Korean Journal of Chemical Engineering (v.29, #1)

The rate at which limestone dissolves is very important in wet flue gas desulfurization process (FGD). High dissolution rates provide better alkalinity, which is important for sulfur dioxide (SO2) absorption. This study investigates the use of urea to improve the dissolution rate of limestone. The dissolution characteristics have been studied by using a pH-Stat method. The dissolution rate constant was measured according to the shrinking core model with surface control, i.e. (1−(1−X)1/3)=k r t. The effect of experimental variables such as temperature, amount of urea, solid to liquid ratio and stirring speed on the dissolution rate of limestone were investigated. Using a central composite design (CCD) of experiments variables, a mathematical model was developed to correlate the experimental variables to the dissolution rate constant. The experimental value was found to agree satisfactorily with predicted dissolution rate constant. The model shows that high temperature and low solid to liquid ratio improves the dissolution rate. The dissolution rate increased slightly with increase in the stirring speed. In the presence of urea the dissolution rate constant increased by 122%. The dissolution reaction follows a shrinking-core model with the chemical reaction control as the rate-controlling step.
Keywords: Temperature; Urea; Dissolution Rate; pH-Stat

The model-based fault diagnosis approach is characterized by a powerful process supervision capability with a priori knowledge about the system under consideration. Nevertheless, system complexity, high dimensionality, process nonlinearity and/or lack of good data often hamper its application in chemical engineering systems. A nonsteady state model based fault detection and diagnosis method for the distillation process was developed, using dynamic simulation to monitor the distillation process and identify abnormal sources when large deviations among measuring variables occur. It continuously updates the inner distillation parameters via on-line correction and predicts the trend of measuring variables and determines the existence of malfunctions simultaneously. The distillation model is dependent on transfer equilibrium, mass and heat balance, and is simulated by Euler and two-tier approach. This method was demonstrated with simulated data of a stripping tower collected from the Tennessee Eastman chemical plant simulator.
Keywords: Fault Diagnosis; Distillation; Dynamic Simulation; Parameter Estimation

Modeling of the non-catalytic semi-batch esterification of palm fatty acid distillate (PFAD) by Seok Won Hong; Hyun Jun Cho; Soo Hyun Kim; Yeong Koo Yeo (18-24).
Biodiesel fuel is one of the most attractive alternatives to the traditional diesel fuel derived from a petroleum refinery. Development of a reliable model for the biodiesel production process requires maximizing economics and enhancing safety in the commercial operation of biodiesel plants. We propose a model which represents effectively the non-catalytic biodiesel production reaction. In the modeling of the reaction, we employ a nonlinear programming scheme to estimate reaction kinetic parameters which minimize a specified objective function. The behavior of the methanol during the reaction is investigated both experimentally and numerically. Imperfect mixing in the liquid phase at the initial reaction stage causes a little discrepancy between the experimental data and results of simulations. Overall, the proposed model represents the biodiesel production reaction effectively.
Keywords: Kinetics; Non-catalyst; Free Fatty Acids; Methyl Esterification; Semi-batch System

This paper reviews a practical application of the optimization algorithm to conceptual design of a heterogeneous catalytic reactor and catalyst and its synthesis. In particular, a simulated annealing (SA) algorithm is mainly used since it provides a reliable optimization solution without being trapped at local optimum points, which arise from nonconvexities and multiplicities in a complex reaction system. Furthermore, it allows a design engineer to evaluate multiple design options of reactor and catalyst systems which satisfy both user-specified objective functions and constraints. In the final stage of optimization, these generated solutions are fine-tuned by using deterministic optimization. To enhance the efficiency of optimization further, a profile-based synthesis is adopted for the optimization algorithm. Lastly, this research takes into account a number of factors for the synthesis of heterogeneous catalytic reactors such as reactor configuration, uniform and non-uniform catalyst type, and fundamental catalyst design parameters including shape and its definite dimensions.
Keywords: Catalyst; Reactor; Optimization; Simulated Annealing; Modelling

Development of chemical accident database: Considerations, accident trend analysis and suggestions by Namjin Jang; Jamin Koo; Dongil Shin; Moon Shik Jo; Yi Yoon; En Sup Yoon (36-41).
Traditionally, regulations, standards, codes and management systems were established after major accidents such as Seveso Directive by Seveso accident, Italy, in 1976, etc. Also, several chemical material and process accident databases were developed and implicated in the world. In this paper, we introduce a set of recently developed databases, such as eMARS (EC), HSEES (USA) and PEC-SAFER (Japan), and describe current development of a chemical accident tracking system in Korea. Especially, we intensively focused on general classification codes, simplified and effective database structure, user friendly interface and intuitional searching methods. Additionally, the chemical accident trends were analyzed by using third grade of accident casualties and property’s loss. Finally, suggestions for applicability improvement of database are proposed. To improve the management and operability of hazardous materials and chemical processes, the systemic approaches are essential using accident database. The developed database and suggested issues in this study can perform an important function in the chemical industries.
Keywords: Chemical Accident; Database; Statistical Analysis; Lessons from Accidents

High-order approximations for unsteady-state diffusion, a linear adsorption and a first-order reaction in a slab, cylinder and sphere catalyst are developed. The approximations are based on a first-, a second-, a third- and a fifth-order approximation of the Laplace domain solutions of the exact model for the catalyst of three geometries. The coefficients in the approximations are functions of Thiele modulus of the respective geometry and easy to determine. The accuracy of the approximation is shown to increase markedly with the approximation order.
Keywords: Mathematical Modeling; Simulation; Approximation; LDF Formula; Transient Response

Deep removal of sulfur from real diesel by catalytic oxidation with halogen-free ionic liquid by Dan Liu; Jianzhou Gui; Yong-Ki Park; Shuang Yang; Yuhuan Gao; Xilai Peng; Zhaolin Sun (49-53).
A halogen-free task-specific ionic liquid (TSIL) of 1-(2-carboxylic acid) ethyl-3-methylimidazolium bisulfate ([(CH2)2COOHmim] [HSO4]) is applied for deep oxidative desulfurization of real diesel as a catalyst and reaction media. The sulfur level of real diesel can be reduced from 200 to 20.5 μg/g at room temperature with small amount of ionic liquid using H2O2 as an oxidant. The used ionic liquid can be easily recycled and no obvious decrease in catalytic activity can be found after recycling five times.
Keywords: Desulfurization; Real Diesel; Catalytic Oxidation; Ionic Liquid; Task-specific

Titania thin films were prepared by using aerosol flame deposition process via the pyrolysis of titanium tetra-isopropoxide (TTIP) precursor. We analyzed the specific surface area, primary and secondary particle sizes, crystal structure, thin film morphology and thickness by BET method, electrophoretic light scattering, X-ray diffraction and scanning electron microscopy, respectively. The specific surface area of TiO2 particles deposited is over three-times larger than that of commercial Degussa P25. Crystallite structure of TiO2 particles can be controlled by changing the ratio of CH4/O2 flow rates. We could prepare TiO2 thin films with single anatase phase by keeping the ratio of CH4/O2 flow rates at 200 ml/min: 1,000ml/min. As N2 carrier gas flow rate to bubbler increases, the primary and secondary particle sizes increase, but decrease with increasing total N2 gas flow rate through the central tube. The shorter the deposition height is, the smaller the deposition area is, but the thin film becomes thicker in the central region.
Keywords: TiO2 Thin Films; TiO2 Crystal Structure; Particle Deposition; Primary and Secondary Particle Sizes; AFD Process

Pd-Cu alloy membrane deposited on alumina modified porous nickel support (PNS) for hydrogen separation at high pressure by Shin-Kun Ryi; Jong-Soo Park; Kyung-Ran Hwang; Dong-Won Kim; Hyo-Sun An (59-63).
This study reports on the hydrogen permeation properties of Pd-Cu alloy membranes at high pressures. A 7 μm thick Pd-Cu alloy membrane was prepared on an alumina-modified porous nickel support (PNS) by our developed magnetron sputtering and Cu-reflow method at 700 °C for 2 hours. The membrane was mounted in a stainless steel permeation cell with a gold-plated stainless steel O-ring. Helium leak testing confirmed that the membrane and membrane module were free of defects. Permeation tests were then conducted using hydrogen at temperatures in the range from 678 to 816 K with a transmembrane pressure difference of 1–20 bars, which showed that the membrane had a hydrogen permeation flux of 1.06 mol m−2 s−1 at a temperature of 816 K and a pressure difference of 20 bars. EDX analysis was carried out after hydrogen permeation test at 816 K and showed that there was no intermetallic diffusion between the Pd-Cu layer and PNS because the alumina layer inhibited it effectively.
Keywords: Hydrogen; Separation; Pd-based; High-pressure Permeation

Biosorption of chromium onto Erythrina Variegata Orientalis leaf powder by Gannavarapu Venkata Vamsi Aditya; Bhagavatula Padma Pujitha; Nalluri Chitti Babu; Paladugu Venkateswarlu (64-71).
The biosorption of chromium from an aqueous solution onto Erythrina Variegata Orientalis leaf powder was investigated in batch operations. The equilibrium agitation time was 180 min. The extent of chromium biosorption increased from 74.2% to 86.4% with decrease in biosorbent size from 150 to 45 μm for a dosage of 30 g/L. The biosorption decreased from 99.1 (0.45 mg/g) to 45.5% (1.64 mg/g) with an increase in chromium initial concentration (C o ) from 22.5 to 180 mg/L. The extent of biosorption was maximum at pH=3. The experimental data were well explained by Langmuir and Redlich-Peterson isotherm models. The biosorption data followed second-order kinetics with a rate constant of 0.078 g/mg-min for 50 g/L of 45 μm size biosorbent. The biosorption was exothermic and feasible. The biosorption was tending towards irreversibility with increasing temperature.
Keywords: Chromium; Biosorption; Erythrina ; Thermodynamics

Chitosan microgel: Effect of cross-linking density on pH-dependent release by Mi Kyoung Kang; Sung Kyeong Hong; Yong Chang Seo; Young Ock Kim; Hyeon Yong Lee; Jin-Chul Kim (72-76).
Chitosan microgels were prepared by a spray-drying method using glutaraldehyde (GA) as a cross-linker. Two kinds of microgels, so-called soft microgel and hard microgel, were prepared using a chitosan to GA ratio of 1: 0.08, and 1: 0.67, respectively. The surfaces of hard microgels were more even that those of soft microgels. The swelling ratio, a measure of degree of swelling, of the soft microgel was pH-sensitive, and it decreased from 1,765% to 1,230%, when the pH increased from 4.0 to 9.0. The deprotonation of amino groups of chitosan could account for the decrease in swelling ratio. The swelling ratio of hard microgels was almost invariable in response to pH change (4.0 to 9.0), and it was much less than that of soft microgels, possibly due to the high cross-linking density. The degree of release from the soft microgels decreased from 65% to 12% when the pH of medium increased from 4.0 to 6.0. FITC-dextran would readily diffuse out of the microgel, possibly due to the larger meshes of the microgels in a strong acidic condition (e.g., pH 4.0). However, the degree of release increased from 12% to 82% when the pH of medium increased from 6.0 to 9.0. In this pH range, the fluorescence dye is believed to be released mainly by a squeezing-out.
Keywords: Chitosan Microgels; Spray Drying; pH-sensitive Swelling Ratio; pH-sensitive Release

Enhanced production of cellobiose dehydrogenase and β-glucosidase by Phanerochaete chrysosporium by EunJi Kim; Han Suk Choi; Seong Woo Kang; Kwang Ho Song; Sung Ok Han; Chulhwan Park; Seung Wook Kim (77-81).
The production of cellobiose dehydrogenase (CDH) and β-glucosidase by Phanerochaete chrysosporium ATCC 32629 was assessed during submerged fermentation. The maximum concentrations of CDH and β-glucosidase were obtained using rice straw as the carbon source. Organic nitrogen sources were more effective in enzyme production than inorganic nitrogen sources. Corn steep liquor (CSL) for CDH production and soy bean meal (SBM) for β-glucosidase production were the most appropriate organic nitrogen sources. Using optimum medium obtained by response surface methodology (RSM), the maximum concentrations of CDH and β-glucosidase achieved in the stirred-tank reactor (STR) were 204 U/L and 140 U/L, respectively. CDH productivity (22.7 U/L·day) was the highest at 9 days.
Keywords: Cellobiose Dehydrogenase; β-Glucosidase; Phanerochaete chrysosporium ; Rice Straw; Response Surface Method

Various isolated soluble and insoluble lignins isolated from ammonia recycle percolation (ARP), dilute sulfuric acid, and hot-water pretreatments and two commercially available lignins (alkali and organo-solv lignin) were tested to evaluate their inhibitory effects on the enzymatic hydrolysis of cellulose. The purpose of this study was to compare the effects by adding various isolated lignins in the enzyme hydrolysis. The results showed that enzyme reaction was generally inhibited by addition of lignins. The order of lignins from most to least inhibitory effects were alkali, ARP-soluble, water-soluble, acid-soluble, ARP-insoluble, and organo-solv lignins. With 0.344 g ARP-soluble or alkali lignin/g-glucan lignin loadings, 72-h digestibilities were decreased by 16% and 20%, respectively. It was also observed that the digestibilities were decreased, as the lignin loadings increased. The hindering effect by ARP-insoluble or organosolv lignin was not significant.
Keywords: Enzyme Inhibition; Pretreatment; Alkali Lignin; Water Soluble Lignin; Acid Soluble Lignin; Organo-solv Lignin

Investigation of CO2 adsorption by bagasse-based activated carbon by Anusorn Boonpoke; Siriluk Chiarakorn; Navadol Laosiripojana; Sirintornthep Towprayoon; Amnat Chidthaisong (89-94).
Bagasse-based activated carbon (BAC) and amine-modified BAC were prepared and investigated for CO2 adsorption capacity. Modifying BAC with amines resulted in a decrease of surface area, but the decreasing magnitude varied depending on type and loading rate of amines. At room temperature, the unmodified BAC was able to adsorb more CO2 than the amine-modified BAC. This ability was related to the higher surface area of unmodified than that of the modified BAC. When temperature increased, CO2 adsorption capacity of all absorbents was decreased. However, above 323 K and a concentration of CO2 lower than 30% v/v, the BAC modified with PEI at 5 and 25 wt% showed higher adsorption capacity. Among all adsorbents under 15% CO2 and 348 K, BAC-PEI25 showed the highest adsorption capacity (0.20 mmol/g).
Keywords: Activated Carbon; Carbon Dioxide Adsorption; Amines; Bagasse

Arsenic adsorption on goethite nanoparticles produced through hydrazine sulfate assisted synthesis method by Malay Kumar Ghosh; Gérrard Eddy Jai Poinern; Touma B. Issa; Pritam Singh (95-102).
Goethite nanoparticles synthesized using hydrazine sulfate as a modifying agent were evaluated for As(V) adsorption capacity. The nanoparticles were characterized for their morphological and structural features. The precipitated goethite particles were spherical with particle size of less than 10 nm. Batch adsorption study was carried out systematically varying parameters such as pH, contact time, initial As(V) concentration and adsorbent doses. The Langmuir isotherm represented the equilibrium data well and the estimated monolayer adsorption capacity at ambient temperature was 76 mg/g, which is significantly higher than most of the adsorbents reported in the literature. Adsorption kinetic data were better represented by the pseudo-second order kinetic model. Intra-particle diffusion played a significant role in the rate controlling process in the initial hour. Desorption study showed that the loaded adsorbent could be regenerated when treated with dilute sodium hydroxide solution of pH 13.
Keywords: Arsenic; Goethite; Adsorption; Isotherms; Nanoparticles

Vapor-liquid equilibrium (VLE) for binary mixtures composed of ethanol+methyl isobutyl ketone, 1-butanol+ methyl ethyl ketone, and 1-butanol+methyl propyl ketone systems was measured using a circulation type equilibrium apparatus at atmospheric pressure. The measured data and literature data for alcohol and ketone systems have been correlated by the UNIversal Quasi-Chemical (UNIQUAC) model with two binary interaction parameters and the non-random lattice fluid equation of state with hydrogen bonding equation of state (NLF-HB EoS) using a single binary interaction parameter. For the NLF-HB EoS calculations, the numbers of proton acceptor for ketones were adjusted between 0 and 1. The calculation results with the NLF-HB EoS are better than those with the UNIQUAC model.
Keywords: Alcohol; Ketone; Vapor-liquid Equilibrium; Hydrogen Bonding

Conductive chitosan/multi walled carbon nanotubes electrospun nanofiber feasibility by Zahra Moridi Mahdieh; Vahid Mottaghitalab; Negin Piri; Akbar Khodaparast Haghi (111-119).
The current study focuses on the electrospinning of chitosan (CHT)/multi walled carbon nanotubes (MWNTs) composite nanofiber using a highly stable dispersion. The acetic acid (1–100%) and trifluoroacetic acid/dichloromethane (TFA/DCM 70: 30) was tested as solvent, and the TFA/DCM (70 : 30) is most preferred for fiber formation process with acceptable electrospinnability. Moreover, a new protocol was used to establish proper technique for preparation of electrospinning solution. FT-IR spectroscopy utilized to infer the extent of interaction between CHT polymer chain and MWNT filaments. A quite simple technique was employed to show the stability of electrospinning solution before nanofiber formation process. Scanning electronic microscope (SEM) was employed to show the influence of spinning parameters on surface morphology of electrospun fiber. Under optimized condition, homogeneous and beadfree CHT/MWNTs nanofibers and known physical characteristics were prepared. The formation of conducting nanofibers based on CHT nanocomposites can be considered as a significant improvement in electrospinning of CHT/CNT dispersion. The direct outcome of the current study includes the homogeneous CHT/MWNTs nanofibers with an average diameter of 275 nm and a conductivity of 9×10−5 S/cm. These results are extremely important for further investigation regarding biomedical applications.
Keywords: Biotechnology; MWNTs; Chitosan; Electrospinning; Biocomposite; Nanocomposite

Optical properties of TiO2 nanorods modified by electron-donating stabilizers by Duc Quy Vo; Eun Woo Shin; Jae-Seong Kim; Sunwook Kim (120-124).
A significant change in the UV-vis absorption of TiO2 nanorods (NRs) was induced by changing electrondonating stabilizer from oleic acid (OA) to acrylic acid (AcA). When TiO2 NRs with an average size of 2.5 nm in diameter and 30 nm in length were dispersed in an aqueous AcA solution, a red shift in the optical absorption (0.73 eV at the band edge and 0.55 eV at the onset) was observed. The red shift was attributed to an increase in the electron density inside the TiO2 NRs. The applicability of the AcA-exchanged TiO2 NRs for the photocatalyst as well as a UV sensor was evaluated. The AcA-exchanged TiO2 NRs showed significant photocatalytic activity on the degradation of toluene in the visible light region. Moreover, thin film of the AcA-exchanged TiO2 NRs on a quartz plate was tested as a UV sensor and it exhibited a good response to a wide range of the UV light.
Keywords: Red Shift; Optical Absorption; TiO2 Nanorod; Photocatalyst; UV Sensor

A highly conductive polypyrrole (PPy)-reduced graphene oxide (RGO) composite with an electrical conductivity of 610 S m−1 was successfully synthesized by the in-situ photopolymerization of pyrrole in a graphene oxide suspension. Graphene oxide (GO) played the role of an electron acceptor and was reduced as it accepted electrons. The reduction of GO was confirmed by the increase in the C/O ratio of RGO with the UV irradiation time as well as the high electrical conductivity of PPy-RGO composite. Through the thermogravimetric analysis, it has been found that the PPy-RGO composite exhibited high thermal stability compared to the GO and PPy. This material was used as an electrode in a supercapacitor cell and showed excellent performance for electrical energy storage. The composite exhibited a specific capacitance of 376 F g−1 at a scan rate of 25 mV s−1.
Keywords: Polypyrrole; Graphene Oxide; Photopolymerization; Supercapacitor; Electrode

Gallium nitride (GaN) epitaxial thin films were deposited on Si substrates by a modified hydride vapor phase epitaxy (MHVPE) technique utilizing the GaN seed-layer formed from liquid source precursor. Tris N,N-dimethyldithiocarbamato gallium(III) (Ga(mDTC)3) powder was dissolved in chloroform (CHCl3) to prepare the liquid source precursor for seed-layer formation. The developed method was found to be suitable for the epitaxial growth of GaN on Si in spite of the large mismatch in lattice constants and thermal expansion coefficients, resulting in device-quality epitaxial films with fairly smooth surface morphology. The epitaxial GaN films obtained in this study had a hexagonal structure with (0002) preferred orientation with the FWHM value of 428.6 arcsec of the (0002) GaN XRD peak. Photoluminescence spectra of GaN films exhibited a strong and sharp peak at 3.41 eV with the FWHM value of 107meV.
Keywords: Gallium Nitride; Hydride Vapor Phase Epitaxy; Seed-layer; Ga(mDTC)3 ; Chemical Vapor Deposition