Gas phase oxidation of 2-methyl-1,3-propanediol to methacrylic acid over heteropolyacid catalysts

• Published in: Catalysis science & technology Vol. 6; no. 17; pp. 6525 - 6535
• Main Authors: Darabi Mahboub, Mohammad Jaber, Lotfi, Samira, Dubois, Jean-Luc, Patience, Gregory S
• Format: Journal Article
• Language: English
• Published: 01.01.2016
• Subjects: Byproducts; Catalysis; Catalysts; Conversion; Methacrylic acid; Oxygen; Polymethyl methacrylates; Selectivity
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/c6cy01025c

The acetone cyanohydrin process (ACH) to produce methyl methacrylate (MMA) relies on expensive and toxic feedstock and suffers from low yield. Methacrylic acid (MAA) esterification to MMA is an alternative to ACH. However, current processes to produce MAA require multiple steps and catalyst lifetimes are short. Here, we report an alternative chemistry based on 2-methyl-1,3-propanediol (2MPDO) which is a co-product of the hydroformylation of allyl alcohol to 1-4 butanediol. The cesium salt of a Keggin-type heteropoly acid (HPA) partially oxidized 2MPDO to MAA. Inserting vanadium into the HPA reduced the Mo 6+ to Mo 5+ , and promoting it with copper increases the selectivity to MAA but decreases the conversion by 11%. The HPA catalyst operated in a gas-phase fluidized bed in which a 0.3 mm nozzle atomized the 2MPDO liquid feed into the bed at 250 °C. The maximum selectivity to MAA and methacrolein (MAC) was 41% and 33%, respectively, at 63% conversion. In the first step, oxygen reacts with 2MPDO to form 3-hydroxy-2-methylpropanal. This intermediate dehydrates to methacrolein (MAC) in the second step, and finally in the third step, oxygen reacts with MAC to form MAA. The main by-products were methane (gas phase) due to decomposition of the reactant and 2-methylpropanal (liquid phase) because of hydrogen transfer of MAC. Heteropolyacids with Cs, V and Cu partially oxidize 2MPDO to methacrylic acid (40% selectivity) in the gas phase at 250 °C.