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Biodiesel Synthesis: A Green Chemistry Solution for Alternative

Energy

Dr. Edlyn V. Malusay, Dr. Rogen A. Doronila

Associate Professor II, College of Arts and Sciences, Notre Dame of Dadiangas University, Philippines

DOI: https://dx.doi.org/10.47772/IJRISS.2025.910000852

Received: 07 November 2025; Accepted: 14 November 2025; Published: 26 November 2025

ABSTRACT

This study investigates the synthesis of biodiesel from waste cooking oil using base-catalyzed

transesterification with different alcohols: methanol, ethanol, and 2-propanol. The primary objective is to

evaluate the biodiesel yield and its physicochemical properties, including pH, color, density, acid value, and

water content, under various molar ratios of oil to alcohol. Methanol emerged as the most effective alcohol,

with a biodiesel yield of up to 98% achieved. This biodiesel exhibited favorable properties such as a low acid

value and an optimal pH, making it suitable for fuel applications. Ethanol and 2-propanol, however, did not

perform well under the tested conditions, yielding lower biodiesel amounts and exhibiting suboptimal

physicochemical properties. The results emphasize the critical role of the oil-to-alcohol ratio in the production

of high-quality biodiesel, with methanol showing superior performance compared to other alcohols. By

optimizing this ratio, the study contributes valuable insights into improving biodiesel yield and quality. These

findings are significant for the development of sustainable biodiesel production techniques, contributing to

global efforts to reduce dependence on fossil fuels and promote renewable energy solutions. By demonstrating

the potential of green chemistry, the study advanced sustainable energy solutions through the production of

high-quality biodiesel from waste cooking oil. Furthermore, by optimizing the methanol-to-oil ratio and

adhering to European standards, the research highlighted how green chemistry can drive innovation toward a

more sustainable energy future.

Keywords: biodiesel synthesis; physicochemical properties; renewable energy transesterification; waste

cooking oil

INTRODUCTION

The increasing global demand for energy, driven by accelerating population growth and economic expansion,

has emerged as a critical concern for the international community. Projections indicate that energy demand will

rise by more than 15% by 2050 compared to 2021 levels (Khan et al., 2024). This upward trajectory has been

consistent, with an average annual growth rate of approximately 2.1% (Zhang et al., 2022). At present, fossil

fuels continue to supply nearly 80% of the world’s energy needs, despite their welldocumented environmental

consequences. The combustion of these fuels significantly contributes to greenhouse gas (GHG) emissions,

including Carbon dioxide (CO₂), methane (CH₄), and black carbon, which intensify global warming and

exacerbate the effects of climate change (Moodley & Trois, 2021; Pandey, 2021). The environmental toll of

continued fossil fuel reliance underscores the urgent need to transition toward more sustainable energy sources

(Ismukurnianto, 2022).

This global issue is particularly pronounced in developing countries such as the Philippines, where GHG

emissions are projected to increase from 25 million tons of Carbon dioxide equivalent (MtCO₂e) in 2020 to

approximately 147 MtCO₂e by 2050 (Bollozos, 2023). This dramatic rise poses significant environmental and

social risks, especially in vulnerable regions like General Santos City. Such areas are increasingly susceptible

to climate-induced threats, including more intense and frequent natural disasters, sea-level rise, ecosystem

disruptions, and negative impacts on public health and livelihoods. These risks highlight the need for robust,

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localized climate mitigation and adaptation strategies aimed at increasing resilience and reducing

environmental harm (BIMP-EAGA, 2022).

Within this context, the shift to renewable energy sources has become imperative to reduce dependence on

fossil fuels and limit their associated emissions. Among various alternatives, biodiesel has gained attention for

its favorable environmental profile. Biodiesel is biodegradable, renewable, and produces significantly fewer

emissions compared to petroleum-based diesel (Prabhu et al., 2021). When synthesized under green chemistry

principles—which emphasize non-toxic materials, renewable inputs, and energy-efficient processes—biodiesel

represents a promising pathway toward cleaner energy production and reduced GHG emissions.

The global relevance of sustainable energy transitions is further emphasized by the United Nations Sustainable

Development Goals (SDGs), particularly Goal 7, which seeks to ensure access to affordable, reliable,

sustainable, and modern energy, and Goal 13, which calls for urgent action to combat climate change and its

impacts. Goal 13 aims to enhance resilience to climate hazards, integrate climate strategies into policy

frameworks, and strengthen institutional capacities for mitigation and adaptation. Goal 7 emphasizes

increasing the share of renewable energy and improving energy efficiency worldwide. Together, these goals

highlight the importance of reducing fossil fuel reliance and transitioning to renewable energy to achieve a

sustainable and resilient future.

Although numerous studies have examined the production of biodiesel from diverse raw materials, including

kaolin and eggshell catalysts (Giwa, 2021), vegetable oils (Kondrasheva, 2023), and Ricinus communis L. seed

oil using Calcium oxide nanoparticles (Jain, 2022), much of the existing literature focuses on yield

optimization and feedstock characteristics (Bôas, 2022). There remains a notable research gap in the

application of green chemistry to biodiesel synthesis, particularly in terms of utilizing waste feedstocks,

enhancing catalyst reusability, and minimizing environmental impact through process optimization.

This study aims to address that gap by systematically investigating the synthesis of biodiesel through green

chemistry approaches. Specifically, the research focuses on the use of waste cooking oil and environmentally

friendly catalysts to produce biodiesel, assessing both the environmental implications and sustainability of the

process. By doing so, this study contributes to the development of alternative energy solutions that align with

global sustainability targets and promote environmental stewardship.

2. Objectives

This study aimed to provide a green chemistry-based solution for sustainable alternative energy production

through the synthesis of biodiesel from waste cooking oil.

Specifically, the research sought to address the following objectives:

1. To determine the percentage yield of biodiesel produced using various molar ratios of alcohol

(ROH) to waste cooking oil (RCOOR), including methanol, ethanol, and 2-propanol.

2. To evaluate the physicochemical properties of the biodiesel produced using different types of

alcohols (methanol, ethanol, and 2-propanol), specifically pH, color, density, acid number and water

content.

3. To determine whether there is a statistically significant difference in the physicochemical properties

among methanol-based, ethanol-based, and 2-propanol-based biodiesel samples.

4. To compare the properties of locally synthesized biodiesel with those of biodiesel conforming to the

European Standard (EN 14214).

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MATERIALS AND METHODS

This study employed an experimental research design to synthesize biodiesel from waste cooking oil using

green chemistry principles. The research compared the effects of three alcohols—methanol, ethanol, and 2-

propanol—at varying molar ratios on biodiesel yield and physicochemical properties. A comparative analysis

was conducted between the properties of locally produced biodiesel and the European Standard for biodiesel

(EN 14214).

The materials used in this study included waste cooking oil (RCOOR), which was used as the feedstock for

biodiesel synthesis. The waste cooking oil was sourced from local providers and was filtered to remove any

particulate matter prior to use. Three different alcohols were employed for the transesterification process:

methanol (CH₃OH), ethanol (C₂H₅OH), and 2-propanol (C₃H₇OH). Sodium hydroxide (NaOH) served as the

base catalyst for the transesterification reaction. The catalyst was prepared by dissolving NaOH in methanol at

a concentration of 1% (w/v). In addition, standard biodiesel (EN 14214), which complies with the European

biodiesel standards, was used as a reference for comparison.

Various apparatus and equipment were utilized throughout the experimental procedure. Glassware including

conical flasks, graduated cylinders, beakers, and burettes were used for preparing the reactants, measuring

liquids, and conducting titrations. A heating mantle was employed to maintain a constant temperature during

the transesterification process, while a magnetic stirrer was used to ensure the thorough mixing of the

reactants. After the reaction, a separation funnel was used to separate the biodiesel from the glycerol. To

measure the density of the biodiesel samples, a refractometer was used, and a pH meter was employed to

determine the pH of the biodiesel. The color of the biodiesel was evaluated using a colorimeter, while a

titration setup was used to determine the acid number. Finally, the water content in the biodiesel was measured

using a Karl Fischer titrator, a specialized instrument for precise water content analysis.

Biodiesel was synthesized using the base-catalyzed transesterification method, where waste cooking oil

(RCOOR) was reacted with different alcohols (methanol, ethanol, and 2-propanol) in the presence of Sodium

hydroxide (NaOH) as a catalyst. For the preparation, a 1% (w/v) NaOH solution was first prepared by

dissolving NaOH in methanol (for methanol trials), ethanol (for ethanol trials), and 2-propanol (for 2-propanol

trials). The catalyst solution was then added to the corresponding alcohol, and the mixture was stirred until

homogeneous. In the transesterification reaction, 100 mL of waste cooking oil was measured into a 500 mL

conical flask, and the alcohol-catalyst mixture was added according to specific molar ratios. The reaction

mixture was then heated to 60 °C and continuously stirred for 1.5 hours to allow the transesterification reaction

to occur. After the reaction, the mixture was cooled to room temperature.

For the separation of the biodiesel, the reaction mixture was transferred to a separation funnel and allowed to

settle for 24 hours. The biodiesel layer (methyl/ethyl/propyl ester) was separated from the glycerol byproducts

and collected for further analysis. The biodiesel was then washed with warm distilled water several times to

remove residual catalyst and impurities. Finally, the purified biodiesel was dried in a vacuum oven at 50°C for

2 hours to remove excess water.

The physicochemical properties of the biodiesel were evaluated to assess its suitability as an alternative fuel.

The properties measured included pH, color, density, acid number, and water content. The pH of the biodiesel

was measured using a calibrated pH meter. The color was observed and compared visually using a

standardized color scale (ASTM D1500). The density was determined using a refractometer as per ASTM

D4052. The acid number was determined by titration with a standardized Potassium hydroxide (KOH)

solution, following ASTM D664. The water content was measured using the Karl Fischer titration method,

according to ASTM E203.

To assess the statistical significance of differences in the physicochemical properties among the biodiesel

samples produced with methanol, ethanol, and 2-propanol, a one-way analysis of variance (ANOVA) was

conducted. A p-value of less than 0.05 was considered statistically significant.

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Finally, the properties of the locally synthesized biodiesel were compared to the European Standard for

biodiesel (EN 14214) in terms of pH, color, density, acid value, and water content. This comparison provided

insight into the compliance of the locally synthesized biodiesel with international quality standards.

RESULTS

This section presents the data on the percentage yield of biodiesel, derived from varying molar ratios of

alcohol (ROH) to waste cooking oil (RCOOR). It also includes the examination of physicochemical properties

of the biodiesel produced using different types of alcohol—methanol, ethanol, and 2-propanol— including pH,

color, density, acid number, and water content. The results provided a comprehensive comparison of how these

factors influenced the quality and yield of biodiesel.

Table 1 presents experimental data on the yield of biodiesel using different types of alcohol and molar ratios

of waste cooking oil to alcohol. The types of alcohol tested include methanol (CH₃OH), ethanol (C₂H₅OH),

and 2-propanol (C₃H₇OH). Also shown in the table are different molar ratios of waste cooking oil to alcohol

(10:30, 5:3, and 5:9), with each experiment replicated three times to record the mass in grams and the

percentage yield.

For methanol at a 10:30 ratio, the replicates (R1, R2, R3) produced masses of 82.311 g, 82.317 g, and 81.945

g, respectively, with a consistent percentage yield of 82%. The mean yield, while not explicitly stated, would

be approximately 82 %. At a 5:3 ratio, the replicates produced masses of 88.093 g, 89.000 g, and 87.985 g,

corresponding to percentage yields of 88 %, 89 %, and 88 %. The mean yield for this ratio is around 88.4 %.

Table 1 Percentage Yield of Biodiesel from varying Molar Ratios of Alcohol (ROH) to Waste Cooking Oil

(RCOOR)

Types of alcohol

Waste cooking oil to

alcohol ratio

Replicate

Mass (g)

Percentage

yield

82.311

10:30

82.317

81.945

Mean

82.191

88.093

Methanol, CH

5:3

89.000

87.985

Mean

88.359

88.33

98.594

5:9

97.844

96.678

Mean

97.705

97.67

Ethanol, C

2-Propanol, C

Note: * Same ratio with methanol

** Negative results

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For the 5:9 ratio, the replicates produced masses of 98.594 g, 97.844 g, and 96.678 g, with percentage yields of

98 %, 98 %, and 97 %. The mean yield was approximately 97.7 %.

In contrast, both ethanol and 2-propanol did not produce positive results under the conditions tested. The table

notes "negative results" with an asterisk explanation indicating that the same ratio used with methanol did not

yield biodiesel with these alcohols.

Table 2 summarizes the outcomes of experiments using different alcohols and waste cooking oil ratios to

produce biodiesel, with a focus on the color of the resulting product. The table was divided based on the

types of alcohol used: methanol (CH₃OH), ethanol (C₂H₅OH), and 2- propanol (C₃H₇OH).

Table 2 The Physicochemical Property of Biodiesel Produced in Terms of colour

Types of alcohol

Waste cooking oil to

alcohol ratio

Replicate

Colour

Yellow

10:30

Yellow

Methanol, CH

5:3

Yellow

Amber

5:9

Amber

Ethanol, C

2-Propanol, C

Note: * Same ratio with methanol

**Negative results

For methanol, three different waste cooking oil to alcohol ratios were tested: 10:30, 5:3,

and 5:9. In the first two ratios (10:30 and 5:3), all replicates (R1, R2, R3)

resulted in yellow- colored biodiesel. The mean color for these ratios also remained yellow. However, for

the 5:9 ratio, the color of the biodiesel changed to amber for all replicates, with the mean color also

recorded as amber.

For ethanol and 2-propanol, the table indicated that the same ratios as methanol were tested (*). However,

the results were negative (**), implying that these alcohols did not produce biodiesel successfully or did not

produce a usable product under the tested conditions.

Table 3 presents data on the pH levels of biodiesel produced using different types of alcohols and waste

cooking oil ratios. This table focuses on how the pH of the resulting biodiesel varies with the type of alcohol

and the ratio of waste cooking oil to alcohol.

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Table 3 The Physicochemical Property of Biodiesel Produced in Terms of pH

Note: *Same ratio with methanol

**Negative results

For methanol (CH₃OH), three waste cooking oil to alcohol ratios were tested: 10:30, 5:3, and 5:9. The pH

values for the 10:30 ratio showed slight consistency, with replicates R1 and R2 having a pH of 7.3 and R3 as

lightly lower pH of 7.2. The 5:3 ratio showed a higher pH level with R1 at 7.6 and R2 and R3 at 7.4. The

highest pH levels were observed in the 5:9 ratio, where R1 and R3 had a pH of 8.6 and R2 a pH of 8.4. These

results indicated that increasing the ratio of alcohol tended to increase the pH of the resulting biodiesel when

methanol was used.

Table 4 shows the density of biodiesel produced using different types of alcohols and various waste cooking oil

to alcohol ratios. This data was crucial because the density of biodiesel is a key factor in determining its

suitability as a fuel.

Table 4 The Physicochemical Property of Biodiesel Produced in Terms of Density

Note: *Same ratio with methanol

**Negative results

Types of Alcohol

Waste Cooking Oil to Alcohol Ratio

Replicate

7.3

10:30

7.3

7.2

7.6

Methanol, CH

5:3

7.4

8.6

5:9

8.4

8.6

Ethanol, C

2-Propanol,

Types of Alcohol

Waste Cooking Oil to

Alcohol Ratio

Replicate

Density (kg/m

) at 20°C

872.021

10:30

869.102

870.981

884.314

Methanol,

5:3

887.306

885.070

894.472

5:9

892.092

895.721

Ethanol,

2-Propanol,

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For methanol (CH₃OH), three waste cooking oil to alcohol ratios were tested: 10:30, 5:3, and 5:9.

The densities for the 10:30 ratio ranged slightly, with R1 at 872.021 kg/m³, R2 at 869.102 kg/m³, and R3 at

870.981 kg/m³. For the 5:3 ratio, the densities were slightly higher, with R1at 884.314 kg/m³, R2 at 887.306

kg/m³, and R3 at 885.070 kg/m³. The highest densities were observed in the 5:9 ratio with R1 at 894.472

kg/m³, R2 at 892.092 kg/m³, and R3 at 895.721 kg/m³.

Table 5 provides data on the acid values of biodiesel produced using different alcohols and waste cooking

oil to alcohol ratios. Acid value is a critical parameter indicating the amount of free fatty acids in the

biodiesel,

which affects its quality and stability.

Table 5 The Physicochemical Property of Biodiesel Produced in Terms of Acid Value

Note: *Same ratio with methanol

**Negative results

For methanol (CH₃OH), three waste cooking oil to alcohol ratios were tested: 10:30, 5:3, and 5:9. At the 10:30

ratio, the acid values for the three replicates (R1, R2,

R3) are 0.4 mg KOH/g, 0.5 mg KOH/g, and 0.4 mg KOH/g, respectively. These values were slightly higher but

still within acceptable limits. For the 5:3 ratio, the acid values are 0.3 mg KOH/g for R1 and R2, and 0.4 mg

KOH/g for R3, showing a slight improvement compared to the 10:30 ratio. At the 5:9 ratio, the acid values

further decreased, with R1 at 0.3 mg KOH/g and both R2 and R3 at 0.2 mg KOH/g, indicating better quality

biodiesel with lower fatty.

For ethanol (C₂H₅OH) and 2-propanol (C₃H₇OH), the table indicated that the same ratios as methanol were

tested (*), but both alcohols resulted in negative outcomes (**). This implied that these alcohols did not

produce biodiesel with acceptable acid values under the tested conditions.

Table 6 provides data on the water content in biodiesel produced using different types of alcohols and

various waste cooking oil to alcohol ratios. Water content was critical parameter in biodiesel quality, as

excessive water could lead to issues in fuel performance and storage stability.

For methanol (CH₃OH), three waste cooking oil to alcohol ratios were tested: 10:30, 5:3, and 5:9. The water

content for the10:30 ratio showed some variation among the replicates, with R1 having a water content of

320 mg/kg, R2 at 346 mg/kg, and R3 at 337 mg/kg. For the 5:3 ratio, the water content was slightly higher,

Types of

Alcohol

Waste Cooking Oil to Alcohol

Ratio

Replicate

Acid Value (mg KOH/g)

0.4

10:30

0.5

0.4

0.3

Methanol,

5:3

0.3

0.4

0.3

5:9

0.2

Ethanol,

2-Propanol,

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with R1 at 394 mg/kg, R2 at 380 mg/kg, and R3 at 437 mg/kg. The highest water content was observed in

the 5:9 ratio, where R1 has 473 mg/kg, R2 has 491 mg/kg,

Table 6 The Physicochemical Property of Biodiesel Produced in Terms of Water Content

Note: *Same ratio with methanol

**Negative results

and R3 has 477 mg/kg. These results indicated that increasing the alcohol ratio led to an increase in the water

content of the biodiesel produced with methanol.

For ethanol (C₂H₅OH) and 2-propanol (C₃H₇OH), the table noted that the same ratios as methanol were tested

(*), but both alcohols resulted in negative outcomes (**). This indicates that these alcohols did not produce

biodiesel successfully or resulted in products with undesirable properties under the tested conditions. This

aligned with the previous findings where methanol was the only alcohol to produce consistent and measurable

biodiesel properties.

The next section presents whether there were significant differences between the physicochemical

properties of methanol biodiesel across three ratios of waste cooking oil to alcohol. This analysis helped

determine the most suitable ratio for biodiesel production based on the measurable outcomes observed in

the previous experiments. By comparing these properties, the researcher identified which ratio offered the

best performance in terms of biodiesel quality and consistency.

The succeeding tables presents the results of analysis of variance (ANOVA) to test the significance of

difference in means between waste cooking oil to alcohol ratios. For post-hoc test results, see Appendix A.

Table 7 summarizes the results of an ANOVA test, assessing differences in biodiesel yields across various oil-

to-alcohol ratios. The between-groups variation, indicating differences due to the ratios, had a sum of squares

(SS) of 372.667 with 2 degrees of freedom (df), and a mean square (MS) of 186.333. The Fvalue of 838.5,

which significantly exceeded the critical F-value (F crit) of 5.143, and a P-value of less than .001, confirmed

that the yield differences are highly significant (Field, 2021; Frost, 2021).

Types of

Alcohol

Waste Cooking Oil

to Alcohol Ratio

Replicate

Water Content (mg/Kg)

320

10:30

346

337

394

Methan

ol, CH

5:3

380

437

473

5:9

491

477

Ethanol

, C

Propanol,

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Table 7 Analysis of Variance in Percentage Yield Between Waste Cooking Oil to Alcohol Ratios

Source of Variation

P-value

F crit

Between Groups

372.667

186.333

838.5

<.001

5.143

Within Groups

1.333

0.222

Total

374

Within-groups variation, showing variability within each group, had an SS of 1.333 with 6 df and an MS of

0.222. The low within-groups variability compared to the between-groups highlighted the substantial impact of

different ratios on biodiesel yield. The total SS is 374 with 8 df, reinforcing that the ratios of waste cooking oil

to alcohol significantly affected biodiesel yield.

The total variation, combining both between-groups and within-groups variations, sums up to 374, with a total

of 8 degrees of freedom. The significant F-value and low P-value implied that the ratios of waste cooking oil to

alcohol had a profound impact on the percentage yield of biodiesel. This finding underscored the necessity of

optimizing the oil-to-alcohol ratio to enhance biodiesel yield efficiency.

Table 8 presents an ANOVA summary that evaluated the variability in pH levels across different ratios of

waste cooking oil to alcohol. The analysis showed a significant effect of the different ratios on pH, indicated

by an F-value of 139.111, which significantly exceeded the critical F-value (F crit) of 5.143. With a P-value

of less than .001, the results affirmed statistically significant differences between the groups.

Table 8 Analysis of Variance in pH Between Waste Cooking Oil to Alcohol Ratios

Source of Variation

P-value

F crit

Between Groups

2.782

1.391

139.111

<.001

5.143

Within Groups

0.06

0.01

Total

2.842

The table details a between-groups sum of squares (SS) of 2.782 with 2 degrees of freedom (df), yielding a

mean square (MS) of 1.391, which represented the average variance among the different ratios. The within-

groups SS was notably smaller at 0.06 with 6 df, resulting in an MS of 0.01, indicating minimal variability

within individual groups of ratios. This low within-group variance reinforced the consistency of pH

measurements within each ratio group.

Table 9 presents the ANOVA results that evaluated the variability in biodiesel density across different waste

cooking oil to alcohol ratios. The table reveals a significant effect of these ratios on biodiesel density,

evidenced by an F-value of 157.510, which substantially exceeded the critical F-value (F crit) of 5.143, and a

P-value of less than. 001. These results confirmed statistically significant differences in density between the

tested groups.

Table 9 Analysis of Variance in Density Between Waste Cooking Oil to Alcohol Ratios

Source of

Variation

P-value

F crit

Between Groups

840.932

420.466

157.510

<.001

5.143

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Within Groups

16.017

2.69

Total

856.949

The between-groups sum of squares (SS) is 840.932 with 2 degrees of freedom (df), resulting in a mean square

(MS) of 420.466. This high MS indicated considerable variability in density due to the different ratios. In

contrast, the within-groups SS was 16.017 with 6 df, yielding an MS of 2.669, which highlighted minimal

variability within each ratio group. The clear difference between the between-groups and withingroups

variances underscored the substantial impact of the oil-to-alcohol ratio on biodiesel density.

Table 10 presents the ANOVA results evaluating the differences in acid values of biodiesel produced using

various waste cooking oil to alcohol ratios. The table revealed significant differences in acid values among the

different ratios, as indicated by an F-value of 9, which exceeded the critical F-value (F crit) of 5.143, and a P-

value of 0.016, suggesting statistical significance.

Table 10 Analysis of Variance in Acid Value Between Waste Cooking Oil to Alcohol Ratios

Source of Variation

P-Value

F cri

Between Groups

0.060

0.030

0.016

5.143

Within Groups

0.020

0.003

Total

0.08

The between-groups sum of squares (SS) was 0.060 with 2 degrees of freedom (df), resulting in a mean square

(MS) of 0.030. This indicated that the variance due to different ratios is substantial. In contrast, the within-

groups SS was 0.020 with 6 df, yielding an MS of 0.003, showed minimal variability within each group. The

total SS of 0.080 with 8 df further confirmed the findings.

Table 11 presents the ANOVA results evaluating the differences in water content of biodiesel produced using

various ratios of waste cooking oil to alcohol. The table showed a significant difference in water content

among the different ratios, evidenced by an F-value of 41.886, which was well above the critical F-value (F

crit) of 5.143, and a P-value of <.001, indicating statistical significance.

The between-groups sum of squares (SS) was 32000.888 with 2 degrees of freedom (df), resulting in a mean

square (MS) of 16000.444. This high MS indicated considerable variability in water content attributable to

the different ratios. In contrast, the within-groups SS was 2292.000 with 6 df, yielding an MS of 382.000,

which suggested lower variability within each group. The total SS was 34292.888 with 8 df.

Table 11 Analysis of Variance in Water Content Between Waste Cooking Oil to Alcohol Ratios

Source of Variation

P-Value

F crit

Between Groups

32000.88

16000.44

41.886

<.001

5.143

Within Groups

2292.00

382.00

Total

34292.88

Table 12 shows the comparison of the properties of synthesized biodiesel with the European standards for

biodiesel quality. The properties analyzed include pH, color, density, acid value, and water content, which were

critical for determining the fuel's suitability and performance.

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Table 12 Comparison of Physicochemical Properties Between the Biodiesel of the Present Study and the

European Standard (EN14214)

Properties

Synthesized Biodiesel

European Standard (EN14214)

7.756

Around pH 7 (neutral)

Color

Yellow

Golden yellow to amber, clear and

uniform

Density at 15°C(kg/m³)

883.453

860-900

Acid Value (mg KOH/g)

0.333

Maximum 0.5

Water Content (mg/kg)

406.111

Maximum 500

The pH of the synthesized biodiesel was 7.756, slightly above the neutral pH of around 7, as specified by the

European Standard. This indicated that the biodiesel was almost neutral, which was desirable as it suggested

stability and minimal corrosiveness, aligning closely with the standard requirements (European Standard,

EN14214).

The color of the synthesized biodiesel was yellow, which matched the European standard description of

biodiesel being a golden yellow to amber color, clear and uniform. This uniform color was an indicator of

good quality and proper processing, ensuring that the fuel was free from impurities and suitable for use

(European Standard, EN14214).

The density of the synthesized biodiesel at 15°C was 883.453 kg/m³, falling within the European standard

range of 860-900 kg/m³. This conformity indicated that the biodiesel had the appropriate mass per unit volume,

which was crucial for engine performance and efficiency (European Standard, EN14214).

The acid value of the synthesized biodiesel was 0.333 mg KOH/g, well below the maximum allowable limit

of 0.5 mg KOH/g set by the European standard. A low acid value was essential for the longevity of the engine

and fuel system, as it indicated low levels of free fatty acids and reduced the risk of corrosion and deposits

(European Standard, EN14214). The water content of the synthesized biodiesel was 406.111 mg/kg, which

was within the European standard maximum of 500 mg/kg. Properly controlled water content was crucial to

prevent microbial growth and avoid issues such as fuel system corrosion and reduced combustion efficiency

(European Standard, EN14214).

DISCUSSION

This part of the study interprets the results related to the biodiesel production process, with a focus on the

effects of varying alcohol-to-oil ratios and different alcohol types on biodiesel yield and quality. It explores the

analysis of key physicochemical properties such as pH, color, density, acid number, and water content, and

how these factors influence the overall performance of the biodiesel. By comparing the performance of

methanol, ethanol, and 2-propanol as alcohols in the transesterification process, this section aims to provide

insights into their roles in optimizing biodiesel production for improved efficiency and quality.

For the data on the yield of biodiesel using different types of alcohol and molar ratios of waste cooking oil to

alcohol, Table 1 suggests that methanol was most effective alcohol for producing biodiesel from waste

cooking oil under the tested conditions, with higher methanol ratios (5:9) showing the highest yields, around

98 %. ethanol and 2-propanol, however, may have required different conditions to be effective or were

inherently less effective in this process.

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Several recent studies highlighted the importance of methanol in biodiesel production. A study of Ulukardesler

(2023) emphasized that the molar ratio of methanol to oil plays acritical role in achieving high biodiesel yields.

Specifically, increasing the methanol to oil ratio can significantly enhance the conversion efficiency, with

yields increasing from 70 % to 95 % as the ratio is raised from 9:1 to 15:1, using KOH as a catalyst. This

aligned with the results in Table1, where varying the methanol ratio directly impacted the yield.

Moreover, the study of Devaraj et al. (2020) confirmed these findings, indicating that methanol is highly

effective in biodiesel production from waste cooking oil, particularly when the correct molar ratios and

catalysts are used. This study also noted that while other alcohols like ethanol and 2-propanol can be used, they

often result in lower yields or negative results under similar conditions. Farouk (2024) proved that the use of

ethanol and 2-propanol was less effective due to its lower reactivity compared to methanol. The different

molecular structures and properties of these alcohols affect the reaction kinetics, often leading to lower yields

and biodiesel with less desirable physical and chemical properties.

Table 2 presents the results of experiments using different types of alcohol and varying molar ratios of waste

cooking oil to alcohol, with a particular focus on the color of the resulting biodiesel. It highlights that methanol

was the only alcohol among the three that produced biodiesel with a consistent color outcome, varying

between yellow and amber depending on the specific oil to alcohol ratio used. The other two alcohols, ethanol

and 2-propanol, failed to produce biodiesel under the tested conditions.

Methanol proved to be highly effective for biodiesel production from waste cooking oil, particularly at

specific ratios. Using methanol-to-oil ratios ranging from 3:1 to 9:1 generally increased biodiesel yield,

though higher ratios may decrease yield due to methanol's emulsifying properties, which could potentially

affect the color of the biodiesel. This aligned with findings of Tsaoulidis et al. (2023) and Velmurugan et al.

(2022) which showed that methanol at different ratios could produce varying biodiesel colors, such as yellow

and amber.

Overall, the inefficiency of these alcohols under tested conditions suggested less favorable outcomes,

including potential color inconsistencies. These insights supported further research focused on optimizing

methanol-based biodiesel production while exploring alternative conditions for ethanol and 2propanol.

Table 3 presents the pH levels of biodiesel produced using different types of alcohols and waste cooking oil

ratios. Velmurugan and Warrier (2022) highlighted that higher methanol concentrations in the

transesterification process can lead to higher pH values, as seen in the production of biodiesel from waste

cooking oil. The increase in the alcohol ratio not only improves yield but also influenced the properties of the

biodiesel, including pH. This aligned with the observation of increased pH levels at higher alcohol ratios.

Also, Neupane (2022) emphasized that increasing the alcohol-to-oil ratio enhanced the biodiesel yield and

conversion efficiency. For instance, a ratio of 6:1 (alcohol to oil) resulted in a 99 % conversion rate,

demonstrating that higher alcohol ratios positively affect the reaction's efficiency and potentially the pH of the

resulting biodiesel.

For ethanol (C₂H₅OH) and 2-propanol (C₃H₇OH), the table noted that the same ratios as methanol were tested

(*). However, both alcohols resulted in negative outcomes (**), indicating they did not produce biodiesel or

produced biodiesel with undesirable properties under the tested conditions. This suggests that methanol was

more effective in producing biodiesel with measurable pH properties compared to ethanol and 2-propanol.

The data presented in Table 3, along with the previous one on color, emphasized that methanol was the most

suitable alcohol among the three tested for biodiesel production. The variations in pH with different ratios of

waste cooking oil to methanol also provided insights into optimizing the production process for desired pH

levels in biodiesel. These findings guided further research and industrial applications in biodiesel production,

focusing on the use of methanol and appropriate oil-to-alcohol ratios.

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Table 4 shows the density of biodiesel produced using different types of alcohol and various waste cooking oil-

to-alcohol ratios. The results indicate a trend where increasing the alcohol ratio led to a higher density in the

biodiesel produced with methanol.

Studies of Ennetta (2022) and Mittal et al. (2022) showed that biodiesel produced with higher methanol ratios

tended to have increased density due to the formation of more methyl esters. Increasing the alcohol ratio also

affected the density of the biodiesel, with higher ratios leading to an increase in density because of the

formation of more ester compounds and the complete conversion of triglycerides into biodiesel.

For ethanol (C₂H₅OH) and 2-propanol (C₃H₇OH), the table indicated that the same ratios as methanol were

tested (*), but both alcohols resulted in negative outcomes (**), meaning they did not produce biodiesel

successfully or resulted in unusable products under the tested conditions. This again highlighted methanol's

superiority in the biodiesel production process in terms of yielding measurable and usable outcomes.

The findings from Table 4, combined with those from the previous tables on color and pH, provides a

comprehensive overview of the physicochemical properties of biodiesel produced using methanol. The data

indicated that methanol not only consistently produces biodiesel but also allowed for control over the density

of the product by adjusting the oil to alcohol ratio. This information is valuable for optimizing biodiesel

production processes to meet specific fuel standards and performance requirement.

Data from Table 5 highlights that methanol is the most effective alcohol for producing biodiesel with

acceptable acid values across different waste cooking oil to alcohol ratios. Lower acid values, particularly

observed at the 5:9 ratio, suggest that this ratio is optimal for producing higher quality biodiesel with reduced

free fatty acid content. This is crucial for ensuring the fuel's stability and reducing the risk of engine corrosion

and deposits.

In this study, the acid values decreased with an increasing alcohol ratio, indicating improved biodiesel quality.

This trend aligned the study of Tayeb (2024), which showed that higher methanol ratios in the

transesterification process tended to reduce the acid value of biodiesel. Lower acid values corresponded to

lower free fatty acid content, which is essential for high-quality biodiesel production.

Studies have shown that higher methanol ratios during the transesterification process reduced the acid value

of the produced biodiesel, resulting in lower free fatty acid content and improved biodiesel quality. Nabgan

(2022) and Ahmed (2022) highlighted that optimizing the methanol to oil ratio is critical for achieving high-

quality biodiesel with low acid values, which are essential for reducing corrosive effects and improving the

fuel's overall performance and stability.

Data about methanol proved to be a superior alcohol for biodiesel production, yielding biodiesel with

desirable acid values across various ratios, while ethanol and 2-propanol failed to produce suitable results.

Optimizing the waste cooking oil to methanol ratio, especially favoring the 5:9 ratio, can significantly

improve biodiesel quality by minimizing acid content.

Moreover, results has shown that the water content in biodiesel could increase with a higher methanol to oil

ratio due to the hygroscopic nature of methanol, which absorbs water from the environment. Studies of Sahani

et al. (2020) and Ishak and Kamari (2019) aligned with the observation that higher methanol content could

introduce more water into the biodiesel. Biodiesel production using used cooking oil and mixed metal oxide

catalysts noted that the optimal methanol-to-oil ratio for their process led to significant biodiesel yield, but also

increased the water contents lightly as the methanol ratio increased.

Additionally, recent advances in transesterification processes highlighted the importance of controlling

water content during biodiesel production, as excessive water could lead to soap formation and decrease the

overall quality of biodiesel. Thus, while a higher methanol ratio could improve the conversion process and

yield, it also necessitated careful management of water content to maintain fuel quality (Farouk, 2024).

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Data on water content, in conjunction with the previous tables on color, pH, and density, showed the

importance of methanol in biodiesel production. Methanol consistently produced biodiesel with measurable

properties, although the water content tended to increase with higher oil to alcohol ratios. This information

was crucial for optimizing biodiesel production processes, as controlling water content was essential for

ensuring fuel quality and performance. By understanding the relationship between the alcohol type, the oil

to alcohol ratio, and the resulting biodiesel properties, producers could fine-tune their processes to achieve

the desired fuel characteristics. Having thoroughly examined the physicochemical properties of biodiesel

produced using different alcohols—methanol, ethanol, and 2-propanol—across various parameters such as

color, pH, density, and water content, we shifted our focus to a comparative analysis.

Table 7 presents the differences in biodiesel yields across various oil-to-alcohol ratios, highlighting the

importance of optimizing this ratio to maximize biodiesel yield efficiency. A study by Vishal et al. (2020)

highlighted that optimizing the ratio is crucial for maximizing biodiesel yield, emphasizing the role of

alcohol in the transesterification process. Similarly, Dwivedi (2022) confirmed that adjusting the oil-toalcohol

ratio significantly affected the yield, supporting the need for precise optimization to enhance biodiesel

production efficiency.

These results were essential for biodiesel production, emphasizing the need for careful selection of the oil-to-

alcohol ratio. The significant differences highlighted by the ANOVA test in optimizing the oil-toalcohol ratio

for biodiesel production were crucial for enhancing yield and efficiency. Study of Zahed (2022) showed that

optimizing the oil-to-alcohol ratio can significantly impact biodiesel yield, leading to more efficient and cost-

effective production processes. The study highlighted the importance of optimizing production parameters for

maximizing yield and efficiency. Similarly, research by Chiedu (2024) emphasized the necessity of careful

selection and optimization of production variables to enhance biodiesel quality and yield.

To assess the variability in pH levels across different waste cooking oil-to-alcohol ratios, Table 8 shows a

substantial variance between groups compared to within groups, emphasizing the significant influence that

different waste cooking oil-to-alcohol ratios have on the pH of biodiesel. This suggests that modifying these

ratios can markedly affect the chemical properties of the resulting biodiesel. These findings are crucial for

optimizing biodiesel formulations to enhance both its quality and performance.

A study by Kamran et al. (2020) supported the notion that optimal ratios were important for improving

biodiesel properties. The study discussed the effects of various transesterification parameters, including the

oil-to-alcohol ratio, on biodiesel properties. The research highlighted that adjusting the methanol ratio

significantly influenced the pH and overall quality of biodiesel. Also, Borah et al. (2020) highlighted that the

methanol to oil ratio played a critical role in determining the pH and other characteristics of biodiesel

produced from waste cooking oil. Their findings underscored the need to finetune these ratios to achieve the

desired chemical properties and enhance biodiesel performance.

These statistical insights emphasized the critical role of precise ratio configurations in achieving desired

biodiesel properties, facilitating targeted improvements in biodiesel production processes.

Table 9 presents a marked difference between the variance among groups and the variance within groups,

indicating that the oil-to-alcohol ratio significantly influences the density of the biodiesel.

Recent studies highlighted the significant impact of the oil-to-alcohol ratio on the density of biodiesel. The

variability in density observed due to different ratios underscored the importance of optimizing these ratios

for biodiesel production. For instance, a study by Jain et al. (2022) emphasized the optimization of alkali-

catalyzed transesterification of rubber oil, which significantly affected the density of the produced biodiesel,

demonstrating the crucial role of alcohol ratio in determining biodiesel properties.

Also, Khan in 2023 investigated the transesterification conditions of rapeseed and sunflower oil, revealing that

the type and concentration of alcohol used could significantly influence the density and overall quality of

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biodiesel. This study supported the notion that adjusting the alcohol ratio was pivotal in achieving optimal

biodiesel characteristics.

It further consolidated the findings, suggesting that optimizing the oil-to-alcohol ratio is crucial for achieving

desired biodiesel density. Such insights were vital for refining biodiesel production processes to improve fuel

quality and efficiency. These statistical analyses underscored the importance of precise ratio configurations in

biodiesel production, which could lead to significant improvements in fuel properties and performance.

Results showed in Table 10 demonstrates the critical impact of the oil-to-alcohol ratio on the acid value of

biodiesel, highlighting the need for precise optimization of these ratios to produce high-quality biodiesel with

desirable acid values. The significant between-group variance relative to within- group variance suggested that

adjusting the ratios could effectively control the acid value, which was vital for biodiesel stability and

performance.

Studies had shown that adjusting these ratios could effectively control the acid value, which was crucial for

biodiesel stability and performance. For instance, research by Dwivedi et al. (2020) demonstrated that

optimizing the alcohol-to-oil ratio significantly influenced biodiesel properties, including acid value, thereby

enhancing fuel quality and engine performance. Additionally, Chavan et al. (2020) highlighted that the correct

ratio was essential for maintaining low acid values, reducing the risk of engine corrosion and improving

biodiesel's overall stability.

This analysis was important for refining biodiesel production processes, ensuring that the produced fuel met

the required standards and enhanced its usability and longevity.

Furthermore, the significant between-group variance relative to within-group variance shown in Table 11

emphasizes the substantial impact of the oil-to-alcohol ratio on biodiesel's water content. These findings

highlighted the importance of optimizing the ratio to achieve biodiesel with lower water content, which was

critical for fuel quality and performance.

Research highlighted that the alcohol-to-oil ratio was one of the most important parameters for the conversion

to biodiesel, influencing the yield and quality significantly. An optimal ratio minimized water content,

improving the biodiesel's stability and reducing potential issues related to engine performance (Mittal, 2022).

Furthermore, studies showed that the correct ratio could help achieve higher biodiesel yields while reducing

impurities, including water content, which was vital for maintaining fuel quality and storage stability (Bashir et

al., 2022).

The findings from Tables 1-6 collectively indicated that methanol was the most effective alcohol for biodiesel

production, yielding consistent and desirable physicochemical properties across various ratios. Ethanol and 2-

propanol were largely ineffective under the tested conditions. This emphasized the necessity of choosing the

right alcohol and optimizing the ratio to achieve high-quality biodiesel.

On another hand, Tables 7 to 11 extend the analysis by using ANOVA to statistically assess the significance of

differences in the physicochemical properties of biodiesel based on waste cooking oil to alcohol ratios. The

ANOVA results from Tables 7-11 collectively confirmed that the ratio of waste cooking oil to alcohol

significantly affected key biodiesel properties.

Optimizing these ratios was crucial for maximizing yield, achieving desired pH levels, ensuring consistent

density, controlling acid value, and minimizing water content. These insights were vital for refining biodiesel

production processes to produce high-quality, efficient, and stable biodiesel.

Table 12 shows the synthesized biodiesel met the European standards (EN14214) for pH, color, density, acid

value, and water content. This compliance suggested that the biodiesel was of high quality and suitable for use

in diesel engines, ensuring good performance, stability, and minimal risk of damage to the engine and fuel

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system. These findings underscored the effectiveness of the production process and the suitability of the

selected waste cooking oil to alcohol ratios in producing high-quality biodiesel.

The adherence of the synthesized biodiesel to the European Standard Biodiesel specifications

(EN14214) was a testament to the success of the green chemistry approach in this study. By achieving

compliance with these standards not only underscored the effectiveness of the production process but also

highlights the successful application of green chemistry principles in developing a sustainable and

environmentally friendly alternative fuel. The European Standard sets rigorous criteria for biodiesel, including

limits on pH, color, density, acid value, and water content, all of which are critical for ensuring that the fuel

performs well in engines without causing damage or inefficiencies.

Additionally, the results demonstrated that the chosen waste cooking oil to methanol ratios not only improved

biodiesel yield but also contributed to the sustainability of the production process. Using waste cooking oil as

a feedstock aligns with green chemistry principles by promoting the recycling of waste materials and reducing

the need for virgin raw materials. This approach not only addressed waste management issues but also

supports resource conservation, making biodiesel production more sustainable and economically viable. In the

context of alternative energy solutions, the application of green chemistry in this study offered notable

benefits. It effectively converted waste products into valuable energy sources, mitigating the environmental

impact of waste disposal.

Additionally, by meeting established standards and optimizing production conditions, the study demonstrated

that biodiesel could serve as a reliable, high-quality alternative to fossil fuels, thereby enhancing its feasibility

and appeal as a sustainable fuel.

In summary, the results of this study affirmed the potential of green chemistry in advancing sustainable energy

solutions through biodiesel production from waste cooking oil. By optimizing the methanol-to-oil ratio and

ensuring compliance with European standards, the research highlighted the effectiveness of green chemistry

principles in producing high-quality biodiesel. The study served as a valuable example of how green

chemistry could drive innovation and contribute to a more sustainable and eco-friendly energy future.

CONCLUSION

Based on the findings of the study, which assessed the effectiveness of various alcohols—specifically

methanol, ethanol, and 2-propanol—in producing biodiesel from waste cooking oil, several key conclusions

were drawn. Firstly, methanol was found to be the most effective alcohol for biodiesel production,

outperforming the other alcohols tested. The use of higher methanol-to-oil ratios enhanced biodiesel yield,

whereas ethanol and 2-propanol either required different conditions or were less suitable for this process. The

study further established that methanol, when used at optimal ratios, improved biodiesel yield and provided

better control over the physicochemical properties, such as pH and density. However, it was noted that

excessively high methanol-to-oil ratios could negatively impact the yield and the color of the biodiesel. The

data also confirmed that methanol consistently produced biodiesel with desirable acid values and measurable

properties, in contrast to ethanol and 2-propanol, which were less effective in this regard. Additionally, the

study highlighted that the waste cooking oil to methanol ratio significantly influenced the key physicochemical

properties of the biodiesel. By optimizing this ratio, the quality of the biodiesel was notably improved, with

reduced acid content and controlled water levels. Finally, the locally produced biodiesel met the European

Standard Biodiesel specifications for pH, color, density, acid value, and water content, confirming its high

quality and suitability for use in diesel engines. These results underscored the effectiveness of the production

process and affirmed that the chosen waste cooking oil-to-alcohol ratios produced biodiesel with excellent

performance and stability.

Furthermore, based on the results of the study, several recommendations were made for those interested in

further research. First, it is advised to optimize biodiesel production by refining the use of methanol,

particularly by determining the optimal methanol-to-oil ratio, reaction time, temperature, and catalyst

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concentration to achieve the highest yield and best quality biodiesel. Second, the ratio of methanol in the

biodiesel production process should be optimized to control and maintain the desired pH levels, which in turn

will improve the quality and stability of the resulting biodiesel. Third, to enhance biodiesel quality, it is

recommended to carefully manage the alcohol ratio during production, as higher ratios tend to increase the

density of the biodiesel by promoting ester formation and ensuring complete triglyceride conversion. Finally,

since the locally produced biodiesel met European standards for pH, color, density, acid value, and water

content, it is recommended to continue using this production process along with the chosen waste cooking oil

to alcohol ratios. This approach has proven effective in producing high-quality biodiesel that performs well in

diesel engines, offering stability and minimizing potential engine damage. Regular adherence to these

standards and ratios will help maintain the effectiveness of the biodiesel production process and the quality of

the final product.

ACKNOWLEDGEMENTS

The researchers extend their sincere appreciation to Notre Dame of Dadiangas University and College of Arts

and Sciences for their invaluable support and assistance throughout the conduct of this study. They also

express their heartfelt gratitude to their families for their steadfast encouragement, and to God for His enduring

guidance throughout the entire research process.

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