SECOND-GENERATION (2G) ETHANOL PRODUCTION FROM AÇAÍ SEED USING SUBCRITICAL WATER HYDROLYSIS PRE-TREATMENT INTEGRATED WITH ACID POST-HYDROLYSIS AND DETOXIFICATION

Euterpe oleracea is an Amazonian palm tree native to northern Brazil. Its fruits, known as açaí, are widely used in the food, pharmaceutical and cosmetic industries. However, they have a low pulp yield, only 10% by mass, the rest being the seed (residual biomass), which often does not receive an environmentally appropriate destination. Within this context, the objective of this work was to produce second-generation (2G) ethanol from açaí seeds as a sustainable energy source. To maximize fermentation efficiency, an integration of subcritical water hydrolysis, acid post-hydrolysis and detoxification was used. Subcritical water hydrolysis was performed with 20 g of açaí seeds at 15 MPa and 10 mL min^-1 for 20 min. The subcritical hydrolysate was concentrated in a rotary evaporator until 50% of the water evaporated, then it was subjected to acid post-hydrolysis in 4% sulfuric acid in an autoclave at 121°C for 60 min. Finally, detoxification was performed with two adsorbents, activated carbon 25 g L^-1 and PoraPak™ Rxn 0.5 g L^-1, both at 45 ºC, 150 rpm for 60 min. The sugars quantified were cellobiose, glucose, xylose and arabinose, with xylose being the sugar with the highest content in the must at 57.68 g L^-1. The fermentation inhibitors evaluated were acetic acid, 5-HMF and furfural. Additionally, the adsorbent that had the highest detoxification efficiency was PoraPak™ Rxn, reducing the acetic acid value and eliminating the other inhibitors. Fermentation was evaluated for 96 hours with 3 different yeast strains: Kluveromyces marxianus, Scheffesomyces stipitis, and Spathaspora passalidarium. Kluveromyces marxianus stood out as the best performer, achieving maximum ethanol production of 8.26 g L^-1 and substrate-to-product conversion of 63%. Therefore, the newly developed method proved to be viable for the production of 2G ethanol from açaí seeds, and can be applied in a biorefinery concept in açaí processing industries.