Etherification of biodiesel by-product glycerol to produce fuel oxygenates

İkizer, Burçin
Biodiesel, which is a renewable and environmentally friendly alternative to petroleum based diesel fuel, is produced by trans-esterification of vegetable oils and animal fats with lower molecular weight alcohols (methanol/ethanol), in the presence of a basic catalyst. Glycerol is the main side product of biodiesel production process. Economics of biodiesel production strongly depends upon the efficient utilization of its byproduct glycerol. The most attractive utilization way is its etherification for the production of fuel oxygenates. In this work etherification of glycerol with C4 (i-butene) and C5 [i-amylene; 2-Methyl-2-Butene (2M2B)] i-olefins were investigated for the production of transportation fuel oxygenates. Etherification of glycerol with 2M2B was firstly studied in the literature during this work. Besides mesoporous SAPO-34 like solid acid catalysts were synthesized in order to bring a new dimension to commercial solid acid catalysts and tested in etherification of glycerol with i-butene reaction. The etherification reactions of glycerol with i-butene were carried out in an autoclave batch reactor using commercial solid acid catalyst such as Amberlyst-36, Dowex DR-2030 and Silicotungstic acid (STA) in a temperature range of 70-120oC. Glycerol etherification results obtained by using i-butene as the reactant, proved the importance of Brønsted acidity of the catalyst, as well as the pore diffusion vi resistance, on the catalytic performance. Silicotungstic acid, with very high acidity, showed very good performance at T≤80oC. However, at higher temperatures it also facilitated the oligomerization of i-butene, which caused negative effect on glycerol etherification. Both Amberlyst-36 and Dowex DR-2030 showed excellent performance in catalyzing glycerol with i-butene at 90 and 120oC. Etherification of glycerol with 2-Methyl-2-Butene (2M2B) was also studied in an autoclave batch reactor using commercial solid acid catalysts such as Amberlyst-36 and Dowex DR-2030. The catalytic activities of Amberlyst-36 and Dowex DR 2030 were quite similar and a significant increase was observed in conversion values, with an increase in catalyst amount. This is due to the increased number of active sites per unit volume of the reaction mixture. Etherification of glycerol with 2M2B was investigated at 120 and 140oC over Amberlyst-36. Effects of reaction time and catalyst loading on glycerol conversion and product distributions were evaluated. Results proved formation of mono-, di- and tri-ethers of glycerol as a result of its etherification with 2M2B at 120-140oC over Amberlyst-36. At 140oC with 0.3 g Amberlyst-36 glycerol fractional conversion values and di-ether selectivity values approaching to 1.0 and 0.7, were highly promising. Microporous, mesoporous and silicotungstic acid impregnated SAPO-34 catalysts were synthesized successfully in order to bring a new dimension to commercial solid acid catalyst for etherification reactions. Activity of mesoporous SAPO-34 and STA@Mesoporous SAPO-34 were tested in etherification of glycerol with i-butene. However it was seen that, these catalyst were not active in etherification of glycerol with i-butene. Results proved that etherification of the biodiesel by-product glycerol could be successfully achieved by using 2M2B, as well as i-butene, to produce fuel oxygenates and improve the economics of biodiesel production.