(579d) Enhanced Acrylate Production from 2-Acetoxypropanoic Acid Esters

Acrylic acid and its esters form polymers that are widely used in adhesives, paints and coatings, diapers, dispersants, etc. Acrylates are traditionally produced via a two-step propylene oxidation process, but recently their production from renewable feed stocks is receiving significant attention. Glycerol, 3-hydroxypropanoic acid, and lactic acid (2-hydroxypropanoic acid) have all been investigated as feed sources; of particular interest here is the formation and subsequent pyrolysis of 2-acetoxypropanoic acid esters (APA esters). Although this route has been known since the 1940’s, our ability to achieve near-quantitative yields of APA and its esters from lactic acid and acetic acid via reactive distillation provides incentive for further study of the pyrolysis step. We have thus examined and identified reactor configurations and conditions for converting APA esters to acrylic acid esters in high yields.   Experiments were done using a continuous packed bed reactor in which various contact materials were placed; APA esters were fed along with a diluent gas and collected in product traps for analysis by gas chromatography.  Low surface area silica with mild surface acidity was found to be the best contact material among several examined. Methyl, ethyl, n-butyl, iso-butyl, and benzyl esters of APA were prepared and pyrolyzed; results show that the acrylate yield decreased as the number of hydrogen atoms on the ester beta-carbon increased. It was also found that use of CO₂ as the diluent gas significantly improved acrylate yields for some esters, as did addition of limited quantities of acetic acid to the APA ester feed.  Acrylate yields as high as 80% of theoretical were observed at optimal reaction conditions.