Corn stover biorefinery based on hydrothermal and membrane processes

Abstract

Corn stover, a widely available agricultural by-product, stands out for its chemical composition rich in cellulose, hemicellulose and lignin. These components make it an ideal candidate for valorization in the context of the circular economy, offering a promising opportunity to reduce the use of fossil fuels and promote sustainable practices in the agri-food industry. In this study, various strategies based on green technologies were explored to maximize the potential of corn stover. An integral approach was chosen, focusing on obtaining secondgeneration chemicals, such as furfural and ethanol, through innovative and sustainable processes. First, pressurized green fluids, specifically water under subcritical conditions, were used to hydrolyse the structural components of the biomass. A mild treatment with subcritical water at a temperature of 180 °C and a pressure of 50 bar was carried out for 3 h, allowing the hydrolysis of the hemicelluloses present in the biomass and the generation of a celluloseenriched solid. During this process, CrCl 3.6 H2O was used as catalyst, a Lewis acid that facilitates the conversion of the released C5 sugars, xylose and arabinose, into furfural. Furfural production yields of 31 % were achieved under the conditions employed, demonstrating the effectiveness of this strategy for obtaining this compound. Subsequently, the cellulose-enriched solid was subjected to enzymatic hydrolysis mediated by Celluclast 1.5 L cocktail, releasing the glucose monomers present in the biomass. The resulting enzymatic hydrolisate was used as a substrate for an alcoholic fermentation catalysed by Ethanol Red®, achieving very attractive values for industrial bioethanol production, with a yield of 91.4%. For the recovery of furfural and ethanol, the pervaporation technique was used as a membrane separation method [1]. A silicone membrane was used to selectively recover furfural and bioethanol. Firstly, the temperature and the bioproduct concentration in the feed as well as the selectivity of the membrane in the presence of other intermediates formed during treatments were optimised. The silicone membrane was selective towards furfural and ethanol with enrichment factors in the range [10.3 – 31.7] and [3.8 – 9.1], respectively. This way, furfural produced by hydrothermal catalytic process was completely recovered in the permeate stream. On the other hand, ethanol obtained from enzymatic hydrolysis + fermentation of the cellulose rich solid phase was recovered with a yield of 60 % (see Figure 1). In summary, this study proves that it is possible to achieve an integral utilisation of corn stover through the production of high-value products such as furfural and ethanol, using green and sustainable technologies. These results not only offer a green and competitive alternative in industrial terms, but also contribute to boosting the circular economy and reducing the environmental impact of the agri-food industry.