INFORM November/December 2025

inform November/December 2025, Vol. 36 (10) • 13

modern society,” said Mohamed El Doukkali, associate profes sor of chemistry at the University of Sultan Moulay Slimane in Morocco and 2024 recipient of the American Cleaning Institute and National Biodiesel Board Glycerine Innovation Award. TO CLEAN OR NOT TO CLEAN Contaminants have been an obstacle to valorizing crude glyc erol, so researchers have been working to either find new, more cost-effective ways to purify it or explore how to use it without purification. The question, Capron said, is whether we have to use pure glycerol or can we use crude glycerol. The first step toward answering this is to better understand how different contaminants affect valorization processes. Capron and his colleagues took steps toward this goal by comparing conversion of pure glycerol and crude glycerol. They found that crude glycerol yielded about half as much end product as the pure form. Next they took pure glycerol and added impurities one at a time and quickly found that MONG was the culprit. “You no longer had access to the active sites,” said Capron. MONG was attaching itself to active sites on their cat alyst, rendering it ineffective. They found that cleaning the catalyst with a solvent after it started losing efficacy would restore it to its original state. However, they also looked into possible ways to make cata lysts that would be less affected by contaminants like MONG. The choice of catalyst material and structure depends heav ily on the desired end product as that determines the type of reaction and reaction conditions used. For example, pyrolysis of glycerol typically runs at 250–300°C and relies on catalysts based on zeolite crystals. Other processes make use of cata lysts made with metals like silver, gold, platinum, palladium or nickel, often deposited on scaffolds of alumina or silica. Capron and colleagues tested catalysts made with different metals and found notable differences in their selectivity and resistance to contaminants. They found that both gold and platinum were highly sensitive to impurities, while silver and palladium were both selective to their target chemicals and more resistant to MONG. PRODUCING PROPYLENE One major area of research into glycerol transformations is in the production of propylene, a simple hydrocarbon used exten sively in plastic manufacturing. With the rapid and accelerating growth in consumer electronic devices, demand for plastics and its precursors like propylene has taken off. However, propylene is typically made from petroleum and the available supply does not always meet demand. Shortages in propylene and fluctua tions in price are making a new and reliable source of the mate rial highly attractive. At the same time there is a growing call for plastic manufacturing that does not rely on fossil fuels and has no carbon dioxide emissions. While other methods like pyrolysis of industrial and urban waste exist, converting crude glycerol to propylene appears to hold promise. There are several methods for converting glycerol into propylene. Steam reforming is one method where carbon and hydrogen bonds are broken apart. The first step is used to

BIOFUEL PRODUCTION

BIODIESEL

EXCESS CRUDE GLYCEROL

BIOTRANSFORMATION

Glycerol

Microbial cells

Value-added compounds

GREENER AND MORE SUSTAINABLE SOLUTION

Source: Wang, et al. , Int J Bio Mac , 261, 129536, 2024.

producer hydrogen or syngas, a mixture of hydrogen and car bon monoxide. Carbon and hydrogen can then be reformed to glycerol. An alternative method that uses an inert atmo sphere rather than steam yields ethylene and smaller amounts of propylene. Both of these processes rely on temperatures of 600-950°C and require bulky equipment, but steam reform ing can be easily integrated into existing petrochemical indus try facilities. Another method, aqueous phase reforming, uses lower temperatures and thus consumes less energy. Hydrodeoxygenation, which uses overlapping deoxygen ation and hydrogenation processes, is another method that El Doukkali and his colleagues are looking into that uses lower temperatures and would have a lower carbon footprint. “We also considered crucial aspects like minimizing costs, energy consumption and greenhouse gas emissions,” said El Doukkali. Whichever method is used, the key to success will be designing an optimal catalyst. As mentioned, many catalysts used in valorizing glycerol use metals like molybdenum, plat inum, palladium or nickel deposited on a scaffold made of a material like alumina or silica. Tweaking the materials used, how they are deposited, and the structure of a catalyst can heav ily influence the catalyst’s efficacy and durability. The goal is to design a catalyst that can work in milder conditions, reduc ing energy use and resisting degradation and the formation of a carbon-rich material known as coke. This material is produced when heating carbon in the absence of air and deposits on a cat alyst’s active sites, keeping them from working. One study found that modifying existing catalysts used in steam reforming can reduce the temperatures needed. Similarly, thoughtful designs could improve the performance and durability of catalysts used in hydrodeoxygenation of glycerol.