1 Introduction

Biodiesel production has garnered significant attention as a sustainable alternative to fossil fuels, driven by the need to reduce greenhouse gas emissions, enhance energy security, and promote rural economic development. Biodiesel, a renewable energy source, is produced through the transesterification of vegetable oils or animal fats with alcohol, resulting in fatty acid methyl esters (FAME) and glycerol. This process not only provides a cleaner-burning fuel but also helps in mitigating the environmental impacts associated with conventional diesel fuel (Jeong et al., 2004; González-García et al., 2012; Herrmann et al., 2013).

The production of biodiesel is a critical component in the global effort to transition towards renewable energy sources. Biodiesel can be produced from various feedstocks, including vegetable oils, animal fats, and waste cooking oils. The transesterification process, typically catalyzed by alkali, acid, or enzymes, converts these feedstocks into biodiesel and glycerol. This process is advantageous due to its relatively simple technology and the high yield of biodiesel it produces (Jeong et al., 2004). The European Union has set ambitious targets for renewable energy in transport, mandating that at least 10% of energy consumption in transport should come from renewable sources by 2020, highlighting the importance of biodiesel in achieving these goals (Herrmann et al., 2013).

Rapeseed oil is one of the most prominent feedstocks for biodiesel production, particularly in Europe. It is favored due to its high oil content and favorable fatty acid composition, which results in biodiesel with excellent cold flow properties and oxidative stability (González-García et al., 2012; Lovasz et al., 2023). The production of biodiesel from rapeseed oil involves several steps, including the extraction of oil from rapeseed, followed by transesterification with alcohols such as methanol or ethanol. Various studies have demonstrated the efficiency of rapeseed oil in biodiesel production, with high conversion rates and favorable environmental profiles (Raman et al., 2019; Santaraite et al., 2020).

The environmental benefits of using rapeseed oil for biodiesel are significant. Life cycle assessments (LCA) have shown that biodiesel from rapeseed oil can substantially reduce greenhouse gas emissions compared to conventional diesel. For instance, the climate change potential from the production and use of rapeseed biodiesel is significantly lower than that of petrochemical diesel, making it a more sustainable option (González-García et al., 2012; Herrmann et al., 2013). Additionally, the byproducts of rapeseed oil biodiesel production, such as rapeseed cake and pellets, can be utilized as renewable energy sources, further enhancing the sustainability of the biodiesel production process (Klugmann-Radziemska and Ciunel, 2013; Zieniuk et al., 2020).

This study elaborates on the current application status and future development prospects of rapeseed oil in biodiesel production. By introducing the background, importance, and main production processes of biodiesel, it lays the foundation for subsequent discussions. The focus is then on analyzing the advantages of rapeseed oil as a biodiesel feedstock, the progress of research, and the existing technical challenges. By reviewing relevant research findings from both domestic and international sources, the study summarizes the best practices and technological innovations in rapeseed oil biodiesel production. Combining the current global energy development trends and environmental policies, the study projects the future development prospects of rapeseed oil in biodiesel production and proposes corresponding strategies and recommendations. This study provides theoretical references and practical guidance for the development of the biodiesel industry, promoting further innovation and application of biodiesel technology.

2 Rapeseed Oil: An Ideal Biodiesel Feedstock

2.1 Composition and characteristics of rapeseed oil

Rapeseed oil is characterized by its high content of unsaturated fatty acids, particularly oleic acid, which constitutes a significant portion of its fatty acid profile. This composition is advantageous for biodiesel production as it contributes to favorable fuel properties such as a high cetane number and good oxidative stability (Rashid et al., 2008; Bogdał et al., 2011). Additionally, rapeseed oil can be chemically modified to improve its thermo-oxidative stability and cold flow properties, making it a versatile feedstock for biodiesel and bio-lubricant applications (Arumugam et al., 2014).

2.2 Comparison with other biodiesel feedstocks

When compared to other common biodiesel feedstocks such as soybean oil and palm oil, rapeseed oil exhibits several superior characteristics. For instance, rapeseed oil has a higher oil yield per hectare, making it a more efficient source of biodiesel (Tanner et al., 2023). Additionally, the biodiesel produced from rapeseed oil generally has a higher cetane number and better cold flow properties compared to soybean oil biodiesel (Rashid et al., 2008). While palm oil is also a high-yield feedstock, its biodiesel tends to have poorer cold flow properties and higher saturated fat content, which can affect engine performance and emissions negatively (Rashid et al., 2008; Bogdał et al., 2011).

2.3 Advantages of using rapeseed oil in biodiesel production

The use of rapeseed oil in biodiesel production offers several advantages. Firstly, rapeseed oil-based biodiesel has been shown to have superior engine performance and lower emissions compared to traditional diesel and other biodiesel types (Arumugam et al., 2014; Mikulski et al., 2020). The high cetane number and good oxidative stability of rapeseed oil biodiesel contribute to efficient combustion and reduced engine wear (Arumugam et al., 2014). Furthermore, the hydroprocessing of rapeseed oil can produce hydrocarbon-based biodiesel that closely resembles conventional diesel, thus ensuring compatibility with existing diesel engines and infrastructure (Šimáček et al., 2009; Šimáček et al., 2010). Additionally, the production process for rapeseed oil biodiesel can be more environmentally friendly, with methods available that reduce the need for water, organic solvents, and catalysts (Tanner et al., 2023).

In summary, rapeseed oil stands out as an ideal feedstock for biodiesel production due to its favorable composition, high yield, and the superior performance of the resulting biodiesel. Its advantages over other feedstocks and the potential for environmentally friendly production methods further enhance its prospects in the biodiesel industry.

3 Production Processes of Biodiesel from Rapeseed Oil

3.1 Extraction of rapeseed oil

The extraction of rapeseed oil is a critical initial step in the production of biodiesel. This process involves several methods, each with its own advantages and limitations. The primary goal is to obtain high-quality oil that can be efficiently converted into biodiesel.

One common method for extracting rapeseed oil is mechanical pressing, which involves crushing the seeds to release the oil. This method is straightforward and does not require the use of solvents, making it environmentally friendly. However, the oil yield from mechanical pressing can be lower compared to other methods.Another widely used method is solvent extraction, which typically involves the use of hexane. This method can extract a higher percentage of oil from the seeds compared to mechanical pressing. However, it requires careful handling and disposal of the solvent to avoid environmental contamination. The use of hexane as a co-solvent has been shown to improve the conversion efficiency of the transesterification process, which is crucial for biodiesel production (Qiu et al., 2011).

In-situ alkaline transesterification is another innovative approach that combines oil extraction and transesterification in a single step. This method has been shown to achieve high conversion rates of rapeseed oil into fatty acid methyl esters (FAME), which are the main components of biodiesel. For instance, a study demonstrated that in-situ alkaline transesterification with methanol could achieve a conversion rate of 98%, making it a highly efficient method for biodiesel production (Qian et al., 2013).

3.2 Transesterification process

The transesterification of rapeseed oil is a pivotal step in converting the extracted oil into biodiesel. This process involves reacting the oil with an alcohol (commonly methanol or ethanol) in the presence of a catalyst to produce fatty acid methyl esters (FAMEs) or fatty acid ethyl esters (FAEEs), which are the chemical constituents of biodiesel.

Several studies have explored different conditions and catalysts to optimize the transesterification process. For instance, the use of subcritical methanol conditions has been shown to yield high amounts of methyl esters even at relatively low pressures, which is advantageous for industrial applications (Encinar et al., 2012). The variables affecting the yield include the type and amount of catalyst, reaction temperature and pressure, and the methanol to oil molar ratio. The presence of co-solvents like hexane can also influence the reaction efficiency (Encinar et al., 2012).

In another approach, in-situ alkaline transesterification has been employed, where the oil extraction and transesterification occur simultaneously. This method has demonstrated high conversion rates of rapeseed oil to FAMEs, with significant reductions in glucosinolate content, making the remaining rapeseed meal suitable for animal feed (Qian et al., 2013). The process parameters, such as the methanol to oil molar ratio and the reaction temperature, are crucial for achieving optimal conversion rates and product quality.

Ultrasonic-assisted transesterification in supercritical ethanol conditions is another innovative method that has been investigated. This technique uses ultrasonic emulsification to enhance the reaction between rapeseed oil and ethanol, resulting in high yields of FAEEs under mild conditions. The use of heterogeneous catalysts, such as ZnO/Al₂O₃ and SrO/Al₂O₃, has been shown to further improve the efficiency of the process (Mazanov et al., 2016). The optimal conditions for this method include a high pressure of 30 MPa and a temperature range of 623 K to 653 K, with an ethanol to oil molar ratio of 12:1 to 20:1 (Mazanov et al., 2016).

3.3 Recent advancements in production technologies

Recent advancements in the production technologies of biodiesel from rapeseed oil have focused on improving efficiency, reducing environmental impact, and optimizing reaction conditions. One notable advancement is the use of ultrasonic-assisted transesterification, which has been shown to significantly enhance the reaction rate and yield. For instance, a study utilizing ultrasonic-assisted biodiesel production from a specific genotype of rapeseed (TERI (OE) R-983) achieved a conversion rate of 87.175% under optimized conditions (Figure 1) (Almasi et al., 2019). This method not only accelerates the reaction but also reduces the energy consumption compared to traditional methods.

Another innovative approach is the hydroprocessing of rapeseed oil, which converts it into hydrocarbon-based biodiesel. This method involves processing the oil at high temperatures and pressures using Ni–Mo/alumina catalysts, resulting in a product that closely resembles conventional diesel fuel in its hydrocarbon composition (Šimáček et al., 2009). This process is advantageous as it produces a biodiesel with properties very similar to those of petroleum diesel, potentially simplifying its integration into existing fuel infrastructure.

Additionally, the direct production of biodiesel from rapeseeds without the need for a catalyst has been explored. This method simplifies the production process by eliminating the need for multiple steps and reducing the use of organic solvents and water, making it more environmentally friendly (Tanner et al., 2023).

3.4 Challenges and solutions in the production process

Despite the advancements, several challenges remain in the production of biodiesel from rapeseed oil. One major challenge is the environmental impact associated with the cultivation of rapeseed, which requires significant fertilizer use and intensive agricultural practices. This can lead to issues such as eutrophication and acidification (González-García et al., 2012). To address this, life cycle assessments (LCA) have been conducted to identify key areas for improvement. For example, optimizing the use of residual straw from rapeseed fields for combustion in power plants can enhance carbon sequestration and reduce overall environmental impact (Herrmann et al., 2013).

Another challenge is the high energy consumption and operational costs associated with traditional transesterification processes. The use of co-solvents like hexane has been shown to lower the operational temperature and improve conversion efficiency, thereby reducing energy consumption (Qiu et al., 2011). Additionally, the development of integrated process designs that combine acid-catalyzed pre-treatment with alkali-catalyzed transesterification can achieve high conversion rates while minimizing investment costs (Elad et al., 2010).

The presence of glucosinolates in rapeseed meal, a byproduct of biodiesel production, poses another challenge as it limits its use as animal feed. However, in-situ alkaline transesterification has been shown to significantly reduce glucosinolate content, making the meal suitable for animal consumption (Qian et al., 2013).

4 Economic Analysis

4.1 Cost comparison of rapeseed oil biodiesel and conventional diesel

The economic viability of rapeseed oil biodiesel compared to conventional diesel is a critical factor in its adoption. Several studies have highlighted the cost dynamics involved in producing and using rapeseed oil biodiesel. One study conducted a comprehensive life cycle cost analysis of using rapeseed oil as a straight vegetable oil (SVO) fuel in agriculture. The findings indicated that while the direct use of SVO reduces the chemical processes involved in converting it into biodiesel, the economic benefits are marginal under current conditions. Specifically, the study found an 8% profit difference favoring conventional diesel over rapeseed SVO in Spain, although this gap could be reduced to 3.7% with changes in key factors such as diesel fuel price, grants, and crop aids (Baquero et al., 2011).

Another study focused on the environmental and economic impacts of biodiesel production from rapeseed oil in Denmark. This research highlighted that the climate change potential from biodiesel production is significantly lower than that of conventional diesel (57 kg CO₂-eq/1,000 km for biodiesel compared to 214 kg CO₂-eq/1,000 km for conventional diesel). However, the study also emphasized the need for improved production methods and the use of residual straw from rapeseed fields to enhance economic viability (Herrmann et al., 2013).

4.2 Market trends and price fluctuations

The market trends and price fluctuations of rapeseed oil biodiesel are influenced by several factors, including fossil fuel prices, agricultural policies, and environmental regulations.The increasing awareness of the environmental impact of petrochemical oil products and the depletion of fossil fuel resources have driven the demand for alternative fuels like biodiesel. The European Union's directive requiring member states to ensure that at least 10% of energy in transport comes from renewable sources by 2020 has further bolstered the market for biodiesel (Herrmann et al., 2013).

However, the market for rapeseed oil biodiesel is also subject to price volatility. The study on the economic analysis of rapeseed SVO in agriculture noted that the fluctuating costs of diesel fuel significantly impact the economic benefits of using rapeseed oil as a biofuel. The study suggested that combined environmental-friendly agriculture supporting policies are necessary to mitigate the slight profit differences and promote the use of rapeseed oil biodiesel (Baquero et al., 2011).

In conclusion, while rapeseed oil biodiesel presents a promising alternative to conventional diesel, its economic viability is closely tied to market trends, price fluctuations, and supportive policies. Further research and development in production methods and policy incentives are essential to enhance its competitiveness and adoption.

4.3 Government policies and subsidies supporting rapeseed biodiesel

Government policies and subsidies play a crucial role in promoting the production and use of rapeseed biodiesel. Various countries have implemented policies to support the biodiesel industry, including tax incentives, subsidies, and mandates for biodiesel blending. These measures aim to reduce greenhouse gas emissions, enhance energy security, and support rural economic development.

For instance, the European Union has been a significant proponent of biodiesel, including rapeseed biodiesel, through its Renewable Energy Directive (RED), which mandates a certain percentage of energy consumption from renewable sources, including biofuels (González-García et al., 2012). This directive has been instrumental in driving the demand for rapeseed biodiesel in Europe. Additionally, subsidies for rapeseed cultivation and biodiesel production help offset the higher costs associated with biodiesel production compared to conventional diesel (Baquero et al., 2011).

In Spain, the government provides diesel fuel grants and crop aids to support the agricultural sector, which indirectly benefits rapeseed biodiesel production. However, the current economic situation still favors the use of conventional diesel due to a slight profit difference (Baquero et al., 2011). To bridge this gap, combined environmentally-friendly agriculture supporting policies are necessary to promote rapeseed biodiesel as a viable alternative.

4.4 Economic viability and profitability of rapeseed biodiesel production

The economic viability and profitability of rapeseed biodiesel production depend on several factors, including production costs, market prices, and government support. The production of biodiesel from rapeseed involves multiple steps, including cultivation, oil extraction, and transesterification, each contributing to the overall cost (Raman et al., 2011; Tanner et al., 2023).Studies have shown that the use of straight vegetable oil (SVO) from rapeseed as a biofuel can be economically beneficial under specific circumstances. For example, a self-supply farming model using rapeseed as its fuel base can help reduce farmers' vulnerability to fluctuating fossil fuel prices and provide clear economic benefits (Baquero et al., 2011). However, the profitability of rapeseed biodiesel production can be affected by factors such as diesel fuel prices, diesel fuel grants, and crop aids.

The environmental benefits of rapeseed biodiesel, such as reduced greenhouse gas emissions and lower dependence on nonrenewable energy sources, also contribute to its economic viability. A life cycle assessment of rapeseed-derived biodiesel showed significant reductions in nonrenewable energy dependence and greenhouse gas emissions compared to conventional diesel (González-García et al., 2012). These environmental advantages can translate into economic benefits through carbon credits and other environmental incentives.

Moreover, the byproducts of rapeseed biodiesel production, such as rapeseed pellets, can be utilized as renewable energy sources, further improving the economic balance of biodiesel production (Klugmann-Radziemska and Ciunel, 2013). The efficient use of these byproducts can enhance the overall profitability of rapeseed biodiesel production.

5 Environmental and Sustainability Aspects

5.1 Environmental benefits of rapeseed biodiesel over fossil fuels

Rapeseed biodiesel offers significant environmental benefits over traditional fossil fuels. One of the primary advantages is the reduction in greenhouse gas (GHG) emissions. For instance, a comprehensive real-time Life Cycle Assessment (LCA) study conducted in Denmark demonstrated that the climate change potential from the production and use of rapeseed biodiesel is 57 kg CO₂-eq per 1,000 km, compared to 214 kg CO₂-eq per 1,000 km for petrochemical diesel (Herrmann et al., 2013). This substantial reduction in CO₂ emissions highlights the potential of rapeseed biodiesel to mitigate climate change.

Additionally, the use of rapeseed biodiesel can decrease nonrenewable energy dependence. A study assessing the environmental life cycle of rapeseed-derived biodiesel in Spain found that using B100 biodiesel instead of conventional diesel could reduce nonrenewable energy demand by 20% (González-García et al., 2012). This shift not only supports energy security but also promotes the use of renewable energy sources.

5.2 Life cycle assessment (LCA) of rapeseed biodiesel

Life Cycle Assessment (LCA) is a crucial tool for evaluating the environmental impacts of rapeseed biodiesel from production to end-use. The Danish LCA study included all relevant process stages, such as rapeseed production, carbon sequestration, N₂O balances, and transportation of products used in the life cycle of biodiesel (Herrmann et al., 2013). The study identified several areas for environmental improvement, such as the increased use of residual straw from rapeseed fields for combustion in power plants and the transition from conventional to enzymatic transesterification processes using bioethanol instead of petrochemical methanol.

Similarly, the Spanish LCA study covered the entire life cycle from crude rapeseed oil production to biodiesel storage, focusing on seven impact categories: abiotic depletion, acidification, eutrophication, global warming, ozone layer depletion, land competition, and photochemical oxidant formation (González-García et al., 2012). The study revealed that rapeseed cultivation is a significant environmental concern due to the high fertilizer doses and intensive agricultural practices required. However, the well-to-wheels comparison indicated that rapeseed biodiesel could reduce GHG emissions by 74% and ozone layer depletion by 44% compared to conventional diesel, despite potential increases in acidification, eutrophication, and photochemical smog (González-García et al., 2012).

5.3 Impact on greenhouse gas emissions

The production and use of rapeseed oil biodiesel have significant implications for greenhouse gas (GHG) emissions. Several studies have demonstrated that biodiesel derived from rapeseed oil can substantially reduce GHG emissions compared to conventional fossil fuels. For instance, a life cycle assessment (LCA) study conducted in Spain revealed that using rapeseed oil biodiesel (B100) instead of petroleum-based diesel could reduce GHG emissions by approximately 74% (González-García et al., 2012). Similarly, another LCA study in Denmark found that the climate change potential from the production and use of rapeseed biodiesel was significantly lower, with emissions of 57 kg CO₂-eq per 1,000 km compared to 214 kg CO₂-eq per 1,000 km for conventional diesel (Herrmann et al., 2013). These reductions are primarily attributed to the renewable nature of biodiesel and the carbon sequestration capabilities of rapeseed crops during their growth phase.

However, it is important to note that the environmental benefits of rapeseed biodiesel are not uniform across all impact categories. While GHG emissions are reduced, other environmental impacts such as acidification, eutrophication, and photochemical smog may increase. For example, the Spanish LCA study reported increases in acidification (+59%), eutrophication (+214%), and photochemical smog (+119%) when using rapeseed biodiesel compared to conventional diesel (González-García et al., 2012). These findings highlight the need for a comprehensive environmental assessment when considering the adoption of rapeseed biodiesel.

5.4 Sustainability considerations and certification

Sustainability considerations for rapeseed biodiesel encompass a range of factors, including land use, resource efficiency, and socio-economic impacts. The cultivation of rapeseed itself poses challenges, as it requires significant inputs of fertilizers and intensive agricultural practices, which can lead to environmental degradation (González-García et al., 2012). Additionally, the energy consumption in the production process, particularly during the transesterification stage, is substantial (Samani et al., 2018).

To address these sustainability challenges, certification schemes and regulatory frameworks have been developed. The European Union, for example, has enacted directives requiring member states to ensure that a certain percentage of energy in transport comes from renewable sources, including biodiesel (Herrmann et al., 2013). Certification schemes such as the Roundtable on Sustainable Biomaterials (RSB) and the International Sustainability and Carbon Certification (ISCC) provide guidelines and standards for sustainable biodiesel production. These certifications consider various sustainability criteria, including GHG emissions, land use, and socio-economic impacts, to ensure that biodiesel production does not lead to adverse environmental or social outcomes.

Moreover, innovative production methods are being explored to enhance the sustainability of rapeseed biodiesel. For instance, a study reported a method to produce biodiesel directly from intact rapeseeds without the need for catalysts, reducing the environmental footprint by minimizing water and solvent use (Tanner et al., 2023). Another study suggested the use of residual straw from rapeseed fields for combustion in power plants, which could further improve the carbon sequestration potential and overall sustainability of the biodiesel production process (Herrmann et al., 2013).

6 Case Studies and Global Perspectives

6.1 Successful implementations of rapeseed biodiesel production

Rapeseed oil has been successfully utilized for biodiesel production in various regions, notably in Europe and Canada. In Europe, the hydroprocessing of rapeseed oil has been a significant technological advancement. This process involves the conversion of rapeseed oil into hydrocarbon-based biodiesel, which is compatible with existing diesel engines. The hydroprocessing method, which operates at temperatures between 260 ℃-340 ℃ and pressures of 7 MPa, has shown promising results with the production of high-quality biodiesel components such as C17 and C18 n-alkanes and i-alkanes (Šimáček et al., 2009).

In Canada, the optimized alkaline-catalyzed transesterification of rapeseed oil has been a key method for biodiesel production. This process involves the use of methanol and potassium hydroxide as a catalyst, achieving a biodiesel yield of 95%-96% under optimal conditions. The produced biodiesel meets the stringent quality standards set by the American Standards for Testing Material (ASTM) and European EN standards, making it a viable alternative to conventional diesel (Rashid and Anwar, 2008).

6.2 Comparative analysis of rapeseed biodiesel adoption in different regions

The adoption of rapeseed biodiesel varies significantly across different regions due to differences in technological approaches and regulatory frameworks. In Europe, the focus has been on hydroprocessing techniques, which produce biodiesel that closely resembles conventional diesel in terms of chemical composition and performance. This method has been particularly successful in countries like Germany and France, where there is strong governmental support for renewable energy initiatives (Šimáček et al., 2009).

In contrast, Canada has primarily adopted the alkaline-catalyzed transesterification method. This approach is more cost-effective and easier to implement on a smaller scale, making it suitable for local biodiesel production facilities. The Canadian biodiesel industry has benefited from government incentives and subsidies, which have encouraged the adoption of biodiesel as a sustainable fuel alternative (Rashid and Anwar, 2008).

6.3 Lessons learned from global case studies

Several lessons can be drawn from the global case studies on rapeseed biodiesel production. Firstly, the choice of production method significantly impacts the quality and yield of the biodiesel. Hydroprocessing, as seen in Europe, produces a high-quality biodiesel that is almost identical to conventional diesel, making it easier to integrate into existing fuel infrastructure (Šimáček et al., 2009). On the other hand, the alkaline-catalyzed transesterification method used in Canada is more accessible and cost-effective, though it may require more stringent quality control measures to meet international standards (Rashid and Anwar, 2008).

Governmental support and regulatory frameworks play a crucial role in the successful adoption of rapeseed biodiesel. Regions with strong policies promoting renewable energy and providing financial incentives for biodiesel production have seen higher adoption rates and more successful implementations. This highlights the importance of policy in driving the transition to sustainable energy sources.

The environmental benefits of rapeseed biodiesel, such as reduced greenhouse gas emissions and lower pollution levels, are significant. These benefits, combined with the economic advantages of using locally produced biodiesel, make rapeseed oil a promising resource for sustainable energy production globally.

7 Future Prospects and Innovations

7.1 Emerging technologies and innovations in rapeseed biodiesel production

Recent advancements in rapeseed biodiesel production have focused on optimizing the efficiency and environmental impact of the process. One notable innovation is the use of ultrasonic-assisted biodiesel production, which has been shown to significantly increase the yield of fatty acid methyl esters (FAME) under optimized conditions (Almasi et al., 2019). Additionally, the application of enzyme catalysts in in situ transesterification processes has demonstrated high efficiency in converting low-quality rapeseed oil into biodiesel, reducing the need for separate extraction and transesterification steps (Figure 2) (Santaraite et al., 2020). These technologies not only enhance the biodiesel yield but also reduce energy consumption and environmental pollutants.

Santaraite et al. (2020) studied the effect of enzyme (Lipozyme TL IM) concentration on the degree of transesterification and triglyceride content in biodiesel under the conditions of an oil-to-ethanol molar ratio of 1:5, a reaction time of 7 hours, and a reaction temperature of 30 ℃. As the enzyme concentration increased, the degree of transesterification significantly improved, reaching nearly 100% at an enzyme concentration of 4%. Simultaneously, the contents of monoglycerides, diglycerides, and triglycerides significantly decreased at this concentration, indicating a highly efficient transesterification reaction. When the enzyme concentration was further increased to 5% and 6%, the degree of transesterification remained stable at a high level, and the triglyceride content approached zero. This indicates that Lipozyme TL IM, as an enzyme catalyst, can efficiently catalyze the transesterification reaction at relatively low concentrations, thereby improving the purity and quality of biodiesel. This study highlights the efficiency and potential application value of enzyme catalysts in biodiesel production.

7.2 Genetic improvements and agricultural practices for higher yield and oil content

Genetic engineering and advanced breeding techniques have been pivotal in developing rapeseed varieties with higher oil content and better agronomic traits. For instance, transgenic rapeseed varieties have been engineered to express novel seed oils and proteins, leading to improved seed-oil yield and quality. Marker-assisted selection has also been employed to develop high oleic and low linolenic acid rapeseed lines, which are ideal for both biodiesel production and agricultural performance (Spasibionek et al., 2020). Furthermore, optimized fertilization systems have been shown to significantly increase rapeseed yield and oil content, thereby enhancing the overall efficiency of biodiesel production (Figure 3) (Lovasz et al., 2023).

Lovasz et al. (2023) studied the regression relationship between different fertilization combinations and rapeseed yield (q ha-1). The fertilization amount increased significantly from no (NoPoKo) to gradually increasing (N160P160K160 to N480P480K480), resulting in a significant increase in rapeseed yield. This proves that fertilization has a positive impact on the growth of rapeseed, not only increasing yield, but also potentially increasing the oil content of rapeseed, providing effective yield increasing measures for improving the overall efficiency of biodiesel production.

7.3 Integration with other renewable energy sources

The integration of rapeseed biodiesel production with other renewable energy sources presents a promising avenue for sustainable energy systems. For example, the use of residual straw from rapeseed fields for combustion in power plants can contribute to carbon sequestration and reduce the overall carbon footprint of biodiesel production (Herrmann et al., 2013). Additionally, rapeseed pellets, a byproduct of biodiesel production, can be utilized as a renewable energy source for heating, further enhancing the sustainability of the biodiesel production process (Klugmann-Radziemska and Ciunel, 2013).

7.4 Potential for scaling up and commercialization

The potential for scaling up rapeseed biodiesel production and its commercialization is significant, given the advancements in production technologies and agricultural practices. The development of more efficient and environmentally friendly production methods, such as the single-step mechanical process for producing biodiesel directly from rapeseeds, offers a scalable solution that reduces the need for water, organic solvents, and catalysts (Tanner et al., 2023). Moreover, life cycle assessments have highlighted the environmental benefits of rapeseed biodiesel, including reduced greenhouse gas emissions and nonrenewable energy dependence, which support its commercial viability (González-García et al., 2012). As these technologies and practices continue to evolve, the commercialization of rapeseed biodiesel is likely to expand, contributing to a more sustainable and diversified energy portfolio.

8 Challenges and Recommendations

8.1 Identification of key challenges in rapeseed biodiesel production

Rapeseed biodiesel production faces several challenges spanning environmental, technical, and economic aspects. The cultivation of rapeseed significantly contributes to environmental issues such as eutrophication and acidification due to the extensive use of fertilizers and intensive agricultural practices. Additionally, rapeseed cultivation is responsible for high greenhouse gas emissions and soil degradation (González-García et al., 2012). The energy return on energy invested (EROEI) for rapeseed biodiesel is relatively low, indicating inefficiencies in the production process. This low energy efficiency can make rapeseed biodiesel less competitive compared to other energy sources (Duren et al., 2015).

The economic feasibility of rapeseed biodiesel is influenced by fluctuating market prices for raw materials and fossil fuels, as well as the high initial investment costs for production facilities. The profitability of biodiesel production is closely related to feedstock cultivation costs and market demand (Yang et al., 2021). Furthermore, conventional transesterification processes require high volumes of chemicals and energy, which can be environmentally detrimental and economically costly. The need for improved and more sustainable production technologies is evident (Tanner et al., 2023).

8.2 Recommendations for overcoming technical, economic, and policy barriers

Implementing sustainable agricultural practices such as crop rotation, reduced fertilizer use, and conservation agriculture can mitigate environmental impacts. Enhancing soil health through organic farming practices can also improve the overall sustainability of rapeseed cultivation (Viccaro et al., 2019). Adopting energy-efficient production technologies such as ultrasonic-assisted transesterification and microwave heating can reduce energy consumption and improve yield. Innovations in catalyst use and process optimization are essential to enhance production efficiency (Azcan and Danisman, 2008; Almasi et al., 2019).

Governments should provide economic incentives such as subsidies and tax breaks to make rapeseed biodiesel more competitive. Policies promoting research and development in biodiesel technologies and supporting the infrastructure for biodiesel production are crucial (Viccaro et al., 2019). Strong policy frameworks that encourage the use of biofuels and mandate blending requirements can stimulate market demand. Ensuring stable policy support can attract investments and foster the development of the biodiesel industry (Herrmann et al., 2013).

8.3 Strategies for enhancing the competitiveness of rapeseed biodiesel

Expanding the market for rapeseed biodiesel by exploring new uses and applications can enhance its competitiveness. Developing co-products such as animal feed from the by-products of biodiesel production can add economic value Optimizing cultivation practices to increase rapeseed yields while reducing environmental impacts can make biodiesel production more sustainable. Utilizing advanced breeding techniques to develop high-yield and resilient rapeseed varieties can also contribute to improved productivity (MacAlister et al., 2020).

Investing in research and development to innovate biodiesel production technologies can lead to cost reductions and efficiency improvements. Exploring alternative feedstocks and enhancing the enzymatic and chemical processes involved can make production more viable (Tanner et al., 2023). Streamlining the supply chain from cultivation to final biodiesel production can reduce costs and increase efficiency. Improving logistics and distribution networks can ensure a stable supply of raw materials and efficient delivery of the final product (Chen and Chen, 2011).

9 Concluding Remarks

The systematic review on the application and development prospects of rapeseed oil in biodiesel production has highlighted several significant findings. Firstly, rapeseed oil has been identified as a highly viable feedstock for biodiesel production due to its high oil yield and favorable cultivation conditions, particularly in regions like southern China and Iran. The transesterification process, which converts rapeseed oil into biodiesel, has been optimized through various methods, including ultrasonic-assisted techniques, which have shown to increase the efficiency and yield of biodiesel production. Additionally, innovative methods such as producing biodiesel directly from rapeseeds without the need for catalysts have been developed, offering more environmentally friendly and cost-effective alternatives.

The future of rapeseed oil in biodiesel production appears promising. The advancements in production techniques, such as the optimization of the transesterification process and the development of single-step production methods, indicate a trend towards more efficient and sustainable biodiesel production. Furthermore, the environmental benefits of using rapeseed oil, including the reduction of cadmium pollution in agricultural fields, add to its appeal as a renewable energy source. As the demand for eco-friendly and renewable energy sources continues to grow, rapeseed oil is well-positioned to play a crucial role in the biodiesel industry.

To fully realize the potential of rapeseed oil in biodiesel production, concerted efforts from researchers, policymakers, and industry stakeholders are essential. Researchers should continue to explore and refine production techniques to enhance efficiency and sustainability. Policymakers need to support these efforts by providing funding for research and development, as well as creating favorable regulatory frameworks that encourage the adoption of biodiesel. Industry stakeholders should invest in the latest technologies and practices to scale up production and reduce environmental impact. By working together, these groups can help ensure that rapeseed oil becomes a cornerstone of the biodiesel industry, contributing to a more sustainable and energy-secure future.

Acknowledgments

Sincere thanks to every peer reviewer for their detailed review and valuable guidance on the initial draft of this article.

Conflict of Interest Disclosure

The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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