Tetraethylammonium Amino Acid Ionic Liquids and CO2 for Separation of Phenols from Oil Mixtures

Phenols have wide applications and much commercial value, and they are obtained from oil mixtures by separation. However, the previous separation agents have low separation efficiency or corrosive halide ions or are difficult to be regenerated. In this work, we designed several tetraethylammonium amino acid (TAAA) ionic liquids (ILs) without corrosive halide ions and found that the ILs could separate phenols from oil mixtures with much higher extraction efficiency and could be regenerated using CO2. The effects of separation time, initial phenol content, TAAA type, water content in TAAA, and phenol type on separation were investigated. It has been found that TAAA can separate phenols with high separation efficiencies, and the maximum separation efficiency of phenol can reach up to 99.0% at a TAAA:phenol mole ratio of 0.60. Meanwhile, ultimate phenol contents can reach as low as 1.40 g/dm3. The initial phenol content almost has no influence on the ultimate phenol contents. For real coal tar oil mixtures, the separation efficiency of phenols can reach up to 98.6%. The TAAAs can be regenerated and reused without significant decreases in separation efficiency of phenols. The separation mechanism has also been proposed based on chemical reactions.