Continuous Liquid-Phase Hydrogenation of 1,4-Butynediol to High Purity 1,4-Butanediol over Particulate Raney Nickel Catalyst in a Fixed Bed Reactor

The work describes the results on the hydrogenation of the 2-butyne-1,4-diol (BYD) to 1,4-butanediol (BAD) over both slurry and particulate Raney nickel catalysts (Ra Ni) in batch and in a fixed bed reactor system. The detailed study on the kinetics of the reaction obtained in batch conditions revealed the existence of four stages in the overall hydrogenation network. In the first region, A, the starting BYD produces exclusively cis-2-butene-1,4-diol (cis-BED) and to a lesser degree the respective 4-hydroxybutanal (gamma-HALD). In the second region, B, the cis-BED takes part in three parallel reactions of hydrogenation to BAD, isomerization to trans-2-butene-1,4-diol (trans-BED), and the formation of additional gamma-HALD. In the third region, C, the trans-BED is mostly engaged in further hydrogenation to BAD, and surprisingly, starts producing the main byproduct, n-butanol (BOL). In the last kinetic region, D, the accumulated 4-hydroxybutanal is slowly hydrogenated to BAD. A completely different reaction profile is observed when the hydrogenation is carried out in an up-flow mode in a fixed bed system. The most important factors controlling the selectivity to BAD are the temperature, the contact time, and the pH of the liquid feed. It is also found that both the surface area of the catalyst and the presence of properly selected promoters, introduced into the Ra Ni system, can lead to a drastic reduction in the level of BOL and can virtually eliminate the formation of the second byproduct, 2-(4-hydroxybutoxy) tetrahydrofuran (HBOTHF).