Characteristic modification of coal-based activated carbon and its methane adsorption capacity
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摘要: 針對無煙煤制備成的煤基活性炭，采用酸式改性、堿式改性和聯合改性的方法對其進行改性處理。通過低溫液氮吸附實驗、傅里葉紅外光譜技術、高壓甲烷吸附實驗，分析了煤基活性炭的表面物理、化學結構、甲烷的吸附能力。借助Langmuir吸附等溫模型、Freundlich模型進行數據擬合，研究了吸附熱力學和動力學特征。結果表明，聯合改性后的煤基活性炭比表面積和孔容均明顯增大，其中比表面積增大66.66%，總孔容增大30.89%；煤基活性炭的甲烷吸附能力明顯提高，甲烷吸附量提升25.686%。煤基活性炭的孔隙結構和表面官能團共同決定了其對甲烷的吸附作用，且較于孔隙結構，表面官能團的極性對甲烷吸附量起主要作用。Abstract: Methane is an important high-quality clean energy that mainly comes from the decomposition of organic waste, natural gas, fossil fuel extracts, etc. Recycling it from a gaseous mixture is beneficial for environmental protection and energy utilization and development. The new coal-based activated carbon is a widely used storage material for methane because of its economic benefit and practicality; thus, coal-based activated carbon modification is greatly significant. This research aims to further reveal the methane adsorption mechanism of coal-based activated carbon by studying the influence of acidic, basic, and combined modifications on methane adsorption and seek a more efficient means of coal-based activated carbon modification. The coal-based activated carbon made from anthracite coal was processed through acidic, basic, and combined modifications. In addition, the physical and chemical structures of the coal-based activated carbon surface and the adsorption ability of methane were precisely analyzed through low-temperature liquid nitrogen adsorption, Fourier infrared spectroscopy, and high-pressure methane adsorption experiments. The characteristics of adsorption thermodynamics and kinetics were also determined by using the Langmuir adsorption isotherm model and the Freundlich model for data fitting. The results show a significant increase in the specific surface area and pore volume of the coal-based activated carbon after combined modification. The specific surface area and the total pore volume increases by 66.66% and 30.89%, respectively. The methane adsorption capacity of the coal-based activated carbon also significantly improved after combined modification. Methane adsorption increases by 25.686%. In addition, both the pore structure and the contained functional groups on the surface jointly determine the methane adsorption, which is mainly affected by the polarity of the surface functional groups rather than the pore structure.
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圖 1 煤基活性炭低溫液氮吸附脫附等溫線. (a)原始煤基活性炭; (b)酸式改性煤基活性炭; (c)堿式改性煤基活性炭; (d)聯合改性煤基活性炭
Figure 1. Liquid N2 adsorption–desorption isotherms of coal-based activated carbons: (a) raw coal-based activated carbon; (b) acid modified coal-based activated carbon; (c) basic modified coal-based activated carbon; (d) combined modified coal-based activated carbon
圖 2 煤基活性炭紅外光譜譜圖. (a)原始煤基活性炭; (b)酸式改性煤基活性炭; (c)堿式改性煤基活性炭; (d)聯合改性煤基活性炭
Figure 2. FT-IR spectra of coal-based activated carbons: (a) raw coal-based activated carbon; (b) acid modified coal-based activated carbon; (c) basic modified coal-based activated carbon; (d) combined modified coal-based activated carbon
圖 3 煤基活性炭甲烷吸脫附等溫曲線. (a) 原始煤基活性炭; (b)酸式改性煤基活性炭; (c)堿式改性煤基活性炭; (d)聯合改性煤基活性炭
Figure 3. Adsorption–desorption isotherms of coal-based activated carbons: (a) raw coal-based activated carbon; (b) acid modified coal-based activated carbon; (c) basic modified coal-based activated carbon; (d) combined modified coal-based activated carbon
圖 4 煤基活性炭甲烷吸附Langmuir等溫線. (a) 原始煤基活性炭; (b) 酸式改性煤基活性炭; (c)堿式改性煤基活性炭; (d) 聯合改性煤基活性炭
Figure 4. Adsorption Langmuir isotherms of coal-based activated carbons: (a) raw coal-based activated carbon; (b) acid modified coal-based activated carbon; (c) basic modified coal-based activated carbon; (d) combined modified coal-based activated carbon
圖 5 煤基活性炭甲烷吸附Freundlich等溫線. (a)原始煤基活性炭; (b)酸式改性煤基活性炭; (c)堿式改性煤基活性炭; (d)聯合改性煤基活性炭
Figure 5. Adsorption Freundlich isotherms of coal-based activated carbons: (a) raw coal-based activated carbon; (b) acid modified coal-based activated carbon; (c) basic modified coal-based activated carbon; (d) combined modified coal-based activated carbon
圖 6 煤基活性炭甲烷吸附量隨時間變化的擬合曲線
Figure 6. Fitting curve of the coal-based activated carbon methane adsorption capacity with time
表 1 煤基活性炭的孔隙結構參數
Table 1. Pore parameters of different coal-based activated carbons
Sample type code SBET/(m2?g?1) Vt/(cm3?g?1) Vmic /(cm3?g?1) Vmes/(cm3?g?1) Vmic/ Vt DV/nm 1 11.8887 0.0259 0.0057 0.0263 0.220 8.7142 H 20.5609 0.0475 0.0082 0.0477 0.173 9.2408 N 9.0909 0.0210 0.0046 0.0216 0.219 9.2400 H-N 19.8141 0.0339 0.0081 0.0319 0.239 6.8436 
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表 2 煤基活性炭等溫吸附模型參數
Table 2. Parameters of the coal-based activated carbon isotherm adsorption model
Sample type code Langmuir model parameters Freundlich model parameters a/
（mL?g?1）b/
MPa?1R2 k n R2 1 24.5483 1.429 0.99883 5.8596 2.8106 0.99234 H 21.5332 0.791 0.99885 3.1350 2.1792 0.99316 N 27.5847 1.299 0.99918 6.3002 2.7842 0.99013 H-N 30.8537 1.734 0.99917 8.4315 3.0915 0.98829
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表 3 煤基活性炭吸附熱力學參數
Table 3. Adsorption thermodynamic parameters of different coal-based activated carbons
Sample type code KP $ \Delta {G^{\ominus}} $/(kJ·mol?1) 1 143.936 ?12.952 H 12.061 ?6.490 N 168.098 ?13.357 H-N 728.509 ?17.179
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表 4 煤基活性炭吸附熱力學參數
Table 4. Adsorption kinetic parameters of different coal-based activated carbons
Sample type code K1/(min?1) q/(mL·g?1) R2 1 0.25627 22.7675 0.9897 H 0.21020 18.2642 0.9959 N 0.20903 25.6990 0.9910 H-N 0.28469 28.6625 0.9942
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