Factorial optimization of biodiesel synthesis from castor-karanja oil blend with methanol-isopropanol mixture through acid/base doped Delonix regia heterogeneous catalysis

Abstract

Since sourcing a single feedstock for biodiesel synthesis is difficult, castor and karanja oils can be used by a novel two-step approach in which oil blends were esterified and methanol-isopropanol mixture was used to transesterify the pre-treated oil blend. Steam activated Delonix regia char was doped with H2SO4 and KOH to prepare acid and base catalysts. The precursor was TGA analysed for thermal stability and fixed carbon content. The activated carbon and catalysts were characterized using SEM, BET, EDAX, XRD and FT-IR. L25 Taguchi matrices were used for optimization of both acid esterification and base transesterification accommodating 6 parameters at 5 levels each. With a maximum FFA conversion of 98.51%, the optimal biodiesel yield was 99.22%. Tested statistical parameters in ANOVA study show good correlation with predicted values and experimental accuracy. It is seen that compatible non-edible oil blends can be used effectively for biodiesel production, and 2-propanol is far more efficient in transesterification than methanol. Thus, the use of this approach can reduce dependency on a single feedstock as well as propagate the use of higher alcohols to favour higher fuel yields. ASTM characterization of product showed acceptable fuel-grade properties. The developed acid catalyst showed good reusability till 3 reuses, while the base catalyst showed good reusability till 7 reuses. The developed catalysts were checked for preparation costs and seen to be far more cost-effective than commercially available activated carbon, hence they have potential for commercialization.