Phase Distribution of Resin and Fatty Acids in Colloidal Wood Pitch Emulsions at Different pH-Levels

Abstract

The distribution of resin and fatty acids (RFAs) between the water phase and the lipophilic phase in colloidal pitch emulsions was determined as a function of pH. Model pitch emulsions were prepared and agitated at different pH, temperature, and NaCl concentration. After filtration, the concentration of dissolved RFAs in the water phase was determined. The experimental data were used for calculation of pK_lw, that is, the pH at which 50% of the acids are dissolved in the water phase. At pH 3, all of the RFAs were associated with the colloidal droplets. The resin acids were dissolved at lower pH than the fatty acids. Among the resin acids, dehydroabietic acid had the lowest pK_lw. The pK_lw of fatty acids depended greatly on the chain length and degree of unsaturation. Fatty acids with more than 20 carbon atoms had a low water solubility even above pH 10. Increasing the NaCl concentration increased the pK_lw. The kinetics of the phase distribution was very rapid.

Keywords:

• Dissolved substances
• fatty acids
• phase distribution
• pitch
• pK_a
• resin acids

This work is part of the activities at the Åbo Akademi Process Chemistry Centre within the Finnish Centre of Excellence Programme (2006–2011) appointed by the Academy of Finland.

Notes

Part of the special issue, Surface and Colloid Chemistry Without Borders: An International Festschrift for Professor Per Stenius on the Occasion of His 70th Birthday.