CN103521263B - Morpholine salt ionic-liquid catalyst, Its Preparation Method And Use - Google Patents

Abstract

The invention relates to a morpholine salt ionic liquid catalyst and a preparation method thereof, and a method for preparing biodiesel from waste grease catalyzed by the morpholine salt ionic liquid. The general formula of the catalyst of the present invention is (I), and it is prepared by the following method: N-methylmorpholine reacts with halogenated alkanes to synthesize an intermediate; uses morpholine to react with an alcoholic solution of an inorganic base or salt to synthesize a morpholine salt; the intermediate and The morpholinium salt is reacted to obtain a morpholinium salt-based ionic liquid catalyst. The ionic liquid is prepared by a two-step method, and the raw material is cheap. Waste oil and alkyl alcohol are used as raw materials, and the morpholine salt ionic liquid of the present invention is used as a catalyst to prepare biodiesel; after the reaction, the ionic liquid and the product are automatically phase-separated. Utilizing the catalyst of the present invention to prepare biodiesel has the following advantages: high catalyst activity and less consumption; mild catalyst preparation conditions, low toxicity and easy degradation; mild reaction conditions and short reaction time; simple reaction process, easy separation of products, and no pollution , high yield.

Description

Morpholine salt-based ionic liquid catalyst, preparation method and use thereof

technical field

The invention relates to a morpholine-based ionic liquid catalyst, a preparation method thereof, and the use and method of using the morpholine ionic liquid catalyst as a catalyst to catalyze waste oil and alkyl alcohol to prepare biodiesel, belonging to the technical field of ionic liquid catalysis.

Background technique

With the development of the economy, human beings have higher and higher requirements for energy and quality of life, which also brings problems such as energy shortage and environmental pollution. Diesel resources are limited, so humans began to turn to the research direction of renewable biodiesel. Biodiesel, also known as fuel methyl ester, is the reaction of triglycerides extracted from animal and plant fats with methanol or ethanol under the action of a certain catalyst, using methoxy to replace the glyceryl groups on long-chain fatty acids, and breaking the glyceryl groups Form three long-chain fatty acid methyl esters, thereby reducing the length of the carbon chain, reducing the viscosity of the oil, improving the fluidity, gasification and combustion performance of the oil, and meeting the standards of commercial fuels.

Ionic liquids, also known as room temperature molten salts, refer to salt compounds that have a melting point below 100°C and are liquid at room temperature, and are composed entirely of anions and cations. In recent years, due to its advantages such as low vapor pressure, non-volatile, low toxicity and easy recycling, it has been widely concerned. Ionic liquids have a wide liquid temperature range, low melting point, good chemical stability, a wide variety and can be designed, high conductivity, wide electrochemical window, can dissolve most organic and inorganic substances, and make chemical reactions proceed smoothly in a homogeneous phase. The volume of the reactor is greatly reduced. At present, it has its application in the fields of electrochemistry, electroplating, organic, analysis, catalysis, lubrication and so on. It can be used to catalyze the preparation of biological oil.

US2009270248 discloses a novel alkaline ionic liquid [Cat ⁺ -Z-Bas] [X ^- ], wherein Cat ⁺ = cationic moiety, Bas = basic moiety, Z = covalent bond connecting Cat ⁺ and Bas; or 1, 2, or 3 aliphatic divalent linking groups, each of which contains 1 to 10 carbon atoms and optionally contains 1, 2, or 3 oxygen atoms; X ^- = anionic moiety, and with the proviso that Bas is not -OH. Its basic part is represented by cations, which are designed to adapt to the catalysis and separation of chemical processes in the most effective way according to the reaction environment. Compared with conventional solvent systems, the ionic liquid of this invention has low vapor pressure, adjustable polarity and performance and high thermal stability. And the basic series of ionic liquids are obtained by reacting alkyl halides with excess diazabicyclo[2,2,2]octane.

WO2012121447A1 discloses a composite ionic liquid, which is used as a catalyst to perform esterification and acetylation reactions to synthesize acetyl tri-n-butyl citrate. The structure of the composite ionic liquid is as follows:

Where X represents HSO ₄ ^- , H ₂ PO ₄ ^- , CH ₃ SO ₃ ^- , BF ₄ ^- . The composite ionic liquid has stronger acidity than inorganic strong acids, and is miscible with raw materials. The synthesis process is simple, the conversion rate is high, the esterification selectivity is greater than 99%, the yield is more than 98%, and there are few by-products, and no decolorization and filtration are required. Etc. Moreover, the catalyst can be used repeatedly, and the subsequent acetylation reaction has low reaction temperature, short production cycle, low equipment investment, low energy consumption and low cost.

CN101856512 discloses a technology for preparing biodiesel from catering waste oils and fats catalyzed by alkaline imidazole-based alkaline ionic liquids. The molecular formula of the alkaline ionic liquid catalyst is:

This invention is mainly to carry out esterification reaction with methanol in the presence of alkaline ionic liquid as catalyst after the waste oil is dewatered, the product is recovered methanol through distillation, the crude ester is washed with saturated sodium chloride water, and then washed with hot water until neutral. Finally, a water-removing agent is added to obtain finished biodiesel. This process is simple to operate and the reaction conditions are mild, but the cost of this process is relatively high, and the industrial value of imidazole is relatively high.

CN102120728A discloses a method for preparing polyoxymethylene dimethyl ether catalyzed by caprolactam-based ionic liquids. Its structural general formula is as follows,

Where m represents an integer from 0 to 8, we usually choose m=0, 3 or 4; X- is hydrogen sulfate, dihydrogen phosphate, p-toluenesulfonate, trifluoromethanesulfonate, methylsulfonate, One of trifluoroacetate, formate, and acetate. By adjusting the types of anions, ionic liquids with different acidities can be prepared, and the synthesized ionic liquids are easier to degrade than imidazole and pyridine ionic liquids, which are more environmentally friendly and have strong reusability.

CN103031217A discloses a method for preparing biodiesel from waste oils and fats catalyzed by pyrrolidone-based alkaline ionic liquids. Its structural general formula is:

Where n represents an integer of 1-8, R is H or C1-C12 alkyl, hydroxyethyl or vinyl, and usually n=1, 2, 3, 4 or 5 alkyl substituents are selected. Under the condition of the ionic liquid, it overcomes the shortcomings of the traditional reaction such as serious corrosion of the catalyst to the equipment, slow reaction rate, long time, high energy consumption, and low yield, and the catalyst has high activity, the reaction process is simple, and the product separation is easy. , No pollution and so on.

Traditional catalysts in the prior art have problems such as severe corrosion to equipment, difficult separation of products, high energy consumption, and low yield. At present, the ionic liquid catalysts used in biodiesel are mainly acidic ionic liquids, and the cost of raw materials for their production is relatively high.

Contents of the invention

One of the objectives of the present invention is to provide a morpholinium salt-based ionic liquid with bifunctional catalytic activity, and one of the objectives is to provide a research method for preparing biodiesel from waste oil by one-step catalysis. The invention adopts waste oil and alkyl alcohol as raw materials and selects morpholine salt ionic liquid as a catalyst, which not only reduces the production cost, but also enables the reaction to proceed in a homogeneous reaction with mild reaction conditions.

To achieve the above object, the present invention adopts the following technical solutions:

A morpholino salt-based ionic liquid catalyst, which is a compound of general formula (I):

Wherein, R is an alkyl group.

Preferably, R is -CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₂ CH ₂ CH ₃ or -CH ₂ CH ₂ CH ₂ CH ₂ One _{of CH2CH3} .

One of object of the present invention also is to provide the preparation method of described morpholine salt ionic liquid catalyst, comprises the steps:

(1) Reaction of N-methylmorpholine and halogenated alkanes in a solvent to synthesize intermediates;

(2) Use morpholine to react with inorganic base or alcohol solution of salt to synthesize morpholine salt;

(3) The intermediate obtained in step (1) is reacted with the morpholinium salt obtained in step (2) in a solvent to obtain a morpholinium salt-based ionic liquid catalyst.

The halogenated alkanes can be chlorinated alkanes, brominated alkanes, iodoalkanes or fluoroalkanes; as a preferred technical solution, in the preparation method of the present invention, the halogenated alkanes described in step (1) are C1-C8 Brominated alkanes, preferably bromoethane, 1-bromopropane, 1-bromo-n-butane, 1-bromo-pentane, bromo-n-hexane, or a mixture of two or more, more preferably For n-butane bromide.

Preferably, the solvent is one or a mixture of methanol, ethanol, acetonitrile, and toluene. According to the yield and purity under the same conditions, acetonitrile is preferred.

Preferably, the molar ratio of N-methylmorpholine to halogenated alkanes is 1:0.5-2, considering the partial loss during the reaction, the amount of 1-bromo-n-butane should be slightly higher than the theoretical value, preferably 1:1 to 2, more preferably 1:1.1.

Preferably, the mass of the solvent is 20% to 50% of the mass of N-methylmorpholine, such as 22%, 25%, 29%, 33%, 38%, 41%, 44%, 47%, 49% %, etc., preferably 20% to 40%. If the amount of solvent is too small, it will affect the progress of the reaction. As the reaction progresses, the concentration will increase, which will affect the stirring. Excessive amount is not conducive to post-processing, and also increases the cost of the reaction. Therefore, the amount of the solvent selected in the present invention is 20% to 50% of the mass of N-methylmorpholine.

Preferably, the reaction temperature in step (1) is 60-120°C, for example, 63°C, 66°C, 71°C, 75°C, 79°C, 84°C, 88°C, 92°C, 99°C, 104°C , 107°C, 110°C, 114°C, 119°C, etc., preferably 60-100°C, more preferably 70-90°C;

Preferably, the reaction time is 5-15h, for example, 5.5h, 6.1h, 6.5h, 7.0h, 7.5h, 9.0h, 9.5h, 11h, 13h, 14.5h, etc., preferably 6-10h, More preferably 6-8h;

Preferably, the reaction is carried out in _N2 environment. Selecting N ₂ environment to synthesize intermediates can improve the yield and purity of the product.

As a preferred technical solution, in the preparation method of the present invention, the inorganic base or salt described in step (2) is a mixture of one or more of NaOH, KOH, NaHCO ₃ , KHCO ₃ , preferably NaOH and /or KOH, more preferably KOH.

Preferably, the alcoholic solution is methanol, ethanol, isopropanol, n-butanol, or a mixture of more than two, preferably methanol and/or ethanol, more preferably methanol.

Preferably, the molar ratio of the morpholine to the inorganic base or salt is 1:0.5-2, for example 1:0.6, 1:0.8, 1:1.1, 1:1.3, 1:1.5, 1:1.7, 1:1.5 1.9 etc., preferably 1:1.

Preferably, the temperature of the reaction is 40-100°C, such as 42°C, 46°C, 49°C, 53°C, 58°C, 63°C, 66°C, 71°C, 75°C, 79°C, 84°C, 88°C °C, 92°C, 99°C, preferably 50-90°C, more preferably 60-80°C.

Preferably, the reaction time is 0.5h-5h, such as 0.7h, 0.9h, 1.2h, 1.7h, 2.1h, 2.5h, 2.9h, 3.5h, 4.0h, 4.5h, 4.9h, etc., Preferably, it is 0.5h-3h, More preferably, it is 1h-2h.

As a preferred technical solution, in the preparation method of the present invention, the solvent described in step (3) is one or a mixture of two or more of methanol, ethanol, dichloromethane or ether.

Preferably, the ratio of the amount of the solvent to the intermediate is 1-20ml/g, that is, 1-20ml of solvent is used per gram of the intermediate, such as 3ml/g, 6ml/g, 9ml/g, 12ml/g , 16ml/g, 19ml/g, etc., preferably 3-15ml/g, more preferably 5-8ml/g.

Preferably, the molar ratio of the intermediate to the morpholinium salt is 0.9˜1.2:1, such as 0.95:1, 1.0:1, 1.05:1, 1.1:1, 1.15:1, etc.

Preferably, the reaction time is 12-24 h, such as 14 h, 16 h, 18 h, 20 h, 23 h, etc., preferably 12-15 h.

Another object of the present invention is to provide the use of the morpholinium salt-based ionic liquid catalyst in the preparation of biodiesel from waste oil.

The method of the application of the present invention is that the waste oil uses the morpholine salt ionic liquid of the present invention as a catalyst, and prepares biodiesel with alkyl alcohol through esterification and transesterification.

As a preferred technical solution, in the method of the use, the waste oil is one or a mixture of two or more of waste oil, acidified oil, and hogwash oil;

Preferably, the mass of the ionic liquid is 1% to 10% of the mass of waste oil, such as 2%, 4%, 6%, 9%, etc., preferably 1% to 7%;

Preferably, the alkyl alcohol is one or a mixture of two or more of methanol, ethanol, isopropanol, and n-butanol;

Preferably, the mass of the alkyl alcohol is 10% to 60% of the mass of the waste oil, such as 12%, 15%, 20%, 25%, 30%, 34%, 39%, 43%, 48%, 52%, 55%, 59%, etc., preferably 10% to 40%;

Preferably, the temperature of the esterification reaction and transesterification reaction is 40-90°C, such as 42°C, 46°C, 49°C, 53°C, 58°C, 63°C, 66°C, 71°C, 75°C, 79°C, 84°C, 88°C, etc., preferably 40-80°C;

Preferably, the reaction time is 1-4 hours, such as 1.2 hours, 1.7 hours, 2.1 hours, 2.5 hours, 2.9 hours, 3.5 hours, 3.8 hours, etc., preferably 1-3 hours.

The present invention has following beneficial effect:

1. The synthesis conditions of the selected ionic liquid are mild, the reaction is simple, and the cost of raw materials is lower than that of imidazole-based ionic liquids that have been studied more at present, providing favorable conditions for realizing industrialization.

2. The selected ionic liquid catalyst has high activity, low dosage and low toxicity.

3. The utilization rate of the raw materials used in the preparation of biodiesel is high, the reaction is carried out in a homogeneous reaction, and the product is automatically phase-separated after the reaction.

4. The selected ionic liquid has a wide temperature range, strong alkalinity, easy control of the reaction process, and strong reusability of the catalyst.

5. The product in the preparation of biodiesel is non-polluting and does not cause problems such as corrosion to equipment. The production process is green and environmentally friendly, and the production cost is reduced.

Detailed ways

The technical solutions of the present invention will be further described below through specific embodiments.

Described alkaline ionic liquid catalyst is:

The preparation method of ionic liquid 1 is as follows:

(1) In _N2 environment, react N-methylmorpholine and ethyl bromide at a molar ratio of 1:1.1 in acetonitrile at 70°C for 12 hours to synthesize an intermediate, wherein the mass of acetonitrile is N-methylmorpholine 20% of the mass;

(2) Use the methanol solution of morpholine and KOH to react at 60°C for 0.5h to synthesize morpholine salt, wherein the molar ratio of morpholine to KOH is 1:1;

(3) The intermediate obtained in step (1) and the morpholine salt obtained in step (2) were reacted in dichloromethane at room temperature for 24 h at a molar ratio of 1:1 to obtain a morpholine salt-based ionic liquid catalyst 1, wherein the solvent The ratio of the amount to the intermediate is 5ml/g.

The preparation method of ionic liquid 2 is as follows:

(1) In _N2 environment, N-methylmorpholine and 1-bromopropane react in methanol at 70°C for 12 hours at a molar ratio of 1:0.8 to synthesize an intermediate, wherein the mass of methanol is N-methyl? 35% of the mass of morphine;

(2) Use the ethanol solution of morpholine and NaOH to react at 60°C for 0.5h to synthesize morpholine salt, wherein the molar ratio of morpholine to NaOH is 1:0.5;

(3) The intermediate obtained in step (1) and the morpholine salt obtained in step (2) were reacted in methanol at room temperature for 24 hours at a molar ratio of 0.9:1 to obtain a morpholine salt-based ionic liquid catalyst 2, wherein the amount of solvent The ratio to the intermediate is 20ml/g.

The preparation method of ionic liquid 3 is as follows:

(1) N-methylmorpholine and 1-iodo-n-butane are reacted in ethanol at 70°C for 12 hours at a molar ratio of 1:1.5 to synthesize an intermediate, wherein the mass of ethanol is 1/2 of the mass of N-methylmorpholine 30%;

(2) Synthesize morpholine salt by reacting morpholine with NaOH and KOH alcohol solution at 60°C for 0.5h, wherein the molar ratio of morpholine to NaOH and KOH is 1:2;

(3) The intermediate obtained in step (1) and the morpholine salt obtained in step (2) were reacted in ethanol at room temperature for 24 hours at a molar ratio of 1.2:1 to obtain a morpholine salt-based ionic liquid catalyst 3, wherein the amount of solvent The ratio to the intermediate was 1 ml/g.

The preparation method of ionic liquid 4 is as follows:

(1) In _N2 environment, N-methylmorpholine and 1-chloro-n-pentane are reacted in toluene at 60°C for 0.5h at a molar ratio of 1:0.5 to synthesize an intermediate, wherein the mass of toluene is N-methyl 40% of the mass of morpholine;

(2) Use the alcohol solution of morpholine and KHCO ₃ to react at 60°C for 0.5h to synthesize morpholine salt, wherein the molar ratio of morpholine to KHCO ₃ is 1:1.5;

(3) The intermediate obtained in step (1) and the morpholine salt obtained in step (2) were reacted in diethyl ether at room temperature for 24 h at a molar ratio of 1.1:1 to obtain a morpholine salt-based ionic liquid catalyst 4, wherein the amount of solvent The ratio to the intermediate is 10ml/g.

The preparation method of ionic liquid 5 is as follows:

(1) In _N2 environment, N-methylmorpholine and 1-bromo-n-hexane are reacted in acetonitrile at 60°C for 0.5h at a molar ratio of 1:2 to synthesize an intermediate, wherein the mass of acetonitrile is N-methyl 50% of the mass of morpholine;

(2) Use the alcohol solution of morpholine and NaHCO ₃ to react at 60°C for 0.5h to synthesize morpholine salt, wherein the molar ratio of morpholine to NaHCO ₃ is 1:1.7;

(3) The intermediate obtained in step (1) and the morpholine salt obtained in step (2) were reacted in a mixed solvent of methanol and ether at room temperature for 24 hours at a molar ratio of 1:1 to obtain a morpholine salt-based ionic liquid catalyst 5 , wherein the ratio of the amount of solvent to the intermediate is 15ml/g.

The following examples are examples of preparing biodiesel using the ionic liquids 1-5 prepared above.

Example 1:

Add 20.13g of pretreated waste grease (its acid value is 13.12) into a 100ml three-necked flask, put it into a water bath with a stirring device, insert a thermometer and a condenser tube, turn on the condensed water, and heat the water bath to a temperature of 40°C. Add 2.18 g of methanol and 0.21 g of ionic liquid (1), heat and reflux at 40°C for 2 h, transfer to a separatory funnel after the reaction, and separate layers, the upper layer of crude biodiesel and methanol, the lower layer of glycerin and catalyst. The lower layer was distilled under reduced pressure at -0.04MPa and 170°C to recover the catalyst, and the upper layer was distilled under normal pressure at 70°C to recover methanol. The content of biodiesel obtained was 83.56% by GC analysis, and its acid value was 0.87.

Example 2:

Add 21.33g of pretreated waste grease (its acid value is 11.96) into a 100ml three-necked flask, put it into a water bath with a stirring device, insert a thermometer and a condenser tube, open the condensed water, and heat the water bath to a temperature of 50°C. Add 5.33g of methanol and 0.43g of ionic liquid (2), heat and reflux at 50°C for 2 hours, transfer to a separatory funnel after the reaction, and separate layers, the upper layer of crude biodiesel and methanol, the lower layer of glycerin and catalyst. The lower layer was distilled under reduced pressure at -0.04MPa and 170°C to recover the catalyst, and the upper layer was distilled under normal pressure at 70°C to recover methanol. The content of biodiesel obtained was 87.57% by GC analysis, and its acid value was measured to be 0.63.

Example 3:

Add 21.57g of pretreated waste grease (its acid value is 12.26) into a 100ml three-necked flask, put it into a water bath with a stirring device, insert a thermometer and a condenser tube, open the condensed water, and heat the water bath to a temperature of 60°C. Add 6.47g of methanol and 0.87g of ionic liquid (3), heat and reflux at 60°C for 2 hours, transfer to a separatory funnel after the reaction, and separate layers, the upper layer of crude biodiesel and methanol, the lower layer of glycerin and catalyst. The lower layer was distilled under reduced pressure at -0.04MPa and 170°C to recover the catalyst, and the upper layer was distilled under normal pressure at 70°C to recover methanol. The content of biodiesel obtained was 97.16% by GC analysis, and its acid value was 0.28.

Example 4:

Add 20.63g of pretreated waste grease (its acid value is 11.46) into a 100ml three-necked flask, put it into a water bath with a stirring device, insert a thermometer and a condenser tube, open the condensed water, and heat the water bath to a temperature of 70°C. Add 7.28g of methanol and 1.02g of ionic liquid (4), heat and reflux at 70°C for 2 hours, transfer to a separatory funnel after the reaction, and separate layers, the upper layer of crude biodiesel and methanol, the lower layer of glycerin and catalyst. The lower layer was distilled under reduced pressure at -0.04MPa and 170°C to recover the catalyst, and the upper layer was distilled under normal pressure at 70°C to recover methanol. The content of biodiesel obtained was 96.87% by GC analysis, and its acid value was measured to be 0.31.

Example 5:

Add 20.56g of pretreated waste grease (its acid value is 12.42) into a 100ml three-necked flask, put it into a water bath with a stirring device, insert a thermometer and a condenser tube, open the condensed water, and heat the water bath to a temperature of 80°C. Add 8.24g of methanol and 1.25g of ionic liquid (5), heat and reflux at 80°C for 2 hours, transfer to a separatory funnel after the reaction, and separate layers, the crude biodiesel product and methanol in the upper layer, glycerin and catalyst in the lower layer. The lower layer was distilled under reduced pressure at -0.04MPa and 170°C to recover the catalyst, and the upper layer was distilled under normal pressure at 70°C to recover methanol. The content of biodiesel obtained was 93.21% by GC analysis, and its acid value was measured to be 0.58.

Embodiment 6:

Add 20.53g of pretreated waste grease (its acid value is 12.35) into a 100ml three-necked flask, put it into a water bath with a stirring device, insert a thermometer and a condenser tube, open the condensed water, and heat the water bath to a temperature of 70°C. Add 6.17g of methanol and 0.83g of ionic liquid (3), heat and reflux at 70°C for 2 hours, transfer to a separatory funnel after the reaction, and separate layers, the upper layer of crude biodiesel and methanol, the lower layer of glycerin and catalyst. The lower layer was distilled under reduced pressure at -0.04MPa and 170°C to recover the catalyst, and the upper layer was distilled under normal pressure at 70°C to recover methanol. The content of biodiesel obtained was 96.88% by GC analysis, and its acid value was measured to be 0.31.

The applicant declares that the present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned examples, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow process can be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (17)

1. a preparation method of morpholine salt ionic liquid catalyst, comprises the steps: (1) N-methylmorpholine and halogenated alkanes react in a solvent to synthesize intermediates; (2) using morpholine to react with an alcoholic solution of an inorganic base or a salt to synthesize a morpholine salt; (3) the intermediate obtained in step (1) reacts in a solvent with the morpholinium salt obtained in step (2) to obtain a morpholinium salt-based ionic liquid catalyst; Described morpholino salt ionic liquid catalyst, it is the compound of general formula (I): Wherein, R is -CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₂ CH ₂ CH ₃ or -CH ₂ CH ₂ CH ₂ CH ₂ CH One of ₂ CH ₃ The halogenated alkane described in step (1) is C1～C8 brominated alkane; The mol ratio of N-methylmorpholine described in step (1) and halogenated alkane is 1:0.5～2; The temperature of reaction described in step (1) is 60～120 ℃, the time of reaction is 5～15h; The mol ratio of morpholine and inorganic base or salt described in step (2) is 1:0.5～2; The temperature of the reaction described in step (2) is 40-100°C, and the reaction time is 0.5h-5h; The molar ratio of intermediate and morpholine salt described in step (3) is 0.9～1.2:1; The reaction time in step (3) is 12-24 hours. 2. the preparation method according to claim 1 is characterized in that, the halogenated alkane described in step (1) is bromoethane, 1-bromopropane, 1-bromo-n-butane, 1-bromo One or more mixtures of n-pentane and 1-bromo-n-hexane. 3. The preparation method according to claim 1, characterized in that, the solvent described in step (1) is 1 or a mixture of more than 2 in methanol, ethanol, acetonitrile, and toluene. 4. the preparation method according to claim 1, is characterized in that, the quality of solvent described in step (1) is 20%～50% of N-methylmorpholine quality. 5. according to the preparation method described in any one of claim 1-4, it is characterized in that, the reaction described in step ( ₁ ) is carried out in N environment. 6. The preparation method according to any one of claims 1-4, characterized in that, the inorganic base or salt described in step (2) is one or two of NaOH, KOH, NaHCO ₃ , KHCO ₃ mixture of the above. 7. according to the preparation method described in any one of claim 1-4, it is characterized in that, the alcohol solution described in step (2) is 1 kind or 2 in methanol, ethanol, Virahol, n-butanol mixture of the above. 8. according to the preparation method described in any one of claim 1-4, it is characterized in that, the solvent described in step (3) is 1 kind or more than 2 kinds in methanol, ethanol, methylene chloride or ether mixture. 9. The preparation method according to any one of claims 1-4, characterized in that the ratio of the amount of the solvent to the intermediate in step (3) is 1-20ml/g. 10. The use of the morpholine salt ionic liquid catalyst prepared by the preparation method according to any one of claims 1-9, characterized in that the morpholine salt ionic liquid catalyst is used to catalyze waste oil to prepare biodiesel. 11. the method for the described purposes of claim 10 is characterized in that, waste grease is catalyzed with the morpholine salt ionic liquid that preparation method described in any one of claim 1-9 makes, with alkyl alcohol by esterification and transesterification to produce biodiesel. 12. The method according to claim 11, characterized in that the waste oil is one or a mixture of two or more of waste oil, acidified oil, and hogwash oil. 13. The method according to claim 11, characterized in that the mass of the ionic liquid is 1% to 10% of the mass of waste oil. 14. The method according to claim 11, wherein the alkyl alcohol is one or a mixture of two or more of methanol, ethanol, isopropanol, and n-butanol. 15. The method according to claim 11, characterized in that the mass of the alkyl alcohol is 10% to 60% of the mass of the waste oil. 16. The method according to claim 11, characterized in that the temperature of the esterification reaction and transesterification reaction is 40-90°C. 17. The method according to claim 11, characterized in that the reaction time is 1-4 hours.