Hankwon Lim

Parametric studies for CO2 reforming of methane in a membrane reactor as a new CO2 utilization process

A one-dimensional reactor model was employed to perform parametric studies for CO2 reforming of methane in a membrane reactor to investigate its feasibility as a new CO2 utilization process. The effect of key variables such as hydrogen permeance and Ar sweep gas flow rate to facilitate H2 transport from a shell side (retentate) to a tube side (permeate) on the performance in a membrane reactor was studied at various temperatures with numerical simulation validated by experimental results. In addition, increase in CH4 conversion and H2 yield enhancement observed in membrane reactor was successfully confirmed by profiles of H2 partial pressure difference between shell and tube sides. From the numerical simulation studies, the feasibility of using a membrane reactor for CO2 reforming of methane was confirmed by increased CH4 conversion and H2 yield enhancement compared to a packed-bed reactor at the same condition, which in turn leads to significant cost reductions due to a reduced operating temperature. Moreover, a window of H2 permeance and a guideline for Ar sweep gas flow rate for the efficient membrane reactor design was obtained from this study.

Hydrogen selectivity and permeance effect on the water gas shift reaction (WGSR) in a membrane reactor

Simulated results are presented using a reaction rate equation and a one-dimensional reactor model for a water gas shift reaction (WGSR) in a membrane reactor (MR) with a feed stream obtained from coal gasifiers. CO conversion in a MR at 423–573 K was higher than equilibrium conversion at the same temperature. The effect of two important parameters of a membrane, hydrogen selectivity and hydrogen permeance, on MR performance was studied and hydrogen selectivity was favorable for enhanced CO conversion, reduced CO concentration, and enhanced fuel-cell grade hydrogen. Hydrogen permeance was also favorable for CO conversion enhancement in a MR due to an increased driving force between the shell side (retentate) and the tube side (permeate) of a membrane. The criteria of a hydrogen permeance of higher than 8×10−8 mol m−2s−1Pa−1 and a hydrogen selectivity of 100 were suggested to produce a fuel-cell grade hydrogen (CO concentration less than 50 ppm) in the permeate and a concentrated CO2 (more than 90%) in the retentate simultaneously in a MR.

Methane steam reforming in a membrane reactor using high-permeable and low-selective Pd-Ru membrane

We performed a methane steam reforming (MSR) reaction through a membrane reactor packed with commercial Ni/Al2O3 catalyst and a tubular Pd-Ru membrane deposited on a YSZ modified porous stainless steel support under mild operating conditions: 773 K and a pressure difference range of 100-250 kPa. We prepared the Pd-Ru membrane with thickness of ~6 μm on a tubular stainless steel support (diameter 12.7mm, length 25 cm) using electroless plating, which was observed for the membrane performance using hydrogen and nitrogen. Gas permeation test carried out at 773 K and 31.4 kPa of pressure difference between retentate and permeate sides showed that the hydrogen permeation rate and nitrogen leakage were ~0.1050mol s−1 m−2 and ~0.0018 mol s−1 m−2, respectively. The MSR reaction was under the following conditions: temperature 773 K, pressure 100-250 kPa, gas hourly space velocity (GHSV) 837 h−1, and steam-to-carbon feed ratio (S/C) 3. The MSR reaction result showed that methane conversion was increased with increasing pressure difference and reached ~77.5% at 250 kPa. In this condition, the composition of carbon monoxide was ~2%, meaning that no two series of water gas shift reactors were needed in our membrane reactor system. Longterm stability test carried out for ~100 h showed that methane conversion and the hydrogen yield remained constant.

Process simulation and economic analysis of reactor systems for perfluorinated compounds abatement without HF effluent

AbstractNew and efficient reactor systems were proposed to treat perfluorinated compounds via catalytic decomposition. One system has a single reactor (S-1), and another has a series of reactors (S-2). Both systems are capable of producing a valuable CaF2 and eliminating toxic HF effluent and their feasibility was studied at various temperatures with a commercial process simulator, Aspen HYSYS®. They are better than the conventional system, and S-2 is better than S-1 in terms of CaF2 production, a required heat for the system, natural gas usage and CO2 emissions in a boiler, and energy consumption. Based on process simulation results, preliminary economic analysis shows that cost savings of 12.37% and 13.55% were obtained in S-2 at 589.6 and 621.4 °C compared to S-1 at 700 and 750 °C, respectively, for the same amount of CaF2 production.

Sorption enhanced catalytic CF4 hydrolysis with a three-stage catalyst-adsorbent reactor

In this study, we developed a three-stage catalyst-adsorbent reactor for the catalytic hydrolysis of CF4. Each stage is composed of a catalyst bed followed by an adsorbent bed using Ca(OH)2 to remove HF. The three stages are connected in series to enhance the hydrolysis of CF4 and eliminate a scrubber to dissolve HF in water at the same time. With a 10 wt-% Ce/Al2O3 catalyst prepared by the incipient wetness method using boehmite and a granular calcium hydroxide as an adsorbent, the CF4 conversion in our proposed reactor was 7%–23% higher than that in a conventional single-bed catalytic reactor in the temperature range of 923–1023 K. In addition, experimental and numerical simulation (Aspen HYSYS®) results showed a reasonable trend of increased CF4 conversion with the adsorbent added and these results can be used as a useful design guideline for our newly proposed multistage reactor system.

Conceptual feasibility studies of a CO X -free hydrogen production from ammonia decomposition in a membrane reactor for PEM fuel cells

COX-free hydrogen production from ammonia decomposition in a membrane reactor (MR) for PEM fuel cells was studied using a commercial chemical process simulator, Aspen HYSYS®. With process simulation models validated by previously reported kinetics and experimental data, the effect of key operating parameters such as H2 permeance, He sweep gas flow, and operating temperature was investigated to compare the performance of an MR and a conventional packed-bed reactor (PBR). Higher ammonia conversions and H2 yields were obtained in an MR than ones in a PBR. It was also found that He sweep gas flow was favorable for XNH3 enhancement in an MR with a critical value (5 kmol h-1), above which no further effect was observed. A higher H2 permeance led to an increased H2 yield and H2 yield enhancement in an MR with the reverse effect of operating temperature on the enhancement. In addition, lower operating temperature resulted in higher XNH3 enhancement and H2 yield enhancement as well as NG cost savings in a MR compared to a conventional PBR.

Techno-economic analysis of a biological desulfurization process for a landfill gas in Korea

ABSTRACT We report techno-economic analysis of a biological desulfurization process to remove H2S and to produce sulfur from a landfill gas (2000 m3 h−1) produced in Korea. With a process simulation model developed using Aspen Plus®, parametric assessment to determine the effect of various operating parameters such as a NaOH flow rate, a NaOH concentration, and a recycle ratio has been carried out. Based on results from process simulation, economic analysis was conducted to evaluate feasibility of this technology in Korea through a cash flow diagram, net present value (NPV), and discounted payback period (DPBP). It was demonstrated that DPBP of 6.9 years and NPV of 0.39 MM

Efficient solid reducing agent CaO/SiO2 hybrid composite for hydrogen fluoride elimination

were obtained with a 10% discount rate.

Solutions of Navier-Stokes Equation with Coriolis Force

An advanced solid reducing agent, i.e., a CaO/SiO2 composite has been optimized to improve the hydrogen fluoride (HF; a green house gas) elimination in semiconductor-based industrial applications. To avoid the Ca(OH)2 formation and enhance the HF removal efficiency of CaO, the hydrophobic properties of silica (SiO2) have used as a catalyst materials to enhance the stability of CaO/SiO2 solid reducing agent in the present investigation. The novel composite structure based on CaO/SiO2 was prepared using various concentrations of hydrophobic nano-silica sol and Ca(OH)2. The composite was characterized by contact angle goniometry, thermogravimetry analysis, and scanning electron microscopy. The water contact angle of the CaO/SiO2 composites significantly increased with increasing SiO2 content. In particular, angles of 61.6°, 73.7°, 84.8°, and 84.9° were obtained for SiO2 concentrations of 20, 40, 60, and 80 wt.%, respectively. These results suggest that the hydrophobic nature of the composites was improved with the addition of 60 and 80 wt.% of SiO2. Moreover, the surface properties were measured using the nitrogen Brunauer–Emmett–Teller method for obtaining the weight ratios (wt.%) and calcinations times. The determined specific surface areas (SSAs) were 16.19, 27.25, 32.86, and 40.56 m2/g for 80:20, 60:40, 40:60, and 20:80 CaO/SiO2 composites, respectively. From the water contact angle and SSA analysis, the optimum hydrophobic nature of CaO/SiO2 composites for HF removal was achieved at a weight ratio of 40:60 (Ca(OH)2/SiO2) at the calcination temperature of 650 °C. The perfluorinated compound (PFC) removal rate is 80 and 88% for a common regenerative catalytic system (RCS) catalyst and the CaO/SiO2 reaction-enhanced (RE)-RCS catalyst, respectively. In addition, higher amount of HF elimination is successfully achieved using CaO/SiO2 solid reducing agent. During the RE-RCS process, SiO2 acts as a catalyst to prevent the formation of Ca(OH)2 when CaO is exposed to water.

Enhanced Oxygen Reduction Reaction Activity Due to Electronic Effects between Ag and Mn3O4 in Alkaline Media

We investigate the Navier-Stokes equation in the presence of Coriolis force in this article. First, the vortex equation with the Coriolis effect is discussed. It turns out that the vorticity can be generated due to a rotation coming from the Coriolis effect, . In both steady state and two-dimensional flow, the vorticity vector gets shifted by the amount of . Second, we consider the specific expression of the velocity vector of the Navier-Stokes equation in two dimensions. For the two-dimensional potential flow , the equation satisfied by is independent of . The remaining Navier-Stokes equation reduces to the nonlinear partial differential equations with respect to the velocity and the corresponding exact solution is obtained. Finally, the steady convective diffusion equation is considered for the concentration and can be solved with the help of Navier-Stokes equation for two-dimensional potential flow. The convective diffusion equation can be solved in three dimensions with a simple choice of .