Advances in Engineering Advances in Engineering features breaking research judged by Advances in Engineering advisory team to be of key importance in the Engineering field. Papers are selected from over 10,000 published each week from most peer reviewed journals.
Significance
Light olefins are major raw materials in the production of petrochemical and polymers. Unfortunately, the difficulty in separating olefins from alkanes attributed to their similar physicochemical properties is still a challenge. Despite the effectiveness of separation methods such as distillation and extraction, no method for separation of halogenated alkanes-olefins has been reported in the literature. Thus, development of alternative and efficient separation processes is highly desirable.
To this note, Chinese Academy of Sciences scientists: Yujia Zhang, Yinxiang Xu, Dr. Junbo Xu, and Professor Chao Yang screened a series of zeolites to separate a mixture of 1-chloropropane (C3H7Cl) and allyl chloride (C3H5Cl) through molecular simulation method. Their work is currently published in the research journal, Chemical Engineering Science.
Zeolites are generally excellent materials for the separation of mixtures due to their properties: high specific surface area, shape selectivity, and appropriate pore size. Using molecular simulation, the authors reasonably obtained accurate and reliable adsorption and diffusion data for both 1-chloropropane and allyl chloride in different zeolites. Also, the structures of zeolites, molecules and dipole moments were optimized through the calculation of the density functional theory. The screening process continued by verification of the diffusion characteristics of the zeolites to determine the membrane flux data through the non-equilibrium molecular dynamics method. This further enables the isolation of zeolites with specific pore geometry.
Zeolites exhibited preference characteristics of adsorption of polar and unsaturated molecules. To this note, under the same operation conditions, adsorption of C3H5Cl was easier with a greater adsorption capacity as compared to C3H7Cl. Among the different zeolites screened i.e. AHT, SBN, PAR, they only adsorbed C3H5Cl but not C3H7Cl due to their adsorption differences. This was attributed to their one-dimension elliptical pore with similar sizes matching their low energy conformation.
Based on the flux data of the membrane of the zeolites, the authors confirmed that they are of great importance in separating a mixture of C3H5Cl / C3H7Cl with ultrahigh selectivity. Furthermore, the thermodynamic analysis was carried out. Both the conformations of C3H5Cl and C3H7Cl were well matched with the pore geometry at 00. However, C3H7Cl required high energy to reach the 00 conformations than C3H5Cl which made it difficult to diffuse into the zeolites. Thus, a pore geometry-based conformation recognition mechanism was proposed for this separation and adsorption phenomena.
Dr. Junbo Xu, the corresponding author in a statement to Advances in Engineering noted that a combination of Grand Canonical Monte Carlo and Non-equilibrium molecular dynamics methods for fast screening of a series of zeolites for separation of C3H5Cl/ C3H7Cl mixture was a great success. Whereas the former was used to primarily screen the materials, the later was further used to verify the diffusion path and obtain flux data. In a nutshell, he is hopefully their study will provide a platform for designing and/or screening nanoporous materials for alkanes-olefins separation.
Only C3H5Cl (marked with yellow) that can twist to the pore preferred cis-conformation with lower energy penalty than C3H7Cl can cross the zeolites.
Reference
Zhang, Y., Xu, Y., Xu, J., & Yang, C. (2019). Computational screening of zeolites for C3H7Cl/C3H5Cl separation and a conformation based separation mechanism. Chemical Engineering Science, 203, 212-219.
