Insights in starch acetylation in sub- and supercritical CO2.

An in-depth study on the acetylation of starch with acetic anhydride (Ac2O) and sodium acetate (NaOAc) as the catalyst in pressurized carbon dioxide (scCO2) in a broad pressure range (8–25MPa) and a temperature of 90°C is provided. Highest degrees of substitution (DS) of 0.29 (1h reaction time) and 0.62 (24h reaction time) were found near the critical point of the mixture (15MPa). The phase behavior of the system CO2, starch and acetic anhydride (Ac2O) was studied in a high pressure view cell. The critical points were a clear function of the temperature and increased from the range of 9.4–10MPa to 14.5–14.8MPa when going from 50 to 90°C (Ac2O mole fraction at the critical point in the range of 0.08–0.09). Acetylation experiments with a range of starch particles sizes showed a clear relation between the DS and the particle size.