State of the art, challenges and prospects in metal–organic frameworks for the separation of binary propylene/propane mixtures

Propylene (C₃H₆) as one of the most crucial raw chemical materials has been widely used in the chemical industry. The high-purity C₃H₆ (higher than 99.5 %) is in great demand for producing polypropylene or other chemical products. C₃H₆ is nevertheless mostly produced by steam cracking naphtha or dry gas refining and is invariably blended with minor impurity gases like propane (C₃H₈). At present, the petrochemical industry depends almost exclusively on the heat-driven cryogenic distillation process for C₃H₆ purification. However, both C₃H₆ and C₃H₈ molecules have very similar physical properties (such as kinetic diameter, boiling point, polarity, etc.), which makes conventional cryogenic distillation inefficient and energy-intensive. To decrease energy consumption, cost-efficient, and tend to be environmentally friendly, adsorptive-based separation using porous materials is expected to accomplish C₃H₆ purification from C₃H₆/C₃H₈ mixtures under ambient conditions. In particular, metal–organic frameworks (MOFs) with high porosity, regular adjustable pore shape and pore environment have promising advantages as porous adsorbents for C₃H₆ purification. This thesis provides an in-depth review of the present MOF materials that show promise for the separation of C₃H₆/C₃H₈ mixtures using adsorptive technology. It focuses particularly on recent developments in the usage of MOFs to achieve reversed C₃H₆/C₃H₈ separation. Meanwhile, we interpret the separation mechanism and further classify the relevant mechanisms of flexible materials, then we also summarize the separation research methods, and related techniques. Ultimately, we propose a bold conjecture regarding the future perspectives and urgent problems in the exploitation of MOFs for C₃H₆ purification in industry and the academic community and give possible development directions.