Mango Kernels Turned Into Biodiesel and Hydrogen-Rich Syngas in One Optimized Process

Every year, millions of tonnes of mango seeds are discarded as waste after the fruit is processed for juice, pulp, and dried products. In Nigeria alone, one of the world’s largest mango producers, the kernels inside those seeds pile up at dumping sites, an untapped reservoir of oil and lignocellulosic fiber. A new study published in Discover Industrial Chemistry and Materials shows that this overlooked agricultural residue can be transformed into two complementary energy carriers at once: a diesel-like biodiesel from the kernel’s oil and a hydrogen-rich biosyngas from the defatted solid residue that remains behind.

The research team, led by Jibrin Mohammed of Nasarawa State University Keffi, together with colleagues at the Federal University of Lafia and Universiti Putra Malaysia, set out to close a gap in the bioenergy literature. While mango kernel oil has been studied before as a biodiesel feedstock, most prior work stopped after extracting the oil and ignored the substantial solid fraction left over. By treating the kernel as a whole biorefinery feedstock, the team demonstrated that both fractions can be converted efficiently, squeezing far more energy out of each kilogram of waste biomass than a single-product approach would allow.

The first stage of the process began with Soxhlet extraction, in which n-hexane solvent was circulated through ground, dried kernels at 65 degrees Celsius for six hours. The extraction recovered 28.14 percent of the kernel mass as oil, a yield comparable to established non-edible feedstocks such as neem seed. Critically, the oil’s free fatty acid content measured just 0.44 percent, below the 0.5 percent threshold at which base-catalyzed transesterification becomes problematic. That means the oil can be converted directly to biodiesel without costly pretreatment steps such as acid esterification, a significant economic advantage for a waste-derived fuel.

Transesterification itself was carried out with sodium methoxide as the catalyst, converting the oil’s triglycerides into fatty acid methyl esters, the chemical constituents of biodiesel. Because the reaction is governed by four interacting variables, the methanol-to-oil molar ratio, catalyst loading, reaction temperature, and reaction time, the team turned to response surface methodology rather than the inefficient one-variable-at-a-time approach. Using a Central Composite Design with 30 experimental trials, they mapped the response surface across the entire operating space and identified the true optimum: a 9:1 methanol-to-oil ratio, 3 weight percent catalyst, 65 degrees Celsius, and 60 minutes of reaction time. Under these conditions the process delivered a biodiesel yield of 92.19 percent.

The statistical rigor of the optimization was striking. The quadratic model fitted to the biodiesel data achieved a coefficient of determination of 0.9948, with an insignificant lack-of-fit test and an adequate precision value of 46.17, far above the threshold of 4 that signals a reliable signal-to-noise ratio. Temperature emerged as the single most influential variable, with an F-value exceeding 1000, followed by the methanol-to-oil ratio. The three-dimensional response surfaces also revealed why multivariate optimization matters: no two-factor combination alone could push yields above roughly 80 percent, while simultaneous tuning of all four parameters unlocked the full 92 percent conversion.

Fuel quality testing against the ASTM D6751 biodiesel standard produced a largely favorable report card. The kinematic viscosity of 2.60 square millimeters per second sat comfortably within the specified range, the cetane number of 51 indicated good ignition quality, the calorific value of 38.62 megajoules per kilogram matched conventional diesel territory, and oxidative stability of 3.12 hours met the minimum specification. Two parameters fell short: the density of 799.40 kilograms per cubic meter and the flash point of 110 degrees Celsius were both below ASTM requirements. The authors note these shortcomings can be addressed through blending or further purification, and they do not diminish the fuel’s overall viability as a renewable diesel substitute.

The real innovation lay in what happened next. Instead of discarding the defatted kernel residue, the team fed it into a laboratory-scale bubbling fluidized-bed gasifier, a stainless-steel reactor 70 millimeters in diameter and 950 millimeters tall, packed with silica sand to stabilize the bed temperature. Steam gasification, the partial oxidation of biomass at high temperature in the presence of steam, breaks the solid material down into a combustible gas mixture dominated by hydrogen and carbon monoxide, with methane and carbon dioxide as secondary constituents. Characterization of the residue beforehand confirmed its suitability: a volatile matter content of nearly 66 percent promotes rapid devolatilization, while low ash and sulfur contents minimize slagging and pollutant formation inside the reactor.

For the gasification stage, the researchers chose a Box-Behnken Design, a response surface approach deliberately suited to thermochemical processes because it avoids running experiments at extreme combinations of variables, where instability and safety risks arise. Seventeen runs explored three factors: gasification temperature, the steam-to-biomass ratio, and particle size. Temperature again proved dominant. Raising the reactor from 700 to 900 degrees Celsius at a steam-to-biomass ratio of 0.6 and a particle size of 2.5 millimeters lifted hydrogen concentration from 29.39 to 37.59 percent, driven by intensified steam reforming and tar-cracking reactions that only proceed effectively at high temperature. The steam-to-biomass ratio boosted hydrogen further, while smaller particles improved heat and mass transfer and accelerated reaction kinetics. Carbon monoxide peaked at 18.85 percent and methane at 10.61 percent under closely related conditions, and the models for all three gases achieved coefficients of determination above 0.998, with validation experiments deviating from predictions by less than 4 percent.

The integrated energy accounting makes the case for the whole-kernel approach. The biosyngas carried a higher heating value of 4.77 megajoules per cubic meter, typical of low-to-medium calorific biomass syngas, while the biodiesel delivered 38.62 megajoules per kilogram as the primary energy carrier. By harvesting both streams from a single feedstock, the process achieves greater overall energy recovery, better resource efficiency, and less waste than either biodiesel production or gasification alone. The authors frame the strategy as particularly relevant for biomass-rich regions such as Nigeria, where biomass still supplies roughly 70 percent of primary energy consumption, much of it through inefficient burning of firewood and charcoal, and where sustainable energy diversification is urgently needed.

The study stops short of a full life cycle assessment and techno-economic analysis, which the authors acknowledge as necessary next steps before commercial deployment. Even so, the work demonstrates a technically sound template for agricultural waste valorization: a statistical framework that pairs a Central Composite Design for liquid fuel synthesis with a Box-Behnken Design for thermochemical conversion, applied to a feedstock that is abundant, cheap, and in direct competition with no food crop. If scaled, the approach could turn mango processing waste from a disposal problem into a distributed source of transport fuel and clean gas, one kernel at a time.

Subject of Research: Integrated conversion of mango kernel biomass into biodiesel and biosyngas via optimized transesterification and steam gasification using response surface methodology

Article Title: Integrated valorization of mango kernel biomass for biodiesel and biosyngas production via optimized transesterification and gasification using response surface methodology

Article References: Mohammed, J., Aremu, M. O., Usman, A., & Muhamad, E. N. (2026). Integrated valorization of mango kernel biomass for biodiesel and biosyngas production via optimized transesterification and gasification using response surface methodology. Discover Industrial Chemistry and Materials, 1(1), Article 8. https://doi.org/10.1007/s44508-026-00009-8

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00009-8

Keywords: mango kernel biomass, biodiesel, biosyngas, transesterification, steam gasification, response surface methodology, central composite design, Box-Behnken design, renewable energy, agricultural waste valorization, hydrogen production, Nigeria bioenergy