A High-Pressure Quartz Spring Method for Measuring Solubility and Diffusivity of CO₂ in Ionic Liquids

Abstract

A high-pressure gravimetric apparatus using a quartz spring for measuring solubility and diffusivity of CO2 in ionic liquids (ILs) was established for the first time. The time-dependent amounts of CO2 were recorded with a telescopic cathetometer and analyzed by using a one-dimensional diffusion model to obtain diffusion coefficients of CO2 in two ILs, namely, 1-n-butyl-3-methyl imidazolium hexafluorophosphate ([bmim][PF6]) and 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim] [BF4]) at pressures up to 10 MPa. Solubility data of CO2 in the two ILs up to 20 MPa were also obtained from its equilibrium masses and compared with those reported in the literature. The Peng–Robinson equation of state with the van der Waals one-fluid mixing rules was employed to correlate the experimental solubility data, revealing satisfactory calculation results. The measured diffusion coefficients of CO2 in [bmim][PF6] and [bmim][BF4] separately increase from 3.550 × 10–10 to 6.064 × 10–10 m2/s and from 7.184 × 10–10 to 9.880 × 10–10 m2/s following the pressure increase from 2.0 to 10.0 MPa at 323.2 K, while those at 5.0 MPa and different temperatures follow the Arrhenius equation, providing the diffusion activation energies of 25.53 and 20.30 kJ/mol for the [bmim][PF6]–CO2 and [bmim][BF4]–CO2 systems, respectively.

Viscosity and self-diffusivity of ionic liquids with compressed hydrofluorocarbons: 1-Hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide and 1,1,1,2-tetrafluoroethane

“…Some examples are demonstrated from the groups of Shiflett at DuPont [27], Noble [28], Baltus [29][30][31], Kroon [32], Rodriguez [33,34], Jalili [35,36], Li [37][38][39], Scovazzo [40,41], etc.…”

Phase equilibria and diffusion behavior of high pressure CO 2 in tetra-n-heptyl ammonium bromide

“…The solubility and absorption kinetic data of CO 2 in both solid and liquid [thepAm][Br] (the SLGE data determine the state of [thepAm][Br]) were measured by the high-pressure quartz spring method [7].…”

“…The position of the bottom of the basket was recorded; the position difference coupled with the buoyant force determined the solubility data and the amount of absorption at different times. However, the buoyancy force in [7] should be written as [15] buo basket spring sample calibration sample = g( ' …”

“…where D i 0 is the self-diffusion coefficient of component i [22,23]; D i ∞ is the mutual diffusion coefficient of component i at infinite [24,25]; η i is the viscosity of component i [26]; η is the viscosity of the mixture; v i is the partial molar volume of component i (L/mol) [7]. Again, x i (i=1, 2) is the molar fraction of component i (x 1 +x 2 =1).…”

“…The SLGE was carried out by using a first melting points (FMP) method[13]. The SGE and GLE and diffusion data ofCO 2 -[thepAm][Br] were implemented by a newly proposed high-pressure quartz spring method[7]. TheSLGE, SGE, and GLE were investigated by using the Peng-Robinson equation of state (PR-EoS) and the combination of the PR-EoS with the NRTL model.…”