Sustainable production of lactic acid from corn stover using catalytic hydrothermal treatments: a comparative study of alkaline and Lewis acid catalysis

Abstract

Corn stover, an abundant lignocellulosic agricultural residue, offers great potential as a feedstock for the sustainable production of high value-added biochemicals, contributing to circular economy strategies and rural development. Among these compounds is lactic acid (LA), a key monomer in the synthesis of polylactic acid (PLA)—an environmentally friendly alternative to petroleumbased plastics due to its biodegradable properties and low environmental impact. PLA is suitable for food packaging and agricultural plastic applications. This study explores two sustainable approaches for second-generation lactic acid production from corn stover (5% w/v) using hydrothermal treatments assisted by catalysts: Ca(OH)₂ for alkaline catalysis and AlCl₃ for Lewis acid catalysis. In the first process, Ca(OH)₂ at 0.3 M achieves a 32% yield (12.4 g/L LA) under isothermal conditions at 260 °C. An excess of catalyst is required to maintain an optimal OH⁻/sugar monomer molar ratio of 2.61. In contrast, in the second process, AlCl₃ at 0.016 M produces a 20.7% yield (7.4 g/L LA) at 190 °C. However, higher AlCl₃ concentrations promote the degradation of dehydration products into levulinic and formic acids, decreasing LA selectivity. Alkaline catalysis required higher temperatures for optimal yield, while Lewis acid catalysis was more temperature-sensitive, as prolonged exposure leads to LA degradation. Both Ca(OH)₂ and AlCl₃ are promising catalysts due to their low cost, availability, and low toxicity, making them viable for converting corn residues into lactic acid in a sustainable biorefinery context.