The lactic acid (LA) production from corn stover using Lewis acid catalysts was optimized. Initially, an equimolar mixture of Al(III)/Sn(II) was used as a catalytic system at 190 °C with 5 wt% biomass. Increasing the catalyst concentration led to higher LA production, showing the optimal results at 16 mM. A low catalyst concentration mainly produced furfural and HMF, dehydration products from the corn stover sugars. Higher catalyst concentration increased LA yield but also produced the degradation of the glucose dehydration products into levulinic and formic acids, reducing LA selectivity. Al(III) was essential for LA formation, while Sn(II) was less effective due to its lower solubility, shown by the presence of Sn(II) in the solid residue after treatments. A total of 16 mM Al(III) yielded the highest LA levels at 190 °C, 7.4 g/L, and 20.7% yield. Increasing the temperature to 210 °C accelerated the LA production while also achieving the lowest energy consumption, which was 0.47 kWh/g LA at the highest LA production point. However, longer treatments at this temperature caused LA degradation. AlCl₃ has been identified as an ideal catalyst for biomass conversion to LA, being inexpensive and low in toxicity.

This study assesses subcritical water hydrolysis (SWH) as a sustainable approach for protein recovery from okara, following isoflavone valorization. The initial extract, obtained at 120 °C, contained over 1200 µg of isoflavones per gram of dry okara. The solid residue underwent a second protein extraction step in both batch and semi-continuous modes. The batch extraction was conducted at 180 °C for 3 h at 5 MPa in a 0.5 L reactor. Under these conditions, total amino acid recovery reached 81 ± 3% (12.6 g/L), with 20 ± 1% of free amino acids, mainly glutamic acid, and a favorable profile of essential amino acids. These results were comparable to protein extraction from untreated okara, indicating that the prior isoflavone extraction did not hinder protein hydrolysis, but rather contributed positively within the cascade framework. Hydrolysis was also performed in a semi-continuous mode in a 2.3 L reactor, with a residence time of 2.75 min, in a two-stage temperature process (180 °C and 270 °C). The second stage yielded a significantly higher extraction than the first one, achieving a total 70.4% protein recovery (1.22 g/L) with 10% of free amino acids, with glutamic acid as the dominant one. Carbohydrate analysis revealed high hydrolysis yields for galactans, arabinans, and xylans, but these exhibited lower thermal stability compared to proteins. Okara emerges as a promising by-product for a bio-cascade process, combining a mild first stage for isoflavone extraction with a more severe second stage for protein extraction/hydrolysis.

This paper presents an integrated biorefinery approach for the sequential conversion of corn stover into high-value platform chemicals, specifically furfural and lactic acid (LA), through a series of hydrothermal, enzymatic and chemical/biotechnological treatments. Initially, subcritical water (subW) treatment (180 ºC, 4 h with CrCl3 as catalyst) was applied to selectively dehydrate the hemicellulose fraction, achieving a maximum furfural yield of 29.1 % with a volumetric productivity of 1.6 g·L⁻¹·h⁻¹. The resulting cellulose-enriched solid (71%) was further subjected to enzymatic hydrolysis, yielding 52 g/L of glucose (82% yield), in contrast to untreated corn stover, which yielded only 32 %.LA production was optimized from this glucose hydrolysate via two comparative routes: alkaline chemocatalysis using Ca(OH)2 as catalyst and microbial fermentation with Lactobacillus delbrueckii. While fermentation provided superior LA yield (93.6 % vs 23.1 %) and higher purity (32.8 g/L vs 10.3 g/L), the alkaline route demostranted a much faster reaction yielding volumetric productivities of 6.9 g/Lh and 0.27 g/Lh, respectively, although it resulted in a more complex mixture of organic acids and oligomeric by-products.Despite the potential overestimation of energy consumption at the laboratory scale, it was concluded that the biotechnological route consumed more energy per gram of corn stover across the tree main stages than the alkaline route, offering a promising alternative to the conventional fermentation process.

This paper presents an integrated biorefinery approach for the sequential conversion of corn stover into high-value platform chemicals, specifically furfural and lactic acid (LA), through a series of hydrothermal, enzymatic and chemica treatments. Initially, subcritical water (subW) treatment (180 ºC, 4 h with CrCl3 as catalyst) was applied to selectively dehydrate the hemicellulose fraction, achieving a maximum furfural yield of 29.1 % with a volumetric productivity of 1.6 g/L·h. The resulting cellulose-enriched solid (71%) was further subjected to enzymatic hydrolysis, yielding 52 g/L of glucose (82% yield), in contrast to untreated corn stover, which yielded only 32 %.LA production was optimized from this glucose hydrolysate via alkaline chemocatalysis using Ca(OH)2 as catalyst. This alkaline route yielded high volumetric productivities of 6.9 g/L·h, but lower LA yield (23.1 %) and concentration (10.3 g/L) than microbial fermentation process from the glucose hydrolysate. Despite the potential overestimation of energy consumption at the laboratory scale, the cascade process offers a promising route to fully valorize corn stover into two valuable building blocks such as furfural and LA yielding also a solid enriched in lignin

This study optimizes lactic acid (LA) production from corn stover using a Lewis acid catalyst. Initially, an equimolar mixture of Al(III):Sn(II) was used as catalyst at 190 °C with 5 wt. % biomass. Increasing catalyst concentration led to more LA, with optimal results at 16 mM, between 5 and 32 mM. Low catalyst concentration produced mainly dehydration products, furfural, and HMF from corn stover sugars. Higher catalyst concentration increased LA but led to degradation of dehydration products into levulinic and formic acids, reducing LA selectivity. Al(III) was essential for LA formation, while Sn(II) was less effective due to low solubility of Sn(II) species, shown by Sn(II) in the solid residue. 16 mM of Al(III) yielded the highest LA levels, 7.4 g/L and 20.7% yield. Increasing temperature to 210 °C accelerated LA production with the lowest energy consumption at the maximum of LA production (0.47 kWh/g LA), though longer treatments caused LA degradation. AlCl3 has been identified as an ideal catalyst for biomass conversion to LA, being cheap and low in toxicity.