Oxidation kinetics of 2‐methyl‐1,3‐propanediol to methacrylic acid in a fluidized bed reactor

Abstract

AbstractMethacrylic acid (MAA) is a specialty monomer for poly methyl methacrylate (PMMA). Partial oxidation of 2‐methyl‐1,3‐propanediol (2MDPO) to MAA is an alternative to commercial technology with fewer process steps, less cost and toxic feedstocks, and longer catalyst lifetime. Here, we evaluated the effect of 2MPDO and oxygen concentrations, reaction temperature, and contact time on product selectivity and 2MPDO conversion over VOCu0.5/Cs(NH4)2PMo12O40. Higher temperature increases selectivity and conversion; MAA selectivity reached 46% at 69% 2MPDO conversion. Higher 2MPDO to O2 ratio favours higher MAA selectivity due to methacrolein (intermediate) oxidation to MAA (a higher ratio favours consecutive oxidation) or lower combustion of MAA to COx. Shorter contact times decrease MAA selectivity. The Mars van Krevelen model characterizes the experimental data better than both the Langmuir‐Hinshelwood or Eley‐Rideal models; The reaction sequence involves both direct and indirect reactions in which 2MPDO reacts to methacrolein (MAC) as an intermediate and then it oxidizes to MAA (indirect) and/or 2MPDO directly oxidizes to MAA but the indirect reaction rate to MAA is 50 times faster than the direct reaction rate. The reaction is first order with respect 2MPDO and oxygen, and the rate‐limiting step is 2MPDO activation on oxidized sites.