Catalysis of Organic..

408“Green” Catalysts for BiodieselConversion / [%]1008060402025 min 45 min 75 min Alcohol:Acid = 1:1T=150°C, 5%wt SZ catalystregenerated01 2 3 4 5 6No. runs / [-]Figure 3. Stability of the sulfated zirconia catalyst in the esterification reaction ofdodecanoic acid with 2-ethylhexanol – conversions given at 25, 45 and 75 minutes.Sulfated titania and tin oxide performed slightly better than the sulfated zirconia(SZ) catalyst. However, SZ is cheaper and readily available on an industrial scale. Itis already applied in several processes (7,8). Zirconia can be modified with sulfateions to form a superacidic catalyst, depending on the treatment conditions (11-16).The calcination temperature strongly affects its activity, the optimal interval being600–700 °C. However, the concentration of H 2 SO 4 used did not affect the catalyticactivity. In our experiments, SZ showed high activity and selectivity for theesterification of fatty acids with a variety of alcohols, from 2-ethylhexanol tomethanol. Increasing the amount of catalyst leads to higher conversions (Figure 2,right). This makes SZ suitable for applications where high activity is required overshort time spans. SZ is also regenerable and thermally stable.Conversion / [%]1008060402000 20 40Time / [min]150°C140°C120°CAlcohol:Acid = 3:1SZ Catalyst 1%wt60Conversion / [%]1008060402000 20 40Time / [min]Alcohol:Acid = 3:1T=140°C, SZ CatalystFigure 4. Esterification of dodecanoic acid with methanol, using an alcohol:acidratio of 3:1 and sulfated zirconia (SZ) as catalyst.3%wt1%wt0%wt60