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Separations
Facile Preparation of Biomass-derived Mesoporous Carbons for Highly Efficient and Selective SO2 Capture Jinghan Zhang, Peixin Zhang, Minyu Li, Ziwei Shan, Jun Wang, Qiang Deng, Zheling Zeng, and Shuguang Deng Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.9b01938 • Publication Date (Web): 18 Jul 2019 Downloaded from pubs.acs.org on July 19, 2019
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Industrial & Engineering Chemistry Research
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Facile Preparation of Biomass-derived Mesoporous
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Carbons for Highly Efficient and Selective SO2 Capture
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Jinghan Zhanga,b, Peixin Zhanga,b, Minyu Lib, Ziwei Shanb, Jun Wanga,b*, Qiang Denga,b,
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Zheling Zenga,b, Shuguang Deng,c*
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a.
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Education, Nanchang University, Nanchang 330031, PR China
Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of
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b.
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Nanchang 330031, Jiangxi, PR China
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c.
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E. Tyler Mall, Tempe, AZ 85287, USA
School of Resource, Environmental and Chemical Engineering, Nanchang University,
School for Engineering of Matter, Transport and Energy, Arizona State University, 551
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*Corresponding author:
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1. Dr. Shuguang Deng, Tel.: +8613813996873, E-mail:
[email protected] (S.
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Deng)
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2. Dr. Jun Wang, E-mail:
[email protected] (J. Wang)
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Abstract
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The efficient elimination of SO2 from flue gases and natural gases is critical for energy
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utilization and environment protection. However, selecting or preparing an efficient
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adsorbent with a high SO2 capacity, good selectivity, and excellent recyclability is very
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challenging, and the adsorption mechanism at atomic level is still controversial. We report
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a facile one-step method for the synthesis of biomass-derived porous carbons with high
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specific surface areas (1195-1449 m2 g-1), mesoporous pore size (4-6 nm) and good SO2
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adsorption properties. Our carbon adsorbents exhibited an outstanding SO2 adsorption
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capacity of 10.7 mmol g-1 at 298 K and 1.0 bar, which is more than twice the SO2 capacity
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of benchmark carbon material cs1000a (approximately 5.0 mmol g-1) and commercial
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ordered mesoporous carbon CKM-3 (5.1 mmol g-1). The new carbon adsorbents also
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showed an unprecedented SO2/CO2, SO2/CH4 and SO2/N2 separation selectivities of 32,
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127 and 2349, respectively, which are comparable with the best performance MOF
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adsorbents. Dynamic breakthrough experiments confirmed the feasibility of efficient
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removal of SO2 from flue gas in an adsorbent column. Even with the presence of water
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vapor, clear and efficient separation of SO2 could also be achieved with excellent recycling
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stability. In addition, density function theory simulation further illustrates that -NOx and -
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OH groups in the carbon frameworks provide strong interactions with SO2 molecules. The
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carbon adsorbents synthesized in this work are promising for flue gas desulfurization and
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natural gas purification applications.
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Keywords: SO2 elimination; high capacity and selectivity; breakthrough experiments;
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DFT simulation; FGD technology.
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1. Introduction The flue gas emissions generated by coal-fired power plants and petroleum refining 2
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industry contain large amount of SO2 that is recognized as the major sources of acid rain,
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fog, and haze.1,2 The traditional flue gas desulfurization technologies via limestone-
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scrubbing or wet-sulfuric-acid methods are effective, but the exhaust gases usually still
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retain as much as 400 ppm of SO2.3,4 Whereas, such small amount of SO2 would react with
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organo-amines solutions of the following CO2-scrubbing process, causing the permanent
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solvent activity loss.5 Thus, developing cutting-edge flue gas desulfurization and
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purification technologies has attracted great attentions, especially for the removal of trace
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SO2 contaminant from flue gases and other SO2-containing gases. The physical adsorption
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of SO2 by porous materials has been regarded as a promising approach for efficient and
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low-cost deep desulfurization. Traditional porous materials including zeolites,6 porous
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polymers,7 and mesoporous silica8 have exhibited a low energy penalty in adsorption-based
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gas mixture separation processes. Unfortunately, these materials generally suffer from
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relatively low adsorption capacity or selectivity. Recently, metal-organic frameworks
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(MOFs) have been employed as an emerging SO2 adsorbent with excellent capacity and
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selectivity.9,10 However, high fabrication cost, low synthesis yields, and irreversible
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structure degradation after exposure to SO2 have severely limited their large-scale
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implements.
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Porous carbons have been considered as potent candidates for practical gas separation
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and purification, owning to their intrinsic advantages such as low fabrication cost, excellent
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structure stability, and high surface property amendment ability.11,12 However, considering 3
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the acidic nature of CO2 and SO2 molecules, and much lower concentration of SO2 than
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that of CO2 in flue gas (CO2: 15%, v/v; SO2: ~3000 ppm), it is very challenging to
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efficiently remove SO2 from CO2 with a high selectivity. With the increasing requirements
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for SO2 adsorption and separation, it is urgent to develop efficient porous carbon
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adsorbents with high adsorption capacity and selectivity.13 For example, Song et al.
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reported a SO2 adsorption capacity of 0.33 mmol g-1 (based on breakthrough curve, 400
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ppm SO2) on nitrogen-doped mesoporous carbon at 308 K and 1 bar.14 Sun et al. prepared
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a N-doped porous carbon showing a SO2 adsorption capacity of 0.75 mmol g-1 (based on
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breakthrough curve, 500 ppm SO2).15 The abovementioned problems prompt us to develop
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advanced porous carbons possessing both high SO2 adsorption capacity and excellent gas-
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mixture selectivity.
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Oil-tea is a unique edible oil and popular functional food in China, whereas, the oil-
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tea shells (OTS) accounts for ~60% of the camellia fruit on a wet weight basis.16,17 Huge
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amount of OTS are produced in the southern China annually, as a lignocellulosic waste,
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OTS are often discarded directly but without effective utilization. Herein, we prepare OTS-
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derived porous carbons via a facile one-step activation method. The pore structures could
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be tuned by altering porogen/OTS ratio and activation temperature. The as-prepared
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carbons possess a large surface area, suitable pore size, and abundant basic adsorption sites.
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An excellent SO2 adsorption capacity of 10.7 mmol g-1 is achieved at 298 K and 1 bar with
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an outstanding SO2/CO2, SO2/CH4, and SO2/N2 selectivity of 32, 127 and 2349, 4
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Industrial & Engineering Chemistry Research
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respectively. The breakthrough curve is measured to further illustrate the separation
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performance with a practical flue gas composition in the presence of water vapor and
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oxygen. Moreover, density functional theory (DFT) calculations are carried out to reveal
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the selective adsorption mechanism between SO2 molecules and heteroatom adsorption
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sites.
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2. Experimental Section
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2.1. Materials.
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The oil-tea shell (OTS) used in this study was kindly provided by Hunan Academy of
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Forestry of China and was crushed to 40 mesh (
