Liquid-phase hydrogenation of dementholized peppermint oil on Pt/Al2O3 catalysts

Abstract

The present work studies the catalytic hydrogenation of the (À)-menthone fraction existing in a dementholized peppermint oil, subproduct of the low-temperature crystallization process of the Arvensis peppermint oil. The aim is to obtain a liquid menthol composition for commercial use that replacing the crystal form. Pt/Al 2 O 3 catalysts with different metal content (1 and 4% Pt) were used and the effect of several operating variables is analyzed: H 2 pressure, reaction temperature, and reactant mass/catalyst mass ratio. Total conversion values ((À)-menthone + (+)-isomenthone) in the order of 95% on the fresh catalyst after 4 h on-stream were obtained for 4%Pt/Al 2 O 3 . These conversion values decrease when the catalyst is reused, which is indicative of deactivation. When the Pt content is reduced, the total conversion values fall drastically. The (À)-menthone to (À)-menthol selectivity values are higher than 90% in every case. #

Liquid phase hydrogenation of dementholized peppermint oil on Pt/Al2O3 catalysts

“…These results showed that Pt(4%)/Al 2 O 3 is a better catalyst than Pt(1%)/Al 2 O 3 for hydrogenation of menthones into menthols. An important deactivation of Pt/Al 2 O 3 catalysts was also observed by Yori et al [3] during the hydrogenation reaction. At present, there are no investigations about the causes of such a deactivation in the hydrogenation of menthone or dementholized peppermint oils.…”

“…In order to fulfill this objective, both fresh and used catalysts were characterized by Fourier transform infrared spectroscopy (FTIR), temperature programmed desorption (TPD), temperature programmed hydrogenation (TPH) and cyclohexane dehydrogenation in gas phase. The correlation of the results obtained by these techniques with previous activity determinations [3] allows to find out the more plausible causes for deactivation of Pt/Al 2 O 3 catalysts. On the basis of these results, a method for regenerating these catalysts is proposed.…”

“…Fresh Pt/Al 2 O 3 catalyst (F), having nominal 1 and 4 wt.% Pt, were prepared as described in a previous work [3]. After reaction, the used catalyst (U) was separated from liquid phase by filtration.…”

“…a mixture of (À)-menthol, (+)-neomenthol, (+)-neoisomentol and (À)-isomenthol [2]. In a previous work, Yori et al [3] have shown that it is possible to hydrogenate more than 90% of the remaining menthones in the dementholized peppermint oil to menthols by using supported Pt(4%)/Al 2 O 3 catalysts. A Pt(1%)/Al 2 O 3 sample converted less than 30% of this remaining menthone.…”

Synthesis of liquid menthol by hydrogenation of dementholized peppermint oil over Ni catalysts

“…In previous papers, 3,4 we confirmed that the catalytic hydrogenation of the (-)-menthone and the (+)-isomenthone fraction remaining in dementholized peppermint oil can transform this substances into (-)-menthol and its isomers thus upgrading a residue of low cost into a product of high commercial value. (-)-Menthone in dementholized peppermint oil can be hydrogenated to produce a mixture of (-)-menthol and (+)-neomenthol.…”