Thermodiffusion of polycyclic aromatic hydrocarbons in binary mixtures

Area of Science:

• Physical Chemistry
• Chemical Engineering
• Materials Science

Background:

• Thermodiffusion, the movement of species driven by temperature gradients, is crucial for understanding natural phenomena like hydrocarbon reservoir stratification.
• Systematic measurements of thermodiffusion in binary organic mixtures are scarce, limiting predictive capabilities.
• Existing data often focuses on benchmark systems, necessitating research on more complex organic solutions.

Purpose of the Study:

• To systematically measure Fickian and thermal diffusion coefficients in binary organic mixtures.
• To investigate the influence of solute molecular structure (aromatic ring size) and solvent properties (alkane chain length) on thermodiffusion.
• To provide experimental data for refining models of thermodiffusion in organic systems.

Main Methods:

• Utilized an optical beam deflection apparatus to simultaneously measure Fickian diffusion (D) and the Soret coefficient (S_T).
• Calculated the thermodiffusion coefficient (D_T) from measured D and S_T.
• Investigated nine binary mixtures of polycyclic aromatic hydrocarbons in alkanes, varying solute and solvent molecular characteristics.

Main Results:

• Fickian diffusion (D) increases with decreasing solvent viscosity and decreasing solute molecular weight.
• Thermal diffusion coefficients (S_T and D_T) exhibit complex behavior, increasing with solute molecular weight for a fixed solvent.
• The impact of solute aromatic ring size on thermodiffusion is more pronounced in shorter-chain alkane solvents.

Conclusions:

• The study provides a systematic dataset on thermodiffusion in organic mixtures, expanding beyond simple systems.
• Results indicate that solute molecular weight and solvent chain length significantly influence both Fickian and thermal diffusion.
• The findings contribute to a better understanding of separation processes in complex liquid mixtures relevant to natural and industrial applications.