, which acts to bring about increased adsorptivity. The higher the bed of adsorbent was, the more NO was produced and the longer the breakthrough time took. The adsorber was designed in a scale-up condition where NO, NO2 and O2 were applied to K–IAC. The adsorbate that consumed the least packed amount was NO2–air followed by NO2–N2, NO–air and NO–N2. The results of the experiment demonstrated that with regard to adsorption of NO and NO2 on K–IAC, the presence of oxygen and the bed depth of adsorbent were the biggest variables to adsorptivity.

Analysis of purge gas temperature in cyclic TSA process

This study analyzes the effect of an operating parameter on the dynamic behavior by performing dynamic simulations of cyclic thermal swing adsorption (TSA) system, in fixed beds packed with activated carbon as an adsorbent. This TSA process purifies and regenerates the ternary mixtures consisted of benzene, toluene and p-xylene. A mathematical model, considering the dynamic variation and spatial distribution of properties within the bed, has been formulated and described by a set of partial differential algebraic equations. The models are based on non-equilibrium, non-isothermal and non-adiabatic conditions. The breakthrough curves of our simulation model are compared with those of Yuns experiments (1999). The cyclic steady-state (CSS) cycles are obtained for the various cases by cyclic simulation. The influences of the purge gas temperature on breakthrough curves, CSS convergence time, cyclic operating step time, purge gas consumed, regeneration energy requirement and adsorption ability at CSS are also discussed.

Effect of mobile phase additives on resolution of some nucleic compounds in high performance liquid chromatography

Here we investigate the chromatographic behavior, with reversed-phase high performance liquid chromatography (RP-HPLC) of nucleic compounds (nucleobases, nucleosides, and nucleotides) on a C18 column in several different mobile phase additives, including1-butyl-3-methylimidazolium tetrafuloroborate ([BMIm][BF4]), 1-ethyl-3-methylimidazolium methylsulfate ([EMIm][MS]) ionic liquids, ammonium formate, and potassium phosphate. The effect of the alkyl group length, the imidazolium ring, and the ionic liquids counterions on retention and resolution of the samples were tested. The results show the potential application of a used buffer system, ion pairing system, and ionic liquid as mobile phase additives in liquid chromatography resolution of nucleic compounds.

Fast determination of Langmuir isotherm parameters in large concentration of one solute

A simple method is presented to obtain the Langmuir isotherm parameters. Although this method is limited to the case of large concentration, a few injections enable the determination of the parameters. For a sample of thymine, with the injection volumes of 1.0 and 1.5 ml, the parameters of a and b are determined as 15.83 ml/ml and 0.12 ml/mg, respectively.

PREDICTION OF THE ASYMMETRIC PEAK PROFILE USING A MATHEMATICAL METHOD WITH A COMPETITIVE LANGMUIR ISOTHERM

The adsorption characteristics of a single component and a binary component in the stationary phase using preparative chromatography were investigated with a six-adsorption isotherm model. These analyses were based on the Langmuir model. Each parameter of the adsorption isotherm was obtained with the adsorption raw data that was calculated by frontal analysis (FA). The experimental data and the values calculated using the adsorption isotherm model were compared. The bi-Langmuir model showed good agreement for phenol while the tri-Langmuir model showed good agreement for caffeine. Each characteristic of adsorption was obtained from these results. The effect of competitive adsorption was investigated using the parameters of the adsorption isotherm model with a single component. There was good agreement between the experimental data and the calculated values.

Simulation of the combined continuous and preparative separation of three close-boiling components in a gas-liquid chromatography

The combined continuous and preparative gas-liquid Chromatographic system was considered for separating continuously three close-boiling components, diethylether, dimethoxymethane, and dichloromethane. Their concentration profiles were simulated by the methematical model, which assumed the uniform distribution of stationary liquid phase and the linearity of the equilibrium isotherm.The operational principles of the system are that the least-absorbed component of the three components can be obtained purely before the elution of the most-absorbed components if the mixture is continuously injected into the one of the two sections (partition section) and at the same time, in the other section (desorption section), the three components remained in the column can be separated by the adjusting the experimental conditions and the column configuration. If the operations in the two sections are simultaneously finished within a time (switching time), continuous separations of the three components are feasible. The effect of the various operating conditions on the resolution is investigated. From the results of the simulations, the resolution is greatly affected by the additional column length in the desorption section and the switching lime can be determined by the desorbenl velocity.

Hydrodesulfurization of Diesel for Molten Carbonate Fuel Cell Applications

Hydrogen production from commercial diesel fuels is an attactive option for energy generation purpose due to the low cost and good availability of diesel fuels. However, in order to utilize commercial diesel fuels, the sulfur contents must be removed down to approximately 0.1 ppm level to protect the fuel cell catalysts from poisoning. Commercial catalysts CoMo/Al2O3 and NiMo/Al2O3 were tested for HDS (Hydrodesulfurization) of model diesel and commercial diesel. The experimental conditions were 250 - 400 °C and LHSV (Liquid Hourly Space Velocity) 0.27 - 2.12 hr -1 . NiMo/Al2O3 was found to be more effective than CoMo/Al2O3 in removing sulfur from model diesel. Based on the experimental results of model diesel, commercial diesel fuel purchased from a local petrol station was tested for HDS using NiMo/Al2O3. The GC-SCD (Gas Chromatography Sulfur Chemiluminescence Detector) results showed that the DMDBT (Dimethyldibenzothiophene) derivatives were fully removed from the commercial diesel fuel proving that HDS with NiMo/Al2O3 is technically feasible for industrial applications.

Analysis of thermal regeneration of cyclic TSA process

Abstract This study analyzes the effects of the purge gas temperature on the dynamic behaviors of a cyclic thermal swing adsorption (TSA) process by dynamic simulations. This TSA process adsorbs and regenerates the ternary mixtures consisted of benzene, toluene and p-xylene (BTX). The models are based on nonequilibrium, nonisothermal and nonadiabatic conditions. The breakthrough curves of our simulation model are compared with those of Yuns experiments (1999). The cyclic steady state (CSS) cycles are calculated for the various cases. The influences of purge gas temperature on breakthrough curves, purge gas consumed, regeneration energy requirement at CSS are also discussed for optimal operation.