Mutual and Thermal Diffusivity of Binary Mixtures of the Ionic Liquids [BMIM][C(CN)₃] and [BMIM][B(CN)₄] with Dissolved CO₂ by Dynamic Light Scattering

Abstract

Ionic liquids (ILs) are promising solvents for gas separation processes such as carbon dioxide (CO2) capture from flue gases. For the design of corresponding processes and apparatus, thermophysical properties of ILs containing dissolved gases are required. In the present study, it is demonstrated that with a single optical setup, mutual and thermal diffusivities as well as refractive indices can be measured quasi-simultaneously for such mixtures. Dynamic light scattering (DLS) from bulk fluids was applied to determine mutual and thermal diffusivities for mixtures of 1-butyl-3-methylimidazolium tricyanomethanide ([BMIM][C(CN)3]) or 1-butyl-3-methylimidazolium tetracyanoborate ([BMIM][B(CN)4]) with dissolved CO2 at temperatures from 303.15 to 333.15 K and pressures between 2 and 26 bar in macroscopic thermodynamic equilibrium. Good agreement with literature data and only slight differences between the diffusivities measured for the two systems at the same temperature and comparable mole fractions of CO2 were found. Increasing mutual diffusivities with increasing mole fractions of CO2 are consistent with decreasing viscosities reported for other IL-CO2 mixtures in the literature and can be attributed to weakening of molecular interactions by the dissolved gas. For the conditions studied, no dependence of the thermal diffusivity on the temperature or the mole fraction of CO2 could be found.

Confinement effect on the dynamics of non-equilibrium concentration fluctuations far from the onset of convection

“…Since confinement (14) is in the direction of the gradient, the problem is most conveniently solved by applying Fourier transforms in time and in the perpendicular xz-directions to Eqs. (13), so as to obtain:…”

“…Thus, understanding NEFs is a basic question in the physics of non-equilibrium fluids and can lead not only to a deeper insight of transport phenomena like free diffusion or thermodiffusion [12][13][14], but also of new phenomena like NE fluctuation-induced (Casimir) forces [15][16][17][18].…”

Mutual and Self-Diffusivities in Binary Mixtures of [EMIM][B(CN)4] with Dissolved Gases by Using Dynamic Light Scattering and Molecular Dynamics Simulations

“…For data evaluation, the values for D 1,self were generally calculated within the first 15 ns of each simulation run to exclude disturbing contributions from statistical artifacts found within the last few nanoseconds of the simulations. In Figure 2 4 ] was measured with an expanded relative uncertainty (k = 2) of less than 1% according to the beam-displacement method detailed by Rausch et al 11 The refractive-index value n fluid = 1.451 obtained at λ 0 = 532 nm, T = 318.05 K, and p = 0.063 bar agrees within combined uncertainties with the value calculated from the correlation in our previous study 37 of 1.445 for the same IL at atmospheric pressure and the same wavelength. Because the temperature and the dissolved gas showed no significant effect on the measured refractive index, n fluid = 1.451 was used for the evaluation of all DLS measurements reported in this study.…”

“…11,12 For binary systems of two different IL solvents containing CO 2 , mutual diffusivities with typical uncertainties of less than 10% (k = 2) were determined at various compositions. 11 Given the huge number of possible IL combinations and the experimental effort associated with the investigation of IL−gas systems at any relevant thermodynamic state, computational approaches are useful alternatives. In detail, molecular dynamics (MD) simulation is a valuable method for the prediction of various thermophysical properties and also allows for an interpretation of experimental data through an insight into the molecular structure of the probed systems.…”

“…The optical and electronic setup is the same as that employed in our previous study. 11 It includes a Nd:YVO 4 laser (wavelength in vacuo λ 0 = 532 nm; operated at 0.5 W), a single-tau and a multi-tau correlator, as well as optical and electro-optical components. The scattered light superimposed with reference light in the form of stray light from the cell windows was detected by two photomultiplier tubes at small scattering angles between 2°and 7°.…”