Concurrent Separation of CO₂ and H₂O from Air by a Temperature-Vacuum Swing Adsorption/Desorption Cycle

Abstract

A temperature-vacuum swing (TVS) cyclic process is applied to an amine-functionalized nanofibrilated cellulose sorbent to concurrently extract CO 2 and water vapor from ambient air. The promoting effect of the relative humidity on the CO 2 capture capacity and on the amount of coadsorbed water is quantified. The measured specific CO 2 capacities range from 0.32 to 0.65 mmol/g, and the corresponding specific H 2 O capacities range from 0.87 to 4.76 mmol/g for adsorption temperatures varying between 10 and 30 °C and relative humidities varying between 20 and 80%. Desorption of CO 2 is achieved at 95 °C and 50 mbar abs without dilution by a purge gas, yielding a purity exceeding 94.4%. Sorbent stability and a closed mass balance for both H 2 O and CO 2 are demonstrated for ten consecutive adsorption−desorption cycles. The specific energy requirements of the TVS process based on the measured H 2 O and CO 2 capacities are estimated to be 12.5 kJ/mol CO2 of mechanical (pumping) work and between 493 and 640 kJ/mol CO2 of heat at below 100 °C, depending on the air relative humidity. For a targeted CO 2 capacity of 2 mmol/g, the heat requirement would be reduced to between 272 and 530 kJ/mol CO2 , depending strongly on the amount of coadsorbed water.

Application of polyethylenimine‐impregnated solid adsorbents for direct capture of low‐concentration CO2

“…In the case of trace or low-concentration CO 2 removal, it also plays a promoting effect but is more sensitive that depends on the RH, which is distinct from the results reported by Steinfeld and coworkers. 45 This should be ascribed to the competitive adsorption between CO 2 and H 2 O at the same adsorption sites. Thus, the moisture should be appropriately controlled to optimize low-concentration CO 2 capture for DAC applications.…”

“…The supports are widely screened including silica materials, [27][28][29][30][31][32][33][34][35] microporous metal-organic framework, 36,37 carbon nanotubes, 38,39 PMMA-based resins, 15,40 mesoporous carbon, 41,42 mesoporous alumina, 43 and nanofibrillated cellulose. 44,45 The amines generally contain primary or secondary alkylamines and alkanolamines, such as polyethylenimine (PEI), [46][47][48] tetraethylenepentamine (TEPA), [49][50][51] and 3-aminopropyltrimethoxysilane. 52 Futhermore, hyperbranched aminosilicas prepared by in situ aziridine polymerization on porous solids have been reported as adsorbents for CO 2 capture from the air.…”

CO2 utilization in the perspective of industrial ecology, an overview

“…Consequently, two DAC processes accommodating "low temperature" sources (e.g. industrial waste heat or solar power) are considered in this article, adsorption with immobilized amines [7] and with anion exchange resin [8].…”

Simultaneous Online Measurement of H2O and CO2 in the Humid CO2 Adsorption/Desorption Process

“…The combination of the humidity sensor with the infrared (IR) CO2 analyzer in series was a simple and practical way to obtain breakthrough and elution curves of CO2 and H2O simultaneously. 13,24 However, the concentration difference between the real H2O and the measured H2O was up to 17% when the humidity sensor-IR CO2 analyzer was used as the online monitor. 24 Generally, the measurement errors of H2O resulted from three sources: (a) the measurement error from meters, (b) the fluctuation of the H2O content in the flow gas, and (c) the adsorbed capacity by the transfer pipe in the setup.…”

“…13,24 However, the concentration difference between the real H2O and the measured H2O was up to 17% when the humidity sensor-IR CO2 analyzer was used as the online monitor. 24 Generally, the measurement errors of H2O resulted from three sources: (a) the measurement error from meters, (b) the fluctuation of the H2O content in the flow gas, and (c) the adsorbed capacity by the transfer pipe in the setup. Therefore, the objective of the present work is to develop a technique with the integration of a dew-point meter and an IR CO2 analyzer as online monitors for simultaneous measurement of H2O and CO2.…”