Brazilian acai berry seeds: an abundant waste applied in the synthesis of carbon-based acid catalysts for transesterification of low free fatty acid waste cooking oil

Residues of acai seeds (Euterpe oleracea Mart.) were a novel source for the synthesis of the acid heterogeneous catalyst applied in the conversion of low free fatty acid waste cooking oil (WCO) to biodiesel. Yield of activated carbon (AC) and catalyst (CAT), as well as density of SO3H groups and total acidity, was analyzed in an entirely random designed experiment using multiple linear regression, one-way ANOVA, and Tukey's post hoc test. Time, temperature, dosage of KOH, and ratio of H2SO4/AC were the predictor variables with 3 levels each, at a significance level of alpha = .05. A significant yield variation portion of AC was explained by the experimental factors (R-2 = .891, F (3, 23) = 62.9, p < .0001), as did the yield of CAT (R-2 = .960, F (3, 23) = 185.7, p < .0001), density of SO3H (R-2 = .969, F (3, 23) = 242.2, p < .0001), and total acidity (R-2 = .973, F (3, 23) = 280.6, p < .0001). Levels of time (p = .001) and KOH dosage (p = .006) were significant to the yield of AC, and temperature levels were not influent on density of SO3H (p = .731) or total acidity (p = .762). CAT showed a S-BET of 249 m(2) g(-1), V-pore of 0.104 cm(3) g(-1), low crystallinity, high thermal stability, and a mesoporous amorphous structure. Optimized catalytic tests resulted in 89% conversion of WCO and 11 cycles of reuse, better than pure H2SO4 or pure KOH (p < .0001) and also better than many biomass-derived catalysts reported in the literature.

Automated summary

The utilization of acai seed residues for the synthesis of acid heterogeneous catalyst proved to be an effective method for converting low free fatty acid waste cooking oil to biodiesel. The catalyst showed high efficiency, thermal stability, and successful conversion rates in experimental tests, outperforming many other biomass-derived catalysts in the literature.