CONVERSION OF BIODIESEL BY-PRODUCT GLYCEROL
TO FUEL ETHERS OVER DIFFERENT SOLID ACID CATALYSTS
Nalan Ozbay1, Nuray Oktar1, Gulsen Dogu1, Timur Dogu2
Chemical Engineering Department, Gazi University, Maltepe, Ankara, Turkey
2
Chemical Engineering Department, METU, Ankara, Turkey
nalanozbay@gazi.edu.tr, nurayoktar@gazi.edu.tr, gdogu@gazi.edu.tr, tdogu@metu.edu.tr
1
Abstract
Biodiesel is a mixture of methyl-esters of fatty acids, which is produced by transesterification
of vegetable oils with methanol. Glycerol is the major side product of biodiesel production
and due to the growing production rate of biodiesel, the availability of glycerol has also been
rapidly increasing in recent years. Environmental concerns and the economics of biodiesel
production enforces the conversion of glycerol to valuable products, such as high quality fuels
or fuel additives. The objective of this study is to produce high quality motor vehicle fuels
and fuel additives starting from glycerol. Oxygenated transportation fuel additives, such as
ethyl-tert butylether, methyl-tert butylether, tert-amyl ethylether etc. are produced by the
reaction of isobutylene or tert-butylether (TBA) with methanol or ethanol over solid acid
catalysts. In the present study, the etherification reaction of glycerol with TBA was
investigated over different solid acid catalysts and product distributions were analyzed.
Activities of Nafion-SAC-13 and alumina based mesoporous catalysts were compared with
the activities of acidic resin catalysts, such as Amberlyst-15, Amberlyst-16 and Amberlyst-35.
Experiments were carried out in a continuous flow reactor at a space time of 18 s.g.cm-3. In
most of the experiments excess amount of TBA was used. Results obtained with
Nafion-SAC-13 showed an increase in activity with temperature over 110oC. Highest activity
was obtained at 160oC (Fig. 1), over which catalyst deactivation was detected. Under these
conditions the main products were mono-ethers. However, an increase in the selectivities of
di-ethers was also observed with an increase in temperature (Fig. 2), using this catalyst.
Acidic resin catalysts, such as Amberlyst-16, Amberlyst-35 and Amberlyst-15 showed
activities at lower temperatures than Nafion-SAC-13 (Fig. 1). Among all these catalysts
Amberlyst-16 showed the highest di-ether selectivity. As for the alumina based mesoporous
catalysts, they showed etherification activity of glycerol at temperatures higher than
polymeric solid acid catalysts. However, these catalysts are more stable at high temperatures.
All these results indicated that glycerol, which is the by-product of biodiesel production, can
be successfully converted to valuable tert-ethers by etherification with TBA over solid acid
catalysts.
Fig.1. Glycerol conversion over different
solid acid catalysts
Fig.2. Selectivity of di-ethers over
different solid acid catalysts