(449ah) A Study on Separating Aromatic and Aliphatic Mixtures Using Deep Eutectic Solvents

The separation of aromatic and aliphatic mixtures is an important process in the industry. Due to the formation of azeotropes, traditional distillation method is not suitable for separating these mixtures. Organic solvents such as sulfolane are the most commonly used solvents in the liquid-liquid-extraction (LLE) process. However, these organic solvents are generally toxic and flammable. So it is necessary to develop a new generation of solvents. Recently, a new generation of solvents deep eutectic solvents (DESs) are considered as an environmental benign solvent, which is a combination of a salt as hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) through hydrogen bond. DESs have many advantages such as easy preparation, low price, biodegradability, and so on. In this work, we synthesized a series of DESs for the separation of toluene from toluene/heptane mixtures and studied the rules of separating aromatics from aliphatics using DESs, and the obtained DESs with good extraction performance were used to separate aromatics from oil mixtures or naphtha. The results showed that (1) the extraction ability for toluene using DESs was greatly influenced by HBAs and HBDs which formed the DESs. The selectivity of toluene was distinctly enhanced by short side chain, small central atom of cation and large anion of HBA, together with adequate position for alkyl chain and appropriate functional group of HBD. It was also found that an increase of extraction temperature at the studied range could enhance the selectivity for toluene. Fig. 1 shows the effect of HBD on selectivity and distribution ratio of toluene, and effect of selected HBD and different HBA on selectivity and distribution ratio of toluene for the separation of toluene + n-heptane mixtures using DES. (2) The obtained high effective DES namely tetraethylammonium chloride (TEAC)- levulinic acid (LA) was used for separating different systems of aromatics/aliphatics mixtures and the results show that TEAC-LA can efficiently separate benzene from cyclohexane. Besides, the length of the aliphatics chain consisting the oil can remarkably influence the purity of the aromatics which are extracted to the bottom phase. The longer of the aliphatics, the larger of the S values, which means better purity of aromatics. (3) It was also found that when the DES of TEAC-LA is mixed with naphtha at a DES/naphtha mass ratio of 1:1, this kind of DES shows excellent extraction performance. The extraction rate of aromatics is 11.5% and the purity of the aromatics extracted in the bottom phase can reach as high as 95.6%, which is better than the results of sulfolane. The extraction performance of TEAC-LA have not any change after four cycles, indicating that the DES have a good recycling property.

The project is financially supported by the Shanxi Scholarship Council of China (2011-086), the National Basic Research Program of Chin(2011CB201303) and the long-term subsidy mechanism from the Ministry of Finance and the Ministry of Education of PRC

Keywords: Deep eutectic solvents, Extraction, Toluene, n-Heptane, Naphtha, Role, Hydrogen bond donor, Hydrogen bond acceptor