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AssigneeE. I. Du Pont de Nemours and Company
InventorsNeville E. Drysdale, Kang Lin, Thomas W. Stambaugh
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An improved process for converting oligomers of alphahydroxycarboxylic acids, such as glycolic and lactic acid, to dimeric cyclic esters, such as glycolide and lactide. The continuous process is conducted at reduced pressures and depolymerizing temperatures in a heated columnar depolymerization zone, coupled with an essentially unheated receiver for unconverted oligomer. By feeding the oligomer to the upper end of the column while coordinating the feed rate with the depolymerization temperature such that a fraction of the oligomer is converted to a vapor product stream containing the cyclic ester and another fraction of the oligomer exits the column at its lower end and passes to the receiver vessel, the dimeric cyclic ester is produced at high production rates and the oligomer is subjected to minimal thermal stress.
In a process for depolymerizing a depolymerizable oligomer of an alpha-hydroxycarboxylic acid of the formula H(OCR.sub.1 R.sub.2 CO).sub.n OH, where R.sub.1 and R.sub.2 are independently hydrogen or C.sub.1 to C.sub.6 alkyl groups and n has a value of from 2 to 30, to a dimeric cyclic ester of the formula ##STR2## which process involves heating the oligomer under reduced pressure in the substantial absence of a stream of gaseous entraining agent for the cyclic ester at a temperature below the decomposition temperature of the cyclic ester, wherein the improvement comprises the steps of:
Dependencies are inferred from the claim text.