Journal of Nanoscience and Nanomaterials

ABSTRACT

Research in the field of renewable feedstock for the preparation to lactic acid (LA) has gained attention. Currently there is an increased need for the utilization of sustainable feedstock like biomass for the production of chemicals and biodegradable polymers. LA has been synthesized traditionally from sugars. However, LA can also be synthesized from cellulose, a naturally occurring polysaccharide. Glycerol, a by-product of biodiesel and bioethanol production, is another promising feedstock for lactic acid production. Both cellulose and glycerol, are renewable and sustainable. They are viewed as waste materials from the industry. However, the conversion of cellulose to lactic acid by way of hydrolysis is challenging, as the biopolymer of glucose, namely, cellulose is a stiff-necked molecule. It is highly recalcitrant. In fact, the rate of hydrolysis of cellulose is two orders of magnitude slower than that of starch. Such slow reaction rates are because of the extensive inter-molecular and intra-molecular hydrogen bonding network. Thus, owing to the high crystallinity of cellulose making its conversion to lactic acid energy intensive, there appears to be one and only one single sustainable choice for lactic acid production and that is glycerol. The potential of metallic species -supported on solid acid, or solid base catalysts for the conversion of glycerol and cellulose to lactic acid is highlighted. Various catalytic routes such as dehydration, hydrogenation, and reformation, including the route of isosaccharinic acid under specific reaction conditions, like the microwave irradiation, sonochemical irradiation and the hydrothermal heating were explored. For the elucidation of reaction mechanism, validation of product structures, and yield optimization, analytical techniques like, NMR are of importance. Catalytic methods, reaction routes, and mechanistic knowledge used for the efficient conversion of cellulose and glycerol into lactic acid developed during the past five years (2021-2025) will be outlined in this work. The work has demonstrated the promise of biomass as a renewable feedstock for the sustainable lactic acid production by connecting waste valorization with green chemical synthesis, highlighting the importance of advanced characterization techniques. The knowledge provided is expected to direct future efforts toward developing affordable, green, and scalable approaches for industrial lactic acid production.

Keywords: Glycerol; Lactic Acid; Base Catalysis; Cu/Solid Base; Poly Lactic Acid; Biodegradable Polymer; CaO; Egg Shells