Strontium pyrophosphate modified by phosphoric acid for the dehydration of lactic acid to acrylic acid

Abstract

The dehydration of lactic acid to acrylic acid over strontium catalysts was investigated. Strontium catalysts were prepared by a precipitation method. The catalysts were calcined at 500 °C for 6 hours in an air atmosphere and characterized by SEM for morphological features, by XRD for crystal phases, by FTIR for structure, by N2 sorption for specific surface area, and by the Hammett indicator method for acidity. As for bare strontium catalysts, the types of anions have significant effects on the activity due to the acidity difference of corresponding strontium salts. Among the tested anions, the pyrophosphate anion displayed an excellent catalytic performance. Adjusting the impregnated involatile acid concentration and immersion time can change the acidity of the catalysts, resulting in a higher catalytic activity. The dehydration of lactic acid is sensitive to the surface acidity of the catalysts. Moderate acidity of the catalysts can efficiently catalyze the dehydration of lactic acid to acrylic acid. Under the optimal reaction conditions, 100% lactic acid conversion and 72.2% selectivity to acrylic acid were achieved over the phosphoric acid impregnated strontium pyrophosphate catalyst.