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. 2025 May 22;10(21):21280–21291. doi: 10.1021/acsomega.4c10777

Techno-Environmental Assessment of Biodiesel Production from Acid Oil via One-Step and Two-Step Esterification

Ni Ni Myint †, Kongpetch Jaruensri †, Netipon Sakulshah †, Anusith Thanapimmetha †, Maythee Saisriyoot †, Nutchapon Chiarasumran †, Hui-Min David Wang ‡, Penjit Srinophakun †,*
PMCID: PMC12138652  PMID: 40487993

Abstract

This study aims to evaluate the techno-environmental impacts of biodiesel production from acid oil using a one-step acid catalyst and a two-step immobilized enzyme and acid catalyst esterification. Acid oil was obtained by purifying crude glycerol with pure glycerol and salt as by-products. The experiment was performed to optimize the conversion of the acid oil to biodiesel. The one-step process involves 4% sulfuric acid, a methanol-to-oil molar ratio of 26:1, and a reaction time of 3.4 h. The two-step esterification comprised two stages: the first stage employed immobilized lipase on chitosan. The optimal conditions of the first stage were a 5:1 methanol-to-oil molar ratio, 37 wt % enzyme loading, and a reaction time of 17 h. The second stage of the two-step process involved 3% sulfuric acid with a methanol-to-oil molar ratio of 15:1 for 4 h. Then, a techno-environmental assessment was performed to compare the midpoint impacts of the one-step and two-step esterification. The study generated 7 cases to investigate the significant environmental effects of glycerol (case 1), particularly on global warming potential. It examined the impact of different electricity sources, natural gas (cases 2, 3, and 6) and hydropower (cases 4, 5, and 7), on biodiesel production. Comparing SC-1 (one-step esterification with an acid catalyst) and SC-2 (two-step esterification with an enzyme and acid catalyst), the study found that SC-2 was technically feasible due to lower energy consumption, less chemical use, and less wastewater, but SC-1 was more environmentally friendly. Due to enzyme preparation, SC-2 has had a higher impact on terrestrial ecotoxicity, human noncarcinogenic toxicity, global warming, and land use. The study suggested that biodiesel factories should purify crude glycerol to minimize its environmental effects and enhance biodiesel production’s ecological benefits and sustainability.

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1. Introduction

Fatty acids, alkyl esters, or biodiesel can be produced by esterifying vegetable oils with alcohol (mostly methanol but often ethanol). It is mixed with diesel fuel made from crude oil to lower the amount of CO2, SOx, and particle matter released during combustion, offering a sustainable alternative to fossil-based fuels. The urgency to mitigate the depletion of fossil resources and curb environmental impacts, including global warming, has made biodiesel an increasingly important alternative.

Biodiesel production involves transesterifying triglycerides or esterifying fatty acids with alcohol. In esterification, free fatty acids (FFAs) are converted into alkyl esters using alcohol, catalyzed by acids or lipase enzyme, resulting in biodiesel and water, as expressed in Scheme . An acid catalyst is preferable, especially for high-acid-value raw materials, to avert saponification. Methanol is primarily favored for biodiesel production due to its straightforward extraction from the final product. It boasts several advantages over other alcohols, including higher conversion rates with waste cooking oils and lower viscosity than alternative alcohol-based biofuels.

Fatty acid+Alcohol⇌Ester(biodiesel)+Water

1. Esterification Reaction Mechanism.

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Lipase, a biological catalyst, is an acid alternative that has not yet been implemented to produce biodiesel on an industrial scale. However, the results of laboratory investigations reveal that it may offer some advantages over the chemical catalyst, especially in terms of a more straightforward purification stage and associated energy savings. Immobilized enzymes provide several benefits, including cost reduction, reusability, easy separation from products, and the ability to work in nonaqueous environments. Key to this process is the choice of various material supports, such as alginate, agarose, chitosan, polyacrylamide, and silica, to immobilize the enzyme and allow it to be reused. Different immobilization methods exist, including adsorption, covalent attachment, encapsulation, and cross-linking. This study used adsorption on chitosan for simple environmental benefits.

A life cycle assessment (LCA) is a systematic analysis of the environmental impacts of a product or process throughout its entire life cycle, from raw material extraction to production, use, and disposal. Various stages must be considered when conducting an LCA for biodiesel production from waste oil, such as acid oil from a biofuel plant and used cooking oil. Different research studies indicate that biodiesel holds promise as an alternative fuel due to its potential for significant cost savings, positive impact on waste disposal, environmental benefits, and alignment with value-added objectives. − According to many LCA studies, bioproducts are environmentally superior to fossil products in some life cycle impact categories, while the picture is often opposite in others. Bioproducts are a highly diverse group of products, and their environmental profile relative to their fossil counterparts is case-specific and, to a high degree, depends on the feedstock used. Chemical effects on environmental impact illustrate the importance of conducting case-specific LCAs for determining bioproducts’ environmental profile relative to fossil ones. It also emphasizes the importance of all relevant impact categories to avoid problem shifting through life cycle impact assessment (LCIA). , Therefore, this techno-environmental assessment of biodiesel production from acid oil involves evaluating technologies and the ecological impacts associated with the entire life cycle of biodiesel.

Crude glycerol has increased from the biodiesel process due to the higher demand for biodiesel consumption. Therefore, the challenges of converting crude glycerol to high-value products were fascinating. One promising conversion is the production of biodiesel from acid oil. As acid oil is wasted from glycerol acidulation (purifying crude glycerol), it contains high free fatty acids and methyl ester. This study aimed to clarify the technology of converting acid oil to biodiesel with the same final biodiesel quality between conventional acid-catalyzed (one-step) and milder conditions of the immobilized enzyme (two-step). At first, an experimental investigation of those two methods was performed to determine the optimum conditions. Then, the environmental impact of those two methods for the production of biodiesel from acid oil was compared. Finally, the more environmentally friendly method was selected, and further suggestions for sustainable biodiesel production from acid oil were proposed.

This study used 2 processes: one-step acid esterification (scenario 1, SC-1) and two-step enzyme and acid esterification (scenario 2, SC-2). The chemicals used in SC-1 and SC-2 were obtained from the experiment. Minitab software optimized the conditions in the one-step, and the Box–Behnken experimental design was used for the two-step esterification. After that, the 1000 kg biodiesel production process was designed in ASPEN, and mass balance calculation was performed. In addition, the life cycle assessment was carried out to determine the main environmental effects of biodiesel production from acid oil. Finally, 7 case assumptions were proposed to identify the critical ecological effect that led to the sustainability of the biodiesel process.

2. Experimental Section

2.1. Raw Materials and Chemicals

The acid oil used in this experiment was sourced from a local commercial biodiesel company. Crude glycerol (glycerol1 in Scheme ) is generated, typically exceeding 10% (w/w), which varies depending on the specific design of the biodiesel production process. − To begin with, the biodiesel by-product in this study, crude glycerol, underwent purification via an acidulation process involving the addition of sulfuric acid, as shown in Scheme . After acidulation, purer glycerol (glycerol2 in Scheme ), acid oil, and salt (Na2So4) are obtained. − As a result, acid oil is counted as waste oil from glycerol purification.

Triglyceride+Alcohol⇌Ester(biodiesel)+Glycerol1
Glycerol1+Soap⇌Glycerol2+Acid oil+Salt

2. Glycerol1 Is Produced from the Transesterification of the Biodiesel Process, and Glycerol2 Is Obtained from the Acidulation Reaction.

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Chemicals used in the one-step esterification, including methanol (99.8%), sulfuric acid (98%), solid potassium hydroxide, toluene (99.9%), isopropyl alcohol (100%), methyl heptadecanoate, and heptane (99%), were procured from Zen Point, ACI Labscan, Fluka (Germany), and Merck (Germany), all of analytical grade. The Lipase (Eversa Transform 2.0) was sourced from the local biodiesel company for the two-step esterification. Food-grade chitosan powder was acquired from Bona Fides. Acetic acid was procured from Qrec Company, 4-nitrophenyl palmitate, and bovine serum albumin were purchased from Sigma. 4-Nitrophenol and Coomassie Brilliant Blue were sourced from TCI. Sodium hydroxide, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate were purchased from Kemaus. Ethanol and Triton X-100 were obtained from Merck.

2.2. One-Step Esterification Process

Before esterification, the water was removed from the acid oil to prevent any potential reverse reaction. , The acid oil was then subjected to esterification using a 4% H2SO4 catalyst under consistent 60 °C and 500 rpm stirring speed. Variations in reaction time (ranging from 1 to 6 h) and the MeOH-to-oil molar ratio (20:1 to 30:1) were introduced to optimize the desired outcome. After the reaction, the crude biodiesel was washed with distilled water (40 °C). Subsequently, biodiesel was purified through dehydration. Analytical methods were employed to determine the biodiesel’s %FFA and %FAME. After acquiring the experimental data, the Minitab program optimized esterification conditions to achieve a %FAME greater than 96.5% while minimizing %FFA. Figure shows the process flowchart of one-step biodiesel production from acid oil.

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Flowchart of the one-step esterification process from acid oil.

2.3. Two-Step Esterification Process

The two-step esterification requires a lipase enzyme and an acid catalyst at the first and second stages, respectively. Immobilized lipase (on chitosan beads) was used in this study, and the methods were the same as in a previous study. The first stage (lipase catalyst) reaction was performed under the optimum conditions gained from Box–Behnken statistical analysis. The target of the final FFA at the first stage was 3%. Then, the mixture was continued to the second stage (acid catalyst), and optimum conditions were investigated, as detailed in the next section. After the reaction, the same biodiesel purification and analysis procedure was performed as one-step esterification. Figure shows the biodiesel production process of a two-step esterification from acid oil.

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Flowchart of the two-step esterification process from acid oil.

2.4. Optimization of Lipase Esterification Using the Box–Behnken Design (First Stage of the Two-Step Esterification)

Table shows 3 parameters and 3 levels used in the Box–Behnken statistical analysis. After parameters and levels were input into the Minitab program, the experimental conditions and runs were designed, as shown in Table . In Table , the software of each run attained the predicted values of the FFAs. The experimental values of FFA were the result of the same run conditions. Finally, the program suggested the optimum conditions (methanol-to-oil ratio of 4.79:1; catalyst loading of 36.82%; reaction time of 16.78 h) as shown in Figure and an equation for the final FFA of 3%, in eq . Please note that 3%FFA was the target for the initial FFA in the second stage of acid esterification conditions. Finally, the optimum conditions predicted by the program (Figure ) were verified by experiment, and the results are shown in Table . With an error of 2.93%, the program’s proposed eq is acceptable and can predict %FFA under the same boundary conditions. In the first stage, the optimum regression values were rounded to the methanol-to-oil ratio of 5:1, a catalyst loading of 37 wt %, and a reaction time of 17 h (Table ).

1. Three Parameters and Three Levels Used in the Box–Behnken Analysis.

    levels
parameters symbol –1 0 1
methanol-to-oil molar ratio X 1 1 3.5 6
catalyst loading (wt %) X 2 15 45 75
reaction time (hour) X 3 6 12 18
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2. Box–Behnken Design of 15 Experiments with Results of Predicted and Experimental FFA.

  parameters
%FFA
run nos X 1 X 2 X 3 predicted value experimental value
1 1 (−1) 15 (−1) 12 (0) 6.43 5.27
2 6 (1) 15 (−1) 12 (0) 5.84 5.50
3 1 (−1) 75 (1) 12 (0) 12.84 13.00
4 6 (1) 75 (1) 12 (0) 3.48 4.65
5 1 (−1) 45 (0) 6 (−1) 9.31 9.21
6 6 (1) 45 (0) 6 (−1) 4.53 3.61
7 1 (−1) 45 (0) 18 (1) 8.52 9.45
8 6 (1) 45 (0) 18 (1) 3.34 3.44
9 3.5 (0) 15 (−1) 6 (−1) 6.42 7.69
10 3.5 (0) 75 (1) 6 (−1) 6.35 6.11
11 3.5 (0) 15 (−1) 18 (1) 3.34 3.59
12 3.5 (0) 75 (1) 18 (1) 7.46 6.25
13 3.5 (0) 45 (0) 12 (0) 4.03 4.03
14 3.5 (0) 45 (0) 12 (0) 4.03 4.05
15 3.5 (0) 45 (0) 12 (0) 4.03 4.03
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Optimization plot from the Box–Behnken response surface method targeting at 3%FFA.

3. Optimal Conditions and Percentage of the Final FFA after the First Step of Lipase Esterification.

parameters symbol predicted value optimum value
methanol-to-oil molar ratio X 1 4.79 5.00
catalyst loading (wt%) X 2 36.82 37.00
reaction time (hour) X 3 16.78 17.00
free fatty acid (%) FFA 3.067 3.157
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Y=13.99−1.641X1−0.0626X2−0.700X3+0.2917X12+0.001434X22+0.01581X32−0.02927X1X2−0.0066X1X3+0.00581X2X3 1

where Y is %FFA, X 1 is the methanol-to-oil molar ratio, X 2 is the catalyst loading, and X 3 is the reaction time.

2.5. Optimum Conditions of Acid Esterification (Second Stage of the Two-Step Esterification)

For the second stage, the investigation was performed by varying the parameters, the molar ratio of 1:6 to 1:18, the catalyst concentration of 1 to 10%, and the reaction time of 1.5 to 4 h, and the results are shown in Figure . The optimum conditions obtained from Figure a–c were a methanol-to-oil ratio of 15:1, 3% H2SO4, and 4 h reaction time, which gave the final FFA, FAME, and viscosity of biodiesel of the two-step esterification of 0.49, 97.33%, and 4.53 cSt, respectively. In Figure d, comparing the FAME of the raw acid oil, biodiesel after the first-stage lipase, and biodiesel after two-stage acid esterification, the FAME of biodiesel increased from 83.13 to 94.60 and 97.33%. Reaching the standard level of higher than 96.5% FAME using only lipase esterification might be possible, but it must take a longer reaction time. Only the first stage using the lipase catalyst took 17 h of the reaction. Therefore, using an acid catalyst in the second stage reduced the reaction time to 4 h (Table ).

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Effect of (a) methanol-to-oil molar ratio at 3% H2SO4 for 1.5 h, (b) H2SO4 concentration at 15:1 methanol-to-oil molar ratio for 1.5 h, (c) reaction time at 15:1 methanol-to-oil molar ratio and 3% H2SO4, and (d) %FAME of raw acid oil and biodiesel at each stage of a two-step reaction. All experiments were operated at 60 °C and 500 rpm.

4. Reaction Conditions of Scenarios 1 and 2.

scenario esterification conditions
SC-1 methanol: oil = 26:1
catalyst = 4% H2SO4
reaction time = 3.4 h
SC-2 first stage:
methanol: oil = 5:1
catalyst = 37% (enzyme loading)
reaction time = 17 h
second stage:
methanol: oil = 15:1
catalyst = 3% H2SO4
reaction time = 4 h
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2.6. Process Simulation

The ASPEN simulation calculated mass balances through interconnected unit operations like acidulation and esterification, which optimized resource utilization. Engineers iteratively adjusted parameters to enhance %FAME efficiency, which was also performed in the response surface experimental design. Although the biodiesel production target was the same, 1000 kg, the masses for input glycerol and acid oil of one-step and two-step esterification were different. Table shows the crude glycerol, acid oil, biodiesel output, and conditions used in this study. In the table, one-step and two-step esterification refer to scenarios 1 (SC-1) and 2 (SC-2).

2.7. Life Cycle Assessment

A life cycle assessment (LCA) was used to compare two biodiesel production processes from acid oil with the aim of finding sustainable and environmentally responsible biofuel solutions. In LCA, the goal and scope include establishing a reference point and a functional unit. This unit is used to quantify all inputs and outputs of the system under study, ensuring consistency and comparability across all processes being analyzed. It serves as the basis for scaling the environmental impacts of the entire life cycle to a standard, meaningful measure. The functional unit for this research was 1,000 kg of biodiesel production. − First, the mass balances obtained from the ASPEN simulator version 12 were used as the data inventory. , Then, the environmental impacts were assessed via SimaPro software version 9.1.1 using Ecoinvent 3.0 as a database. ReCiPe 2016 was selected as the life cycle impact (LCIA) assessment to convert inventory data into more minor environmental impact indicators. This method helps quantify the potential effects of different processes on various environmental categories, providing two levels of 18 midpoint indicators and 3 end-point indicators to more comprehensively assess environmental impacts. This inclusive evaluation encompasses the entire biodiesel production life cycle, from raw material acquisition to end-of-life disposal, meticulously considering variables such as greenhouse gas emissions, energy utilization, and resource depletion by focusing only on midpoint indicators. Through a systematic comparison of the environmental attributes associated with the two esterification processes, the study attempts to pinpoint the most sustainable approach for biodiesel production from acid oil, facilitating informed decision-making toward environmental stewardship and resource conservation. Therefore, 7 cases were set for both scenarios to investigate the proper technology and primary source of environmental issues for sustainability.

  • 1.

    The inventory of crude glycerol input was considered to be exclusive.

  • 2.

    Inventories were assessed without crude glycerol input, but all chemicals were considered. Pure glycerol and salts were counted as by-products, and natural gas was a source of electricity.

  • 3.

    It is the same as case 2, but pure glycerol and salts were not considered.

  • 4.

    Like case 2, hydropower was used for electrical generation instead of natural gas.

  • 5.

    Same as case 3, but used electricity from hydropower.

  • 6.

    All chemicals included crude glycerol, pure glycerol (by-product), and salts (by-product); natural gas was the energy source.

  • 7.

    Same as case 6, but with hydropower.

Case 1 was the reference when the environmental impacts were assessed using only crude glycerol. In this study, the ecological effects of glycerol were retrieved from the Ecoinvent 3.0 database of crude glycerol from palm biodiesel. In cases 2 and 3, crude glycerol was purified through acidulation to get pure glycerol and salt. The difference between cases 2 and 3 was that pure glycerol and salt were considered by-products (case 2) or neglected (case 3), and natural gas was used as an energy source in both cases. Cases 4 and 5 were similar to cases 2 and 3 regarding chemical considerations, but hydropower energy sources were considered. Finally, all chemicals (crude glycerol and by-products) were included (in cases 6 and 7), but energy sources were changed from natural gas (case 6) to hydropower (case 7). In all cases, scenarios 1 and 2 were accessed and compared.

3. Results and Discussion

3.1. Mass Balances of One-Step and Two-Step Esterification

Table shows the mass balances of one-step (scenario 1, SC-1) and two-step esterification (scenario 2, SC-2). As mentioned, different glycerol inputs of each step were needed to produce the same 1000 kg of biodiesel from acid oil (functional unit). Higher methanol and more wastewater were in SC-1 due to higher methanol-to-oil ratio reaction conditions and more water needed for biodiesel purification. Please note that water was also produced during esterification (eq ) and treated as wastewater (Table ). In SC-2, water was added at the first stage to make the enzyme work more efficiently. In both SC-1 and SC-2, water (biodiesel moisture) was removed according to the biodiesel commercial specification in the purification step. After the mass balance was established according to the optimum results of the experiment, the processes of both SC-1 and SC-2 were designed as shown in Figures and , respectively.

5. Mass Balance of One-Step and Two-Step Esterification.

biodiesel production input (kg) output (kg)
one-step acid esterification    
1. acidulation    
1.1 crude glycerol 7901.4  
1.2 sulfuric acid 237  
1.3 glycerol (78.8% of crude glycerol)   6226.3
1.4 acid oil (13% of crude glycerol)   1013.7
1.5 sodium sulfate salt (8.2% of crude glycerol)   884.9
2. pretreatment    
2.1 water as moisture   13.5
3. esterification    
3.1 acid oil 1013.7  
3.2 methanol 772.2  
3.3 sulfuric acid 13.9  
3.4 biodiesel   1000
3.5 wastewater   45.5
4. purification    
4.1 water 2720  
4.2 excess methanol   687.6
4.3 water as moisture   55.2
4.4 wastewater   2731.5
two-step lipase (first stage) and acid (second stage) esterification    
1. acidulation    
1.1 crude glycerol 8010  
1.2 sulfuric acid 240.3  
1.3 sulfuric acid   6311.9
1.4 glycerol (78.8% of crude glycerol)   1041.3
1.5 acid oil (13% of crude glycerol)   897.1
1.6 sodium sulfate salt (8.2% of crude glycerol)    
2. first stage lipase esterification    
2.1 acid oil 1041.3  
2.2 lipase 9.4  
2.3 methanol 149.1  
2.4 water 104.1  
2.5 biodiesel   1013.9
2.6 excess methanol   64.7
2.7 wastewater   225.3
3. second stage acid esterification    
3.1 biodiesel 1013.9 1000
3.2 methanol 382.5  
3.3 sulfuric acid 10.4  
3.4 wastewater   46.1
4. purification 2110.3  
4.1 water   43.1
4.2 water as moisture   298.2
4.3 excess methanol   2129.7
4.4 wastewater    
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Simulation model for the one-step esterification (scenario 1).

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Simulation model for the one-step esterification reaction (scenario 2).

3.2. Comparative LCA on Two Esterification Processes

Figures – illustrate the process’s comprehensive impact, highlight the process’s broader ecological footprint, and pinpoint the 10 most environmental impact categories of this study. Both one-step (SC-1, in blue) and two-step esterification (SC-2, in pink) showed the same impact trends. However, SC-2 showed slightly higher impacts of global warming due to higher crude glycerol used (8010 kg) compared to SC-1 (7901.4 kg) in the process. Case 1 of both scenarios showed crude glycerol’s highest impacts, particularly on global warming and land use (Figure ). Crude glycerol was a by-product of biodiesel from palm oil and methanol. Therefore, crude glycerol’s environmental impact involves palm plantation, palm oil extraction, palm oil purification, biodiesel production, etc. Our board’s ecological footprint showed that glycerol was crucial for sustainable process development in this study. Thus, using crude glycerol was an excellent option to lower the environmental impact of biodiesel production from palm oil.

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Global warming potential and the land use effects on 7 cases of both scenarios.

10.

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Marine eutrophication, ozone formation, and the delicate particulate matter affect 7 cases of both scenarios.

As mentioned, this study proposed crude glycerol utilization by separating crude glycerol into acid oil, pure glycerol, and salt through an acidulation process. Two assumptions were considered here: pure glycerol and salt as by-products (cases 2 and 4) or neglected (cases 3 and 5). As shown in Figures and , considering pure glycerol and salt as by-products (cases 2 and 4) had positive environmental impacts on 10 categories. On the other hand, ignoring pure glycerol and salt (cases 3 and 5) had minor adverse effects. This study supported the current situation of commercial biodiesel factories in purifying their crude glycerol and selling pure glycerol and salt to other factories or customers. Pure glycerol can be distilled for a higher purity of over 99% for food and cosmetic products. Sodium sulfate salt can be sold as fertilizer to the farmers nearby.

The sources of energy, natural gas (cases 2 and 3) and hydropower (cases 4 and 5), were also compared. The effect of energy sources was evident in fossil resource scarcity (Figure ) over the other 9 categories (Figures , , and ). Hydropower had less impact than natural gas (comparing cases 2 and 4; cases 3 and 5). From this study, natural gas energy has broader ecological implications. Some researchers proposed that energy sources could lead to environmental taxation. − Lower ecological footprints should be minimized to avoid adverse effects, and stringent environmental regulations should be implemented to change to renewable energy sources. However, for those 4 cases, more implications for fossil resource scarcity are found in SC-1 (blue) than in SC-2 (pink). Although the reaction time of acid esterification of both steps is almost the same (Table , ignoring 17 h of enzyme step as no mixing occurred), higher volume in SC-1 (methanol-to-oil ratio of 26.1:1) consumed higher energy input than SC-2 (methanol-to-oil ratio of 5:1 and 15:1 in first stage and second stage). In addition, less steam input was needed in SC-2 due to mild lipase esterification conditions at room temperature. Therefore, less impact was found in SC-2 than in SC-1. Nevertheless, cases 3 and 5 were high in fossil resource scarcity. Natural gas is a fossil fuel and is rapidly depleting. Hydropower is an alternative energy source. Therefore, because of hydropower, case 5 had a lower impact than case 3. Alternative energy sources are essential to overcome the finite resources of fossil fuels.

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Fossil resource scarcity, marine ecotoxicity, and human carcinogenic toxicity effects on 7 cases of both scenarios.

9.

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Mineral resource scarcity and terrestrial acidification affect 7 cases of both scenarios.

The last discussion was on cases 6 and 7, where all chemicals, crude glycerol, pure glycerol (by-product), and salt (by-product), were considered. Natural gas and hydropower were energy sources in cases 6 and 7, respectively. Global warming and land use were higher in fossil resource scarcity, marine ecotoxicity, human carcinogenic toxicity, mineral resource scarcity and terrestrial acidification, marine eutrophication, ozone formation, and delicate particulate matter. Except for the effect of fossil resources scarcity, the ecological impact on the other 9 categories was much the same between SC-1 and SC-2. The higher fossil resource scarcity effect of SC-1 than that of SC-2 is due to higher energy consumption over different volumes of chemicals, as discussed earlier. If we compare cases 6 (natural gas) and 7 (hydropower), case 7 has less impact than case 6 in both scenarios. Overall, the analysis demonstrates that the effects of global warming and land use (Figure ) are higher than the other 8 vital environmental categories.

The 18 midpoint impact category (Table ) compares cases 4 and 7 of both scenarios. The difference between cases 4 and 7 was glycerol; others were the same (chemicals, by-products, and hydropower). Case 4 (excluding crude glycerol) was generally good for the environment, as it negatively impacted all 10 categories. As seen in Table of case 4, the global warming potential in SC-1 (one-step esterification) was −14,755.9 kg CO2 eq and higher than in SC-2 (two-step esterification, −15,002.5 kg CO2 equiv) due to higher energy consumption resulting from conditions in Table . However, with the glycerol inventory of case 7, the impact of the global warming potential turns the opposite. SC-2 had 10 kg CO2 eq higher than SC-1. This little impact came from the higher crude glycerol used in scenario 2. The results confirmed the significant effects of crude glycerol and brought it to utilization. Purifying crude glycerol and using the acid oil for biodiesel production were environmentally friendly. Otherwise, the environmental impact on global warming was extraordinarily high for unutilized crude glycerol (case 1 in Figure ).

6. Techno-Environmental Impacts of Biodiesel Production Using One-Step and Two-Step Esterification .

  scenario 1
 scenario 2
  one-step esterification
 two-step esterification
item case 4 case 7 case 4 case 7
1. chemical input        
1.1 glycerol (kg)   7901.4   8010.0
1.2 methanol (kg) 772.2 772.2 531.6 531.6
1.3 sulfuric acid (kg) 250.9 250.9 250.7 250.7
1.4 water (kg) 2720.0 2720.0 2214.4 2214.4
1.5 enzyme (kg)     9.4 9.4
2. energy input (kWh) 217.62 217.62 170.47 170.47
3. midpoint impact categories        
3.1 global warming potential (kg CO2 eq) (14,755.9) 3855.8 (15,002.5) 3865.0
3.2 stratospheric ozone depletion (kg CFC11 equiv) 0.0 0.0 0.0 0.0
3.3 ionizing radiation (kBq Co-60 equiv) (103.3) 3.1 (101.6) 6.2
3.4 ozone formation, human health (kg NOx eq) (18.5) 3.9 (18.7) 4.0
3.5 fine particulate matter formation (kg PM2.5 equiv) (16.2) 3.0 (16.3) 3.1
3.6 ozone formation, terrestrial ecosystems (kg NOx eq) (20.5) 4.5 (20.7) 4.6
3.7 terrestrial acidification (kg SO2 equiv) (40.2) 7.6 (40.3) 8.2
3.8 freshwater eutrophication (kg P eq) (1.2) 0.1 (1.2) 0.1
3.9 marine eutrophication (kg N eq) (21.2) 5.7 (21.3) 5.9
3.10 terrestrial ecotoxicity (kg 1,4-DCB) (20,493.3) 176.1 (20,377.9) 575.6
3.11 freshwater ecotoxicity (kg 1,4-DCB) (235.7) 1.9 (239.5) 1.4
3.12 marine ecotoxicity (kg 1,4-DCB) (287.8) (7.5) (293.0) (8.8)
3.13 human carcinogenic toxicity (kg 1,4-DCB) (154.2) 15.1 (155.2) 16.3
3.14 human noncarcinogenic toxicity (kg 1,4-DCB) (2279.5) (574.1) (2,203.8) (474.9)
3.15 land use (m2a crop eq) (9158.3) 2407.1 (9216.5) 2507.9
3.16 mineral resource scarcity (kg Cu eq) (48.4) 2.4 (49.0) 2.5
3.17 fossil resource scarcity (kg oil eq) (548.4) 701.0 (717.0) 549.6
3.18 water consumption (m3) (228.3) 62.4 (223.1) 71.7
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a

Note: The values in brackets mean negative.

Interestingly, 3 environmental categories of terrestrial ecotoxicity, human noncarcinogenic toxicity, and land use (negative values in Table ) of SC-1 had a better environmental impact than SC-2. Please note that enzyme esterification was used in SC-2, and only chemical esterification was used in SC-1. As a result, more significant impacts of SC-2 came from enzyme esterification. Enzyme production emitted terrestrial ecotoxicity, human noncarcinogenic toxicity, land use, and global warming of 637, 220, 69, and 119 kg of CO2 eq, respectively. Enzyme production did not affect global warming the most because of mild room-temperature conditions. Minerals used in fermentation broth generated emissions and dominated terrestrial ecotoxicity. These minerals affected human beings, which was related to noncancer toxicity. The enzyme production also affected the land use category due to the high amount of water used compared to chemical esterification.

This study suggested that using crude glycerol as the source of the raw material of acid oil for biodiesel production and selling pure glycerol and salt as by-products (case 7) revealed significant environmental benefits. Biodiesel production using SC-1 showed better ecological effects. SC-2 was high in terrestrial ecotoxicity due to the enzyme production process, which could be improved by developing new enzyme production techniques, for example, using fewer minerals or mineral substitutions for a more sustainable process.

4. Conclusions

In conclusion, this research marks a significant investigation of biodiesel production, showcasing a controversial approach to biodiesel production from acid oil. Acid oil was obtained from crude glycerol acidulation, with pure glycerol and salt as by-products. The experimental results showed that biodiesel could be produced in one-step esterification (SC-1) using an acid catalyst or two-step esterification (SC-2) using lipase at the first stage and acid in the second stage from acid oil. Milder conditions of lipase catalysts are of interest compared to conventional sulfuric acid. − Technically, SC-2 used fewer chemicals and consumed less water and energy. The study scaled production to 1000 kg for environmental concerns and set it as a functional unit for LCA analysis. The target of the environmental impact assessment of SC-1 and SC-2 was investigated and compared. −

The comprehensive analysis included 18 life cycle assessment inventories (LCAI) to assess the environmental impacts across various midpoint categories, but only 10 categories were significant, particularly global warming (case 1). Pure glycerol and salt as by-products (cases 2, 4, 6, and 7) positively impacted the environment, considering only crude glycerol (case 1). The choice of energy sources, such as natural gas (cases 2, 4, and 6) and hydropower (cases 3, 5, and 7), showed minimal differences in global warming potential but had more pronounced effects on land use and fossil resource scarcity. − Notably, the study uncovered unexpected adverse effects across 10 midpoint categories, raising concerns about the environmental viability of crude glycerol. If crude glycerol and by-products were neglected (case 4 in Table ), SC-2 had higher positive impacts on terrestrial ecotoxicity and global warming. However, if crude glycerol and by-products had been included, SC-1 would have been preferable due to the lower overall emission (case 7, Table ). The high global warming impact came from the large amount of crude glycerol used in acidulation (only 13% was acid oil). Finally, the exciting suggestion for both scenarios would be to use a lower methanol-to-oil molar ratio and a shorter reaction time.

Supplementary Material

ao4c10777_si_001.pdf (243.9KB, pdf)

Acknowledgments

The authors express their gratitude to the NCHU-KU Collaboration Project, the KU-Biodiesel Project, and the Faculty of Engineering at Kasetsart University for their financial support and provision of facilities. Thanks to Kittitat Sirivechphongkul and Taratron Suwaleerat for their invaluable guidance in initiating the LCA investigation and formatting.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.4c10777.

  • The impact assessment results of 18 impact categories for the seven cases of 2 scenarios (PDF)

N.N.M.: data curation, formal analysis, investigation, methodology, validation, and writing the original draft and reviewing. K.J.: data curation, investigation, and methodology. N.S.: software and visualization. A.T. and M.S.: data curation, formal analysis, validation, and visualization. N.C.: conceptualization, methodology, formal analysis, software, validation, and visualization. H.-M.D.W.: conceptualization, formal analysis, and funding acquisition. P.S.: conceptualization, methodology, funding acquisition, project administration, supervision, writing, reviewing, and editing.

The authors declare no competing financial interest.

References

  1. Rial R. C.. Biofuels versus climate change: Exploring potentials and challenges in the energy transition. Renewable Sustainable Energy Rev. 2024;196:114369. doi: 10.1016/j.rser.2024.114369. [DOI] [Google Scholar]
  2. Alves, C. T. ; Hocevar, L. S. ; Guarieiro, L. L. N. . Biodiesel Technologies: Recent Advances, New Perspectives, and Applications. Biodiesel Plants-Fueling the Sustainable Outlooks: Fueling the Sustainable Outlooks 2025.
  3. Zhang B., Gao M., Tang W., Wang X., Wu C., Wang Q., Cheung S. M., Chen X.. Esterification efficiency improvement of carbon-based solid acid catalysts induced by biomass pretreatments: Intrinsic mechanism. Energy. 2023;263(Part B):125606. doi: 10.1016/j.energy.2022.125606. [DOI] [Google Scholar]
  4. John M., Abdullah M. O., Hua T. Y., Nolasco-Hipólito C.. Techno-economical and energy analysis of sunflower oil biodiesel synthesis assisted with waste ginger leaves derived catalysts. Renew. Energy. 2021;168:815–828. doi: 10.1016/j.renene.2020.12.100. [DOI] [Google Scholar]
  5. Maheshwari P., Haider M. B., Yusuf M., Klemeš J. J., Bokhari A., Beg M., Al-Othman A., Kumar R., Jaiswal A. K.. A review on latest trends in cleaner biodiesel production: Role of feedstock, production methods, and catalysts. J. Clean. Prod. 2022;355:131588. doi: 10.1016/j.jclepro.2022.131588. [DOI] [Google Scholar]
  6. Mandari V., Devarai S. K.. Biodiesel production using homogeneous, heterogeneous, and enzyme catalysts via transesterification and esterification reactions: A critical review. Bioenerg. Res. 2022;15:935–961. doi: 10.1007/s12155-021-10333-w. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Verma M. L., Kumar S., Das A., Randhawa J. S., Chamundeeswari M.. Chitin and chitosan-based support materials for enzyme immobilization and biotechnological applications. Environ. Chem. Lett. 2020;18:315–323. doi: 10.1007/s10311-019-00942-5. [DOI] [Google Scholar]
  8. Hosseinzadeh-Bandbafha H., Nizami A. S., Kalogirou S. A., Gupta V. K., Park Y. K., Fallahi A., Sulaiman A., Ranjbari M., Rahnama H., Aghbashlo M., Peng W.. Environmental life cycle assessment of biodiesel production from waste cooking oil: A systematic review. Renewable Sustainable Energy Rev. 2022;161:112411. doi: 10.1016/j.rser.2022.112411. [DOI] [Google Scholar]
  9. Hauschild, M. Z. Introduction to LCA Methodology. In Life Cycle Assessment; Hauschild, M. ; Rosenbaum, R. ; Olsen, S. , Eds.; Springer: Cham, 2018. [Google Scholar]
  10. Musharavati F., Sajid K., Anwer I., Nizami A. S., Javed M. H., Ahmad A., Naqvi M.. Advancing biodiesel production system from mixed vegetable oil waste: a life cycle assessment of environmental and economic outcomes. Sustainability. 2023;15(24):16550. doi: 10.3390/su152416550. [DOI] [Google Scholar]
  11. Ngo, H. H. ; Nguyen, T. K. L. ; Guo, W. ; Zhang, J. ; Liang, S. ; Ni, B. . Life-cycle assessment on sequestration of greenhouse gases for the production of biofuels and biomaterials. In Biomass, Biofuels, Biochemicals; Elsevier, 2022; pp 179–202 10.1016/B978-0-12-823500-3.00008-X. [DOI] [Google Scholar]
  12. Liu Y., Zhong B., Lawal A.. Recovery and utilization of crude glycerol, a biodiesel byproduct. RSC Adv. 2022;12(43):27997–28008. doi: 10.1039/D2RA05090K. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Calderona M. J. P., Dumancas G. G., Gutierrezd C. S., Lubgubane A. A., Alguno A. C., Malaluan R. M., Lubguban A. A.. Producing polyglycerol polyester polyol for thermoplastic polyurethane application: A novel valorization of glycerol, a byproduct of biodiesel production. Heliyon. 2023;9(9):e19491. doi: 10.1016/j.heliyon.2023.e19491. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Salehi A., Karbassi A., Ghobadian B., Ghasemi A., Doustgani A.. Simulation process of biodiesel production plant. Environ. Prog. Sustain. 2019;38(6):e13264. doi: 10.1002/ep.13264. [DOI] [Google Scholar]
  15. Myint N. N., Thanapimmetha A., Saisriyoot M., Chiarasumran N., Srinophakun T. R., Gozan M., Srinophakun P.. Process simulation and economic feasibility of biodiesel production from acid oil, a byproduct of glycerol acidulation. Agric. Nat. Resour. 2023;57(1):153–162. doi: 10.34044/j.anres.2023.57.1.16. [DOI] [Google Scholar]
  16. He Q. S., McNutt J., Yang J.. Utilization of the residual glycerol from biodiesel production for renewable energy generation. Renew. Sustain. Energy Rev. 2017;71:63–76. doi: 10.1016/j.rser.2016.12.110. [DOI] [Google Scholar]
  17. Chol C. G., Dhabhai R., Dalai A. K., Reaney M.. Purification of crude glycerol derived from biodiesel production process: Experimental studies and techno-economic analyses. Fuel Process. Technol. 2018;178:78–87. doi: 10.1016/j.fuproc.2018.05.023. [DOI] [Google Scholar]
  18. Mena-Cervantes V. Y., Hernández-Altamirano R., Tiscareño-Ferrer A.. Development of a green one-step neutralization process for valorization of crude glycerol obtained from biodiesel. Environ. Sci. Pollut. Res. 2020;27:28500–28509. doi: 10.1007/s11356-019-07287-0. [DOI] [PubMed] [Google Scholar]
  19. Thepchan, K. Statistical Model and Operation Cost Estimation of Esterification of 3–90% Free Fatty Acid Palm Oil. M.E. Thesis, Kasetsart University: Thailand, 2015. [Google Scholar]
  20. Jaruensri, K. ; Srinophakun, P. ; Thanapimmetha, A. ; Saisriyoot, M. ; Chiarasumran, N. . Preparation of Lipase Immobilized on Chitosan Beads for Biodiesel Production from Acid Oil, The 32nd Annual Meeting of the Thai Society for Biotechnology and International Conference (TSB2020). 2020. [Google Scholar]
  21. Harding K. G., Dennis J. S., von Blottnitz H., Harrison S. T. L.. A life-cycle comparison between inorganic and biological catalysis for the production of biodiesel. J. Clean. Prod. 2008;16(13):1368–1378. doi: 10.1016/j.jclepro.2007.07.003. [DOI] [Google Scholar]
  22. Sampattagul S., Nutongkaew P., Kaitsiriroat T.. Life cycle assessment of palm oil biodiesel production in Thailand. J. Renew. Energy Smart Grid Technol. 2011;6(1):1–14. [Google Scholar]
  23. Dufour J., Iribarren D.. Life cycle assessment of biodiesel production from free fatty acid-rich wastes. J. Renew. Energy. 2012;38(1):155–62. doi: 10.1016/j.renene.2011.07.016. [DOI] [Google Scholar]
  24. Bansod Y., Crabbe B., Forster L., Ghasemzadeh K., D’Agostino C.. Evaluating the environmental impact of crude glycerol purification derived from biodiesel production: A comparative life cycle assessment study. J. Clean. Prod. 2024;437:140485. doi: 10.1016/j.jclepro.2023.140485. [DOI] [Google Scholar]
  25. Ashnani M. H. M., Johari A., Hashim H., Hasani E.. Life cycle assessment of palm oil biodiesel production in Malaysia. Applied Mechanics and Materials. 2014;465:1080–1086. doi: 10.4028/www.scientific.net/AMM.465-466.1080. [DOI] [Google Scholar]
  26. Pires V. D., Cavalcante R. M., Young A. F.. Process simulation and economic evaluation of biodiesel production from several feedstocks in Brazil. Braz. J. Chem. Eng. 2023;28:1–28. doi: 10.1007/s43153-023-00412-0. [DOI] [Google Scholar]
  27. Voultsos I., Katsourinis D., Giannopoulos D., Founti M.. Integrating LCA with Process Modeling for the Energetic and Environmental Assessment of a CHP Biomass Gasification Plant: A Case Study in Thessaly, Greece. Eng. 2020;1(1):2. doi: 10.3390/eng1010002. [DOI] [Google Scholar]
  28. Rybaczewska-Błażejowska M., Jezierski D.. Comparison of ReCiPe 2016, ILCD 2011, CML-IA baseline and IMPACT 2002+ LCIA methods: a case study based on the electricity consumption mix in Europe. Int. J. Life Cycle Assess. 2024;29:1799–1817. doi: 10.1007/s11367-024-02326-6. [DOI] [Google Scholar]
  29. Lee T. C., Anser M. K., Nassani A. A., Haffar M., Zaman K., Abro M. M. Q.. Managing natural resources through sustainable environmental actions: a cross-sectional study of 138 countries. Sustainability. 2021;13(22):12475. doi: 10.3390/su132212475. [DOI] [Google Scholar]
  30. Shanmughom R., Raghu S. K.. Purification strategies for crude glycerol: A transesterification derivative. AIP Conf. Proc. 2023;(1):2863. doi: 10.1063/5.0155313. [DOI] [Google Scholar]
  31. Ogedengbe A., Achiobu K., Scoccimarro S., Brunet S., Gagnon G., Fabrik M., Ibrahim H.. Valorization of sodium sulfate waste to potassium sulfate fertilizer: experimental studies, process modeling, and optimization. Int. J. Green Energy. 2020;17(8):521–528. doi: 10.1080/15435075.2020.1763361. [DOI] [Google Scholar]
  32. Zhang Y., McKechnie J., Cormier D., Lyng R., Mabee W., Ogino A., Maclean H. L.. Life cycle emissions and cost of producing electricity from coal, natural gas, and wood pellets in Ontario, Canada. Environ. Sci. Technol. 2010;44(1):538–544. doi: 10.1021/es902555a. [DOI] [PubMed] [Google Scholar]
  33. Yue X.-L., Gao Q.-X.. Contributions of natural systems and human activity to greenhouse gas emissions. Adv. Clim. Chang. Res. 2018;9(4):243–252. doi: 10.1016/j.accre.2018.12.003. [DOI] [Google Scholar]
  34. Usapein P., Chavalparit O.. Life cycle assessment of producing electricity in Thailand: a case study of natural gas power plant. MATEC Web Conf. 2017;103:05009. doi: 10.1051/matecconf/201710305009. [DOI] [Google Scholar]
  35. Sibt-e-Ali M., Xiqiang X., Javed K., Javaid M. Q., Vasa L.. Greening the future: assessing the influence of technological innovation, energy transition and financial globalization on ecological footprint in selected emerging countries. Environ. Dev. Sustain. 2024:1–27. doi: 10.1007/s10668-024-05076-5. [DOI] [Google Scholar]
  36. Gracey E. O., Verones F.. Impacts from hydropower production on biodiversity in an LCA frameworkreview and recommendations. Int. J. Life Cycle Assess. 2016;21:412–428. doi: 10.1007/s11367-016-1039-3. [DOI] [Google Scholar]
  37. Azad A. K., Jadeja A. C., Doppalapudi A. T., Hassan N. M., Nabi M. N., Rauniyar R.. Design and Simulation of the Biodiesel Process Plant for Sustainable Fuel Production. Sustainability. 2024;16(8):3291. doi: 10.3390/su16083291. [DOI] [Google Scholar]
  38. Gupta H., Thakkar K., Kachhwaha S. S., Kodgire P.. Biodiesel production from waste cooking oil using sequential process intensification technique (ultrasound and microwave) IOP Conf. Ser.: Mater. Sci. Eng. 2021;1146(1):012005. doi: 10.1088/1757-899X/1146/1/012005. [DOI] [Google Scholar]
  39. Luo Q., Wang K., Yang Y., Tian X., Wang R., He B.. Continuous biodiesel production from acidic oil using a combination of acidic and alkaline composite catalytic membranes in flow-through membrane reactors. New. J. Chem. 2023;47(8):4033–4042. doi: 10.1039/D2NJ03412C. [DOI] [Google Scholar]
  40. Bisen P. S., Sanodiya B. S., Thakur G. S., Baghel R. K., Prasad G. B.. Biodiesel production with special emphasis on lipase-catalyzed transesterification. Biotechnol. Lett. 2010;32(8):1019–1030. doi: 10.1007/s10529-010-0275-z. [DOI] [PubMed] [Google Scholar]
  41. Alsultan A. G., Asikin-Mijan N., Ibrahim Z., Yunus R., Razali S. Z., Mansir N., Islam A., Sivasangar S., Taufiq-Yap Y. H.. A Short Review on Catalyst, Feedstock, Modernised Process, Current State and Challenges on Biodiesel Production. Catalysts. 2021;11:1261. doi: 10.3390/catal11111261. [DOI] [Google Scholar]
  42. Chatterjee R., Sharma V., Mukherjee S., Kumar S.. Life cycle assessment of bio-diesel productionA comparative analysis. J. Inst. Eng. (India):Ser. C. 2014;95:143–149. doi: 10.1007/s40032-014-0105-5. [DOI] [Google Scholar]
  43. Musharavati F., Sajid K., Anwer I., Nizami A. S., Javed M. H., Ahmad A., Naqvi M.. Advancing Biodiesel Production System from Mixed Vegetable Oil Waste: A Life Cycle Assessment of Environmental and Economic Outcomes. Sustainability. 2023;15(24):16550. doi: 10.3390/su152416550. [DOI] [Google Scholar]
  44. Tibesigwa T., Iezzi B., Lim T. H., Kirabira J. B., Olupot P. W.. Life cycle assessment of biodiesel production from selected second-generation feedstocks. Cleaner Eng. Technol. 2023;1(13):100614. doi: 10.1016/j.clet.2023.100614. [DOI] [Google Scholar]

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