Recently, Ye Mao, a researcher at the National Engineering Laboratory of Methanol to Alkenes, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, and Liu Zhongmin, a member of the Chinese Academy of Sciences, have made new progress in the study of mass transfer of nanoporous crystalline materials. Related work was published in the form of a newsletter in the new publication "Communications Chemistry" of "Nature" Publishing Group. Nanoporous crystal materials have been widely used in heterogeneous catalysis and chemical separation processes. Common nanoporous crystal materials include various molecular sieves and metal organic framework materials (MOF).
Due to the size limitation of nanopores, the mass transfer process of guest molecules in such materials is very complicated and has a decisive influence on many catalytic reactions and separation processes. For a long time, the diffusion of guest molecules in the crystal channels is considered to be the step of controlling the mass transfer rate. But in fact, due to changes in the external environment of the material and natural defects existing at the surface interface of the material, the guest molecules also have mass transfer resistance at the surface interface before entering the internal pores of the crystal. At present, conventional methods cannot independently measure the surface mass transfer resistance coefficient and intragranular diffusion coefficient of nanoporous crystal materials. The measured result is actually an apparent diffusion coefficient, which also includes the surface interface mass transfer resistance and the pore channel The influence of diffusion resistance is difficult to be directly used in the design and optimization of nanoporous crystalline materials.
In this work, the team derived a method for calculating the mass transfer resistance of guest molecules at the surface interface of nanoporous crystalline materials. The method has simple mathematical form and clear physical meaning. Using this method, the mass transfer rate at the surface of the material and the diffusion rate in the crystal channel can be directly calculated from the simple guest molecule absorption rate curve. The results of NMR experiments verified the reliability of the method. Using this method, the researchers investigated in detail the effects of the crystal size, crystal interface properties, and environmental factors of the silicon aluminum phosphate (SAPO) molecular sieve on the surface interface mass transfer and diffusion in the pores.
This method opens up a simple and convenient way to quantitatively study the mass transfer process of guest molecules in nanoporous crystalline materials. It has strong universality and can be used for mass transfer studies of nanoporous crystalline materials such as molecular sieves and MOF.
The above research work was supported by the National Natural Science Foundation of China's major research project integration project of "Mesoscale Mechanism and Regulation in the Process of Multiphase Reaction".
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