The formation of benzyl ethers of potato starch by etherification with benzyl chloride is base catalyzed and is therefore carried out at high pH. In a suspension of starch granules the rate of starch ether formation is found not to be linearly related to the concentration of hydroxyl ions in the water phase of the suspension. At the same pH widely different rates of reaction can be observed, to be due to the tendency of the starch granules to “absorb” hydroxyl ions when electrolytes are added to the suspension. The rate of formation of the benzyl ether of starch is found to be linearly related to the amount of hydroxyl ions “absorbed” by the starch. The rate of the side reaction leading to benzyl alcohol turned out to be higher in the presence of starch than in water of the same pH.
Experiments are carried out on the acetylation of potato starch by vinylacetate in suspension in various types of continuous flow reactors. The reactors used were a cascade of four mixing vessels, each of equal size, a cascade of 4 mixers of increasing size, and a tubular reactor. The percentage of the vinylacetate which is bound to the starch under optimum conditions varies with the reactor type used. The product quality, as measured by the variation in viscosity of a starch acetate solution with time, is found to be lower for the starch acetates produced in the cascade reactors than for batchwise produced material of the same DS. This is shown to be due to the variation in DS of the individual starch granules. Starch acetates produced in the tubular reactor have a quality comparable to the acetates produced batch‐wise. An approximate design for a commercial acetylation plant is presented.
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