Continuous synthesis of menthol from citronellal and citral over Ni-beta-zeolite-sepiolite composite catalyst

One-pot continuous synthesis of menthols both from citronellal and citral was investigated over 5 wt% Ni supported on H-Beta-38-sepiolite composite catalyst at 60-70 degrees C under 10-29 bar hydrogen pressure. A rela-tively high menthols yield of 53% and 49% and stereoselectivity to menthol of 71-76% and 72-74% were obtained from citronellal and citral respectively at the contact time 4.2 min, 70 degrees C and 20 bar. Citral conversion noticeably decreased with time-on-stream under 10 and 15 bar of hydrogen pressure accompanied by accu-mulation of citronellal, the primary hydrogenation product of citral, practically not affecting selectivity to menthol. A substantial amount of defuctionalization products observed during citral conversion, especially at the beginning of the reaction (ca. 1 h), indicated that all intermediates could contribute to formation of menthanes. Ni/H-Beta-38-sepiolite composite material prepared by extrusion was characterized by TEM, SEM, XPS, XRD, ICP-OES, N-2 physisorption and FTIR techniques to perceive the interrelation between the physico-chemical and catalytic properties.

Automated summary

One-pot continuous synthesis of menthols from citronellal and citral was investigated using a 5 wt% Ni supported catalyst. The reaction conditions were optimized to achieve high yields and stereoselectivity to menthol. The conversion of citral decreased with time-on-stream accompanied by the accumulation of citronellal and the formation of defunctionalization products.