Continuous Flow Preferential Hydrogenation of an Octanal/Octene Mixture Using Cu/Al₂O₃ Catalysts

Abstract

γ-Alumina-supported catalysts with varying copper loadings (5–25 wt %) were prepared by incipient wet impregnation and characterized by various characterization techniques. These catalysts were tested for the selective hydrogenation of octanal in a mixture containing 10 wt % octanal and 2 wt % octene diluted in octanol. The reactions were carried out in a continuous flow fixed-bed reactor in a down flow mode with varying pressures, liquid hourly space velocities, and hydrogen (H 2 )-to-aldehyde molar ratios. The catalyst activities were assessed over a temperature range between 100 and 180 °C using hydrogen gas as the hydrogen source. The results obtained showed that under these experimental conditions, copper preferentially hydrogenates the aldehyde and the copper content exhibited no significant influence on the catalyst activity or product selectivity. Kinetic modeling revealed that both octanal and octene hydrogenation were first-order reactions, although octene conversion was very low until octanal conversion had reached a significant level. The activation energy for octanal hydrogenation is higher than the octene hydrogenation. A maximum octanal conversion of >99% was obtained at 160 °C, and the best selectivity toward octanol of 99% was achieved at 100 °C (53% conversion). The pressure played a small role with regards to octanal conversion and selectivity toward octanol, whereas it exhibited a significant influence on the octene conversion. Increasing the hydrogen-to-aldehyde ratio was found to have a direct influence on both octanal and octene conversion.

Recent Progress in Continuous‐Flow Hydrogenation

“…Other reported Cu‐based catalysts in continuous‐flow hydrogenation of carbonyl compounds are based on Cu/Al 2 O 3 . Selective hydrogenation of an octanal/octene mixture (consisting of 10 wt % octanal and 2 wt % octene in octanol) using Cu/Al 2 O 3 catalysts was demonstrated by Friedrich and co‐workers . The results showed that Cu/Al 2 O 3 hydrogenated the aldehyde 70 preferentially and that the activity of the catalyst was related to the number of intermediate acid strength sites but not to the Cu content, specific surface area, and pore volume.…”

Water: Friend or Foe in Catalytic Hydrogenation? A Case Study Using Copper Catalysts

“…Water impact studies were carried out at 160 • C and with a hydrogen-to-aldehyde ratio of 2 (H 2 :octanal, 2:1). These conditions were established in a previous study as the optimum for octanal conversion and octanol selectivity [25]. Once steady-state conversion was reached using the fresh feed, the water-spiked feed was introduced to the system.…”

Facile Synthesis of Electrically Conductive and Heatable Nanoparticle/Nanocarbon Hybrid Aerogels

“…These processes involve the calcination or thermal reduction of nanoparticles, which consequently affect the metal electronic configuration, surface area, particle size, morphology, and reducibility. Among these MMOs, Cu-Al 2 O 3 nanoparticles, fabricated by solvent-deficient precipitation methods, have gained great attention in catalytic hydrogenation applications. − For instance, the octanal conversion efficiency of up to 99% from a mixture of octanal and octene using the Cu-Al 2 O 3 catalyst has been achieved because the unpaired electrons in the d -band of copper adsorb hydrogen to promote catalytic efficiency . So far, very few studies have attempted the synthesis of Cu-Al 2 O 3 nanoparticles from the CuAl-LDH precursor.…”

“…11−13 For instance, the octanal conversion efficiency of up to 99% from a mixture of octanal and octene using the Cu-Al 2 O 3 catalyst has been achieved because the unpaired electrons in the d-band of copper adsorb hydrogen to promote catalytic efficiency. 11 precursor. Many catalytic reactions were shown to be temperature-dependent and were typically heated with the aid of external, low-efficient, and high energy-demanding radiative heat transfer processes.…”