THE KINETICS OF THE ACETYLATION OF GELATINIZED POTATO STARCH

The reaction rates, in the base-catalysed acetylation of gelatinised a queous starch (4 wt%), by vinylacetate (ViAc), were investigated in a semibatch reactor at temperatures ranging from 20 to 50 degrees C. The desired starch acetylation reaction is accompanied by an undesired pa rallel base-catalysed hydrolysis reaction of vinylacetate and a consec utive hydrolysis reaction of the acetylated starch. The rate equations are: Starch acetylation: R(ViAc) = -k(1) c(ViAc) c(RO-) Starch acetat e hydrolysis: R(RAc) = -k(2) c(RAc) c(OH-) Vinylacetate hydrolysis: R( ViAc) = -k(3) c(ViAc) c(OH-) where k(1,2,3) = k(1,2,3') c(H2O), c(ViAc ) is the vinylacetate concentration, c(RO-) is the concentration of th e dissociated starch hydroxyl group, c(RAc) is the concentration of ac etylated starch and c(OH-) is the sodium hydroxide concentration; k is the reaction rate constant. The temperature dependency of the rate co nstants was measured as: Acetylation of starch: k(1) = 1.14 10(14) e ( -93,200/RT) (m(3) s(-1) mol(-1)) Deacetylation of the starch ester: k( 2) = 9.28 10(1) e (-46,650/RT) (m(3) s(-1) mol(-1)) Hydrolysis of viny lacetate: k(3) = 1.84 10(3) e (-31,975/RT) (m(3) s(-1) mol(-1)) where R (gas constant) = 121.8 J/mol degrees C.