Soo Chool Lee

The effect of water on the activation and the CO2 capture capacities of alkali metal-based sorbents

Alkali metal-based sorbents were prepared by the impregnation either of potassium carbonate (K2CO3) or of sodium carbonate (Na2CO3) on the supports (activated carbon (AC) and Al2O3). The CO2 absorption and regeneration properties were measured in a fixed bed reactor at the low temperature conditions (CO2 absorption at 60 ‡C and regeneration at 150 °C). The potassium carbonate which was supported on the activated carbon (K2CO3/AC) was clarified as a leading sorbent, of which the total CO2 capture capacity was higher than those of other sorbents. This sorbent was completely regenerated and transformed to its original phase by heating the used sorbent. The activation process before CO2 absorption needed moisture nitrogen containing 1.3–52 vol% H2O for 2 hours either at 60 ‡C or at 90 °C. The activation process played an important role in CO2 absorption, in order to form new active species defined as K2CO3· 1.5 H2O, by X-ray diffraction. It was suggested that the new active species (K2CO3·1.5H2O) could be formed by drying the K4H2(CO3)3·1.5H2O phase formed after pre-treatment with excess water.

Improvement of H2S Sensing Properties of SnO2-Based Thick Film Gas Sensors Promoted with MoO3 and NiO

The effects of the SnO2 pore size and metal oxide promoters on the sensing properties of SnO2-based thick film gas sensors were investigated to improve the detection of very low H2S concentrations (<1 ppm). SnO2 sensors and SnO2-based thick-film gas sensors promoted with NiO, ZnO, MoO3, CuO or Fe2O3 were prepared, and their sensing properties were examined in a flow system. The SnO2 materials were prepared by calcining SnO2 at 600, 800, 1,000 and 1,200 °C to give materials identified as SnO2(600), SnO2(800), SnO2(1000), and SnO2(1200), respectively. The Sn(12)Mo5Ni3 sensor, which was prepared by physically mixing 5 wt% MoO3 (Mo5), 3 wt% NiO (Ni3) and SnO2(1200) with a large pore size of 312 nm, exhibited a high sensor response of approximately 75% for the detection of 1 ppm H2S at 350 °C with excellent recovery properties. Unlike the SnO2 sensors, its response was maintained during multiple cycles without deactivation. This was attributed to the promoter effect of MoO3. In particular, the Sn(12)Mo5Ni3 sensor developed in this study showed twice the response of the Sn(6)Mo5Ni3 sensor, which was prepared by SnO2(600) with the smaller pore size than SnO2(1200). The excellent sensor response and recovery properties of Sn(12)Mo5Ni3 are believed to be due to the combined promoter effects of MoO3 and NiO and the diffusion effect of H2S as a result of the large pore size of SnO2.

Effects of Textural Properties on the Response of a SnO2-Based Gas Sensor for the Detection of Chemical Warfare Agents

The sensing behavior of SnO2-based thick film gas sensors in a flow system in the presence of a very low concentration (ppb level) of chemical agent simulants such as acetonitrile, dipropylene glycol methyl ether (DPGME), dimethyl methylphosphonate (DMMP), and dichloromethane (DCM) was investigated. Commercial SnO2 [SnO2(C)] and nano-SnO2 prepared by the precipitation method [SnO2(P)] were used to prepare the SnO2 sensor in this study. In the case of DCM and acetonitrile, the SnO2(P) sensor showed higher sensor response as compared with the SnO2(C) sensors. In the case of DMMP and DPGME, however, the SnO2(C) sensor showed higher responses than those of the SnO2(P) sensors. In particular, the response of the SnO2(P) sensor increased as the calcination temperature increased from 400 °C to 800 °C. These results can be explained by the fact that the response of the SnO2-based gas sensor depends on the textural properties of tin oxide and the molecular size of the chemical agent simulant in the detection of the simulant gases (0.1–0.5 ppm).

The adsorption properties of organic sulfur compounds on zeolite-based sorbents impregnated with rare-earth metals

Abstract Dimethyl disulfide (DMDS) and dimethyl sulfide (DMS) are non-polar, stable, organic sulfur compounds found in liquefied petroleum gas, and their oxidation in the atmosphere results in the formation of tropospheric sulfur dioxide, which is subsequently converted into sulfuric acid, as the main factor of acid rain. In the present study, adsorption processes were devised based on the use of modified zeolite impregnated with rare-earth metals (Ce, La or Pr) for the adsorption of DMDS and DMS, and their sorption capacities were compared with that of commercial zeolite [Zeolite-Y, Ultra Stable Y(USY)]. The adsorption capacities of adsorbents were tested using a micro liquid flow reactor at room temperature. USY impregnated with cerium oxide (UC-10) had excellent DMDS and DMS adsorption capacities as compared with the other adsorbents tested. It was found that impregnation of USY with rare-earth metal such as Ce improved the sulfur adsorption capacity of zeolite. The form of the Ce promoter impregnated into USY was determined by FT-Raman spectroscopy. Adsorbents were characterized by X-ray fluorescence spectrometer, X-ray diffraction, and BET and the results obtained are discussed.

Effects of alkali-metal carbonates and nitrates on the CO2 sorption and regeneration of MgO-based sorbents at intermediate temperatures

The effects of alkali-metal carbonates and nitrates on the CO2 sorption and regeneration of MgO-based sorbents were investigated in the presence of 10 vol% CO2 and 10 vol% H2O in an intermediate temperature range, 300 to 450 °C. The CO2 capture capacities of the MgO-based sorbents promoted with Na2CO3 and K2CO3 were 9.7 and 45.0 mg CO2/g sorbent, respectively. On the other hand, a MgO-based sorbent promoted with both Na2CO3 and NaNO3 exhibited the highest CO2 capture capacity of 97.4mg CO2/g sorbent at 200 °C in 10 vol% CO2, which was almost ten-times greater than that of the MgO-based sorbent promoted with Na2CO3. The CO2 sorption rate of these sorbents was higher than that of the MgO-based sorbents promoted with alkali-metal nitrates due to the formation of Na2Mg(CO3)2 or K2Mg(CO3)2 by the alkali-metal carbonate and the eutectic reaction of the alkali-metal nitrates. In addition, the reproducibility problem of double-salt sorbents obtained by the precipitation method was completely resolved by impregnating MgO with alkali-metal carbonates and nitrates. Furthermore, we found that their desorption temperatures are lower than those of the MgO-based sorbents promoted with alkali-metal carbonates due to the eutectic reaction during the regeneration process.

Selective O-Alkylation Reaction of Hydroquinone with Methanol over Cs Ion-Exchanged Zeolites

O-alkylation reaction of hydroquinone with excess methanol was performed by using alkali metal ion-exchanged zeolite catalysts in a slurry type reactor to substitute the solid zeolite catalysts for the homogeneous liquid phase catalysts. This was also done to produce selectively mono-alkylated 4-methoxyphenol, a valuable intermediate for the perfume, flavor, food and photo industries. The effects of the basicity of various zeolites and reaction conditions such as temperature, reaction time and the amount of catalyst on the catalytic activity and selectivity were tested to maximize the yield of 4-methoxyphenol. Thus far, 84% selectivity at 95% conversion of hydroquinone was obtained at the optimum reaction conditions (240 ‡C, reaction with 0.6 g catalyst for 16 h), which was thought to result from the strong basic property and shape selectivity of the Cs ion-exchanged NaX zeolite.

The removal of the acetonitrile using activated carbon-based sorbent impregnated with sodium carbonate

To remove acetonitrile, various activated carbon (AC)-based sorbents impregnated with alkali or alkaline earth metal were tested in a fixed-bed quartz reactor at 30 °C. The AC-based sorbents impregnated with sodium (NaAC) showed more enhanced acetonitrile removal capacities than that of the pure AC sorbent despite a notable decrease in their surface areas and pore volumes. The NaAC-10 sorbent (with 10 wt% sodium carbonate) especially showed an excellent acetonitrile removal capacity (15mg CH3CN/g sorbent) and regeneration ability, which indicates that the alkali metal was the adsorption site of the acetonitrile.

Regenerable potassium-based alumina sorbents prepared by CO2 thermal treatment for post-combustion carbon dioxide capture

Potassium carbonate supported on alumina is used as a solid sorbent for CO2 capture at low temperatures. However, its CO2 capture capacity decreases immediately after the first cycle. This regeneration problem is due to the formation of the by-product [KAl(CO3)(OH)2] during CO2 sorption. To overcome this problem, a new regenerable potassium-based sorbent was fabricated by CO2 thermal treatment of sorbents prepared by the impregnation of δ-alumina with K2CO3 in the presence of 10 vol% CO2 and 10 vol% H2O. The CO2 capture capacities of the new regenerable sorbents were maintained over multiple CO2 sorption tests. These results can be explained by the fact that the sorbent prepared by CO2 thermal treatment did not form any by-product during CO2 sorption. Based on these results, we suggest that the regeneration properties of potassium-based sorbents using δ-alumina could be significantly improved by the use of the CO2 thermal treatment developed in this study.

Self-assembly growth of electrically conductive chitosan nanofibrous scaffold

AbstractWe report on the synthesis of an electrically conductive chitosan nanofibrous scaffold (NFS) by a “simple template free self-assembly method” from biopolymer chitosan in the presence of inorganic acids as dopants and ammonium persulphate (APS) as an initiator. The morphology of the chitosan nanofibers scaffold (CS-NFS) was examined by field emission scanning electron microscopy (FE-SEM). Physiochemical characterizations of the CSNFS were analyzed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. It is found that the morphology and structure of the CS-NFS strongly depend on the kinds of dopant used. Cyclic voltammogram measurement reveals that CS nanofibers have high electrocatalytic activity compared to chitosan powder. The CS nanofibers are expected to be useful in electrical, optical, and electrochemical devices.