Batch and semibatch partial oxidation of starch by hydrogen peroxide in the presence of an iron tetrasulfophthalocyanine catalyst: The effect of ultrasound and the catalyst addition policy

Oxidized starch is important for paper coating because of its good mechanical and sizing properties. Traditionally, starch oxidation is performed by different heavy metals as catalysts and chlorites or chlorines as oxidizing agents. In this study, an environmentally friendly method was developed, utilizing iron tetrasulfophthalocyanine as a catalyst only in small amounts and hydrogen peroxide as a clean oxidant. It has been previously shown that the method works well, but analysis of the kinetic data as well as catalyst deactivation was difficult because of the semibatch operation mode. In this study, hydrogen peroxide was employed in a batch mode, allowing more simple analysis methods for determining the degree of substitution, starch degradation, and hydrogen peroxide decomposition kinetics. Additionally, the effect of adding the catalyst continuously into the solution, as well as the influence of ultrasound treatment on starch prior to oxidation, was studied. The batch-mode results showed DS_COOH = 0.73 for 100 anhydroglucose units at 52 °C and pH 10, whereas adding the catalyst continuously increased DS _COOH to 1.62. An increased DS_COOH was obtained with the ultrasound-treated starch, which shows that ultrasound is a promising method for enhancing the reaction performance.