Methanol dehydrogenation in a slurry reactor: evaluation of copper chromite and iron/titanium catalysts

The dehydrogenation of methanol to formaldehyde is a cornerstone in the concept of environmentally-benign synthesis through in situ generation of formaldehyde. This reaction was studied in a slurry reactor at temperatures between 598 and 673 K over four different catalysts: Raney copper, copper chromite, 3% Mn/copper chromite and iron/titanium (FeTi) alloy. The three copper-based catalysts were effective at promoting methanol dehydrogenation, and the differences in activity and selectivity between these catalysts were relatively small at 598 K, 2.75 MPa, 10/1 N2/methanol feed ratio, and 12,000 sL/kg-hr space velocity. At these conditions, methyl formate was the primary product with the copper catalysts, and the formaldehyde concentration was near chemical equilibrium with Raney copper and 3% Mn/copper chromite. The FeTi catalyst was ineffective on a weight basis, although its activity was comparable to the copper catalysts on a surface area basis. Deactivation of the copper chromite catalyst was relatively slow at 673 K, after an initial period of stabilization. The slurry liquid, 1,2,3,4-tetrahydroquinoline (THQ), was dehydrogenated and alkylated to some extent during the reaction.