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 (STYCP) was 1724–77 082 gCPkgcat
–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%.