低碳烷烃烯烃在超微孔柔性Cu（Qc）2上的吸附行为

doi:10.11949/0438-1157.20210676

摘要/Abstract

摘要：

采用实验研究与分子模拟相结合的方法研究了低碳烷烃烯烃在超微孔柔性Cu(Qc)₂上的吸附热力学、动力学和吸附分离机理。用常温合成方法制备了超微孔金属-有机骨架材料Cu(Qc)₂，测定了低碳烷烃烯烃（CH₄/C₂H₄/C₂H₆/C₃H₆/C₃H₈）在Cu(Qc)₂上的吸附相平衡和吸附动力学。使用Materials Studio中的Fortcite模块模拟低碳烷烃烯烃在超微孔柔性Cu(Qc)₂上的吸附机理以及材料的结构形变。结果表明Cu(Qc)₂具有优良的C₂H₆/C₂H₄吸附选择性和吸附动力学，而对C₃H₈/C₃H₆的吸附选择性很低。273 K和0.1 MPa下，C₂H₆/C₂H₄在Cu(Qc)₂上的IAST选择性达4.6。298 K和0.05 MPa下C₂H₆/C₂H₄在Cu(Qc)₂上的扩散时间常数分别达1.42×10^-3和1.48×10^-3_{s^-1，扩散活化能分别为16.62 和16.43 kJ/mol。应用装填Cu(Qc)₂的固定床可在常温条件下实现C₂H₆/C₂H₄二元混合气的完全分离。模拟结果显示Cu(Qc)₂为二维堆叠结构，材料会由于吸附不同分子而发生不同程度的结构形变。甲烷易从变大的层间扩散脱附，导致其在材料上的吸附量很低；C₂H₆/C₂H₄两者都能稳定吸附在层中的孔道中，其分离推动力主要来源于两种气体在材料上明显的吸附热差异；C₃H₈/C₃H₆会分别吸附在两种不同的环境，吸附热差异小导致Cu(Qc)₂对C₃H₈/C₃H₆的吸附选择性低。}

关键词: Cu(Qc)₂, 吸附, 分离, 烷烃/烯烃, 动力学

Abstract:

The adsorption thermodynamics, kinetics and separation behavior of light alkanes/alkenes (CH₄/C₂H₄/C₂H₆/C₃H₆/C₃H₈) on ultramicroporous and flexible metal-organic frameworks (MOFs) Cu(Qc)₂ were systematically studied by using combination of experimental and simulation methods. Ultramicroporous and flexible Cu(Qc)₂ was synthesized using a room temperature synthesis method for alkanes/alkenes separation. The adsorption isotherms and kinetic curves of these alkanes/alkenes on Cu(Qc)₂ were measured. The adsorption behavior of these light hydrocarbons on the Cu(Qc)₂ and the deformation of the material structure were studied by means of the Fortcite module of the Materials Studio. The results showed that Cu(Qc)₂ had excellent C₂H₆ /C₂H₄ adsorption selectivity and adsorption kinetics, while its adsorption selectivity to C₃H₈ /C₃H₆ was very weak. At 273 K and 0.1 MPa, the IAST selectivity of Cu(Qc)₂ for C₂H₆/C₂H₄ reached as high as 4.6. At 298 K and 0.05 MPa, the diffusion time constants of C₂H₆ and C₂H₄on Cu(Qc)₂ reached 1.42×10^-3 and 1.48×10^-3 s^-1, respectively, and the activation energy of diffusion was 16.62 and 16.43 kJ/mol, respectively. The application of fixed bed packed with Cu(Qc)₂ can realize the complete separation of C₂H₆/C₂H₄ binary mixture under normal temperature conditions. The simulation results showed that Cu(Qc)₂ was a two-dimensional stack structure, which would undergo different degrees of structural deformation when different molecules were adsorbed. Methane would be ready to diffuse and desorb from the enlarged layer, resulting in a very low adsorption capacity; both C₂H₆ and C₂H₄ can be stably adsorbed in the pores in the layer, and the separation driving force mainly comes from the difference in the adsorption heats of the two molecules; C₃H₈ and C₃H₆ would be separately adsorbed in two different environments of Cu(Qc)₂, and the small difference in adsorption heats of these molecules makes the C₃H₈/C₃H₆ adsorption selectivity low.

Key words: Cu(Qc)₂, adsorption, separation, alkanes/alkenes, kinetics

中图分类号:

TQ 028.1

唐瑜佞, 王勋, 彭俊洁, 吴颖, 李忠. 低碳烷烃烯烃在超微孔柔性Cu（Qc）₂上的吸附行为[J]. 化工学报, 2021, 72(11): 5664-5674.

Yuning TANG, Xun WANG, Junjie PENG, Ying WU, Zhong LI. Adsorption behavior of light alkanes/ alkenes on ultramicroporous flexible Cu(Qc)₂[J]. CIESC Journal, 2021, 72(11): 5664-5674.

图/表 12

图1 Cu(Qc)2的SEM图

Fig.1 SEM image of the as-synthesized Cu(Qc)2

图2 Cu(Qc)2的晶体结构

Fig.2 Crystal structure of Cu(Qc)2

图3 Cu(Qc)2的热重分析曲线

Fig.3 Thermogravimetric analysis curve of Cu(Qc)2

图4 Cu(Qc)2对CO2的吸附-脱附等温线(196 K)

Fig.4 CO2 adsorption-desorption isotherms at 196 K of Cu(Qc)2

图5 不同温度下烷烃烯烃吸附等温线

Fig.5 Adsorption isotherms of alkanes/alkenes at different temperatures

图6 烷烃烯烃在Cu(Qc)2上的等容吸附热

Fig.6 Isosteric heats of alkanes/alkenes adsorption on Cu(Qc)2

图7 不同温度下Cu(Qc)2对C2H6/C2H4的吸附选择性

Fig.7 Selectivity of Cu(Qc)2 for C2H6/C2H4 mixture at different temperatures

图8 不同温度和0.5 bar下Cu(Qc)2对C2H6/C2H4的吸附动力学曲线

Fig.8 Experimental kinetic adsorption curves of C2H6/C2H4 in Cu(Qc)2 at different temperatures and 0.5 bar

表1 C2H6 /C2H4在Cu（Qc）2和其他吸附剂上的扩散时间常数比较

Table 1 Comparison of diffusion time constants of C2H6/C2H4 in Cu（Qc）2 and other adsorbents

材料	温度/K	D/r²×10³/s^-1		文献
材料	温度/K	C₂H₄	C₂H₆	文献
Cu(Qc)₂	298	1.48	1.42	本文
Cu(Qc)₂	303	1.72	1.61	本文
Cu(Qc)₂	308	1.94	1.77	本文
Ag-Ca-4A	298	0.98	—	[46]
Ag⁺-resin	298	0.103	0.107	[47]

图9 C2H6/C2H4 (1∶1)在Cu(Qc)2固定床上的吸附透过曲线(298 K)

Fig.9 Breakthrough curves of C2H6/C2H4 (1∶1) through the fixed bed of Cu(Qc)2 (298 K)

图10 Cu(Qc)2在不吸附或分别吸附甲烷、乙烷、乙烯、丙烷、丙烯情况下的稳态(总能量最低)结构原子颜色:Cu 橙色,N 蓝色,O 红色,C 灰色, H 白色

Fig.10 Optimized structure of Cu(Qc)2 when adsorbing no gas, methane, ethane, ethylene, propane and propene, respectivelyColor code: Cu orange, N blue,O red,C gray, H white

图11 结构优化过程中不同吸附质分子对Cu(Qc)2结构密度的影响

Fig.11 Influence of different adsorbates on the density of Cu(Qc)2 during structural optimization

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低碳烷烃烯烃在超微孔柔性Cu（Qc）₂上的吸附行为

Adsorption behavior of light alkanes/ alkenes on ultramicroporous flexible Cu(Qc)₂

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