Continuous-Flow Ammoxidation of 2-Methylpyrazine to 2-Cyanopyrazine with High Space-Time Yield in a Microreactor

A microreactor (MR) with a vaporization microchamber and a sinusoidal wave microchannel was fabricated to synthesize 2-cyanopyrazine (CP) directly with an aqueous 2-methylpyrazine (MP) solution. A continuous-flow process with high space-time yield was achieved under the premise of strong exothermality of this ammoxidation reaction. The vanadium metal oxide catalysts with four different supports (α-Al₂O₃, γ-Al₂O₃, ZSM-5(50), ZSM-5(80)) were evaluated by simply stacking in the wave microchannel from 350 to 540 °C. The process parameters (temperature, reactant ratio, and size of catalysts) were optimized with the selected CrVPO/γ-Al₂O₃ catalyst, and an optimal ammoxidation process with MP conversion (X _MP) of 71.5% and CP selectivity (S _CP) of 93.7% was obtained by a volume space velocity (GHSV) of 13 081 h^-1 at 480 °C. Correspondingly, the space-time yield of CP (STY_CP) was 1724-77 082 g_CPkg_cat ^-1h^-1, which was the highest value ever reported for this reaction. Meanwhile, the ammoxidation reaction showed a great continuous-synthesis stability of 50-h running in the microreactor with the CP yield (Y _CP) remaining 56%-68%.