Diffusivities in Binary Mixtures of n-Decane, n-Hexadecane, n-Octacosane, 2-Methylpentane, 2,2-Dimethylbutane, Cyclohexane, Benzene, Ethanol, 1-Decanol, Ethyl Butanoate, or n-Hexanoic Acid with Dissolved He or Kr Close to Infinite Dilution

Abstract

Diffusive mass transport in binary mixtures of a liquid solvent and dissolved helium (He) or krypton (Kr) close to infinite dilution is investigated by determining the Fick diffusion coefficient D 11 experimentally with dynamic light scattering (DLS). Equilibrium molecular dynamics (EMD) simulations are used to access the solute self-diffusion coefficient D 1, which is equal to D 11 at the limit of infinite dilution. To address how the molecular characteristics of the solvent influence molecular diffusion, a wide range of different solvents is considered, including n-decane, n-hexadecane, n-octacosane, ethanol, 1-decanol, cyclohexane, benzene, 2-methylpentane, 2,2-dimethylbutane, ethyl butanoate, and n-hexanoic acid. Mixtures are investigated between (303 and 448) K and up to 6.5 MPa. The average expanded experimental uncertainty (k = 2) of D 11 from DLS experiments is 8.6%, and the average expanded statistical uncertainty (k = 2) of D 1 from EMD simulations is 5.8%. Solvent force fields (FF) used in EMD simulations to describe interactions within and between molecules are primarily based on the all-atom optimized potentials for liquid simulation (OPLS) FF, and a temperature-dependent modification developed within our research group is applied. The average absolute relative deviation of the simulated D 1 with respect to the experimental D 11 is 14%. Results from DLS and EMD show that diffusive mass transport in mixtures containing dissolved He for a given solvent is (20–50)% greater than in those with Kr. In comparison to mixtures based on linear alkanes, those based on branched alkanes have larger D 11, while mixtures based on oxygenated and cyclic components have smaller D 11.

Mutual and Thermal Diffusivities in Mixtures of Cyclohexane, n-Hexadecane, n-Octacosane, or n-Hexanoic Acid with Carbon Dioxide Obtained by Dynamic Light Scattering and Molecular Dynamics Simulations

“…To evaluate the validity of the simulation results using the L-OPLS-T FF in this work, the liquid dynamic viscosity η L and density ρ L for the n -C 16 H 34 + CO 2 mixture is compared to literature data in Figure S1 of the Supporting Information. The description of the double-bonded C and O atoms of n -C 6 H 12 O 2 is given by Pluhackova et al This FF choice is validated by our previous publication, which included n -C 6 H 12 O 2 as a solvent with dissolved helium (He) or krypton (Kr) close to the infinite dilution limit …”

“…To describe the interactions between two unlike atoms, ε ij and σ ij , arithmetic or geometric mixing rules based on the LJ parameters between a single atom-type are used . Previous investigations using the OPLS FF for cyclic hydrocarbons yielded overpredicted of up to 55% for the liquid organic hydrogen carrier dicyclohexylmethane and underpredicted D 11 by nearly 30% for binary mixtures of C 6 H 12 with dissolved He or Kr . To remedy this, the σ i of the C and the H descriptions are reduced by 2.0% for the modeling of C 6 H 12 in this work.…”

“…Thus far, 73 binary gas–liquid combinations have been investigated within this project close to infinite dilution of the dissolved gas and T up to 423 K. ,− As solvents, linear, branched, cyclic, and oxygenated alkanes as well as primary alcohols and ionic liquids were selected, covering molar masses from 46 to 504 g·mol –1 , a viscosity range from about 0.3–112 mPa·s at a T of about 298 K, and a dipole moment up to 1.76 debye. The dissolved gases consist of 1–11 atoms and comprise molar masses ranging from 2 to 152 g·mol –1 , acentric factors between −0.39 and 0.38, and a dipole moment up to 1.34 debye.…”

“…A slight discoloration was already observed in a previous study focusing on the investigation of D 11 in n-C 6 H 12 O 2 with dissolved He or Kr. 12 To exclude the possibility that this observed change in the sample could have any influence on D 11 , repetition measurements were performed at the end of the measurement series. Here, matching D 11 values were obtained within uncertainties.…”

“…Considerable efforts are spent on characterizing the molecular transport of mass in corresponding mixtures. Available experimental and theoretical studies in the literature often focus on the investigation of a few, specific gas–liquid systems and/or on a limited range of composition. − To gain a fundamental understanding on how the molecular characteristics influence the diffusive mass transport, a systematic variation of the solvent and solute molecules has to be performed . To further understand the influence of the resulting fluid structure and phase behavior, including possible immiscibility, on D 11 , investigations have to be performed over a wide range of mixture composition.…”