Liquid–Liquid Extraction of Toluene from n-Heptane Using Butane-1,4-diol + 2-Methyl-pentane-2,4-diol Liquid Mixtures

Abstract

In order to investigate the effect of using 2-methyl-2,4-pentanediol as a co-solvent to 1,4-butanediol in the extraction of toluene from n-heptane, liquid–liquid equilibrium (LLE) phase compositions (tie-line data) were experimentally measured and thermodynamically modeled for the system n-heptane + toluene + 1,4-butanediol + 2-methyl-2,4-pentanediol at 298.2 and 313.2 K and 0.1 MPa. The direct analytical method was used to obtain the LLE data using a double-walled glass cell. The phase equilibrium samples were quantitatively analyzed using gas chromatography. The quaternary systems were successfully correlated using the NRTL and UNIQUAC thermodynamic models. Selectivity and solvent capacity were evaluated at various concentrations of co-solvent and compared to that of using pure 1,4-butanediol. The pseudo-ternary systems studied were found to demonstrate type II or type I phase behavior depending on temperature and co-solvent concentration. The presence of 2-methyl-2,4-pentanediol was found to have significantly improved solvent capacity at the cost of reduced selectivity.

Use of Glycerol + 2-Methylpentane-2,4-diol Liquid Mixtures in the Separation of Toluene from n-Heptane via Liquid–Liquid Extraction

“…The experimental method used to perform the measurements was the direct analytical method, which involves charging an equilibrium cell with the solvent and carrier liquid and thereafter incrementally injecting solute into the system and determining the resulting tie-lines. The equipment and the method were successfully used in numerous previous studies. ,,− The experimental procedure followed the technique as suggested by Alders . Initially, 30 cm 3 of the solvent mixture consisting of glycerol and 2-methyl-2,4-pentanediol was charged to a jacketed 100 cm 3 cell, together with 20 cm 3 of n -heptane.…”

“…This motivates the need to understand the phase behavior of the system in question with 2-methyl-2,4-pentanediol as a cosolvent. The effect of 2-methyl-2,4-pentanediol on the distribution coefficient of 1,4-butanediol was then studied by measurement of quaternary LLE data for the system n -heptane + toluene + 1,4-butanediol + 2-methyl-2,4-pentanediol at (298.2 and 313.2) K and 0.1 MPa . It was found that 2-methyl-2,4-pentanediol significantly improves the capacity of 1,4-butanediol at high molar ratios of cosolvent to solvent mixtures.…”

“…UNIFAC (LL) was found to have inaccurately predicted immiscibility between 2-methyl-2,4-pentanediol and n-heptane at all compositions, implying that UNIFAC (LL) is inappropriate for the system. 24 It was thereafter experimentally noted that 2-methyl-2,4-pentanediol forms a two-phase region with longer-chain alkanes while maintaining complete solubility with toluene. The authors thereafter hypothesized that 2-methyl-2,4-pentanediol may be used as a cosolvent to improve the solvent characteristics (specifically capacity) of 1,4-butanediol and glycerol.…”

“…UNIFAC (LL) was found to have inaccurately predicted immiscibility between 2-methyl-2,4-pentanediol and n -heptane at all compositions, implying that UNIFAC (LL) is inappropriate for the system . It was thereafter experimentally noted that 2-methyl-2,4-pentanediol forms a two-phase region with longer-chain alkanes while maintaining complete solubility with toluene.…”

Hydrocarbon Extraction with Ionic Liquids

“…Extraction agent selection is undoubtedly a key factor in achieving efficient liquid–liquid extraction. Generally, organic solvents with high boiling points are used as extraction agents, such as sulfolane (SUL), N -methyl­pyrrolidone (NMP), dimethyl sulfoxide (DMSO), glycols, N -formyl­morpholine, and silicone oil. − Among them, SUL is widely used in aromatic hydrocarbon extraction due to its special properties . However, these solvents have unavoidable drawbacks, including (i) being partially dissolved in hydrocarbons, causing secondary pollution of products; (ii) inevitable volatile losses; and (iii) poor thermal stability resulting in solvent degradation during regeneration processes.…”