Levulinic acid production from lignocellulosic biomass using lignin-catalyst

Abstract Purpose This work developed a new solid carbonaceous acid catalyst on lignin-based and used it to convert cellulose into levulinic acid (LA), resorting a mixture of straw and sugarcane bagasse (1:1 ratio) as reagent and catalyst. Methods Pretreated straw and sugarcane bagasse in dry block reactors. The solid/liquid ratio for all tests was 1:20 at 110°C. Used a 22 rotational central composite design to optimize cellulose extraction and lignin precipitation, cellulose extraction: varying NaOH concentration (0.2 to 5% w/v) and reaction time (3 to 117 min), and lignin precipitation: testing different pH values (3 to 10) and residence time (6 to 69 min). Synthesized the catalysts through an incomplete lignin carbonization followed by sulfonation. Cellulosic pulp was treated with the catalyst at 140°C (1:8 solid/liquid ratio). Results Under reaction conditions of 110°C, 117 min, solid/NaOH (4.4% w/v) and 1:20 ratio, more than 91% of the lignin dissolved into the black liquor, recovering a solid with a cellulose content higher than 78%. Furthermore, lignin was fully recovered as precipitate by reducing the black liquor pH to 3 (11 g of recovered precipitate/liter of liquor) and used to synthesize a 7.3 mmol/g total acid site density catalyst, which converted the cellulose up to 17.11% and obtained LA yields of up to 38.55%, when applied an 8:10 catalyst/cellulose ratio (w/w). Conclusion The proposed process has the potential to enable the inclusion of LA among the by-products of the national sugar-energy sector, increasing its competitive potential.