University of Twente Student Theses


Study of water adsorption on an amine adsorbent for Direct Air Capture of CO2

García Martínez, J.B. (2020) Study of water adsorption on an amine adsorbent for Direct Air Capture of CO2.

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Abstract:To limit the negative consequences of climate change on the environment, negative emissions of CO2 will likely be needed. One way to reach them is via the use of Direct Air Capture (DAC) technologies. A promising technology is the use of solid amine sorbents via a low temperature sorbent DAC process. One such process is being developed by the SPT department, and a key issue is the co-adsorption of atmospheric water vapor, because it increases the energy demand of the process. This work is focused on the characterization of several aspects of water adsorption over an amine adsorbent material (Lewatit VP OC 1065TM) which is being studied as the benchmark for the process. Two methods were used to measure the equilibrium water adsorption capacity under different conditions of Relative Humidity (RH) and temperature. First, the method used by Veneman et al.[1], based on the measurement of water breakthrough curves. After several experiments and extensive testing, it was concluded that the method is too imprecise, inaccurate and inconsistent. Previously published literature data published may also be subject to these problems. The second method, based on gravimetric measurements, was developed to overcome the shortcomings of the first and determined to be sufficiently precise and consistent. Additionally, an improved gravimetric method is described and recommended for use in further research. The equilibrium capacity measurements show a Type V adsorption isotherm behavior with a temperature dependence and an energetically weak interaction between adsorbate and adsorbent. The GAB isotherm was selected to develop a temperature dependent isotherm model of the system. This is the main output of this work and describes the system well at the relevant ranges of humidity (5-85%) and temperature (5-35ºC). The adsorption heat of water over Lewatit was estimated to be on the range of ∆Hads,W = (63 − 50) kJ/mol. Hysteresis experiments showed an outstandingly wide hysteresis loop, in contrast with expectations from previous literature[1] and analyses of pore condensation in the material. This behavior could have significant implications for process operation. Finally, the energy requirements of the DAC process were estimated. Operation at low values of RH minimizes energy use, so arid climates are recommended. To produce pure CO2 from ambient air using steam as purge gas for regeneration of the sorbent, lower temperatures result in reduced energy consumption.
Item Type:Essay (Master)
Unknown organization, Enschede
Faculty:TNW: Science and Technology
Subject:35 chemistry, 58 process technology
Programme:Chemical Engineering MSc (60437)
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