多孔炭吸附剂的乙烯-乙烷选择性反转机制

doi:10.11949/0438-1157.20210125

摘要/Abstract

摘要：

烯烃是重要的化工原料，吸附分离技术可在温和工况下实现烯烃纯化，而吸附剂的烷烃选择性是实现高效化工分离过程的关键。基于分子模拟，提出调节孔道尺寸以控制多孔炭优先吸附乙烯或乙烷的选择性反转机制；控制活化条件，实验制备出不同孔径的多孔炭材料并验证了乙烯-乙烷选择性反转规律。结果表明，多孔炭的石墨化表面优先吸附乙烷；随着孔径尺寸的增大，可出现优先吸附乙烯的孔道区间；若孔径进一步增大，多孔炭可回归到优先吸附乙烷的石墨化表面吸附特征。选择性反转机制适用于不同形状的孔道结构。因此，可利用微孔孔道的限域作用放大多孔炭表面的烷烃选择性，并得到高性能的烷烃选择性吸附剂。

关键词: 吸附, 分离, 烷烃选择性, 多孔炭, 分子模拟

Abstract:

Alkenes are important raw materials in chemical industry. Adsorption separation technology can achieve alkene purification under mild working conditions. Adsorbent of alkane selectivity is the key to achieve effective chemical separation processes. With the help of molecular simulation, we proposed the mechanism of tuning ethane/ethylene selectivity by controlling pore size. Porous carbon adsorbents with distinct average pore size, showing ethylene and ethane selectivity, were prepared via different activation processes. The experimentally validated mechanism suggests that: (1) Graphene surface is ethane-selective; (2) Porous carbon undergoes the reversed selectivity of ethane-ethylene-ethane with the increase in its pore size. This mechanism can be applied to porous carbon of different pore shapes. Hence, effective alkane-selective adsorbent can be obtained by amplifying the alkane-selective feature within the confined micropore of the porous carbon adsorbent.

Key words: adsorption, separation, alkane-selective, porous carbon, molecular simulation

中图分类号:

TQ 028.1

温怡静, 张博, 陈晓霏, 赵思洋, 周欣, 黄艳, 李忠. 多孔炭吸附剂的乙烯-乙烷选择性反转机制[J]. 化工学报, 2021, 72(9): 4768-4774.

Yijing WEN, Bo ZHANG, Xiaofei CHEN, Siyang ZHAO, Xin ZHOU, Yan HUANG, Zhong LI. Selectivity reversion mechanism of porous carbon for ethane-ethylene separation[J]. CIESC Journal, 2021, 72(9): 4768-4774.

图/表 7

图1 石墨化碳层模型C510H62 (a)；狭缝孔模型C510H62×2(b) ；孔径示意图（灰色球代表碳原子，白色球代表氢原子）(c)

Fig.1 Molecular models of graphitic carbon layer C510H62(a); Slit pore C510H62×2 (b); Schematic diagram of aperture (Gray and white balls represent carbon and hydrogen atoms, respectively)(c)

图2 DFT优化结构后的乙烯(a)、乙烷(b)分子模型

Fig.2 Molecular models of ethylene (a) and ethane(b) after DFT geometrically optimization

表1 乙烯和乙烷的分子动力学直径和最小分子笼的尺寸

Table 1 Kinetic diameter and molecular cage size of ethylene and ethane

吸附质	动力学直径^[31]/?	最小分子笼尺寸
吸附质	动力学直径^[31]/?	x/?	y/?	z/?
乙烯	4.16	5.09	4.35	3.98
乙烷	4.44	5.11	4.34	4.58

图3 碳层表面对乙烯、乙烷的放热吸附焓(a)；乙烯(b)和乙烷(c)在碳层表面的吸附构型

Fig.3 Exothermic adsorption enthalpies of ethylene, ethane on the surface of graphitic carbon(a); Adsorption configuration of ethylene(b) and ethane (c) on the surface of graphitic carbon

图4 乙烯和乙烷的放热吸附焓随孔道尺寸变化的规律(a)；发生选择性反转时乙烯(b)和乙烷(c)在孔道中的吸附构型

Fig.4 Exothermic adsorption enthalpies of ethylene and ethane changes with the size of slit pore(a); The adsorption configuration of ethylene (b) and ethane(c) in the pore when selectivity reversion occurs

图5 两种多孔炭常温下的乙烯和乙烷等温线(a)；平均孔径(b)

Fig.5 Ethylene and ethane isotherms at room temperature(a), average pore diameter (b) of two kinds of carbon materials

图6 乙烯和乙烷的放热吸附焓随孔道尺寸变化的规律

Fig.6 Exothermic adsorption enthalpies of ethylene and ethane changing with pore size

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