Refining and impurity removing method for by-product crude glycerine in biodiesel prepared from waste oil and fat

Abstract

The invention discloses a refining and impurity removing method for a by-product crude glycerine in biodiesel prepared from waste oil and fat. The method comprises the following steps: mixing glycerol esterified oil and alcohol-containing crude glycerol, performing pretreatment, and then performing first settling separation to obtain first grease and alcohol-containing glycerol soap; the alcohol-containing glycerin soap is subjected to dealcoholization treatment and low-boiling-point removal treatment, and dealcoholized glycerin soap is obtained; and carrying out molecular distillation treatment on the dealcoholized glycerin soap, and then carrying out secondary settling separation to obtain refined glycerin. The method provided by the invention is simple, avoids the use of additional acid-base solution, does not need to consume a large amount of water, does not generate a large amount of solid waste salt, and has the advantages of environmental protection, low energy consumption and less solid waste.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crude glycerol refining, and particularly relates to a method for refining and removing impurities from crude glycerol which is a byproduct in the preparation of biodiesel from waste oil. BACKGROUND

[0002] Biodiesel is a kind of bio-liquid fuel considered to be environmentally friendly, which is prepared from waste oil (kitchen waste oil, slightly water oil, acidified oil, etc.). This bio-fuel can be used like diesel. The most common method for preparing biodiesel is transesterification. Fatty acid esters are generated by the reaction of waste oil and alcohol (generally methanol) in the presence of a catalyst. Crude glycerol is the main byproduct of the production process, which is complex in composition and generally includes glycerol, methanol, fatty acid methyl ester, fatty acid potassium soap, potassium hydroxide, etc. If crude glycerol is directly distilled, due to the presence of fatty acid potassium soap and potassium hydroxide, fatty acid methyl ester will be converted into monoglyceride and diglyceride, etc. under high temperature conditions, and part of the glycerol will polymerize, resulting in a large amount of asphalt and low yield of refined glycerol.

[0003] In the refining process of crude glycerol, the traditional process usually adopts hydrochloric acid solution acidification treatment to reduce the fatty acid potassium soap (RCOOK) in the raw material into free fatty acid (RCOOH) and generate potassium chloride (KCl), and the potassium hydroxide (KOH) is further neutralized to generate salts; after separating the acidified oil, the acid crude glycerol solution is neutralized with sodium hydroxide (NaOH) to make the crude glycerol solution alkaline for subsequent rectification and purification. However, in this process, a large amount of water is consumed in the multi-step acid-base neutralization reaction, and a large amount of salt is generated, resulting in high energy consumption in the subsequent dehydration process and a large amount of solid waste salt.

[0004] Therefore, it is urgent to propose a new method for refining and removing impurities from alcohol-containing crude glycerol to solve the above problems. SUMMARY

[0005] The present application aims to overcome the above technical deficiencies and provide a method for refining and removing impurities from crude glycerol which is a byproduct in the preparation of biodiesel from waste oil, to solve the technical problem that the refining process of crude glycerol in the prior art consumes a large amount of water and generates a large amount of salt, resulting in high energy consumption in the subsequent dehydration process and a large amount of solid waste salt.

[0006] The present application provides a method for refining and removing impurities from crude glycerol which is a byproduct in the preparation of biodiesel from waste oil, comprising the following steps: The glycerol esterified oil and alcohol-containing crude glycerol are mixed and then pretreated, followed by first sedimentation separation to obtain first oil and alcohol-containing glycerol soap; The alcohol-containing glycerol soap is subjected to alcohol removal treatment and low-boiling removal treatment to obtain alcohol-removed glycerol soap; The alcohol-removed glycerol soap is subjected to molecular distillation treatment, followed by second sedimentation separation to obtain refined glycerol; wherein, The glycerol esterified oil is an esterification product of waste oil and glycerol, and the alcohol-containing crude glycerol is a byproduct of crude glycerol in the process of preparing biodiesel from waste oil.

[0007] Compared with the prior art, the beneficial effects of the present application include: The present application uses glycerol esterified oil to pretreat alcohol-containing crude glycerol, and utilizes the neutralization reaction and saponification reaction of free fatty acids in the glycerol esterified oil and alkali in the alcohol-containing crude glycerol. At the same time, due to the presence of alkali, partial transesterification of glycerol esterified oil and alcohol in the alcohol-containing crude glycerol will also occur in the pretreatment stage, which reduces the alkali and alcohol content in the alcohol-containing glycerol soap obtained by the first settling separation, increases the glycerol concentration, and also recovers part of the fatty acid methyl ester dispersed in the alcohol-containing crude glycerol to the first oil, reducing the loss of carried fatty acid methyl ester. Subsequently, through simple dealcoholization treatment, low-boiling removal treatment, molecular distillation treatment and settling separation treatment, refined glycerol meeting the standard requirements can be obtained. The method of the present application is simple, avoids the use of additional acid and alkali solutions, does not need to consume a large amount of water, and also does not produce a large amount of solid waste salt, having the advantages of green environmental protection, low energy consumption and less solid waste. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 is a process flow chart of an embodiment of the method for refining and removing impurities of the byproduct crude glycerol in the preparation of biodiesel from waste oil provided by the present application. DETAILED DESCRIPTION

[0009] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0010] Please refer to Figure 1 The present application provides a method for refining and removing impurities of the byproduct crude glycerol in the preparation of biodiesel from waste oil, comprising the following steps: S1, mixing glycerol esterified oil and alcohol-containing crude glycerol and then pretreating, and then obtaining first oil and alcohol-containing glycerol soap by first settling separation; S2, dealcoholizing and removing low-boiling substances from the alcohol-containing glycerol soap to obtain dealcoholized glycerol soap; S3, molecular distillation treatment of the dealcoholized glycerol soap, and then obtaining refined glycerol by second settling separation; wherein, The glyceride esterified oil is an esterification product of waste oil and glycerol, and its composition includes: 1% to 5% of monoglyceride, 10% to 20% of diglyceride, 75% to 85% of triglyceride, and an acid value of less than or equal to 3 mg KOH / g (including but not limited to 0.5 mg KOH / g, 0.8 mg KOH / g, 1 mg KOH / g, 1.2 mg KOH / g, 1.5 mg KOH / g, 2 mg KOH / g, 2.5 mg KOH / g, 3 mg KOH / g, etc.); The alcohol-containing crude glycerol is a by-product of crude glycerol in the process of preparing biodiesel from waste oil, and its composition includes: 40% to 50% of glycerol, 30% to 40% of methanol, 10% to 15% of fatty acid methyl ester, 5% to 8% of fatty acid potassium soap and 0.5% to 3% of potassium hydroxide.

[0011] The glyceride esterified oil is an esterification product of waste oil and glycerol, and its composition includes: 1% to 5% of monoglyceride, 10% to 20% of diglyceride, 75% to 85% of triglyceride, and an acid value of less than or equal to 3 mg KOH / g (including but not limited to 0.5 mg KOH / g, 0.8 mg KOH / g, 1 mg KOH / g, 1.2 mg KOH / g, 1.5 mg KOH / g, 2 mg KOH / g, 2.5 mg KOH / g, 3 mg KOH / g, etc.);

[0012] In the embodiment, in step S1, the alcohol-containing crude glycerol is added in an amount of 18% to 25% of the mass of the glyceride esterified oil, including but not limited to 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc. The present application can realize the full recycling of glyceride esterified oil and alcohol-containing crude glycerol in the preparation of biodiesel from waste oil.

[0013] In the embodiment, in step S1, alcohol is also added during the pretreatment process. The present application can play a role in demulsification by adding alcohol during the pretreatment process, and promote the separation of the first oil and the alcohol-containing glycerol soap.

[0014] Further, in step S1, the alcohol is methanol, and the amount of alcohol added is 8% to 10% of the mass of the glyceride oil, including but not limited to 8%, 8.5%, 9%, 9.5%, 10%, etc. If the amount of alcohol added is too low, it will lead to poor separation of the first oil and alcohol-containing glycerol soap in the first settling separation process, and the subsequent operation cannot be carried out; if the alcohol is added too much, it will lead to high alcohol consumption and high energy consumption.

[0015] In this embodiment, in step S1, the pretreatment temperature is 56 to 66°C, including but not limited to 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, etc., and the pretreatment time is 1 to 3h, including but not limited to 1h, 1.5h, 2h, 2.5h, 3h, etc.

[0016] In this embodiment, in step S1, the first settling separation temperature is 56 to 66°C, including but not limited to 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, etc., and the first settling separation time is 2 to 4h, including but not limited to 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0017] In this embodiment, in step S2, a vacuum alcohol removal method is used, the vacuum alcohol removal temperature is 80 to 100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc., the vacuum alcohol removal time is 30 to 90min, including but not limited to 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc., and the vacuum residual pressure is 8000 to 15000Pa, including but not limited to 8000Pa, 9000Pa, 10000Pa, 11000Pa, 12000Pa, 13000Pa, 14000Pa, 15000Pa, etc. By using the vacuum alcohol removal method and cooperating with the above process parameters, the alcohol in the alcohol-containing glycerol soap can be well removed.

[0018] In this embodiment, in step S2, a vacuum thin film low-boiling removal method is used. In the process of vacuum thin film low-boiling removal, the material inlet temperature is 140 to 160°C, including but not limited to 140°C, 145°C, 150°C, 155°C, 160°C, etc., the material outlet temperature is 160 to 180°C, including but not limited to 160°C, 165°C, 170°C, 175°C, 180°C, etc., the vacuum residual pressure is 4000 to 6000Pa, including but not limited to 4000Pa, 4500Pa, 5000Pa, 5500Pa, 6000Pa, etc., and the material residence time is 10 to 15s. By using the vacuum thin film low-boiling removal method and cooperating with the above process parameters, the low-boiling substances in the glycerol soap can be well removed.

[0019] In this embodiment, in step S3, a short-path molecular distillation is used.

[0020] In this embodiment, step S3 comprises: S31, subjecting the dealcoholized glycerol soap to primary molecular distillation to obtain a first light phase and a first heavy phase; S32, subjecting the first heavy phase to secondary molecular distillation to obtain a second light phase and a second heavy phase; S33, subjecting the first light phase and / or the second light phase to secondary settling separation to obtain refined glycerol; wherein, The first light phase is a mixture of glycerol and a small amount of fatty acid methyl ester, and the first heavy phase is a remaining concentrate; The second light phase is a mixture of glycerol and a small amount of fatty acid methyl ester, and the second heavy phase is glycerol pitch (composed of fatty acid potassium, fatty acid methyl ester, polyglycerol, potassium hydroxide, etc.).

[0021] In the present application, by adopting multi-stage molecular distillation, the content of impurities can be reduced under the premise of improving the glycerol yield.

[0022] Further, in step S31, during the primary molecular distillation, the material outlet temperature is 190-210℃, including but not limited to 190℃, 195℃, 200℃, 205℃, 210℃, etc., the vacuum residual pressure is 100-200Pa, including but not limited to 100Pa, 120Pa, 140Pa, 160Pa, 180Pa, 200Pa, etc., and the material residence time is 10-15s.

[0023] Further, in step S32, during the secondary molecular distillation, the material outlet temperature is 210-230℃, including but not limited to 210℃, 215℃, 220℃, 225℃, 230℃, etc., the vacuum residual pressure is 20-80Pa, including but not limited to 20Pa, 30Pa, 40Pa, 50Pa, 60Pa, 70Pa, 80Pa, etc., and the material residence time is 10-15s.

[0024] In this embodiment, in step S3, the temperature of the secondary settling separation is 56-66℃, including but not limited to 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, etc., and the time of the secondary settling separation is 12-36h, including but not limited to 12h, 18h, 24h, 30h, 36h, etc.

[0025] Example 1 (1) To the waste oil glycerolysis oil (monoglyceride 3.4%, diglyceride 12.5%, triglyceride 80.7%, acid value 1 mg KOH / g), 20% of alcohol-containing crude glycerol (glycerol 44.3%, methanol 36.5%, fatty acid methyl ester 12.8%, fatty acid potassium soap 5.5%, potassium hydroxide 0.77%) and 8% of methanol were added, and the mixture was pretreated at 65℃ for 2 hours, then poured into a separatory funnel, and the mixture was settled and separated at 65℃ for 3 hours to obtain the first oil and alcohol-containing glycerol soap.

[0026] (2) The alcohol-containing glycerol soap was vacuum-dealcoholized at a temperature of 90℃ for 30 min, and a vacuum residual pressure of 12000 Pa to obtain the first dealcoholized glycerol soap; the first dealcoholized glycerol soap was vacuum-dealcoholized at a material inlet temperature of 150℃, a material outlet temperature of 170℃, a vacuum residual pressure of 5000 Pa, and a material residence time of 10-15 s to obtain the second dealcoholized glycerol soap.

[0027] (3) The second dealcoholized glycerol soap was subjected to primary short-path molecular distillation at a material outlet temperature of 200℃, a vacuum residual pressure of 100 Pa, and a material residence time of 10-15 s to obtain the first light phase and the first heavy phase; the first heavy phase was subjected to secondary short-path molecular distillation at a material outlet temperature of 220℃, a vacuum residual pressure of 50 Pa, and a material residence time of 10-15 s to obtain the second light phase and the second heavy phase; the first light phase and the second light phase were mixed and poured into a separatory funnel, and the mixture was settled and separated at 60℃ for 24 hours to obtain refined glycerol and crude fatty acid methyl ester.

[0028] Example 2 (1) To the waste oil glycerolysis oil (monoglyceride 3.4%, diglyceride 12.5%, triglyceride 80.7%, acid value 1 mg KOH / g), 20% of alcohol-containing crude glycerol (glycerol 44.3%, methanol 36.5%, fatty acid methyl ester 12.8%, fatty acid potassium soap 5.5%, potassium hydroxide 0.77%) and 8% of methanol were added, and the mixture was pretreated at 65℃ for 2 hours, then poured into a separatory funnel, and the mixture was settled and separated at 65℃ for 3 hours to obtain the first oil and alcohol-containing glycerol soap.

[0029] (2) The alcohol-containing glycerol soap was vacuum-dealcoholized at a temperature of 90℃ for 30 min, and a vacuum residual pressure of 12000 Pa to obtain the first dealcoholized glycerol soap; the first dealcoholized glycerol soap was vacuum-dealcoholized at a material inlet temperature of 150℃, a material outlet temperature of 170℃, a vacuum residual pressure of 5000 Pa, and a material residence time of 10-15 s to obtain the second dealcoholized glycerol soap.

[0030] (3) The second dealcoholized glycerol soap is subjected to primary short-path molecular distillation, the material outlet temperature is 190°C, the vacuum residual pressure is 200 Pa, and the material residence time is 10-15 s, to obtain a first light phase and a first heavy phase; the first heavy phase is subjected to secondary short-path molecular distillation, the material outlet temperature is 210°C, the vacuum residual pressure is 80 Pa, and the material residence time is 10-15 s, to obtain a second light phase and a second heavy phase; the first light phase and the second light phase are mixed and then poured into a separatory funnel, and the mixture is kept at 65°C for 12 hours for settling separation, to obtain refined glycerol and crude fatty acid methyl ester.

[0031] Example 3 (1) 25% of alcohol-containing crude glycerol (glycerol 46.3%, methanol 34.2%, fatty acid methyl ester 12.7%, potassium soap of fatty acid 6.1%, potassium hydroxide 0.55%) and 10% of methanol are added to waste oil glyceride oil (monoglyceride 4.9%, diglyceride 19.2%, triglyceride 75.7%, acid value 1.5 mg KOH / g), the mixture is pretreated at 60°C for 1 hour, and then poured into a separatory funnel, and the mixture is kept at 60°C for 2 hours for settling separation, to obtain a first oil and alcohol-containing glycerol soap.

[0032] (2) The alcohol-containing glycerol soap is subjected to vacuum dealcoholization, the temperature for vacuum dealcoholization is 100°C, the time for vacuum dealcoholization is 60 min, and the vacuum residual pressure is 8000 Pa, to obtain a first dealcoholized glycerol soap; the first dealcoholized glycerol soap is subjected to vacuum dealcoholization, the material inlet temperature is 160°C, the material outlet temperature is 180°C, the vacuum residual pressure is controlled to be 4000 Pa, and the material residence time is 10-15 s, to obtain a second dealcoholized glycerol soap.

[0033] (3) The second dealcoholized glycerol soap is subjected to primary short-path molecular distillation, the material outlet temperature is 210°C, the vacuum residual pressure is 150 Pa, and the material residence time is 10-15 s, to obtain a first light phase and a first heavy phase; the first heavy phase is subjected to secondary short-path molecular distillation, the material outlet temperature is 230°C, the vacuum residual pressure is 20 Pa, and the material residence time is 10-15 s, to obtain a second light phase and a second heavy phase; the first light phase and the second light phase are mixed and then poured into a separatory funnel, and the mixture is kept at 56°C for 36 hours for settling separation, to obtain refined glycerol and crude fatty acid methyl ester.

[0034] Comparative Example 1 Compared with Example 1, the only difference is that step (1) is omitted, and the alcohol-containing crude glycerol is directly subjected to subsequent steps (2) and (3).

[0035] Comparative Example 2 Compared with Example 1, the only difference is that step (3) is as follows: (3) The second dealcoholized glycerol soap is subjected to vacuum reduced pressure distillation, the temperature in the tower is 185 DEG C, the vacuum residual pressure is 1000 Pa, the circulating reboiling heating is carried out, the light phase rises to the top of the tower and is condensed, and then is collected and poured into a separatory funnel, and then is kept at 60 DEG C for 24 hours to separate and obtain refined glycerol and crude fatty acid methyl ester.

[0036] Test group The refined glycerol, crude fatty acid methyl ester and glycerol pitch obtained in the above examples and comparative examples are tested, and the test results are shown in Table 1. Among them, The glycerol content in the refined glycerol is tested according to GB / T 13206-22; The yield of refined glycerol = the mass of refined glycerol / (the mass of alcohol-containing crude glycerol x the glycerol content in the alcohol-containing crude glycerol) x 100%; In examples 1-3 and comparative example 1, the yield of crude fatty acid methyl ester = the mass of crude fatty acid methyl ester / (the mass of the first light phase + the mass of the second light phase) x 100%; in comparative example 2, the yield of crude fatty acid methyl ester = the mass of crude fatty acid methyl ester / the mass of light phase x 100%; In examples 1-3 and comparative example 1, the yield of glycerol pitch = the mass of the second heavy phase / the mass of the second dealcoholized glycerol soap x 100%; in comparative example 2, the yield of glycerol pitch = the mass of the heavy phase / the mass of the second dealcoholized glycerol soap x 100%.

[0037] Table 1

[0038] Note: In Table 1, the crude fatty acid methyl ester also includes components such as monoglyceride, diglyceride, triglyceride, etc.

[0039] As shown in Table 1, by using the method of the examples of the present application, the yield of refined glycerol is high (the yield is ≥98%), the purity is high (the glycerol content is ≥95%), the methyl ester loss is low (≤5%), the glycerol pitch amount is low (≤3%), and the method also has the advantages of green environmental protection, low energy consumption, less solid waste and high economic value.

[0040] Compared with example 1, in comparative example 1, the alcohol-containing crude glycerol is directly subjected to dealcoholization treatment, low boiling point removal treatment, molecular distillation treatment and second sedimentation separation to prepare refined glycerol, and the yield and purity of the obtained refined glycerol are significantly reduced, and the glycerol pitch amount is large; in comparative example 2, vacuum reduced pressure distillation is used instead of molecular distillation, and the yield and purity of the obtained refined glycerol are also significantly reduced, and the glycerol pitch amount is large, which shows that by using glycerol esterified oil to pretreat the alcohol-containing crude glycerol and combining with the subsequent first sedimentation separation, dealcoholization treatment, low boiling point removal treatment, molecular distillation treatment and second sedimentation separation, the refined glycerol meeting the standard requirements can be obtained. The method of the present application is simple, and the glycerol yield is high, and has extremely high economic value.

[0041] The above description of the specific embodiments of the present application is not intended to limit the scope of the present application. Any other corresponding changes and modifications made according to the technical concept of the present application should be included in the scope of protection of the claims of the present application.

Claims

1. A method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, characterized in that, Includes the following steps: Glyceryl esterified oil and alcohol-containing crude glycerol are mixed and pretreated, and then separated by a first sedimentation to obtain a first oil and an alcohol-containing glycerol soap. The alcohol-containing glycerol soap is subjected to a dealcoholization treatment and a low-boiling point removal treatment to obtain a dealcoholized glycerol soap. The dealcoholized glycerol soap was subjected to molecular distillation, followed by a second sedimentation separation to obtain refined glycerol; wherein, The glycerol esterified oil is an esterification product of waste oil and glycerol, and the alcohol-containing crude glycerol is a by-product of the process of preparing biodiesel from waste oil.

2. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, according to claim 1, is characterized in that... The composition of the glycerol esterified oil includes: 1%~5% monoglyceride, 10%~20% diglyceride, 75%~85% triglyceride, and an acid value ≤3 mg KOH / g; the composition of the alcohol-containing crude glycerol includes: 40%~50% glycerol, 30%~40% methanol, 10%~15% fatty acid methyl ester, 5%~8% fatty acid potassium soap, and 0.5%~3% potassium hydroxide.

3. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, according to claim 1, is characterized in that... The amount of crude glycerol containing alcohol added is 18% to 25% of the mass of the glycerol esterified oil.

4. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, according to claim 1, is characterized in that... During the pretreatment process, an alcohol is also added; the alcohol is methanol, and the amount of alcohol added is 8% to 10% of the mass of the glycerol esterified oil.

5. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, according to claim 1, is characterized in that... The pretreatment temperature is 56~66℃, and the pretreatment time is 1~3h; the first sedimentation separation temperature is 56~66℃, and the first sedimentation separation time is 2~4h.

6. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, according to claim 1, is characterized in that... The method employs vacuum de-alcoholization, wherein the vacuum de-alcoholization temperature is 80~100℃, the vacuum de-alcoholization time is 30~90min, and the vacuum residual pressure is 8000~15000Pa.

7. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, according to claim 1, is characterized in that... The method of removing low-boiling point using vacuum thin film is adopted. During the process of removing low-boiling point using vacuum thin film, the material inlet temperature is 140~160℃, the material outlet temperature is 160~180℃, the vacuum residual pressure is 4000~6000Pa, and the material residence time is 10~15s.

8. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, according to claim 1, is characterized in that... The steps of molecular distilling the dealcoholized glycerol soap followed by a second sedimentation separation to obtain refined glycerol include: The dealcoholized glycerol soap was subjected to first-stage molecular distillation to obtain a first light phase and a first heavy phase. The first heavy phase is subjected to two-stage molecular distillation to obtain the second light phase and the second heavy phase. The first light phase and / or the second light phase are subjected to a second sedimentation separation to obtain refined glycerol.

9. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils according to claim 8, is characterized in that, During the first-stage molecular distillation process, the material outlet temperature is 190~210℃, the vacuum residual pressure is 100~200Pa, and the material residence time is 10~15s. During the secondary molecular distillation process, the material outlet temperature is 210~230℃, the vacuum residual pressure is 20~80Pa, and the material residence time is 10~15s.

10. The method for refining and removing impurities from crude glycerol, a byproduct in the preparation of biodiesel from waste oils, according to claim 1, is characterized in that... The temperature of the second sedimentation separation is 56~66℃, and the time of the second sedimentation separation is 12~36h.

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