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Title:Capture and recovery of organic gases with electrothermal swing adsorption and post-desorption treatment
Author(s):Mallouk, Kaitlin Engle
Director of Research:Rood, Mark J
Doctoral Committee Chair(s):Rood, Mark J
Doctoral Committee Member(s):Bond, Tami C; Zhang, Yuanhui; Koloustou-Vakakis, Sotiria
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
activated carbon
organic gases
air quality
activated carbon fiber cloth, electrothermal regeneration, electrothermal desorption
Abstract:Several industrial processes, including foam packaging manufacturing, use liquefied organic gases (boiling points (Tb) < 20°C) as inert feedstocks. These processes produce low concentration (e.g., 2,000 ppmv) organic gas streams that must be treated to prevent emissions of the organic gases to the atmosphere. The organic gases are typically not reused in the process and are instead thermally oxidized. The ability to selectively capture, concentrate, and reuse the effluent organic gases is expected to increase the opportunities to manufacture materials in a more sustainable manner and improve the economics of industrial processes that emit organic gases to the atmosphere. Activated carbon fiber cloth (ACFC) with electrothermal swing adsorption (ACFC-ESA) has been shown to be an effective means of capturing and recovering organic vapors (Tb > 50°C). However, additional gas treatment needs to be coupled downstream of the ACFC-ESA system to extend this technology to capture and recover organic gases. To this end, a new bench-scale ACFC-ESA gas recovery system (GRS) with post-desorption condensation was developed and tested with four organic gases and under a select range of process conditions to assess its effectiveness for capturing and recovering organic gases. The GRS was tested to determine the mass collection efficiency and energy requirements for recovering liquid adsorbate from a carrier gas containing select concentrations of each adsorbate. The four adsorbates tested were: isobutane, R134A, n-butane, and dichloromethane. The inlet relative pressure of the adsorbates ranged from 8.3x10-5 to 3.4x10-3. The GRS successfully captured and recovered all relative pressures and adsorbates of interest except dichloromethane, which was chemically incompatible with components of the GRS. Of the remaining adsorbates (i.e., isobutane, R134A, and n-butane), each was captured and recovered with greater than 99% mass collection efficiency, which meets existing emission reduction requirements for packaging manufacturing. The heating and compression energy required to capture and liquefy the gases ranged from 1,200 to 52,000 kJ/mol liquefied depending on the relative pressure of the inlet adsorbate. This energy consumption is 0.87 – 138 times that to recover vapors with boiling points ranging from 56.5 - 101°C using the Vapor Phase Removal and Recovery System (VaPRRS), which is similar to the GRS, but does not include compression and cooling and thus cannot liquefy low boiling point organic gases. The GRS system was also modified to capture isobutane from a carrier gas with select relative humidities that ranged from 5-80% while maintaining the water vapor concentration of the carrier gas. During this testing, the clean, humid adsorption carrier gas and the N2 used to inert the system during desorption were recirculated for the first time, which resulted in a reduction in the amount of water vapor and N2 required to operate the system once it reached steady state. In an industrial setting, this new ability to recycle the carrier gas stream is expected to improve system sustainability and reduce operating costs because it eliminates the need for re-humidification, decreases the demand for N2 production to inert the adsorption vessels during desorption, and reduces energy requirements. The energy required to capture and recover isobutane (relative pressure = 6.7x10-4) with relative humidities ranging from 5 to 80% ranged from 2910 – 5750 kJ/mol liquefied. Experiments with recirculating carrier gas showed that the energy requirements to capture and recover liquid isobutane from a high relative humidity adsorption stream were significantly lower at the 95% confidence level than in experiments without carrier gas recirculation. Based on these results, implementing ACFC-ESA with carrier gas recirculation, particularly for humid adsorption gas streams, reduces the humidification energy requirements by 60%, the energy to supply N2 by 25 to 60%, and the total energy to capture and recover liquid isobutane (heating, compression, water and N2 energy) by 38%, while also reusing resources such as N2 and water. This research is a significant advancement over previous research accomplishments because the GRS expands the applicability of ACFC-ESA to compounds with boiling points below 20°C. Additionally, characterization of the GRS using mass and energy balances has shown that it can be used for compounds with boiling points ranging from -26.5°C to -0.5°C so long as those compounds have a reasonable, reversible affinity for ACFC. Finally, demonstrating that operation of this technology with humidified gas streams and carrier gas recirculation reduces the water vapor, N2, and overall energy requirements makes the technology more likely to be adopted by industries that generate low concentration organic gas streams.
Issue Date:2016-07-14
Rights Information:Copyright 2016 Kaitlin Engle Mallouk
Date Available in IDEALS:2016-11-10
Date Deposited:2016-08

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