Purification of MDI Isomers Using Dynamic Falling Film Melt Crystallization: Experiment and Molecular Simulation

Xueying Lian; Peng He; Liguo Wang; Yan Cao; Kelin Huang; Shuang Xu; Jiaqiang Chen; Huiquan Li

doi:10.1021/acsomega.2c01021

Purification of MDI Isomers Using Dynamic Falling Film Melt Crystallization: Experiment and Molecular Simulation

ACS Omega. 2022 Jun 10;7(25):21492-21504. doi: 10.1021/acsomega.2c01021. eCollection 2022 Jun 28.

Authors

Xueying Lian^{1

2}, Peng He², Liguo Wang^{2

3}, Yan Cao², Kelin Huang¹, Shuang Xu², Jiaqiang Chen², Huiquan Li^{2

4}

Affiliations

¹ Guangxi Key Laboratory for Polysaccharide Materials and Modifications, key Laboratory of Chemical and Biological Transformation Process of Guangxi Higher Education Institutes, School of Chemistry and Chemical Engineering of Guangxi Minzu University, Nanning 530006, China.
² Key Laboratory of Green Process and Engineering, National Engineering Research Center of Green Recycling for Strategic Metal Resources, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China.
³ Dalian National Laboratory for Clean Energy, Dalian 116023, China.
⁴ School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.

Abstract

In this work, the isomer mixture of 4,4'-diphenylmethane diisocyanate (MDI) and 2,4'-MDI was separated and purified by dynamic falling film melt crystallization, and 99.3% purity and 50.8% yield of 4,4'-MDI could be obtained under optimized conditions. The separation mechanism was simulated by density functional theory (DFT) and molecular dynamics (MD) simulation. Results showed that compared with 2,4'-MDI, 4,4'-MDI molecules could form a more stable and symmetrical crystal structure due to their stronger charge density symmetry and electrostatic potential energy. Furthermore, the separation phenomenon and the formation of the crystal structure were observed according to the radial distribution function (RDF) and orientation correlation function obtained from MD simulation. Finally, the attachment energy (AE) model was used to observe and compare different crystal surfaces; it was proposed that the aggregation of 4,4'-MDI was attributed to the polar attraction between isocyanate groups according to the results of the orientation correlation function. It was also observed that compared with 2,4'-MDI, 4,4'-MDI molecules on the (110) crystal surface were easier to form crystal structures.