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 degrees 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 (X-AAH) and the selectivity of the reaction (S-SA) 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 S-SA is relatively low (2-18%). Empirical models were developed to quantify the effects of the process variables on DS, XAAH and S-SA. The temperature, water content and NaOAc to starch ratio have the highest effect on the DS, X-AAH and S-SA 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. (C) 2010 Elsevier Ltd. All rights reserved.