Acetalization
of diols with furfural and subsequent hydrogenation
of acetal products provided potential fuel additives that could be
blended into commercial diesel. Glycerol could be an interesting polyol
for acetalization with furfural due to its low cost, and it is produced
as a byproduct in very large amount in the process of biodiesel production.
In this work, glycerol acetalization with furfural has been selected
as a model reaction. Acetalization reaction was performed under neat
conditions (solventless) with 1:1 molar ratio of furfural and glycerol
at room temperature over various acid catalysts, including homogeneous
and heterogeneous acids. Among several catalysts, Zr-Mont, a heterogeneous
solid acid having controlled acidity, gave as high as 78% isolated
yield of acetal products. Interestingly, acetal products can be isolated
in pure form by performing extraction using cyclohexane that enables
selective extraction of product, and unreacted glycerol and furfural
were left in aqueous phase, which can be recycled. Further, to make
fuel components from isolated acetal product of glycerol and furfural,
hydrogenation was performed over a series of supported noble-metal
catalysts under low H2 pressure at room temperature. Among
them, 5% Pd/C showed very high activity for ring hydrogenation that
resulted in high yield of hydrogenation products. However, hydrogenated
product contains free hydroxyl group that needs to be subsequently
etherified or acetylated. Interestingly, etherified derivative was
obtained in high yield compared to acetylated derivative. In addition,
several other diols were treated with furfural and their products
were subsequently hydrogenated over 5% Pd/C under very low H2 pressure. The properties of resulting compounds were investigated
so as to find most suitable candidates as additives to commercial
diesel.
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