Jinan University Achieves Breakthrough in Propylene/Propane Separation

Recently, the research team at the Jinan University(JNU) based on the adsorption/desorption technology over metal‐organic frameworks (MOF) for the first time proposes an orthogonal array dynamic screening mechanism to successfully construct the separation mechanism‐based frame material (JNU‐3), which can be used in adsorptive separation of propylene from propane.MOF is a kind of crystalline porous materials with a definite composition and structure formed by self‐assembled metal nodes and organic ligands.Compared with the traditional porous materials (such as molecular sieves, activated carbon, etc.), MOF has customizable and tailorable frameworks and a variety of channel structures.The separation of olefins/alkanes by MOF is mainly based on the π electron complexation of bare metal sites and the screening function of channel size.The bare metal sites can co‐adsorb alkanes to some extent but cannot separate high‐purity olefins along with its moisture sensitivity.In contrast, the rigid molecular sieve effect can minimize the co‐adsorption of alkanes and maximize the olefin/alkanes selectivity.Since molecules with a matched right size must pass through a lot of pores, adsorption equilibrium cannot be reached, resulting in a slowed down adsorption/desorption kinetics and lower energy efficiency.

In order to grapple with the above‐mentioned problem,the research team has successfully constructed a 3D grid structure of the JNU‐3 material, in which the crystallographic A‐axis is a one‐dimensional channel of 4.5×5.3 A.On both sides of the one‐dimensional channel are the neatly arranged molecular pockets.The molecular pockets and the one-dimensional channel are connected by a dynamic “gourd shaped” window of about 3.7 A in diameter, which can selectively capture propylene molecules, leading to better propylene/propane separation effect.The research team by means of in‐situ single crystal diffraction and simulation calculations has shed light on the screening mechanism and dynamic process of the interactions between propylene/propane molecules and JNU‐3 material.

It has been discovered by research that when a mixture of propylene/propane (with a molar ratio of 50/50) at a temperature of 298K was routed under a flowrate of 1.0 mL/min through a packed bed, propane can pass the packed bed at first without being contaminated by propylene, and the purity of propane collected thereby can reach more than 99.99%.After a period of time the adsorbent will be saturated, and propylene begins to penetrate, and eventually propylene and propane in the exiting airflow can rapidly attain an equimolar concentration

In the course of propylene desorption when the flow rate of mixed gas reaches 1.0 mL/min and 6.0 mL/min, the propylene (with a purity of 99.5%) separation capacity can reach 34.2 L/kg and 53.5 L/kg, respectively, as revealed by the desorption curve.Under the conditions covering a relative humidity of 50% and a flowrate of propylene/propane equimolar mixture equating to 6.0 mL/min, the propylene (with a purity of 99.5%) separation capacity can reach 44.9 L/kg, which has demonstrated the excellent performance of JNU material.