Chemists Turn Biomass Into Lactic Acid, Paving the Way for Plastic-Free Future

Lactic acid rarely makes headlines, yet this humble three-carbon molecule sits at the heart of one of the most urgent transitions in modern chemistry. It flavors food, stabilizes pharmaceuticals, and, most importantly, serves as the monomer for polylactic acid, a biodegradable polymer that could help the world escape its dependence on petroleum-derived plastics. Today, nearly all industrial lactic acid is made by fermenting sugars with bacteria, a process that delivers high purity but demands strict pH control, lengthy reaction times, and expensive purification. Worse, it typically consumes edible feedstocks such as glucose, sucrose, and starch, putting chemical production in direct competition with the food supply. Raw materials alone can account for more than a third of total production cost.

A comprehensive new review published in Discover Green Chemistry argues that a quiet revolution is underway. Researchers led by Xinli Tang, Huayue Sun, and Jiankui Sun of North China University of Science and Technology systematically survey two decades of progress in chemically catalyzing the conversion of biomass, especially non-edible lignocellulosic material such as straw, wood, and agricultural waste, into lactic acid. Their analysis organizes the field into three competing routes: alkaline catalysis, acid catalysis, and an emerging family of photocatalytic and photothermal approaches that harness sunlight to drive the reaction at room temperature. Each route, the authors conclude, shares a common reaction network but differs in which step limits the overall rate, a unifying insight that could accelerate catalyst design across the entire field.

That shared network begins with sugars. Glucose, a six-carbon aldose, must first be isomerized into fructose, a transformation that Lewis acid sites catalyze through an intramolecular hydride shift known as the Lobry de Bruyn–van Ekenstein rearrangement. Fructose then undergoes retro-aldol cleavage, splitting into two three-carbon fragments, dihydroxyacetone and glyceraldehyde. These trioses dehydrate to pyruvaldehyde, which finally rearranges into lactic acid via a 1,2-hydride shift. Because fructose skips the isomerization step, it consistently outperforms glucose under identical conditions, while xylose, a five-carbon sugar, inevitably sacrifices part of its carbon skeleton to glycolic or formic acid, capping its lactic acid yield. The review reports yields exceeding 70 percent for glucose and up to 97 percent under optimized acid catalysis, but warns that raw lignocellulose typically delivers less than 50 percent because the recalcitrant lignin matrix blocks catalyst access and poisons active sites.

Alkaline catalysis, the oldest chemical route, exploits strong bases such as sodium and potassium hydroxide to cleave carbon-carbon bonds under hydrothermal conditions at or above 473 kelvin. Early work by Yan and colleagues showed that calcium and barium hydroxides form transition complexes with sugar intermediates, promoting selective C3–C4 bond cleavage, and that cellulose and starch could be converted directly to lactic acid in yields near 19 percent. More strikingly, Li’s group later achieved a 95.4 percent lactic acid yield from glucose at room temperature under anaerobic conditions, using barium hydroxide both as catalyst and as a reactant that traps the product as barium lactate. Yet the route carries a heavy price: high alkali concentrations generate salt waste, corrosion, and costly neutralization steps, and homogeneous bases cannot be recycled at all, making the economics unattractive for large-scale production.

Heterogeneous base catalysts attempt to resolve these problems. Layered double hydroxides of magnesium and aluminum, for example, enabled Albuquerque and colleagues to convert hydroxyacetone to lactic acid with 100 percent selectivity at just 40 degrees Celsius, using a recyclable solid base that eliminates neutralization entirely. Copper-based systems have proven particularly versatile: CuO supported on zirconia achieved complete glycerol conversion with 94.6 percent lactic acid selectivity, while copper oxide loaded on magnesia delivered a 70 percent yield from glucose at a relatively mild 393 kelvin. Glycerol itself, a cheap byproduct of biodiesel production, has emerged as a star feedstock, with noble-metal and copper catalysts converting it to lactic acid at yields of 80 to 96 percent, its simple C3 structure sidestepping the isomerization bottleneck that plagues six-carbon sugars.

Acid catalysis, however, is where the review places its strongest bet. Lewis acid zeolites, metal oxides, and rare-earth catalysts convert carbohydrates directly in water without the neutralization burden of alkaline chemistry. Tin-substituted beta zeolite, whose isolated tetrahedral Sn4+ sites act as water-tolerant Lewis acids, achieved a 67.1 percent lactic acid yield from glucose, while hierarchical zirconium zeolites reached 67.9 percent from xylose. Dealuminated ZSM-5 supported with erbium pushed yields to 69.1 percent by suppressing the formation of humins, the insoluble carbonaceous byproducts that plague sugar conversion. Rare-earth metals proved even more striking: erbium chloride delivered lactic acid from cellulose at yields up to 91 percent, and ytterbium chloride converted sugarcane bagasse to lactic acid within 15 minutes. Computational studies showed that heavier lanthanide ions lower the energy barrier for the critical C3–C4 bond cleavage, explaining their exceptional activity.

The most eye-catching numbers, though, come from the newest branch of the field: photocatalysis and its hybrid cousin, photothermal catalysis. Cao and colleagues developed a nitrogen-doped titanium dioxide catalyst that produced lactic acid from sugars with a 98.9 percent yield at just 60 degrees Celsius within 30 minutes under visible light. Huang’s team engineered a highly crystalline carbon nitride with structural oxygen that converted glucose at room temperature in 50 minutes, while Liu’s triazole-modified carbon nitride delivered yields of 85.5 to 98.3 percent from various sugars with 98.6 percent selectivity. Life cycle assessments attached to these systems are remarkable: the fluorine-doped carbon nitride route was calculated to generate only 0.7 kilograms of carbon dioxide equivalent per kilogram of lactic acid, roughly one-sixth of the petrochemical route, with an 87.8 percent reduction in fossil resource depletion.

Photocatalysis has historically been hobbled by poor selectivity. Mechanistic work by Zhang and colleagues revealed why: on pristine titanium dioxide, pyruvaldehyde preferentially follows low-barrier proton-coupled electron transfer pathways, producing unwanted C3 oxygenates, while the selective hydride shift to lactic acid faces a barrier of 1.22 electron volts. The solution proved elegant. By introducing oxygen vacancies that create Lewis acid sites and adding plasmonic gold nanoparticles that convert absorbed light into localized heat, the researchers steered the reaction toward the desired Cannizzaro-type pathway, achieving more than 90 percent lactic acid selectivity, a 3.4-fold improvement. Similar atomic-level heterojunctions, such as copper–sulfur moieties embedded in a cadmium zinc sulfide host, boosted glycerol conversion tenfold with selectivity above 95 percent, demonstrating that rational catalyst architecture can overcome the intrinsic kinetic limitations of light-driven chemistry.

Economics and durability remain the field’s stubborn obstacles. A landmark techno-economic assessment based on a 50,000-ton-per-annum plant suggested that erbium chloride-catalyzed glucose conversion could deliver an internal rate of return above 20 percent, but only if the expensive rare-earth catalyst is efficiently recovered and reused. Metal leaching from zeolites in hot water, carbonaceous fouling of oxide surfaces, and photocorrosion of semiconductors all erode catalyst lifetimes, and the review proposes a stability ranking that places zirconia and niobia at the top, followed by tin zeolites, carbon nitride photocatalysts, and layered double hydroxides. The authors argue that acid catalysis currently offers the best near-term balance of yield, feedstock flexibility, and practicality, while photocatalysis represents the most sustainable long-term option, pending breakthroughs in quantum efficiency and compatibility with real, untreated biomass.

What emerges from this sweeping analysis is a field in transition, moving from model sugars toward genuine waste streams, from precious metals toward abundant copper, zinc, and aluminum, and from brute-force heating toward sunlight-driven, carbon-negative chemistry. If researchers can marry the anti-leaching catalyst designs and standardized regeneration protocols the review calls for with the ambient-condition promise of photothermal systems, lactic acid could shift from a fermentation commodity to a cornerstone of the sustainable bioeconomy, and the biodegradable plastics built from it may finally compete with, and replace, the petrochemical polymers that now choke the planet.

Subject of Research: Chemo-catalytic conversion of biomass into lactic acid using alkaline, acid, and photocatalytic processes

Article Title: Research progress in the preparation of lactic acid from biomass by chemical catalytic process

Article References: Tang, X., Sun, H., Shi, Q., Zheng, D., Xie, J., & Sun, J. (2026). Research progress in the preparation of lactic acid from biomass by chemical catalytic process. Discover Green Chemistry, 1(1), Article 36. https://doi.org/10.1007/s44509-026-00038-8

Image Credits: AI Generated

DOI: 10.1007/s44509-026-00038-8

Keywords: lactic acid, biomass, catalysis, Lewis acid, photocatalysis, photothermal catalysis, polylactic acid, lignocellulose, zeolites, rare-earth catalysts, green chemistry, bioplastics