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

Abstract

The invention discloses a method for producing distillation-free biodiesel from low-acid-value waste oil and fat, which comprises the following steps: degumming the low-acid-value waste oil and fat, and removing metal ions to obtain first oil and fat; dehydrating the first grease and removing low boiling points to obtain second grease; performing molecular distillation deacidification on the second grease to obtain third grease; performing transesterification on the third grease and methanol under the action of a base catalyst to obtain fourth grease; dealcoholizing the fourth grease to obtain fifth grease; washing the fifth grease to obtain sixth grease; and dehydrating the sixth grease to obtain the distillation-free biodiesel. The production method is simple and low in energy consumption, the biodiesel does not need to be distilled, and the fatty acid methyl ester content of the obtained biodiesel is larger than or equal to 96.5%.

Description

Technical Field

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

[0002] Biodiesel generally refers to fatty acid methyl esters produced by the transesterification reaction between animal and vegetable oils containing fatty acid triglycerides and methanol. 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 96.5% or more. As a renewable energy source with broad development prospects, biodiesel is facing important development opportunities under the background of global energy transformation and environmental protection. However, many challenges need to be overcome to achieve sustainable development of the industry. It is of great significance to promote the continuous growth of the biodiesel industry and make greater contributions to the global energy and environmental cause through efforts in various aspects such as technological innovation, policy support, market cultivation and international cooperation. At present, the main problems in the production of biodiesel are high raw material costs, lack of vegetable oil raw materials, and high production process costs of biomass conversion to biodiesel. The main components of waste oil are fatty acid triglycerides, and another part is fatty acids and impurities. From the perspective of physical and chemical properties, the components of waste oil are similar to those of animal and vegetable oils, and the physical and chemical properties have not changed significantly. After proper pretreatment, it can be used as a raw material for the production of biodiesel. Therefore, it is a common practice to use waste oil to convert into biodiesel.

[0003] Alkali-catalyzed transesterification (abbreviated as alkaline-catalyzed method) is one of the common production methods of biodiesel, but it has very high requirements for the content of free fatty acids and water in the raw materials. In actual production, it is often required that the lower the acid value of oil, the better. The higher the acid value, the greater the amount of catalyst used, the more fatty acid soaps are generated by neutralization and saponification reaction, and the amount of fatty acid methyl esters carried and lost increases simultaneously. Directly using waste oil as raw material cannot meet the requirements of alkaline-catalyzed biodiesel production, and it is often necessary to pre-treat it first. However, at present, biodiesel produced from waste oil raw materials still needs to go through a complex and energy-intensive distillation process to control the fatty acid methyl ester content to above 96.5%, which in turn will significantly reduce the yield of biodiesel and significantly increase production energy consumption. Distillation-free biodiesel is biodiesel obtained by omitting the distillation step in the traditional biodiesel production process. Compared with the traditional biodiesel distillation and refining process, the distillation-free method for producing biodiesel has the advantages of simplifying the production process, reducing production costs, reducing energy consumption, and greatly increasing the yield of biodiesel. Internationally, distillation-free biodiesel generally uses refined vegetable oils (salad oil) as raw materials. 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 raw materials.

[0004] Therefore, there is an urgent need to provide a method for producing distillation-free biodiesel from low-acid value waste oils, so as to significantly reduce production energy consumption while obtaining distillation-free biodiesel. Summary of the invention

[0005] The purpose of this application is to overcome the above-mentioned technical deficiencies, propose a method for producing distillation-free biodiesel from low-acid value waste oil, and solve the technical problem in the prior art that it is difficult to use waste oil as raw material to produce biodiesel with a fatty acid methyl ester content of ≥96.5% by a distillation-free method.

[0006] The present application provides a method for producing distillation-free biodiesel from low-acid-value waste oil, comprising the following steps: Degumming and removing metal ions from low-acid-value waste oil to obtain a first oil; Dehydrating and de-boiling the first oil to obtain a second oil; Performing molecular distillation and deacidification on the second oil to obtain a third oil; Conducting an ester exchange reaction on the third oil and methanol under the action of an alkali catalyst to obtain a fourth oil; Dealcoholizing the fourth oil to obtain a fifth oil; washing the fifth fat to obtain a sixth fat; The sixth oil is dehydrated to obtain distillation-free biodiesel.

[0007] Compared with the prior art, the beneficial effects of this application include: The present application uses low-acid waste oil as raw material, and sequentially undergoes degumming, metal ion removal, dehydration, low boiling point removal, and molecular distillation deacidification treatment to reduce the metal ion, colloid, water and fatty acid content in low-acid waste oil, and avoids the degradation of biodiesel quality due to oil hydrolysis and saponification reaction caused by alkali in the subsequent transesterification reaction; the present application can convert the third oil into crude fatty acid methyl ester through transesterification reaction, and finally obtain high-quality distillation-free biodiesel through simple dealcoholization, washing and dehydration. The production method of the present application is simple, low in energy consumption, and no distillation of biodiesel is required. The fatty acid methyl ester content of the obtained biodiesel is ≥96.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a process flow chart of an implementation method for producing 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 producing 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 to obtain a first oil; S2, dehydrating and de-boiling the first oil to obtain a second oil; S3, performing molecular distillation and deacidification on the second oil to obtain a third oil; S4, subjecting the third oil and methanol to an ester exchange reaction under the action of an alkali catalyst to obtain a fourth oil; S5, dealcoholizing the fourth oil to obtain a fifth oil; S6, washing the fifth grease to obtain a sixth grease; S7. Dehydrating the sixth oil to obtain distillation-free biodiesel.

[0011] The present application uses low-acid waste oil as raw material, and sequentially undergoes degumming, metal ion removal, dehydration, low boiling point removal, and molecular distillation deacidification treatment, which can reduce the metal ion, colloid, water and fatty acid content in low-acid waste oil, and avoid the degradation of biodiesel quality due to oil hydrolysis and saponification reaction caused by alkali in the subsequent transesterification reaction; the present application can convert the third oil into crude fatty acid methyl ester (i.e., the fourth oil) through transesterification reaction, and finally obtain high-quality distillation-free biodiesel after simple dealcoholization, washing, and dehydration. The inventor found in the experimental process that by adopting the means of first dehydration, low boiling point removal, and then molecular distillation deacidification, not only can the operation be made more stable, but also the generation of by-products can be reduced, and the fatty acid methyl ester content and yield in biodiesel can be increased. The production method of the present application is simple, energy-saving, and there is no need to distill biodiesel. The fatty acid methyl ester content of the obtained biodiesel is ≥96.5%.

[0012] In this embodiment, in step S1, 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, the low-acid-value waste oil can be swill oil, gutter oil, acidified oil, palmitic acid oil, etc.

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

[0014] In this embodiment, in step S1, the total metal ion content of the first oil is ≤10 ppm, and the phosphorus content thereof is ≤3 ppm.

[0015] The present application does not limit the process of degumming and demetallization, and those skilled in the art can make a choice according to the actual situation. In some specific embodiments of the present application, the process of degumming and demetallization includes: degumming and demetallization of low-acid waste oils and fats with oxalic acid and citric acid, followed by a first heat preservation sedimentation separation to obtain a first oil and fat. Among them, the amount of oxalic acid added is 0.1%-1.0% of the mass of the low-acid waste oil and fat, including but not limited to 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1% and the like; the amount of citric acid added is 0.1%-1.0% of the mass of the low-acid waste oil and fat, including but not limited to 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1% and the like; oxalic acid and citric acid are added in the form of an aqueous solution, and the amount of the aqueous solution of oxalic acid and citric acid added is 3%-10% of the mass of the low-acid waste oil and fat, including but not limited to 3%, 4%, 5%, 6%, 7%, 8%, 9% and the like. %, 10%, etc.; the temperature for degumming and metal ion removal 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 metal ion removal is 10-90 minutes, including but not limited to 10 minutes, 30 minutes, 50 minutes, 70 minutes, 90 minutes, etc.; the temperature for the first heat preservation sedimentation separation is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the time for the first heat preservation sedimentation separation is 2-10 hours, including but not limited to 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, etc. The present application uses oxalic acid and citric acid to degumming and metal ion removal from low acid value waste oils and fats, and cooperates with the above-mentioned process parameters to control the total metal ion content of the first oil and fat within 10ppm and the phosphorus content within 3ppm.

[0016] In this embodiment, in step S2, the water content of the second oil is ≤0.1%. In this application, by reducing the water content to within 0.1%, it is more conducive to the smooth progress of the subsequent transesterification reaction, reducing by-products and increasing the fatty acid methyl ester content.

[0017] The present application does not limit the process of dehydration and de-low boiling, and those skilled in the art can choose according to actual conditions. In some specific embodiments of the present application, vacuum dehydration and de-low boiling are adopted. Among them, the temperature of vacuum dehydration and de-low boiling is 90-120℃, including but not limited to 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, etc.; the vacuum residual pressure is 8000-15000Pa, including but not limited to 8000Pa, 9000Pa, 10000Pa, 11000Pa, 12000Pa, 13000Pa, 14000Pa, 15000Pa, etc.; the time of vacuum dehydration and de-low boiling is 30-90 minutes, including but not limited to 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, etc. By adopting the above-mentioned process parameters, the present application can control the water content of the second oil to within 0.1%.

[0018] In this embodiment, in step S3, the acid value of the third oil is ≤1 mg KOH / g. By reducing the acid value to within 1 mg KOH / g, the present application is more conducive to the smooth progress of the subsequent transesterification reaction, reducing by-products and increasing the fatty acid methyl ester content.

[0019] In this embodiment, in step S3, two-stage molecular distillation is used for deacidification; wherein, during the process of the first-stage molecular distillation, the vacuum residual pressure is 100-500Pa, including but not limited to 100Pa, 9000Pa, 200Pa, 300Pa, 400Pa, 500Pa, etc.; the temperature is 180-220°C, including but not limited to 180°C, 190°C, 200°C, 210°C, 220°C, etc.; the acid value of the first-stage molecular distillation oil is controlled within 5mg KOH / g; during the process of the second-stage molecular distillation, the vacuum residual pressure is 20-80Pa, including but not limited to 20Pa, 30Pa, 40Pa, 50Pa, 60Pa, 70Pa, 80Pa, etc.; the temperature is 210-240°C, including but not limited to 210°C, 220°C, 230°C, 240°C, etc. By adopting the above-mentioned process parameters, the present application can control the acid value of the third oil to within 1mg KOH / g.

[0020] In this embodiment, in step S4, the base catalyst is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium methoxide, potassium methoxide, and calcium hydroxide.

[0021] In this embodiment, in step S4, the amount of the alkaline catalyst added is 0.3%-0.5% of the mass of the third oil, including but not limited to 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0022] In this embodiment, in step S4, the amount of methanol added is 20%-35% of the mass of the third oil, including but not limited to 20%, 22%, 25%, 28%, 30%, 32%, 35%, etc.

[0023] In this embodiment, in step S4, the temperature of the ester exchange reaction is 56-66°C, including but not limited to 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, etc.; the time of the ester exchange reaction is 1-9 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, etc.

[0024] In this embodiment, in step S4, after the transesterification reaction is completed, a second heat preservation sedimentation separation is also performed. Specifically, the temperature of the second heat preservation sedimentation separation is 56-66°C, including but not limited to 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, etc.; the time of the second heat preservation sedimentation separation is 1-9 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, etc.

[0025] In some preferred embodiments of the present application, a tertiary transesterification reaction is adopted.

[0026] Among them, during the primary ester exchange reaction, the amount of base catalyst added is 0.25%-0.4% of the mass of the third oil, including but not limited to 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4% and the like; the amount of methanol added is 18%-25% of the mass of the third oil, including but not limited to 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% and the like.

[0027] Among them, during the secondary ester exchange reaction, the amount of base catalyst added is 0.05%-0.10% of the mass of the third oil, including but not limited to 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1% and the like; the amount of methanol added is 1%-5% of the mass of the third oil, including but not limited to 1%, 2%, 3%, 4%, 5% and the like.

[0028] Among them, during the tertiary ester exchange reaction, the amount of base catalyst added is 0.05%-0.10% of the mass of the third oil, including but not limited to 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1% and the like; the amount of methanol added is 1%-5% of the mass of the third oil, including but not limited to 1%, 2%, 3%, 4%, 5% and the like.

[0029] Among them, the temperature of each stage of ester exchange reaction is 56-66°C, including but not limited to 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, etc.; the time of each stage of 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.

[0030] After the ester exchange reaction at each stage is completed, the second heat preservation sedimentation separation is carried out. Specifically, the temperature of the second heat preservation sedimentation separation at each stage is 56-66°C, including but not limited to 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, etc.; the time of the second heat preservation sedimentation separation at each stage is 1-3 hours, including but not limited to 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.

[0031] The base catalysis method can produce biodiesel at a high yield at a lower temperature. In order to make the reaction more complete, a large amount of base catalysts and methanol are often added. However, due to the introduction of a large amount of base catalysts and methanol, it will not only cause a waste of raw materials, but also cause subsequent separation difficulties. The present application adopts a three-stage transesterification reaction, and the base catalyst and methanol are added in sections, and at the same time, the above-mentioned process parameters are matched to make the transesterification reaction more complete, and the triglyceride residue in the fatty acid methyl ester is controlled within 0.2%, the diglyceride residue is controlled within 0.2%, and the monoglyceride residue is controlled within 0.7%, and the amount of base catalyst and methanol is reduced, so as to avoid the difficulty of subsequent removal of base catalysts and alcohols due to the excessive amount of base catalysts and alcohols, and the loss of fatty acid methyl esters caused during the removal process, thereby improving the content and yield of fatty acid methyl esters in biodiesel.

[0032] More preferably, the crude glycerol obtained from the secondary transesterification reaction is returned to the primary transesterification reaction, the crude glycerol obtained from the tertiary transesterification reaction is returned to the secondary transesterification reaction, and the crude glycerol obtained from the primary transesterification reaction is processed separately.

[0033] In this embodiment, in step S5, the methanol residue in the fifth oil is less than 0.1%.

[0034] The present application does not limit the method of dealcoholization, and those skilled in the art can choose according to actual conditions. In some specific embodiments of the present application, a vacuum dealcoholization method is adopted. Among them, 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, 9000Pa, 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. The present application can control the alcohol residue in the fifth oil to within 0.1% by adopting the method of vacuum dealcoholization and coordinating the above-mentioned process parameters.

[0035] In this embodiment, in step S6, the soap residue in the sixth oil is less than 50 ppm.

[0036] The present application does not limit the washing method, and those skilled in the art can choose according to actual conditions. In some specific embodiments of the present application, washing is carried out by water washing, followed by third heat preservation sedimentation separation to obtain the sixth grease. Wherein, the amount of water added is 5%-10% of the mass of the fifth grease, including but not limited to 5%, 6%, 7%, 8%, 9%, 10%, etc.; the washing temperature is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the washing time is 15-30 minutes, including but not limited to 15 minutes, 17 minutes, 20 minutes, 22 minutes, 25 minutes, 28 minutes, 30 minutes, etc.; the temperature of the third heat preservation 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 heat preservation sedimentation separation is 2-4 hours, including but not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc. The present application adopts a water washing method and cooperates with the above-mentioned process parameters to control the soap residue in the sixth oil to within 50 ppm.

[0037] In this embodiment, in step S7, the residual water in the non-distillation biodiesel is less than 0.1%.

[0038] The present application does not limit the dehydration method, and those skilled in the art can choose according to actual conditions. In some specific embodiments of the present application, a vacuum dehydration method is adopted. Among them, the temperature of vacuum dehydration is 90-120°C, including but not limited to 90°C, 100°C, 110°C, 120°C, etc.; the vacuum residual pressure is 3000-5000Pa, including but not limited to 3000Pa, 3500Pa, 40000Pa, 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. The present application adopts the method of vacuum dehydration and cooperates with the above-mentioned process parameters to control the water residue in the crude fatty acid methyl ester obtained after dehydration to within 0.1%.

[0039] Example 1 (1) Degumming and metal ion removal Add 1000g of slop oil with an acid value of 10mg KOH / g, a sulfur content of 35ppm, and 0.8% unsaponifiable matter 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 of 5% by weight of the oil, and in the mixed acid solution, oxalic acid is 0.7% by weight of the oil, and citric acid is 0.3% by weight of the oil. Maintain stirring reaction at 85°C for 30 minutes, pour into an insulated separatory funnel, insulate at 85°C for 6 hours, and remove the wastewater solution at the bottom. Clear oil is tested for metal ions according to ASTM D5185-18, and the total metal ion content is 9ppm, including 2ppm of phosphorus.

[0040] (2) Vacuum dehydration and low boiling point removal 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%.

[0041] (3) Molecular distillation to remove fatty acids: First-stage molecular distillation: vacuum residual pressure is controlled at 100Pa, oil feed temperature is controlled at 220℃, defatty acid oleic acid value is tested according to GB / T5530, and the acid value test result is 3.6mg KOH / g; Secondary molecular distillation: vacuum residual pressure is controlled at 20Pa, oil feed temperature is controlled at 240°C, defatty acid oleic acid value is tested according to GB / T5530, and the acid value test result is 0.8mg KOH / g.

[0042] (4) Base-catalyzed transesterification Primary transesterification reaction: Add oil with an acid value of 0.8 mg KOH / g to a 2000 ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 65°C, add a mixed solution containing 0.3% potassium hydroxide by weight of oil and 20% methanol by weight of oil. Maintain stirring at 65°C for 2 hours, pour into a heat-insulating separating funnel, keep at 65°C for 2 hours, remove the crude glycerol solution at the bottom, and the crude methyl ester enters the secondary transesterification reaction.

[0043] Secondary transesterification reaction: Add the crude methyl ester from the primary reaction into a 2000ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 65°C, add a mixed solution containing 0.05% potassium hydroxide by weight and 3% methanol by weight of oil, and maintain stirring at 65°C for 2 hours. Pour the mixture into an insulated separating funnel, and keep it at 65°C for 2 hours to separate by sedimentation. Remove the crude glycerol solution at the bottom, and the crude methyl ester enters the tertiary transesterification reaction, and the crude glycerol returns to the primary transesterification reaction.

[0044] Tertiary transesterification reaction: Add the secondary reaction crude methyl ester to 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 65°C, add a pre-prepared mixed solution containing 0.05% potassium hydroxide by weight of oil and 3% methanol by weight of oil, maintain 65°C for stirring and reaction for 2 hours, pour into a heat-insulating separatory funnel, keep 65°C for sedimentation and separation for 2 hours, remove the crude glycerol solution at the bottom, and return the crude glycerol to the secondary transesterification reaction. Crude fatty acid methyl ester is tested according to EN14105. The target requirement for triglycerides is less than 0.2%, and the test result is less than 0.1%; the target requirement for diglycerides is less than 0.2%, and the test result is 0.18%; the target requirement for monoglycerol fatty acid ester content is less than 0.7%, and the test result is 0.68%. Qualified crude fatty acid methyl ester enters the vacuum dealcoholization process.

[0045] (5) 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 methanol content was tested and the methanol content test result was 0.08%.

[0046] (6) 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 95°C, add distilled water that is 10% of the weight of the methyl ester and stir and wash for 30 minutes. Pour it into a heat-insulating separating funnel, keep it at 85°C for 4 hours, and remove the wastewater 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 32ppm.

[0047] (7) Vacuum dehydration Desoaped 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 933g of fatty acid methyl ester (biodiesel). The water content 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 96.7%; the total glycerol content was tested according to EN14105, and the test result was 0.17%; the sulfur content was tested according to SH / T0689, and the test result was 10.2ppm; the acid value was tested according to GB / T5530, and the test result was 0.3mg KOH / g.

[0048] 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 29 ppm, and an unsaponifiable matter content of 0.9%. The second oil obtained after treatment according to steps (1) and (2) of Example 1 is treated by the following steps (3) and (4): (3) Molecular distillation to remove fatty acids: First-stage molecular distillation: vacuum residual pressure is controlled at 200Pa, oil feed temperature is controlled at 200℃, defatty acid oleic acid value is tested according to GB / T5530, and the acid value test result is 4.1 mg KOH / g; Secondary molecular distillation: vacuum residual pressure is controlled at 30Pa, oil feed temperature is controlled at 210°C, defatty acid oleic acid value is tested according to GB / T5530, and the acid value test result is 0.9 mg KOH / g.

[0049] (4) Base-catalyzed transesterification Primary transesterification reaction: Add oil with an acid value of 0.9 mg KOH / g to a 2000 ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 60°C, add a mixed solution containing 0.25% potassium hydroxide by weight of oil and 18% methanol by weight of oil. Maintain stirring at 60°C for 3 hours, pour into a heat-insulating separating funnel, keep at 60°C for 1 hour, remove the crude glycerol solution at the bottom, and the crude methyl ester enters the secondary transesterification reaction.

[0050] Secondary transesterification reaction: add the crude methyl ester from the primary reaction into a 2000ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 60°C, add a mixed solution containing 0.10% potassium hydroxide by weight of oil and 5% methanol by weight of oil, maintain stirring at 60°C for 3 hours, pour into an insulated separating funnel, keep at 60°C for sedimentation and separation for 1 hour, remove the crude glycerol solution at the bottom, and the crude methyl ester enters the tertiary transesterification reaction, and the crude glycerol returns to the primary transesterification reaction.

[0051] Tertiary transesterification reaction: Add the secondary reaction crude methyl ester to 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 60°C, add a pre-prepared mixed solution containing 0.10% potassium hydroxide by weight of oil and 5% methanol by weight of oil, maintain 60°C stirring reaction for 3 hours, pour into a heat-insulating separatory funnel, keep 60°C for sedimentation separation for 1 hour, remove the bottom crude glycerol solution, and return the crude glycerol to the secondary transesterification reaction. Crude fatty acid methyl ester is tested according to EN14105. The target requirement for triglycerides is less than 0.2%, and the test result is less than 0.1%; the target requirement for diglycerides is less than 0.2%, and the test result is 0.17%; the target requirement for monoglycerol fatty acid ester content is less than 0.7%, and the test result is 0.62%. Qualified crude fatty acid methyl ester enters the vacuum dealcoholization process.

[0052] The crude fatty acid methyl ester was treated by steps (5) to (7) of Example 1 to finally obtain 928 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 97.2%; the total glycerol content was detected according to EN14105, and the test result was 0.15%; the sulfur content was detected according to SH / T0689, and the test result was 9.4 ppm; the acid value was detected according to GB / T5530, and the test result was 0.3 mg KOH / g.

[0053] Example 3 The raw material oil is 1000 g of hogwash oil with an acid value of 15 mg KOH / g, a sulfur content of 26 ppm, and an unsaponifiable matter content of 0.5%. The second oil obtained after treatment according to steps (1) and (2) of Example 1 is treated by the following steps (3) and (4): (3) Molecular distillation to remove fatty acids: First-stage molecular distillation: vacuum residual pressure is controlled at 500Pa, oil feed temperature is controlled at 220℃, defatty acid oleic acid value is tested according to GB / T5530, and the acid value test result is 3.9 mg KOH / g; Secondary molecular distillation: vacuum residual pressure is controlled at 50Pa, oil feed temperature is controlled at 230°C, defatty acid oleic acid value is tested according to GB / T5530, and the acid value test result is 0.9 mg KOH / g.

[0054] (4) Base-catalyzed transesterification Primary transesterification reaction: Add oil with an acid value of 0.9 mg KOH / g to a 2000 ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 65°C, add a mixed solution containing 0.3% potassium hydroxide by weight of oil and 22% methanol by weight of oil. Maintain stirring at 65°C for 3 hours, pour into a heat-insulating separating funnel, keep at 65°C for sedimentation and separation for 3 hours, remove the crude glycerol solution at the bottom, and the crude methyl ester enters the secondary transesterification reaction.

[0055] Secondary transesterification reaction: add the crude methyl ester from the primary reaction into a 2000ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 65°C, add a mixed solution containing 0.05% potassium hydroxide by weight and 1% methanol by weight. Maintain stirring at 65°C for 3 hours, pour into a heat-insulating separating funnel, keep at 65°C for sedimentation and separation for 3 hours, remove the crude glycerol solution at the bottom, and the crude methyl ester enters the tertiary transesterification reaction, and the crude glycerol returns to the primary transesterification reaction.

[0056] Tertiary transesterification reaction: Add the secondary reaction crude methyl ester to 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 65°C, add a pre-prepared mixed solution containing 0.05% potassium hydroxide by weight of oil and 1% methanol by weight of oil, maintain 65°C for stirring and reaction for 3 hours, pour into a heat-insulating separatory funnel, keep 65°C for sedimentation and separation for 3 hours, remove the bottom crude glycerol solution, and return the crude glycerol to the secondary transesterification reaction. Crude fatty acid methyl ester is tested according to EN14105. The target requirement for triglycerides is less than 0.2%, and the test result is less than 0.1%; the target requirement for diglycerides is less than 0.2%, and the test result is 0.15%; the target requirement for monoglycerol fatty acid ester content is less than 0.7%, and the test result is 0.56%. Qualified crude fatty acid methyl ester enters the vacuum dealcoholization process.

[0057] The crude fatty acid methyl ester was treated by steps (5) to (7) of Example 1 to finally obtain 942 g of fatty acid methyl ester (biodiesel). The water content was detected according to ISO662, and the water content was 0.07%; the fatty acid methyl ester content was detected according to EN14103, and the test result was 97.3%; 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 9.1 ppm; the acid value was detected according to GB / T5530, and the test result was 0.25 mg KOH / g.

[0058] Comparative Example 1 Compared with Example 1, the only difference is that step (2) is adjusted as follows: Pour the clear oil into a 2000ml three-necked flask, install a stirrer and a thermometer, heat the electric heating bowl slowly under stirring, start the water ring vacuum pump, control the vacuum residual pressure to 12000Pa, the solution temperature to 80℃, and dehydrate for 10 minutes. According to ISO662, the water content of the solution was tested, and the water content test result was 0.22%.

[0059] The second oil obtained in step (2) was treated by steps (3) to (7) of Example 1, and finally 911 g of distillation-free biodiesel was obtained. Performance test of distillation-free biodiesel: water content was detected according to ISO662, and the water content was 0.02%; fatty acid methyl ester content was detected according to EN14103, and the test result was 95.2%; total glycerol content was detected according to EN14105, and the test result was 0.19%; sulfur content was detected according to SH / T0689, and the test result was 10.8 ppm; acid value was detected according to GB / T5530, and the test result was 0.6 mg KOH / g.

[0060] Comparative Example 2 Compared with Example 1, the only difference is that step (4) is adjusted as follows: Primary transesterification reaction: Add oil with an acid value of 0.8 mg KOH / g to a 2000 ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 65°C, add a mixed solution containing 0.4% potassium hydroxide by weight of oil and 26% methanol by weight of oil. Maintain stirring at 65°C for 2 hours, pour into a heat-insulating separating funnel, keep at 65°C for 2 hours, remove the crude glycerol solution at the bottom, and the crude methyl ester enters the secondary transesterification reaction.

[0061] Secondary transesterification reaction: Add the crude methyl ester from the primary reaction into a 2000ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring conditions. When the temperature reaches 65°C, maintain the stirring reaction at 65°C for 2 hours, pour it into an insulated separating funnel, keep it at 65°C for 2 hours, remove the crude glycerol solution at the bottom, and the crude methyl ester enters the tertiary transesterification reaction, and the crude glycerol returns to the primary transesterification reaction.

[0062] Tertiary ester exchange reaction: Add the crude methyl ester from the secondary reaction into a 2000ml three-necked flask, install a stirrer and a thermometer, and slowly heat the electric bowl under stirring. When the temperature reaches 65°C, maintain stirring at 65°C for 2 hours, then pour into a heat-insulating separating funnel, keep at 65°C for 2 hours, and remove the crude glycerol solution at the bottom.

[0063] The crude fatty acid methyl ester was treated by steps (5) to (7) of Example 1 to finally obtain 902 g of biodiesel. The water content was detected according to ISO662, and the water content was 0.02%; the fatty acid methyl ester content was detected according to EN14103, and the test result was 94.3%; the total glycerol content was detected according to EN14105, and the test result was 0.35%; the sulfur content was detected according to SH / T0689, and the test result was 10.6 ppm; the acid value was detected according to GB / T5530, and the test result was 0.5 mg KOH / g.

[0064] Comparative Example 3 Compared with Example 1, the only difference is that palmitic acid oil with an acid value of 91 mg KOH / g, a sulfur content of 36 ppm and an unsaponifiable matter content of 0.7% is used as the raw material.

[0065] The high acid value waste oil was treated by steps (1) to (7) of Example 1, and finally 550 g of biodiesel was obtained. Performance test of distillation-free biodiesel: the water content was tested according to ISO662, and the water content was 0.01%; the fatty acid methyl ester content was tested according to EN14103, and the test result was 95.8%; the total glycerol content was tested according to EN14105, and the test result was 0.19%; the sulfur content was tested according to SH / T0689, and the test result was 11 ppm; the acid value was tested according to GB / T5530, and the test result was 0.35 mg KOH / g.

[0066] In summary, the present application uses low-acid-value waste oil as raw material, and sequentially undergoes degumming, metal ion removal, dehydration, low-boiling point removal, molecular distillation deacidification, ester exchange reaction, dealcoholization, washing, and dehydration to produce distillation-free biodiesel, and the method is simple and has low energy consumption; the fatty acid methyl ester content in the biodiesel produced by the present application is controlled to be above 96.5%, the sulfur content is controlled to be within 15ppm, and the total glycerol content is controlled to be within 0.25%; by adopting the above steps and further coordinating certain process parameters, the present application can also obtain high-quality biodiesel with a fatty acid methyl ester content of above 96.5%, while controlling the yield of biodiesel to above 90%.

[0067] 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 producing distillation-free biodiesel from low-acid-value waste oils, characterized in that: The following steps are involved: Degumming and removing metal ions from low-acid-value waste oil to obtain a first oil; Dehydrating and removing the low boiling point of the first oil to obtain a second oil; Performing molecular distillation and deacidification on the second oil to obtain a third oil; Conducting an ester exchange reaction between the third oil and methanol under the action of an alkali catalyst to obtain a fourth oil; Dealcoholizing the fourth oil to obtain a fifth oil; Washing the fifth fat to obtain a sixth fat; The sixth oil is dehydrated to obtain distillation-free biodiesel.

2. The method for producing distillation-free biodiesel from low-acid-value waste oils 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 total metal ion content of the first oil is ≤10ppm, and the phosphorus content is ≤3ppm; and / or, The water content of the second oil is ≤0.1%; and / or, The acid value of the third oil is ≤1 mg KOH / g; and / or, The methanol residue in the fifth oil is less than 0.1%; and / or, The soap residue in the sixth oil is less than 50 ppm; and / or, The water residue in the distillation-free biodiesel is less than 0.1%, and the fatty acid methyl ester content is ≥96.5%.

3. The method for producing distillation-free biodiesel from low-acid-value waste oils according to claim 1, characterized in that: The degumming and metal ion removal process comprises: using oxalic acid and citric acid to degumming and metal ion removal from low acid value waste oil, and then performing a first heat preservation sedimentation separation to obtain a first oil; 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 degumming and demetallization is 80-100°C, and the time of degumming and demetallization is 10-90 minutes; and / or, The temperature of the first heat preservation sedimentation separation is 80-100° C., and the time of the first heat preservation sedimentation separation is 2-10 hours.

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

5. The method for producing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: Two-stage molecular distillation is used for deacidification; During the first-stage molecular distillation, the vacuum residual pressure is 100-500Pa, the temperature is 180-220°C, and the acid value of the first-stage molecular distillation oil is controlled within 5mg KOH / g; During the secondary molecular distillation process, the vacuum residual pressure is 20-80Pa and the temperature is 210-240°C.

6. The method for producing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: The alkaline catalyst is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium methoxide, potassium methoxide, and calcium hydroxide; The amount of the alkaline catalyst added is 0.3%-0.5% of the mass of the third oil; The amount of methanol added is 20%-35% of the mass of the third oil; The temperature of the transesterification reaction is 56-66° C., and the time of the transesterification reaction is 1-9 hours; After the transesterification reaction is completed, a second heat preservation sedimentation separation is performed, and the temperature of the second heat preservation sedimentation separation is 56-66° C., and the time of the second heat preservation sedimentation separation is 1-9 hours.

7. The method for producing distillation-free biodiesel from low-acid-value waste oils according to claim 6, characterized in that: A three-stage transesterification reaction is used; wherein, During the primary transesterification reaction, the amount of the base catalyst added is 0.25%-0.4% of the mass of the third oil, and the amount of the methanol added is 18%-25% of the mass of the third oil; During the secondary transesterification reaction, the amount of the base catalyst added is 0.05%-0.10% of the mass of the third oil, and the amount of the methanol added is 1%-5% of the mass of the third oil; During the tertiary transesterification reaction, the amount of the base catalyst added is 0.05%-0.10% of the mass of the third oil, and the amount of methanol added is 1%-5% of the mass of the third oil; The temperature of each level of transesterification reaction is 56-66°C, and the time of each level of transesterification reaction is 1-3 hours; After the ester exchange reaction at each stage is completed, the second heat preservation sedimentation separation is carried out, and the temperature of the second heat preservation sedimentation separation at each stage is 56-66° C., and the time of the second heat preservation sedimentation separation at each stage is 1-3 hours.

8. The method for producing distillation-free biodiesel from low-acid-value waste oils according to claim 1, characterized in that: The fourth oil is subjected to 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.

9. The method for producing distillation-free biodiesel from waste oils with low acid value according to claim 1, characterized in that: The oil is washed with water and then separated by a third heat preservation sedimentation to obtain a sixth oil; wherein, The amount of water added is 5%-10% of the mass of the fifth oil; The washing temperature is 80-100°C and the washing time is 15-30 minutes; The temperature of the third thermal insulation sedimentation separation is 80-100° C., and the time of the third thermal insulation sedimentation separation is 2-4 hours.

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

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