Selective synthesis of a valuable unsaturated fatty alcohol via
catalytic and non-catalytic liquid-phase methyl oleate reduction
Abstract
The upgrading of oleyl alcohol synthesis via methyl oleate reduction
using NaBH4 without H2 supply was investigated. It was possible to
synthesize selectively the valuable unsaturated fatty alcohol with high
yields. Non-catalytic and catalytic experiments were developed trying to
improve the low final oleyl alcohol yield previously obtained. The
effect of reaction temperature, methyl oleate/NaBH4 molar ratio and
properties of different catalysts on final oleyl alcohol yield was
analyzed. Thus, alumina-supported metal (M) catalysts (M = Fe, Ce, Mo)
were synthesized by impregnation at incipient wetness. The M/Al2O3
catalysts were characterized in their chemical, textural, structural and
acid-base properties using ICP, N2 physisorption, XRD and NH3 and CO2
TPD. During non-catalytic methyl oleate reduction final methyl oleate
conversion and oleyl alcohol yield of 94% were obtained using a methyl
oleate/NaBH4 molar ratio of 0.11 at 333 K. Catalytic activity of M/Al2O3
solids did not correlate with basic site number but increased as acid
site number and ionic potential of M cations increase. This suggests
that cations with high acid site number and polarizing power are the
ones that promote the polarization of the ester C=O and anion [BH4]-
bonds favoring de methyl oleate conversion. In addition, the reaction
mechanism for fatty acid methyl ester reduction was investigated from a
theoretical approach using Density Functional Theory method at
B3LYP/6-31++G(d,p) computational level. Results obtained during
theoretical calculations confirmed that the formation of reducing
alcoxyborohydride species is energetically favored and allowed to
understand the events at microscopic level involved in the reaction
mechanism.