Release kinetics of esterified p-coumaric acid and ferulic acid from rice straw in mild alkaline solution

- Rice straw was treated by NaOH for release of p-coumaric and ferulic acids.
- Release kinetics of esterified p-coumaric and ferulic acids were studied.
- Ferulic acid was released considerably faster than p-coumaric acid.
- The kinetics were governed by NaOH accessibility and ester-site localization.

The release kinetics of esterified p-coumaric acid (PCA) and ferulic acid (FA) from rice straw under a mild alkaline condition were investigated to collect fundamental data for the design of a recovery process. The results showed that the straw size, NaOH concentration, and temperature were the key parameters governing release kinetics. The analysis demonstrated that FA is released considerably faster than PCA. The close relationship between lignin and the PCA dissolution indicates a reciprocal and/or simultaneous release. Moreover, PCA is broadly distributed in the lignin network but tends to be located more densely in the lignin fraction which is not easily solubilized by alkaline treatment. In contrast, the release of FA is strongly affected by removal of lignin fraction which is easily solubilized. These results suggest that the release kinetics are controlled by the accessibility of NaOH to their ester sites in the lignin/hemicellulose network, and by their localization.