Acetylene absorption by ionic liquids: A multiscale analysis based on molecular and process simulation

A COSMO-based/Aspen Plus multiscale simulation methodology was used to evaluate a wide variety of ionic liquids (ILs), more than 300, as potential acetylene absorbents. First, by means of Conductor-like-Screening Model for Real Solvents (COSMO-RS) method, molecular simulations were conducted to select ILs with adequate thermodynamic (Henry's law constants) and kinetic (diffusion coefficients) properties as acetylene absorbents, using N,N-dimethylformamide (DMF) as benchmark industrial solvent for such solute absorption. Then, the operating units of acetylene absorption of an acetylene and argon mixture, and exhausted solvent regeneration were modeled in Aspen Plus. Simulations of absorption column using equilibrium based design model demonstrated that at least two ILs (1-butyl-3-methylimidazolium cation and acetate and sulfonate anions) present competitive solvent performance in acetylene absorption respect to DMF. In contrast, process analyses with a more realistic rate-based column model revealed that the mass transfer rate clearly controls the acetylene absorption with ILs compared to DMF, due to their viscosity differences. Finally, modeling solvent regeneration stage showed clear advantages of using ILs as acetylene absorbents since efficient acetylene recovery is achieved by flash distillation (vacuum pressure and temperature increase), operation hindered in the case of DMF due to is high volatility, requiring the solvent regeneration by a distillation equipment with higher operating and investment costs. Current COSMO-based/Aspen Plus approach has been demonstrated useful to perform preliminary analyses of the potential application of ILs in new separation processes, before starting with experimental essays, highly demanding in cost and time.