Green Starch Conversion Technology : Studies on Starch Acetylation in Supercritical CO2
Chemical Product Design and Engineering (CPD&E)
Chemical Product Design & Engineering - III (CPD&E - 3)
Keywords: acetylation; potato starch; starch acetate; supercritical CO2
Supercritical CO2 has shown to be an excellent solvent and processing aid for polymer processing. It has physical properties that make it attractive as medium for chemical reactions. Supercritical CO2 is considered to be ‘green’, it is non-flammable, relatively non toxic and inert. Another advantage is the ease of separation from the (reacting) system by simple reduction of the pressure (Savage et al.,1995; Eckert et al.,1996; Beckman.,2004).
With these advantages, supercritical CO2 could be an excellent alternative for common solvents like water for chemical and physical modifications of starch. Recently, Harris et al, have shown that starch modification reactions can be done in supercritical CO2 (Harris et al., 1999). However, further studies are required to assess the potential of supercritical CO2 for starch modification, to broaden the scope of reactions and to gain insights in the processes taking place on a molecular and starch particle level.
Starch acetates are commercially produced modified starch products with a broad range of applications. The products are commonly made by reacting starch with an acetate source like acetic anhydride in water. Selectivity is a key issue and considerable amounts of acetic acid are produced by the simultaneous reaction of the anhydride with water, limiting the effectiveness of the anhydride. We present the experimental results of the acetylation reaction of starch in supercritical CO2 in a batch reactor, where the effects of several variables such as pressure (60 – 98 bar), temperature (40 – 90oC), rotational speed (200 – 1500 1/min), and amount of reactant (2 – 4.35 equiv/AGU) on the degree of substitution (DS) as well as selectivity of the reaction were explored.
The DS and selectivity depend strongly on the pressure of the system. It became clear that performing the reaction at elevated pressures in the supercritical region of CO2 provides the possibility to increase the DS and the selectivity value of the final product. We also observed that higher temperatures and pressures induce starch gelatinization and also has a positive effect on the selectivity of the process. FTIR analysis on the products clearly showed the presence of a carbonyl group, (C=O stretching at 1723 cm-1), confirming that the reaction was successful. These and more detailed experimental results will be reported and the performance of supercritical CO2 will be compared with that of water.
References:
Beckman, E.J. (2003). Supercritical and near-critical CO2 in green chemical synthesis and processing. J. of Supercritical Fluids. 28: 121-191.
Eckert, C.A., B.L. Knutson, and P.G. Debenedetti. (1996). Supercritical fluids as solvents for chemical and material processing. Nature 383 : 313-318.
Harris, R., Jureller, H. Sharon, Kerschner, L. Judith, Trzasko, T.Peter, Humphreys and W.R. Robert. (1999). Polysaccharide Modification in Densified Fluids. US Patent.5,977,348.
Savage, P.E., S. Gopalan, T.I. Mizan, C. J. Martino, and E.E. Brock. (1995). Reactions at Supercritical Conditions : Applications and Fundamentals. AIChE J.41(7): 1723 - 1778.
Presented Thursday 20, 09:52 to 10:11, in session Chemical Product Design & Engineering - III (CPD&E - 3).
