Thermodynamics insights of lignin dissolution in deep eutectic solvents

Area of Science:

• Green Chemistry
• Biorefining
• Thermodynamics

Background:

• Lignin dissolution is crucial for biorefineries, but efficient green solvents are lacking.
• Deep eutectic solvents (DESs) show promise, but their thermodynamic mechanisms for lignin dissolution need elucidation.
• Understanding lignin-DES interactions is key to designing effective solvents.

Purpose of the Study:

• To investigate the thermodynamic aspects of lignin dissolution in various DESs.
• To determine the heat of dissolution and solubility of lignin in acidic, neutral, and alkaline DESs.
• To correlate DES physicochemical properties with lignin dissolution thermodynamics.

Main Methods:

• High-precision solution microcalorimetry was used to measure the heat of lignin dissolution.
• Lignin solubility in different DESs was determined.
• Thermodynamic parameters (free energy, enthalpy, entropy) were calculated.

Main Results:

• Lignin dissolution in alkaline DESs was significantly more exothermic than in acidic or neutral DESs.
• Lignin dissolution is thermodynamically unfavorable (positive free energy change).
• The dissolution process is enthalpically favorable but entropically controlled, with interaction entropy being unfavorable.

Conclusions:

• Thermodynamic insights reveal lignin dissolution in DESs is complex, influenced by enthalpy and entropy.
• Alkaline DESs offer more vigorous exothermic dissolution, but overall spontaneity is limited by entropy.
• These findings provide a foundation for designing improved DESs for lignin biorefining applications.