Lactide production from dehydration of aqueous lactic acid feed
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United States of America Patent
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Dec 28, 1993
Grant Date -
N/A
app pub date -
Sep 18, 1990
filing date -
Sep 18, 1990
priority date (Note) -
Expired
status (Latency Note)
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Abstract
The present invention is directed to a method for making L-lactide from aqueous L-lactic acid. Aqueous lactic acid feed for present purposes comprehends an aqueous mixture of one or more of L.sub.1 A, L.sub.2 A, and L.sub.3 A, optionally with LD being present. L-lactic acid is the preferred feed configuration for making L-lactide, and is to be understood even though the configuration symbol is not used throughout this application. Aqueous lactic acid feed is treated for removal of water therefrom until a degree of polymerization (DP) not substantially above about 2 is reached. The treatment then is ceased to produce a crude LD product. LD then is separated from the crude LD product. A preferred treatment involves heating the feed at elevated temperature to remove water. LD can be separated from the crude LD product by a variety of techniques to produce an LD-depleted product. This LD-depleted product, optionally augmented with additional aqueous lactic acid and/or water then can be readmitted to the process for making additional lactide. This cyclic or recycle process embodiment of the present invention enables very high lactide conversions to be realized.
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