Method for preparing biodiesel based on thorough transesterification of waste grease glyceride oil

Abstract

The invention discloses a method for preparing biodiesel based on thorough transesterification of waste grease glyceride oil. The method comprises the following steps: mixing waste grease glyceride oil and alcohol-containing crude glycerin, then carrying out pretreatment, and then carrying out first settling separation to obtain first grease and first alcohol-containing glycerin soap; carrying out ester exchange treatment on the first grease, and then carrying out second settling separation to obtain second grease; carrying out washing treatment on the second grease, and then carrying out third settling separation to obtain third grease; and carrying out low-boiling-point removal treatment on the third grease to obtain the biodiesel. According to the present invention, the alcohol-containing crude glycerol is adopted to carry out mixing pretreatment on the waste grease glycerol esterified oil, then the ester exchange treatment is performed, and finally the washing treatment and the low-boiling-point removing treatment are performed to prepare the biodiesel, such that the advantages of simple process, low alkali catalyst and alcohol consumption, small grease loss and complete ester exchange reaction are provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biodiesel, and particularly relates to a method for preparing biodiesel through complete transesterification of glycerol esterification oil of waste oil. BACKGROUND

[0002] Due to the increasing depletion of petrochemical fuel resources and the urgent need for environmental protection, the development of clean energy is attracting more and more attention. Energy researchers around the world are actively exploring the development of alternative fuels and renewable energy. Among them, biodiesel is one of the core research directions.

[0003] At present, the key factor restricting the development of biodiesel is the price of raw materials, and finding a cheap raw material and converting it is the key direction of research. Waste oil meets the needs of preparing biodiesel due to its cheapness and wide source. Preparing biodiesel from waste oil not only can solve the impact of waste oil on food safety and environmental protection, but also can solve the problem of high cost of biodiesel raw materials. However, the traditional waste oil biodiesel transesterification process has problems of large amount of catalyst and alcohol, large oil loss, and incomplete transesterification reaction.

[0004] Therefore, it is urgent to provide a new biodiesel production method to solve the above problems. SUMMARY

[0005] The present application aims to overcome the above technical deficiencies and provide a method for preparing biodiesel through complete transesterification of glycerol esterification oil of waste oil, which solves the technical problems of large amount of catalyst and alcohol, large oil loss, and incomplete transesterification reaction in the waste oil biodiesel transesterification process in the prior art.

[0006] The present application provides a method for preparing biodiesel through complete transesterification of glycerol esterification oil of waste oil, comprising the following steps: The glycerol esterification oil of waste oil and alcohol-containing crude glycerol are mixed and then pretreated, and then subjected to first sedimentation separation to obtain first oil and first alcohol-containing glycerol soap; The first oil is subjected to transesterification treatment, and then subjected to second sedimentation separation to obtain second oil; The second oil is subjected to washing treatment, and then subjected to third sedimentation separation to obtain third oil; The third oil is subjected to low-boiling removal treatment to obtain biodiesel; wherein, The glycerol esterification oil of waste oil is the esterification product of waste oil and glycerol, and the alcohol-containing crude glycerol is the by-product crude glycerol in the process of preparing biodiesel from waste oil.

[0007] Compared with the prior art, the present application has the following advantages: The application has the advantages of simple process, low alkali catalyst and alcohol consumption, small oil loss and complete transesterification reaction. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 is a process flow chart of an embodiment of the method for preparing biodiesel by complete transesterification of waste oil glycerol esterification oil provided by the application. DETAILED DESCRIPTION

[0009] In order to make the purpose, technical solutions and advantages of the application clearer, the application is 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 application and do not limit the application.

[0010] Please refer to Figure 1 The application provides a method for preparing biodiesel by complete transesterification of waste oil glycerol esterification oil, comprising the following steps: S1, mixing the waste oil glycerol esterification oil and alcohol-containing crude glycerol, then pretreating, then first settling and separating to obtain first oil and first alcohol-containing glycerol soap; S2, transesterifying the first oil, then second settling and separating to obtain second oil; S3, washing the second oil, then third settling and separating to obtain third oil; S4, removing low-boiling substances from the third oil to obtain biodiesel; wherein, The waste oil glycerol esterification 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 ≤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 byproduct 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 potassium fatty acid soap, and 0.5% to 3% of potassium hydroxide.

[0011] The present application can realize the full recycling of glycerol esterification oil and alcohol-containing crude glycerol in the preparation of biodiesel from waste oil.

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

[0013] In the present embodiment, in step S1, alcohol is also added during the pretreatment process. By adding alcohol during the pretreatment process, the present application can achieve the effect of demulsification and promote the separation of the first oil and the first 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 waste oil glycerol esterification oil, including but not limited to 8%, 8.5%, 9%, 9.5%, 10%, etc. If the amount of alcohol added is too low, the separation effect of the first oil and the first alcohol-containing glycerol soap in the first settling separation process will be poor, and subsequent operations cannot be performed. If the amount of alcohol added is too high, the consumption of alcohol will be large and the processing energy consumption will be high.

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

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

[0017] In the embodiment, step S2 includes: S21, the first oil and fat is subjected to a first transesterification reaction, and then subjected to a first second sedimentation separation to obtain a first transesterification oil and fat and a second alcohol-containing glycerol soap; S22, the first transesterification oil and fat is subjected to a second transesterification reaction, and then subjected to a second second sedimentation separation to obtain a second transesterification oil and fat and a third alcohol-containing glycerol soap; S23, the second transesterification oil and fat is subjected to a third transesterification reaction, and then subjected to a third second sedimentation separation to obtain a second oil and fat and a fourth alcohol-containing glycerol soap.

[0018] The present application can make the transesterification reaction more complete and improve the reaction conversion rate by adopting multi-stage transesterification reaction.

[0019] In the embodiment, alcohol and alkali catalyst are also added in the process of the first transesterification reaction, the second transesterification reaction and the third transesterification reaction.

[0020] Further, in step S21, the alcohol is methanol, and the amount of the alcohol added is 14%-18% of the mass of the waste oil glyceride esterification oil, including but not limited to 14%, 15%, 16%, 17%, 18%, etc.

[0021] Further, in step S21, the alkali catalyst is at least one of potassium hydroxide, sodium hydroxide, sodium methoxide, sodium carbonate and potassium carbonate, and the amount of the alkali catalyst added is 0.2%-0.3% of the mass of the waste oil glyceride esterification oil, including but not limited to 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, etc.

[0022] Further, in step S21, the temperature of the first transesterification reaction is 56-66 DEG C, including but not limited to 56 DEG C, 58 DEG C, 60 DEG C, 62 DEG C, 64 DEG C, 66 DEG C, etc., and the time of the first transesterification reaction is 1-3h, including but not limited to 1h, 1.5h, 2h, 2.5h, 3h, etc.

[0023] Further, in step S21, the temperature of the first second sedimentation separation is 56-66 DEG C, including but not limited to 56 DEG C, 58 DEG C, 60 DEG C, 62 DEG C, 64 DEG C, 66 DEG C, etc., and the time of the first second sedimentation separation is 2-4h, including but not limited to 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0024] Further, in step S22, the alcohol is methanol, and the amount of alcohol added is 1% to 3% of the mass of the waste oil glyceride esterification oil, including but not limited to 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0025] Further, in step S22, the base catalyst is at least one of potassium hydroxide, sodium hydroxide, sodium methoxide, sodium carbonate, and potassium carbonate, and the amount of base catalyst added is 0.04% to 0.08% of the mass of the waste oil glyceride esterification oil, including but not limited to 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, etc.

[0026] Further, in step S22, the temperature of the secondary ester exchange reaction 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 time of the secondary ester exchange reaction is 1 to 3 hours, including but not limited to 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.

[0027] Further, in step S22, the temperature of the secondary second sedimentation separation 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 time of the secondary second sedimentation separation is 2 to 4 hours, including but not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc.

[0028] Further, in step S23, the alcohol is methanol, and the amount of alcohol added is 0.2% to 0.7% of the mass of the waste oil glyceride esterification oil, including but not limited to 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, etc.

[0029] Further, in step S23, the base catalyst is at least one of potassium hydroxide, sodium hydroxide, sodium methoxide, sodium carbonate, and potassium carbonate, and the amount of base catalyst added is 0.01% to 0.03% of the mass of the waste oil glyceride esterification oil, including but not limited to 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, etc.

[0030] Further, in step S23, the temperature of the tertiary ester exchange reaction 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 time of the tertiary ester exchange reaction is 1 to 3 hours, including but not limited to 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.

[0031] Further, in step S23, the temperature of the tertiary second sedimentation separation 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 time of the tertiary second sedimentation separation is 2 to 4 hours, including but not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc.

[0032] Further, in steps S21, S22 and S23, the base catalyst is added by being previously dissolved in alcohol.

[0033] Further, the mass fraction of the alcohol solution of the base catalyst is 2% to 6%, including but not limited to 2%, 3%, 4%, 5%, 6%, etc.

[0034] Further, in steps S21, S22 and S23, the second alcohol-containing glycerol soap is returned to the pretreatment stage, the third alcohol-containing glycerol soap is returned to the first-stage transesterification reaction stage, and the fourth alcohol-containing glycerol soap is returned to the second-stage transesterification reaction stage. By returning the second alcohol-containing glycerol soap to the pretreatment stage, the present application can use the second alcohol-containing glycerol soap to pretreat the glycerol esterified oil, so that the alcohol and the base catalyst in the second alcohol-containing glycerol soap participate in the reaction again, reducing the amount of alcohol and base catalyst and lowering the production cost. By returning the third alcohol-containing glycerol soap to the first-stage transesterification reaction stage, the alcohol and the base catalyst in the third alcohol-containing glycerol soap can participate in the reaction again, further reducing the amount of alcohol and base catalyst, lowering the production cost, and improving the reaction conversion rate and product purity. By returning the fourth alcohol-containing glycerol soap to the second-stage transesterification reaction stage, the alcohol and the base catalyst in the fourth alcohol-containing glycerol soap can participate in the reaction again, further reducing the amount of alcohol and base catalyst, lowering the production cost, and improving the reaction conversion rate and product purity.

[0035] In the present embodiment, in step S3, methanol aqueous solution is used for washing. By using methanol aqueous solution to wash the second oil (mainly including fatty acid methyl ester, free glycerol, base, a small amount of soap, etc.), the present application can avoid the emulsification of the third oil.

[0036] Further, in step S3, the mass fraction of methanol in the methanol aqueous solution is 40% to 60%, including but not limited to 40%, 45%, 50%, 55%, 60%, etc.

[0037] In the present embodiment, in step S3, multi-stage washing is used. By using multi-stage washing, the present application can improve the washing effect of the second oil.

[0038] Further, in each stage of washing, the amount of methanol aqueous solution added is 5% to 10% of the mass of the second oil, including but not limited to 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0039] Further, the temperature of each stage of washing is 56 to 66℃, including but not limited to 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, etc., and the time of each stage of washing is 10 to 60 min, including but not limited to 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, etc.

[0040] Further, the temperature of each stage of the third sedimentation separation is 56-66℃, including but not limited to 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, etc., and the time of each stage of the third sedimentation separation is 2-4h, including but not limited to 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0041] Further, the wastewater of the next stage of washing is returned to the previous stage of washing, so as to reduce the amount of washing water while improving the washing effect of the second oil.

[0042] In the present embodiment, step S3 comprises: S31, the second oil is subjected to primary washing, followed by primary third sedimentation separation, to obtain primary washing oil and primary washing wastewater; S32, the primary washing oil is subjected to secondary washing, followed by secondary third sedimentation separation, to obtain the third oil and secondary washing wastewater.

[0043] In the present embodiment, in step S4, during the low-boiling removal treatment, vacuum low-boiling removal is adopted, the material inlet temperature is 140-160℃, including but not limited to 140℃, 145℃, 150℃, 155℃, 160℃, etc., the material outlet temperature is 160-180℃, including but not limited to 160℃, 165℃, 170℃, 175℃, 180℃, etc., the material residence time is 10-15s, and the vacuum residual pressure is 5000-6000Pa, including but not limited to 5000Pa, 5200Pa, 5400Pa, 5600Pa, 5800Pa, 6000Pa, etc. By controlling the temperature, time and vacuum residual pressure of the low-boiling removal within the above ranges, the water and alcohol contents in the biodiesel can be controlled within 0.1%.

[0044] Example 1 (1) To the waste oil glycerol esterification oil (monoglyceride 3.8%, diglyceride 12.1%, triglyceride 80.4%, acid value 1 mg KOH / g), 20% of alcohol-containing crude glycerol (glycerol 42.1%, methanol 39.2%, fatty acid methyl ester 11.8%, potassium soap of fatty acid 5.9%, potassium hydroxide 0.75%) and 8% of methanol were added, 65℃ pretreatment for 2 hours, poured into a separatory funnel, and 65℃ heat preservation sedimentation separation for 3 hours to obtain the first oil and the first alcohol-containing glycerol soap.

[0045] (2) To the first oil and fat above, add 6% of potassium hydroxide methanol solution (mass fraction 4%) and 9% of methanol in the mass of glyceride oil of waste oil, and carry out first transesterification reaction at 65°C for 2 hours, pour into a separatory funnel, and carry out settling separation at 65°C for 3 hours to obtain first transesterification oil and second alcohol-containing glycerol soap (the second alcohol-containing glycerol soap can be returned to the pretreatment); to the first transesterification oil above, add 1.5% of potassium hydroxide methanol solution (mass fraction 4%) in the mass of glyceride oil of waste oil, and carry out second transesterification reaction at 65°C for 2 hours, pour into a separatory funnel, and carry out settling separation at 65°C for 3 hours to obtain second transesterification oil and third alcohol-containing glycerol soap (the third alcohol-containing glycerol soap can be returned to the first transesterification reaction); to the second transesterification oil above, add 0.5% of potassium hydroxide methanol solution (mass fraction 4%) in the mass of glyceride oil of waste oil, and carry out third transesterification reaction at 65°C for 2 hours, pour into a separatory funnel, and carry out settling separation at 65°C for 3 hours to obtain second oil and fourth alcohol-containing glycerol soap (the fourth alcohol-containing glycerol soap can be returned to the second transesterification reaction).

[0046] (3) To the second oil above, add 6% of methanol aqueous solution (mass fraction of methanol 50%) in the mass of the second oil, and carry out stirring washing at 65°C for 30 minutes, pour into a heat preservation separatory funnel, and carry out settling separation at 65°C for 4 hours to obtain first washing oil and first washing wastewater; to the first washing oil above, add 6% of methanol aqueous solution (mass fraction of methanol 50%) in the mass of the second oil, and carry out stirring washing at 65°C for 30 minutes, pour into a heat preservation separatory funnel, and carry out settling separation at 65°C for 4 hours to obtain third oil and second washing wastewater.

[0047] (4) Under stirring condition, vacuum remove low boiling point of the third oil above, the material inlet temperature is 150°C, the material outlet temperature is 170°C, the material residence time is 10-15s, control the vacuum residual pressure to be 5000Pa, to obtain biodiesel.

[0048] Example 2 (1) To glyceride oil of waste oil (monoglyceride 4.2%, diglyceride 14.7%, triglyceride 76.4%, acid value 0.5 mg KOH / g), add 18% of alcohol-containing crude glycerol (glycerol 40.1%, methanol 38.4%, fatty acid methyl ester 14.5%, potassium fatty acid soap 5.5%, potassium hydroxide 1.2%) and 8% of methanol in the mass of glyceride oil of waste oil, and carry out pretreatment at 56°C for 3 hours, pour into a separatory funnel, and carry out settling separation at 56°C for 4 hours to obtain first oil and first alcohol-containing glycerol soap.

[0049] (2) To the first oil and fat above, add 5% of potassium hydroxide methanol solution (mass fraction of 4%) and 12% of methanol in the mass of glyceride oil of waste oil, and carry out first transesterification reaction at 56°C for 3 hours, pour into a separatory funnel, and carry out settling separation at 56°C for 4 hours to obtain first transesterification oil and second alcohol-containing glycerol soap (the second alcohol-containing glycerol soap can be returned to the pretreatment); to the first transesterification oil above, add 1.3% of potassium hydroxide methanol solution (mass fraction of 4%) in the mass of glyceride oil of waste oil, and carry out second transesterification reaction at 56°C for 3 hours, pour into a separatory funnel, and carry out settling separation at 56°C for 4 hours to obtain second transesterification oil and third alcohol-containing glycerol soap (the third alcohol-containing glycerol soap can be returned to the first transesterification reaction); to the second transesterification oil above, add 0.7% of potassium hydroxide methanol solution (mass fraction of 4%) in the mass of glyceride oil of waste oil, and carry out third transesterification reaction at 56°C for 3 hours, pour into a separatory funnel, and carry out settling separation at 56°C for 4 hours to obtain second oil and fourth alcohol-containing glycerol soap (the fourth alcohol-containing glycerol soap can be returned to the second transesterification reaction).

[0050] (3) To the second oil above, add 10% of methanol aqueous solution (mass fraction of methanol of 40%) in the mass of the second oil, and carry out stirring washing at 56°C for 60 minutes, pour into a temperature-maintained separatory funnel, and carry out settling separation at 56°C for 3 hours to obtain first washing oil and first washing wastewater; to the first washing oil above, add 10% of methanol aqueous solution (mass fraction of methanol of 40%) in the mass of the second oil, and carry out stirring washing at 56°C for 60 minutes, pour into a temperature-maintained separatory funnel, and carry out settling separation at 56°C for 3 hours to obtain third oil and second washing wastewater.

[0051] (4) Under stirring conditions, vacuum remove low boiling point from the third oil above, the material inlet temperature is 140°C, the material outlet temperature is 160°C, the material residence time is 10-15s, and the vacuum residual pressure is controlled to be 6000 Pa to obtain biodiesel.

[0052] Example 3 (1) To glyceride oil of waste oil (1.1% of monoglyceride, 10.2% of diglyceride, 84.1% of triglyceride, and acid value of 1.5 mg KOH / g), add 25% of alcohol-containing crude glycerol (47.2% of glycerol, 35.1% of methanol, 10.4% of fatty acid methyl ester, 6.6% of potassium fatty acid soap, and 0.5% of potassium hydroxide) and 10% of methanol in the mass of glyceride oil of waste oil, and carry out pretreatment at 60°C for 3 hours, pour into a separatory funnel, and carry out settling separation at 60°C for 2 hours to obtain first oil and first alcohol-containing glycerol soap.

[0053] (2) To the first oil above, add 7% of potassium hydroxide methanol solution (mass fraction of 4%) and 8% of methanol in the mass of glyceride oil of waste oil, and carry out primary transesterification reaction at 60℃ for 3 hours, pour into a separatory funnel, and carry out settling separation at 60℃ for 2 hours to obtain primary transesterification oil and second alcohol-containing glycerol soap (the second alcohol-containing glycerol soap can be returned to the pretreatment); to the primary transesterification oil above, add 1.7% of potassium hydroxide methanol solution (mass fraction of 4%) in the mass of glyceride oil of waste oil, and carry out secondary transesterification reaction at 60℃ for 3 hours, pour into a separatory funnel, and carry out settling separation at 60℃ for 2 hours to obtain secondary transesterification oil and third alcohol-containing glycerol soap (the third alcohol-containing glycerol soap can be returned to the primary transesterification reaction); to the secondary transesterification oil above, add 0.3% of potassium hydroxide methanol solution (mass fraction of 4%) in the mass of glyceride oil of waste oil, and carry out tertiary transesterification reaction at 60℃ for 3 hours, pour into a separatory funnel, and carry out settling separation at 60℃ for 2 hours to obtain second oil and fourth alcohol-containing glycerol soap (the fourth alcohol-containing glycerol soap can be returned to the secondary transesterification reaction).

[0054] (3) To the second oil above, add 5% of methanol aqueous solution (mass fraction of methanol 60%) in the mass of the second oil, and carry out stirring washing at 60℃ for 10 minutes, pour into a heat preservation separatory funnel, and carry out settling separation at 60℃ for 2 hours to obtain primary washing oil and primary washing wastewater; to the primary washing oil above, add 5% of methanol aqueous solution (mass fraction of methanol 60%) in the mass of the second oil, and carry out stirring washing at 60℃ for 10 minutes, pour into a heat preservation separatory funnel, and carry out settling separation at 60℃ for 2 hours to obtain third oil and secondary washing wastewater.

[0055] (4) Under stirring condition, vacuum remove low boiling point of the third oil above, the material inlet temperature is 160℃, the material outlet temperature is 180℃, the material residence time is 10-15s, and the vacuum residual pressure is controlled to be 5000Pa to obtain biodiesel.

[0056] Comparative Example 1 Compared with Example 1, the only difference is that there is no step (1), and the glyceride oil of waste oil is directly subjected to transesterification treatment, washing treatment and vacuum low boiling point removal treatment in sequence to prepare biodiesel, and the transesterification treatment step is as follows: To the waste oil glycerolysis oil (monoglyceride 3.8%, diglyceride 12.1%, triglyceride 80.4%, acid value 1 mg KOH / g), 9.75% of potassium hydroxide methanol solution (mass fraction 4%) and 21.24% of methanol based on the mass of the waste oil glycerolysis oil were added, and the first ester exchange reaction was carried out at 65°C for 2 hours, poured into a separatory funnel, and settled and separated at 65°C for 3 hours to obtain the first ester exchange oil and the second alcohol-containing glycerol soap (the second alcohol-containing glycerol soap can be returned to the pretreatment) ; to the above-mentioned first ester exchange oil, 1.5% of potassium hydroxide methanol solution (mass fraction 4%) based on the mass of the waste oil glycerolysis oil was added, and the second ester exchange reaction was carried out at 65°C for 2 hours, poured into a separatory funnel, and settled and separated at 65°C for 3 hours to obtain the second ester exchange oil and the third alcohol-containing glycerol soap (the third alcohol-containing glycerol soap can be returned to the first ester exchange reaction) ; to the above-mentioned second ester exchange oil, 0.5% of potassium hydroxide methanol solution (mass fraction 4%) based on the mass of the waste oil glycerolysis oil was added, and the third ester exchange reaction was carried out at 65°C for 2 hours, poured into a separatory funnel, and settled and separated at 65°C for 3 hours to obtain the second oil and the fourth alcohol-containing glycerol soap (the fourth alcohol-containing glycerol soap can be returned to the second ester exchange reaction).

[0057] Comparative Example 2 Compared with Example 1, the only difference is that no alcohol-containing crude glycerol is added in step (1), but the same amount of potassium hydroxide and methanol as in the alcohol-containing crude glycerol is directly added, and methanol is also added, and step (1) is as follows: (1) To the waste oil glycerolysis oil (monoglyceride 3.8%, diglyceride 12.1%, triglyceride 80.4%, acid value 1 mg KOH / g), 3.75% of potassium hydroxide methanol solution (mass fraction 4%) and 12.24% of methanol based on the mass of the waste oil glycerolysis oil were added, and the pretreatment was carried out at 65°C for 2 hours, poured into a separatory funnel, and settled and separated at 65°C for 3 hours to obtain the first oil and the first alcohol-containing glycerol soap.

[0058] Comparative Example 3 Compared with Example 1, the only difference is that only the second ester exchange is used in step (2), and step (2) is as follows: (2) to the above first oil, add 6.3% of potassium hydroxide methanol solution (mass fraction of 4%) and 9% of methanol in the mass of the glyceride oil of the waste oil, and carry out first transesterification reaction at 65°C for 2 hours, pour into a separatory funnel, and carry out settling separation at 65°C for 3 hours to obtain first transesterification oil and second alcohol-containing glycerol soap (the second alcohol-containing glycerol soap can be returned to the pretreatment); to the above first transesterification oil, add 1.7% of potassium hydroxide methanol solution (mass fraction of 4%) in the mass of the glyceride oil of the waste oil, and carry out second transesterification reaction at 65°C for 2 hours, pour into a separatory funnel, and carry out settling separation at 65°C for 3 hours to obtain second oil and third alcohol-containing glycerol soap (the third alcohol-containing glycerol soap can be returned to the first transesterification reaction).

[0059] Comparative Example 4 Compared with Example 1, the difference is that, in step (3), water washing is used instead of methanol water washing.

[0060] Test Group The biodiesels prepared in the above examples and comparative examples are subjected to performance test, and the test results are shown in Table 1. Among them, the yield of biodiesel = mass of biodiesel / mass of glyceride oil × 100%.

[0061] Table 1

[0062] As can be seen from Table 1, by mixing the glyceride oil of the waste oil and the alcohol-containing crude glycerol after pretreatment, the application can not only reduce the amount of alkali catalyst and alcohol, but also improve the transesterification degree, so that the content of triglyceride in the biodiesel is ≤0.1%, the content of diglyceride is ≤0.2%, the content of monoglyceride is ≤0.5%, the content of free glycerol is ≤0.08%, the total glycerol content is ≤0.2%, the transesterification degree is complete, the content of fatty acid methyl ester is high (>97%), and the yield of biodiesel is high (>93%).

[0063] Compared with Example 1, in Comparative Example 1, the glyceride oil of the waste oil is directly subjected to transesterification treatment, washing treatment and vacuum low boiling treatment in turn to prepare biodiesel, and the amount of methanol and alkali catalyst is obviously higher, but the content of fatty acid methyl ester in the biodiesel and the yield of biodiesel are significantly reduced, and the transesterification degree is not complete, which shows that the method of the application can not only further improve the content of fatty acid methyl ester in the biodiesel and the yield of biodiesel and the transesterification degree, but also significantly reduce the amount of alkali catalyst and alcohol, which has great economic efficiency.

[0064] Compared with Example 1, in Comparative Example 2, the alcohol-containing crude glycerol was not added, but an equivalent amount of methanol and alkali catalyst in the alcohol-containing crude glycerol was pretreated, the amount of methanol and alkali catalyst was significantly higher, but the fatty acid methyl ester content in the biodiesel and the biodiesel yield were still significantly reduced, and the transesterification degree was incomplete, which indicated that the method of the application not only could further improve the fatty acid methyl ester content in the biodiesel and the biodiesel yield and the transesterification degree, but also could reduce the amount of alkali catalyst and alcohol, which had great economic efficiency.

[0065] Compared with Example 1, in Comparative Example 3, only secondary ester exchange was used, although the amount of methanol and alkali catalyst was the same, the transesterification degree was significantly reduced, the fatty acid methyl ester content in the biodiesel was significantly reduced, and the content of monoglyceride, diglyceride, triglyceride and other components was increased, which indicated that the method of the application could significantly improve the transesterification degree and the biodiesel yield and the fatty acid methyl ester content in the biodiesel, which had great economic efficiency.

[0066] Compared with Example 1, in Comparative Example 4, water was used instead of methanol aqueous solution in the washing process, the third oil appeared emulsification phenomenon, which led to poor layering effect when the oil was separated by sedimentation, resulting in oil loss, which led to the decrease of the fatty acid methyl ester content in the biodiesel and the significant reduction of the biodiesel yield.

[0067] The specific embodiments of the application described above do not constitute a limitation on the protection scope of the application. Any various other corresponding changes and modifications made according to the technical concept of the application should be included in the protection scope of the claims of the application.

Claims

1. A method for preparing biodiesel from waste oil glycerol esterified oil through complete transesterification, characterized in that, Includes the following steps: Waste glycerol esterified oil and alcohol-containing crude glycerol are mixed and pretreated, and then separated by a first sedimentation to obtain the first oil and the first alcohol-containing glycerol soap. The first oil was subjected to transesterification, followed by a second sedimentation separation to obtain the second oil; The second grease is washed and then separated by a third sedimentation process to obtain the third grease; The third oil is subjected to a low-boiling-point treatment to obtain biodiesel; wherein... The waste oil glycerol esterified oil is an esterification product of waste oil and glycerol, and the alcohol-containing crude glycerol is a by-product of the waste oil to biodiesel production process.

2. The method for preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 1, characterized in that, The composition of the waste oil glycerol esterified oil includes: 1%~5% monoglyceride, 10%~20% diglyceride, 75%~85% triglyceride, and an acid value ≤3mg 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 preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 1, characterized in that, The amount of crude glycerol containing alcohol added is 18% to 25% of the mass of the waste oil glycerol esterified oil.

4. The method for preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 1, 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 waste oil glycerol esterified oil.

5. The method for preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 1, characterized in that, The pretreatment temperature is 56~66℃, and the pretreatment time is 1~3h; The temperature of the first sedimentation separation is 56~66℃, and the time of the first sedimentation separation is 2~4h.

6. The method for preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 1, characterized in that, The step of subjecting the first oil to transesterification followed by a second sedimentation separation to obtain the second oil includes: The first oil was subjected to a primary transesterification reaction, followed by a primary and secondary sedimentation separation to obtain a primary transesterified oil and a second alcohol-containing glycerol soap. The primary transesterified oil is subjected to a secondary transesterification reaction, followed by a secondary sedimentation separation to obtain a secondary transesterified oil and a third alcohol-containing glycerol soap; The secondary transesterified oil is subjected to a tertiary transesterification reaction, followed by a tertiary second sedimentation separation to obtain a second oil and a fourth alcohol-containing glycerol soap.

7. The method for preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 6, characterized in that, In the primary transesterification reaction, the secondary transesterification reaction, and the tertiary transesterification reaction, alcohols and base catalysts are also added; wherein, In the primary transesterification reaction, the alcohol is methanol, and the amount of alcohol added is 14% to 18% of the mass of the waste oil glycerol esterified oil; the alkaline catalyst is at least one selected from potassium hydroxide, sodium hydroxide, sodium methoxide, sodium carbonate, and potassium carbonate, and the amount of the alkaline catalyst added is 0.2% to 0.3% of the mass of the waste oil glycerol esterified oil; the temperature of the primary transesterification reaction is 56 to 66°C, and the time of the primary transesterification reaction is 1 to 3 hours; In the secondary transesterification reaction, the alcohol is methanol, and the amount of alcohol added is 1% to 3% of the mass of the waste oil glycerol esterified oil; the alkaline catalyst is at least one selected from potassium hydroxide, sodium hydroxide, sodium methoxide, sodium carbonate, and potassium carbonate, and the amount of the alkaline catalyst added is 0.04% to 0.08% of the mass of the waste oil glycerol esterified oil; the temperature of the secondary transesterification reaction is 56 to 66°C, and the time of the secondary transesterification reaction is 1 to 3 hours; In the tertiary transesterification process, the alcohol is methanol, and the amount of alcohol added is 0.2% to 0.7% of the mass of the waste oil glycerol esterified oil; the alkaline catalyst is at least one selected from potassium hydroxide, sodium hydroxide, sodium methoxide, sodium carbonate, and potassium carbonate, and the amount of the alkaline catalyst added is 0.01% to 0.03% of the mass of the waste oil glycerol esterified oil; the temperature of the tertiary transesterification reaction is 56 to 66°C, and the time of the tertiary transesterification reaction is 1 to 3 hours.

8. The method for preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 6, characterized in that, The temperature for the first-stage second sedimentation separation is 56~66℃, and the time for the first-stage second sedimentation separation is 2~4h; the temperature for the second-stage second sedimentation separation is 56~66℃, and the time for the second-stage second sedimentation separation is 2~4h; the temperature for the third-stage second sedimentation separation is 56~66℃, and the time for the third-stage second sedimentation separation is 2~4h.

9. The method for preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 1, characterized in that, The washing process uses a methanol-water solution; the methanol-water solution contains 40% to 60% methanol by mass. Multi-stage washing is employed, with the amount of methanol aqueous solution added during each stage of washing being 5% to 10% of the mass of the second oil. The washing temperature for each stage is 56 to 66°C, and the washing time for each stage is 10 to 60 minutes. The temperature for the third sedimentation separation at each stage is 56 to 66°C, and the third sedimentation separation time for each stage is 2 to 4 hours.

10. The method for preparing biodiesel based on complete transesterification of waste oil glycerol esterified oil according to claim 1, characterized in that, In the process of removing low-boiling point material, vacuum removal is adopted, with the material inlet temperature at 140~160℃, the material outlet temperature at 160~180℃, the material residence time at 10~15s, and the vacuum residual pressure at 5000~6000Pa.

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