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ISSN: 0115-6454

Vol. 37, 2018, pp. 13-24 OPEN ACCESS

The Official Research Journal Publication of Western Mindanao State University

Formerly WMSU Research Journal

Charcoal Briquettes Manufactured from Dried Mango Leaves (DML)–

An Alternative Solid Fuel Source

Sarah R. Ycaza and Juanita T. Barre

Chemistry Department, College of Science and Mathematics,

Western Mindanao State University, Zamboanga City, Philippines

Corresponding author: sarahycaza@yahoo.com

ABSTRACT

Briquettes from agriculture waste dried mango leaves (DML) as a source of alternative

fuel were produced and reported in this study. Briquettes are compacted mass of charcoal fines

with binders, which are shaped under pressure. The briquettes were produced starting with the

pyrolysis of dried mango leaves. The carbon produced was mixed with 20% starch as a binder by

manual press method. The briquettes were sun-dried for 48 hours. The physical and thermal

properties of the briquettes were then evaluated and the results were compared with those of

wood and coconut charcoal. The friability test results indicate that the briquettes are compact and

stable and will not easily crumble. The bulk density was determined to be at 1.0234g/cc. Results

also show the following combustion related properties of the briquettes: a calorific value of

7,471.97; volatile matter 27.86-28.39; percentage ash content 20.73-20.81; moisture 13.77-

14.81%; fixed carbon 36.42-37.20%; kindling point 64.54-68.26 sec; burning time120.81-123.7

min; and boiling time 30.81-33.72 min. Statistical analysis using One-way Analysis of Variance

(ANOVA) shows that the combustion characteristics of the briquettes from dried mango leaves

vary significantly with the related properties analyzed that of coconut shell and wood charcoal;

however, they do not differ in the moisture content. The briquettes produced may not be of

superior quality as that of fossil fuels, but is a potential alternative to the costly fuels. Hence, the

dried mango leaves charcoal briquettes can be a cheap alternative solid fuel source to be used for

domestic purposes.

Keywords: carbonization, calorific value, friability, briquettes, Zamboanga Peninsula

Ycaza, S. R. and Barre, J. T. (2018). Charcoal Briquettes Manufactured from Dried Mango

Leaves (DML)– An Alternative Solid Fuel Source. Ciencia 37, 13-24. Retrieved from

www.wmsu.edu.ph/research_journal

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INTRODUCTION

Fossil fuels are the leading sources of fuel energy, since they generate a large amount of

energy from a minimal quantity, have high heating power and good quality combustion

characteristics (Riddell et al., 2018). The world’s energy source of fossil fuels encompasses

83%, however, predicted to decrease in 2020 for about 76% (Taylor, 2010). Fossil fuel is not a

renewable source of energy. Aside from being non-renewable, its usage can cause air pollution

by releasing toxic air pollutants and carbon dioxide (CO2), which is the most important human-

produced climate-altering greenhouse gas. Its health impacts especially in children include

mortality and neurodevelopmental problems (Perera, 2018).

There are already existing solutions through a shift from fossil fuels to clean energy

(Watts, 2015). Examples of these are solar power, wind, tides and geothermal energy. Further,

according to Food and Agriculture Organization (FAO, 2010a), coals and charcoals are good

substitutes for fossil fuels but are also nonrenewable and will contribute to deforestation. Thus,

other renewable sources of fuels need to be explored to save the environment from getting

denuded.

Mangifera indica L. (mango trees), being considered evergreens undergo regular

abscission that happens many times a year to sustain its health and growth (Shah et al., 2010).

Abscission is the process by which trees naturally shed off leaves or other parts of the tree that

are no longer needed. Shedding of leaves helps trees to conserve water and energy. As

unfavorable weather approaches, hormones in the trees trigger the process of abscission whereby

the leaves are actively cut-off of the tree by specialized cells (Conners, 2017). Dried mango

leaves (DML) can be utilized as a renewable source of energy through charcoal briquettes.

Charcoal briquettes are compacted mass of charcoal fines with a binder which is shaped

under pressure. These charcoal briquettes from agro-wastes can generate alternative sources of

energy, therefore, energy supply will increase and the demand for non-renewable energy will

decrease (Romallosa, 2017). It can also help in solid waste management, save the environment

since the extraordinary collection of wood for fuel has resulted in deforestation in highly

populated areas (UCS, 2011). Further, it is easy to transport and store (DOST-FPRDI, 2015).

Zamboanga Peninsula ranked second (2nd

) in mango production in the Philippines (PSA,

2018). Thus, it is expected that the source of agro-waste materials does not easily run out

because trees naturally produce leaves. This briquette-making will benefit the residents as the

end users, the makers of the briquettes as part of its livelihood, and the community who can avail

of the charcoal briquette product aside from benefiting from healthier surroundings.

METHODS

The fallen dried mango leaves (DML) were collected from the residential area of the

researcher and was stored in covered plastic pails located inside a well-ventilated room. Figure 1

shows the leaves used in this study.

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Figure 1. Sun drying and storing the mango leaves.

Carbonization of the leaves was done using an improvized pyrolysis equipment made of

cast iron pots. Pyrolysis is the thermal decomposition of materials at elevated temperatures in an

inert atmosphere (Lettieri & Al-Salem, 2011). It involves the change of chemical

composition and is irreversible. The carbonization process includes: (1) compacting the

carbonizer with the DML to minimize airflow; (2) kindling; (3) covering the pan with a metal lid

after producing a thick smoke; and (4) harvesting the carbonized leaves and storing in resealable

plastic bags for briquette production (Figures 2 A-D).

Figure 2. Carbonization process of DML.

A simple wooden briquette machine was fabricated (Fig. 3). The design of which was

patterned from Biomass Briquette Lever Press by Commando (2018).

Figure 3. Fabricated briquette machine used in the study.

A B C D

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The carbonized leaves were mixed with 20% cassava starch paste and were made into

briquettes using the fabricated briquette machine. Cassava starch possessed good ductility, good

binding ability, self-curing properties and hygroscopicity-resistance in their incorporated

composites (Oluwole & Avwerosuoghene, 2015). Cassava starch paste was made by mixing 20g

of starch and 80g of water then cooked over moderate heat until thick. This paste was added to

100g of carbonized leaves which in turn was made into briquettes (cylindrical-shaped) with

dimensions of 3.80cm long and 2.70cm in diameter. The briquettes produced were dried under

the sun for 48 hours then stored in resealable plastic bags to avoid moisture absorption and

desorption.

The evaluation of the briquette regarding its physical, chemical, and thermal properties

was done. For the physical tests, bulk density and friability tests were conducted. The bulk

density of the charcoal briquette was determined by taking the mass of the pulverized charcoal

which was packed in a pre-weighed 10ml graduated cylinder.

The mass of charcoal obtained was divided by the volume of the graduated cylinder.

Friability test was done by tying together five (5) briquettes with a string. The bundle of

briquettes was dropped from five (5) meters above a concrete floor five times. The friability was

measured in terms of Impact to Resistance Index (IRI), using the equation below:

IRI= 100 x N/n

Where:

IRI = Impact to Resistance Index;

N = Number of drops; and

n = Total number of pieces after N drops.

For the chemical test, a proximate analysis was done. The moisture content of the

briquettes was determined by oven method in which ten grams of sample was dried at 105oC in a

laboratory oven until constant weight was obtained. The loss of mass after drying is the water

content of the briquettes. The percent moisture was calculated using the equation for percent

moisture content.

% Moisture= (loss of weight of sample/weight of sample)*100

Ash content was determined by placing the dry sample from moisture determination in

the furnace at 700-800oC for one hour or until constant weight was obtained. Percent ash was

calculated using the equation below:

% Ash = [(weight of residue/weight sample (before drying)] * 100

Volatile matter (VM) was determined using one (1.000) gram of dry sample ignited in a

covered crucible at 950oC for seven minutes in a furnace. The weight loss was taken to be the

measure of the volatile matter in the sample. This was calculated using the equation below:

% VM= (loss of weight/weight of dry sample)*100

Fixed carbon was determined by subtracting the percentages of volatile matter, moisture,

and ash from a sample. Combustion characteristics of the briquettes were evaluated in terms of

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the kindling time, boiling time and burning rate of the briquettes (Water Boiling Test) in which

200 grams of briquettes was used. Two hundred (200) grams of briquettes was ignited. The time

it took for the fuel to form ember was taken as the kindling time. The boiling time was

determined by boiling 1000ml of distilled water in a stainless pot. The time the water boiled after

kindling time was taken as the boiling time. The burning time was taken as the time the fuel had

no more embers and had turned to ashes.

Cost analysis was done by computing the costs of producing 800 briquettes which

include the raw materials, labor, and other sundry charges. This was compared to the price of

coconut shell and wood charcoal.

Analysis of Variance (ANOVA) was used to determine if the DML charcoal briquettes

are comparable to the regular coconut shell and wood charcoal as solid fuel in terms of friability,

density, proximate analysis, and thermal properties.

RESULTS AND DISCUSSION

Fifty percent (50%) by mass of charcoal could be obtained from DML. Ten (10)

briquettes can be produced from 200 grams of mango leaves charcoal. The cassava starch binder

that was used had a concentration of 20% by mass. The briquette machine could produce

approximately 800 per day. Figure 4 shows the actual briquettes produced.

Figure 4. Briquettes produced from DML.

Physical Characteristics of the DML Charcoal Briquettes Produced

The physical properties of the charcoal briquettes are critical since it can affect the

usability of the fuel. If the briquettes are not compact enough and easily broken that it makes it

difficult to handle, this will result in much waste due to damage.

Friability Test

The durability of the briquette was evaluated using the friability test. The result showed

that no briquette was broken even with a dropping height of five (5) meters indicating that DML

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charcoal briquettes are strong and durable. The durability of the briquettes could be attributed to

the amount of binder used and the resinous substances in the mango leaves. Less durable

briquettes tend to shatter easily to produce many fines. This is undesirable for solid fuels since it

can affect the air flow of the stove.

Bulk Density

The bulk density of the briquettes was 1.0234g/cc. Bulk density is a measure of the

compactness of the charcoal fine in the briquettes. It is a contributory factor for the ignition

property of the briquettes. If the briquette is less compact, it will ignite faster and will reduce the

kindling time compared to solid fuels with a very high value of bulk density.

Proximate Analysis of DML Charcoal Briquettes

The proximate analysis of the charcoal briquettes could give light to the quantitative

aspect of the capacity of heat the fuel can generate. Results of the proximate analysis of DML,

charcoal briquettes, wood charcoal and coconut shell charcoal are summarized in Table 1

Table 1. Proximate analysis of coconut shell charcoal, wood charcoal and DML charcoal

briquettes.

Proximate Analysis

Type of Charcoal

Coconut

Wood

DML Briquette

% Moisture 17.2073 ± 5.0357 15.4520 ± 2.5667 14.2900 ± 0.9348

% Ash content 13.5967 ± 2.7689 24.4287 ± 0.1537 20.7693 ± 0.0773

% VCM 11.3127 ± 0.0921 17.4787 ± 1.0465 28.1293 ± 0.4795

% Fixed Carbon 57.8833 ± 7.1516 42.6407 ± 2.4770 36.8113 ± 0.7092

a. Moisture Content

Results show that the moisture content of the DML charcoal briquettes is 14.2900%.

Typical charcoal contains 5-10% water. The high moisture content could be due to the

absorption of moisture from the air in the surroundings and the conditions of carbonization.

Since the carbonization of charcoal was done in a closed container, some pyroligneous acids and

tars could be absorbed back to the charcoal. This caused the charcoal to be hygroscopic resulting

to increased moisture content. However, the moisture content in DML charcoal briquettes is still

within the quality standard for moisture content in charcoal (5-15%) (FAO, 2010b).

In terms of moisture, there is no significant difference (p=0.064) among the means of the

three groups. While in terms of kindling time, there is a significant difference (p=0.000) in the

means of the three groups. The wood has the highest mean (129.6%) as compared to dried

mango leaves (66.4%) and coconut shell (125.2667%). Using the Scheffe’s test, a significant

difference exists among all the groups.

b. Ash Content

The ash content of the DML charcoal briquettes was found to be 20.7693%. The ash

content is a measure of the minerals that make up the DML charcoal briquettes and the non-

combustible material in it. For solid fuels, the ash content ranges from 0.5% to more than 5%.

The ash content in commercial briquettes depends on the type of binder used. If the binder used

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was clay it will have high ash content. However, for this study only cassava starch was used.

Therefore, the ash must have been from the leaves.

Statistical analysis shows that in terms of ash content, there is a significant difference

(p=0.000) in the means of the three groups. The wood has the highest mean (24.4287%) as

compared to dried mango leaves (20.7693%) and coconut (13.5967%). Using the Scheffe’s test,

significant difference exists among all the groups.

c. Volatile Combustible Matter (VCM)

The VCM in solid fuel includes the tarry residues and the other liquid except for water

that was not removed during the carbonization process. The VCM content in DML charcoal

briquettes is 28.1293%. This might be due to the conditions of the carbonization process since it

was conducted at a fairly low temperature and in a very short time in the carbonizer which

resulted in the incomplete removal of the VCM. Moreover, the carbonizer was covered which

could have caused the reabsorption of the VCM by the charcoal. If the carbonization was done

at a temperature approximately 300oC, the VCM will be around 50%, but when the temperature

is between 500-600oC, the VCM will be lower around 30%; however, when the temperature

becomes around 1000oC, the VCM will be almost zero. Based on the ash content of the DML

charcoal briquettes, it could be implied that the carbonization occurred at 500-600oC. The effect

of VCM on the calorific value of the fuel depends on the composition of the VCM.

On the composition of the volatile matter, if the VCM contains flammable gas, the

calorific value will increase; but if not, it will decrease the calorific value of the fuel. VCM also

affects kindling time. It can be seen from the result that the DML charcoal briquettes had high

VCM with kindling time of only 66 seconds. Moreover, a high VCM charcoal has the advantage

of producing lesser fines which will make it convenient to transport and store.

Concerning VCM, there is a significant difference (p=0.000) in the means of the three

groups. The dried mango leaves have the highest mean (28.1293%) as compared to coconut shell

(11.3127%) and wood (17.4787%). Using the Scheffe’s test, a significant difference exists

among all the groups.

d. Fixed Carbon Content

The produced DML charcoal briquettes contain 36.8113% fixed carbon. This is the most

important component in solid fuels since it is the basis for the calorific value. As can be seen

from the data, it falls below the range of the fixed carbon content of typical charcoal which is 50-

95% (FAO, 2010b). This could be due to the conditions of carbonization which was set so that

the dried leaves will burn very quickly without turning to ashes. These conditions could cause

the volatile matter to be high and the fixed carbon low. The fixed carbon content of the charcoal

could be increased if the volatile combustible matter and moisture would be reduced during

carbonization. However, if the volatile combustible matter is too low the friability and ease of

kindling of the briquettes would be compromised since volatile combustible matter contributes to

the durability of the material and the ease of ignition of the fuel.

In terms of Fixed Carbon, there is a significant difference (p=0.000) among the means of

the three groups. The coconut shell has the highest mean (57.8833%) as compared to dried

mango leaves (36.8113%) and wood (42.6407%). Using the Scheffe’s test, significant difference

exists among all the groups.

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Thermal Properties of the DML Charcoal Briquettes

Table 2 summarizes the thermal properties of the DML charcoal briquettes. Thermal

properties are the most important properties of any fuel. A good quality fuel must be easy to

ignite, emit enough heat and burn slowly.

Table 2. Thermal properties of coconut shell charcoal, wood charcoal and DML charcoal

briquettes.

Thermal Properties

Type of Charcoal

Coconut Wood DML Briquette

Calorific Value (kcal/kg) 10,559.04 7,269.24 7,471.97

Kindling Time (s) 125 ± 5 130 ± 5 66 ± 3

Boiling Time (min) 15.47 ± 1.76 19.87 ± 2.20 32.27 ± 2.63

Burning Time (min) 105.47 ± 1.77 109.87 ± 2.20 112.53 ± 2.63

a. Calorific Value of the DML charcoal Briquettes

The fixed carbon content is one of the primary factors responsible for the calorific value

of solid fuels. This explains why, among the three (3) fuels studied, coconut shell which

contains the highest fixed carbon gave the highest calorific value.

b. Kindling Time

Several factors affect the kindling or ignition time of a solid fuel. The VCM content of

solid fuel is one of the measures of its ignition properties which means that the higher the VCM,

the easier for the fuel to ignite. The DML charcoal briquettes contain high VCM content and

have a kindling time of 66 minutes. Moisture content has an inverse relationship with the

kindling time of the fuel. The presence of moisture can lower the kindling time. The moisture

content of 14.29% of DML charcoal briquettes is within the range of the suggested value in the

literature which is 5%-15% (FAO, 2010). In terms of the VCM content, DML charcoal briquette

had the highest value for kindling time, while lowest in coconut charcoal.

c. Boiling Time

Boiling test was to determine how many minutes it will take for one (1) liter water to boil

using 200 grams of DML charcoal briquettes and stainless covered steel pot. The DML charcoal

briquettes took the longest time to boil while coconut shells charcoal the shortest.

In terms of boiling time, there is a significant difference (p=0.000) among the means of

the three groups. The dried mango leaves have the highest mean boiling time (32.2667min) as

compared to coconut shell (15.4667min) and wood (19.8667min). Using the Scheffe’s test, a

significant difference exists among all the groups.

d. Burning Time

For the burning time, DML charcoal briquettes have a burning time of 112.53 minutes.

The compactness of the charcoal briquettes affects the burning time of the fuel. A high amount

of trapped air leads to shorter burning time of fuel. The burning time could be improved with a

better briquetting machine that could minimize the air entrapped in the product.

In terms of burning time, there is a significant difference (p=0.000) among the means of

the three groups. The DML has the highest mean burning time (122.2667min) as compared to

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coconut shell (105.4667min) and wood (109.8667min). Using the Scheffe’s test, a significant

difference exists among all the groups.

Comparison of the Chemical and Thermal Properties of DML Charcoal Briquettes, Coconut

Shell and Wood Charcoal

Figures 5 and 6 present the bar graph of the different parameter studied in this research.

Figure 5. Comparison of chemical and thermal properties

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Figure 6. Comparison of calorific value of the DML briquettes, coconut and wood charcoal

(BTU/lb).

In terms of Calorific Value, there is a significant difference (p=0.000) among the means

of the three groups. The coconut shell has the highest mean (10559.0427kcal/kg) as compared to

wood (7269.2440kcal/kg) and dried mango leaves (7471.9727kcal/kg). Using the Scheffe’s test,

a significant difference lies between the wood and the dried mango leaves.

Overall results show that the combustion characteristics of the briquettes from dried

mango leaves vary significantly with the related properties analyzed that of coconut shell and

wood charcoal; however, they do not differ in the moisture content.

Table 3 shows the expected cost of the production of DML charcoal briquettes.

Table 3. Costing of briquette production.

Per 800 briquettes (1-day work) Cost (Pesos)

Gathering of Leaves 50.00

Briquette Production (Carbonization,

briquetting and bagging)

300.00

Other materials 25.00

Total 375.00

The cost of briquette manufacturing is P375.00 per 800 briquettes. The briquettes

produced may not be of superior quality as the fossil fuels, but is a potential alternative to the

costly fuels. This is supported by the works of Emerhi (2011) using mixed wood residue which

encouraged briquette production as an alternative to firewood for the household cheap energy

source. In the works of Onaji and Siemons (1993), production of charcoal briquettes from the

cotton stalk in Malawi was also conducted and presented a form of less-costly bioenergy source.

0

2000

4000

6000

8000

10000

12000

Cal Value BTU/lb

Dried Mango Leaves

Charcoal BriquettesCoconut shell Charcoal

Wood Charcoal

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CONCLUSION

Dried mango leaves (DML) as an agro-waste can be an essential alternative solid fuel in

the form of charcoal briquettes. Having compared the chemical and thermal properties of the

regularly used solid fuels (coconut shell charcoal and the wood charcoal), the results confirm that

DML is comparably durable and resistant to impact as manifested in friability test. The bulk

density was indicative of the compactness of the product. The chemical analysis reveals that the

fixed carbon content was below the standard however it could be increased by using a more

efficient briquetting machine. The volatile combustible matter was high which contributed to the

ease of kindling of the solid fuel. Other chemical parameters are within the range for solid

charcoal fuel. For the thermal properties, the product had a calorific value of 7.471.97 BTU/lb

which falls within the range of the value of charcoal fuels. The produced briquettes where easy

to ignite and gave low heat but with prolonged burning time. Overall findings reveal that the

DML charcoal briquettes could be an alternative source of solid fuel.

ACKNOWLEDGEMENT

The researchers acknowledged the financial support of Western Mindanao State

University through its Institutional Research Fund.

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