OCL 2025, 32, 7DOI: 10.1051/ocl/2025003© Y.Y. Boko-Haya et al., Published by EDP Sciences, 2025

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Research Article

Assessment of the combustion properties and energy potential of Ricinodendron heudelotii (Pax Heckel) husks☆

Évaluation des propriétés de combustion et du potentiel énergétique des coques de Ricinodendron heudelotii (Pax Heckel)

Yves Yatindo Boko-Haya¹,2* orcid, Christine A.I.N. Ouinsavi² orcid, Jérémy Valette³ orcid, Gilles Vaitilingom³ orcid and Clément Agbangla¹

¹ Laboratoire de Génétique Moléculaire et d’Analyse des Génomes, Faculté des Sciences et Techniques, Université d’Abomey-Calavi, 01BP 526, Cotonou, Bénin
² Laboratoire d’Etudes et de Recherches Forestières (LERF), Faculté d’Agronomie, Université de Parakou, BP 123 Parakou / Benin
³ CIRAD, Unité de Research BioWooEB, 34000, Montpellier, France

* Corresponding author: tadagbemetin@gmail.com

Received: 20 June 2024 Accepted: 22 February 2025 Published online: 24 March 2025

Abstract

The use of biomass, such as seed husks, for fuel production through pyrolysis is a key technology aimed at replacing fossil fuels with renewable energy sources, thereby contributing to a cleaner environment. This study assesses the energy potential and chemical composition of the husks of Ricinodendron heudelotii, highlighting their suitability for biofuel production. The proximate analysis of the kernel husks revealed ash, volatile matter, fixed carbon, and moisture contents of 18.80%, 59.80%, 21.40%, and 8.60%, respectively. The elemental analysis showed carbon, hydrogen, and nitrogen ratios of 47.0%, 4.52%, and 0.54%, respectively. Additionally, the lower heating value was determined to be 18.29 MJ/kg for the husks (dry basis). This composition, comparable to that of other energy crops cultivated globally for energy production, suggests that R. heudelotii could compete with standardized species used as raw materials for biofuels. This study opens up new possibilities for using Ricinodendron heudelotii husks as significant woody biomass fuel for domestic or industrial heating.

Résumé

L’utilisation de biomasse, telle que les coques de graines, pour la production de carburant par pyrolyse, est une technologie clé visant à remplacer les combustibles fossiles par des énergies renouvelables, contribuant ainsi à un environnement plus propre. Cette étude évalue le potentiel énergétique et la composition chimique des coques de Ricinodendron heudelotii, mettant en évidence leur aptitude à la production de biocarburant. L’analyse immédiate des coques d’amandes a révélé des proportions de cendres, de matières volatiles, de carbone fixe et d’humidité de 18,8 %, 59,8 %, 21,4 % et 8,6 % respectivement. L’analyse élémentaire a fourni des ratios de carbone, d’hydrogène et d’azote de 47,0 %, 4,52 % et 0,54 % respectivement. En outre, la valeur calorifique inférieure a été déterminée à 18,29 MJ/kg pour les coques (base sèche). Cette composition, comparable à celle d’autres plantes énergétiques cultivées mondialement pour la production de biocombustible, suggère que R. heudelotii pourrait rivaliser avec des espèces standardisées utilisées comme matières premières pour les biocarburants. L’étude ouvre de nouvelles perspectives pour l’utilisation des coques de Ricinodendron heudelotii comme un combustible biomasse ligneux important pour le chauffage domestique ou industriel.

Key words: Oleaginous seeds / biomass valorization / higher heating value / pyrolysis / renewable fuels

Mots clés : Graines oléagineuses / valorisation de la biomasse / pouvoir calorifique supérieur / pyrolyse / carburants renouvelables

☆

Contribution to the Topical Issue: “Non-Food Uses Of Oil- And Protein- Crops / Usages Non Alimentaires des Oléoprotéagineux”.

Highlights

The study evaluates the energy potential and chemical composition of Ricinodendron heudelotii husks for biofuel production.

Proximate analysis reveals 18.8% ash, 59.8% volatile matter, and 21.4% fixed carbon, comparable to standard energy crops.

The husks have a lower heating value of 18.29 MJ/kg, indicating their bioenergy potential.

R. heudelotii husks could serve as a fossil fuel alternative, promoting cleaner energy.

1 Introduction

The Sustainable Development Goal (SDG) addressing the use of energy for cooking is SDG 7, specifically target 7.1, which aims to "ensure universal access to affordable, reliable, and modern energy services by 2030." This includes access to clean, safe, and sustainable cooking solutions, replacing traditional methods such as wood or charcoal use, which are often inefficient and polluting. The latest report from the International Energy Agency shows that among the 2.3 billion people worldwide who still lack access to clean cooking facilities, Asia and sub-Saharan Africa are the main areas of concern, with more than 1.2 billion and 990 million respectively in 2022. The rate of access to clean cooking facilities in sub-Saharan Africa is below 20%, with an increasing number of people without access to clean cooking (https://www.iea.org/reports/sdg7-data-and-projections/access-to-clean-cooking, consulted on May 18, 2024). The traditional use of wood and charcoal for cooking is responsible for indoor air pollution from cooking smoke, which causes approximately 3.7 million premature deaths per year. Furthermore, the use of wood and charcoal for cooking negatively impacts the environment through deforestation and climate change (Vihi et al., 2022; Bockarie et al., 2020).

The use of biogas, improved cookstoves, or less polluting cooking fuels are some recommended solutions (Negash et al., 2021). Among the less polluting cooking fuels, pyrolyzed seed husks represent a viable and less polluting solution, particularly suited to rural populations (Azeta et al., 2021). These fuels, produced from biological resources like plants, animal waste, and organic waste, are known as "biofuels."

The pyrolysis process of biological resources (biomass), such as wood, cereals, or seed husks, involves heating organic matter in the absence of oxygen to produce bio-oil, charcoal, and flammable gas (Yang et al., 2014; Dhyani and Bhaskar, 2018; Husain et al., 2020; Azeta et al., 2021). This method has great potential for long-term waste management as it reduces the amount of unused plant products while reducing greenhouse gas emissions, contributing to addressing climate change concerns. Numerous studies on lignocellulosic biomass have demonstrated various conversion technologies that can transform lignocellulosic biomass into biofuels (Abdullah et al., 2022; Ramesh et al., 2021; Anwar et al., 2014). The pyrolysis of raw biomass is considered a promising technology for producing renewable fuels and reducing greenhouse gas emissions (Aboelela et al., 2023; Fan et al., 2011).

Oleaginous seeds are an important source of renewable energy as they contain a large amount of oil that can be used directly as fuel in diesel engines (Torres-García et al., 2020). In a context of increasingly accentuated climate change, the diversification of energy sources has become very urgent. According to the International Energy Agency’s report (2022), diversifying energy sources in Africa is essential to reduce dependence on imported fossil fuels. Biofuels produced from oleaginous plants can play a key role in this transition by offering a renewable and local energy option, especially in rural areas where access to energy is limited.

Sub-Saharan Africa is characterized by the presence of numerous untapped oleaginous trees with the greatest potential for biofuels (Hounsou-Dindin et al., 2022; Ambali et al., 2011). The sustainable management of oleaginous plants in bioenergy can help reduce dependence on fossil fuels, combat climate change, and promote sustainable agriculture (Zhang et al., 2018). However, potential biomass resources have not been studied, particularly the waste from oleaginous plants integrated into agro-systems and widely distributed geographically.

Ricinodendron heudelotii, a Euphorbiaceae forest tree, is widely distributed throughout West, Central, and East Africa (Tchoundjeu and Atangana, 2006; Leonard, 1961). R. heudelotii is an important species in agroforestry as it is often associated with economically valuable species such as cocoa (Theobroma cacao L.), oil palm (Elaeis guineensis), and coffee (Coffea arabica L.), as highlighted by the work of Franzel et al. (2007), Mollet et al. (1995) and Djeugap et al. (2013) in Cameroon and Nigeria. Many traditional uses and numerous anti-inflammatory and antioxidant activities have been recognized by various studies (Nguyen et al., 2022; Kinge et al., 2019; Yakubu et al., 2019; Ene-Obong et al., 2018; Boko-haya et al., 2017). The fruit of this tree is a yellow-green indehiscent capsule, generally spherical, measuring 2 to 5 cm in length and 2.5 to 4 cm in width; it typically contains 1, 2, or 3 seed lobes and can weigh between 19 and 47 g (Ngo Mpeck et al., 2003). The single seed is spherical, rough on the surface, weighs 2 g, is reddish-black in color, and contains a yellow kernel inside. The production and marketing of the kernels are growing, allowing local farmers to make profits (Ndumbe et al., 2018; Cosyns et al., 2011; Tabuna, 1999). Previous studies have highlighted a significant variation in kernel size with high levels of carbohydrates (6.11–8.83%), proteins (49.9–65.2%), and lipids (43.1–67%) [(Boko-haya et al., 2022; Manga et al., 2000; Yirankinyuki et al., 2018; Coulibaly et al., 2018)]. Several parts of the fruit, such as the mesocarp, the endocarp constituting more than 20% of the fresh fruit, and the seed husks are often considered waste. However, their valorization as a potential raw material for biofuel production could offer additional sources of income to fight poverty (Ejigu, 2008; Adeoye et al., 2022).

The objective of this study was to evaluate the potential of R. heudelotii seed shells fuel energy sources by determining the energy content of the husks and comparing them with other common fuels. The results will help clarify the viability of R. heudelotii husks as a renewable energy source.

2 Materials and methods

2.1 Description of the collection site

The seeds used originated from the southern phytogeographic zone of Benin (6°25’E to 7°30’N), characterized by a Guineo-Congolese climate with annual rainfall ranging from 900 to 1300 mm. This region includes the Plateau phytodistrict, which is dominated by semi-deciduous dense forests on hydromorphic soils, with annual rainfall between 1100 and 1300 mm (Adomou et al., 2006).

2.2 Sampling

Mature fruits that had fallen to the ground were collected, and the seeds were extracted. In Akassato (6°30’25.207"N, 2°20’58.382"E), with an average temperature of 27 °C, these seeds were alternately dried in the shade and under sunlight. This process promoted the natural detachment of the kernels from the shell walls, facilitating the extraction of intact kernels after a light cracking of the extremely hard husks (Fig. 1).

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Fig. 1

Husks of Ricinodendron heudelotii.

2.3 Evaluation of fuel characteristics

The moisture content (MC) of the solid fuel was determined according to the standard NF EN ISO 18134-3. One gram of the sample was heated in an oven at 105 °C until a constant mass was obtained. The samples were then cooled in a desiccator and their mass was measured and compared to their initial mass before heating to determine the MC.

For ash content, 1 gram of the biomass sample (Mbiomass) was calcined in a muffle furnace (NF EN ISO 18122) maintained at 550 °C until a constant mass was obtained. The samples were then cooled in a desiccator and their mass was measured (MAsh). The ash content was calculated on a dry mass basis according to equation (1). equation(1)

For volatile matter, it was calculated according to the standard NF EN ISO 18123. Approximately 1 g of the biomass sample (Mbiomass) was heated in a muffle furnace for 7 min at 900 °C without oxygen. The samples were then cooled in a desiccator and their mass was measured (Mresidue). The volatile matter was calculated on a dry mass basis according to equation (2). equation(2)

The fixed carbon is the remaining carbon after the removal of volatile matter and ash. The fixed carbon content (CF) is deduced by difference on a dry basis and is given by the formula: CF(%) = 100 − (MV (%) + Ash content (%))

Elemental analyses were performed using an Elementar Vario Macro Cube CHN analyzer according to the standard EN ISO 16948 for raw biomass (and adapted for vegetable oil) of R. heudelotii. Before analysis, samples were wrapped in tin foil and three tests were performed for the sample. The carbon, hydrogen, and nitrogen contents were determined respectively from the quantification of CO₂, H₂O, and N₂ (after reduction of NOx) produced by the combustion of the samples. All results from triple repetition (MC and ash) and double repetition (MV, C, H, and N) are reported with a precision of 0.20%.

2.4 Calorific values

The calorific value was determined according to EN ISO 18125 standard, using an Isoperibol Fixed Bomb Parr 6200 automatic bomb calorimeter, under an O2 atmosphere to ensure complete combustion of the sample. The calorimetric equivalent (Ecal) was determined before starting the experiments using benzoic acid. Approximately 0.5 g of biomass mass was required to perform the calorific tests. Three repetitions were analyzed for the biomass material. The higher heating value (HHV) is defined as the amount of heat released per unit mass of fuel (initially at 25 °C) when burned and brought back to a temperature of 25 °C (Basu, 2013). The calorimeter automatically calculates the highest calorific value of the received sample HHV, taking into account the correction of the fuse combustion according to equation (3). equation(3)

where K₁ is a conversion factor (4.18 × 10⁻⁶ MJ cal⁻¹); Ecal is the calorimetric equivalent of the calorimeter device in Cal.° C⁻¹; Tm and Ti are the maximum and initial temperatures in °C; L is the length of the burned fuse in cm; Ept is the higher heating value of the constant volume fuse wire in cal cm⁻¹ (= 2.3 cal cm⁻¹); and M is the mass of the sample in kg. The higher heating value on a dry basis (HHV db) and the corresponding lower heating values at constant pressure for a dry sample (LHV db) were calculated in accordance with the CEN/TS 14918 standard (Biofuels, 2005) using equations (4) and (5). equation(4) equation(5)

with X: Hydrogen content of the sample in % dry basis. Calorific analyses were duplicated for each sampling modality, and all results are given with a precision of ±1%.

3 Results and discussion

Proximate, ultimate, and calorific value analyses of the raw husks of Ricinodendron heudelotii is reported for the first time in this study. Table 1 presents the results of proximate, ultimate, and calorific value analyses of the raw husks of Ricinodendron heudelotii, compared to other species whose shell characteristics are considered standard solid fuels. The concentration of essential chemical elements for evaluating the energy potential of the raw husks of R. heudelotii indicates that the average ash content is 18.80 ± 0.69%, which is higher than other standardized biomasses such as peanut husks, argan husks, palm husks, and sunflower husks, which have ash contents of 3.25%, 1.50%, 1.35%, and 1.20%, respectively. However, despite this high value, it is similar to the current ash content (18.30%) of rice husks used in boilers (Kaniapan et al., 2021; Nazar et al., 2021).

The moisture content of R. heudelotii seed husks is 8.60 ± 0.15%, which is lower than all other referenced species except for coconut husks, which have a moisture content of 7.82%. Moisture content influences the lower calorific value, combustion efficiency, and mechanical durability of solid biofuels (Shojaeiarani et al., 2019). Low moisture content in biofuels increases their energy efficiency as less energy is required to evaporate the water from the fuel before it can be burned. Additionally, the observed moisture content remains low compared to the limit value (usually below 10%) required for the optimal operation of boilers. The average volatile matter content of R. heudelotii husks is 59.80± 0.46%, lower than that of sunflower husks (82.70%) (Turzyński et al., 2021) and peanut husks (80.24%) (Perea-Moreno et al., 2018). Generally, biofuels with low volatile matter tend to burn more efficiently and produce fewer emissions.

On average, the fixed carbon content of R. heudelotii husks is 21.40 ± 1.12%, which is lower than that of palm and argan husks (26.14% and 28%, respectively), but higher than that of peanut and sunflower husks (13.40% and 16.10%, respectively) already used as energy sources. The proximate analysis of R. heudelotii husks compared to various plants already utilized shows great potential for energy production or biochar.

The elemental chemical analysis of the raw husks of Ricinodendron heudelotii revealed a higher concentration of carbon (47.0%) and a lower nitrogen content (0.54%) on a dry basis. These results are consistent with those of referenced species considered standard solid fuels, where the carbon content of raw biomass ranged from 39.22% (coconut husks) to 53.29% (oil palm husks) and the nitrogen content ranged from 0.005% (argan husks) to 1.03% (peanut husks).

These findings confirm that raw biomasses are predominantly composed of the element carbon (Biaye, 2022). The high carbon content suggests a high energy density. Indeed, there is a linear relationship between the carbon content (C) and the higher heating value (Demirbaş et Demirbaş, 2004; Sedai et al., 2016).

The higher heating values (HHV) of 19.25 MJ/kg and lower heating values (LHV) of 18.29 MJ/kg obtained for R. heudelotii husks are among the highest when compared to standardized species. These values are notably similar to those reported for peanut husks (18.54 MJ/kg and 17.11 MJ/kg, respectively) according to a previous study (Perea-Moreno et al., 2018). Furthermore, they are comparable to those measured for the trunk of Acacia holosericea (18.13 MJ/kg), recognized as a decent biomass for biofuel production (Reza et al., 2019). These findings highlight the substantial energy potential of R. heudelotii husks in comparison to the husks of other standardized species used as reference solid fuels. These energy-rich husks can be used as fuel in household stoves. This high energy potential is likely due to the elevated fixed carbon content (21.40%).

Table 1

Proximate, ultimate, and calorific values of raw husks of R. heudelotii compared to other species considered as standard solid fuels.

4 Conclusion

This study highlights the potential of Ricinodendron heudelotii (Pax Heckel) husks as a biofuel source. The elemental and proximate compositions, along with the calorific values, are comparable to those of established biofuel species. R. heudelotii husks demonstrate suitability for use in household or improved cookstoves, offering a sustainable alternative that could help reduce deforestation and air pollution from smoke. However, further research is necessary to evaluate the socio-economic and environmental implications of adopting R. heudelotii husks as a fuel source. Establishing a framework for integrating such renewable resources into the country’s energy strategies is essential to support future sustainable development initiatives.

Conflicts of interest

The authors declare no conflicts of interest in regards to this article.

Author contribution statement

Conceptualization: B.Y., G.V., O.C,; Supervision : OC, AG, GV.; Validation : G.V., O.C., Survey, Original draft preparation : B.Y., Writing, Mehods and analysis : J.V., G.V., Review & Editing : G.V., O.C.; J.V. Resources : G.V.

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Cite this article as: Boko-Haya YY, Ouinsavi CAIN, Valette J, Agbangla C, Vaitilingom G. 2025. Assessment of the combustion properties and energy potential of Ricinodendron heudelotii (Pax Heckel) husks. OCL 32: 7. https://doi.org/10.1051/ocl/2025003

All Tables

Table 1

Proximate, ultimate, and calorific values of raw husks of R. heudelotii compared to other species considered as standard solid fuels.

In the text

All Figures

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Fig. 1

Husks of Ricinodendron heudelotii.

In the text

Fig. 1

Husks of Ricinodendron heudelotii.

Table 1

Proximate, ultimate, and calorific values of raw husks of R. heudelotii compared to other species considered as standard solid fuels.

Parameters | R. heudelotii | ¹Sunflower | ²Peanut | ³Argan | ⁴Palm | ⁵Coconut
% Fixed Carbon (db) | 21.40 ± 1.12 | 16.10 | 13.40 | 28 | 26.14 ± 0.15 | 12.04 ± 0.04
% Humidity (db) | 8.60 ± 0.15 | 9.61 | 9.72 | 9.50 | 8.92 ± 0.17 | 7.82 ± 0.02
% Volatile matter (db) | 59.80 ± 0.46 | 82.70 | 80.24 | 61 | 72.02 ± 0.21 | 79.91 ± 0.05
% Ash (db) | 18.80 ± 0.69 | 1.20 | 3.25* | 1.50 | 1.35 ± 0.53 | 0.23 ± 0.003
% Carbon (db) | 47.0 ± 1.98 | 46.21 | 46.42 | 51.33 | 53.29 ± 0.09 | 39.22 ± 0.71
% Hydrogen (db) | 4.52 ± 0.15 | 6.06 | 6.84 | 6.32 | 6.15 ± 0.11 | 4.46 ± 0.08
% Nitrogen (db) | 0.54 ± 0 | 0.88 | 1.03 | 0.005 | 0.30 ± 0.01 | 0.22 ± 0.02
HHV (MJ/kg) | 19.25 ± 0.08 | 18.11 | 18.54* | 18.3 | 18.72 | 9.62 ± 0.50
LHV (MJ/kg) | 18.29 ± 0.11 | – | 17.11* | 17 | 17.27** | –

Note: results of R. heudelotii are given as the mean ± standard error of three analyses. ¹(Turzyński et al., 2021); ²(*Perea-Moreno et al., 2018; Varma et al., 2022); ³(Rahib et al., 2021); ⁴(Shrivastava et al., 2021); **(Pawlak-Kruczek et al., 2020); ⁵(Sarkar and Wang, 2020); db = dry basis.