基于微量热法对多孔碳与双氧水相互作用过程的传质阻力分析

doi:10.11949/0438-1157.20220260

摘要/Abstract

摘要：

多孔材料作为催化剂对现代化学工业起到重要推动作用，但其纳米受限孔道造成的界面传递问题不容忽视。直接法合成双氧水（H₂O₂）过程中，揭示H₂O₂脱附过程传递与反应竞争博弈的介尺度机制是提高产率的关键。线性非平衡热力学为解耦界面扩散及反应提供了统一框架，但缺少合适通量测定方法。因此，本文设计多孔碳与H₂O₂相互作用的微量热实验，结合分子模拟及孔结构表征实验揭示多孔碳材料的界面传递结构，实现了非平衡热力学的定量传质阻力分析，进一步获取了表界面浓度场的动态变化。研究结果表明：微量热法是定量解耦并揭示扩散-反应机制的有效线性非平衡热力学阻力分析方法；介孔结构、生物骨架结构及担载1%（质量） Pd元素均能增强H₂O₂在多孔碳中的传质通量，但实现超高通量需要扩散与反应阻力的匹配；非平衡热力学阻力解耦方法是揭示多相反应过程介尺度机制的重要定量描述方法，有望为过程的调控及优化提供理论依据。

关键词: 多孔材料, 界面传递, 介尺度, 非平衡热力学, 扩散, 反应, 微量热, 传质阻力

Abstract:

Porous materials play an important role in modern chemical industry, but the interfacial transfer phenomena caused by their nano-confinement pores cannot be ignored. For direct oxidation synthesizing hydrogen peroxide (H₂O₂), revealing the mesoscale relationship between mass transfer of desorbing H₂O₂ and reaction is the key to improving the yield. Linearized non-equilibrium thermodynamics has provided a unified framework for decoupling the interfacial diffusion and reaction, but in this case, a suitable method of measuring mass transfer flux was lacked. Therefore, the microcalorimetry experiments measuring the heat effect of interaction between porous carbons and H₂O₂ were designed in this paper. With the help of molecular simulation and pore characterization, the structures for interfacial transfer were revealed, and the quantitative mass transfer resistance analysis of non-equilibrium thermodynamics was realized, then the dynamic change of H₂O₂ concentration was obtained. The results showed that microcalorimetry is an effective linearized non-equilibrium thermodynamic resistance analysis method. Mesoporous structure, biological skeleton texture and supporting 1%(mass) palladium can enhance the mass transfer flux of H₂O₂ in porous carbon, but the realization of ultra-high flux requires the matching of diffusion and reaction resistance. The resistance decoupling of non-equilibrium thermodynamics is an important quantitative description method to reveal the mesoscale mechanism of heterogeneous reaction process, which is expected to provide a theoretical basis for the regulation and optimization of the process.

Key words: porous material, interfacial transfer, mesoscale, non-equilibrium thermodynamics, diffusion, reaction, microcalorimetry, mass transfer resistance

中图分类号:

O 414.19

曹健, 叶南南, 蒋管聪, 覃瑶, 王士博, 朱家华, 陆小华. 基于微量热法对多孔碳与双氧水相互作用过程的传质阻力分析[J]. 化工学报, 2022, 73(6): 2543-2551.

Jian CAO, Nannan YE, Guancong JIANG, Yao QIN, Shibo WANG, Jiahua ZHU, Xiaohua LU. Mass transfer resistance analysis of the interaction between porous carbon and hydrogen peroxide based on microcalorimetry[J]. CIESC Journal, 2022, 73(6): 2543-2551.

图/表 10

表1 本实验所用试剂及材料

Table1 Reagents and materials used in this experiment

化学品	CAS号	纯度（质量分数）	供应商
H₂O₂	7722-84-1	≥30%	上海凌峰化学试剂有限公司
正丙醇	71-23-8	99.7%	Aladdin
氯化钾	7758-02-3	≥99.995%	Aladdin
商业碳Cabot	—	—	美国卡博特公司 (型号：Norit)
生物骨架碳BioMC	—	—	实验室自制
1% Pd/BioMC	—	—	实验室自制
1% Pd/Cabot	—	—	实验室自制
超纯水	—	—	实验室超纯水机自制 (型号：PLUS-E2-10TJ)

图1 线性非平衡热力学传质模型

Fig.1 Linear non-equilibrium thermodynamic mass transfer model

图2 多孔碳反应/吸附H2O2过程示意图

Fig.2 Schematic diagram of reaction or adsorption between porous carbon and H2O2

图3 四种多孔碳材料与H2O2相互作用的微量热实验结果

Fig.3 Microthermal experiment results of interaction between four porous carbon materials and H2O2

表2 多孔碳材料的BET表征结果

Table 2 The BET characterization of porous carbon materials

多孔碳材料	比表面积 a_p/ (m²/g)	孔容V_g/(m³/g)
多孔碳材料	比表面积 a_p/ (m²/g)	介孔	微孔
Cabot	705	0.414×10^-6	0.241×10^-6
BioMC	863	1.561×10^-6	0.160×10^-6
1% Pd/Cabot	796	0.424×10^-6	0.287×10^-6
1% Pd/BioMC	927	1.619×10^-6	0.181×10^-6

图4 H2O2的传质通量

Fig.4 Mass transfer flux of H2O2

图5 四种多孔碳材料的总传质阻力

Fig.5 Total mass transfer resistance of four porous carbon materials

表3 传质系数求解结果

Table 3 Results of mass transfer coefficients

传质系数	数值
k_s,null/ (mg/(m²·s))	1.516×10^-5
k_s,pd/ (mg/(m²·s))	3.988×10^-4
k_d,meso/ (mg/(m³·s))	2.038×10⁵
k_d,micro/ (mg/(m³·s))	8.318×10⁴

图6 界面处H2O2浓度的时空变化

Fig.6 Temporal and spatial variation of H2O2 concentration at the interface

表4 四种多孔碳的传质阻力分布

Table 4 Mass transfer resistance distribution of four porous carbons

多孔碳材料	扩散阻力 $\frac{1}{k_{d} A}$ /(s/mg)			反应阻力 $\frac{1}{k_{s} a_{p}}$ / (s/mg)	总阻力 $\frac{1}{K_{A}}$ / (s/mg)
多孔碳材料	介孔阻力 $\frac{1}{k_{d, m e s o} V_{m e s o}}$	微孔阻力 $\frac{1}{k_{d, m i c r o} V_{m i c r o}}$	扩散总阻力	反应阻力 $\frac{1}{k_{s} a_{p}}$ / (s/mg)	总阻力 $\frac{1}{K_{A}}$ / (s/mg)
1%(质量)Pd/BioMC	101	2221	97	90	187
1%(质量)Pd/Cabot	388	1406	1794	105	1899
BioMC	105	2523	100	3466	3566
Cabot	398	1674	2072	4323	6395

表4 四种多孔碳的传质阻力分布

Table 4 Mass transfer resistance distribution of four porous carbons

多孔碳材料	扩散阻力 $\frac{1}{k_{d} A}$ /(s/mg)			反应阻力 $\frac{1}{k_{s} a_{p}}$ / (s/mg)	总阻力 $\frac{1}{K_{A}}$ / (s/mg)
多孔碳材料	介孔阻力 $\frac{1}{k_{d, m e s o} V_{m e s o}}$	微孔阻力 $\frac{1}{k_{d, m i c r o} V_{m i c r o}}$	扩散总阻力	反应阻力 $\frac{1}{k_{s} a_{p}}$ / (s/mg)	总阻力 $\frac{1}{K_{A}}$ / (s/mg)
1%(质量)Pd/BioMC	101	2221	97	90	187
1%(质量)Pd/Cabot	388	1406	1794	105	1899
BioMC	105	2523	100	3466	3566
Cabot	398	1674	2072	4323	6395

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