A hydroxyl-functional basic ionic liquid, a preparation method thereof, and a method for catalyzing oil palm oil to prepare biodiesel

Abstract

The application discloses a hydroxyl functional basic ionic liquid and a preparation method thereof, and a method for preparing biodiesel from cyperus oil, and relates to the field of biodiesel preparation methods.The chemical structure of the hydroxyl functional basic ionic liquid is as follows: wherein R is OH, imidazole or morpholine, and the method for preparing the biodiesel is as follows: taking cyperus oil and a short-chain alcohol as raw materials, taking the hydroxyl functional basic ionic liquid as a catalyst, and preparing the biodiesel through an ester exchange reaction.After the reaction is completed, the novel hydroxyl functional basic ionic liquid and the product are automatically separated.The hydroxyl functional basic ionic liquid catalyzes the preparation of the biodiesel, and the reaction process is simple, the product is easy to separate, the yield is high, no pollution is caused, the method is friendly to the environment, the prepared biodiesel has few impurities, the purity is high, and the yield of the biodiesel is as high as 98%.

Description

Technical Field

[0001] This invention relates to the field of biodiesel preparation methods, specifically to a hydroxyl-functionalized alkaline ionic liquid and its preparation method, as well as a method for catalyzing the preparation of biodiesel from tiger nut oil. Background Technology

[0002] The increasing scarcity of fossil fuels has accelerated the development of environmentally friendly and renewable energy sources. Among numerous renewable resources, biodiesel, due to its wide availability of raw materials, good biodegradability, excellent lubrication properties, high safety, environmental friendliness, high cetane number, and good low-temperature fluidity, is considered the most ideal substitute for fossil fuels and has gained widespread attention. In recent years, to promote the development of the biodiesel industry, my country has promulgated a number of policies to support, encourage, and regulate the biodiesel industry. Therefore, vigorously developing biodiesel is of significant strategic importance for sustainable economic development, promoting energy substitution, reducing environmental pressure, and controlling air pollution.

[0003] Biodiesel is generally a mixture of long-chain fatty acid esters obtained by the esterification of free fatty acids (FFA) or the transesterification of triglycerides (TG) from animal and vegetable oils (such as soybean oil, palm oil, sunflower oil, etc.) and short-chain alcohols (such as methanol, ethanol, propanol, etc.) under acid or base catalysis. Common catalysts used for catalyzing the FFA esterification or TG transesterification of oils include traditional chemical acid-base catalysts and biological enzyme catalysts.

[0004] Homogeneous acid catalysts used in industry, such as sulfuric acid and hydrochloric acid, are suitable for producing biodiesel from FFA and oils with high water content. However, these catalysts are highly corrosive, causing significant damage to equipment and pipelines, increasing equipment maintenance costs. Furthermore, they generate numerous side reactions during the reaction, easily forming coke deposits and reducing catalytic efficiency. Additionally, the subsequent acid removal process is complex and produces large amounts of wastewater, causing environmental pollution. Compared to acid catalysts, basic catalysts have advantages such as shorter reaction times, lower temperatures, and higher catalytic rates. However, basic catalysts easily induce saponification reactions in high-acid-value oil reaction systems, leading to difficulties in product separation. The subsequent product washing process is complex, energy-intensive, and highly polluting. While solid acid-base catalysts solve the problem of difficult separation between homogeneous acid-base catalysts and products, the heterogeneous system results in a slower mass transfer rate, affecting the effective collision between the catalyst and reactants, leading to reduced catalytic activity.

[0005] Compared to chemical acid-base catalysts, enzyme catalysts offer advantages such as milder reaction conditions, higher specificity, and environmental friendliness. However, enzyme-catalyzed reactions have longer reaction times and are easily deactivated in methanol systems, resulting in low recovery rates. Although the development of immobilized lipases has effectively improved their reusability, their high cost and design complexity limit their large-scale application in industrial production. Therefore, in recent years, researchers have focused on developing novel and highly efficient catalysts for biodiesel synthesis.

[0006] Functional ionic liquids (FILs), as a novel class of organic solvents and catalysts, possess many excellent properties, such as no significant vapor pressure, non-flammability and non-explosiveness, high safety, good thermal and chemical stability, recyclability, economic and environmental friendliness, and structural designability, attracting widespread attention from researchers. FILs are molten salts composed of organic cations and inorganic or organic anions at room temperature or near room temperature. They are diverse in type, and by changing or adjusting the composition of the cations and anions, FILs with different structures and properties can be designed and constructed. Based on their acid-base properties, FILs can be divided into functional acidic ionic liquids (FAILs) and functional basic ionic liquids (FBILs).

[0007] FAILs have been widely used to catalyze the esterification of FFA or the transesterification of TG to produce biodiesel. For example, Yang Junwei et al. synthesized an acidic functional ionic liquid, [BSO3HMIM]HSO4, in a two-step process and applied it to catalyze the transesterification of Jatropha curcas fruit oil to produce biodiesel. The results showed that under optimized conditions (6 wt% [BSO3HMIM]HSO4, 12 molar ratio of alcohol to oil, 5 h reaction time, and 120 °C reaction temperature), the biodiesel yield reached 93.4%. Although this catalyst showed good catalytic activity in the transesterification of Jatropha curcas fruit oil to produce biodiesel, FAILs catalyzing the transesterification of oils with short-chain alcohols generally suffer from problems such as long reaction time, high temperature, and low catalytic efficiency.

[0008] Existing technologies also disclose methods for preparing biodiesel through the transesterification reaction of oils and short-chain alcohols catalyzed by FBILs. For example, Li Xuefei et al. synthesized 1-butyl-3-methylimidazolium salt ([Bmim]Im), an imidazole anionic basic ionic liquid, in a two-step reaction and applied it to catalyze the transesterification reaction of soybean oil and methanol to prepare biodiesel. Another example is Chinese invention patent application number 201210391389.8, which discloses a functionalized basic ionic liquid and its application in biodiesel preparation; and Chinese invention patent application number CN200510082972.0, which discloses a biodiesel synthesis method based on ionic liquids. However, the functional activity and yield of the currently disclosed functional basic ionic liquids in preparing biodiesel from oils and short-chain alcohols need further improvement. Summary of the Invention

[0009] The present invention aims to provide a hydroxyl-functional alkaline ionic liquid and its preparation method, as well as a method for catalyzing the preparation of biodiesel from tiger nut oil, so as to improve the functional activity of the functional alkaline ionic liquid and the yield of biodiesel prepared by catalyzing oils and short-chain alcohol esters.

[0010] To solve the above technical problems, the specific solution adopted by the present invention is as follows: a hydroxyl-functionalized alkaline ionic liquid, the general chemical structural formula of which is as follows:

[0011]

[0012] Where R is OH, imidazole, or morpholine.

[0013] A method for preparing the above-mentioned hydroxyl-functionalized alkaline ionic liquid.

[0014] When R is imidazole or morphine, the following steps are included:

[0015] 1) An intermediate was synthesized from 3-chloro-1,2-propanediol and a bicyclic guanidine compound in a first organic solvent for later use;

[0016] 2) Imidazole or morpholine salts are synthesized by reacting imidazole or morpholine with an alcoholic solution of an inorganic base, and then set aside for later use;

[0017] 3) The intermediate synthesized in step 1) is reacted with the imidazole salt or morpholine salt synthesized in step 2) in a second organic solvent, i.e.

[0018] A hydroxyl-functionalized alkaline ionic liquid was prepared.

[0019] When R is OH, the following steps are included:

[0020] 1) An intermediate was synthesized from 3-chloro-1,2-propanediol and a bicyclic guanidine compound in a first organic solvent for later use;

[0021] 2) The intermediate synthesized in step 1) is reacted with an alcoholic solution of an inorganic base to obtain a hydroxyl-functionalized basic ionic liquid.

[0022] As a further optimization of the above technical solution, the reaction temperature for intermediate synthesis is 80-120℃.

[0023] As a further optimization of the above technical solution, the molar ratio of the intermediate to the inorganic base, imidazole salt or morpholine salt is 1:0.5-1:2.

[0024] As a further optimization of the above technical solution, the inorganic base is KOH or NaOH.

[0025] As a further optimization of the above technical solution, the first organic solvent is one of toluene, acetonitrile, tetrahydrofuran and ethyl acetate; the second organic solvent is ethanol.

[0026] A method for preparing biodiesel from tiger nut oil using the aforementioned hydroxyl-functionalized alkaline ionic liquid as a catalyst.

[0027] As a further optimization of the above technical solution, biodiesel is produced by using tiger nuts oil and short-chain alcohols as raw materials and adding hydroxyl-functional alkaline ionic liquids to carry out transesterification under condensation conditions.

[0028] As a further optimization of the above technical solution, the molar ratio of short-chain alcohol to tiger nut oil is 6:1-14:1, and the amount of hydroxyl functional alkaline ionic liquid used is 0.5-3% of the mass of tiger nut oil.

[0029] As a further optimization of the above technical solution, the temperature of the transesterification reaction is 40-80℃ and the reaction time is 1-4h.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The hydroxyl-functionalized alkaline ionic liquid synthesized by this invention has advantages such as simple synthesis process, relatively low price, high catalytic activity, low dosage, mild reaction conditions, and short reaction time. Furthermore, after the catalytic reaction, the hydroxyl-functionalized alkaline ionic liquid and the product automatically separate into phases, making it easy to recover. The biodiesel synthesized by the hydroxyl-functionalized alkaline ionic liquid exhibits a high yield, up to 98%, with a density of 0.86-0.90 g·cm³ at 20°C. -1 The kinetic viscosity at 40℃ is 1.9-6.0 μm. 2The biodiesel synthesized in this invention has the following properties: closed-cup flash point >130℃, ignition point >130℃, moisture content <0.05%, and acid value <0.8 mg KOH / g. It meets the requirements of ASTM 6751 standard. The biodiesel obtained by combining high-oleic tiger nut oil with hydroxyl functional ionic liquid in this invention is rich in monounsaturated fatty acid methyl esters and has high purity, giving the biodiesel good low-temperature fluidity and storage stability.

[0032] Tiger nut oil, a high-oleic acid oilseed resource, offers a sustainable source of raw materials. It is characterized by strong resistance to adverse conditions, tolerance to poor soil and salinity, low susceptibility to pests and diseases, preference for sunlight, ease of cultivation and management, non-competition with grain crops for land, and suitability for large-scale planting. Tiger nut tubers are high-yielding and rich in oil, making it one of the most ideal non-grain biomass energy plants discovered to date. Furthermore, its relatively low planting cost reduces the production cost of biodiesel. Biodiesel synthesized from high-oleic acid tiger nut oil has a high content of monounsaturated fatty acids (oleic acid), resulting in fatty acid methyl esters with lower cold filter plugging point and cloud point. Therefore, using high-oleic acid tiger nut oil as a raw material can effectively lower the pour point and viscosity of biodiesel, giving it better low-temperature fluidity at room temperature. In addition, high-oleic acid biodiesel exhibits superior storage stability compared to conventional biodiesel.

[0033] Based on this, this invention uses tiger nut oil and short-chain alcohols as raw materials and hydroxyl-functionalized alkaline ionic liquids as catalysts to efficiently produce biodiesel with high stability and good low-temperature fluidity. The development of a method for preparing biodiesel from tiger nut oil using hydroxyl-functionalized alkaline ionic liquid catalysis provides a new approach for the efficient industrial production of biodiesel and also broadens the application scope of tiger nut oil. Attached Figure Description

[0034] Figure 1 The infrared spectra of the synthesized hydroxyl functional alkaline ionic liquids 1-3 described in this invention are shown below.

[0035] Figure 2 The yield curve of biodiesel preparation from tiger nut oil transesterification reaction catalyzed by the hydroxyl functional ionic liquid 1-3 described in this invention is shown as a function of time.

[0036] Figure 3 The reaction rate of biodiesel preparation by ion liquid 1-3 catalyzing tiger nut oil transesterification in this invention is measured within 3 hours, wherein the reaction temperature is 60°C, the alcohol-to-oil molar ratio is 10, and the catalyst dosage is 1% of the tiger nut oil mass.

[0037] Figure 4 A comparison chart of the fatty acid composition of tiger nut oil and tiger nut oil-based biodiesel;

[0038] Figure 5Schematic diagram of the principle of using hydroxyl-functionalized alkaline ionic liquid to catalyze the preparation of biodiesel from tiger nut oil.

[0039] Figure 6 This study analyzes the physicochemical properties of the biodiesel synthesized from tiger nut oil in this invention. Detailed Implementation

[0040] This invention discloses a hydroxyl-functionalized basic ionic liquid catalyst, the general chemical structural formula of which is as follows:

[0041]

[0042] Where R is OH, imidazole, or morpholine.

[0043] Examples 1-6 below are examples of preparing hydroxyl-functionalized alkaline ionic liquid catalysts.

[0044] Example 1

[0045] When R is OH, the hydroxyl-functionalized basic ionic liquid catalyst is ionic liquid 1, and its chemical structural formula is:

[0046]

[0047] The preparation method of ionic liquid 1 is as follows:

[0048] (1) 0.2 mol (22.11 g) of 3-chloro-1,2-propanediol was placed in a round-bottom flask, and 40 mL of toluene was added. Under uniform stirring with a magnetic stirrer, an equal amount of the bicyclic guanidine compound 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (0.2 mol, 27.8 g) was added, and the reaction was carried out at 100 °C with magnetic stirring for 12 h. After the reaction was completed, the product was repeatedly washed with ethyl acetate. After washing, the product was rotary evaporated and dried under vacuum to constant weight to obtain a pale yellow ionic liquid intermediate.

[0049] (2) The ionic liquid intermediate obtained in step (1) was dissolved in 100 mL of ethanol solution with an equimolar amount of KOH (0.2 mol, 11.22 g), and reacted at 30 °C for 12 hours. After the reaction was completed, the insoluble impurities were removed by filtration, and the solvent was removed by rotary evaporation of the filtrate to obtain hydroxyl functional basic ionic liquid 1 with a yield of 82.5%.

[0050] Example 2

[0051] When R is imidazole, the hydroxyl-functionalized basic ionic liquid catalyst is ionic liquid 2, and its chemical structural formula is:

[0052]

[0053] The preparation method of ionic liquid 2 is as follows:

[0054] (1) 0.2 mol (22.11 g) of 3-chloro-1,2-propanediol was placed in a round-bottom flask, and 40 mL of toluene was added. Under uniform stirring with a magnetic stirrer, an equal amount of the bicyclic guanidine compound 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (0.2 mol, 27.8 g) was added, and the reaction was carried out at 100 °C with magnetic stirring for 12 h. After the reaction was completed, the product was repeatedly washed with ethyl acetate. After washing, the product was rotary evaporated and dried under vacuum to constant weight to obtain a pale yellow ionic liquid intermediate.

[0055] (2) A certain amount of imidazole (0.2 mol, 13.62 g) and KOH (0.2 mol, 11.22 g) in methanol solution were stirred at room temperature for 1 h, and the solvent was removed by rotary evaporation to obtain imidazole salt.

[0056] (3) The ionic liquid intermediate obtained in step (1) and the imidazole salt obtained in step (2) were dissolved in 100 mL of ethanol solution and reacted at 30 °C for 12 hours. After the reaction was completed, insoluble impurities were removed by filtration, and the solvent was removed by rotary evaporation of the filtrate to obtain hydroxyl functional basic ionic liquid 2 with a yield of 92.4%.

[0057] Example 3

[0058] When R is morpholine, the hydroxyl-functionalized basic ionic liquid catalyst is ionic liquid 3, and its chemical structural formula is:

[0059]

[0060] The preparation method of ionic liquid 3 is as follows:

[0061] 1) 0.2 mol (22.11 g) of 3-chloro-1,2-propanediol was placed in a round-bottom flask, and 40 mL of toluene was added. An equal amount of the bicyclic guanidine compound 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (0.2 mol, g) was added under constant stirring with a magnetic stirrer. The reaction was carried out at 100 °C under magnetic stirring for 12 h. After the reaction was complete, the product was repeatedly washed with ethyl acetate. The washed product was then rotary evaporated and dried under vacuum to constant weight to obtain a pale yellow ionic liquid intermediate.

[0062] (2) A certain amount of morpholine (0.2 mol, 17.42 g) and KOH (0.2 mol, 11.22 g) in methanol solution were stirred at room temperature for 1 h, and the solvent was removed by rotary evaporation to obtain imidazole salt.

[0063] (3) The ionic liquid intermediate obtained in step (1) and the morpholine salt obtained in step (2) were dissolved in 100 mL of ethanol solution at a molar ratio of 1:1. The mixture was placed at 30 °C and reacted for 12 hours. After the reaction was completed, the insoluble impurities were removed by filtration. The solvent was removed by rotary evaporation of the filtrate to obtain hydroxyl functional basic ionic liquid 3 with a yield of 89.0%.

[0064] It should be noted that, Figure 1 The infrared spectra of the hydroxyl functional alkaline ionic liquids 1-3 synthesized in this invention are shown.

[0065] Example 4

[0066] In this embodiment, the hydroxyl functional alkaline ionic liquid is the same as R in Example 1, therefore its structural formula is the same as the chemical structural formula of Example 1, and will not be described again here.

[0067] The preparation method of the hydroxyl-functionalized basic ionic liquid in this embodiment is as follows:

[0068] (1) 0.2 mol (22.11 g) of 3-chloro-1,2-propanediol was placed in a round-bottom flask, and 40 mL of toluene was added. An equal amount of the bicyclic guanidine compound 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (0.2 mol, 27.8 g) was added under uniform stirring with a magnetic stirrer. The reaction was carried out at 80 °C under magnetic stirring for 12 h. After the reaction was complete, the product was repeatedly washed with ethyl acetate. After washing, the product was rotary evaporated and dried under vacuum to constant weight to obtain a pale yellow ionic liquid intermediate.

[0069] (2) Dissolve the ionic liquid intermediate obtained in step (1) and a certain molar amount of KOH in 100 mL of ethanol solution, and react at 30 °C for 12 hours. The molar ratio of the intermediate to KOH is 1:0.5. After the reaction is completed, filter to remove insoluble impurities, and remove the solvent by rotary evaporation to obtain hydroxyl functional alkaline ionic liquid.

[0070] Example 5

[0071] In this embodiment, the hydroxyl functional alkaline ionic liquid is the same as R in Example 1, therefore its structural formula is the same as the chemical structural formula of Example 1, and will not be described again here.

[0072] The preparation method of the hydroxyl-functionalized basic ionic liquid in this embodiment is as follows:

[0073] (1) 0.2 mol (22.11 g) of 3-chloro-1,2-propanediol was placed in a round-bottom flask, and 40 mL of acetonitrile was added. Under uniform stirring with a magnetic stirrer, an equal amount of the bicyclic guanidine compound 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (0.2 mol, 27.8 g) was added, and the reaction was carried out at 120 °C with magnetic stirring for 12 h. After the reaction was completed, the product was repeatedly washed with ethyl acetate. After washing, the product was rotary evaporated and dried under vacuum to constant weight to obtain a pale yellow ionic liquid intermediate.

[0074] (2) Dissolve the ionic liquid intermediate obtained in step (1) and a certain molar amount of NaOH in 100 mL of ethanol solution, and react at 30 °C for 12 hours. The molar ratio of the intermediate to KOH is 1:2. After the reaction is completed, filter to remove insoluble impurities, and remove the solvent by rotary evaporation to obtain hydroxyl functional alkaline ionic liquid.

[0075] Example 6

[0076] In this embodiment, the hydroxyl functional alkaline ionic liquid is the same as R in Example 2, therefore its structural formula is the same as the chemical structural formula of Example 2, and will not be described again here.

[0077] The preparation method of the hydroxyl-functionalized basic ionic liquid in this embodiment is as follows:

[0078] (1) 0.2 mol (22.11 g) of 3-chloro-1,2-propanediol was placed in a round-bottom flask, and 40 mL of tetrahydrofuran was added. Under uniform stirring with a magnetic stirrer, an equal amount of the bicyclic guanidine compound 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (0.2 mol, 27.8 g) was added. The reaction was carried out at 120 °C under magnetic stirring for 12 h. After the reaction was completed, the product was repeatedly washed with ethyl acetate. After washing, the product was rotary evaporated and dried under vacuum to constant weight to obtain a pale yellow ionic liquid intermediate.

[0079] (2) A certain amount of imidazole (0.2 mol, 13.62 g) and KOH (0.2 mol, 11.22 g) in methanol solution were stirred at room temperature for 1 h, and the solvent was removed by rotary evaporation to obtain imidazole salt.

[0080] (3) Dissolve the ionic liquid intermediate obtained in step (1) and the imidazole salt obtained in step (2) in 100 mL of ethanol solution, and react at 30 °C for 12 hours. After the reaction is completed, filter to remove insoluble impurities, and remove the solvent by rotary evaporation to obtain hydroxyl functional alkaline ionic liquid.

[0081] Examples 7-15 below are examples of preparing biodiesel using the ionic liquids 1-3 prepared above.

[0082] Example 7

[0083] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 70 °C. 9.1 mL of methanol (molecular ratio of methanol to oil was 10:1) and 0.30 g of ionic liquid 1 (1.5 wt%) were added. The mixture was heated under reflux at 70 °C for 3 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and catalyst ionic liquid 1. The upper layer was subjected to vacuum distillation to remove methanol, yielding a biodiesel sample. Gas chromatography analysis was performed to determine the composition, and the biodiesel yield was calculated to be 96.8%.

[0084] The biodiesel synthesized in this embodiment has a density of 0.86 g·cm³ at 20°C, as determined by testing. -1 The kinetic viscosity at 40℃ is 4.3 μm. 2 The pour point (PP) and cold filter plugging point (CFPP) of the biodiesel synthesized from tiger nut oil are -7℃ and -6℃, respectively, indicating that the biodiesel has good low-temperature fluidity. It should be noted that the pour point and CFPP represent the lowest temperature at which the oil can be poured and the highest temperature at which it cannot pass through a filter within 1 minute, respectively. These values ​​can accurately describe the oil's flow properties and storage stability at low temperatures.

[0085] Example 8

[0086] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 70 °C. 9.1 mL of methanol (molecular ratio of methanol to oil was 10:1) and 0.40 g of ionic liquid 2 (2 wt%) were added. The mixture was heated under reflux at 70 °C for 3 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and the catalyst ionic liquid 2. The upper layer was subjected to vacuum distillation to remove methanol, yielding a biodiesel sample. Gas chromatography analysis was performed to determine the composition, and the biodiesel yield was calculated to be 95.9%.

[0087] The biodiesel synthesized in this embodiment has a density of 0.88 g·cm³ at 20°C, as determined by testing. -1 The kinetic viscosity at 40℃ is 4.6 μm. 2 / s. The pour point (PP) and cold filter plugging point (CFPP) of the biodiesel synthesized from tiger nut oil are -6℃ and -4℃, respectively, indicating that the biodiesel has good low-temperature fluidity.

[0088] Example 9

[0089] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 60 °C. 9.1 mL of methanol (molecular ratio of methanol to oil was 10:1) and 0.20 g of ionic liquid 3 (1 wt%) were added. The mixture was heated under reflux at 60 °C for 3 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and the catalyst ionic liquid 3. The upper layer was subjected to vacuum distillation to remove methanol, yielding a biodiesel sample. Gas chromatography analysis was performed to determine the composition, and the biodiesel yield was calculated to be 97.7%.

[0090] The biodiesel synthesized in this embodiment has a density of 0.85 g·cm³ at 20°C, as determined by testing. -1 The kinetic viscosity at 40℃ is 4.1 μm. 2 / s. The pour point (PP) and cold filter plugging point (CFPP) of the biodiesel synthesized from tiger nut oil are -8℃ and -6℃, respectively, indicating that the biodiesel has good low-temperature fluidity.

[0091] Example 10

[0092] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 50 °C. 7.3 mL of methanol (molar ratio of alcohol to oil was 8:1) and 0.20 g of ionic liquid 3 (1 wt%) were added. The mixture was heated under reflux at 50 °C for 2.5 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and the catalyst ionic liquid 3. The upper layer was subjected to vacuum distillation to remove methanol, yielding a biodiesel sample. Gas chromatography analysis was performed to determine the composition, and the biodiesel yield was calculated to be 84.16%.

[0093] Example 11

[0094] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 60 °C. 10.96 mL of methanol (molecular ratio of methanol to oil was 12:1) and 0.10 g of ionic liquid 3 (0.5 wt%) were added. The mixture was heated under reflux at 60 °C for 2.5 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and the catalyst ionic liquid 3. The upper layer was subjected to vacuum distillation to remove methanol, yielding a biodiesel sample. Gas chromatography analysis was performed to determine the composition, and the biodiesel yield was calculated to be 92.20%.

[0095] Example 12

[0096] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 60 °C. 9.1 mL of methanol (molecular ratio of methanol to oil was 10:1) and 0.20 g of ionic liquid 3 (1 wt%) were added. The mixture was heated under reflux at 60 °C for 2 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and the catalyst ionic liquid 3. The upper layer was subjected to vacuum distillation to remove methanol, yielding a biodiesel sample. Gas chromatography analysis was performed to determine the composition, and the biodiesel yield was calculated to be 94.6%.

[0097] Example 13

[0098] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 40 °C. 13.8 mL of ethanol (ethanol-to-oil molar ratio of 10:1) and 0.20 g of ionic liquid 1 (1 wt%) were added. The mixture was heated under reflux at 40 °C for 4 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and catalyst ionic liquid 1. The upper layer was subjected to vacuum distillation to remove methanol, yielding the biodiesel sample.

[0099] Example 14

[0100] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 80 °C. 21.05 mL of n-butanol (molar ratio of alcohol to oil was 10:1) and 0.6 g of ionic liquid 1 (3 wt%) were added. The mixture was heated to reflux at 80 °C for 1 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and catalyst ionic liquid 1. The upper layer was subjected to vacuum distillation to remove methanol, yielding a biodiesel sample. Gas chromatography analysis was performed to determine the composition, and the biodiesel yield was calculated to be 86.2%.

[0101] Example 15

[0102] 20 g of tiger nut oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 80 °C. 9.1 mL of methanol (molecular ratio of methanol to oil was 10:1) and 0.20 g of ionic liquid 3 (1 wt%) were added. The mixture was heated under reflux at 80 °C for 3 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and the catalyst ionic liquid 3. The upper layer was subjected to vacuum distillation to remove methanol, yielding a biodiesel sample. Gas chromatography analysis was performed to determine the composition, and the biodiesel yield was calculated to be 92.3%.

[0103] Comparative Example 1

[0104] Add 20g of tiger nut oil to a 100mL three-necked round-bottom flask, place it in an oil bath equipped with a stirrer, insert a thermometer and a condenser, turn on the cooling water, set the heating temperature to 60℃, add 9.1mL of methanol (molecular ratio of methanol to oil is 10:1) and 0.20g of potassium hydroxide (1wt%), heat at 60℃ under reflux for 2.5h, wash the product with water after the reaction is complete, and analyze the composition of the biodiesel sample by gas chromatography and calculate the biodiesel yield to be 91.4%.

[0105] The biodiesel synthesized in this comparative example had a density of 0.89 g·cm³ at 20°C, as determined by testing. -1 The kinetic viscosity at 40℃ is 4.9 μm. 2 / s. The pour point (PP) and cold filter plugging point (CFPP) of biodiesel synthesized from tiger nut oil are -4℃ and -3℃, respectively.

[0106] The catalyst used in this reaction is a potassium hydroxide alkaline catalyst. Under optimal reaction conditions (reaction temperature 60℃, alcohol-to-oil molar ratio 10, catalyst dosage 1%), the yield of biodiesel produced by the potassium hydroxide-catalyzed transesterification reaction of tiger nut oil is slightly lower than that produced by ionic liquid catalysts 1-3 under optimal reaction conditions (Examples 7, 8, and 9). However, the subsequent water washing process with KOH is cumbersome, the catalytic system is prone to saponification leading to difficulties in product separation, and the wastewater generated during the water washing process easily causes environmental pollution and water waste, resulting in poor economic benefits.

[0107] Comparative Example 2

[0108] 20g of tiger nut oil was added to a 100mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and a condenser were inserted, and the cooling water was turned on. The heating temperature was set to 60℃. 7.3mL of methanol (molecular ratio of methanol to oil was 8:1) and 0.6g of alkaline ionic liquid 1-butyl-3-methylmorpholine salt [Hnmm]Im (3wt%) were added. The mixture was heated at 60℃ for 2 hours. After the reaction was completed, the reactants were poured into a separatory funnel and allowed to stand for separation. The lower layer of glycerol and the catalyst phase were separated. The glycerol and the catalyst phase were recovered by vacuum distillation. The upper layer of methyl ester was separated by vacuum distillation to remove methanol and then washed three times with hot 10% NaCl solution to separate biodiesel. The biodiesel yield was calculated to be 91.3%.

[0109] The biodiesel synthesized in this comparative example had a density of 0.88 g·cm³ at 20°C, as determined by testing. -1 The kinetic viscosity at 40℃ is 4.6 μm. 2 / s. The pour point (PP) and cold filter plugging point (CFPP) of biodiesel synthesized from tiger nut oil are -5℃ and -4℃, respectively.

[0110] The catalyst used in this reaction is a basic morpholine salt ionic liquid, which, compared to ionic liquid catalysts 1-3, does not contain hydroxyl groups in its structure. Under optimal reaction conditions (reaction temperature 60℃, alcohol-to-oil molar ratio 8:1, catalyst dosage 3%), the yield of biodiesel produced by the [Hnmm]Im-catalyzed transesterification reaction of tiger nut oil is slightly lower than that of ionic liquid catalysts 1-3 under optimal reaction conditions. The amount of catalyst used in this catalytic process is 1.5 to 3 times that of the hydroxyl-functionalized ionic liquid catalysts 1-3, indicating that the ionic liquid without hydroxyl groups in its structure has slightly lower basicity and reactivity. This further illustrates the structural and performance superiority of the hydroxyl-functionalized ionic liquid of this application.

[0111] Comparative Example 3

[0112] 20g of tiger nut oil was added to a 100mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 65℃. 7.3mL of methanol (molar ratio of methanol to oil 8:1) and 0.8g of basic choline-based ionic liquid ChIm (4wt%) were added. The reaction was heated at 65℃ for 3 hours. After the reaction was completed, the reaction solution was allowed to cool naturally and transferred to a separatory funnel. The mixture was allowed to stand and separate into layers. The upper layer was crude biodiesel, and the lower layer was the ionic liquid phase, which still contained glycerol and unreacted methanol. The ionic liquid phase was recovered by vacuum distillation. The crude biodiesel was then processed to obtain refined biodiesel. Finally, it was dehydrated and dried using a vacuum distillation apparatus to obtain relatively pure biodiesel. The calculated biodiesel yield was 91.9%.

[0113] The biodiesel synthesized in this comparative example had a density of 0.89 g·cm³ at 20°C, as determined by testing. -1 The kinetic viscosity at 40℃ is 4.8 μm. 2 / s. The pour point (PP) and cold filter plugging point (CFPP) of biodiesel synthesized from tiger nut oil are -4℃ and -3℃, respectively.

[0114] The catalyst used in this reaction is the basic choline-based ionic liquid ChIm. Compared with ionic liquid catalysts 1-3, under optimal reaction conditions (reaction temperature 65℃, alcohol-to-oil molar ratio of 8, catalyst dosage of 4wt%), the yield of biodiesel produced by the ChIm-catalyzed transesterification reaction of tiger nut oil is slightly lower than that of ionic liquid catalysts 1-3 under optimal reaction conditions. The amount of catalyst used in this catalytic process is 2 to 4 times that of the hydroxyl-functionalized ionic liquid catalysts 1-3, indicating the advantage of the ionic liquid catalyst in this invention.

[0115] Comparative Example 4

[0116] 20g of soybean oil was added to a 100mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 60℃. 9.0mL of methanol (molecular ratio of methanol to oil was 10:1) and 0.20g of ionic liquid 1 (1wt%) were added. The mixture was heated under reflux at 60℃ for 2.5h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and catalyst ionic liquid 3. After removing methanol from the upper layer by vacuum distillation, the biodiesel sample was analyzed by gas chromatography, and the biodiesel yield was calculated to be 85.9%.

[0117] The biodiesel synthesized in this comparative example had a density of 0.88 g·cm³ at 20°C, as determined by testing. -1 The kinetic viscosity at 40℃ is 4.9 μm. 2 / s. The pour point (PP) and cold filter plugging point (CFPP) of biodiesel synthesized from soybean oil are -2℃ and -1℃, respectively, indicating that the low-temperature fluidity of biodiesel derived from soybean oil is slightly worse than that derived from tiger nut oil. However, it still meets the ASTM biodiesel standard.

[0118] The raw material used in this reaction is soybean oil. Compared to tiger nut oil, soybean oil has an oleic acid content of 20%–45%, which is lower than that of tiger nut oil (67%–74%). Oleic acid, as a monounsaturated fatty acid, produces fatty acid methyl esters with lower cold filter plugging point and pour point. Therefore, biodiesel prepared from soybean oil has a higher cold filter plugging point, pour point, and viscosity than biodiesel prepared from tiger nut oil. In the examples, biodiesel synthesized from high-oleic tiger nut oil maintains fluidity more easily at low temperatures.

[0119] Comparative Example 5

[0120] 20 g of palm oil was added to a 100 mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 60 °C. 9.3 mL of methanol (molecular ratio of methanol to oil was 10:1) and 0.20 g of ionic liquid 2 (1 wt%) were added. The mixture was heated under reflux at 60 °C for 2.5 h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and catalyst ionic liquid 3. After removing methanol from the upper layer by vacuum distillation, the biodiesel sample was analyzed by gas chromatography, and the biodiesel yield was calculated to be 90.7%.

[0121] The biodiesel synthesized in this comparative example had a density of 0.90 g·cm³ at 20°C, as determined by testing. -1The kinetic viscosity at 40℃ is 5.6 μm. 2 The pour point (PP) and cold filter plugging point (CFPP) of biodiesel synthesized from palm oil are 6℃ and 10℃, respectively, indicating that the low-temperature fluidity of palm oil-based biodiesel is slightly worse than that of tiger nut oil-based biodiesel.

[0122] The feedstock oil used in this comparative example is palm oil. The saturated fatty acid content in palm oil is higher than that in tiger nut oil. Saturated fatty acids have longer carbon chains, leading to stronger intermolecular forces and a greater tendency to form crystal structures, thus reducing the low-temperature fluidity of the biodiesel product. This further illustrates the superior performance of using ionic liquids 1-3 as catalysts and tiger nut oil as feedstock in the biodiesel preparation method described in this application.

[0123] Comparative Example 6

[0124] 20g of Acer truncatum seed oil was added to a 100mL three-necked round-bottom flask and placed in an oil bath equipped with a stirrer. A thermometer and condenser were inserted, and the cooling water was turned on. The heating temperature was set to 60℃. 9.1mL of methanol (molecular ratio of methanol to oil was 10:1) and 0.20g of ionic liquid 3 (1wt%) were added. The mixture was heated under reflux at 60℃ for 2.5h. After the reaction was completed, the mixture was transferred to a separatory funnel and allowed to stand and separate into layers. The upper layer consisted of crude biodiesel and methanol, while the lower layer consisted of glycerol and the catalyst ionic liquid 3. After removing methanol from the upper layer by vacuum distillation, the biodiesel sample was analyzed by gas chromatography, and the biodiesel yield was calculated to be 93.2%.

[0125] The biodiesel synthesized in this comparative example was found to have a density of 0.89 g·cm⁻¹ at 20°C and a kinetic viscosity of 5.3 Mm at 40°C. 2 The pour point (PP) and cold filter plugging point (CFPP) of the biodiesel synthesized from Acer truncatum seed oil were 1°C and 4°C, respectively, indicating that the low-temperature fluidity of the biodiesel derived from Acer truncatum seed oil was slightly inferior to that derived from tiger nut oil. This further demonstrates the superior low-temperature fluidity of the biodiesel prepared from tiger nut oil in this invention.

[0126] Figure 2 The figures show the yield of biodiesel prepared from tiger nut oil via transesterification catalyzed by the hydroxyl functional ionic liquids 1-3 described in Examples 7-9 over time. Figure 2 The novel ionic liquids 1-3 can intuitively express the changing trend of biodiesel products synthesized from tiger nut oil over time, indicating that the three ionic liquids have good catalytic activity. Figure 3 The reaction rate for the preparation of biodiesel from tiger nut oil via transesterification catalyzed by ionic liquids 1-3 in Examples 7-9 was measured over 3 hours, with a reaction temperature of 60°C, an alcohol-to-oil molar ratio of 10, and a catalyst dosage of 1% of the tiger nut oil mass.Figure 3 This demonstrates that the transesterification reaction of tiger nut oil catalyzed by the three ionic liquids of this invention follows a pseudo-first-order reaction pattern. Compared with the second-order reaction, the pseudo-first-order reaction catalyzed by ionic liquids 1-3 exhibits a higher reaction rate, showcasing the advantage of high ionic liquid catalytic efficiency.

[0127] Figure 4 A comparative diagram of the fatty acid composition of tiger nut oil and tiger nut oil-based biodiesel demonstrates that the process of preparing biodiesel by catalyzing the transesterification of tiger nut oil with ionic liquid 1-3 does not affect the fatty acid composition and content of tiger nut oil. It preserves the original fatty acid composition of tiger nut oil, resulting in biodiesel synthesized from it having a high level of methyl oleate, thus giving tiger nut oil-based biodiesel good low-temperature fluidity. Figure 5 The catalytic mechanism of ionic liquid 3 for the transesterification reaction of tiger nut oil to prepare biodiesel. Figure 6 For the physicochemical analysis of the biodiesel obtained in this invention, by Figure 6 It can be seen that the biodiesel obtained in this invention has high purity. The high purity is reflected in the fact that the fatty acid methyl ester content in the final biodiesel is above 98%, and the total content of other impurities in the biodiesel, including monoglycerides, diglycerides, water, and free fatty acids, is less than 1%.

[0128] In summary, by comparing Comparative Examples 1-3 and the ionic liquid catalyst 1-3 of this application under optimal reaction conditions (Examples 7, 8, and 9), it can be seen that when other alkaline liquid catalysts are used to catalyze the preparation of biodiesel from tiger nut oil and short-chain alcohols, the biodiesel yield is weaker than that of the alkaline liquid catalyst in this application. This is because the hydroxyl groups in the hydroxyl-functionalized alkaline ionic liquid catalyst of this application have the following effects during the catalytic process:

[0129] 1. Enhanced basicity: The hydroxyl group has strong electrophilic properties, thus easily absorbing electrons from the environment to form the OH- mode. This endows hydroxyl-functionalized basic ionic liquids with stronger basicity, providing basic centers for activating substrates and catalytic reactions. This high basicity can improve the reaction activity of the catalyst.

[0130] 2. Reduced activation energy: During catalysis, hydroxyl groups can undergo hydrogen bonding or proton transfer reactions with the substrate or intermediate, thereby reducing the activation energy of the reaction.

[0131] 3. Increased water solubility: The dihydroxyl functional alkaline ionic liquid contains a dihydroxyl group with a structure similar to glycerol, giving it better water solubility. This improved water solubility allows the catalyst to better adapt to the aqueous reaction environment. In the initial stage of the reaction between oils and methanol to produce biodiesel, the reaction easily occurs at the methanol-oil interface, thereby increasing the reaction rate and lowering the activation energy.

[0132] 4. Emulsifying Properties in Methanol and Oil-Based Two-Phase Systems: Hydroxyl-functionalized basic ionic liquids exhibit emulsifying properties in the reaction system of methanol and oils. This emulsifying property effectively promotes the uniform mixing of methanol and oils and provides a larger interfacial contact area, which is beneficial to the reaction. This emulsifying property contributes to the reaction and increases the biodiesel yield.

[0133] Because the cation structure of hydroxyl-functionalized basic ionic liquids contains two hydroxyl groups (OH), which are electrophilic and readily accept electrons or negative charges, they can absorb electrons from their surroundings to form OH- anions. The presence of two hydroxyl groups in the structure of hydroxyl-functionalized basic ionic liquids enhances their electron affinity, further strengthening their basicity. This stronger basicity results in higher reactivity. Furthermore, the hydroxyl group structure in hydroxyl-functionalized basic ionic liquids is similar to that of glycerol, leading to better water solubility. In contrast, hydroxyl-functionalized basic ionic liquids exhibit greater solubility in methanol. Therefore, in the initial stages of the reaction between tiger nut oil and methanol to produce biodiesel, the reaction readily occurs at the methanol-oil interface, further increasing the reaction rate and lowering the activation energy. In addition, hydroxyl-functionalized ionic liquids also exhibit emulsifying properties in the methanol and oil two-phase system, which helps the reaction proceed towards the formation of fatty acid methyl esters, thereby increasing the yield of biodiesel.

[0134] By comparing Comparative Examples 1-6 with the Examples, it can be seen that the biodiesel synthesized from high-oleic tiger nut oil as raw material and through the hydroxyl-functionalized alkaline ionic liquid catalytic reaction of this application has low fluidity and storage stability.

[0135] Comparing the low fluidity and storage stability of the biodiesel prepared in Comparative Examples 1-3 and the examples, it can be seen that when the raw material is tiger nut oil and the catalyst is potassium hydroxide, alkaline ionic liquid 1-butyl-3-methylmorpholine salt or alkaline choline ionic liquid ChIm (in the prior art), the low fluidity and storage stability of the prepared biodiesel are weaker than those of the biodiesel in the examples.

[0136] Comparing the low fluidity and storage stability of the biodiesel prepared in Comparative Examples 4-6 and the examples, it can be seen that when the catalyst is the hydroxyl-functional alkaline ionic liquid of this application and the raw material is other oils (such as soybean oil, palm oil, and Acer truncatum seed oil), the low-temperature fluidity and storage stability of the prepared biodiesel are lower than those in Comparative Examples 1-3. On the one hand, using high-oleic tiger nut oil as a raw material to prepare biodiesel can effectively reduce the freezing point and viscosity of biodiesel, so that it has good fluidity at room temperature or even low temperature. On the other hand, the low-temperature fluidity and storage stability of biodiesel can only be improved due to the interaction between the alkaline ionic liquid and high-oleic tiger nut oil.

[0137] The main reasons why the low-temperature fluidity and storage stability of biodiesel in this application can be effectively improved are as follows:

[0138] High oleic acid content: The low-temperature fluidity of biodiesel mainly depends on the fatty acid composition of the feedstock oil. Tiger nut oil is rich in oleic acid, a monounsaturated fatty acid whose fatty acid methyl esters have low cold filter plugging point and cloud point. Therefore, using high-oleic tiger nut oil as a feedstock can effectively reduce the pour point and viscosity of biodiesel, giving it good fluidity at room temperature and even low temperatures. Compared to other feedstocks, biodiesel synthesized from high-oleic tiger nut oil maintains its fluidity more easily at low temperatures.

[0139] The storage stability of high-oleic tiger nut oil is related to two factors. Firstly, the natural antioxidants in its raw material, such as tocopherols and carotenoids, can slow down the oxidation rate of biodiesel, thus improving its storage stability. Secondly, the choice of catalyst also plays a role. For example, while using strong alkaline catalysts like KOH to prepare biodiesel can promote transesterification, it can also lead to side reactions, such as saponification, affecting the stability of the biodiesel. The hydroxyl-functionalized ionic liquid catalyst used in this application, however, requires mild reaction conditions for tiger nut oil, better preserving its original fatty acid composition and unsaturation, thereby improving the stability of the biodiesel.

[0140] The principle of preparing biodiesel by catalyzing the transesterification reaction of tiger nut oil with hydroxyl-functionalized alkaline ionic liquid is as follows: Figure 5As shown, the process of preparing biodiesel from tiger nut oil via transesterification catalysis using a hydroxyl-functionalized ionic liquid involves three consecutive reactions. First, the hydroxyl group in the hydroxyl-functionalized ionic liquid is an electron-withdrawing group and also the basic active center of the catalyst, capable of activating methanol to form a methoxy anion. Next, the activated methoxy anion nucleophilically attacks the carbonyl group on the triglyceride in tiger nut oil, forming a tetrahedral intermediate. Then, through electron transfer and nucleophilic substitution reactions, this tetrahedral intermediate forms a diglyceride intermediate and one molecule of fatty acid methyl ester (biodiesel). The diglyceride then undergoes nucleophilic substitution by two molecules of methoxy anion, yielding two molecules of fatty acid methyl ester and one molecule of glycerol as a byproduct. During the catalytic reaction, the hydroxyl group in the hydroxyl-functionalized basic ionic liquid acts as the active center of the catalyst, accelerating the reaction of tiger nut oil and promoting biodiesel production. Simultaneously, it acts as a passivating agent, inhibiting side reactions and thus improving the purity and storage stability of the biodiesel. Therefore, the improvement in low fluidity and storage stability is due to the interaction between the hydroxyl-functionalized basic ionic liquid and the high-oleic tiger nut oil.

[0141] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing biodiesel from catalytic tiger nut oil, characterized in that, Biodiesel was produced by using hydroxyl-functionalized alkaline ionic liquid as a catalyst, using tiger nut oil and short-chain alcohols as raw materials, and adding hydroxyl-functionalized alkaline ionic liquid under condensation conditions to carry out transesterification reaction. The chemical structural formula of this hydroxyl-functionalized basic ionic liquid is: or ; The molar ratio of short-chain alcohol to tiger nut oil is 6:1-14:1, and the amount of hydroxyl-functionalized basic ionic liquid used is 0.5-3% of the mass of tiger nut oil. The temperature for transesterification is 40-80 ℃, and the reaction time is 1-4 h.

2. The method for preparing biodiesel from catalytic tiger nut oil according to claim 1, characterized in that, The preparation method of hydroxyl-functionalized basic ionic liquid includes the following steps: 1) An intermediate was synthesized from 3-chloro-1,2-propanediol and a bicyclic guanidine compound in a first organic solvent and set aside for later use; 2) Morpholine salts are synthesized by reacting morpholine with an alcoholic solution of an inorganic base, and are kept for later use; 3) The intermediate synthesized in step 1) is reacted with the morpholine salt synthesized in step 2) in a second organic solvent, i.e. A hydroxyl-functionalized alkaline ionic liquid was prepared. Or, including the following steps, 1) An intermediate was synthesized from 3-chloro-1,2-propanediol and a bicyclic guanidine compound in a first organic solvent and set aside for later use; 2) The intermediate synthesized in step 1) is reacted with an alcoholic solution of an inorganic base to obtain a hydroxyl-functionalized basic ionic liquid.

3. The method for preparing biodiesel from catalytic tiger nut oil according to claim 2, characterized in that, In step 1), the reaction temperature for intermediate synthesis is 80-120 ℃.

4. The method for preparing biodiesel from catalytic tiger nut oil according to claim 2, characterized in that, The molar ratio of the intermediate to the inorganic base or morpholine salt is 1:0.5-1:

2.

5. The method for preparing biodiesel from catalytic tiger nut oil according to claim 2, characterized in that, The inorganic base is KOH or NaOH.

6. The method for preparing biodiesel from catalytic tiger nut oil according to claim 2, characterized in that, The first organic solvent is one of toluene, acetonitrile, tetrahydrofuran, and ethyl acetate; the second organic solvent is ethanol.

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