Silver-Based Alcohol-Functionalized Solvent for Efficient Separation of Olefins

Abstract

Olefins are important chemical raw materials, and separating alkanes/olefins in oil products is very important. However, alkanes and olefins with the same number of carbons have similar physicochemical properties and structures; therefore, separating them is difficult. This study designed and synthesized a series of silver-based alcohol-functionalized solvents for separating the cyclohexene/cyclohexane system, based on the salt effect and the π–π* coordination between Ag⁺ and the unsaturated double bonds of olefins. We screened BF₄^–, which has a large ionic radius and weak interactions, as the anion and 1,2-propanediol (1,2-PG), which has two hydroxyl groups (−OH), as the organic ligand. We relied on the interactions between –OH in the ligand to affect the electron cloud density of Ag⁺ after it coordinated with –OH. This allows the empty orbitals of Ag⁺ remaining after coordination with two 1,2-PGs to ligate with the carbon–carbon double bond (–CC), achieving efficient, highly selective cyclohexene separation. At the same time, at a low cyclohexene concentration, compound [Ag­(cyclohexene)₂(1,2-PG)₂]­BF₄ also exhibited a strong salt effect, which further improved the selectivity and extraction capacity of cyclohexene. Under optimal operating conditions, with an initial cyclohexene concentration of 20 mol %, the distribution coefficient of cyclohexene was as high as 5.456, and the selectivity was as high as 1362. The single-stage extraction rate of cyclohexene reached 94.24%. Furthermore, in the 1-hexene/n-hexane system, the distribution coefficient of 1-hexene was as high as 6.733, and the selectivity was 647.4. These results are significantly better than those reported for other extractants. The silver-based alcohol-functionalized solvents developed in this study exhibit high efficiency and robust separation performance and are environmentally benign.