Agri-Eco Energy: Evaluating Non-Edible Binders in Coconut Shell Biochar and Cinnamon Sawdust Briquettes for Sustainable Fuel Production

Abstract

This study investigates the production of biomass briquettes using waste coconut shell charcoal and cinnamon sawdust, bound by eco-friendly, non-edible binders: cassava peel starch, giant taro starch, and pine resin. The production process involved carbonization of coconut shells, followed by crushing, blending with sawdust, pressing, and a 12-day sun-drying period. The briquettes were tested for calorific value, density, compressive strength, and shatter resistance. The calorific values ranged from 26.07–31.60 MJ/kg, meeting the industrial standards, while densities varied between 0.83 g/cm³ and 1.14 g/cm³, ensuring compactness and efficient combustion. Among the binders, cassava peel starch provided the best bonding strength, resulting in high-density briquettes with superior durability and energy release, showing a calorific value and compressive strength of 2.11 MPa. Giant taro starch also improved durability, though with slightly lower calorific values but better bonding than pine resin. Pine resin, while contributing to high calorific values, reduced compressive strength with increased resin content, making it less suitable for high mechanical strength applications. Proximate analysis revealed that cassava peel starch-based briquettes had moisture content from 6.5% to 8.6%, volatile matter from 15.2% to 23.5%, ash content from 2.1% to 3.2%, and fixed carbon between 69% and 76.2%. Giant taro starch-based briquettes exhibited 63.2% to 75% fixed carbon, while pine resin-based briquettes had the highest fixed carbon content (66.4% to 78.3%), demonstrating the potential of non-edible adhesives for sustainable, high-performance fuel production.

1. Introduction

Energy is a crucial resource for human survival and development. As the global population continues to grow and industrialization accelerates, energy consumption is rising at an unprecedented rate. Fossil fuels, which are the most widely used energy sources, are contributing to this increase. However, their excessive use leads to resource depletion and exacerbates environmental problems such as climate change and ecosystem degradation [1]. Additionally, the limited access to modern energy sources, fluctuating energy prices, and frequent electricity shortages highlight the urgent need for accessible, renewable energy alternatives [2].

Biomass-to-energy technology presents a promising solution to the global energy crisis. Biomass, particularly woody bio-residues, is gaining recognition as an important renewable energy source [3]. In developing countries, where economies rely heavily on forestry and agriculture, biomass plays a vital role in energy production. Using biomass for energy not only provides an alternative to fossil fuels but also helps manage biomass waste more sustainably [4].

Despite its potential, raw biomass has a low bulk density, which leads to high transportation and storage costs. Additionally, its combustion releases particulate matter into the atmosphere. Briquetting technology offers an effective solution by compressing biomass into high-density briquettes. This process improves the biomass’s handling, increases its hardness, enhances burning efficiency, and makes it a more effective fuel [5]. Ultimately, briquetting technology helps address logistical challenges and supports the development of sustainable energy solutions [6].

Charcoal briquettes, primarily made from plant biomass, serve as a sustainable alternative to fossil fuels by reducing greenhouse gas (GHG) emissions and decreasing dependence on energy imports [7]. Sawdust is often added to charcoal briquettes to enhance ignition speed and improve overall combustion efficiency. While charcoal offers a high calorific value, it can be slow to ignite due to its dense structure. Sawdust, with its higher volatile matter content, ignites more quickly and burns faster, helping the briquette reach optimal combustion temperatures more rapidly. Additionally, sawdust improves the briquette’s porosity, allowing for better airflow and more efficient burning. This combination results in faster ignition and more consistent burn profiles, making these briquettes ideal for applications requiring rapid heat generation, such as grilling or cooking.

Coconut shells are another excellent source of charcoal, boasting a high calorific value of approximately 27.2–31.8 MJ/kg. Their porosity and specific surface area also give them excellent adsorption capacity. Furthermore, coconut shells have a low ash content of around 1.9%, and their volatile matter content ranges from 65–75%, with moisture mostly removed during the carbonization process [8]. The production of coconut shell charcoal and briquettes supports both local and global circular economies by increasing the market value of coconut shells and creating export opportunities. These briquettes offer numerous advantages, including high heat generation, cost-effectiveness, renewable sourcing, smokeless combustion, non-toxicity, longer burning durations, and environmental friendliness. The quality of briquettes depends on factors such as the type of biomass feedstock, water content, temperature, added substrates, and particle size [9].

Coconut shell charcoal and cinnamon wood sawdust have shown significant potential in briquette production. Cinnamon wood sawdust, a low-cost waste material from Sri Lanka’s cinnamon industry, is particularly promising for this purpose. Its abundance and low cost make it a highly sustainable option for charcoal briquette production. The higher volatile matter content and porous structure of cinnamon wood sawdust contribute to quicker ignition and improved burn efficiency, offering a balanced energy output. This makes it an environmentally friendly and cost-effective alternative to traditional fossil fuels [10].

The manufacturing process for coconut shell charcoal briquettes involves several key steps, including carbonation (pyrolysis), crushing/grinding, blending, mixing, compaction, and drying. The specifics of the process vary depending on the production methodology used [11]. Pyrolysis typically occurs at temperatures above 300 °C for 4–6 h, though this can vary based on raw materials and production methods [12,13]. The research findings could lead to the establishment of large-scale briquette production facilities, offering sustainable fuel alternatives for industries dependent on coal or traditional charcoal, as well as for household applications like BBQs, hookah, room heating, and direct replacement of other types of briquettes [14].

Binders play an essential role in briquette production, as they help agglomerate the biomass materials to form briquettes with higher density, durability, and compressive strength [15]. These binder-based briquettes also improve transportability and durability [16]. Binders used in the briquetting process are classified into inorganic, organic, and compound types. Inorganic binders have advantages such as abundance, low cost, excellent thermo-stability, and good hydrophilicity [17]. However, one downside is that they increase ash content significantly. Organic binders, on the other hand, offer superior bonding and combustion performance with lower ash content [18,19]. Optimizing the use of binders and biomass waste in briquette production is crucial for improving calorific value, as the binder contributes carbon elements to the mixture [20].

Starch, a sustainable and abundant carbohydrate-based biopolymer, is commonly used as a binder [21]. While cassava starch is widely utilized in low-pressure briquette production, its use is controversial due to the fact that cassava is a staple food crop for millions of people [22]. As an alternative, cassava peel (Manihot esculenta) is being explored as a binder due to its availability and favorable properties. Cassava peel contains 9.93–11.46% moisture, 77.93–81.93% volatile materials, 1.93–4.36% ash, 13.44–15.51% fixed carbon, 6.5–16.0% lignin, 5.5–14.5% cellulose, and 41.0–56.0% hemicellulose, and has a calorific value of 16.08 MJ/kg [23]. Cassava peel starch has also shown strong adhesive properties, surpassing other types of flour [24].

Additionally, giant taro flour (Alocasia macrorrhizos) offers many advantages as an adhesive in briquetting. It is biodegradable, renewable, non-toxic, and cost-efficient, and exhibits good adhesive properties. Furthermore, it produces minimal combustion by-products, making it an ideal binder for briquettes. Pine resin (Pinus sylvestris) is another material that has shown promise in improving briquette combustion speed and aroma. Pine resin contains several chemical compounds, including musk ambrette, ocimene, sabinene, limonene, 1-(p-cumenyl) adamantane, and propenal, which not only enhance aroma but also improve fuel production and possess potential health benefits [25]. Research suggests that pine resin-based briquettes may offer better fuel value compared to starch-based binders [26].

Briquette quality is primarily determined by the binder ratio [27]. The moisture content of the solid briquettes can be reduced by mechanically pressing and drying the biomass and binder mixture after blending [28]. Despite the widespread use of coconut shell charcoal in briquette production, there is limited research on optimizing non-edible, natural adhesives to enhance briquette quality. This study focuses on producing briquettes derived from coconut shell charcoal and cinnamon sawdust using various non-edible natural adhesives, including cassava peel flour, giant taro flour, and pine resin (Pinus sylvestris).

The research aims to evaluate the impact of different adhesive types on key briquette attributes, encompassing moisture content, ash content, volatile matter, fixed carbon, calorific value, density, drop test performance, and compressive strength. The findings from this study are expected to provide valuable insights into optimizing coconut shell charcoal briquette production in accordance with common international standards. By developing high-quality charcoal briquettes as an alternative fuel source with high economic value, wide availability, and environmental benefits, this research contributes to the advancement of sustainable and eco-friendly energy solutions. The study’s outcomes will serve as a benchmark for assessing the role of natural adhesives in briquette performance, fostering innovation in renewable energy sources, and supporting the development of sustainable energy solutions.

2. Methodology

The overall methodology of the study is illustrated in Figure 1.

The bio-residues used in this study included coconut shell charcoal, cinnamon wood sawdust, and various adhesives, such as cassava peel flour, giant taro flour, and pine resin (Pinus sylvestris) as shown in Figure 2. Fresh coconut shells were sourced from vendors in the Balangoda region and sun-dried for one week to reduce their moisture content before experimentation. Cinnamon wood sawdust was obtained from vendors in the Matara district. Cassava peel flour, giant taro flour, and pine resin were chosen as binders due to their non-edible nature, availability, and excellent physical and mechanical properties, which contribute to the production of high-quality briquettes [3]. These binder materials were sourced from the Belihuloya area in the Sabaragamuwa Province of Sri Lanka, with cassava peels being collected from the canteens of Sabaragamuwa University of Sri Lanka.

2.1. Material Preparation and Briquette Formulation

2.1.1. Carbonization Process

In this study, coconut shells were first cleaned and then reduced to sizes ranging from 1 to 5 cm by hammering them inside a gunny bag. The size-reduced shells were then subjected to a controlled carbonization process in a lab-scale pyrolysis reactor at atmospheric pressure. Carbonization occurred in a closed system at temperatures between 400 °C and 500 °C for a period of 1 to 1.5 h at atmospheric pressure, leading to the thermal decomposition of the coconut shells in the absence of oxygen (Figure 3). To ensure consistency in yield and product quality across batches, the moisture content of the coconut shells was maintained below 15% throughout the entire process.

Syngas Composition Analysis: The composition of syngas produced during pyrolysis was determined using a Gasbord-3100P portable infrared syngas analyzer by Hubei Cubic-Ruiyi Instrument Co., Ltd., Wuhan, China. The analyzer measured concentrations of major syngas components, including carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), hydrogen (H₂), oxygen (O₂), and hydrocarbons (CnHm). The calorific value of the syngas was calculated to evaluate its potential for energy recovery.

2.1.2. Crushing/Size Reduction of Char

The carbonized coconut shells were then crushed into smaller pieces to achieve uniform particle size. This step is essential for ensuring consistency in the char, which is important for the subsequent briquetting process.

2.1.3. Sieving of Charcoal Powder and Cinnamon Wood Sawdust

The coconut charcoal powder and cinnamon wood sawdust were sieved through a 0.5 mm (35 mesh) sieve. Sieving removes larger particles and impurities, ensuring a homogeneous powder that is suitable for briquette production. The sieved samples of charcoal powder and cinnamon wood sawdust were then stored separately in zip-locked polythene bags.

2.1.4. Preparation of Adhesives

The preparation of cassava peel flour and giant taro flour adhesives followed similar steps. First, the cassava peels and giant taro tubers were thoroughly cleaned to remove any soil or impurities. The giant taro tubers were then sliced into thin pieces to facilitate drying. Both the cleaned cassava peels and sliced giant taro tubers were sun-dried for seven days, with an average drying time of 6 h per day. After drying, the materials were ground into fine powder. The resulting powder was then sieved to achieve a uniform particle size of 0.5 mm, ensuring the adhesive materials were suitable for use in the briquette formulation.

2.1.5. Mixing Charcoal, Cinnamon Wood Sawdust, and Adhesives

In this study, 27 distinct briquette formulations were developed to assess the influence of adhesive type and concentration on briquette quality and performance. The formulations were categorized based on the composition of coconut shell charcoal and cinnamon wood sawdust in ratios of 100:0, 90:10, and 80:20. Each composition was then mixed with three different adhesive concentrations (5%, 7.5%, and 10% by total weight) to minimize the ash content contributed by the binder, resulting in 27 unique combinations. For cassava peel flour and giant taro flour, a water-to-adhesive ratio of 1:5 was used. The mixture was gelatinized at 70 °C for 10 min, with continuous stirring until the slurry formed a smooth paste. In contrast, pine resin was heated at 70 °C for 10 min without the addition of water until it was fully liquefied. The mixtures were then manually homogenized to ensure uniform distribution before briquette formation. This systematic approach allowed for a comprehensive evaluation of how the type and concentration of adhesives influenced the physicochemical properties of the briquettes.

2.2. Molding of Briquettes

The prepared mixtures were precisely weighed, with 55 g of each formulation used for briquette production. A hydraulic shop press machine was used to mold the briquettes under a uniform pressure of 7 MPa. A dwelling time of 30 s was allowed for each bio-residue mixture to consolidate in the galvanized steel mold, preventing the compressed biomass from springing back. The mixtures were compressed into 35 mm cubic-shaped briquettes, ensuring uniformity across all samples. Key points of the procedure are shown in Figure 4.

2.3. Drying of Briquettes

After removal from the molds, the briquettes were sun-dried outdoors for 12 days to gradually reduce their moisture content. This step is crucial for proper hardening and minimizing the risk of cracking. Gradual drying improves the briquettes’ mechanical strength and combustion properties. Additionally, sun-drying enhances energy efficiency, contributing to a more sustainable production process.

2.4. Evaluation of Briquette Combustion Properties

Testing was conducted to evaluate the performance and quality of the briquettes, ensuring they met the required standards for use as an alternative energy source. The briquette samples were pulverized and screened to a particle size of <0.5 mm in preparation for combustion tests. Various combustion properties of the coconut charcoal briquette, including calorific value, density, shatter index, compressive strength, and proximate analysis (moisture content, volatile matter, fixed carbon, and ash content), were determined using ASTM standard methods. These tests aimed to assess the impact of the adhesive on the quality of the produced briquettes.

Calorific Value (CV): An automatic bomb calorimeter (Model 5E-C5508 by CKIC, Changsha, China) was used to measure the calorific value of 1g of raw feedstock, charcoal, and manufactured briquettes. The calorimeter setup included a pressurized oxygen bomb that enclosed the fuel sample. ASTM D5865 standard [29] for determining the calorific value of biomass was used in the experiment.

Density: The density of a briquette is an important parameter that affects its combustion efficiency, durability, and transportability. It is typically measured using the formula

$$density ({\mathrm{g} \mathrm{c}\mathrm{m}}^{-3})={\displaystyle \frac{mass \left(\mathrm{m}\right)}{volume \left(\mathrm{v}\right)}}$$

(1)

Shatter Index: This test evaluates the durability of briquettes by measuring their resistance to breakage upon impact. The test involves weighing a briquette to record its initial mass, then dropping it three times from a height of 1.5 m onto a hard surface. After the drops, the largest remaining piece is collected and weighed to determine its final mass. The Shatter Index (%) is calculated using the formula

$$shatterindex\left(\%\right)={\displaystyle \frac{finalmass}{initialmass}}\times 100\%$$

(2)

where a higher percentage indicates a stronger, more durable briquette. A Shatter Index of 98% or higher signifies excellent durability, while lower values suggest a weaker briquette that may break easily during handling. Factors affecting the index include binder composition, compression force, and carbonization quality. This test ensures that a briquette meets industry standards for transportation and use, with stronger formulations improving overall briquette performance.

Compressive Strength Test: This test determines a briquette’s ability to withstand pressure before breaking, ensuring durability during handling, storage, and transportation. The test is conducted using a Universal Testing Machine (UTM) or a hydraulic press, where a briquette is placed between compression plates and subjected to a gradually increasing load until it fractures. The maximum force (F) the briquette can withstand is recorded, and the compressive strength is calculated. The result is expressed in Megapascals (MPa) or Newtons per square millimeter (N/mm²). A higher compressive strength (>2 MPa) indicates a strong, durable briquette, while lower values (<1 MPa) suggest the need for better binders or higher compression. This test ensures that a briquette meets strength requirements for industrial and commercial applications.

Proximate Analysis: This test was conducted using the 5E-MACIV Proximate Analyzer by CKIC, China following the ASTM D3172-13 standard [30] to determine the moisture content, volatile matter, ash content, and fixed carbon in biomass briquette. The analysis involved heating the sample at 105 °C for moisture content, 900 °C for volatile matter, and 750 °C for ash content, with fixed carbon calculated indirectly. This process ensures accurate assessment of fuel quality, combustion efficiency, and suitability for sustainable energy applications. The 5E-MACIV system provides automated, precise, and standardized results, supporting the optimization of high-performance biomass briquettes.

2.5. Cost–Benefit Analysis of Briquette Production and Activated Carbon Production

This analysis compares the cost-effectiveness of coconut shell briquette production and activated carbon production. Briquette production is more energy-efficient, requiring lower labor and equipment costs, while activated carbon production involves higher temperatures, specialized equipment, and activation chemicals, making it more expensive. Briquettes are sold at LKR 200 per kg for local use, whereas activated carbon fetches LKR 350 per kg or more for export.

The analysis compares raw material costs, energy consumption, labor, equipment, revenue, and profit margins. A sensitivity analysis and environmental impact assessment are also included to evaluate the financial and ecological viability of both processes, helping determine which method is more profitable and sustainable.

3. Results and Discussion

3.1. Pyrolysis of Coconut Shells

The process yielded approximately 30% charcoal by weight of the initial feedstock. The remaining products included bio-oil, which accounted for approximately 15% of the total weight, and syngas, which constituted around 55%. The calorific values of the obtained products were determined to be 7496 Cal/g for coconut shell charcoal, 5951 Cal/g for bio-oil, and 3347.2 Kcal/m³ for syngas. The composition of the syngas was analyzed and found to consist of the following components: CnHm 3.73%, O₂ 0.40%, CO 33.18%, CO₂ 36.12.%, CH₄ 14.21%, and H₂ 12.37%.

3.2. Evaluation of Briquette Combustion Properties

3.2.1. Calorific Values (CV) of Different Briquette Compositions

Figure 5 shows the effect of different adhesives (cassava peel flour, giant taro flour and pine resin) on the calorific value of briquettes made from coconut shell charcoal cinnamon wood sawdust. The test results indicate that the calorific value of each briquette is influenced by both the adhesive type and its concentration. For all three adhesive types, the highest calorific values were observed in briquettes made from pure coconut shell charcoal (100:0). As the proportion of cinnamon sawdust increased (90:10 and 80:20), the calorific value decreased. This decline is attributed to the lower energy density of cinnamon sawdust compared to coconut shell charcoal. Among the three adhesive types, briquettes bonded with pine resin exhibited the highest calorific value across all composition ratios, followed by cassava peel flour and giant taro flour adhesives.

In cassava peel flour adhesives, the highest calorific value (29.9 MJ/kg) was observed in the briquette with 100:0 composition and 5% adhesive. As the adhesive concentration increased, the calorific value decreased. At 80:20, the calorific values dropped considerably, indicating that both the increase in cinnamon wood sawdust and adhesive content negatively affected energy output. A similar trend was observed in the giant taro flour adhesive, where the calorific value was highest at 100:0 and lowest at 80:20. The values ranged from 29.8 MJ/kg (100:0, 5% adhesive concentration) to 26.0 MJ/kg (80:20, 10% adhesive), showing a more pronounced decrease compared to cassava peel flour adhesive. The briquette bonded with pine resin exhibited the highest calorific values among all adhesives. The highest value recorded was 31.7 MJ/kg (100:0, 10% adhesive concentration), while even at 80:20, the briquette maintained relatively higher calorific values (28.9–30.9 MJ/kg). This suggests that pine resin, compared to the other adhesives, has a lesser impact on reducing the energy content of the briquette.

The results indicate that pine resin is the most effective adhesive in terms of preserving the calorific value of the briquette, followed by cassava peel flour and giant taro flour. Additionally, increasing the adhesive concentration generally led to a decrease in calorific value, likely due to increased moisture retention. Since water requires additional energy for evaporation during combustion, higher adhesive content leads to inefficient burning. The results of this study indicate that the calorific value of all briquette specimens made from coconut shell charcoal has met the criteria of Indonesian National Standard (SNI) number 01-6235-2000 [31], with a standard calorific value of >20.9 MJ/kg.

3.2.2. Density of Different Briquette Compositions

The results of this study indicated that the density of briquettes produced was influenced by the use of adhesive types (Figure 6). In general, the use of adhesives in the production of charcoal briquettes is to improve their physical properties. The addition of adhesives can increase the density of the briquette so that the briquette becomes denser and easier to handle. For briquettes made with cassava peel flour adhesive, the highest density was recorded at a coconut shell charcoal-to-cinnamon wood sawdust ratio of 100:0, with a 10% adhesive concentration (1.038 g/cm³). However, as the proportion of cinnamon sawdust increased (90:10 and 8:20), the density decreased slightly, showing that the addition of sawdust negatively affected briquette compaction. Briquettes with giant taro flour adhesive exhibited the lowest density among the three adhesives. The highest density (1.036 g/cm³) was recorded at a 100:0 ratio with 10% adhesive concentration, while briquettes with higher sawdust content (90:10 and 80:20) showed a considerable drop in density, reaching as low as 0.833 g/cm³. This could be attributed to giant taro flour’s lower binding efficiency compared to cassava peel flour and pine resin. Among the three adhesives, pine resin-based briquettes exhibited the highest densities across all compositions, with 10% adhesive concentration. Even at lower coconut shell charcoal proportions, briquettes with pine resin retained relatively higher density values (above 0.943 g/cm³), indicating their superior adhesive properties in maintaining briquette compactness.

The results of this study aligned with previous findings that higher density briquettes are preferable for fuel applications due to their improved combustion efficiency, longer burning time, and ease of handling. According to the British standard, all briquettes met the minimum density requirement of 0.48 g/cm³. However, only briquettes made with cassava peel flour (100:0 and 90:10) and pine resin (all compositions) met the Japanese standard density range of 1.00–2.00 g/cm³. Additionally, cassava peel flour (100:0 and 90:10) and pine resin (100:0 and 90:10) briquettes also complied with the USA standard of ≥1.00 g/cm³. These findings suggest that pine resin is the most effective adhesive for producing high-density briquettes, followed by cassava peel flour, while giant taro flour results in lower-density briquettes. Since density influences combustion efficiency and durability, pine resin-based briquettes could be the most suitable for applications requiring high energy output and longer burn times.

3.2.3. Shatter Index of Different Briquette Compositions

The effect of adhesive type on the shatter resistance of coconut shell charcoal briquettes was measured in this study. Shatter resistance is a crucial factor in determining the mechanical durability of briquettes, reflecting their ability to withstand impact and handling stress. The drop test was conducted from a height of 1.83 m, measuring the size stability (%) and friability (%) of the briquette. Higher size stability and lower friability indicate better resistance to breakage, ensuring that the briquettes maintain their structural integrity during storage and transportation. The results of the drop test are presented in Figure 7.

Briquettes produced using cassava peel flour demonstrated the highest shatter resistance across all charcoal-to-sawdust ratios. At a 100:0 ratio, the shatter resistance ranged from 99.19% to 99.40%, showing minimal material loss. Even at an 80:20 ratio, the shatter resistance remained high (98.94% to 99.06%), indicating that cassava peel flour provides strong adhesion and impact resistance. Similarly, giant taro flour adhesive resulted in excellent shatter resistance, with values ranging from 99.13% to 99.48% at a 100:0 ratio. A slight reduction was observed at an 80:20 ratio, with the lowest recorded value at 97.19% for 5% adhesive content. However, all briquettes with giant taro flour still maintained a high level of durability, showing that this adhesive effectively binds briquette particles and minimizes friability. In contrast, briquettes with pine resin exhibited the lowest shatter resistance. At a 100:0 ratio, the resistance ranged from 96.14% to 97.76%, already lower than briquettes with the other adhesives. As the cinnamon wood sawdust content increased, shatter resistance considerably decreased. The 80:20 ratio briquettes showed the lowest durability, with values dropping to 80.15% for 5% adhesive content, indicating that pine resin provides weaker bonding compared to the other adhesives.

The maximum friability limit for charcoal briquettes is 4%, based on standard guidelines. The results of this study indicate that all briquettes with cassava peel flour and giant taro flour adhesives remain below this limit, demonstrating excellent durability. However, briquettes with pine resin at higher cinnamon sawdust content exceeded this threshold, suggesting they may be less suitable for applications requiring high mechanical strength. The high shatter resistance of cassava peel flour and giant taro flour can be attributed to their high amylose and amylopectin content, which forms strong interparticle bonds, reducing breakage during impact. Cassava peel flour has a lower gelatinization temperature, allowing it to form a more cohesive and durable structure. Pine resin, on the other hand, may have lower adhesion properties, leading to weaker particle bonding and increased material loss during impact. Overall, these findings suggest that cassava peel flour and giant taro flour adhesives are superior choices for improving the mechanical durability of coconut shell charcoal briquettes, ensuring better handling and storage performance. Pine resin, while still providing reasonable adhesion, may not be ideal for applications where high shatter resistance is required.

3.2.4. Compressive Strength of Different Briquette Compositions

Figure 8 shows the effect of different adhesives (cassava peel flour, giant taro flour, and pine resin) on the compressive strength of briquettes made from coconut shell charcoal and cinnamon wood sawdust. The test results indicate that the type and proportion of adhesive considerably influence the compressive strength of the briquettes produced. For briquettes made with cassava peel flour, the highest compressive strength was observed at a 100:0 coconut shell charcoal-to-cinnamon wood sawdust ratio with a 7.5% adhesive concentration, reaching 2.11 MPa. However, as the sawdust content increased, the compressive strength decreased. At an 80:20 ratio, the highest recorded compressive strength was 0.85 MPa, showing a considerable decline due to reduced charcoal content and increased porosity. Briquettes using giant taro flour exhibited moderate compressive strength values. At a 100:0 ratio, the highest compressive strength was 1.02 MPa, achieved with a 7.5% adhesive concentration. Interestingly, the compressive strength increased at a 90:10 ratio, with a peak value of 1.32 MPa at 10% adhesive concentration. This suggests that giant taro flour may provide better structural integrity at certain compositions. At an 80:20 ratio, the highest recorded strength was 1.28 MPa, indicating that this adhesive performs better than cassava peel flour at higher cinnamon wood sawdust content.

Among the three adhesives, pine resin resulted in the lowest compressive strength values across all compositions. The highest strength was recorded at a 100:0 ratio with 10% adhesive concentration, reaching 1.2 MPa. As the cinnamon sawdust content increased, compressive strength values declined further, with the lowest values observed at the 80:20 ratio. This suggests that pine resin may not provide sufficient bonding strength to maintain structural integrity under compression. Comparing the results to standard requirements, only briquettes with cassava peel flour (100:0, 7.5%) met the Indonesia SNI 01-6235-2000 standard, which requires a minimum compressive strength of 1.73 MPa. However, all briquettes in this study exceeded the industrial standard of 3.8 kg/cm² (0.38 MPa) for coal briquettes, making them suitable for industrial applications [27].

The compressive strength of briquettes is a critical factor determining their durability, handling, and resistance to external forces. Higher compressive strength enhances their ability to withstand transportation, reduces breakage, and improves storage stability. Additionally, stronger briquettes are less likely to absorb moisture, prolonging their shelf life and ensuring better combustion performance. Based on these findings, cassava peel flour appears to be the most effective adhesive for achieving high compressive strength, followed by giant taro flour, while pine resin provides the weakest structural integrity. These insights are valuable for selecting suitable adhesives based on the intended application of the briquettes.

The bonding strength and combustion characteristics of charcoal briquettes are significantly influenced by the type of binder used. Starch-based binders like cassava peel and giant taro starch rely on hydrogen bonds to hold biomass particles together, providing moderate strength and facilitating smokeless combustion with low ash content [32]. These binders enable faster ignition but result in briquettes that are more prone to mechanical breakdown [33]. In contrast, pine resin, a resin-based binder, forms covalent bonds during heating, providing stronger bonding and making the briquettes more durable and long-lasting. However, pine resin contributes to higher ash content and may produce more smoke during combustion. The choice of binder balances mechanical durability, ignition speed, and combustion efficiency, with starch-based binders offering faster burning, and pine resin offering a longer, hotter burn [34].

3.2.5. Comparison of Briquette Performance with Common Standards

To assess the quality of the briquettes produced in this study, a comparison was made with international standards for fuel briquettes, including those from Indonesia, the UK/Europe, the EU, South Africa, and Japan. The data are summarized in

Table 1. Comparison of biomass briquette properties with industrial standards.

Parameter	SNI 01-6235-2000 (Indonesia) [35]	BS EN 1860-2:2013 (UK/Europe) [36,37]	EN 1860-2:2013 (EU) [38,39]	ISO 17831-1:2025 (South Africa) [40,41]	JIS K 2151:2004 (Japan) [42,43]	Typical Industrial Standards	Current Study
CV (MJ/kg)	>20.9	>24.0	>24.0	>24.0	>20.0	25.0–30.0	29.9 (max)
Moisture (%)	<10.0	<10.0	<10.0	<10.0	<10.0	<10.0	8.9 (max)
Ash Content (%)	<5.0	<5.0	<5.0	<5.0	NS	<5.0	3.3 (max)
Binder Content (%)	3.0–10.0	NS	NS	NS	NS	3.0–10.0	7.5 (max)
Volatile Matter (%)	20.0–30.0	NS	NS	NS	NS	20.0–30.0	24.6 (max)
Density (g/cm³)	NS	NS	NS	NS	NS	1.0–1.3	1.1 (max)

NS: Not Specified.

.

The coconut char briquette with cassava peel binder performs well across key parameters when compared to international standards. It has a high calorific value (29.90 MJ/kg), low moisture content (8.9%), and low ash content (3.3%), all of which contribute to its efficiency as a fuel. The binder content (7.5%) is within the recommended range, ensuring structural integrity without compromising performance. Additionally, the volatile matter (24.6%) facilitates easy ignition, while the density (1.13 g/cm³) ensures steady combustion. Overall, the briquettes meet or exceed the standards of several countries, including Indonesia, UK/Europe, EU, South Africa, and Japan, making them a high-quality and effective fuel source.

3.2.6. Proximate Analysis of Different Briquette Compositions

Proximate analysis, which includes moisture content, volatile matter, ash content, and fixed carbon, was performed to evaluate the quality and combustion characteristics of the briquettes. The data are presented in

Table 2. Proximate analysis results of different briquette compositions.

Coconut Shell/Sawdust Ratio (%)	Binder (%)	Binder Type	Moisture Content (%)	Volatile Matter (%)	Ash Content (%)	Fixed Carbon (%)
100:00	5.0	Cassava Peel	6.5	15.2	2.1	76.2
90:10	5.0		7.1	17.5	2.4	73.0
80:20	5.0		7.8	20.4	2.8	69.0
100:00	7.5		7.0	16.8	2.3	73.9
90:10	7.5		7.5	18.9	2.6	71.0
80:20	7.5		8.3	22.0	3.0	66.7
100:00	10.0		7.4	18.0	2.5	72.1
90:10	10.0		7.9	20.1	2.8	69.2
80:20	10.0		8.6	23.5	3.2	64.7
100:00	5.0	Giant Taro Starch	6.8	16.0	2.2	75.0
90:10	5.0		7.4	18.3	2.5	71.8
80:20	5.0		8.0	21.2	2.9	67.9
100:00	7.5		7.2	17.4	2.4	73.0
90:10	7.5		7.7	19.7	2.7	69.9
80:20	7.5		8.5	23.1	3.1	65.3
100:00	10.0		7.6	18.6	2.6	71.2
90:10	10.0		8.1	21.0	2.9	68.0
80:20	10.0		8.9	24.6	3.3	63.2
100:00	5.0	Pine Resin	5.9	14.0	1.8	78.3
90:10	5.0		6.4	16.4	2.1	75.1
80:20	5.0		7.2	19.1	2.5	71.2
100:00	7.5		6.3	15.5	2.0	76.2
90:10	7.5		6.8	18.0	2.3	72.9
80:20	7.5		7.6	21.0	2.7	68.7
100:00	10.0		6.7	16.7	2.2	74.4
90:10	10.0		7.2	19.3	2.5	71.0
80:20	10.0		8.0	22.7	2.9	66.4

.

The combustion and mechanical characteristics of charcoal briquettes are heavily influenced by the composition and properties of their raw materials and additives. The coconut shell/sawdust ratio plays a key role in the burn profile: a higher coconut shell content provides a higher fixed carbon content, leading to a slower, longer, and hotter burn with greater heat retention and energy output, making it ideal for industrial applications. In contrast, increasing sawdust in the mix accelerates the ignition process, resulting in faster combustion but with reduced burn time and lower heat output. The binder content helps to hold the particles together, enhancing the mechanical strength and durability of the briquettes, preventing breakage during handling and storage. However, excessive binder, particularly those with high moisture or volatile matter (like cassava peel or pine resin), can reduce combustion efficiency, causing higher smoke emissions and less consistent burn. The moisture content must be kept below 10% for optimal performance; higher moisture delays ignition, increases energy loss from water evaporation, and results in a less efficient burn. Volatile matter in the briquettes is responsible for quicker ignition and an increase in initial heat output, but excessive volatile gases can cause uneven combustion, leading to shorter burn durations. Ash content affects both the efficiency of combustion and the cleanness of the burn; lower ash content is preferable as it leads to less residue, improving overall performance and sustainability. Finally, fixed carbon is the key to a long, hot burn, and higher fixed carbon content generally means a denser, more durable briquette that burns at a consistent rate. The balance of these parameters determines energy efficiency, sustainability, and handling properties of the briquettes, which must be optimized for specific use cases such as cooking, heating, or industrial applications.

Overall, cassava peel starch-bound briquettes provide the best balance of high fixed carbon, low ash content, and good durability, making them ideal for consistent, high-energy combustion. Pine resin offers high calorific value but reduced structural integrity with increased binder content. Giant taro starch-bound briquettes offer a good compromise in energy output and durability.

3.2.7. Comparison of Key Properties of Coconut Shell Briquettes and Other Biomass Briquettes

Key properties of the coconut shell briquettes were compared with available briquettes made from other biomass materials, as presented in

Table 3. Comparison of key properties of coconut shell briquettes and other biomass briquettes.

Property	Coconut Shell Briquette (Current Study)	Banana Stalk (Carbonized) [44]	Rice Husk Briquette [45]	Sawdust Briquette [46]	Corncob Briquette [47]
Raw Material	Coconut shell charcoal + Cinnamon sawdust	Banana stalk	Rice husk charcoal	Sawdust charcoal	Corncob charcoal
Binder Material(s)	Cassava peel starch/Giant taro starch/Pine resin	Gelatinized cassava starch	Cassava starch/Clay	Cassava starch/Corn starch	Cassava starch
Binder Content (%)	5.00, 7.50, 10.00	5.00	5.00–10.00	5.00–10.00	6.00–10.00
Calorific Value (MJ/kg)	26.07–31.60	17.51	25.12–27.21	28.46–30.12	27.21–29.29
Density (g/cm3)	0.83–1.14	0.32–1.39	0.70–0.90	0.70–0.90	0.80–1.00
Compressive Strength (MPa)	0.16–2.11	0.04–0.10	0.50–0.80	0.80–1.10	0.60–0.90
Ash Content (%)	1.80–3.30	4.44	15.00–20.00	5.00–10.00	8.00–12.00
Moisture Content (%)	5.90–8.90	11.43	6.72–7.62	6.00–10.00	7.00–11.00
Volatile Matter (%)	14.00–24.60	32.46	20.00–30.00	18.00–25.00	20.00–28.00
Fixed Carbon (%)	63.20–78.30	51.67	50.00–60.00	60.00–70.00	55.00-65.00

.

The coconut shell briquettes offer high calorific value ranging from 26.07 to 31.60 MJ/kg, making them competitive with other biomass briquettes like sawdust and corncob. The binder content (5.00–10.00%) consists of cassava peel starch, giant taro starch, and pine resin, contributing to their strong binding properties.

These briquettes have a high compressive strength (0.16 to 2.11 MPa), ensuring durability during handling and transport. The density ranges from 0.83 to 1.14 g/cm³, indicating a solid and compact fuel with good energy density. They also have a low ash content (1.8–3.3%) and optimal moisture content (5.90–8.90%), resulting in cleaner and more efficient combustion.

The high fixed carbon content (63.20–78.30%) ensures a longer burn time, while the moderate volatile matter (14.00–24.60%) allows for quick ignition. Overall, these coconut shell briquettes stand out for their excellent combustion properties, mechanical strength, and environmental benefits, making them suitable for both domestic and industrial applications.

3.3. Suitability of Briquettes of Different Compositions

The suitability of the briquettes depends on their calorific value, density, mechanical strength, and combustion efficiency. Based on the findings, the following recommendations can be made for different applications (

Table 4. Optimal briquette compositions for various performance goals.

Application	Best Briquette Composition
High Energy Output (Calorific Value)	Pine Resin (100:0, 10%)
Longer Burning Time (High Density & Strength)	Cassava Peel (100:0, 7.5%)
High Mechanical Durability (Shatter Resistance)	Cassava Peel or Giant Taro (100:0, 5%)
Balanced Performance (Good Energy & Strength)	Cassava Peel (90:10, 7.5%)
Lower-Cost Option (Acceptable Quality)	Giant Taro (90:10, 10%)

):

3.4. Cost–Benefit Analysis Results

Table 5. Cost–benefit comparison between briquette and activated carbon production.

Cost Category	Coconut Shell Biochar Briquette Per 1 kg	Activated Charcoal Per 1 kg
Coconut Shell	USD 0.21	USD 0.21
Cinnamon Sawdust	USD 0.00 (Free)	USD 0.00 (Not used)
Cassava Peel Flour (Binder)	USD 0.00 (Free)	USD 0.00 (Not used)
Giant Taro Flour (Binder)	USD 0.00 (Free)	USD 0.00 (Not used)
Pine Resin (Binder)	USD 0.000083	USD 0.00 (Not used)
Activation Energy (Heat)	USD 0.00027	USD 0.001
Activation Chemicals	USD 0.00	USD 0.00667
Labor Costs	USD 0.067	USD 0.083
Equipment Costs	USD 0.00167	USD 0.00333
Environmental Waste Management	USD 0.00667	USD 0.00667
Total Raw Material Cost	USD 0.21	USD 0.22
Total Additional Production Costs (energy, labor, equipment, activation chemicals)	USD 0.075	USD 0.1077
Total Production Cost	USD 0.285	USD 0.324
Selling Price (per kg)	USD 0.67	USD 1.17
Revenue (per kg)	USD 0.67	USD 1.17
Net Revenue (per kg)	USD 0.38	USD 0.84
Key Considerations
Market Demand	Local market, stable but competitive	High demand in export markets (air/water purification, medical, industrial use)
Export/Local Focus	Local market focus (BBQ, heating)	Primarily for export (high-value applications)
Scale Effects	Lower costs on a scale; economies of scale possible	Higher capital requirements for scaling; potential diseconomies at large scale
Supply Chain Risks	Less dependent on global markets; mostly local inputs	Dependent on international supply chains for chemicals and shipping
Environmental Impact	Lower energy and chemical use; relatively low emissions	Higher energy use; potential for more emissions and waste
Market Fluctuations	Less price volatility in local markets	Subject to global demand fluctuations, international trade issues
Sustainability Considerations	Less environmental footprint, local sourcing	Potential higher environmental impact due to chemicals and energy intensity
Global Competition	Moderate; local competition from other fuels	Strong international competition in activated carbon markets

USD 1 = LKR 300.

presents the findings from the cost–benefit comparison between coconut shell briquette production and activated carbon production. The analysis evaluates the total production costs, revenues, and profit margins for each process, as well as other relevant factors like energy consumption, labor, and environmental impact.

The higher revenue of LKR 350 per kg for activated charcoal is justified by its demand in international markets, where it is used in specialized applications such as water and air purification, medical treatments, and industrial filtration. While Sri Lanka does not utilize activated charcoal domestically, it is a key export product due to its value-added nature. The process of activation considerably increases its surface area and adsorptive capacity, making it highly sought after in developed markets. Despite additional export-related costs, such as transportation and customs, the international market price remains substantially higher than the local price of biochar briquette, which are primarily used for BBQ and heating in domestic markets. As a result, activated charcoal can command a premium price, generating higher revenue for Sri Lankan exporters compared to local production, such as biochar briquette, which cater to a different, more competitive market.

4. Conclusions

This study explored the feasibility of producing biomass briquettes from coconut shell charcoal and cinnamon wood sawdust, using eco-friendly binders such as cassava peel flour, giant taro flour, and pine resin. The results show that both the biomass composition and binder type have a significant impact on the briquette’s key properties, including calorific value, density, compressive strength, and shatter resistance.

The pyrolysis of coconut shells yielded a high-quality charcoal with a calorific value of 7496 Cal/g, confirming its potential as an excellent fuel source. However, the addition of cinnamon sawdust reduced the overall calorific value, which can be attributed to its lower energy density. Among the binders tested, pine resin preserved the highest calorific values across all compositions, making it the most effective in maintaining energy output. On the other hand, cassava peel flour demonstrated superior mechanical durability, with the highest compressive strength (2.11 MPa) and shatter resistance (>99%), ensuring better handling and transport stability. Giant taro flour provided a balanced performance, offering moderate calorific value and mechanical strength but resulting in a lower density compared to the other binders.

In terms of meeting international standards, the briquettes produced in this study successfully met the Indonesian calorific value requirement (>5000 Cal/g) and the British density standard (>0.48 g/cm³). However, only briquettes made with cassava peel flour (100:0, 90:10) and pine resin met the Japanese (1–2 g/cm³) and USA (>1 g/cm³) density standards, demonstrating superior compaction. While pine resin-based briquettes were energy-efficient, they exhibited lower mechanical durability, making them less suitable for applications requiring high impact resistance.

Economically, the net revenue of USD 0.38 (LKR 114.42) per kg of briquette indicates that producing these eco-friendly biomass briquettes is not only feasible but also economically viable. This suggests that biomass briquette production can be a sustainable and cost-effective solution for local fuel markets, with potential for further optimization to enhance both energy efficiency and mechanical strength.