Biofuel production from green seed canola oil using zeolites

Abstract

Solid acid catalysts are of interests for various organic reactions. Among the solid acids, heteropoly acids (HPA) show strong and Brønsted acidity. Especially, 12-tungstophosphoric acid (TPA) (H3PW12O40) possesses super acidity (Brønsted acidity) and higher thermal stability compared to other HPAs. The major disadvantages of using this heteropoly acid are lower surface area (1–10m2/g) and solubility in polar media. These problems can be avoided by supporting TPA on various carriers. In this work, tungsten oxide (WO3) and TPA was supported on H-Y, H-β and H-ZSM-5 zeolite catalysts. The catalysts were characterized extensively using BET, XRD, FTIR, Raman, XPS and NH3-TPD. Their catalytic activity was tested by esterification of the free fatty acid (FFA) present in the green seed canola (GSC) oil, and transesterification of the GSC oil, using a stirred tank reactor for biodiesel production. In this study, TPA impregnated H-Y zeolite showed higher catalytic activity for esterification, and TPA impregnated H-β zeolite showed higher catalytic activity for the transesterification reaction compared to other catalysts. A 55% TPA/H-β showed optimum catalytic activity for both esterification and transesterification. It yielded 99.3wt% ester, when 3.3wt% catalyst (based on green seed canola oil) and 21.3:1 methanol to green seed canola oil molar ratio were used at 200°C, reaction pressure of 4.14MPa and reaction time of 6.5h. Glycerol is the major by-product during transesterification reaction of vegetable oils. This catalyst (55% TPA/H-β) was experimented for etherification of pure glycerol, and maximum conversion of glycerol (100%) was achieved in 5h at 120°C, 1MPa, 1:5 molar ratio (glycerol:TBA), 2.5% (w/v) catalyst loading. Later, these conditions were used to produce glycerol ether successfully from the glycerol derived after transesterification of green seed canola oil. A mixture of GSC derived biodiesel and glycerol ether was defined as biofuels. The properties of biofuels were evaluated and compared to those reported with ASTM standard for pure biodiesel. The reaction kinetics and reaction mechanism of the esterification–transesterification and etherification reactions were also analyzed.