The reaction rates, in the base-catalysed acetylation of gelatinised aqueous starch (4 wt%), by vinylacetate (ViAc), were investigated in a semibatch reactor at temperatures ranging from 20 to 50°C. The desired starch acetylation reaction is accompanied by an undesired parallel base-catalysed hydrolysis reaction of vinylacetate and a consecutive hydrolysis reaction of the acetylated starch. The rate equations are: Starch acetylation: &AC =-k, cvic CRO-Starch acetate hydrolysis: &A= =-kz CRAM con-Vinylacetate hydrolysis: &tic =-k3 CViAc COW where k1,2,3 = k1,2,3, cHIO, CViAc is the vinylacetate concentration, cRo-is the concentration of the dissociated starch hydroxyl group, cRAc is the concentration of acetylated starch and con-is the sodium hydroxide concentration; k is the reaction rate constant. The temperature dependency of the rate constants was measured as: Acetylation of starch: Deacetylation of the starch ester: Hydrolysis of vinylacetate: where R (gas constant) = 121.8 J/mol"C.
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