Bioprocess development for levulinic acid production using sugarcane biomass

Abstract

Developing technologies for converting lignocellulosic biomass to products such as energy, fuels, and value-added chemicals is an important step in making biorefineries a feasible alternative to the current oil-based productive system. In this study, the conversion of lignocellulosic biomass composed of a mixture of bagasse and sugarcane straw into a cellulose pulp and a sulfonated carbonaceous solid catalyst synthesized from lignin fraction were investigated, as well as the use of this solid acid catalyst to convert cellulose to levulinic acid, an important chemical platform. To overcome this challenge, firstly, the fractionation of lignocellulosic biomass was optimized. Then, tests were carried out to find the best condition for isolation of the soluble lignin from black liquor produced in the optimal condition of delignification. The lignin precipitate was subjected to carbonization tests followed by functionalization tests with concentrated sulfuric acid to synthesize the catalyst. This catalyst was then used to convert cellulose into levulinic acid (LA). The experimental design for cellulose recovery and lignin removal showed that under relatively mild reaction conditions of 110 °C, 117 min, and a solid/NaOH (4.4% w/v) ratio of 1:20, more than 91% of the lignin was dissolved into the black liquor, recovering a solid with a cellulose content higher than 78%. Lignin was fully recovered in the form of precipitate by simply reducing the pH of the black liquor to 3 (under this condition 11 g of precipitate were recovered per liter of liquor). Having the recovered lignin, it was then possible to synthesize a solid carbonaceous catalyst with a total acid site density of 1.48 mmol/g which was able to convert up to 17.11% of the cellulose and obtain yields of up to 38.55% of levulinic acid when a catalyst/cellulose ratio of only 8:10 (w/w) was used. Overall, the future of LA production using carbonaceous acid catalysts looks promising. As research in this area continues, there is the potential to further improve the production process and make it more cost-effective and sustainable. This could lead to wider adoption of this technology and increased use of levulinic acid in various industrial applications, including as a platform chemical to produce a range of chemicals and materials.