Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-I-6starch granules, but after a certain reaction time (240 min) starch partially depolymerized andswelled, resulting in the formation of reducing end units and increase of surface, leading toenhanced reaction rates (Fig. 2). Glucose units and its oxidized monomer units were detectedby HPLC after hydrolysis of polymer (Fig. 3a). SEM pictures showed a loss of smoothness ofthe starch granules, which is desirable due to a bigger contact surface of the starch with areagent (Fig. 3b). Higher yields of oxidized starch were achieved using lower amounts ofH 2 O 2 , but at the cost of lower DS values. Higher pH (8-10) favored carboxyl formation andneutral pH (7) favored carbonyl formation. A mathematical model was developed.Table 1. Degree of substitution and yield of oxidizedstarch at different reaction conditions# a / b / cd DS COOH/100AGUd DS CO/100 AGUd yield%1 55/8.4/22 0.92 2.05 872 55/8.4/11 0.46 1.87 963 55/7.0/22 0.68 2.15 89e 4 52/10.0/5 0.45 0.66 985 52/7.0/5 0.28 1.55 99DS COOH / 100 AGU1.00.80.60.40.20.00 100 200 300 400 500time (min)a temp. °C b pH c H 2 O 2 flow (ml/h) d after 420 minutese 500 ml reactor, 130 g starch and 70 mg cat, 4hFig. 2. Kinetics in starch oxidation at 55°C at pH 8.4 andH 2 O 2 flow of 22 ml/h (○), at pH 7 and H 2 O 2 flow of 22ml/h (□), at pH 8.4 and H 2 O 2 flow of 11 ml/h (◊).a) b)Fig. 3. a) Carboxyl and carbonyl contents identified by hydrolytically breaking down starch to single glucoseunits and analyzed with HPLC, b) SEM pictures of native (1) and oxidized starch (2).4. ConclusionsKinetics of starch oxidation was studied at 55 °C over FePcS catalyst using H 2 O 2 as anoxidant. Higher yields were obtained with less lower oxidant amounts, and more alkalineconditions favored carboxyl formation, while neutral conditions favored carbonyl formation.HPLC succeeded to identify carboxyl and carbonyl contents by breaking down the polymer tosingle units.References1. A.B. Sorokin, S.L. Kachkarova-Sorokina, C. Donzé, C. Pinel, P. Gallezot, Topics Catal. 27 (2004) 67-76.2. T. Heinze, T. Liebert, Prog. Polym. Sci. 26 (2001) 1689-1762.38