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Several strategies for researching and developing the use of plant oils as fuel to produce biodiesel are being explored. Energy shortages and environmental pollution represent major challenges faced by human society today. In order to ensure sustainable economic development, many countries are actively working on developing renewable plant-based energy sources; by taking advantage of local conditions, plant oils are used as alternatives to conventional fuel oils, thereby pursuing a path of diversified energy utilization and comprehensive exploitation. Promoting a shift in the energy consumption structure from being based on a single source to one that is more diversified has become a major trend in the international development of new energy sources. The use and promotion of biodiesel represent an effective approach to addressing the issue of energy substitution at the current stage. Diesel produced from vegetable oil is called biodiesel; it is a monoalkyl ester of long-chain fatty acids. Natural oils are primarily composed of triglycerides of straight-chain fatty acids; after transesterification with methanol, their molecular weight is reduced to a level similar to that of diesel, granting them properties akin to those of diesel. Biodiesel contains no sulfur or aromatics, has a high cetane number, and is a high-quality clean diesel. These long-chain fatty acid monoalkyl esters are biodegradable, have a high flash point, are non-toxic, and contain low levels of volatile organic compounds. They possess excellent lubricating properties and solvency, and they also serve as raw materials for producing biodegradable fine chemical products with high added value (Min Enze, 2005). To develop biodiesel, the West has taken a series of proactive measures in terms of policies and industry regulations (Li Bing, 2005). To facilitate its wider use, countries such as the United States, Germany, and Italy have established technical standards for biodiesel, thereby improving the biodiesel industry 4L4~ ； Furthermore, **incentive policies should be implemented, such as providing subsidies for the price of biodiesel, so that its price becomes more competitive compared to other types of diesel. Currently, the biodiesel production capacity in the United States is 3×105 tons per year, while Japan’s biodiesel production capacity also reaches 4×105 tons per year. The total production capacity of biodiesel in the EU can reach 3×106 tons per year, with an estimated annual production capacity of 8–3×10 tons by 2010 (Zhu Jianliang and Zhang Guanjie, 2004). The raw materials used for producing biodiesel are mainly edible oil crops such as rapeseed, soybeans, and peanuts, as well as waste oils from the food service industry (Min Eun-ze et al., 2005). Compared to other countries, there is still a significant gap in biodiesel production in our country; it remains at the stage of preliminary research. The industrialization of biodiesel has just begun, and **no set of policies aimed at supporting, providing incentives for, and promoting this industry has been established yet. Nor have any unified standards for biodiesel been set, nor has a strategy for its industrial development been formulated. Based on China’s current consumption levels (6×107 to 7×107 tons of diesel per year), if 10% by volume of biodiesel is added to petroleum-based diesel, then 6×106 to 7×106 tons of biodiesel need to be produced annually. It is expected that within the next 10 years, bio-diesel products will account for 20% to 30% of the market share. With the ongoing deepening of reform and opening up, and amid the favorable conditions of global economic integration and China’s accession to the WTO, China’s economic level will continue to rise, leading to an increasing demand for energy. Meanwhile, with the entry into force of the Kyoto Protocol, the development and utilization of biomass energy will become an important strategy for China as well as countries around the world. Therefore, it is even more urgent to accelerate the industrialization of efficient and clean biodiesel (Wan Quan, 2005). To this end, this paper proposes several strategies for researching and developing plant-based biodiesel production using fuel oils. 1 Scientific screening and optimization of fuel oil plants 1.1 Current status of fuel oil plant development Fuel oil plants mainly include oil-producing plants and those with the ability to produce hydrocarbons in a highly reduced form; these plants have compositions similar to those of petroleum and can be used as substitutes for petroleum (also known as “petroleum trees,” and are mostly plants that contain latex). The value of developing fuel oil plants was recognized by insightful individuals long ago, but it was not until after the oil crisis of 1973 that countries began to pay widespread attention to the use of such plants. Especially after the International Conference on New and Renewable Energy held in Nairobi, the capital of Kenya, in 1981, there was a surge worldwide in the development and use of plant-based fuel oils. Our country has a vast territory, spanning five major climate zones: the tropical zone, the **zone, the warm temperate zone, the temperate zone, and the cold temperate zone. The climate and soil diversity give rise to a very rich source of fuel oil plants. According to \"Chinese Oil Plants,\" there are 108 families, 397 genera, and 814 species of oil plants in China. The large number of such plant species in China ranks it among the top countries in the world. China has 6 families of rich-oil plants, as well as over 14 families of medium- and low-rich-oil plants (Shi Peili and Bao Weikai, 1994). Among the more than 60 excellent energy tree species recommended by the U.S. National Academy of Sciences for cultivation in various climate zones around the world, nearly half are native to China or have already been introduced there. From these abundant oil-rich plants, a large number of fuel oil plants with promising development potential can be selected. 1.2 Several highly promising fuel oil crops The raw material resources for fuel oil constitute the most important part of the entire biodiesel industry; their cost level plays a decisive role in determining the price of biodiesel. Vip Information http://www.cqvip.com 314 23(3) At present, the oil sources in our country are mainly herbaceous oils, which are mostly used to produce edible oils. Meanwhile, our country also needs to import large amounts of edible oils to meet the needs of its population; therefore, the raw materials used for producing biodiesel in our country should shift to woody oils. Woody oil crops have the following characteristics: wide adaptability ； Plant once, harvest for years ； Preserve soil and water, conserve water sources, and improve the environment ； Does not compete with crops for land ； Some high-quality woods and certain special chemical raw materials can be provided (Li Jian et al., 2005). Woody oil crops possess enormous potential for development and broad prospects for growth, and they play an irreplaceable role in the future development of the fuel oil industry. Based on the resource characteristics of China’s ecological regions, we have made a simple classification of the planting areas for fuel oil plants (Table 1). At the same time, by reviewing a large amount of literature, we selected 5 woody oil-bearing plants and 1 wild herbaceous oil-bearing plant for focused introduction. 1.2.1 Jatropha curcas: Jatropha is a deciduous shrub or small tree belonging to the genus Jatropha in the Euphorbiaceae family. It is native to Brazil and is widely distributed in tropical and subtropical regions. In our country, it is mainly found in provinces and regions such as Guangdong, Guangxi, Yunnan, Sichuan, Guizhou, Taiwan, Fujian, and Hainan. Jatropha prefers bright light and warm climates; it is tolerant of drought and poor soil conditions, and can grow in gravelly soil, coarse sandy soil, and areas with exposed limestone. It can be used for afforestation on barren mountains. The oil content of Jatropha seeds ranges from 35% to 40%, while that of the kernels is as high as 50% to 60%. On average, each mu of land can produce 650 kg of Jatropha seeds, from which 180 kg of oil can be extracted and processed (She Zhuhua et al., 2005). Although its seeds are high in oil content, they are poisonous and generally not edible. Due to its high oil content and good fluidity, it mixes well with diesel, gasoline, and alcohol; after being blended together, they do not separate over time. As the most suitable renewable biofuel resource in tropical regions, it has the following distribution of oil-producing plants as shown in Table 1: Region – Northeast, Northwest, North China, Southwest, Southeast; Types of energy plants – Cold-resistant plants such as Xanthoceras sorbifolium and castor; Early-blooming shrubs and herbs such as Prunus avium and Hippophae rhamnoides; Other plants such as Phellodendron amurense; Plants like Jatropha curcas; Photinia serrulata, Erythrina variegata, Broussonetia papyrifera, palms, and Melia toosendan. It holds good prospects for development (Lin Juan et al., 2004). 1.2.2 ~ I(Cornus wilsoniana): The Guangpi tree is a deciduous shrub or tree belonging to the Cornaceae family; it is widely distributed and can be found in sparse forests at altitudes below 1,000 meters in provinces such as Hunan, Hubei, Jiangxi, Guizhou, Sichuan, Guangdong, and Guangxi. The Betula luminifera is a sun-loving tree species (its seedlings prefer shade); it has deep and extensive root systems, and it is not particular about the type of soil ； It grows best in soil with deep layers, loose texture, fertility and moisture, good drainage, and a pH level between 5.5 and 7.5. Kapok is an excellent woody oil crop species. Both the kernel and the pulp contain oils; the oil content in the dried fruit is 33% to 36%, while the oil extraction rate is 25% to 30%. It is adaptable and grows rapidly. Even when planted using seedlings, they will bear fruit in 6 to 8 years, and reach full fruit production around 12 years of age. Under favorable growing conditions, the yield per plant can exceed 52 kg, while under normal conditions it ranges from 5 to 10 kg per plant. At 60 plants per mu, the yield of fresh fruit per mu ranges from 300 to 600, which corresponds to 42 to 84 kg of oil (Li Zhengmao et al., 1996). 1.2.3 Xanthoceras sorbifolia: Xanthoceras sorbifolia is a deciduous tree, shrub, or large bush belonging to the genus Xanthoceras in the family Sapindaceae; it can also be cultivated as a tall tree. Xanthoceras sorbifolium is naturally distributed in Shaanxi, Shanxi, Hebei, Inner Mongolia, Ningxia, Gansu, Henan and other regions, with a higher concentration in Shaanxi, Shanxi, Hebei and Inner Mongolia. The Xanthoceras sorbifolium has a well-developed root system, strong sprouting ability, and rapid growth ； Loves light; tolerates partial shade ； It has strong adaptability to soil conditions, tolerates poor fertility and thin soils, as well as salinity and alkalinity; it also has excellent drought resistance. Xanthoceras sorbifolium is an excellent woody oil-bearing tree species unique to China; its seeds contain 45% to 50% oil, while the kernel contains 70% oil. It forms flower buds in the same year it is sown, and can begin to bloom and bear fruit after 2–3 years. A 10-year-old tree can produce over 50 kg of fruit per plant, while trees that are 30–60 years old yield 15–35 kg per plant. It is oil-yellow and transparent, has medicinal properties, and its oil cakes can be used as feed and fertilizer. Its wood grain is fine and beautiful, with a breast diameter of up to 30 cm, making it an excellent material for furniture. Furthermore, its leaves can be processed to be used as a tea substitute, and it is also an excellent tree species for landscaping (Gao Qiming et al., 2005). 1.2.4 Pistacia chinensis: Pistacia chinensis is a deciduous woody tree of the Anacardiaceae family, used for producing oil as well as for timber; it can grow up to 25 meters in height. Phellodendron amurense is widely distributed in China, ranging from Hebei and Shandong in the north to Guangdong and Guangxi in the south, to Taiwan in the east, and to Yunnan, Sichuan, and Gansu in the west. Among these regions, provinces such as Hebei, Henan, Shanxi, and Shaanxi have the highest distribution of this plant. Sophora japonica prefers light and cannot tolerate severe cold ； It can grow in acidic, neutral, and slightly alkaline soils ； It has strong resistance to sulfur dioxide and smoke; its resistance to smoke is classified as grade II, and its disease resistance is also high (Yang Zhiling et al., 2003). The oil content of Sophora tonkinensis seeds is 42.5%, while the oil extraction rate is 20% to 30%. The seeding rate is about 10 thousand seeds per mu; the seedlings grown in the same year reach a height of around 60 cm, with 20,000 to 25,000 seedlings per mu. It has a long lifespan, capable of living for over 300 years. Young trees grow slowly but then accelerate in growth; they can begin to flower and bear fruit after 4 years. When the diameter at breast height reaches 15 cm, each tree produces 50–75 kg of fruit per year ； With a breast diameter of 30 cm, it yields 100–150 kg of fruit per year (Pei Huiming and Chen Mingqi, 2005). 1.2.5 Cerasus humilis: Cerasus humilis is a deciduous shrub belonging to the Rosaceae family. It has a wide distribution range, being found in provinces and regions such as Heilongjiang, Jilin, Liaoning, Inner Mongolia, Hebei, and Shandong. Prunus spinosa is a highly adaptable shrub with the \"four tolerances\" – tolerance to cold, salinity, poor soil conditions, and drought. Prunus avium kernels contain about 50% oil, but they also have around 6.2% amygdalin, which breaks down under the action of acids and enzymes to produce the highly toxic substance hydrocyanic acid; therefore, they are not used as edible oils. Euonymus generally begins to flower and bear fruit in the second year after planting. In areas where growth is more concentrated, there are about 2,000 plants per mu; under normal wild conditions, the yield per plant is around 110 g (Liu Zhiguo and Hao Fang, 2005). 1.2.6 Salicornia bigelivii: Salicornia bigelivii is a plant of the genus Salicornia in the family Amaranthaceae; it is an annual herb that grows to a height of 20–40 cm, and in certain regions it can reach 50–60 cm in height. Spartina is particularly well-suited for growing in the coastal areas of our country. European sea buckthorn is produced in provinces and regions of China such as Liaoning, Hebei, Shanxi, Shaanxi, Ningxia, Gansu, Shandong, and Jiangsu. Spartina can tolerate drought but not waterlogging. It can be planted in beach saline-alkali lands, salt marshes, or light sandy soils; it can be irrigated directly with seawater, or mixed with fresh water, and nitrogen fertilizers such as urea, ammonium phosphate, and nitric acid can be applied. Seeding is generally done in March to April, flowering occurs in mid-June, and maturity comes in September to October; the growth period is about 210 days. The seeds of sea buckthorn contain large amounts of oil and protein, with an oil content of 23% to 33%, which is higher than that of soybeans, sunflower seeds, and many other protein-rich plants. At the same time, Sargassum has high economic value; in addition to improving soil quality, it can also absorb large amounts of CO2, sequestering 5.2×10 kg of carbon per hectare. Sargassum straw is an excellent alternative to wood, thereby reducing deforestation and protecting forest resources. Combining the cultivation of Sargassum with high-density aquaculture will effectively eliminate the organic pollution caused by aquaculture in seawater (Lin Xiuxiang, 2002). Meanwhile, with the development of the urban food service industry, huge amounts of waste animal and vegetable oils are generated, and these waste oils cause pollution to the ecological environment. According to the China Edible Oil Information Network, the total consumption of edible oil in China in 2000 was approximately 1.2×10^6 tons. If 10% of this total consumption is taken into account, then 1.2×10^5 tons of waste oil are generated. A large amount of waste oil from the food service industry is also an important component of biodiesel raw materials. According to statistics from the Afforestation Department of the **Ministry of Forestry, there are currently 8×10 hm² of uncultivated mountainous and barren lands suitable for forestry in China (Hou Fulin and He Jilin, 2000). These substantial land resources, along with abundant fuel crop resources, provide a solid material foundation for the development of fuel crop forests in China. It is foreseeable that, while making numerous contributions to humanity, green plants will surely provide new sources of energy for us. 1.2 Criteria for screening and optimization: Fuel oil crops are a renewable energy source with regenerative properties, meaning that once planted, they can yield benefits for many years. At the same time, plant energy is also a type of “environmental” resource; when selecting plants, in addition to providing energy, they also serve to green barren mountains, prevent soil erosion, protect the environment, and maintain ecological balance. Plant-based energy does not pose the risks associated with nuclear energy, nor does it have the limitations of wind, tidal, or geothermal energy. It is hardly restricted by geographical factors, requires no long-distance transportation, and can be cultivated on barren mountains, slopes, and unused land without competing with agricultural use. This approach not only helps to protect the ecological environment but also generates economic benefits, achieving a balance among energy supply, economic advantages, and ecological sustainability. Although plant resources for fuel oil are mainly found in tropical and subtropical regions, compared to petrochemical energy sources, their distribution is relatively even, with almost every region having some plant-based energy resources with potential for development. Therefore, suitable geographical location, high oil content, great economic value, and significant ecological benefits are the criteria for the selection and optimization of fuel oil plants (Fu Yaoxin, 2001). VIP Information http://www.cqvip.com 316 23(3) 2 Making greater use of genetic modification technology to improve the quality of fuel crops. Genetic modification technology allows for the transfer of genes from certain organisms to other species, thereby altering their genetic material and enabling these organisms to meet human needs in terms of traits, nutritional value, and quality. Genetic engineering of oil plants carried out in recent years has primarily focused on improving important agronomic traits such as oil content, quality, and disease resistance. There are two ways to increase the oil content: one is to raise the yield per unit area of this variety, thereby increasing the total oil production ； Secondly, with constant yield per unit area, increasing the oil content of the seeds also increases the oil production (Wang Wei, 1997). Currently, the oil content in the seeds of major fuel oil plant species ranges from 20% to 45%, and traditional breeding methods have so far failed to develop varieties with a higher oil content. Modern biotechnology provides new methods for the improvement of oil crops. In the seeds of genetically modified oil crops, a single fatty acid component can account for up to 90%. Biodiesel is obtained by breaking down triglycerides whose main component is C18; therefore, we can use genetic engineering to increase the concentration of this specific fatty acid in plant seed oils. This approach allows us to **improve the quality of plants used as fuel sources, and thus enhance the quality of biodiesel as well**. Currently, genetic engineering technology has made significant progress in improving the quality of rapeseed. \"Super oil rapeseed\" is created using antisense gene technology to restrict the pathways through which rapeseed produces proteins, thereby increasing oil production and raising the content of vegetable oil (Shi Dongqiao et al., 2001). Greiner et al. (1999) isolated a gene from plants such as rapeseed, sunflower, peanut, and soybean that can effectively inhibit the activity of jasmonates. Conversin is a gene that promotes plant cell growth; when plants are engineered with this gene, which can inhibit its activity, the synthesis of their DNA strands is disrupted. This enables the plants to produce more nutrients, thereby increasing their oil content. Since the mid-1990s, the agricultural biotechnology industry, centered on genetic modification technology, has had a profound impact on global agriculture. Meanwhile, with the progress of human civilization, people have become more cautious about their own behavior, paying particular attention to their health and ecological balance. The genes used in plant genetic engineering can come from the plants themselves, as well as from animals and microorganisms, or even from artificially synthesized genes; this range is far broader than that of conventional sexual cross-breeding. Genetically modified products are something that has not been achieved through other technologies in history; as a result, there is still a lack of knowledge and experience regarding the impact of genetically modified plants on human health and the ecological environment. Abroad, foods produced from genetically modified plants are not intended for human consumption, which provides a great advantage for the development of the biodiesel industry. We believe that as research progresses, it will be possible to control the key genes responsible for plant oil content, which will **significantly improve the utilization of oil crops and promote the development of biodiesel (Chen Jicheng and Zhou Ruibao, 2004). 3 Developing independent and innovative biodiesel production technologies. Currently, the methods for producing biodiesel can be roughly summarized into the following 4 types: direct mixing method, microemulsion method, high-temperature pyrolysis method, and transesterification method (Table 2) (Ma and Hanna). 1999 ； Yang Yan et al., 2002 ； Demirbas，2003)。 In industrial production, vegetable oil is commonly used as a raw material to produce biodiesel through an esterification reaction. 3.1 Production process of biodiesel As shown in Figure 1, vegetable oils are pre-treated to remove impurities, moisture, and free acids, and then undergo an esterification reaction with methanol in the presence of a catalyst. After the reaction is complete, separation by layering is carried out; the upper layer consists of crude biodiesel, while the lower layer contains glycerol. Rough biodiesel is refined to produce biodiesel (methyl ester of fatty acids) (Nie Kaili, 2003 ； Yang Jiguo et al., 2004 ； Sheng Mei et al., 2004 ； Stavarache et al., 2005) 3.2 Chemical transesterification The main reaction equation is shown in Figure 2. Water and free acids are major enemies of the transesterification reaction, as they are toxic to the catalyst. The feed oil and catalyst must be treated before the reaction. Reduce the acid value and moisture content of the crude oil, while also carrying out dehydration and drying treatment on the catalyst (Li Changzhu et al., 2004) ； Li Weimin and Xu Chunming, 2005). The current biodeiesel production technology primarily relies on the liquid alkali-catalyzed transesterification process. This process is complex, and strict requirements are placed on the raw materials. 3 VIP Information: http://www.cqvip.com 2006, Zhao Chen et al.: Several strategies for producing biodeiesel from plant-based fuels. 3 1 7 Plant pretreatment, refining, esterification reaction, mixing, water removal, purification. Fig. 1 Flow chart of biodiesel preparation. Fig.1 Flow chart of biodiesel production H2. C0oR cH . . R2 3CH3OH ； ； Catalyst = CH2-COOR3; vegetable oil; methanol; CH2-OH; CH3-OH; glycerol. Fig. 2: The main equation for transesterification. R1COOCH3 + R2COOCH3 → R3COOCH3 + R2CH3OH. Biodiesel. Marked with ●● for catalyst; symbols like “/” and “–” indicate various processes such as removal of impurities, elimination of low-value acids, etc. Vip Information: http://www.cqvip.com 318 23(3). Waste emissions can cause environmental pollution, etc. Our country should accelerate the development of biodiesel production technologies with low environmental pollution in order to continuously reduce production costs. The new processes currently under development in China include a new high-pressure alcoholysis process, enzyme-catalyzed transesterification process, dual-solvent multiphase catalytic transesterification process, ultrasonic transesterification process, and solid-base catalyzed transesterification process (Min Enze, 2005). In summary, there are various methods for producing biodiesel. While cost is a key consideration, the choice of method should be based on different practical circumstances, and innovation is required in aspects such as the process flow, reaction conditions, product yield, and treatment of waste materials. Building on existing technologies and continuously incorporating mature foreign techniques, as well as taking into account specific conditions, an innovative biodiesel production process tailored to China’s national circumstances has been developed. 4 Politically, efforts should be made to promote the cultivation and processing of fuel oil crops. The future development of biodiesel is primarily constrained by the low yield and high price of raw vegetable oils, as well as by competition with petroleum diesel. Therefore, the production of biodiesel must be integrated with agricultural production to be viable. Some areas **have plans to cultivate oilseed plants on a large scale, with farms covering thousands of hectares intended to provide the raw materials for plant oils used in the production of methylated biodiesel. Our country possesses abundant plant oil resources; by taking local conditions into account and combining agricultural production with environmental protection, it is possible to increase the area dedicated to oilseed crops, thereby providing raw materials for biodiesel production. While producing biodiesel, the solid residues remaining after oil extraction can be further processed to obtain substances with important pharmacological activities, which can then be used as raw materials for pharmaceuticals or animal feed. At the same time, it is also possible to produce biodegradable lubricants, paint solvents, industrial solvents, and glycerin of high added value, which constitutes another way to reduce costs. The biodiesel project is a systematic endeavor that involves a range of issues such as a country’s energy policies, strategies, environmental regulations, fiscal policies, tax laws, biofuel infrastructure, and the development of automotive technologies. Looking at the situation abroad, the United States classifies biofuels as **strategic** projects, offering financial and tax incentives, as well as legislative safeguards for environmental protection; for example, the **Clean Air Act** sets clear requirements in this regard. The agencies involved in biofuel projects include not only the Department of Energy but also the Department of Agriculture, the Environmental Protection Agency, various local **authorities**, the industrial sector, and several research institutions. In the EU, to encourage the development of biofuels, taxes on the biofuel industry have been reduced by 90%. To date, although my country does not have specific regulations regarding biofuels, many existing laws can be applied, such as the Law on the Prevention and Control of Air Pollution. Since the raw materials for biofuels are currently mostly derived from waste, and as renewable products, relevant preferential policies can be applied (the Renewable Energy Law Draft issued in 2005 and officially implemented in 2006). Therefore, there is already a policy foundation for the development of biofuels in our country. Moreover, our country has **included biofuels as an important part of the development strategy for the 11th Five-Year Plan**, and it is expected that a series of preferential policies related to them will be introduced in the future. 5 Conclusion When selecting and utilizing raw materials for biodiesel, factors such as the yield of the crude oil, its fatty acid composition, the transesterification reaction, and the yield obtained must be taken into consideration; meanwhile, the cost of the resulting biodiesel is the most important factor. To identify raw materials that are widely distributed, highly adaptable, economically viable, yield high amounts, and are inexpensive, we need to conduct extensive scientific research to provide theoretical support for establishing a framework suitable for the development of biodiesel in our country. China’s biodiesel industry has been included in **strategic development plans**. By taking advantage of the country’s vast territory, abundant energy resources, and diverse species, and by considering the ecological and geographical distribution of plants in China, various environmentally friendly and efficient fuel-producing plants that are suitable for these conditions have been selected and cultivated. Optimizing the distribution and production of such energy plants across the country, as well as establishing specialized production areas for them, holds great significance and practical value for the preservation of germplasm resources of energy plants, their propagation and dissemination, as well as their development and utilization. Researching and developing plant-based biodiesel from fuel oil will help alleviate the energy shortage faced in China’s current economic development, and it will also assist in addressing the issues related to agriculture, rural areas, and farmers, as well as ecological and environmental protection challenges. Vigorously promoting the large-scale cultivation of fuel oil crops, improving technologies for the chemical esterification and bioenzymatic synthesis of biodiesel, utilizing genetic engineering techniques, as well as providing subsidies and tax incentives for the cultivation and production of biodiesel are the main strategies for the development of the biodiesel industry at present.