Potential uses of Caryocar brasiliense Camb. (pequi) charcoalAbstract
Caryocar brasiliense Camb., popularly known as pequi, is a tree species native to Brazil with significant cultural, social, and environmental value, especially in the northern region of the state of Minas Gerais. However, during its commercialization process, a significant challenge is the proper utilization of the waste generated from its shell. This study aims to characterize the biomass and charcoal obtained from pequi bark, evaluating different carbonization temperatures (350, 400, and 450°C). The lignocellulosic characterization indicated a high content of extractives (56.82%) and holocellulose and lignin contents of 29.43% and 13.74%, respectively. The proximate analysis showed 71.36% volatile material, 20.63% fixed carbon, and 8.01% ash, while the calorific value found for the biomass was 18.99 MJ kg-1. In the charcoal, increasing the final carbonization temperature was directly proportional, resulting in higher percentages of ash, fixed carbon, pH, electrical conductivity, and calorific value, with the exception of volatile material and charcoal gravimetric yield, which decreased. The results demonstrated the technical feasibility of converting pequi bark into charcoal, with potential applications in the energy sector, effluent treatment, and as a soil conditioner. It also contributes to regional sustainable development and the mitigation of greenhouse gas emissions.
Keywords:
semiarid; Caryocar brasiliense; charcoal; pyrolysis; solid waste
Resumo
Caryocar brasiliense Camb., popularmente conhecido como pequi, é uma espécie arbórea nativa de grande valor cultural, social e ambiental, especialmente para a região norte do Estado de Minas Gerais, Brasil. Contudo, durante o seu processo de comercialização, enfrenta-se uma problemática quanto ao aproveitamento dos resíduos gerados por sua casca. O presente estudo tem como objetivo caracterizar a biomassa e o carvão obtido a partir da casca de pequi, avaliando diferentes temperaturas (350, 400 e 450ºC) de carbonização. A caracterização lignocelulósica indicou um elevado teor de extrativos (56,82%) e teores de holocelulose e lignina de 29.43% e 13.74%, respectivamente. A análise imediata apresentou 71,36% de material volátil, 20,63% de carbono fixo e 8,01% de cinzas, enquanto o poder calorífico encontrado para biomassa foi de 18,99 MJ kg-1. No carvão, o aumento da temperatura final da carbonização foi diretamente proporcional resultando em um aumento no percentual de cinzas, carbono fixo, pH, condutividade elétrica e poder calorífico, com exceção do material volátil e rendimento gravimétrico do carvão, que diminuíram. Os resultados demonstraram a viabilidade técnica da conversão da casca de pequi em carvão, com potencialidades para aplicação nos setores energéticos, de tratamentos de efluentes e como condicionador solos. Além de contribuir para o desenvolvimento sustentável regional e na mitigação de emissões de gases de efeito estufa.
Palavras-chave:
semiárido; Caryocar brasiliense; carvão vegetal; carbonização; resíduos sólidos
1. Introduction
The northern region of the state of Minas Gerais, Brazil, located in the biome, is economically recognized for the commercialization of pequi (Caryocar brasiliense Camb), an endemic species of the biome protected by Law No. 10.883 (Minas Gerais, 1992), and of great cultural and economic value for local communities. The collection of its fruits is carried out by extractivists and traditional communities, who play an important role in environmental preservation and conservation, in addition to contributing to food supply and self-consumption (De Oliveira et al., 2019). Among the groups that stand out in this region are the traditional peoples known as "geraizeiros," a symbol of resistance, who have strong ties to the Nascentes Geraizeiras Sustainable Development Reserve, from which a large quantity of native fruits is obtained, including pequi (De Melo et al., 2023).
The pequi has various applications, such as in the pharmaceutical industry, cosmetics, and oil extraction (Escobar et al., 2016; Delalibera et al., 2024; Sobral et al., 2025). According to the Brazilian Institute of Geography and Statistics (IBGE, 2023), in 2023, Minas Gerais produced 39.630 tons of pequi, and initiatives such as the Cooperativa Grande Sertão and the Pequi Nucleus are working to promote strategies for organizing and improving the Local Productive Arrangement (APL) of pequi in the northern region of the state.
However, the production and commercialization of pequi generate a significant amount of waste, primarily composed of fruit shells, with an estimated 80% being discarded (Magrin, 2024), often without proper environmental disposal. In this context, alternatives for the reuse of these peels arise, such as in the form of organic substrate, textile effluent adsorbent, composite panels, flour for culinary use, bioethanol, as well as for obtaining extract in studies on cardiovascular diseases, among others (Da Costa et al., 2017; Barroso et al., 2019; Moreira et al., 2020; Magrin, 2024).
A promising solution for the utilization of this residual biomass is the thermal conversion of pequi peels through carbonization, which primarily produces charcoal, and as byproducts, non-condensable gases and condensable liquids (Crombie and Masek, 2014). The thermal conversion process can reduce waste volume by up to 95% (Abreu and Henkes, 2019), in addition to facilitating the formation of a new product with new characteristics. This material, due to its high calorific value (Lopes et al., 2023), can be used in the form of briquettes and pellets (Pedroso et al., 2018; Lima et al., 2024), also showing potential in contaminant removal. Examples include methylene blue, an effluent from the textile industry (Patias et al., 2015), and glyphosate, a herbicide widely used in weed control and with a high risk of soil and water contamination (Borba et al., 2019).
When applied to soil and commercial substrate, it is referred to as biochar (Feitosa et al., 2020). Studies show that the combination of biochar from pequi peel with organic material can improve the physicochemical attributes of the substrate (Basílio et al., 2020). In the evaluation of bean development, the addition of this biochar corrected soil acidity and increased the levels of exchangeable bases, in addition to showing potential as a source of potassium (Silva et al., 2022).
In addition, the use of this biomass as biochar promotes the maintenance of carbon in the soil in the form of pyrogenic carbon (Teixeira et al., 2015), as carbonization facilitates the formation of carbon in its most resistant and stable form (Conz, 2015). By remaining in the soil for many years, biochar is capable of long-term carbon sequestration, contributing to the mitigation of greenhouse gas emissions such as CO2, N2O, and CH4, as the biomass used for its production does not decompose quickly (Kurniawan et al., 2023). Liu et al. (2019), when reviewing 28 studies to quantify the impacts of biochar application on greenhouse gas emissions and crop yield using gas intensity on a yield scale, observed that biochar significantly reduced gas emissions on a yield scale by 29%.
In socioeconomic terms, the reuse of residual biomass in the carbonization process presents great potential to increase the income of family farmers. Law 15.089 of 2025 (Brasil, 2025) established the National Policy for the Sustainable Management, Planting, Extraction, Consumption, Marketing, and Transformation of Pequi and other native fruits and products from the Cerrado, with the main objective of integrating the populations that traditionally explore the Cerrado into the rational use and management of this biome, within an environmental sustainability perspective. This initiative can be an important support for integrating the carbonization activity. In addition, new programs and partnerships with cooperatives can be developed to implement this practice, promoting environmental sustainability and generating income for extractivist families.
Despite the great importance of pequi and the potential for utilizing its residual biomass, there are still few scientific studies focused on the pyrolytic conversion of this biomass. Therefore, research is needed on the sustainability of its management, the feasibility of using it as an adsorbent, soil conditioner, and the economic viability of the energy products derived from these residues. Based on these gaps, the present study aimed to characterize the biomass and charcoal obtained from pequi peel, evaluating different carbonization temperatures during the pyrolysis process, with the goal of contributing to the development of sustainable technologies for the reutilization of these residues.
2. Materials and Methods
The pequi husks were collected at the Municipal Market of the Municipality of Montes Claros, Minas Gerais, Brazil (16°42'56"S; 43°51'58"W; 624m). For the preparation and characterization of the biomass, air-drying was carried out in a covered shed for a period of seven days. Approximately 3.7 kg of dried pequi shells were subjected to pyrolysis in a muffle furnace at temperatures of 350, 400, and 450 °C, in triplicate, with a residence time of 30 minutes. The carbonized and dry husks were ground in a Willey mill and classified using sieves with mesh sizes of 40 and 60 mesh for characterization.
The biomass was characterized for its extractives content according to the TAPPI T204 cm-97 standard (TAPPI, 1997a), with adaptations. A 1-gram dry sample (40 and 60 mesh fraction) was used along with the following chemical reagents: ethyl alcohol, toluene, and distilled water. The lignin content was determined according to the TAPPI T222 om-98 standard (TAPPI, 1997b). The holocellulose content was obtained by the difference between the extractives and lignin content.
Proximate analyses were performed on the biomass samples and the resulting biochars according to ASTM D1762-84 (ASTM, 2007) to determine the contents of moisture, ash, volatile matter, and fixed carbon. The characterization of biochar for pH and electrical conductivity (EC) was performed according to the method described by Rajkovich et al. (2012). For the analysis of the hydrogen ion potential (pH), 1 g of biochar was added to 20 mL of deionized water and continuously stirred for 1.5 hours to ensure sufficient equilibration of the solution. The pH value was then measured using a pH meter. Electrical conductivity (EC) was then measured using a conductometer.
The higher heating value was determined according to NBR 8633 (ABNT, 1984). Bulk density was determined according to NBR 6922 (ABNT, 1981) by weighing the charcoal in a container with a known volume. The energy density was obtained by multiplying the higher heating value by the bulk density.
For statistical analysis, simple linear and polynomial models were fitted to describe the behavior of the variables as a function of carbonization temperature. The selection of the most appropriate model was based on the relationship between each variable and the carbonization temperature. The analyses were performed using Microsoft Excel software, version 2019.
3. Results and Discussions
Table 1 presents the average values of the physicochemical characterizations of the pequi shell biomass and charcoal, as well as the gravimetric yield in charcoal. A high percentage of extractives (56.82%) was observed, higher than that found in rice husks (10.38%), cupuaçu husks (5.95%), pequi husks (34.47%), and pequi seeds (40.73%), according to Miranda et al. (2020) and Borges et al. (2022). This indicates a great potential to be recovered as raw material, especially for biodiesel production (Ghesti et al., 2022), in addition to contributing to the reduction of energy used during thermal decomposition, also resulting in a reduction of the process (Mishra and Mohanty, 2018).
The lignin (13.74%) and holocellulose (29.43%) percentages are similar to those found in pequi seeds and shells (Miranda et al., 2020; Martins et al., 2021; Ghesti et al., 2022; Lima et al., 2024). The high lignin content has a direct impact on the gravimetric yield of charcoal, as biomass rich in lignin tends to show higher yields. On the other hand, the low holocellulose percentage indicates a lower presence of cellulose and hemicellulose, which also contributes to a higher production of charcoal (Martins et al., 2021; Lima et al., 2024).
The moisture content present in the biomass was higher than that found in the charcoal, which is an expected behavior, as one of the first steps in thermal degradation is the removal of moisture, where a significant loss of water occurs, resulting in a reduction of the material's moisture content, similar to the values described by Rambo et al. (2015), Basílio et al. (2020), and Martins et al. (2021). In energetic terms, it is known that the moisture percentage is inversely proportional to the calorific value (Lopes et al., 2023), as the water present in the biomass does not contribute to the release of energy; on the contrary, it absorbs part of it to be evaporated.
Fixed carbon is the most resistant form of carbon (Conz, 2015), and its percentage is influenced by the loss of volatile material (Weber and Quicker, 2018). Biochar contains between 70 and 80% carbon (Trazzi et al., 2018). In this study, the charcoal at 450ºC presented the highest percentage of fixed carbon (73.72%), as at this temperature the degradation of extractives, holocellulose, and volatile material had already occurred, leaving the carbon in its elemental form. Depending on the biomass and other characteristics, this carbon can remain in the soil for an extended period. Other effects can also be expected, such as the reduction of greenhouse gases (CO2, N2O, and CH4) in the soil through adsorption, thereby contributing to carbon sequestration, which is essential for the carbon credit market, offering a potential solution for mitigating climate change.
The ash content showed higher values than those reported in the literature by Conz (2015), Basílio et al. (2020), and Martins et al. (2021). In the energy sector, a high ash concentration reduces the calorific value, volatile material, and fixed carbon (Lopes et al., 2023). However, this percentage is still lower than that found in mineral-origin coals. In the agronomic context, a higher concentration of ash indicates a greater presence of inorganic material, which contributes to soil fertility by increasing nutrient availability and also helping to correct pH.
The coals exhibited an alkaline pH, close to the values found by Silva (2017) for biochar from pequi peel produced at 450°C and by Feitosa et al. (2020) for charcoal from banana peel and orange bagasse at temperatures of 400°C and 600°C. This alkalinity has the potential to neutralize soil acidity (Centurião et al., 2021) due to the release of ions, contributing to agricultural productivity.
The reduction of volatile material, moisture, and gravimetric yield of coal (GCY), as the temperature progresses, is attributed to the release of functional groups, which can be related to the increase in the number of pores and, consequently, to the increase in the surface area (Ngambia et al., 2024) and coal stability. These characteristics show promising potential for use as adsorbents in the mitigation of contaminant agents in water.
The bulk density of the biomass (167.7 kg m-3) was lower than that found in cupuaçu (467 kg m-3) and macaúba epicarp (177 kg m-3) (Evaristo et al., 2016). Following the thermal treatment, a reduction in the density of the charcoal was observed, indicating that the degradation of chemical components and the loss of moisture influenced the material's weight, demonstrating that the thermal conversion helps reduce the volume of the pequi shell biomass residue, optimizing its transportation.
The calorific value of the biomass (18.99 MJ kg-1) can be considered high, close to that found for pequi seeds (18.40 MJ kg-1) and corn (18.6 MJ kg-1), but slightly lower than that found in pequi shells (20.45 MJ kg-1) and in the epicarp (20.85 MJ kg-1) and endocarp (20.94 MJ kg-1) of macaúba (Pierri et al., 2016; Evaristo et al., 2016; Mumbach et al., 2024). This value is explained by the high content of extractives and volatile material present in the shell, which have characteristics that enhance the energy potential and provide ignition in the carbonization process. In the charcoal, the calorific value was higher than that observed in the biomass, explained by the higher percentage of fixed carbon, which has a high energy value, as observed at a temperature of 450ºC (25.70 MJ kg-1).
The energy density in the biomass (3070.68 MJ m-3) is lower than that found in the epicarp (3640 MJ m-3) and endocarp (10450 MJ m-3) of macaúba, but higher than that found in bean straw (1084.1 MJ m-3) and corn cobs (2209.2 MJ m-3) (Dionizio et al., 2019), which also presented higher values than those observed in the charcoals, although the latter had a higher calorific value. However, among the coals, there was no significant difference, especially those obtained at 350ºC and 450ºC. When compared to the literature, they are lower than those observed in the coal from the epicarp and endocarp of macaúba, coffee husk, bean straw, and corn cob (Evaristo et al., 2016; Dionizio et al., 2019).
According to the evaluated energetic characteristics, such as calorific value and energy density, it is observed that the biomass of pequi husk presents an energy potential similar to or higher than other plant residues, with a high concentration of energy per volume, making pequi a viable alternative for the bioenergy sector.
According to the model adjustments used to analyze the correlation between the evaluated parameters and the carbonization temperature (Figure 1), all equations were statistically significant based on the F-test, and all parameter coefficients were statistically significant according to the t-test (p < 0.05). The carbonization temperature had a significant influence on the physicochemical properties of the biochar produced from pequi shell. The selection of appropriate mathematical models, whether linear or polynomial, allowed for an accurate description of the variation trends of the parameters as a function of temperature, contributing to the understanding of thermal effects on the material and to the development of strategies aimed at optimizing the quality of the biochar produced. Only the variable Energy Density (DE, MJ m−3) did not exhibit an adjustable behavior to the proposed models and, therefore, was not modeled.
Relationship between the variables and the carbonization temperature. The source: Prepared by the authors themselves.
Moreover, the coals produced in the present study have viable characteristics for different industrial sectors. The temperature of 350ºC shows the best potential within the agronomic sector, with a high percentage of nutrients and pH, as well as a good percentage of fixed carbon. Temperatures of 400 and 450°C also present potential for agronomic and forestry applications; however, due to their higher concentrations of fixed carbon and lower levels of volatile material, they have characteristics that make them viable for energy utilization. Due to the medium percentage of volatiles and gravimetric yield, the 400°C charcoal presents a better balance between porosity and mass, making it suitable for use as an adsorbent of contaminant agents. However, in environmental terms, all the charcoals have characteristics that help minimize environmental impacts, through the adsorption of gases and the retention of carbon present in the biomass.
4. Conclusion
Pequi shell has shown feasibility for the production of charcoal through carbonization. The resulting charcoal exhibited significant physicochemical variations depending on the carbonization temperature, with notable increases in fixed carbon content, reductions in volatile matter, and higher calorific values at elevated temperatures (400 and 450 °C), indicating its potential for energy applications. In contrast, carbonization at 350 °C produced charcoal with higher nutrient content and elevated pH levels, making it more suitable for agronomic applications.
The utilization of this waste contributes to regional sustainable development, mitigating environmental impacts and generating income for the extractive communities in the region. The charcoal from pequi peel is a valuable and multifunctional alternative with potential for use in various sectors, including energy, agriculture, and the environment. Its utilization not only contributes to the sustainability of biomass production and consumption but also generates positive impacts on the economic development of regions traditionally involved in pequi harvesting. By integrating pequi peel charcoal into sustainable production chains, the importance of circular bioeconomy and the valorization of agricultural waste in Brazil is reinforced.
Acknowledgements
To the Foundation for Research Support of the State of Minas Gerais (FAPEMIG), the National Council for Scientific and Technological Development (CNPq), and the Coordination for the Improvement of Higher Education Personnel (CAPES), for the funding and scholarship that made this research possible, and to the technicians and professors responsible for the Biodigestion and Energy Production laboratories for their support.
Data Availability Statement
The research data analyzed in this study are not publicly available by any means.
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Editor:
Takako Matsumura Tundisi
