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Performance of a CO 2 sorbent for indoor air cleaning applications: Effects of environmental conditions, sorbent aging, and adsorption of co‐occurring formaldehyde
Author(s) -
Tang Xiaochen,
Houzé de l’Aulnoit Sébastien,
Buelow Mark T.,
Slack Jonathan,
Singer Brett C.,
Destaillats Hugo
Publication year - 2020
Publication title -
indoor air
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.387
H-Index - 99
eISSN - 1600-0668
pISSN - 0905-6947
DOI - 10.1111/ina.12695
Subject(s) - sorbent , sorption , adsorption , relative humidity , formaldehyde , moisture , chemistry , hvac , materials science , chromatography , air conditioning , composite material , meteorology , physics , organic chemistry , thermodynamics
Indoor air cleaning systems that incorporate CO 2 sorbent materials enable HVAC load shifting and efficiency improvements. This study developed a bench‐scale experimental system to evaluate the performance of a sorbent under controlled operation conditions. A thermostatic holder containing 3.15 g sorbent was connected to a manifold that delivered CO 2 ‐enriched air at a known temperature and relative humidity (RH). The air stream was also enriched with 0.8‐2.1 ppm formaldehyde. The CO 2 concentration was monitored in real‐time upstream and downstream of the sorbent, and integrated formaldehyde samples were collected at different times using DNPH‐coated silica cartridges. Sorbent regeneration was carried out by circulating clean air in countercurrent. Almost 200 loading/regeneration cycles were performed in the span of 17 months, from which 104 were carried out at reference test conditions defined by loading with air at 25°C, 38% RH, and 1000 ppm CO 2 , and regenerating with air at 80°C, 3% RH and 400 ppm CO 2 . The working capacity decreased slightly from 43‐44 mg CO 2 per g sorbent to 39‐40 mg per g over the 17 months. The capacity increased with lower loading temperature (in the range 15‐35°C) and higher regeneration temperature, between 40 and 80°C. The CO 2 capacity was not sensitive to the moisture content in the range 6‐9 g/m 3 , and decreased slightly when dry air was used. Loading isothermal breakthrough curves were fitted to three simple adsorption models, verifying that pseudo‐first‐order kinetics appropriately describes the adsorption process. The model predicted that equilibrium capacities decreased with increasing temperature from 15 to 35°C, while adsorption rate constants slightly increased. The formaldehyde adsorption efficiency was 80%‐99% in different cycles, corresponding to an average capacity of 86 ± 36 µg/g. Formaldehyde was not quantitatively released during regeneration, but its accumulation on the sorbent did not affect CO 2 adsorption.