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Title CO2 Capture Using Ionic Liquids
Author Arshad, Muhammad Waseem
Supervisor Thomsen, Kaj (Center for Phase Equilibria and Separation Processes, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2009
Abstract Current post combustion CO2 capture systems in power plants typically employ amine based solvent, such as monoethanolamine (MEA), to capture CO2 from flue gas followed by a desorption (or solvent regeneration) step, usually a stripping column, to recover the captured CO2 and regenerate the solvent. The MEA solvent has high heat of reaction with CO2 that leads to higher stripping energy consumption during CO2 recovery, thus making amine scrubbing an energy expensive process. The solvents suggested for CO2 capture in this work belong to a group of compounds called ionic liquids (ILs). Many ILs have shown a remarkably good CO2 solubility. Ionic liquids have also shown good selective CO2 absorption, thus making ILs a potential candidate for CO2 capture from flue gas. Since CO2 absorption in ILs involves physisorption (physical absorption) rather than chemisorption (chemical absorption) of CO2 in amine based solvents, there is a potential to develop energy efficient ionic liquid based absorption-stripping process. Two ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) and 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) are investigated in this work for their CO2 solubility at 25 oC and low pressures (up to 10 bar) using High Pressure Microbalance (HP balance). Since, the HP balance is being used for the first time to measure the gas (CO2) solubility in liquids (ionic liquids) at low pressures, it is important to check the reliability of the equipment for these kinds of solubility measurements. A process evaluation is also made on the basis of energy consumption for CO2 absorption and recovery in ionic liquids using temperature-swing technique and compared with state-of-the-art MEA-based CO2 capture technology. The CO2 solubility results are not good enough and are also not in good agreement with the data published in literature. The disagreement in data is due to some technical problems in the experimental setup e.g. problem in geometry (alignment) of the pressure tube of HP balance, inadequate vacuum system, pressure drop in the system,improper pressure control system and related problems. Some recommendations are presented to overcome these problems. Since, no good solubility results are obtained, the process evaluation is made using Henry’s constants reported in literature. The amount (kilogram) of ionic liquid required per kilogram of CO2 capture and corresponding energy required to recover the captured CO2 in the stripping column are calculated. Both ionic liquids require significantly greater energy to capture and recover CO2 compared to MEA solvent due to low CO2 carrying capacity of the ionic liquids which results in high solvent amount requirements per kilogram CO2 capture. But the CO2 carrying capacity of the ionic liquids can be increased by tailoring the choice of anions and cations of the ionic liquids, thus parameters (Henry’s constant at 25 oC and 100 oC) for a theoretical ionic liquid that would be competitive to MEA are presented.
Pages 148
Fulltext
Original PDF CO2Captureusingionicliquid.pdf (2.38 MB)
Admin Creation date: 2009-03-17    Update date: 2009-11-24    Source: dtu    ID: 240068    Original MXD