Kinetics of the Diffusion and Chemical Reaction of Ethylene Oxide in Starch Granules in a Gas Solid System

Abstract

AbstractThe hydroxyethylation of potato starch was studied in a gas‐solid system. The rate of diffusion of ethylene oxide into the granules, the solubility of ethylene oxide in native starch and the rate of reaction between gaseous ethylene oxide and alkaline starch powder were measured. The partial pressure of ethylene oxide was kept at a constant value close to atmospheric pressure, the temperature was varied between 303 and 323 K.The ratio of the ethylene oxide concentrations in the starch granules and in the gas phase. mEO, is almost independent of the water content of the granules. The dependence of EO on temperature can be described with the Van 't Hoff equation: mEO = 5.93 · 10−5 exp (33390/RT). The rate of diffusion of ethylene oxide in the granules with a narrow size distribution does not follow Fick's law but it can be described with relaxation controlled diffusion (Case II diffusion). The parameter u of this model, the front velocity, appears to depend on the persentage moisture W, present in the granules.