Direct Separation of Olefins from Aromatics or Sulfides: Influence of the Structure and Content of Olefins and Aromatics

In order to disclose the separation of olefins from aromatics or thiophene compounds by organic solvents, vapor-liquid equilibrium data for ternary systems of olefins + aromatics/thiophenes + sulfolane (SUL) /N-methyl-2-pyrrolidone (NMP) were investigated at atmospheric pressure in a modified Rose dual-circulating vapor liquid distiller. This work primarily focused on studying the relationship between separation efficiency on olefins and the structure and concentration of olefins and aromatics. From the point view of structure, the results showed that more methyl existing on both olefins and aromatics could lead to stronger hydrogen bond interaction with solvents than that of olefins and aromatics, which do not indude methyl in their molecular structure. So there was higher olefin-separating efficiency for the systems containing 1-hexene (HEX)/3-methylthiophene (MTHI)/1,2,4-trimethylbenzene (TMB) than those of 2,4,4-trimethylpentene (TMP)/thiophene (THI)/toluene (TOL), respectively. Besides, when it came to the concentration of olefins or aromatics in model gasoline, the effect of separating olefin appeared remarkable when the concentration of olefins was below 40% or the concentration of aromatics was above 60%. When the separation effect of solvents was compared, the SUL outperformed the NMP because of the large relative volatility observed for the systems of "HEX + THI/MTHI/TOL/TMB". It is worth noting that the two oxygen atoms on SUL locating the same orientation help form stronger hydrogen bonds between compounds and SUL than that of NMP. These findings powerfully facilitated the structure-effect relationship for separation of olefins from aromatic chemical compounds, which give a clear direction for upgrading of clean gasoline by efficient separation of olefins and removal of sulfides from FCC gasoline.