Cobalt-catalyzed amination of 1,3-propanediol: Effects of catalyst promotion and use of supercritical ammonia as solvent and reactant

The catalytic synthesis of 1,3-diaminopropane from 1,3-propanediol and ammo nia was studied in a continuous fixed-bed reactor in the pressure range 50 to 150 bar. The unsupported Co-based catalysts applied were characterized b y N-2 physisorption, XRD, XPS, TPR, and ammonia adsorption using pulse ther mal analysis and DRIFT spectroscopy. The latter investigations revealed tha t the best catalyst, 95 wt% Co-5 wt% Fe, contained only very weak acidic si tes, unable to chemisorb ammonia. The absence of strong acidic and basic si tes was crucial to suppress the various acid/base-catalyzed side reactions (retro-aldol reaction, hydrogenolysis, alkylation, disproportionation, dime rization, oligomerization). Other important requirements for improved diami nopropane formation were the use of excess ammonia (molar ratio NH3/diol > 20) and the presence of the metastable beta-Co phase. A small amount of Fe additive could efficiently hinder the transformation of this phase into the thermodynamically stable alpha-Co phase and thus prevent catalyst deactiva tion up to 10 days on stream. Application of supercritical ammonia almost d oubled the selectivity to amino alcohol and diamine. The selectivity enhanc ement in the near-critical region is attributed to elimination of the inter phase mass transport limitations and to the resulting higher surface ammoni a concentration. (C) 1999 Academic Press.