| Separation of compounds with similar structure remains a big challenge in the chemical industry. Sterol compounds are receiving increased attention due to their promising applications in drugs and food additives. As a result, separation and purification of them is of great significance. Cholesterol and24-desmosterol, vitamin D3and tachysterol3are typical bioactive compounds with medial molecule size, and have quite similar structure. The only difference between them is the position of the double bond or whether there is a double bond in the side chain of the steroid skeleton. Such separations are generally accomplished by chromatographic process, which consumes not only a large amount of solvent but also energy for subsequent solvent recovery. Recently, a great number of works have shown ionic liquid-based liquid-liquid extraction (LLE) a promising and cost-efficient method. In this article, solubility of sterol analogues was measured, separation performance of both cholesterol and24-desmosterol system, vitamin D3and tachysterob system were studied, and COSMO-RS was applied in the prediction of solubility, distribution coefficients and selectivity.Solubility is the basic property of a compound and is useful in the separation processes. The solubility of cholesterol and24-desmosterol in organic solvents was collected and the solubility of vitamin D3in methanol, acetonitrile, ethyl acetate, ethanol, acetone and1-propanol at temperature range from248.2K to273.2K was measured by static equilibrium method. Based on the obtained solubility data, COSMO-RS was applied to evaluate the solubility of cholesterol,24-desmosterol and vitamin D3in organic solvents and ILs, and the qualitative trend was in accordance with the experimental results, indicating that COSMO-RS is an effective tool for solvent screening.By studying the ionic liquid-based LLE of cholesterol and24-desmosterol, it was glad to find that [bmim][SCN] achieved the highest selectivity up to2.45and [bmim][OAc] gained distribution coefficient as high as5.935for cholesterol, which may be quite difficult for weakly polar natural compounds. By studying the LLE of vitamin D3and tachysteroh, organic solvents sulfolane showed the optimal extraction performance, giving only a selectivity of1.44for tachysterol3over vitamin D3. ILs with unsaturated bonds demonstrated high selectivity probably due to their different π-π interactions with the two compounds. Pyrrolidinium-based ionic liquid, e.g.[bmpr][NTf2] provided the highest selectivity up to1.77. Acceptable selectivity and distribution coefficients were observed by a combination of organic solvents and ILs as extracting agents. Besides, the effect of concentrations, anions, cations and structural substituent of ILs was investigated, which may provide rational strategy for design of novel ILs for extractive separation of structural analogues.COSMO-RS was applied to evaluate the extraction performance of cholesterol and24-desmosterol in hexane-IL binary systems. A better understanding of functionality of structural moieties in ILs was achieved. COSMO-RS provided a qualitative trend of simulated extraction performance, and even a quantitatively correct description of selectivity of24-desmosterol over cholesterol. Accordingly, it can be efficiently used to screen the IL candidates for the mentioned separation requirement, and make predictions. In order to evaluate the feasibility of the extractive process for a practical production, continuous multistage fractional extraction was performed by calculations. The theoretical purity and recovery of target componds by continuous multistage fractional extraction were simulated, demonstrating the superiority of using ILs as extractant for selective separation. |
PDF Full Text Request