Post and direct functionalization of supported 12-tungstophosphoric heteropolyanions, characterization, and their performance for production of biodiesel from unrefined green seed canola oil

Functionalized mesoporous aluminosilicates were successfully synthesized using 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltriethoxysilane (MPTS) through two different techniques of post and direct functionalization. 12-tungstophosporic heteropoly acid (HPW) was then immobilized on the functionalized carriers via wet impregnation method. The attachment of carriers with HPW and their performance with respect to activity and reusability were studied for transesterification reaction to produce biodiesel from unrefined green seed canola oil (UGSC). The synthesized catalysts were analyzed in terms of textural properties, stability, acidity, chemical state, and composition by BET, XRD, Pyridine FTIR, XPS, Raman, TGA, ICP, and NH3-TPD as well as 29Si and 31P MAS NMR. BET, XRD, and Raman results confirmed the well dispersion of HPW over the carriers overcoming leaching problem of active phase to the reaction media. Successful functionalization of carriers leading to a stronger HPW attachment to minimize leaching was evaluated through reusability study and ICP analysis. Direct functionalized catalyst with amino group showed better catalytic activity (93.6%) than direct functionalized catalyst with thiol group (90.2%) under optimum reaction conditions of 5.9 wt % of catalyst, methanol to oil (M/O) molar ratio of 27.2, for 8 h at 200 degrees C and 4 MPa. This shows that 3-aminopropyltriethox-ysilane is a preferred linker over 3-mercaptopropyltriethoxysilane. Direct functionalized catalyst with amino group retained 93% of its initial activity after 5 cycles revealing its significant reusability and its potential of being applied at industrial scale.

Automated summary

Functionalized mesoporous aluminosilicates were synthesized using two different techniques of post and direct functionalization. Heteropoly acid was immobilized on the carriers and their performance for transesterification reaction was studied. The catalysts were analyzed for their properties and the direct functionalized catalyst with amino group showed higher catalytic activity and reusability compared to the one with thiol group.