Green starch conversions: Studies on starch acetylation in densified CO2

The acetylation of potato starch with acetic anhydride (AAH) and sodium acetate (NaOAc) as catalyst in densified CO2 was explored in a batch reactor setup. The effects of process variables such as pressure (6–9.8 MPa), temperature (40–90 °C), AAH to starch ratio (2–5 mol/mol AGU), NaOAc to starch ratio (0.1–0.8 mol/mol AGU) and water content (1–15.2%, w/w) on the degree of substitution (DS), the anhydride conversion (XAAH) and the selectivity of the reaction (SSA) were explored. At these conditions, acetylated potato starch with a range of DS values (0.01–0.46) is accessible in densified CO2. The XAAH varied between 10 and 80%, whereas the SSA is relatively low (2–18%). Empirical models were developed to quantify the effects of the process variables on DS, XAAH and SSA. The temperature, water content and NaOAc to starch ratio have the highest effect on the DS, XAAH and SSA values. For comparison, a number of experiments were performed in water and the results confirm that densified CO2 is a good solvent for the starch acetylation reaction.