Novel separation process of gaseous mixture of SO{sub 2} and O{sub 2} with ionic liquid for hydrogen production in thermochemical sulfur-iodine water splitting cycle
- Clena Energy Research Center, Energy and Environment Technology Division, Korea Institute of Science and Technology, Hawolgokdong 39-1, Seongbukgu, Seoul 139-791 (Korea, Republic of)
- Department of Chemical and Biological Engineering, Korea University, Anamdong, Seongbukgu, Seoul 136-701 (Korea, Republic of)
Sulfur-Iodine cycle is the most promising thermochemical cycle for water splitting to produce hydrogen which can replace the fossil fuels in the future. As a sub-cycle in the thermochemical Sulfur-Iodine water splitting cycle, sulfuric acid (H{sub 2}SO{sub 4}) decomposes into oxygen (O{sub 2}) and sulfur dioxide (SO{sub 2}) which should be separated for the recycle of SO{sub 2} into the sulfuric acid generation reaction (Bunsen Reaction). In this study, absorption and desorption process of SO{sub 2} by ionic liquid which is useful for the recycle of SO{sub 2} into sulfuric acid generation reaction after sulfuric acid decomposition in the thermochemical Sulfur-Iodine cycle is investigated. At first, the operability as an absorbent for the SO{sub 2} absorption and desorption at high temperature without the volatilization of absorbents which is not suitable for the recycle of absorbent-free SO{sub 2} after the absorption process. The temperature range of operability is determined by TGA and DTA analysis. Most of ionic liquids investigated are applicable at high temperature desorption without volatility around 300 deg. C except [BMIm] Cl, and [BMIm] OAc which show the decomposition of ionic liquids. To evaluate the capability of SO{sub 2} absorption, each ionic liquid is located in the absorption tube and gaseous SO{sub 2} is bubbled into the ionic liquid. During the bubbling, the weight of the system is measured and converted into the absorbed SO{sub 2} amount at each temperature controlled by the heater. Saturated amounts of absorbed SO{sub 2} by ionic liquids at 50 deg. C are presented. The effect of anions for the SO{sub 2} absorption capability is shown in the order of Cl, OAc, MeSO{sub 3}, BF{sub 4}, MeSO{sub 4}, PF{sub 6}, and HSO{sub 4} when they are combined with [BMIm] cation. [BMIm]Cl has the largest amount of SO{sub 2} absorbed which can be the most promising absorbent; however, from the point of operability at high temperature which includes desorption process, [BMIm]Cl is vulnerable to high temperature around 250 deg. C based on the TGA/DTA analysis. As the second largest SO{sub 2} absorbing ionic liquid, [BMIm]OAc is not stable at the temperature around 200 deg. C either. The effect of temperature for SO{sub 2} absorption by ionic liquids at 1 atm is presented with respect to ionic liquids. The amount of absorbed SO{sub 2} decreases as temperature increases for all ionic liquids experimented. At low temperature the difference of the absorbed SO{sub 2} between each ionic liquid is bigger than that of at high temperature. The effect of partial pressure of SO{sub 2} to the absorbed SO{sub 2} amount is presented. The partial pressure of SO{sub 2} is controlled by changing the ratio between inert He and SO{sub 2}. The amount of absorbed SO{sub 2} increases as partial pressure of SO{sub 2} increases for [DMIm] MeSO{sub 4}. The trends of SO{sub 2} absorption depending on the temperature which is mentioned earlier are also recognized. Until now, the solubility of SO{sub 2} in the ionic liquids is investigated. However, in the sulfur cycle, oxygen exists together with SO{sub 2} as the products of sulfuric acid decomposition after H{sub 2}O removal by condensation. The solubility of oxygen in the ionic liquid, which can be expected as negligible because of its non-polarity of the molecule, is measured with the same apparatus by changing the feeding gas into oxygen. Solubility of oxygen and SO{sub 2} is compared where [EMIm] EtSO{sub 4} is used as an absorbent at 1 atm 50 deg. C. The amount of absorbed oxygen is much less than that of SO{sub 2} by the order difference. The absorption mechanism of SO{sub 2} in the ILs is known as physical absorption by many researchers these days, where chemical absorption is also reported with some ionic liquids. Physical absorption property of ionic liquids is necessary for the recycle process of the absorbed pure SO{sub 2} into sulfuric acid generation reaction. By the FT-IR spectra, the physical absorption is verified with the fact that no spectra peak position change of ionic liquids before and after SO{sub 2} absorption except the generated SO{sub 2} peak in the spectrum. The effect of anion in the interaction between SO{sub 2} and ionic liquids during absorption process is analyzed by FT-IR spectra. Peak shift, is recognized by comparing SO{sub 2} absorbed [BMIm] PF{sub 6} and [BMIm] BF{sub 4} spectrum. The amount of interaction which results in the absorption amount difference may not analyzed quantitatively; however, it can be verified qualitatively because only anion is the difference between two spectrum conditions. Based on the properties of SO{sub 2} absorbing ionic liquid mentioned, continuous SO{sub 2} separation process of the gaseous SO{sub 2}/O{sub 2} mixture in the thermochemical sulfur-iodine cycle can be realized after acquiring more properties of ionic liquid which is useful for the process design in the near future. (authors)
- Research Organization:
- American Institute of Chemical Engineers - AIChE, 3 Park Avenue New York, NY 10016-5991 (United States)
- OSTI ID:
- 21238860
- Resource Relation:
- Conference: AIChE 2007 Spring National Meeting, Houston, TX (United States), 22-27 Apr 2007; Other Information: Country of input: France; 3 refs
- Country of Publication:
- United States
- Language:
- English
Similar Records
Advances in Acid Concentration Membrane Technology for the Sulfur-Iodine Thermochemical Cycle
Pressure Swing Absorption Device and Process for Separating CO{sub 2} from Shifted Syngas and its Capture for Subsequent Storage