Study On The Adsorption/Desorption Of Low-concentration CO₂in Confined Space On Novel Amine-modified Carbon Nanotubes

To meet the life support need in confined spaces, such as spacecraft, space laboratory and submarine, it is essential to study the feasible CO2capture technology. In recent years, solid amine adsorbents have significant advantages in CO2capture technology, while accompanied with some problems, such as adsorption efficiency, dynamic and thermal stability is not high or the limited amino functional group induced low adsorption capacity. In this paper, according to these problems, we developed a series of low-concentration CO2adsorbents by grafting-impregnating two amine compounds on the porous CNTs support, and their adsorption and desorption performances were studied.The textural properties and chemical composition of the pretreated CNTs were analyzed. It indicated that the average pore size of CNTs was increased from12.26nm to15.45nm after amine grafting, which was beneficial to the tetraethylenepentamine (TEPA)/polyethyleneimine (PEI) dispersion. The novel amine-modified carbon nanotubes, a-CNT-TEPA and a-CNT-PEI, had a uniform diameter and higher nitrogen content than directly impregnated samples. Therefore, more amino compound ensured the higher adsorption capacity. The experiment data ko of a-CNT-TEPA and a-CNT-PEI in the breakthrough model was2.5515×103,1.7186x103cm3/(min·g), respectively.For the capture of2%CO2, within the temperature of10-40℃, the maximum adsorption capacities of a-CNT-TEPA and a-CNT-PEI were reached at35℃, which were138.09mg/g and105.48mg/g respectively. The results suggested that the adsorbents were comfortable for confined space. At the same time, a-CNT-TEPA and a-CNT-PEI accelerated the adsorption process in the situation of a little water existed in confined space, which indicated their well water resistance property.The cycle of CO2adsorption/desorption experiment with a-CNT-TEPA and a-CNT-PEI showed that the adsorbed CO2could be completely desorbed via thermal desorption at100℃, and the adsorption performance remained stable even after cycling for many times. Compared with the thermal desorption, the vacuum desorption conducted at100℃and5kPa had a higher adsorption index, and the time for effectively desorb CO2by a-CNT-TEPA and a-CNT-PEI almost decreased by half. The adsorbent of using TEPA had a better adsorption capacity, adsorption efficiency and desorption ability than that of using PEI, but litter lower thermal stability. Therefore we prefer a-CNT-TEPA for adsorbing low-concentrations CO2in confined space.