Direct conversion of glycerol to acrylic acid via integrated dehydration–oxidation bed system

Acrylic acid can be successfully produced in a single reactor via subsequent oxidation of the glycerol-dehydrated products. Selective dehydration of glycerol to acrolein was studied at 275–400 °C over HZSM-5, HBeta, HMordenite and HY. The V–Mo oxides (15–70 mol%V) on silicic acid support (20–100 wt% mixed oxides loading) were then included as a second bed for subsequent oxidation of the dehydrated products. Over the acid zeolites, acrolein and acetol are mainly generated, together with acetaldehyde, propionaldehyde, pyruvaldehyde and other oxygenates as secondary products. A complete conversion of glycerol with high selectivity to acrolein (up to 81 mol%) can be obtained when medium pore zeolites (HZSM-5) and low glycerol concentration (10–30 wt%) was used at 300 °C. A separated-sequential bed system provides high selectivity for acrylic acid with small amount of acetic acid and acetaldehyde (∼15 mol%). The catalyst with high V content promotes total oxidation of the dehydrated products to CO while that with highly dispersed V–Mo–O phases affords 98% selectivity to acrylic acid with 48% acrolein conversion.

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► Over HZSM-5, glycerol dehydrated to acrolein then oxidized to acrylic acid over VMoOx.
► Complete glycerol conversion required over HZSM-5 to avoid decomposition over VMoOx.
► Selective oxidation obtained over highly dispersed VMoOx with <20 mol%V content
► Acrylic acid selectivity in 2nd bed, determined by acrolein selectivity in 1st bed.
► Diluted feed (<30%) at 300 °C, 0.2 atm O2 provides optimal dehydration–oxidation.