Method for preparing distillation-free biodiesel from low-acid-value waste oil

Abstract

The invention discloses a method for preparing distillation-free biodiesel from low-acid-value waste oil and fat, which comprises the following steps of: degumming the low-acid-value waste oil and fat, removing metal ions, and dehydrating for the first time to obtain pretreated oil and fat; carrying out subcritical ester exchange reaction on the pretreated grease and methanol to obtain crude fatty acid methyl ester; and carrying out dealcoholization, alkali washing, water washing and secondary dehydration on the crude fatty acid methyl ester to obtain the distillation-free biodiesel. The method is simple, energy consumption is low, no extra catalyst needs to be added, the content of fatty acid methyl ester in the prepared biodiesel is 96.5% or above, and the yield can reach 99% or above.

Description

Technical Field

[0001] The present application relates to the technical field of biodiesel, and in particular to a method for preparing distillation-free biodiesel from waste oils and fats with low acid value. Background Art

[0002] Biodiesel is a renewable clean fuel, which is mainly produced by transesterification of vegetable oil, animal fat or waste oil. As a renewable energy with broad development prospects, biodiesel is facing important development opportunities in the context of global energy transformation and environmental protection. However, many challenges need to be overcome to achieve sustainable development of the industry. At present, there are generally two process routes for preparing biodiesel: one is the "distillation-free method", which has the advantages of less equipment and simpler process; the other is the "esterification and distillation method", which has high equipment investment, complex process flow, high energy consumption, low biodiesel yield, but good oil quality, and is currently a common method. The quality of biodiesel is closely related to the fatty acid methyl ester content in biodiesel, and biodiesel requires that the fatty acid methyl ester content must reach more than 96.5%. Internationally, distillation-free biodiesel generally uses refined vegetable oil (salad oil) as raw material. However, waste oil raw materials have complex composition, high impurity content, and dark color, and general technology cannot produce distillation-free biodiesel. At present, there is no report on the production of distillation-free biodiesel based on waste oil.

[0003] Subcritical transesterification technology usually uses methanol as a reactant to undergo an ester exchange reaction with triglycerides in vegetable oils or animal fats under subcritical conditions to produce biodiesel (fatty acid methyl esters) and by-product glycerol. Compared with traditional base-catalyzed transesterification methods, this technology has higher selectivity and conversion rate. However, the alcohol-to-oil ratio of the subcritical transesterification method is too high, resulting in a waste of methanol and increasing the difficulty of subsequent separation. At the same time, in order to improve the conversion rate of biodiesel, it is often necessary to add a certain catalyst, which will also increase the difficulty of subsequent separation.

[0004] Therefore, there is an urgent need to provide a method for preparing distillation-free biodiesel from low-acid value waste oils and fats, so as to significantly increase the fatty acid methyl ester content in biodiesel, reduce production energy consumption, and simplify the process. Summary of the invention

[0005] The purpose of this application is to overcome the above-mentioned technical deficiencies and propose a method for preparing distillation-free biodiesel from low-acid value waste oil, so as to solve the technical problems in the prior art that the preparation of biodiesel using waste oil as raw material cannot take into account both high fatty acid methyl ester content and high yield and the post-processing is difficult.

[0006] The present application provides a method for preparing distillation-free biodiesel from waste oil with low acid value, comprising the following steps: Degumming, removing metal ions and first dehydrating the low acid value waste oil to obtain pretreated oil; The pretreated oil and methanol are subjected to a subcritical transesterification reaction to obtain crude fatty acid methyl esters; The crude fatty acid methyl ester is subjected to dealcoholization, alkali washing, water washing and second dehydration to obtain distillation-free biodiesel.

[0007] Compared with the prior art, the beneficial effects of this application include: The present application can remove the colloid, metal ions and water in the low acid value waste oil by degumming and removing metal ions and first dehydration of the low acid value waste oil; the present application can convert the triglyceride in the oil into fatty acid methyl ester (biodiesel) by subcritical transesterification of the pretreated oil and methanol; the present application can remove the unreacted methanol in the fatty acid methyl ester by dealcoholization; the present application can remove the unreacted free fatty acids, free glycerol, monoglyceride and other impurities in the crude fatty acid methyl ester by alkali washing, and reduce the acid value of the crude fatty acid methyl ester; the present application can remove the residual alkali after alkali washing of the crude fatty acid methyl ester by water washing; the present application can reduce the water content in the biodiesel by the second dehydration. The method of the present application is simple, has low energy consumption and does not require the addition of additional catalysts. The fatty acid methyl ester content in the prepared biodiesel is above 96.5%, and the yield can reach above 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a process flow chart of an embodiment of a method for preparing distillation-free biodiesel from low-acid value waste oils provided in the present application. DETAILED DESCRIPTION

[0009] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0010] See also Figure 1 The present application provides a method for preparing distillation-free biodiesel from low-acid-value waste oil, comprising the following steps: S1, degumming and removing metal ions from low acid value waste oil and fat, and first dehydrating to obtain pretreated oil and fat; S2, performing a subcritical transesterification reaction on the pretreated oil and methanol to obtain crude fatty acid methyl ester; S3, the crude fatty acid methyl ester is dealcoholized, alkali washed, water washed, and subjected to a second dehydration to obtain distillation-free biodiesel.

[0011] The present application can remove gum, metal ions and water in low-acid-value waste oils by degumming and removing metal ions and performing a first dehydration on low-acid-value waste oils; the present application can convert triglycerides in oils into fatty acid methyl esters (biodiesel) by performing a subcritical ester exchange reaction on pretreated oils and methanol; the present application can remove unreacted methanol in fatty acid methyl esters by dealcoholization; the present application can remove unreacted free fatty acids, free glycerol, monoglycerides and other impurities in crude fatty acid methyl esters by alkali washing, and reduce the acid value of crude fatty acid methyl esters; the present application can remove residual alkali after alkali washing of crude fatty acid methyl esters by water washing; the present application can reduce the water content in biodiesel by a second dehydration. The inventors found during the experiment that if the alkali washing step is set before the subcritical transesterification (i.e., the subcritical transesterification is performed after the pre-treated oil is alkali washed), most of the fatty acids in the raw materials will be converted into fatty soaps, and the effective components participating in the subsequent reactions will be reduced, which will eventually lead to a significant decrease in the yield of distillation-free biodiesel; while the process sequence of the present application can make the biodiesel have a very high fatty acid methyl ester content and yield. The method of the present application is simple, has low energy consumption, and does not require the addition of additional catalysts. The fatty acid methyl ester content in the prepared biodiesel is above 96.5%, and the yield can reach above 99%.

[0012] In this embodiment, the acid value of the low-acid-value waste oil is ≤20 mg KOH / g. The present application does not limit the type of low-acid-value waste oil, and those skilled in the art can select it according to actual conditions. For example, it can be sewage oil, kitchen waste oil, palmitic acid oil, acidified oil, etc.

[0013] In some specific embodiments of the present application, the acid value of the low-acid-value waste oil is ≤20 mg KOH / g, the sulfur content is ≤35 ppm, and the unsaponifiable matter content is ≤1%.

[0014] In this embodiment, the metal ion content in the pretreated oil is ≤10ppm, the phosphorus element is ≤2ppm, and the water residue is ≤0.1%.

[0015] The present application does not limit the method of degumming and removing metal ions, and those skilled in the art can choose according to actual conditions. In some specific embodiments of the present application, the process of degumming and removing metal ions includes: mixing low acid value waste oil, oxalic acid and citric acid, stirring and reacting, and then performing a first static sedimentation separation to obtain the waste oil after degumming and removing metal ions.

[0016] Among them, the added amount of oxalic acid is 0.1%-1.0% of the mass of low acid value waste oil and fat, including but not limited to 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc.

[0017] Among them, the added amount of citric acid is 0.1-1.0% of the mass of low acid value waste oil and fat, including but not limited to 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc.

[0018] Among them, oxalic acid and citric acid are added in the form of aqueous solution, and the addition amount of the aqueous solution of oxalic acid and citric acid is 3%-10% of the mass of low acid value waste oil, including but not limited to 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% and the like.

[0019] The temperature for degumming and demetallization is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the time for degumming and demetallization is 10-90 minutes, including but not limited to 10 minutes, 30 minutes, 50 minutes, 70 minutes, 90 minutes, etc.

[0020] Among them, the temperature of the first static sedimentation separation is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the time of the first static sedimentation separation is 2-10 hours, including but not limited to 2 hours, 4 hours, 6 hours, 8 hours, etc.

[0021] The present application adopts the above-mentioned degumming and metal ion removal process and cooperates with the above-mentioned process parameters to control the metal ion content in the pretreated oil and fat within 10 ppm and the phosphorus element within 2 ppm.

[0022] The present application does not limit the first dehydration method, and those skilled in the art can select it according to actual conditions. In some specific embodiments of the present application, vacuum dehydration is used for the first dehydration.

[0023] Among them, the temperature of vacuum dehydration is 90-120℃, including but not limited to 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, etc.; the residual pressure of vacuum dehydration is 8000-15000Pa, including but not limited to 8000Pa, 9000Pa, 10000Pa, 11000Pa, 12000Pa, 13000Pa, 14000Pa, 15000Pa, etc.; the time of vacuum dehydration is 30-90 minutes, including but not limited to 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, etc.

[0024] The present application adopts a vacuum dehydration method and cooperates with the above-mentioned process parameters to control the water residue in the pretreated oil to less than 0.1%.

[0025] In this embodiment, the amount of methanol added is 20%-35% of the mass of the pretreated oil, including but not limited to 20%, 22%, 25%, 28%, 30%, 32%, 35%, etc.

[0026] In this embodiment, the temperature of the subcritical ester exchange reaction is 220-230°C, including but not limited to 220°C, 222°C, 224°C, 226°C, 228°C, 230°C, etc.; the pressure of the subcritical ester exchange reaction is 5.0-6.0MPa, including but not limited to 5.0MP, 5.2MP, 5.4MP, 5.6MP, 5.8MPa, 6.0MP, etc.; the time of the subcritical ester exchange reaction is 1-9 hours, including but not limited to 1 hour, 3 hours, 5 hours, 7 hours, 9 hours, etc.

[0027] In this embodiment, after the subcritical transesterification reaction is completed, a second static sedimentation separation is further performed.

[0028] Among them, the temperature of the second static sedimentation separation is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the time of the second static sedimentation separation is 1-9 hours, including but not limited to 1 hour, 3 hours, 5 hours, 7 hours, 9 hours, etc.

[0029] In some preferred embodiments of the present application, a three-stage subcritical transesterification reaction is adopted.

[0030] Among them, during the primary subcritical transesterification reaction, the amount of methanol added is 15%-25% of the mass of the pretreated oil, including but not limited to 15%, 18%, 20%, 22%, 25%, etc.

[0031] Among them, during the secondary subcritical transesterification reaction, the amount of methanol added is 5%-10% of the mass of the pretreated oil, including but not limited to 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0032] Among them, during the three-stage subcritical transesterification reaction, the amount of methanol added is 3%-8% of the mass of the pretreated oil, including but not limited to 3%, 4%, 5%, 6%, 7%, 8%, etc.

[0033] Among them, the temperature of each subcritical ester exchange reaction is 220-230°C, including but not limited to 220°C, 222°C, 224°C, 226°C, 228°C, 230°C, etc.; the pressure of each subcritical ester exchange reaction is 5.0-6.0MPa, including but not limited to 5.0MP, 5.2MP, 5.4MP, 5.6MP, 5.8MPa, 6.0MP, etc.; the time of each subcritical ester exchange reaction is 1-3 hours, including but not limited to 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.

[0034] After each subcritical transesterification reaction is completed, each second static sedimentation separation is carried out.

[0035] Furthermore, the temperature of the second static sedimentation separation at each level is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the time of the second static sedimentation separation at each level is 1-3 hours, including but not limited to 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.

[0036] Among them, the crude glycerol from the secondary ester exchange returns to the primary ester exchange reaction, and the crude glycerol from the tertiary ester exchange returns to the secondary ester exchange reaction.

[0037] The present application adopts three-stage subcritical transesterification and cooperates with the above-mentioned process parameters to reduce the methanol content while improving the conversion rate of fatty acid methyl ester without the need to add additional catalysts.

[0038] In this embodiment, after the crude fatty acid methyl ester is dealcoholated, the methanol residue is ≤0.1%.

[0039] The present application does not limit the method of dealcoholization, and those skilled in the art can select according to actual conditions. In some specific embodiments of the present application, a vacuum dealcoholization method is adopted.

[0040] Wherein, the temperature of vacuum dealcoholization is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the vacuum residual pressure is 8000-15000Pa, including but not limited to 8000Pa, 9000, 10000Pa, 11000Pa, 12000Pa, 13000Pa, 14000Pa, 15000Pa, etc.; the time of vacuum dealcoholization is 30-90 minutes, including but not limited to 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, etc.

[0041] The present application adopts a vacuum dealcoholization method and cooperates with the above-mentioned process parameters to control the methanol residue in the crude fatty acid methyl ester after dealcoholization to less than 0.1%.

[0042] In this embodiment, after the crude fatty acid methyl ester is washed with alkali, the acid value is ≤0.45 mg KOH / g.

[0043] In this embodiment, the alkali washing process includes: washing the dealcoholized crude fatty acid methyl ester with a sodium hydroxide solution, and then performing a third static sedimentation separation to obtain the alkali-washed crude fatty acid methyl ester.

[0044] Among them, the mass fraction of the sodium hydroxide solution is 2%-5%, including but not limited to 2%, 3%, 4%, 5% and the like; the amount of the sodium hydroxide solution added is 5%-10% of the mass of the crude fatty acid methyl ester after dealcoholization, including but not limited to 5%, 6%, 7%, 8%, 9%, 10% and the like.

[0045] The alkali washing temperature is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the alkali washing time is 15-30 minutes, including but not limited to 15 minutes, 20 minutes, 25 minutes, 30 minutes, etc.

[0046] Among them, the temperature of the third static sedimentation separation is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the time of the third static sedimentation separation is 3-6 hours, including but not limited to 3 hours, 4 hours, 5 hours, 6 hours, etc.

[0047] The present application adopts the alkaline washing method and cooperates with the above-mentioned process parameters to control the acid value of the crude fatty acid methyl ester after alkaline washing to within 0.45 mg KOH / g, and remove impurities such as free fatty acids, free glycerol, monoglycerides, etc. in the crude fatty acid methyl ester.

[0048] In this embodiment, after the crude fatty acid methyl ester is washed with water, the soap residue is ≤50 ppm.

[0049] In this embodiment, the water washing process includes: washing the crude fatty acid methyl ester after alkali washing with pure water, and then performing a fourth static sedimentation separation to obtain the crude fatty acid methyl ester after water washing.

[0050] The amount of pure water added is 5%-10% of the crude fatty acid methyl ester after alkali washing, including but not limited to 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0051] The water washing temperature is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the water washing time is 15-30 minutes, including but not limited to 15 minutes, 20 minutes, 25 minutes, 30 minutes, etc.

[0052] Among them, the temperature of the fourth static sedimentation separation is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the time of the fourth static sedimentation separation is 2-4 hours, including but not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc.

[0053] The present application adopts a water washing method and cooperates with the above-mentioned process parameters to control the soap residue of the crude fatty acid methyl ester after water washing to within 50 ppm.

[0054] In this embodiment, after the crude fatty acid methyl ester is dehydrated, the residual water is controlled within 0.1%.

[0055] The present application does not limit the second dehydration method, and those skilled in the art can select it according to actual conditions. In some specific embodiments of the present application, vacuum dehydration is used for the second dehydration.

[0056] Among them, the temperature of vacuum dehydration is 90-120℃, including but not limited to 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, etc.; the residual pressure of vacuum dehydration is 3000-5000Pa, including but not limited to 3000Pa, 3500Pa, 4000Pa, 4500Pa, 5000Pa, etc.; the time of vacuum dehydration is 30-90 minutes, including but not limited to 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, etc.

[0057] The present application adopts a vacuum dehydration method and cooperates with the above-mentioned process parameters to control the water residue of the crude fatty acid methyl ester after dehydration to less than 0.1%.

[0058] Example 1 (1) Degumming and metal ion removal Add 1000g of slop oil with an acid value of 20mg KOH / g, a sulfur content of 33ppm, and unsaponifiable matter of 0.9% to a 2000ml three-necked flask. Install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 85°C, add a mixed acid solution containing 5% of the weight of the oil, and in the mixed acid solution, the amount of oxalic acid added is 0.7% of the weight of the oil, and the amount of citric acid added is 0.3% of the weight of the oil. Maintain stirring reaction at 85°C for 30 minutes, pour into an insulated separatory funnel, keep warm at 85°C for 6 hours, and remove the wastewater solution at the bottom. The clear oil is tested for metal ions according to ASTM D5185-18, and the total metal ion content is 8ppm, of which the phosphorus content is 1ppm.

[0059] (2) Vacuum dehydration Pour the clear oil into a 2000ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric heating bowl under stirring. Turn on the water ring vacuum pump, control the vacuum residual pressure to 12000Pa, the solution temperature to 120℃, and dehydrate for 60 minutes. The water content of the solution is tested according to ISO662, and the water content test result is 0.05%.

[0060] (3) Subcritical transesterification Add clear oil and methanol with a weight of 20% of the oil to the autoclave, start stirring, slowly increase the temperature and pressure, start timing when the temperature reaches 225°C and the pressure reaches 5.0MPa, maintain the reaction for 2 hours, cool below 100°C and stop stirring, let stand for sedimentation separation for 2 hours, open the top drain valve, then slowly open the bottom valve to drain the crude glycerin, close the bottom valve, add 5% methanol from the top valve to carry out secondary ester exchange reaction, start stirring again, slowly increase the temperature and pressure, start timing when the temperature reaches 225°C and the pressure reaches 5.0MPa, maintain the reaction for 2 hours, Stop stirring when the temperature drops below 100°C, let the mixture stand for 2 hours, open the top drain valve, then slowly open the bottom valve to drain the crude glycerol, close the bottom valve, add 3% methanol from the top valve to carry out a tertiary transesterification reaction, continue stirring, slowly increase the temperature and pressure, start timing when the temperature reaches 225°C and the pressure reaches 5.0MPa, maintain the reaction under this condition for 2 hours, stop stirring when the temperature drops below 100°C, open the top drain valve, open the bottom valve, transfer the liquid into an insulated separatory funnel, let the mixture stand for 2 hours, remove the crude glycerol at the bottom, and carry out vacuum dealcoholization of the crude fatty acid methyl ester.

[0061] (4) Vacuum dealcoholization Pour the crude fatty acid methyl ester into a 2000ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric heating bowl under stirring conditions. Turn on the water ring vacuum pump, control the vacuum residual pressure to 12000Pa, the solution temperature to 95℃, and dealcoholize for 60 minutes. According to ISO662, the alcohol content of the solution was tested, and the methanol content test result was 0.08%.

[0062] (5) Alkaline washing Pour the dealcoholized fatty acid methyl ester into a 2000ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric heating bowl under stirring conditions. When the temperature reaches 85°C, add 10% of the weight of the methyl ester in alkaline water (i.e., a 3% sodium hydroxide solution) and stir and wash for 30 minutes. Pour into a heat-insulating separatory funnel, keep it at 85°C for 4 hours, and remove the wastewater solution at the bottom. The acid value of fatty acid methyl ester is tested according to GB / T5530, and the test result is 0.3mg KOH / g.

[0063] (6) Washing Alkaline washed fatty acid methyl ester is poured into a 2000ml three-necked flask, equipped with a stirrer and a thermometer. Under stirring conditions, the electric heating bowl is heated slowly to 95°C, and distilled water of 10% of the weight of the methyl ester is added for stirring and washing for 30 minutes. Pour into a heat-insulating separatory funnel, keep warm at 85°C for 4 hours, and remove the waste water solution at the bottom. The soap content of fatty acid methyl ester is tested according to GB / T5533, and the soap residue test result is 28ppm.

[0064] (7) Vacuum dehydration Fatty acid methyl ester was poured into a 2000ml three-necked flask, equipped with a stirrer and a thermometer. Under stirring conditions, the electric heating bowl was heated slowly, the water ring vacuum pump was turned on, the vacuum residual pressure was controlled to be 5000Pa, the solution temperature was 120℃, and dehydration was performed for 60 minutes to obtain 998g of fatty acid methyl ester (biodiesel). The water content of the solution was tested according to ISO662, and the water content was 0.03%; the fatty acid methyl ester content was tested according to EN14103, and the test result was 96.8%; the total glycerol residue was tested according to EN14105, and the test result was 0.19%; the sulfur content of fatty acid methyl ester was tested according to SH / T0689, and the test result was 9.1ppm; the acid value was tested according to GB / T5530, and the test result was 0.3mgKOH / g.

[0065] Example 2 The raw material oil is 1000 g of hogwash oil with an acid value of 18 mg KOH / g, a sulfur content of 31 ppm, and an unsaponifiable matter content of 0.6%. The pretreated oil obtained after treatment according to steps (1) and (2) of Example 1 is treated by the following step (3): Add clear oil and methanol with a weight of 18% of oil to the autoclave, start stirring, slowly increase the temperature and pressure, start timing when the temperature reaches 230°C and the pressure reaches 6.0MPa, maintain the reaction condition for 1 hour, cool below 100°C and stop stirring, let stand for sedimentation separation for 3 hours, open the top drain valve, then slowly open the bottom valve to drain the crude glycerin, close the bottom valve, add 7% methanol from the top valve to carry out secondary ester exchange reaction, start stirring again, slowly increase the temperature and pressure, start timing when the temperature reaches 230°C and the pressure reaches 6.0MPa, maintain the reaction condition for 1 hour, Stop stirring when the temperature drops below 100°C, let the mixture stand for 3 hours to settle and separate, open the top drain valve, then slowly open the bottom valve to drain the crude glycerol, close the bottom valve, add 3% methanol from the top valve to carry out a tertiary transesterification reaction, continue to stir, slowly increase the temperature and pressure, start timing when the temperature reaches 230°C and the pressure reaches 6.0MPa, maintain the reaction under this condition for 1 hour, stop stirring when the temperature drops below 100°C, open the top drain valve, open the bottom valve, transfer the liquid into an insulated separatory funnel, let the mixture stand for 3 hours to separate and separate, remove the crude glycerol at the bottom, and carry out vacuum dealcoholization of the crude fatty acid methyl ester.

[0066] The crude fatty acid methyl ester was treated by steps (4) to (7) of Example 1 to finally obtain 996 g of fatty acid methyl ester (biodiesel). The water content was detected according to ISO662, and the water content was 0.04%; the fatty acid methyl ester content was detected according to EN14103, and the test result was 96.7%; the total glycerol content was detected according to EN14105, and the test result was 0.21%; the sulfur content was detected according to SH / T0689, and the test result was 12.4 ppm; the acid value was detected according to GB / T5530, and the test result was 0.4 mg KOH / g.

[0067] Example 3 The raw material oil is 1000 g of hogwash oil with an acid value of 17 mg KOH / g, a sulfur content of 29 ppm, and an unsaponifiable matter content of 0.8%. The pretreated oil obtained after treatment according to steps (1) and (2) of Example 1 is treated by the following step (3): Add clear oil and methanol with a weight of 15% of the oil to the autoclave, start stirring, slowly increase the temperature and pressure, start timing when the temperature reaches 220°C and the pressure reaches 5.5MPa, maintain the reaction condition for 3 hours, cool below 100°C and stop stirring, let stand for sedimentation separation for 1 hour, open the top drain valve, then slowly open the bottom valve to drain the crude glycerin, close the bottom valve, add 10% methanol from the top valve for secondary ester exchange reaction, then start stirring, slowly increase the temperature and pressure, start timing when the temperature reaches 220°C and the pressure reaches 5.5MPa, maintain the reaction condition for 3 hours, Stop stirring when the temperature drops below 100°C, let the mixture stand for 1 hour to settle and separate, open the top drain valve, then slowly open the bottom valve to drain the crude glycerol, close the bottom valve, add 5% methanol from the top valve to carry out a tertiary transesterification reaction, continue to stir, slowly increase the temperature and pressure, start timing when the temperature reaches 220°C and the pressure reaches 5.5MPa, maintain the reaction under this condition for 3 hours, stop stirring when the temperature drops below 100°C, open the top drain valve, open the bottom valve, transfer the liquid into an insulated separatory funnel, let the mixture stand for 1 hour to separate and separate, remove the crude glycerol at the bottom, and carry out vacuum dealcoholization of the crude fatty acid methyl ester.

[0068] The crude fatty acid methyl ester was treated by steps (4) to (7) of Example 1 to finally obtain 995 g of fatty acid methyl ester (biodiesel). The water content was detected according to ISO662, and the water content was 0.05%; the fatty acid methyl ester content was detected according to EN14103, and the test result was 96.5%; the total glycerol content was detected according to EN14105, and the test result was 0.18%; the sulfur content was detected according to SH / T0689, and the test result was 8.2 ppm; the acid value was detected according to GB / T5530, and the test result was 0.3 mg KOH / g.

[0069] Comparative Example 1 Compared with Example 1, the only difference is that palmitic acid oil with an acid value of 97 mg KOH / g, a sulfur content of 44 ppm and an unsaponifiable matter content of 0.7% is used as the raw material.

[0070] The high acid value waste oil was treated by steps (1) to (7) of Example 1, and finally 989 grams of biodiesel was obtained. Performance test of distillation-free biodiesel: the water content was tested according to ISO662, and the water content was 0.04%; the fatty acid methyl ester content was tested according to EN14103, and the test result was 93.7%; the total glycerol content was tested according to EN14105, and the test result was 0.15%; the sulfur content was tested according to SH / T0689, and the test result was 18.7 ppm; the acid value was tested according to GB / T5530, and the test result was 1.6 mg KOH / g.

[0071] Comparative Example 2 Compared with Example 1, the only difference is that step (3) is adjusted as follows: Add clear oil and methanol with an oil weight of 28% to the autoclave, start stirring, slowly increase the temperature and pressure, start timing when the temperature reaches 225°C and the pressure reaches 5.0MPa, maintain the reaction for 2 hours, cool below 100°C and stop stirring, let stand for sedimentation separation for 2 hours, open the top drain valve, then slowly open the bottom valve to drain the crude glycerin, close the bottom valve, continue the secondary transesterification reaction, start stirring again, slowly increase the temperature and pressure, start timing when the temperature reaches 225°C and the pressure reaches 5.0MPa, maintain the reaction for 2 hours, Cool to below 100°C and stop stirring, let stand and settle for 2 hours, open the top drain valve, then slowly open the bottom valve to drain the crude glycerol, close the bottom valve, continue the tertiary transesterification reaction, continue stirring, slowly increase the temperature and pressure, start timing when the temperature reaches 225°C and the pressure reaches 5.0MPa, maintain the reaction conditions for 2 hours, cool to below 100°C and stop stirring, open the top drain valve, open the bottom valve, transfer the liquid into an insulated separatory funnel, let stand and settle for 2 hours, remove the crude glycerol at the bottom, and vacuum dealcoholize the crude fatty acid methyl ester.

[0072] The crude fatty acid methyl ester was treated by steps (4) to (7) of Example 1 to obtain 978 g of biodiesel. The water content was detected according to ISO662, and the water content was 0.05%. The fatty acid methyl ester content was detected according to EN14103, and the test result was 94.4%. The total glycerol content was detected according to EN14105, and the test result was 0.17%. The sulfur content was detected according to SH / T0689, and the test result was 9.3 ppm. The acid value was detected according to GB / T5530, and the test result was 0.8 mg KOH / g.

[0073] The present application prepares distillation-free biodiesel by sequentially degumming and removing metal ions from low-acid waste oils, first dehydration, subcritical transesterification, dealcoholization, alkali washing, water washing, and second dehydration. The method is simple, the yield is high, and the post-processing is simple. The fatty acid methyl ester content of the distillation-free biodiesel prepared in the present application is controlled to be above 96.5%, the sulfur content is controlled to be within 15ppm, the total glycerol content is controlled to be within 0.25%, and the yield is above 99%.

[0074] The specific implementation methods of the present application described above do not constitute a limitation on the protection 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 protection scope of the claims of the present application.

Claims

1. A method for preparing distillation-free biodiesel from low-acid-value waste oils, characterized in that: The following steps are involved: Degumming, removing metal ions and first dehydrating the low acid value waste oil to obtain pretreated oil; Performing a subcritical transesterification reaction on the pretreated oil and methanol to obtain crude fatty acid methyl ester; The crude fatty acid methyl ester is subjected to dealcoholization, alkali washing, water washing and a second dehydration to obtain distillation-free biodiesel.

2. The method for preparing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: The acid value of the low-acid-value waste oil is ≤20mg KOH / g, the sulfur content is ≤35ppm, and the unsaponifiable matter content is ≤1%; and / or, The metal ion content of the pretreated oil is ≤10ppm, the phosphorus element is ≤2ppm, and the water residue is ≤0.1%; and / or, The fatty acid methyl ester content in the distillation-free biodiesel is ≥96.5%.

3. The method for preparing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: The degumming and metal ion removal process comprises: mixing low acid value waste oil, oxalic acid and citric acid, stirring and reacting, and then performing a first static sedimentation separation to obtain the waste oil after degumming and metal ion removal; wherein, The amount of oxalic acid added is 0.1%-1.0% of the mass of the low acid value waste oil; and / or, The amount of citric acid added is 0.1-1.0% of the mass of the low acid value waste oil; and / or, The oxalic acid and the citric acid are added in the form of an aqueous solution, and the amount of the aqueous solution of the oxalic acid and the citric acid added is 3%-10% of the mass of the low acid value waste oil; and / or, The temperature of the degumming and metal ion removal is 80-100° C., and the time of the degumming and metal ion removal is 10-90 minutes; and / or, The temperature of the first static sedimentation separation is 80-100° C., and the time of the first static sedimentation separation is 2-10 hours.

4. The method for preparing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: The first dehydration is carried out by vacuum dehydration; wherein, The temperature of the vacuum dehydration is 90-120° C., the residual pressure of the vacuum dehydration is 8000-15000 Pa, and the time of the vacuum dehydration is 30-90 minutes.

5. The method for preparing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: The amount of methanol added is 20%-35% of the mass of the pretreated oil; and / or, The temperature of the subcritical transesterification reaction is 220-230° C., the pressure of the subcritical transesterification reaction is 5.0-6.0 MPa, and the time of the subcritical transesterification reaction is 1-9 hours; and / or, After the subcritical transesterification reaction is completed, a second static sedimentation separation is further performed, and the temperature of the second static sedimentation separation is 80-100° C., and the time of the second static sedimentation separation is 1-9 hours.

6. The method for preparing distillation-free biodiesel from waste oils with low acid value according to claim 5, characterized in that: A three-stage subcritical transesterification reaction is used; wherein, During the primary subcritical transesterification reaction, the amount of methanol added is 15%-25% of the mass of the pretreated oil; and / or, During the secondary subcritical transesterification reaction, the amount of methanol added is 5%-10% of the mass of the pretreated oil; and / or, During the three-stage subcritical transesterification reaction, the amount of methanol added is 3%-8% of the mass of the pretreated oil; and / or, The temperature of each subcritical transesterification reaction is 220-230°C, the pressure of each subcritical transesterification reaction is 5.0-6.0MPa, and the time of each subcritical transesterification reaction is 1-3 hours; and / or, After each subcritical transesterification reaction is completed, each second static sedimentation separation is carried out, and the temperature of each second static sedimentation separation is 80-100° C., and the time of each second static sedimentation separation is 1-3 hours.

7. The method for preparing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: The second dealcoholization is carried out by vacuum dealcoholization; wherein, The temperature of the vacuum dealcoholization is 80-100° C., the vacuum residual pressure is 8000-15000 Pa, and the time of the vacuum dealcoholization is 30-90 minutes.

8. The method for preparing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: The alkali washing process comprises: washing the crude fatty acid methyl ester after dealcoholization with a sodium hydroxide solution, and then performing a third static sedimentation separation to obtain the crude fatty acid methyl ester after alkali washing; wherein, The mass fraction of the sodium hydroxide solution is 2%-5%; and / or, The amount of the sodium hydroxide solution added is 5%-10% of the mass of the crude fatty acid methyl ester after dealcoholization; and / or, The alkali washing temperature is 80-100°C, and the alkali washing time is 15-30 minutes; and / or, The temperature of the third static sedimentation separation is 80-100° C., and the time of the third static sedimentation separation is 3-6 hours.

9. The method for preparing distillation-free biodiesel from waste oils and fats with low acid value according to claim 1, characterized in that: The water washing process comprises: washing the crude fatty acid methyl ester after alkali washing with pure water, and then performing a fourth static sedimentation separation to obtain the crude fatty acid methyl ester after water washing; wherein, The amount of pure water added is 5%-10% of the crude fatty acid methyl ester after alkali washing; and / or, The water washing temperature is 80-100°C, and the water washing time is 15-30 minutes; and / or, The temperature of the fourth static sedimentation separation is 80-100° C., and the time of the fourth static sedimentation separation is 2-4 hours.

10. The method for preparing distillation-free biodiesel from waste oils and fats with low acid value according to claim 1, characterized in that: The second dehydration is carried out by vacuum dehydration; wherein, The temperature of the vacuum dehydration is 90-120° C., the residual pressure of the vacuum dehydration is 3000-5000 Pa, and the time of the vacuum dehydration is 30-90 minutes.

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