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摘要: 本研究采用溶胶-凝胶法制备了MWCNTs摩尔比例分别为38%、52%和66%的多壁碳纳米管-二氧化硅复合吸附剂MWCNTs-SiO2-2、MWCNTs-SiO2-4、MWCNTs-SiO2-6 (CS2、CS4、CS6)。研究了MWCNTs含量、温度(30−60 ℃)、水蒸气浓度(1%−5%)和循环次数对甲苯吸附量的影响,并进行了吸附动力学分析。研究结果表明: 在30−60 ℃内,吸附甲苯的能力大小为:AC(活性炭) < CS2 < CS4 < CS6,其中CS6对甲苯的吸附量高达50.28 mg/g。温度每升高10 ℃,穿透时间降低10−20 min,水蒸气浓度每增加1%,吸附含量约下降3.5%。甲苯传质速率最快的阶段可用准二级吸附动力学模型很好的描述,此时,粒内扩散起主要作用。MWCNTs摩尔百分比为38%−66%,含量越多越易于吸附甲苯,且再生后的MWCNTs-SiO2吸附剂官能团种类不发生改变,仍能保持良好的吸附性能。Abstract: In this study, multi-walled carbon nanotube (MWCNTs)-SiO2 composite adsorbents MWCNTs-SiO2-2, MWCNTs-SiO2-4, MWCNTs-SiO2-6 (CS2, CS4, CS6) with molar percentages of MWCNTs of 38%, 52%, and 66% were synthesized using the sol-gel method. The effects of the MWCNT content, temperature (30−60 °C), water vapor concentration (1%−5%), and the number of cycles on the adsorption capacity of toluene were studied, and an adsorption kinetics analysis was performed. The results showed that the adsorption capacity for toluene at 30−60 °C was AC (activated carbon) < CS2 < CS4 < CS6, and the adsorption capacity of CS6 to toluene was up to 50.28 mg/g. For every 10 °C increase in temperature, the penetration time decreased by 10−20 min, and the adsorption content decreased by 3.5% for every 1% increase in water vapor concentration. The phase with the fastest mass transfer rate of toluene could be described by the quasi-secondary adsorption kinetics model, in which intraparticle diffusion plays a major role. The mole percentage of MWCNTs ranged from 38% to 66%, the higher the content was, the easier it was to adsorb toluene. The functional group types of the MWCNTs-SiO2 adsorbent after regeneration did not change, and the adsorbent maintained good adsorption performance.
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Table 1 Textural properties of MWCNTs-SiO2 composites
Adsorbent Average
pore diameter
/nmBET surface
area
/(m2·g−1)Total
pore volume
/(cm3·g−1)Micropore volume
/(cm3·g−1)Micropore surface
area
/(m2·g−1)AC 0.635 936.124 1.034 − − CS2 0.478 1671.678 1.251 0.12 245.47 CS4 0.483 1299.342 1.137 0.24 394.53 CS6 0.492 946.055 0.916 0.28 465.33 Table 2 Fitting related parameters of each sample model
Mathematical model Sample qe /(mg·g−1) k1.ad /(g·mg−1·min−1) R2 P ${\rm{ln} }\left( { {q_{\rm{e} } } - {q_{{t} } } } \right) = {\rm{ln} }{q_{\rm{e} } } - {k_{1.{\rm{ad} } } }t$ CS2 42.2 0.026 0.845 −0.919 CS4 49.72 0.027 0.900 −0.949 CS6 50.28 0.021 0.839 −0.916 $\dfrac{t}{ { {q_{{t} } } } } = \dfrac{1}{ { {k_{2.{\rm{ad} } }q_{\rm{e} }^2} } } + \dfrac{1}{ {q_{\rm{e} } } }t$ CS2 42.2 0.00058 0.997 0.998 CS4 49.72 0.00045 0.995 0.992 CS6 50.28 0.0003 0.992 0.992 ${q_{{t} } } = {k_{ {\rm{pi} } } }{t^{0.5} } + C$ CS2 3.4378 −9.1951 0.969 0.98 CS4 3.7524 −12.397 0.97 0.99 CS6 4.296 −15.47 0.98 0.986 ${q_{{t} } } = \dfrac{1}{\beta }{\rm{ln} }\left( {\alpha \beta } \right) + \dfrac{1}{\beta }{\rm{ln} }t$ CS2 0.968 0.065 0.94 0.94 CS4 0.827 0.059 0.92 0.96 CS6 0.674 0.054 0.91 0.95 note: k1.ad and k2.ad are the first and second rate constants respectively, g·mg−1·min−1. qt is the toluene absorption of MWCNTs-SiO2 at time t, mg·g−1; kpi is the intraparticle diffusion rate constant, mg·(g·min0.5)−1; α, β and C are constants -
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