A method for preparing biodiesel using lipase catalysis

Abstract

The present application discloses a method for preparing biodiesel using lipase catalysis, which relates to the field of biodiesel. The biodiesel enzymatic reaction process comprises: raw oil pretreatment, enzymatic transesterification reaction, acid reduction treatment, and fatty acid salt modification. The acid reduction treatment step comprises: passing the obtained crude biodiesel through an oil-water separator to further remove water, passing the dehydrated crude biodiesel into a reactor containing a low concentration of potassium hydroxide methanol solution for multiple acid reduction reactions, and obtaining acid-reduced biodiesel after the reaction. Methylacrylic anhydride and tertiary butylhydroquinone are subjected to an esterification reaction, and the synthesized product is subjected to a halogenation reaction with copper chloride. The resulting product is used to modify the fatty acid salts in the acid-reduced biodiesel to obtain the biodiesel of the present application. The present application has the effects of reducing the acidity of biodiesel, avoiding saponification reaction, improving anti-emulsification ability, and lowering the freezing point.

Description

Technical Field

[0001] The present application relates to the field of biodiesel, and in particular to a method for preparing biodiesel using lipase catalysis. Background Art

[0002] Biodiesel refers to fatty acid methyl esters or ethyl esters formed by esterification of vegetable oils, animal oils, waste oils, or microbial oils with methanol or ethanol. It is a typical "green energy" with good environmental performance, good fuel performance, and renewable characteristics. Traditional biodiesel production processes mostly use acid-base catalysts. At present, lipase is more widely used for biodiesel production. The enzymatic catalytic process has the advantages of mild reaction conditions, low alcohol dosage, and no pollutant emissions. However, a certain amount of unreacted free fatty acids will remain in the produced biodiesel. These acidic substances not only affect the quality of biodiesel, but also the performance and service life of diesel engines. Therefore, reducing the content of free fatty acids has become one of the problems that must be solved in the production of biodiesel.

[0003] For related technology, see Chinese invention patent application publication number CN1382762A, which discloses a process for producing biodiesel from waste animal and vegetable oils. This process uses a low-concentration alkaline solution to neutralize the free fatty acids in the crude biodiesel product, converting them into fatty acid salts, which are then removed by water washing. This method effectively reduces the acid value of the biodiesel product.

[0004] Regarding the above-mentioned related technologies, the inventors believe that there are the following defects: when the alkaline solution neutralizes the fatty acids in biodiesel, a saponification reaction easily occurs in a water environment to generate soap, which affects the quality of biodiesel and reduces the yield of biodiesel. Summary of the Invention

[0005] In order to reduce the occurrence of saponification reaction, lower the fatty acid content of biodiesel, and ensure the quality of biodiesel products, the present application provides a method for preparing biodiesel using lipase catalysis.

[0006] In a first aspect, the present application provides a method for preparing biodiesel using lipase catalysis, which adopts the following technical solution:

[0007] A method for preparing biodiesel using lipase catalysis includes: a raw oil pretreatment process, an enzymatic transesterification reaction process, and an acid reduction treatment process. The acid reduction treatment process includes the following steps:

[0008] The obtained crude biodiesel is dehydrated, and 0.3-1.2 parts by mass of a 10% potassium hydroxide methanol solution is added to the dehydrated crude biodiesel to perform an acid reduction reaction. After the acid reduction reaction is completed, an acid reduction product is obtained, and the acid reduction product is dehydrated again; after several rounds of the above acid reduction reaction, the acid-reduced biodiesel is obtained.

[0009] By adopting the above technical scheme, by controlling the amount of potassium hydroxide methanol solution, reaction time and reaction temperature, and removing free fatty acids in biodiesel through several acid reduction reactions, the saponification reaction in the biodiesel acid reduction process can be effectively avoided. This is because the saponification reaction refers to the reaction of an alkaline solution with oil esters to generate alcohols and fatty acid salts, but the reaction rate is slow at room temperature, while the reaction rate of the neutralization of fatty acids with alkaline solution to generate fatty acid salts is faster. In addition, the esters in biodiesel are easily hydrolyzed under the catalysis of alkali. Therefore, by controlling the reaction temperature, time and content of the alkaline solution, the occurrence of saponification reaction can be effectively reduced and the acid reduction reaction of the alkaline solution and fatty acids can be promoted. The saponification reaction can be reduced by dehydrating before the acid reduction reaction because whether it is the acid reduction reaction of fatty acids with alkaline solution or the saponification reaction of oils and fats with alkaline solution, the product contains fatty acid salts, and fatty acid salts are an emulsifier that is easily emulsified in water and difficult to separate. Therefore, timely dehydration can inhibit the emulsification of fatty acid salts.

[0010] Preferably, the conditions for the acid reduction reaction are a reaction temperature of 40-60° C. and a reaction time of 25-50 min.

[0011] By adopting the above technical solution, by controlling the reaction temperature, time and content of the alkaline solution, the occurrence of saponification reaction can be effectively reduced, and the acid reduction reaction of the alkaline solution and fatty acids can be promoted;

[0012] Preferably, the method for preparing biodiesel using lipase catalysis further comprises: a fatty acid salt modification process, specifically comprising the following steps:

[0013] S1. Methacrylic anhydride and tert-butylhydroquinone in a weight ratio of 1:(2-3) are subjected to an esterification reaction in the presence of a toluenesulfonic acid catalyst. After the esterification reaction is completed, the mixture is allowed to stand at room temperature, the toluenesulfonic acid catalyst is removed by filtration, and unreacted methacrylic anhydride and tert-butylhydroquinone are removed by centrifugation to obtain methacrylic acid-tert-butylphenol ester; copper chloride catalyst and ethanol solution are added to the obtained methacrylic acid-tert-butylphenol ester, heated and stirred, and after the reaction is completed, copper chloride is removed by filtration to obtain a filtrate, and the filtrate is subjected to reduced pressure distillation to remove ethanol to obtain chloromethacrylic acid-tert-butylphenol ester;

[0014] S2 10-23 parts of chloromethacrylate prepared in S1 - tert-butyl tert-phenol ester was added to the acid-treated biodiesel, 1.2-3 parts of aluminum chloride was added as a catalyst, the acid-treated biodiesel was modified with fatty acid salts, the reaction was completed by filtering to remove aluminum chloride, and biodiesel was obtained;

[0015] S3. The obtained biodiesel was distilled under reduced pressure at a pressure of 0.2 MPa and a temperature of 210°C for 5-6 hours to obtain refined biodiesel.

[0016] By adopting the above technical solution, the fatty acid salt in biodiesel is modified, which can reduce the easy emulsification property of the fatty acid potassium in biodiesel and at the same time achieve the effect of lowering the freezing point of biodiesel.

[0017] Preferably, the weight ratio of the methacrylate-tert-butylphenol to copper chloride is 1:(1-3).

[0018] By adopting the above technical solution, copper chloride is used as a substituent to undergo a halogenation reaction with methacrylate-tert-butylphenol to generate chloromethacrylate-tert-butylphenol, which can be used to modify the fatty acid salt in biodiesel, thereby reducing the easy emulsification property of the fatty acid potassium in the biodiesel.

[0019] Preferably, the reaction temperature of the fatty acid salt modification reaction is 50-65° C., and the reaction time is 2-5 h.

[0020] By adopting the above technical solution, chloromethacrylate-tert-butylphenol ester is reacted with fatty acid salt to undergo a nucleophilic substitution reaction to generate fatty acid-methacrylate-tert-butylphenol ester and potassium chloride, the easy emulsification property of fatty acid potassium in biodiesel can be reduced, and the freezing point of biodiesel can also be reduced.

[0021] Preferably, the crude oil pretreatment process comprises the following steps:

[0022] The crude oil is preliminarily filtered to remove insoluble solid impurities to obtain coarsely filtered crude oil; an aqueous formic acid solution is added to the coarsely filtered crude oil for stirring and degumming; the degummed crude oil is flash-dehydrated at a temperature of 90-100°C and a pressure of 0.01-0.02 MPa; the dehydrated crude oil is further finely filtered to remove trace impurities therein, thereby obtaining pretreated oil.

[0023] By adopting the above technical solution, insoluble solid impurities in the raw oil can be removed, especially raw oil such as catering waste oil, which usually contains a large amount of food residues, which can be removed when passing through the filter pool. After removing the impurities, the phospholipids and other colloidal substances in the raw oil can be removed by degumming, and it also plays the role of water washing to remove impurities. The raw oil can be quickly dehydrated by flash dehydration. At the same time, the reaction is set under vacuum system conditions, and the oil is not easily oxidized. Finally, further fine filtration is carried out through a three-stage filter. The accuracy of the three-stage filter can reach 1μm, which can effectively filter out trace impurities.

[0024] Preferably, the enzymatic transesterification reaction process comprises the following steps:

[0025] 50-80 parts of pretreated oil, 4.8-7.2 parts of methanol solution, and 4-6 parts of solvent are subjected to a transesterification reaction under the catalysis of 1.8-6 parts of immobilized lipase; after the reaction, the lower layer of glycerol is separated by centrifugation, and then the upper layer of methyl ester and oil are added again to 4.8-7.2 parts of methanol solution and 4-6 parts of solvent, and a transesterification reaction is carried out under the catalysis of 1.8-6 parts of immobilized lipase. After the reaction, the methyl ester and oil are separated by centrifugation; after the reaction, crude biodiesel is obtained after several cycles of the above reaction steps;

[0026] By adopting the above technical solution, using lipase as a catalyst, and carrying out transesterification to prepare biodiesel, it is possible to effectively avoid the problems of equipment damage and multiple side reactions caused when acid and alkali are used as catalysts. When lipase is used as a catalyst, the free fatty acids in the oil and fat react with the added methanol to produce fatty acid methyl esters, which are the main components of biodiesel. At the same time, the triglycerides in the oil and fat react with methanol under the promotion of lipase to produce fatty acid methyl esters and glycerol. By controlling the amount of methanol solution to carry out transesterification multiple times, the contact between lipase and methanol in the reaction can be reduced, the activity of lipase can be better protected, and the yield can also be increased. Due to the relatively large density of glycerol, after completing a transesterification reaction, glycerol is removed by centrifugation, and then the separated methyl esters and oil are sent to the next reactor to reduce the contact between glycerol and lipase and protect the activity of lipase. Preferably, the immobilized lipase can be selected from Novozymes 435 lipase, Thermomyces lanuginosa lipase, and Candida antarctica immobilized lipase.

[0027] By adopting the above technical solution, the use of immobilized lipase can alleviate the toxic effects of methanol and glycerol on the enzyme to a certain extent and improve the operational stability of the enzyme. This is because the cost of lipase catalyst is relatively high, free lipase is extremely unstable and easily affected by the environment, and the glycerol solution generated by methanol and transesterification reaction can easily lead to lipase inactivation.

[0028] Preferably, the solvent is petroleum ether.

[0029] By adopting the above technical solution, the addition of solvent can reduce the concentration of the reaction substrate, increase the contact surface area with lipase, reduce the toxic effect of the reactant on the enzyme, significantly improve the esterification rate, and increase the yield.

[0030] Preferably, the reaction conditions of the transesterification reaction are: reaction temperature 40-60° C., reaction pressure 0.1-0.2 MPa, and reaction time 7-9 h.

[0031] By adopting the above technical solution and using transesterification reaction, free fatty acids in oils and fats can undergo esterification reaction with added methanol to generate fatty acid methyl esters, which are the main components of biodiesel.

[0032] In summary, this application includes at least one of the following beneficial technical effects:

[0033] 1. By adopting the above technical solution, the amount of potassium hydroxide methanol solution, reaction time, and reaction temperature are controlled to remove free fatty acids in biodiesel through several acid reduction reactions, effectively avoiding saponification during the biodiesel acid reduction process. 2. By adopting the above technical solution, the use of immobilized lipase can alleviate the toxic effects of methanol and glycerol on the enzyme to a certain extent, thereby improving the operational stability of the enzyme.

[0034] 3. By adopting the above technical solution, using chloromethylacrylate-tert-butylphenol ester and fatty acid salt to carry out nucleophilic substitution reaction, the easy emulsification property of fatty acid potassium in biodiesel can be reduced, and at the same time, the effect of lowering the freezing point of biodiesel can be achieved. DETAILED DESCRIPTION

[0035] The present application is further described in detail below with reference to the embodiments.

[0036] Example

[0037] Example 1

[0038] The present invention discloses a method for preparing biodiesel using lipase catalysis, comprising the following steps:

[0039] S1. The waste cooking oil is passed through a filter tank for primary filtration to remove insoluble solid impurities from the waste cooking oil, obtaining coarsely filtered waste cooking oil. The coarsely filtered waste cooking oil is passed through a settling kettle, where 4 kg of a 90% by mass formic acid solution is added for degumming. The degummed waste cooking oil is passed through a vacuum dehydration kettle for flash dehydration at 100°C and 0.01 MPa. The dehydrated waste cooking oil is then finely filtered through a three-stage filter to remove trace impurities, obtaining pretreated oil.

[0040] S2. 1.8 kg of immobilized lipase catalyst was fixed inside reactor No. 1. In this example, the immobilized lipase catalyst selected was Thermomyces lanuginosus lipase. 50 kg of pretreated oil was introduced into the reactor from the top. 4.8 kg of methanol solution and 4 kg of petroleum ether were introduced from the bottom of the reactor. The reaction temperature was controlled at 40°C, the pressure was 0.1 MPa, and the reaction time was 7 h. After the reaction was completed, the resulting methyl ester, glycerol, and unreacted oil mixture was fed to a glycerol separator and centrifuged at 40°C and 2600 rpm to separate the glycerol. The glycerol was recovered from the bottom of the separator.

[0041] S3. After the removal of glycerol, the methyl ester and oil were sent to the reactor No. Ⅱ to repeat the step of S2. After the reaction, the glycerol was separated by a glycerol separator; the separated methyl ester and oil were sent to the reactor No. Ⅲ to repeat the step of S2. After the glycerol was separated by a glycerol separator, crude biodiesel was obtained;

[0042] S4. The crude biodiesel obtained was further dehydrated by passing it through an oil-water separator. The dehydrated crude biodiesel was introduced into a reactor, and 0.3 kg of a 10% potassium hydroxide methanol solution was added to the reactor for acid reduction reaction. The reaction temperature was controlled at 40 ° C and the reaction time was 25 min. After the reaction, a primary acid reduction product was obtained. The primary acid reduction product was then dehydrated by passing it through an oil-water separator, and after dehydration, it was introduced into the reactor again to repeat the above acid reduction step to obtain a secondary acid reduction product after dehydration.

[0043] S5. Place 50 kg of methacrylic anhydride in an esterification reactor, add tert-butylhydroquinone at a weight ratio of 1:2, add p-toluenesulfonic acid as a catalyst at a solid-liquid ratio of 0.05:1, control the reaction temperature to 90 ° C, and carry out the esterification reaction for 4 hours. After the esterification reaction is completed, let it stand to room temperature and filter to remove p-toluenesulfonic acid; place it in a centrifuge and centrifuge at 30 ° C and 1200 rpm to obtain the upper layer of methacrylic acid-tert-butyl tert-phenol ester. Take 25 kg of methacrylic acid-tert-butyl tert-phenol ester and add it to the reactor. Add copper chloride catalyst to the reactor at a weight ratio of 1:1, add 0.01 kg of ethanol, heat to 50 ° C, stir and react for 4 hours, filter and remove copper chloride after the reaction to obtain a filtrate, and distill the filtrate under reduced pressure at 60 ° C and 0.10.1 MPa to remove ethanol to obtain chloromethacrylic acid-tert-butyl tert-phenol ester;

[0044] S6 10kg S6 prepared chloromethacrylate - tert-butyl tert-phenol ester and 10kg S5 obtained by the secondary acid reduction product was introduced into the reactor, 1.2kg of aluminum chloride was added as a catalyst, the reaction temperature was controlled at 50 ° C, the reaction time was 2h for fatty acid salt modification reaction, the reaction was completed by filtration to remove aluminum chloride, that is, biodiesel;

[0045] S7. The obtained biodiesel is distilled under reduced pressure at a pressure of 0.2 MPa and a temperature of 210° C. for 5-6 hours to obtain refined biodiesel.

[0046] Example 2-15

[0047] The difference between Example 2-15 and Example 1 is that the process parameters of the transesterification reaction in Example 2-15 are different, as shown in Table 1:

[0048] Table 1 Process parameters of transesterification reaction

[0049]

[0050]

[0051]

[0052] Examples 16-33

[0053] The difference between Example 16-33 and Example 1 is that the process parameters of the biodiesel acid reduction treatment and the fatty acid salt modification reaction in Examples 16-33 are different, as shown in Table 2:

[0054] Table 2 Process parameters of acid reduction treatment and fatty acid salt modification reaction

[0055]

[0056]

[0057]

[0058] Comparative Example:

[0059] Comparative Examples 1-12

[0060] The difference between Comparative Examples 1-12 and Example 1 is that the process parameters of the transesterification reaction in Comparative Examples 1-12 are different, as shown in Table 3:

[0061] Table 3 Process parameters of transesterification reaction

[0062]

[0063]

[0064] Comparative Examples 13-30

[0065] The difference between Comparative Example 13-30 and Example 1 is that the process parameters of the biodiesel acid reduction treatment and the fatty acid salt modification reaction in Comparative Example 13-30 are different, as shown in Table 4:

[0066] Table 4 Process parameters of acid reduction treatment and fatty acid salt modification reaction

[0067]

[0068]

[0069]

[0070] Performance testing

[0071] 1. The kinematic viscosity of the biodiesel produced in Examples 1-15 and Comparative Examples 1-12 was measured using GB / T 265, "Method for Determination of Kinematic Viscosity and Calculation of Dynamic Viscosity of Petroleum Products," to evaluate the extent of the transesterification reaction. Kinematic viscosity is used to evaluate the progress of the transesterification reaction because fatty acid esters have lower viscosities than their corresponding fatty acids. Therefore, a lower kinematic viscosity of the biodiesel indicates a higher fatty acid ester content in the product and a more complete transesterification reaction.

[0072] 2. The lipase activity after the reaction in Examples 1-15 and Comparative Examples 1-12 was compared with the lipase activity before the experiment using GB / T 5523-2008 "Inspection of Cereals and Oils - Determination of Lipase Activity in Cereals and Oilseeds" to calculate the rate of change.

[0073] 3. The acid value of the biodiesel in Examples 1-33 and Comparative Examples 1-30 was tested using GB / T 7304 “Determination of Acid Value of Petroleum Products and Lubricants (Potentiometric Titration)”.

[0074] 4. Using the test method of GB / T 7305 "Determination of Water Separability of Petroleum and Synthetic Liquids" at a temperature of 54°C, 40 ml of the biodiesel from Examples 16-33 and Comparative Examples 13-30 were stirred with 40 ml of water. The time for the emulsion layer to decrease to 3 ml (denoted as 40-37-3) was recorded, expressed in minutes. The shorter the water separation time, the better the effect.

[0075] 5. The freezing point of the biodiesel in Examples 16-33 and Comparative Examples 13-30 was measured using GB / T 510 “Determination of freezing point of petroleum products”.

[0076] The specific test results are as follows:

[0077] (1) The kinematic viscosity, enzyme activity change rate, and acid value of the biodiesel before acid reduction treatment in Examples 1-15 and Comparative Examples 1-12 are shown in Table 5.

[0078] Table 5 Kinematic viscosity and enzyme activity change rate of biodiesel

[0079]

[0080]

[0081] From the experimental results of Examples 1-3, it can be seen that the lipase of Thermomyces lanuginosus and Novozymes 435

[0082] The experimental results of Examples 1-3 show that the lipase from Thermomyces lanuginosus and Novozymes 435 have higher catalytic activity and, under the same conditions, the esterification reaction progresses slightly faster than the immobilized lipase from Candida antarctica. Furthermore, the results of Examples 1, 4, and 5 and Comparative Examples 1 and 2 show that a greater amount of immobilized lipase reduces the kinematic viscosity of the biodiesel, indicating a greater rate of transesterification. However, when the amount of immobilized lipase exceeds 6 kg, the kinematic viscosity does not change much.

[0083] From the results of Examples 1, 6, 7 and Comparative Examples 3, 4, it can be seen that the higher the methanol content, the lower the kinematic viscosity, that is, the faster the transesterification reaction progresses. However, when the amount of methanol is greater than 7.2, the kinematic viscosity begins to increase again.

[0084] From the results of Examples 1, 8, 9 and Comparative Examples 5 and 6, it can be seen that with the increase in the amount of solvent added, the kinematic viscosity continues to decrease, and the lipase activity after the reaction remains at a high activity, indicating that the addition of solvent is beneficial to protecting the activity of the enzyme and improving the esterification rate. When the amount of solvent added reaches 6 kg, the kinematic viscosity begins to increase.

[0085] From the results of Examples 1, 10, 11 and Comparative Examples 7, 8, it can be seen that increasing the reaction temperature can reduce the kinematic viscosity, but when the temperature exceeds 60°C, the kinematic viscosity begins to rise again; as the reaction temperature increases, the lipase activity gradually decreases.

[0086] From the results of Examples 1, 12, 13 and Comparative Examples 9 and 10, it can be seen that the effect of reaction pressure on kinematic viscosity also shows a trend of first increasing and then decreasing. The kinematic viscosity gradually decreases at 0.08-0.2 MPa, and when the pressure exceeds 0.2 MPa, the kinematic viscosity begins to increase; as the reaction pressure increases, the lipase activity gradually decreases.

[0087] From the results of Examples 1, 14, and 15 and Comparative Examples 11 and 12, it can be seen that the effect of reaction time on kinematic viscosity shows a trend of first increasing and then decreasing. As the reaction time increases, the kinematic viscosity increases, but when the reaction time exceeds 90 minutes, the kinematic viscosity of the obtained biodiesel no longer changes; as the reaction time increases, the lipase activity gradually decreases.

[0088] (2) The specific test results of the acid value of biodiesel in Examples 16-21 and Comparative Examples 13-18 are shown in Table 6.

[0089] Table 6 Acid value of biodiesel in Examples 16-21 and Comparative Examples 13-18

[0090]

[0091] From the comparison of Table 5 and Table 6, it can be seen that the acid value of the biodiesel provided by the present application is significantly reduced before and after the acid reduction treatment.

[0092] The test results of Example 1 and Comparative Example 13 show that the acid value increases as the mass fraction of the potassium hydroxide methanol solution increases. The results of Examples 1, 16, 17, and Comparative Example 14 show that the acid value gradually decreases as the content of the potassium hydroxide methanol solution increases; however, when the content of the potassium hydroxide methanol solution exceeds 1.2 kg, the acid value begins to rise again.

[0093] From the test results of Examples 1, 18, 19 and Comparative Examples 15, 16, it can be seen that the effect of the temperature of the acid reduction reaction on the acid value is a state of first decreasing and then increasing. When the temperature exceeds 60°C, the acid value begins to increase.

[0094] From the test results of Examples 1, 20, 21 and Comparative Examples 17, 18, it can be seen that as the acid reduction reaction time increases, the acid value gradually decreases, but when the reaction time exceeds 50 min, the acid value begins to increase.

[0095] (3) The specific test results of the demulsibility and freezing point of the biodiesel in Examples 22-33 and Comparative Examples 19-30 are shown in Table 7.

[0096] Table 7 Demulsibility and freezing point of biodiesel in Examples 22-33 and Comparative Examples 19-30

[0097]

[0098]

[0099] The test results of Examples 1, 22, and 23 and Comparative Examples 19 and 20 show that the weight ratio of methacrylic anhydride to tert-butylhydroquinone affects both the demulsibility and the freezing point of the modified biodiesel. When the proportion of tert-butylhydroquinone increases, the demulsibility of the modified biodiesel is improved and the freezing point is reduced. When the weight ratio of methacrylic anhydride to tert-butylhydroquinone exceeds 1:3, the demulsibility of the biodiesel no longer changes, and the freezing point begins to rise.

[0100] The test results of Examples 1, 24, and 25 and Comparative Examples 21 and 22 show that when the weight ratio of methacrylate-tert-butylphenol to copper chloride increases, the demulsification ability of the modified biodiesel is improved and the freezing point is reduced; when the weight ratio of methacrylate-tert-butylphenol to copper chloride reaches 1:3, the demulsification ability and freezing point of the biodiesel no longer change.

[0101] The test results of Examples 1, 26, and 27 and Comparative Examples 23 and 24 show that in the fatty acid salt modification reaction, aluminum chloride is used as a catalyst. As the aluminum chloride content increases, the anti-emulsification ability of biodiesel increases and the freezing point decreases; however, when the catalyst content exceeds 3 kg, the anti-emulsification ability and freezing point of biodiesel no longer change, and the freezing point begins to rise.

[0102] The test results of Examples 1, 28, 29 and Comparative Examples 25 and 26 show that when the content of chloromethacrylate-tert-butylphenol increases, the demulsification ability is improved and the freezing point is reduced. When the amount of chloromethacrylate-tert-butylphenol exceeds 23 kg, the demulsification ability no longer changes.

[0103] From the test results of Examples 1, 30, 31 and Comparative Examples 27, 28, it can be seen that increasing the temperature of the modification reaction can improve the anti-emulsification ability of biodiesel and reduce the freezing point. However, when the temperature exceeds 60°C, the anti-emulsification ability decreases and the freezing point increases.

[0104] From the test results of Examples 1, 32, 33 and Comparative Examples 29, 30, it can be seen that increasing the modification reaction time can improve the anti-emulsification ability of biodiesel and reduce the freezing point. However, when the time exceeds 5h, the anti-emulsification ability decreases and the freezing point increases.

[0105] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing biodiesel using lipase catalysis, characterized in that: A method for preparing biodiesel using lipase catalysis includes: a raw oil pretreatment process, an enzymatic transesterification reaction process, an acid reduction treatment process, and a fatty acid salt modification process; The acid reduction treatment process comprises the following steps: Dehydrating the obtained crude biodiesel, adding 0.3-1.2 parts by mass of a 10% potassium hydroxide methanol solution to the dehydrated crude biodiesel for an acid reduction reaction, obtaining an acid reduction product after the acid reduction reaction, and dehydrating the acid reduction product again; and performing the above acid reduction reaction several times to obtain acid-reduced biodiesel. The fatty acid salt modification process specifically comprises the following steps: S1. Methacrylic anhydride and tert-butylhydroquinone in a weight ratio of 1:(2-3) are subjected to an esterification reaction in the presence of a toluenesulfonic acid catalyst. After the esterification reaction is completed, the mixture is allowed to stand at room temperature, the toluenesulfonic acid catalyst is removed by filtration, and unreacted methacrylic anhydride and tert-butylhydroquinone are removed by centrifugation to obtain methacrylic acid-tert-butylphenol ester; copper chloride catalyst and ethanol solution are added to the obtained methacrylic acid-tert-butylphenol ester, heated and stirred, and after the reaction is completed, copper chloride is removed by filtration to obtain a filtrate, and the filtrate is subjected to reduced pressure distillation to remove ethanol to obtain chloromethacrylic acid-tert-butylphenol ester; S2 10-23 parts of chloromethacrylate prepared in S1 - tert-butyl tert-phenol ester was added to the acid-treated biodiesel, 1.2-3 parts of aluminum chloride was added as a catalyst, the acid-treated biodiesel was modified with fatty acid salts, the reaction was completed by filtering to remove aluminum chloride, and biodiesel was obtained; S3. The obtained biodiesel was distilled under reduced pressure at a pressure of 0.2 MPa and a temperature of 210°C for 5-6 hours to obtain refined biodiesel.

2. The method for preparing biodiesel using lipase catalysis according to claim 1, characterized in that: The conditions for the acid reduction reaction are a reaction temperature of 40-60° C. and a reaction time of 25-50 min.

3. The method for preparing biodiesel using lipase catalysis according to claim 1, characterized in that: The weight ratio of the methacrylate-tert-butylphenol to copper chloride is 1:(1-3).

4. The method for preparing biodiesel using lipase catalysis according to claim 1, characterized in that: The reaction temperature of the fatty acid salt modification reaction is 50-65° C., and the reaction time is 2-5 hours.

5. The method for preparing biodiesel using lipase catalysis according to claim 1, characterized in that: The raw oil pretreatment process comprises the following steps: The crude oil is preliminarily filtered to remove insoluble solid impurities to obtain coarsely filtered crude oil; an aqueous formic acid solution is added to the coarsely filtered crude oil for stirring and degumming; the degummed crude oil is flash-dehydrated at a temperature of 90-100°C and a pressure of 0.01-0.02 MPa; the dehydrated crude oil is further finely filtered to remove trace impurities therein, thereby obtaining pretreated oil.

6. The method for preparing biodiesel using lipase catalysis according to claim 1, characterized in that: The enzymatic transesterification reaction process comprises the following steps: 50-80 parts of pretreated oil, 4.8-7.2 parts of methanol solution and 4-6 parts of solvent are subjected to transesterification reaction under the catalysis of 1.8-6 parts of immobilized lipase; after the reaction, the lower layer of glycerol is separated by centrifugation, and then the methyl ester and oil in the upper layer are added again to 4.8-7.2 parts of methanol solution and 4-6 parts of solvent, and transesterification reaction is carried out under the catalysis of 1.8-6 parts of immobilized lipase. After the reaction is completed, the methyl ester and oil are separated by centrifugation; after the reaction is completed, the crude biodiesel is obtained after several times of the above reaction steps.

7. The method for preparing biodiesel using lipase catalysis according to claim 6, characterized in that: The immobilized lipase is selected from one of Novozymes 435 lipase, Thermomyces lanuginosus lipase, and Candida antarctica immobilized lipase.

8. The method for preparing biodiesel using lipase catalysis according to claim 6, characterized in that: The solvent is petroleum ether.

9. The method for preparing biodiesel using lipase catalysis according to claim 6, characterized in that: The reaction conditions of the transesterification reaction are: reaction temperature 40-60° C., reaction pressure 0.1-0.2 MPa, and reaction time 7-9 h.

Images