Corresponding Author: Lina
Lestari
E-mail: [email protected]
INTRODUCTION
The increase in the area of oil
palm (elaeis guineensis jacq.) plantations has implications for the increase in
the amount of biomass waste produced (Babinszki et al., 2021). Palm kernel shell
is one of the largest palm oil processing wastes, reaching 60% of the
production of kernel oil. The shell is the hard part of the oil palm fruit that
serves to protect the contents or kernel of the oil palm. Similar to coconut
shells, palm kernel shell waste can also be processed into an artificial solid
fuel as an alternative fuel called briquettes. Based on previous research, the
chemical composition of oil palm shells consists of carbon 50.70%, hydrogen
6.15%, nitrogen 1.71%, oxygen 34.70%, ash 6.50%, and cellulose (Aziz et al., 2019).
The utilization of palm kernel
shells for briquetting requires an appropriate method, especially in preparing
the shell material into charcoal. Charcoal is a solid material produced from the
thermal degradation of biomass under conditions of little or no oxygen. In the
process of charcoal production or carbonization, water and volatile matter are
released, while the carbon remains. Carbonization temperature will greatly
affect the charcoal produced so that determining the right temperature will
determine the quality of the charcoal (Rodrigues et al., 2023).
Compared to charcoal, activated charcoal is more
practical, attractive and clean. Activation can break hydrocarbon bonds by
oxidizing surface molecules. This is very necessary to enlarge the pore surface
area of charcoal (Yulianti
et al., 2019). Activation also aims to reduce volatile matter so
that the briquette flame rate is low and expand the pore, namely by breaking
hydrocarbon bonds or oxidizing surface molecules so that the charcoal changes
its properties, namely its surface area increases and affects adsorbs (Lestari, Raharjo, et al., 2023). Activation treatment reduces water content and
volatile matter. However, ash and carbon levels increase. If volatile matter is
high, combustion can start at low temperatures, which indicates that the
charcoal is easy to ignite and burn. However, this will cause the combustion
process to become rapid and uncontrollable (Raharjo et al., 2023).
Microwaves lie between infrared radiation and radio
waves in the electromagnetic spectrum region. Microwaves are waves with
wavelengths between 0.001 and 1m and frequencies between 300 and 0.3 GHz.
Microwaves can theoretically be converted into heat through interaction with
dielectric materials. Carbon materials are generally good microwave absorbents,
they are easily heated using microwave radiation. This character makes carbon
materials able to transform due to microwave heating, resulting in new carbon with
desired properties or characteristics (Udyani et al., 2019). The novelty in this study is the character of palm
kernel shell charcoal that changes due to microwave heating, namely an increase
in fix carbon and heating value. This increase is attributed to the evaporation
of water and volatile matter during microwave activation. The research aims to
highlight the potential of microwave heating in altering carbon materials to
achieve desired properties and characteristics.���
In this research, charcoal production uses a kiln drum
model carbonization reactor that has been tested for white teak wood material (Lestari, Saleh, et al., 2023). The purpose of this experiment is to determine the
production efficiency of the carbonization reactor in producing charcoal, the
carbonization rate, and the rate of palm kernel shell material demand. This is
very important to ensure that the carbonization reactor functions economically.
Furthermore, charcoal is activated using microwave because it provides
advantages, including relatively small energy required, faster heating, even
heating, and a high level of safety (Zulaechah et al., 2017). This experiment aims to determine the right
activation power and time for the activation process of palm kernel shell
charcoal. Furthermore, the purpose of this study is to measure the moisture
content, ash content, volatile matter, fixed carbon and calorific value of
charcoal and activated charcoal. Characterization of these parameters is
important to review whether the activated charcoal is feasible to be used as
material for making briquettes as alternative energy.
METHOD
Tools and Materials
The tools used in
this research are a carbonization reactor, 70 mesh and 80 mesh sieves, balance
sheet, infrared thermometer, microwave for activation, furnace and cup for
proximate test, which includes water content, ash content, volatile matter, a
set of DSC (Differential Scanning Calorimeter) tools to measure calorific
value. The materials of this research are oil palm shells, plant branch waste
for carbonization, and water to extinguish the charcoal.
Research Procedure
The working procedure carried out in this study is as
follows:
Preparation Stage
The steps taken in
this process are drying the palm kernel shells and carbonizing fuel with solar
heat.
Carbonization Stage
����������� Palm
kernel shell waste that has been further nested using a carbonization reactor
with the following process:
a. Cutting the palm kernel shell 7 cm before putting it in
the carbonization reactor
b. Measuring palm kernel shell mass (m1)
c. Putting the palm kernel shells into the reactor that has
been designed before, so that it fills 80% of the reactor.
d. Inserting the igniting material into the igniting chamber
e. Close the top of the reactor to ensure that no oxygen
enters,
f.
The
igniter is switched on
g. Measuring the temperature in the reactor through the
chimney. Temperature measurement aims to control the temperature in the reactor
to be constant at the highest temperature.
h. Observe from the air control hole on the chimney, to make
sure the charcoal material has burned completely or not. At a certain time,
dense smoke comes out of the chimney
i.
Once
the smoke from the chimney is no longer dense, it is clearer, indicating that
the carbonization process has been completed.
j.
Extinguishing
the fire in the reactor by sprinkling the charcoal with water, then removing
the charcoal.
k. Drying the charcoal
l.
Calculating
the mass of charcoal (m2)
Figure 1. Carbonization reactor system design
Charcoal Production Efficiency Calculation
Production efficiency is measured using the following
formula:
EP (%) = 
Description:
EP (%): Production Efficiency (%)
m₁ ����� :
Mass of carbonized palm kernel shell (kg)
m₂ ����� :
Charcoal mass (kg)
Carbonization Rate Calculation
The rate of carbonization can be measured using the
following formula
RC = 
Description:
R�������� :
Carbonization rate (kg/h)
m2������ :
Mass of charcoal (kg)
t��������� : Duration
of carbonization (hour)
Material Requirement Rate Calculation
The material requirement rate can be calculated using the
following formula:
RMR = 
Description:
RMR�� : The rate of
material requirements (kg/hour)
m₁������ : Mass
of biomass (kg)
t��������� : Length
of time for active charcoal formation (hours)
Grinding and Sieving
The steps taken in the grinding and sieving stage are:
a. Grinding the dried charcoal using a mortar and pestle.
b. Store the charcoal in a dry container before sifting it.
c. Set up a 70 mesh and 80 mesh sieve, with the 70 mesh
sieve on top.
d. Sifting charcoal.
e. Take the charcoal that lies between the 70 mesh and 80
mesh sieves. Then store the charcoal in a dry and closed container.
Charcoal Activation
The activation process of swit shell charcoal in this
study was carried out using a microwave, namely by placing the charcoal in a
cup and putting it in the microwave. Activating the charcoal with a microwave
with a certain power and time. Storing the activated charcoal in a dry and
closed container.
Calculation of Moisture Content
����������� This
procedure is based on (ULFI, 2016) and American Society of Testing and Materials (ASTM) D
2866-70 as follows:
a. Weighing activated charcoal samples
b. Place the cup in the oven and heat at 105˚C for 3
hours.
c. Remove the cup from the oven and store in a desiccator
and then weigh until constant weight.
The moisture content of activated charcoal can be
measured using the following formula:
M (%) = 
�100%
Description:
M(%)��������������� :
Moisture (water content) (%)
m1��������������������
: Mass of empty cup (grams)
m2��������������������
: Mass of empty cup + mass of sample (grams)
m3��������������������
: Mass of sample after heating at 105˚C (grams) (ULFI,
2016).
Ash Content
����������� The
steps in measuring ash content are based on (ULFI, 2016) and American Society of Testing and Materials (ASTM) D
2866-70 as follows:
a. Weighing activated charcoal samples
b. Place the cup in a furnace at 700˚C for 3 hours.
c. Remove the cup from the furnace and cool in a desiccator
and then weigh it.
The ash content analysis of activated charcoal can be
measured using the following formula:
AC (%) = 
� 100%
Description:
AC (%)������������� :
Ash Content (%)
m1��������������������
: Mass of empty cup (grams)
m2��������������������
: Mass of empty cup + mass of sample (grams)
m3��������������������
: Mass of sample after heating at 700˚C for 3 hours (grams) (ULFI, 2016).
a. Volatile Matter
The steps of volatile matter characterization are as
follows:
1) Weighing activated charcoal samples
2) Cover the cup with aluminum foil and put it in the
furnace at 900˚C for 7 minutes.
3) Remove the cup from the furnace and cool in a desiccator.
Volatile matter analysis of activated charcoal can be
measured using the following formula:
KHZ (%)
= 
Volatile Matter = KZH (750˚C) - moisture content
Description:
KZH�� ������������������������ : Substance Loss Rate
RESTROOMS����������� :
Empty Cup Mass (gram)
MS���������������������������� :
Sample Mass (gram)
MC+SP(750˚C)�������� :
Mass of cup + mass of the sample after heating at 750˚C (grams) (Hasan
et al., 2017).
b. Fixed Carbon
The procedure for determining the bound carbon content
refers to the ASTM D.2172-12 standard. The fixed carbon content test is
determined by subtracting 100% from the sum of the percentages of water
content, volatile matter content and ash content. (Hasan et al., 2017).
RESULTS
AND DISCUSSION
Carbonization Result
The carbonization process is carried out using a
carbonization reactor, as shown in Figure 1, which is designed using tools made
of drums as the reactor body, iron cylinders as chimneys, and iron plates as
covers. The limited air supply aims to prevent further combustion so that a
high charcoal yield is obtained due to the formation of charcoal perfectly.
����������� During the carbonization process,
the combustion temperature is continuously observed by using an infrared
thermometer, and the measurement results are recorded at an interval of 2
minutes. The stability of the combustion temperature must be maintained by
adding an igniter so that the carbonization process takes place quickly. This
process will continue until thick to clear smoke comes out of the chimney,
indicating that the palm kernel shell material has been carbonized completely.
The expected result of carbonization is to create black charcoal, not ash,
which can be visually identified by looking at the color of the charcoal. The
carbonized charcoal is sprinkled with water to stop the process and and then
dried in the sun.
����������� The following calculates the
carbonization reactor's carbonization efficiency, charcoal formation rate, and
material requirement rate.�
Table 1.
Charcoal formation efficiency, charcoal formation rate,
and palm kernel shell carbonization demand
rate
|
Mass Of
Biomass
(Kg)
|
Charcoal
Masks
(Kg)
|
Length Of
Carbonization
Time (Hours)
|
Carbonization
Efficiency
(%)
|
Carbonization
Rate (Kg/H)
|
Material
Requirement Rate (Kg/H)
|
|
45
|
28
|
6.3
|
62.2222
|
4.4444
|
7.1429
|
The carbonization efficiency is 62.2222%, meaning that
the reactor can produce charcoal, where the mass of charcoal formed is 62.2% of
the mass of the palm kernel shell. This reduction in mass is due to the fact
that in this process, water evaporates at temperatures up to 200˚C. At
200-500˚C, the cellulose, hemicellulose, and lignin components are
decomposed into a liquid fraction and a gas fraction containing CO and
CO₂ as its main components. Each biomass component undergoes dehydration
and depolymerization processes in this region, with repeated intramolecular
binding, resulting in low molecular weight fragments breaking down into liquid
and gaseous products. The high molecular weight fragments formed by
condensation are equal to the burnt part and the undecomposed part. The mass
loss of the material decreases at temperatures above 500˚C, but
polycondensed aromatic carbon increases with the formation of H₂ in the
charcoal range of 80˚C to 700˚C (Gunawan, S., Banu N., 2022).
����������� The carbonization rate of the
reactor is 4.4444 kg/hour, meaning that the reactor can produce a mass of
4.4444 kg of charcoal for one hour. The material requirement Moreover,e of
7.1429 kg/hour means that the reactor can produce a mass of 7.1429 kg of palm
kernel shells for one hour. If you look at the description by Gunawan et al.,
2017 above, this figure is related to temperature changes during carbonization
as in the following figure:
Figure 2. Graph of carbonization rate
The highest temperature of the carbonization reactor measured during the
carbonization process was 548.7℃, and the lowest temperature of
the carbonization reactor was 225.2℃. A mass of 45kg of palm kernel
shells produced 28kg of charcoal. The duration of carbonization is influenced
by the hard texture of palm kernel shell biomass. The 7cm chopped palm kernel
shell causes the biomass to be quite dense in the reactor, so it takes a long
time for the chimney to emit clear smoke.�
Visually, the charcoal produced was black and lacked visible ash.�
Microwave Activation, Proximate Test, and Calorific Value
Activation of palm kernel shell
charcoal with a particle size of 70 mesh-80 mesh was tested at 150 watts of
power. Observing the temperature changes and physical changes of the charcoal,
activation can be done in 2 minutes to 4 minutes. If it exceeds 4 minutes, the
charcoal will smolder, and ash will form. Furthermore, activation was carried
out for 2 minutes, 3 minutes, and 4 minutes, respectively, and the moisture
content, ash content, volatile matter, and calorific value were measured.
The following is a characterization of moisture content, ash content,
volatile matter, fixed carbon, and calorific value of microwave-activated palm
kernel shell charcoal at 150 watts.�
Table 2. Proximate analysis and calorific value of palm
kernel shell-activated charcoal
|
No.
|
Activation Time
(Minutes)
|
Moisture Content (%)
|
Ash Content (%)
|
Volatile
Matter
(%)
|
Fixed
Carbon (%)
|
Calorific Value (Cal/Gr)
|
|
1
|
Without
activation
|
5.900
|
6.1234
|
19.1357
|
68.8409
|
5400.00
|
|
2
|
2
|
5.6530
|
6.9721
|
17.7388
|
69.6361
|
5634.23
|
|
3
|
3
|
5.1661
|
7.1813
|
15.4982
|
72.1545
|
6634.12
|
|
4
|
4
|
4.4834
|
7.5697
|
14.4250
|
73.5219
|
7532.27
|
Figure
3. Graph of proximate test of palm kernel shell charcoal
The decrease in moisture content due to activation is due to the
evaporation of water contained in the charcoal. Although the water content of
charcoal without activation has met the quality as a raw material for briquette
making, of course this decrease in water content can improve its quality. The
moisture content of activated charcoal meets the quality of briquetted charcoal
according to the SNI 01-6235-2000 standard, which is less than 8% (National, 2000).
Controlling the activation time up to 4 minutes caused the ash content to
increase, not exceeding the threshold of charcoal quality as briquette-making
material, which is a maximum of 8%, according to SNI 01-6235-2000 standard (National, 2000). From the measurement of ash
content, although activation causes ash content to increase, this increase is
still controlled during activation by observing changes in temperature and
charcoal color.
Volatile matter of activated charcoal decreased from 19.1357% to
14.4250%. According to the SNI 01-6235-2000 standard (National, 2000), the maximum volatile matter
recommended for the quality of briquette material is 15%, which is fulfilled
from the charcoal activated for 4 minutes.
The data shows that the fixed carbon of activated charcoal is higher than
that of charcoal without activation. Fix carbon increases with an increase in
activation time due to the reduction of water content and volatile matter. This
is as expected, given that fix carbon affects the heating value.
From the above experiments,
microwave activation has a higher economic value than conventional heating.
Activation with a furnace has been carried out at a temperature of 650oC for 5
minutes, showing quality that also meets the standards. (Lestari et al., 2020). However, it requires much
energy.� The very real advantage of
microwaves over other methods is the time coefficient, which is easily
controlled and energy efficient. Microwaves have the fastest heating capability
of all ovens. The heat distribution is greater even as the material absorbs the
microwaves and converts them into heat. The main difference between
conventional and microwave processes is that the heating element supplies heat
to the sample, and some of the heat is concentrated along the surface. In
contrast, in a microwave furnace, the material will absorb microwave energy and
convert it into heat (Sudiana et al., 2017).
Charcoal without activation has a heating value of 5400 cal/gram.
Although this calorific value meets the quality requirements as briquettes, the
significant increase in calorific value due to microwave activation for 2
minutes, 3 minutes, and 4 minutes to produce 5634.23 cal/gr, 6634.12 cal/gr,
7532.27 cal/gr, respectively certainly provides very important information in
the repertoire of charcoal material science as a raw material for briquetting.
During controlled activation, although more ash is formed, water and volatile
matter evaporate in greater quantities so that the fixed carbon increases,
which results in the calorific value increasing significantly.�
Figure 4. the effect of microwave activation time on the
calorific value of briquettes
CONCLUSION
Palm kernel shell
charcoal can be produced with a carbonization reactor with an efficiency of
62.2222%, a carbonization rate of 4.4444 kg/hour, and a material requirement
rate of 7.1429 kg/hour. Microwave-activated charcoal has better characteristics
as a raw material for briquetting than charcoal without activation. Activation
time of 4 minutes on charcoal sieved with 70 mesh and 80 mesh sieves in stages
gave the highest calorific value of 7532.27 cal/gr with the lowest moisture
content of 4.4834%, ash content of 7.5697%, and volatile matter of 14.4250%,
fixed carbon of 73.5219%.
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