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Separations
Rapid CO2 adsorption over hierarchical ZSM-5 with controlled mesoporosity Xingchi Qian, Gaozhi Bai, Pingping He, Zhaoyang Fei, Qing Liu, Zhuxiu Zhang, Xian Chen, Jihai Tang, Mifen Cui, and Xu Qiao Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b03325 • Publication Date (Web): 15 Nov 2018 Downloaded from http://pubs.acs.org on November 20, 2018
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Industrial & Engineering Chemistry Research
Rapid CO2 adsorption over hierarchical ZSM-5 with controlled mesoporosity Xingchi Qiana, Gaozhi Baia, Pingping Hea, Zhaoyang Feia, Qing Liu*a, Zhuxiu Zhanga, Xian Chena, Jihai Tanga,b, Mifen Cuia, Xu Qiao**a,b a
College of Chemical Engineering, State Key Laboratory of Materials-Oriented
Chemical Engineering, Nanjing Tech University, Nanjing 210009, PR China b
Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM),
Nanjing 210009, PR China *Corresponding author. Tel.: +86 025 83587168; fax: +86 025 83587168, E-mail:
[email protected] **Corresponding author. Tel.: +86 025 83172298; fax: +86 025 83172298, E-mail:
[email protected] ACS Paragon Plus Environment
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Abstract: Alkyltrimethoxysilanes with different chain length (trimethoxypropylsilane, trimethoxyoctylsilane
and
dodecyltrimethoxysilane)
were
utilized
as
mesopore-generating agent to synthesize hierarchical ZSM-5 samples with different amount of mesoporous volume. The samples were characterized by X-ray powder diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscope (SEM), transmission electron microscopy (TEM) and CO2-temperature-programmed desorption (CO2-TPD). With the growth of chain length, the alkyltrimethoxysilanes showed low reactivity and affinity for the surfaces of zeolite precursors due to the increase of hydrophobic character of the alkyl moiety, which resulted in the decrease of mesoporous volume. CO2 adsorption behaviours of the samples including adsorption
capacity,
adsorption
kinetics,
adsorption
selectivity,
adsorption
thermodynamics and adsorbent stability were studied. The experimental results indicated that hierarchical ZSM-5 modified by trimethoxypropylsilane exhibited the highest mesopores volume (0.12 cm3·g-1), corresponding to the fastest capture rate (about 2.5 times of conventional ZSM-5) and the highest capture capacity (2.15 mmol·g-1 at 25 °C and 100 kPa). Therefore, hierarchical ZSM-5 synthesized by the alkyltrimethoxysilanes with short chain length can generate the more extra mesopores and active adsorption sites, which provided a new strategy to regulate the structure of ZSM-5 for rapid CO2 adsorption. Keywords: Hierarchical ZSM-5, CO2 adsorption, Alkyltrimethoxysilanes, Adsorption rate
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Industrial & Engineering Chemistry Research
1. INTRODUCTION At present, the massive emission of CO2 into the atmosphere results in greenhouse effect and ocean acidification.1,
2
Carbon capture technology can
effectively alleviate the climate change problem brought by greenhouse gas and provide ample time for developing renewable energy.3,
4
Among the numerous
technologies including absorption, adsorption and membrane separation,5 carbon capture using solid adsorbents is considered to be a promising technique owing to its simplicity of operation, less energy requirements, excellent cycle stability, and low capital costs.6, 7 Highly porous zeolites have been widely investigated for the separation of CO2.8-13 However, most of the procedures spend long time reaching saturation due to narrow pore size and slow adsorption rates.10 To overcome this diffusion limitation, the approach comes to mind by researchers is to increase the pore size of zeolites. Several strategies aimed at enlarging pore size have been established, such as dealumination or desilication treatments,14-16 hard templates,17, 18 or supramolecular soft templates.19-21 Especially, the synthesis of zeolites with highly mesoporous by using organosilane as a mesopores-generating agent has recently been concerned.22 Chen and co-workers.23 synthesized a
mesoporous
dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium
LTA zeolite chloride
utilizing as
a
mesopore-generating agent. And the mesoporous LTA showed faster CO2 adsorption rate (about threefold) but lower CO2 adsorption capacities at 100 kPa compared to microporous LTA zeolite. It is generally known that the narrow micropores (
