Highly efficient absorption of methyl tert-butyl ether with ionic liquids

In this work, the technology for absorbing methyl tert-butyl ether (MTBE) with ionic liquids (ILs) is first proposed and systematically investigated from the molecular level to system scale. The imidazolium-based ILs, [BzMIM][Tf2N] and [AMIM][Tf2N] are screened from 272 IL species using the COSMO-RS model. The absorption mechanism at the molecular level is explored by combined characterization techniques (i.e. 1H NMR and FT-IR) with quantum chemical (QC) calculations (i.e. binding energy and weak interaction analyses). The vapour-liquid equilibrium (VLE) of MTBE-IL and MTBE-triethylene glycol (TEG) systems are experimentally determined and predicted through the UNIFAC-Lei model. The results show that the model can well quantitatively predict the VLE of these mixed systems. Moreover, the equilibrium absorption capacities of MTBE in ILs and TEG are measured and the magnitude is in the order of [BzMIM][Tf2N] > [AMIM][Tf2N] > TEG. The equilibrium stage and rate-based models on the basis of the UNIFAC-Lei model is established to perform the process design and optimization for MTBE absorption. When achieving the same separation task (i.e., MTBE content in the product gas less than 500 ppm in mole fraction), the mixed absorbent of [AMIM][Tf2N] + TEG has the lower loss of product gas and the lower energy demands (i.e., heating and cooling energy along with exergy demands) compared with the pure TEG and pure IL processes. This validates that ILs are potential absorbents and IL-based mixed absorbents may be the better strategy for achieving highly efficient absorption of MTBE.