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 (scCO(2)) in a broad pressure range (8-25 MPa) and a temperature of 90 degrees C is provided. Highest degrees of substitution (DS) of 0.29 (1 h reaction time) and 0.62 (24 h reaction time) were found near the critical point of the mixture (15 MPa). 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 9.4-10 MPa to 14.5-14.8 MPa when going from 50 to 90 degrees 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. (C) 2011 Elsevier Ltd. All rights reserved.