Abstract
Seven kinds of malto-oligosaccharides (MO) with different number of glucose units, NG, were synthesized and their deoxygenation behavior in boiler water was examined by using a test boiler system simulated actual high pressure boilers. All the MOs were used in forms of phosphate adducts. In order to perfectly remove the oxygen, the mole ratio of glucose units against oxygen is necessary to take greater value than k=2.0, regardless of NG value of MO.
In this condition, the removal of oxygen was about 1 mole of oxygen per 1 mole of glucose unit constituting MO. The main reaction products of MO were lactic acid (C=3), glycolic acid (C=2), gluco-iso-saccharinic acid (C=6), and dideoxypentonic acid (C=5) in a mole ratio of 2.6:2.1:1.0:1.2. A small amount of diacethyl was detected in vapor. These resultss did not agree with the deoxygenation mechanism that the MO was assumed to decompose by the cleavage of glucoside bonds between glucose units. New reaction mechanism was proposed that the oxidative decomposition of MO occurs only at a terminal glucose unit with reducing hydrogen, through two parallel reaction steps called ‘direct oxidation’ and ‘hydrolysis-oxidation’ processes. The reaction mole ratio of glucose unit with oxygen, and the amounts of organic acids formed are quantitatively explained.
