A Type III porous liquid with high separation performance for linear/branched C4 olefin mixtures

Abstract

C₄ olefins are essential petrochemical feedstocks, yet their separation remains highly challenging and energy-intensive due to their similar boiling points. This study introduces a green Type III porous liquid platform designed for efficiently separating linear and branched butenes, prepared by dispersing metal–organic framework (CALF-20M) nanoparticles into the sterically hindered solvent 1,3-dimethyl-2-imidazolidinone (DMI). At an optimal particle loading of 30 wt%, the system achieved exceptional separation factors (294.9 for 1,3-butadiene/iso-butene and 122.5 for 1-butene/iso-butene) while maintaining a low viscosity that decreased from 10.00 cP at 293.2 K to 6.35 cP at 353.2 K. The desorption heats of 1-butene and 1,3-butadiene ranged from 46.97 to 7.98 kJ mol⁻¹ and from 56.27 to 16.75 kJ mol⁻¹, respectively, decreasing with increasing gas uptake. Complete desorption was accomplished under vacuum at 353.2 K within 45 minutes, and the material exhibited excellent stability over seven consecutive adsorption–desorption cycles without detectable performance degradation. Its selectivity toward linear versus branched olefins significantly exceeds that of conventional membranes and most adsorption-based separations using solid porous adsorbents. The combination of environmental friendliness, high separation efficiency, excellent fluidity, and robust stability makes this system highly promising for the continuous separation of C₄ olefins.