Papers by Author: Chu Sik Park

Abstract: The hydrogen reduction and water-splitting oxidation for hydrogen storage and release on the iron oxide mediums with Ce, Mo or Ce-Mo additives were carried out using a fixed bed reactor at atmospheric pressure. A sole Ce additive was an outstanding material for the improvement of the reactivity in the reduction and oxidation of iron oxide medium, even though the medium with Ce was easily deactivated during repeated cyclic reactions due to sintering. A sole Mo additive was a good material for the improvement for the durability. In the mediums with the Ce-Mo additives, therefore, the degree of deactivation and the reactivity of the mediums were gradually decreased with the increase of the amount of Mo. Among the iron oxide mediums with Ce-Mo additives, a FeCeMo-5 medium exhibited the good durability while the maintaining the considerable reactivity during the cyclic reactions.

Abstract: The H₂SO₄ phase and HI_x phase solution produced from Bunsen reaction section in SI (Sulfur-iodine) process were supplied to the phase separator for the continuous operation of SI process. However, the separation of Bunsen products in the phase separator is difficult because an excess of HI_x phase solution existed in the phase separator than the H₂SO₄ phase solution. Therefore, the additional supply of H₂SO₄ to the phase separator as the phase separation method was considered for improvement of phase separation efficiency. In this work, the variations in volume ratio and composition of each phase solution were examined after the Bunsen product mixing on the HI_x phase/H₂SO₄ phase volume ratio. As the results, the variation in composition of products increases with increase of the HI_x phase/H₂SO₄ phase volume ratio after mixing. It was also found that the high variations in composition and volume ratio of Bunsen products by mixing in the presence of excess HI_x phase. From the results, we concluded that the phase separation method, additional supply of H₂SO₄ phase solution to the phase separator, is effective in Bunsen product separation when the variation in composition is little.

Abstract: The Sulfur-Iodine thermochemical hydrogen production process (SI process) has been focused as one of the most promising method for hydrogen production by water splitting. SI process consists of three sections as follow; (1) Bunsen reaction, (2) H₂SO₄ decomposition and (3) HI decomposition. The O₂ produced in a H₂SO₄ decomposition section could be supplied directly to the Bunsen reaction section without additional separation. Meanwhile, the reactant solution supplied to a Bunsen reaction section could be supplied as the type of a HI_x (I₂ + HI + H₂O) solution, since only the separation of I₂ in a HIx solution recycled from a HI decomposition section is very difficult. Therefore, we carried out the reaction using SO₂ and SO₂-O₂ mixture gases in presence of the HI_x solution to identify the effect of O₂ in the Bunsen reaction. From the results, the amount of I₂ unreacted under the feed of SO₂-O₂ mixture gases was very small higher than those under the feed of SO₂ gas only, while the amount of HI produced was relatively decreased. In addition, the amount of impurities in each phase produced from the Bunsen reaction with the HIx solution was hardly affected by the O₂/SO₂ molar ratios.

Abstract: In DME to olefins (DTO) reaction, SAPO-34 catalyst with CHA structure is well known to be one of the catalysts with good performance. However, the SAPO-34 catalyst is easily deactivated due to coke deposition during DTO reaction. In this study, MeAPSO-34 catalysts (Me=Mn, Co) were prepared for the increase of the catalyst lifetime and their properties have been characterized by XRD and SEM. The DTO reaction was carried out over the MeAPSO-34 catalysts, and the results were compared with the SAPO-34 catalyst. The lifetime of MeAPSO-34 catalysts with high DME conversion and selectivity of light olefins was prolonged than that of the SAPO-34 catalyst. It may be concluded that the decrease of strong acid sites, which were responsible for the formation of coke, affect on the lifetime of the MeAPSO-34 catalysts. In addition, the CoAPSO-34 catalyst with a Co additive showed the best performance in terms of the catalytic lifetime and the selectivity to light olefins.

Abstract: Pt catalysts have been researched and used for HI decomposition. Specifically, the effects of supports and reduction temperature on metal dispersion were investigated in this paper. Metal dispersion was high measured, in the order of Pt/Al₂O₃, Pt/ZrO₂, and Pt/SiO₂. HI conversion results coincided with the metal dispersion. With effect on reduction temperature, Pt dispersion was measured as 2.9 %, 26 %, and 60 % each 1173K, 973K, and 773 K. In addition, HI conversion presented 7.8%, 16.3%, and, 19.4% respectively. Consequently, Pt dispersion, influenced by supports and reduction temperature was considered to be crucial role in HI conversion.

Abstract: The Sulfur-Iodine (SI) thermochemical hydrogen production process is promising method for the massive production of hydrogen using the high temperature thermal energy of VHTR. For continuous operation of SI process, the conditions of Bunsen reaction are considered as the pressurized conditions with ca. 373~393K temperature and the composition of Bunsen products should be kept constant during the reaction. Therefore, we carried out the continuous Bunsen reaction using a counter-current flow reactor at pressurized condition to investigate the phase separation characteristics of pressurized Bunsen reaction. As the results, the composition of Bunsen product was maintained constantly as the evidence for the steady-state operation. The continuous reaction was operated without occurrence of side reactions, and a H₂SO₄ phase and HI_x phase as the product contains a small amount of impurities (HI in a H₂SO₄ phase and H₂SO₄ in a HI_x phase). We concluded that the pressurized Bunsen reaction is favorable to the continuous operation of SI process than the atmospheric reaction.

Abstract: A SAPO-34 catalyst is well known to be one of the best catalysts for DME to olefins (DTO) reaction. Main products of the reaction were light olefins such as ethylene, propylene and butenes. However, the main problem is rapid deactivation of the SAPO-34 catalyst due to coke deposition during DTO reaction. In this study, various SAPO-34/ZrO2 catalysts added with ZrO2 were prepared for improving the lifetime and their physicochemical properties have been characterized by XRD and SEM. The DTO reaction over various SAPO-34/ZrO2 catalysts was carried out using a fixed bed reactor. All SAPO-34/ZrO2 catalysts showed similar activity and selectivity in the DTO reaction. The SAPO-34(9wt%)/ZrO2 catalyst was showed the best performance for the catalyst lifetime.

Abstract: The sulfur-iodine (SI) cycle, thermochemical water splitting using heat energy from nuclear, is one of the most promising methods for massive hydrogen production. For continuous operation of Bunsen reaction section in SI process, the reactants (SO2, I2 and H2O) were fed to the reactor and the products (a H2SO4 phase and a HIx phase) were sent to storage tanks continuously during the reaction. In this study, we investigated the phase separation characteristics of continuous Bunsen reaction on the reactor shape and temperature. It was found that the reactor shape has little affected on the composition of Bunsen products. It was also observed that the phase separation characteristics of the continuous Bunsen reaction were similar to those for the semi-batch Bunsen reaction.

Abstract: Chemical hydrogen storage and release of iron-based oxide mediums were investigated by hydrogen reduction and water splitting oxidation (Fe3O4 + 4H2 ⇌ 3Fe + 4H2O). In this study, all metal oxide mediums were prepared by coprecipitation method using urea solution as precipitant. The redox reactions of the mediums were conducted using a fixed bed quartz reactor under atmospheric pressure. The theoretical amount of hydrogen storage that can be obtained from the redox reaction of iron oxide is calculated to be 4.8wt% on the basis of 1g-Fe. However, in case of using the iron oxide medium without additives, the medium was rapidly deactivated due to the agglomeration of Fe metals in the hydrogen reduction step of repeated redox cycles. In this study, therefore, Mo and Zr additives were added to iron oxide to improve the reactivity of the medium and to prevent the agglomeration of that. As a result, the reactivity for oxidation of the mediums was largely improved with the addition of Mo additive. It was concluded that change in the valence of Mo cations affected the redox behavior of the mediums.