In an article published in Catalysts, a team of researchers including Jaime Ñanculeo, Benjamín Nahuelcura, Mara Cea, Norberto Abreu, Karla Garrido-Miranda, Sebastián Meier, Juan Miguel Romero-García, and María Eugenia González detail a new, cost-effective method for producing biodiesel. Their study, “Microwave-Assisted Biodiesel Production Using Activated Oat Hull-Derived BiocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More as Catalyst,” investigates how activating biochar with potassium hydroxide (KOH) can enhance its catalytic properties. The process uses waste cooking oil (WCO) as a feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More and is significantly accelerated by microwave irradiation. The research aims to provide a straightforward and cost-effective approach for biofuel production by valorizing agricultural waste.

The researchers synthesized an activated biochar catalyst from oat hulls, an agricultural waste product, through a process involving KOH activation and pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More. This activation process was found to significantly increase the biochar’s specific surface area (SSA). The optimal conditions for producing the catalyst, identified through an experimental design, were found to be a temperature of 600∘C for three hours and a KOH/biomass ratio of 2. Under these conditions, the catalyst achieved a maximum SSA of 637.28 m2/g. By contrast, a non-activated biochar sample showed a rough surface with limited porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More, which would restrict catalytic activity. The high SSA and porous structure of the activated biochar are crucial, as they improve the transfer of mass during the reaction and increase the number of available active sites.

The activated biochar proved to be a highly efficient catalyst for converting WCO into biodiesel, or fatty acid methyl esters (FAME). When tested in a microwave-assisted transesterification reaction, the catalyst achieved a maximum FAME yield of 100% in just one minute. This rapid conversion time is a major advancement, as the reaction with non-activated biochar was almost negligible. The impressive efficiency is attributed to the basic active sites generated by the KOH activation, which facilitate the deprotonation of methanol—a key step in the transesterification process. The microwave-assisted technology further enhanced the reaction by improving heat transfer and increasing the molecular vibration of methanol, which lowered the activation energy required.

The study also evaluated the reusability of the activated biochar catalyst across three successive reaction cycles. The FAME yield from the unwashed catalyst dropped significantly from 100% in the first cycle to about 51% by the third cycle, a 49% reduction in catalytic activity. In the case of methanol-washed catalysts, the FAME yield started at around 97% but was undetectable by the third cycle. This decline in catalytic activity was attributed to potassium leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More from the catalyst’s active sites into the reaction mixture. The authors highlight that this finding underscores the need for optimization strategies to improve the catalyst’s stability and reusability for long-term use.

An economic and energy evaluation of the process estimated a catalyst production cost of USD 176.97/kg. The high cost of KOH and HCl required for the activation and neutralization steps were the primary contributors to this price. However, the overall biodiesel production cost was estimated at just USD 8.9/kg of FAMEs. This low production cost is a direct result of the high FAME yield (100%) and the extremely short reaction time (1 minute) achieved under the optimal conditions (150∘C, 2.5% catalyst dosage, and a WCO/MeOH molar ratio of 1/12). The researchers conclude that this straightforward and cost-effective approach has significant potential for scaling up, offering a promising solution for the efficient and environmentally friendly production of biodiesel from waste materials, contributing to a more sustainable energy future.

Source: Nanculeo, J., Nahuelcura, B., Cea, M., Abreu, N., Garrido-Miranda, K., Meier, S., Romero-García, J.M., & González, M.E. (2025). Microwave-Assisted Biodiesel Production Using Activated Oat Hull-Derived Biochar as Catalyst. Catalysts, 15(8), 729.