2. Aromatic-N Alkane Separation
The Selectivity and distribution coefficient are defined as
S = (X2II/X2I) / (X1II/X1I)
Here, X2II and X1II are mole fraction of aromatic and aliphatic component in extract phase respectively.
X2I and X1I are mole fraction of aromatic and aliphatic component in raffinate phase phase respectively. The extract phase is the ionic liquid rich phase and the raffinate phase is the aliphatic rich phase.
D2 = X2II/X2I
D2 is the distribution coefficient of aromatic component.
It is desired that the value of selectivity and distribution coefficient be large for a solvent so that lesser amount of solvent is required for extraction. Generally an optimum value of selectivity and distribution coefficient is chosen.
Separation…show more content… The interaction of aromatic compounds with ionic liquids is by sandwich like structure formation between the ionic liquid cation and the aromatic component. The ∏-∏ bond between the aromatics and the ionic liquid cation ring favors the interaction of aromatics with ionic liquids . The solubility of various hydrocarbons with ionic liquids decreases from aromatics> cyclic hydrocarbons> olefins> n-paraffins. This is as per the decreases of the ease of interaction of ionic liquids with the hydrocarbons. The aromatic nature decreases from aromatic hydrocarbon to n-alkane. The widest area of immiscibility is observed with n-alkanes . As the n-alkane chain length increases, the immiscibility region of the ternary phase diagram increases. This is irrespective to the ionic liquid used. The solubility of ionic liquids in the aliphatics is negligible. The tie line points of the raffinate phase lie on the binary mixture line of aromatic/aliphatic in the ternary diagram. This indicates that the raffinate phase does not require recovery of ionic liquid from it. This results in saving of cost and energy for the regeneration of ionic…show more content… It is in most cases higher than the traditionally used organic solvent Sulfolane. Much analysis has been done on the usefulness of ionic liquids as compared to Sulfolane for selective extraction of aromatics [1, 2, 19, 20]. The solubility of n-alkanes in ionic liquid is least and it decreases with increase in the chain length of the n-alkane, as the ionic liquid aromatic cation cannot dissolve the longer chain n-alkane hydrocarbon with relatively more paraffinic nature . As the alkyl chain length on the aromatic ring increases, its solubility in the ionic liquid decreases, as the aromatic character of the hydrocarbon then shifts more towards paraffinic. This is ahown in the work of M. S. Al-Tuwaim et al. . The selectivity decreases as the amount of aromatics in feed increases. This is because the interactions between the aromatics and the ionic liquid cation weakens in the presence of more paraffinic hydrocarocarbons