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 (γ-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 γ-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).

The current study describes the results on the selective hydrogenation of the 2-butyne-1,4-diol to 1,4-butanediol over Raney Ò nickel catalysts both in batch and in CSTR mode. The detailed kinetic analysis of the reaction in batch mode revealed the existence of three characteristic regions. In the first region, A, the starting 2-butyne-1,4-diol produces primarily cis-2-butene-1,4-diol.In the second region, B, the dominant species is cis-2-butene-1,4-diol, which is either hydrogenated to 1,4-butanediol or isomerizes to trans-2-butene-1,4-diol. In the third region, C, the accumulated 4-hydroxybutanal is slowly hydrogenated to 1,4-butanediol. When the same reaction was carried out in a CSTR mode, the only products detected initially are the 1,4-butanediol and n-butanol. The first by-product detected immediately after the end of the first stage is the linear hemiacetal between the 4-hydroxybutanal with 1,4-butanediol. This species has been used as convenient tracer for determining the length of the selective region of the catalyst performance.

Net propylene glycol (1,2 propanediol) yields of up to 94% at 100% glycerol conversion have been achieved over a fixed bed Raney Ò Cu catalyst in trickle bed mode, at relatively low total pressure, 14 bar (200 psig), and minimal feedstock dilution (20 wt% water). The main identified byproducts are ethylene glycol and ethanol (each \2%), with methanol and 1,3 diol both \1%. The other key operating parameters for high yields are a narrow optimum in temperature (near 205°C), and a high H 2 / liquid flow ratio, about 375/0.05 by volume. The effects of chromium promotion have also been studied for effects on side reactions and rates. Our evidence points to initial dehydrogenation as the rate-limiting step in a likely three step mechanism.

Propylene glycol is formed in yields of up to 95% at 100% conversion using a Raney Cu catalyst in a fixed bed reactor. The reaction uses an 80% aqueous glycerol solution and a hydrogen pressure of 600 psi. The primary byproduct is ethylene glycol formed in 1−3% yield. In a reaction run continuously for 24 d using a sample of a commercial preparation of Raney Cu, the selectivity to propylene glycol at 100% glycerol conversion was 94.6% with a space−time yield (STY) of 0.49 g of 1,2-propylene glycol/mL Raney Cu/h. Ethylene glycol was formed in 2.5% yield, while methanol, ethanol, n-propanol 1,3propylene glycol, and acetol were present in less than 1% yield.

The unique value of the Raney Ò catalyst is revealed through surface modifications that have extended this familiar platform into novel materials with enhanced productivity in practical hydrogenations. The illustrative examples each yielded new compositions through use of non-nickel metals: as efficient dopants (Pd, Pt), as an inexpensive alloy diluent (Fe) and substrate for plating, or as the primary catalyst metal (Raney Ò Cu) in a recently identified process upgrading a renewable feedstock. A perspective on the surface chemistry of metals links the various approaches.