Production of Biodiesel from Microalgae Using Transesterification

Batch Reactor with the Assistance of Calcium Oxide Hydrotalcite

Catalyst

Yustia Wulandari Mirzayanti

, M. Amirul Fatah

, Rendy Meydianto A. Y. Tengker

and Dian Yanuarita Purwaningsih

Department of Chemichal Engineering, Institute Technology Adhi Tama Surabaya,

Arif Rahman Hakim No. 100, Surabaya, Indonesia

Keywords: Alternative Energy, Biodiesel, Microalga Nannochloropsis sp., In-Situ Batch Reactor, Transesterification,

Cao/Hydrotalcite.

Abstract: Research the process of making biodiesel as alternative energy using microalgae Nannochloropsis s.p using

the In-Situ transesterification method. The manufacturing process is carried out in two stages: in situ

transesterification using a batch reactor and distillation process purification. The research was carried out

using the fixed variable, namely the molar ratio of oil, algae content: solvent, namely 1:20, and the

independent variable stirring speed in batch reactors of 50, 100, 150, 200, and 250 rpm with the catalyst used

being a CaO/Hydrotalcite heterogeneous catalyst. This study obtained the highest crude biodiesel yield of

38.36% and the lowest Free Fatty Acid (FFA) content of 2.76 mg NaOH/gram sample at a stirring speed of

250 rpm.

1 INTRODUCTION

The Energy and Mineral Resources (EMR) sector is a

sector that plays a vital role in supporting the national

economy. The Energy and Mineral Resources sector

includes coal, new and renewable energy, oil and gas.

Currently, Indonesia still has a high dependence on

fossil energy, where dependence on coal is 38%, oil

and natural gas is 51%, while on new and renewable

energy, it is still relatively low at 11%. Since 2004,

Indonesia has become an oil importer country. In

2020, energy consumption increased due to the

COVID-19 pandemic, where production is

approximately 700 thousand bpd, and consumption is

1.5 million bpd. Biodiesel is a biofuel that is an

alternative to petroleum diesel fuel. Biodiesel is an

ester hydrocarbon compound derived from long-

chain fatty acids. The components of biodiesel

depend on the type of material used as raw material

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because it is related to the chemical structure of oil or

lipid compounds produced from raw materials, such

as the number of carbon atoms, as well as the number

of double bonds in the lipid hydrocarbon bonds. The

main raw material for making biodiesel in Indonesia

today is Crude Palm Oil (CPO). At the same time,

Crude Palm Oil is also the raw material for making

cooking oil, so if biodiesel production expands, it can

cause a potential scarcity of cooking oil. The cause of

biodiesel is currently an alternative fuel that is quite

popular because biodiesel is an environmentally

friendly fuel, its raw materials are easy to get, and the

manufacturing process is not complex. Biodiesel is

generally made from vegetable materials, including

plant oils and animal fats.

Microalgae can absorb solar energy and bind CO

efficiently, producing energy through photosynthesis

(Astuti and Sriwuryandari, 2010). Microalgae can be

cultivated easily because they use solar energy to

180

Mirzayanti, Y., Fatah, M., Tengker, R. and Purwaningsih, D.

Production of Biodiesel from Microalgae Using Transesteriﬁcation Batch Reactor with the Assistance of Calcium Oxide Hydrotalcite Catalyst.

DOI: 10.5220/0012107900003680

In Proceedings of the 4th International Conference on Advanced Engineering and Technology (ICATECH 2023), pages 180-185

ISBN: 978-989-758-663-7; ISSN: 2975-948X

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

photosynthesize. The high growth rate allows

microalgae to produce more biodiesel feedstock than

plant oils or animal fats. Some microalgae have a high

lipid content which can be used as an alternative in

biodiesel feedstock. The total lipid content of each

microalga varies from 20-50%, but some microalgae

have a lipid content of more than 40% (Patmawati et

al, 2014). The use of microalgae as an alternative raw

material for biodiesel production has considerable

potential. Indonesia occupies the third position in

replacing fossil fuels with microalgae biodiesel in the

future (Batten et al, 2011). The reason microalgae is

a raw material that has considerable potential is the

characteristics of the microalgae itself. Microalgae is

biomass with a high growth rate, easy to cultivate,

environmentally friendly, easy to dry, and has a high

lipid content that is easy to extract.

In a previous study, Edo et al. (2020) researched

making biodiesel from the microalgae

Nannochloropsis sp. using the in-situ

transesterification method with the help of a sulfuric

acid catalyst. The results showed that the variable

molar ratio of microalgae to methanol 1:7 showed the

highest crude biodiesel yield of 12% and the lowest

FFA content of 0.399 mg NaOH/gr (Mirzayanti et al,

2020). In the same year, Septianto et al. (2020) also

researched making biodiesel from the microalgae

Nannochloropsis sp. using the transesterification

method with the help of a CaO/hydrotalcite catalyst.

The results showed that at a molar ratio of oil to

methanol 1:15 with 10% catalyst weight%, the

highest Fatty Acid Methyl Ester (FAME) content was

61.77%, and biodiesel yield was 60.39% (Septianto et

al, 2020). In another research conducted by Retya et

al. (2022) on the production of biodiesel from the

microalgae Nannochloropsis sp. using the

microwave-assisted in situ transesterification method

with the help of a NaOH catalyst, the results showed

a molar ratio of oil to methanol of 1:10 with a catalyst

concentration of 0.4 M NaOH to obtain a biodiesel

yield of 60.39% and an FFA of 0.0088 mg NaOH/gr

(Retya et al, 2022).

In this research, the Nannochloropsis sp.

microalgae type is used as a raw material for biodiesel

using the In-Situ transesterification method. The

catalyst used was a CaO/hydrotalcite heterogeneous

catalyst with methanol as a solvent as well as a

reactant in the in-situ transesterification process and

n-hexane as a co-solvent which was carried out using

a batch reactor that had been designed. The research

used a fixed variable, the molar ratio of oil algae

content and solvent 1:20, and the independent

variable is stirrer speed in a batch reactor.

2 LITERATURE REVIEW

Microalgae are classified as autotrophic organisms

that reproduce through the process of photosynthesis.

The unicellular structure found in microalgae allows

them to convert solar energy into chemical energy

easily (Liu et al, 2016). It is estimated that microalgae

can produce 200 times more oil content than other oil-

producing plants (Sharma et al, 2012). Microalgae are

also known as marine plants with advantages over

other fuel sources. They do not require large areas,

produce biomass quickly, and use CO

gas in the

growth process to reduce air pollution (Gultom,

2018). Generally, there are three different microalgae

growth conditions: phototrophic, heterotrophic, and

mixed. Under phototrophic conditions, microalgae

are highly dependent on sunlight as energy and CO

as carbon sources. Phototrophic conditions are often

referred to as autotrophic photosynthesis. The second

condition, namely the growth of heterotrophic

microalgae, requires organic carbon as an energy

source. Some commonly used organic nutrient

sources include glucose, acetate, and glycerol.

Microalgae growth is also influenced by its

physiological properties (Hindarso et al, 2015). The

physiology of this microalgae species can affect

nutrient uptake and its culture media. Naturally,

microalgae plants that live in open ponds will quickly

grow to cover the pond's surface. If the microalgae

physiology is very good, these conditions can

stimulate biomass production with high oil and starch

content. However, certain physiological responses do

not allow microalgae to survive in these ponds. Of the

several microalgae studied, the type of microalgae

Nannochloropsis sp. can produce lipid products.

Lipid content in microalgae Nannochloropsis sp.

is quite high, namely 31% to 68% of its dry weight

(Chisti, 2013). Nannochloropsis sp. is microalgae

that are yellow-green, round, small in size, and 2-4

µm in diameter (Salam et al, 2016). There are

membrane-enclosed cell walls, mitochondria,

chloroplasts, and nuclei in the morphology of

Nannochloropsis sp. The chloroplast is bell-shaped,

located at the edge of the cell, and has a light-sensitive

stigma. Nannochloropsis sp. has six species:

Nannochloropsis graditana, Nannochloropsis

granulata, Nannochloropsis limnetic,

Nannochloropsis oceanica, Nannochloropsis salina,

Nannochloropsis oculate. Microalgae also have an

essential function in marine ecosystems. Acts as a

natural food for zooplankton and fish larvae because

it is rich in carbohydrates, proteins, fats, minerals, and

amino acids. Nannochloropsis sp. is a widely

cultivated microalga and is rich in benefits, especially

Production of Biodiesel from Microalgae Using Transesteriﬁcation Batch Reactor with the Assistance of Calcium Oxide Hydrotalcite

Catalyst

181

regarding health. It is perfect for consumption by

zooplankton, such as rotifers, because it has a high

content of Eicosapentaenoic Acid (EPA) and

Docosahexaenoic Acid (DHA) (Meria et al, 2021).

The transesterification reaction is a chemical

reaction between triglycerides and alcohol that uses a

catalyst to produce monomers known as biodiesel

products. Common solvents in the method other than

methanol are NaOH, carbonates, and alkoxides such

as sodium methoxide, CO

, sodium propoxide, and

sodium butoxide. Several kinds of catalysts can be

used in the transesterification method, such as an

acid, alkaline, or heterogeneous catalyst. In the

transesterification method, a reaction occurs to form

triglycerides contained in the raw material with

methanol as a solvent using a catalyst. During the

reaction process, triglycerides create methyl esters,

fatty acids, and glycerol; the glycerol layer will

decrease in the existing biodiesel. In addition, there is

an in-situ transesterification method, a direct

transesterification process of biomass rich in lipids or

oil without knowing the extract and the purification

process separately. During the process, the raw

material will directly react with alcohol using a

catalyst. This transesterification process can coincide

with the response or first reactant process followed by

an extraction process (Panjaitan et al, 2018).

3 EXPERIMENTAL METHODS

3.1 Preparation of Catalyst

Catalyst CaO/hydrotalcite was prepared by the

method of incipient wetness impregnation.

Hydrotalcite as much as 10 grams in the oven for 12

hours at a temperature of 100

C. CaCO

is calcined to

CaO in a furnace for 3 hours at 900°C then weighed

with a loading ratio of 1:1 to hydrotalcite. After the

CaO is calcined, the CaO is cooled and dissolved in

distilled water. The incipient wetness impregnation

method was used for hydrotalcite by spraying it with

CaO solution in stages. The CaO-Hydrotalcite

mixture dried in an oven for 12 hours at 100°C. The

dry CaO-Hydrotalcite mix was then calcined in a

furnace for 3 hours at 900°C (Heraldy et al, 2017).

3.2 In Situ Transesterification

Microalgae Nannochloropsis sp. was weighed and

then put into a batch reactor along with methanol and

CaO/hydrotalcite catalyst according to the variables

set. The top nozzle of the reactor is closed, and the

stirrer and reactor heater are turned on with the

stirring speed according to the variable set until the

reaction time has been determined. After the reaction

time has been reached, the product mixture is

removed from the reactor through the bottom nozzle

and then cooled to room temperature. The residue in

the product mixture is separated from the filtrate

using a filtrate vacuum. The filtered residue was

washed using 30 mL of a combination of methanol-

n-hexane 1:1 (v/v) to recover the remaining biofuel.

The filtrate was put into a separatory funnel, n-hexane

was added with a ratio of 1:1 (v/v), then shaken and

allowed to stand until two layers were formed for 30

minutes. The bottom layer was removed from the

separatory funnel and added n-hexane with a ratio of

1:1 (v/v), then shaken and allowed to stand until two

layers were formed for 8 hours. The top layer is

washed using distilled water to bind the remaining

catalyst and glycerol, which is still left in the mixture.

The top layer is considered a transesterification

product and then refined to separate the biofuel and

solvent.

3.3 Refining

The product from the transesterification reaction is

put into a boiling flask, then placed on a hotplate, and

a solvent container is placed at the end of the

condenser. The heater is turned on until the

temperature in the boiling flask reaches 70 °C.

Heating can be stopped if all the n-hexane solvent has

evaporated with no more steam dripping at the end of

the condenser. The distillation product is cooled

down to room temperature. The distillate product was

put into the oven at 70 °C for 4 hours to evaporate the

solvent and water contained in the product. The

product is cooled and then analyzed for its yield and

acid number (SNI 7182:2015). The formula for yield

calculation is as follows:

Yield =

   

   

× 100%

(1)

The formula for Free Fatty Acid (FFA) calculation is

as follows:

FFA =

 ×  × 



(2)

= Molecular mass

= Concentration of NaOH

= Consumption of NaOH

= Wei

ht of crude biodiesel

ICATECH 2023 - International Conference on Advanced Engineering and Technology

182

4 RESULTS AND DISCUSSION

Research on making biodiesel from microalgae

Nannochloropsis sp. using the in-situ

transesterification batch reactor with the help of a

CaO/hydrotalcite catalyst was carried out in 3 stages,

namely the catalyst synthesis stage, the

transesterification stage, and the distillation stage.

The catalyst synthesis stage is carried out to

manufacture CaO/hydrotalcite catalyst using the

incipient wetness impregnation method, where

Hydrotalcite is impregnated by spraying it with CaO

solution according to the specified variables. CaO is

obtained from the compound CaCO

calcined at 900

°C. In a study by Royani et al. (2016), when CaCO

is calcined to a temperature of 900 °C, it will

decompose into CaO and CO

(Royani et al, 2016). In

the In-Situ transesterification stage, a series of

processes run simultaneously. The first is extracting

oil from the base material, which is carried out by

methanol and co-solvent n-hexane. Then the

triglycerides react with methanol to form methyl

esters in the transesterification reaction. Methanol is

a reactant in the transesterification reaction and a

lipid-extracting solution contained in microalgae. N-

hexane acts as a co-solvent in the extraction process.

Adding n-hexane as a co-solvent can increase the

lipid extracted from microalgae (Panjaitan et al,

2018). CaO/Hydrotalcite catalyst can speed up the

transesterification reaction at the in-situ

transesterification stage (Januar, 2014).

Figure 1 shows the effect of stirring speed on

biodiesel yield based on variations in reactor stirring

speed. Figure 1 shows that the stirring speed affects

the yield of crude products formed. The faster the

stirring speed is given, the more yield of crude

products is formed. It happens because the stirring

speed can increase the material particles' movement.

Collision activity and contact between one particle

and another material particle are becoming more

frequent, causing chemical reactions to occur more

rapidly (Miskah et al, 2017). Adding n-hexane to

transesterification can optimize the yield result

because n-hexane as a co-solvent can contact first

with the lipid in microalgae and then reacts with

methanol (Dianursanti, 2015). The highest yield of

crude product is found at the variable stirring speed

of 250 rpm, producing a crude yield of 38.36%. The

results obtained were lower when compared to the

previous study by Retya (2022), which was 71.7%.

This is because the method used is in situ microwave-

assisted transesterifications. Microwave radiation is

more effective in breaking down microalgae cells

(Barqi, 2015; Khan, 2021). Therefore, the lipid

extraction process runs faster. Methanol, as a solvent,

is also very good at absorbing microwave radiation to

support the transesterification reaction (Retya et al,

2022).

Figure 1: Effect of Stirrer Speed on Yield Biodiesel

Figure 2: Effect of Stirrer Speed on Free Fatty Acid Content

of Biodiesel

Figure 2 shows the effect of stirring speed on FFA

crude levels based on stirrer speed variations. Figure

2 shows that the stirring rate affects the formed FFA

crude product. The FFA crude product that is formed

is related to the yield of the produced crude product.

The greater the yield of crude product, the smaller the

FFA crude product formed. It happens because the

conversion of biodiesel becomes larger and

suppresses the conversion of FFA formation. FFA

levels in crude biodiesel products must be minimized

because FFA can react with metals at high

temperatures inside the engine when biodiesel is used

(Adhani et al, 2016). In the FFA test results, the

lowest FFA content was obtained at the variable

Production of Biodiesel from Microalgae Using Transesteriﬁcation Batch Reactor with the Assistance of Calcium Oxide Hydrotalcite

Catalyst

183

stirring speed of 250 rpm with an acid number content

of 2.76 mg NaOH/gram sample. The acid value in

biodiesel is still above the Standar Nasional

Indonesia (SNI) 7182: 2015 quality standard, which

is 0.5 mg NaOH/gram sample. The FFA level in the

biodiesel product formed is still higher when

compared to research conducted by Baqi (2022), and

Julrohiniar (2022), where the FFA levels produced

were 0.52 mg NaOH/gram sample and 0.321 mg

NaOH/gram sample. It is due to the biodiesel

manufactured by Baqi (2022) using a base catalyst

KOH and Julrohiniar (2022) using an SO

/TiO

base

catalyst in which the contained fatty acids are

transformed into dimethyl ether (Baqi et al, 2022;

Julrohiniar et al, 2022). The crude biodiesel product

is shown in Figure 3.

Figure 3: The Crude Biodiesel Product

5 CONCLUSION

Based on this research, it can be concluded that

biodiesel production from microalgae

Nannochloropsis sp with CaO/hydrotalcite catalyst

using the in-situ transesterification batch reactor

produced the highest yield is 38.36% at a reactor

stirring speed of 250 rpm, and the lowest Free Fatty

Acid content is 2.76 mg NaOH/gram of sample at a

reactor stirring speed of 250 rpm.

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Production of Biodiesel from Microalgae Using Transesteriﬁcation Batch Reactor with the Assistance of Calcium Oxide Hydrotalcite

Catalyst

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