Mechanism analysis and liquid-liquid equilibrium of methyl tert-butyl ether separation from petroleum wastewater azeotrope by green mixed solvent

Petroleum wastewater contains large amounts of methyl tert-butyl ether (MTBE) and ethanol azeotropes. Efficiently and cleanly separating these azeotropes while conserving energy and reducing the emission of petroleum wastewater is an urgent problem that needs to be solved. In this work, the process of extracting MTBE from petroleum wastewater with water and ionic liquids (ILs) mixed extractant was clarified, and a complete method of evaluating the extraction performance based on the COSMO-SAC model, liquid-liquid extraction measurement, and micro-scale analysis mechanism is proposed. The COSMO-SAC model was used to determine organic solvents and ILs with the best extraction performance from among more than 250 ILs. A mixed solvent of water and the IL 1-ethyl-2,3-dimethylimidazolium ethylsulfate ([EMMIM][EtSO4]) at different molar ratios was selected for the liquid-liquid extraction experiment. It was found that the distribution coefficients and selectivity were maximum when the molar ratio of [EMMIM][EtSO4] to water was 1:2. Combined with molecular dynamics simulations and quantum chemical calculations, the interaction mechanisms of different solvents with MTBE and ethanol were revealed on the micro-level. This work provides a prototype for the high-efficiency extraction of MTBE from petroleum wastewater using a new mixed solvent of ILs and water, and it provides an application prospect for the efficient and green recycling of MTBE.