A kind of low-condensation biodiesel and preparation method thereof

Abstract

The present invention provides a low-condensation biodiesel and a preparation method thereof, belonging to the technical field of bio-oil products. The preparation method comprises the following steps: (1) acid reduction process: (2) pre-hydrogenation process; (3) deep hydrogenation refining process; (4) hydrogenation isomerization process: the product of deep hydrogenation refining is subjected to the hydrogenation isomerization process to reduce the condensation point. The preparation method of isomerization hydrogenation catalyst comprises the following steps: a. mixing a microporous molecular sieve with a NaOH aqueous solution, reflux stirring, cooling, suction filtering, washing with water to neutrality, and drying to obtain a pre-treated molecular sieve; b. mixing the pre-treated molecular sieve with H2PtCl6, stirring to a paste, standing, and drying to obtain a catalyst precursor; c. heating the catalyst precursor, heat-insulating and roasting to obtain an isomerization hydrogenation catalyst; (5) performing a deep hydrogenation refining process again to obtain a low-condensation biodiesel. The preparation method of the present invention has a high yield, and the prepared low-condensation biodiesel meets the use standard.

Description

Technical Field

[0001] The invention belongs to the technical field of bio-oil products, and in particular relates to low-condensation biodiesel and a preparation method thereof. Background Art

[0002] Typically, biodiesel has a high freezing point, which means it can become very viscous or even solidify at lower temperatures, leading to problems such as engine filter clogging. To address this problem, low freezing point biodiesel was developed. Low freezing point biodiesel is a specially treated biodiesel designed to lower its freezing point at low temperatures. Low freezing point biodiesel is mainly used in areas with low winter temperatures to ensure normal operation of engines under low temperature conditions. In addition, it can also be used in a variety of equipment and vehicles that require low temperature starting performance.

[0003] The second generation of biodiesel is mainly produced by hydrogenation and deoxygenation to produce oxygen-free normal alkane compounds. Compared with the first generation of biodiesel, the chemical structure of the second generation of biodiesel is similar to that of petrochemical diesel, and its main properties are also similar. It has the advantages of high cetane number and low sulfur content, and can be added to petrochemical diesel in a larger proportion.

[0004] In order to protect the environment and utilize waste, in recent years, waste cooking oil has become one of the raw materials for preparing biodiesel. The invention patent with application number CN202011248311.1 discloses a process for producing low-condensation biodiesel and a combined hydrogenation reactor and reactor system, which can use a variety of oil raw materials to prepare low-condensation biodiesel. However, in practice, it is found that when waste cooking oil is used as its raw material for preparation, due to the complex composition of waste cooking oil, it may contain a variety of impurities, such as moisture, solid particles, oxidation products, etc., which may affect the activity and reaction efficiency of the catalyst, resulting in the use of traditional catalysts in the equipment, with low yields, and the overall quality of the prepared biodiesel is poor.

[0005] Therefore, there is an urgent need for a low-condensation biodiesel and a preparation method thereof. Summary of the invention

[0006] The purpose of the present invention is to provide a low-condensation biodiesel and a preparation method thereof.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing low-condensation biodiesel comprises the following steps:

[0009] (1) Acid reduction process: waste oil from which mechanical impurities have been removed, ethanol with a mass of 3-4 times that of the waste oil, water with a mass of 2-3% that of the waste oil, and mixed bacteria are added to a reactor and reacted aerobically at 40-45°C for 2-3 hours; after the reaction is completed, the heavy phase and light phase containing bacteria are separated after static stratification, and the light phase is evaporated to remove water and ethanol to obtain pretreated waste oil; the mixed bacteria include Bacillus subtilis, Pseudomonas aeruginosa, and Rhodococcus erythrorhizium, and the amount of Bacillus subtilis is 10 4 -10 5 CFU / g waste oil; the amount of Pseudomonas aeruginosa is 10 3 -10 4 CFU / g waste oil; the amount of the red coccus is 10 5 -10 6 CFU / g waste oil;

[0010] (2) Pre-hydrogenation process: The pre-treated waste oil is subjected to the pre-hydrogenation process in a hydrogenation reactor, with a reaction temperature of 200-250°C, a pressure of 10-15 MPa, and a volume ratio of hydrogen to waste oil (100-150): 1;

[0011] (3) Deep hydrotreating process: The product of the pre-hydrotreating process is subjected to a deep hydrotreating process at a reaction temperature of 350-400°C, a pressure of 10-15 MPa, and a volume ratio of hydrogen to waste oil (1000-1200): 1;

[0012] (4) Hydroisomerization process: The product of deep hydrogenation refining is subjected to the hydroisomerization process to reduce the freezing point. The reaction temperature is 350-360°C, the pressure is 25-30MPa, the volume ratio of hydrogen to waste oil is (500-600): 1, and the volume space velocity of the isomerization hydrogenation catalyst is 0.5-1.5h -1 ;

[0013] The preparation method of the isomerization hydrogenation catalyst comprises the following steps:

[0014] a. Mix the microporous molecular sieve and NaOH aqueous solution in a weight ratio of 1: (20-30), reflux and stir at 80-85°C for 6-8h, cool, filter, wash with water until neutral, and dry to obtain the pretreated molecular sieve;

[0015] b. Mix the pretreated molecular sieve and H2PtCl6 in a weight ratio of 1: (0.05-0.1), stir until a paste, let stand at 25-30°C for 4-6 hours, and then dry at 70-75°C for 25-30 hours to obtain a catalyst precursor;

[0016] c. Raise the temperature of the catalyst precursor to 250-300°C and calcine for 3-5 hours to obtain an isomerization hydrogenation catalyst;

[0017] (5) Deep hydrogenation refining process again: The reaction products of the hydroisomerization process are further refined by deep hydrogenation refining process, with the reaction temperature of 350-400°C, pressure of 10-15MPa, volume ratio of hydrogen to waste cooking oil (1000-1200): 1, to obtain low-condensation biodiesel.

[0018] Furthermore, the preparation method of the microporous molecular sieve comprises the following steps:

[0019] Step 1, mixing mica powder and sodium hydroxide and calcining them to obtain clinker;

[0020] Step 2: adding deionized water and n-propylamine to the clinker and stirring to obtain a silica-alumina gel;

[0021] Step 3: Place the silica-alumina gel in a crystallization kettle for crystallization at a temperature of 180-185° C. for 30-35 hours to obtain a microporous molecular sieve.

[0022] The present invention uses the commercially available SKI-110 isomerization catalyst (Liaoning Haitai Technology Development Co., Ltd.) to carry out the hydrogenation isomerization process, and the yield of low-condensation biodiesel is not ideal. This may be caused by the poor catalytic process of the commercially available product for the gutter oil raw material. The present invention uses microporous molecular sieves and H2PtCl6 to prepare an isomerization hydrogenation catalyst, which can improve the yield of low-condensation biodiesel. Analysis shows that the microporous molecular sieves prepared by the present invention have the characteristics of high specific surface area, which means that they can provide more active sites for reactant adsorption. More active sites can increase the contact opportunities between reactants and catalysts, thereby improving reaction efficiency and product yield. At the same time, the microporous molecular sieve has a regular pore structure, which is conducive to the reactant molecules entering the pores and contacting with the catalyst active center, and also facilitates the smooth escape of product molecules. A good pore structure can reduce the occurrence of side reactions and improve the selectivity of the target product. In the catalyst preparation process, the microporous molecular sieve can be used as a carrier to help the precious metal (Pt) be evenly dispersed on its surface. Uniform dispersion can avoid the aggregation of metal particles, thereby increasing the number of active sites and improving the activity and selectivity of the catalyst. The pore structure and surface properties of microporous molecular sieves help reduce unwanted side reactions, such as over-hydrogenation or cracking, thereby improving the selectivity and yield of the target product.

[0023] Furthermore, the mica powder comprises the following components in percentage by mass: 46-50% SiO2, 35-39% Al2O3, 0.5-1.5% Fe2O3, 1-2.5% K2O, 0.5-2.5% Na2O, 1-3% CaO, and 3-6% H2O.

[0024] Furthermore, the mica powder includes the following components in mass percentage: 49.8% SiO2, 37.8% Al2O3, 1.2% Fe2O3, 2.3% K2O, 2.0% Na2O, 2.1% CaO, and 4.8% H2O.

[0025] The present invention uses mica powder of a specific composition to prepare a microporous molecular sieve, which can make the prepared low-condensation biodiesel more in line with the use standard. Mainly, the chemical composition of the mica powder can affect the pore size of the microporous molecular sieve finally prepared. By selecting and adjusting the composition of the mica powder, the pore size of the molecular sieve can be accurately controlled, thereby allowing molecules of a specific size to enter the pores. This selectivity helps to improve the selective hydroisomerization of specific components in biodiesel, thereby optimizing the quality and performance of the product.

[0026] Furthermore, the weight ratio of the mica powder to sodium hydroxide is 1:(1.6-1.8).

[0027] Furthermore, the calcination temperature is 630-650° C., and the calcination time is 2-3 hours.

[0028] Furthermore, the amount of deionized water added is 10-30 mL / 1 g mica powder, and the stirring time is 5-6 h.

[0029] Furthermore, the molar ratio of n-propylamine to deionized water is 1:(120-150).

[0030] Furthermore, in step c, the heating rate of the catalyst precursor is 1.2-1.5° C. / min.

[0031] When the heating rate of the catalyst precursor of the present invention is 1.2-1.5°C / min, the service life of the isomerization hydrogenation catalyst prepared is longer. Because the heating rate of the catalyst precursor during the calcination process will affect the formation of its internal structure. If the heating rate is too fast, the following problems may occur: uneven cracking; structural defects: rapid heating may cause stress concentration inside the catalyst, forming microcracks or other structural defects, which will reduce the service life of the catalyst. A slow and uniform heating rate (1.2-1.5°C / min) can ensure that the moisture and organic matter in the catalyst precursor (such as chloride ions in the Pt precursor) are gradually discharged to avoid structural damage caused by local overheating. This helps to form a more uniform and stable catalyst structure. At the same time, a slow heating rate can reduce the impact of thermal shock on the catalyst structure. If the heating rate is too fast, the temperature difference between the inside and outside of the catalyst material will cause thermal stress, thereby damaging the structural integrity of the catalyst. An appropriate heating rate helps the catalyst material to form a more stable crystal structure at high temperature, thereby improving its thermal stability and chemical stability and extending its service life. A slow heating process helps to optimize the dispersion of the precious metal (Pt) on the carrier. Too fast a heating may cause metal particles to aggregate, reducing the number of active sites, thus affecting the performance of the catalyst. At the same time, slow heating can reduce the occurrence of side reactions, ensuring that the catalyst does not undergo unnecessary chemical changes during the calcination process, thereby maintaining its original activity and selectivity. The present invention controls the heating rate of the catalyst precursor to 1.2-1.5°C / min, thereby ensuring that the catalyst undergoes a uniform and mild heat treatment process during the calcination process, which helps to form a more uniform and stable catalyst structure, thereby improving the service life and performance of the catalyst.

[0032] Furthermore, the mass concentration of the NaOH aqueous solution is 25-30%.

[0033] When the water content in the waste oil is greater than 0.5% or the free fatty acid content is greater than 3%, the water and free fatty acids contained in these raw oils will cause the final acid value of the product to be high, and the standard acidity of biodiesel (in terms of KOH) specified in NB / T10897-2021 is ≤5mg / 100mL. In order to solve the above problems, the present invention pre-treats the waste oil to reduce the acidity of low-condensation biodiesel. The present invention uses specific strains for compounding, ferments the waste oil, converts the free fatty acids in the waste oil into esters or degrades them, and the product obtained by subsequent hydrogenation reaction of the pretreated waste oil meets the NB / T10897-2021 standard. At the same time, it was found in the experiment that the strains acted synergistically to affect the performance of the subsequent products, especially the condensation point and acidity. The analysis shows that the strains restrict each other, prevent the production of excessive esters, affect the composition of the subsequent reaction products, and then affect the condensation point of the product.

[0034] The invention also provides low-condensation biodiesel prepared by the preparation method.

[0035] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0036] 1. The preparation method of the present invention has high yield, and the prepared low-condensation biodiesel meets the use standards. The prepared isomerization hydrogenation catalyst has a long service life.

[0037] 2. The present invention can improve the yield of low-condensation biodiesel by using microporous molecular sieve and H2PtCl6 to prepare isomerization hydrogenation catalyst.

[0038] 3. The present invention uses mica powder of a specific composition to prepare microporous molecular sieves, which can make the prepared low-condensation biodiesel more in line with the use standards.

[0039] 4. When the heating rate of the catalyst precursor of the present invention is 1.2-1.5°C / min, the service life of the obtained structured hydrogenation catalyst is longer.

[0040] 5. The present invention pre-treats waste cooking oil, thereby reducing the acidity of low-coagulation biodiesel. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The strains used in the present invention were purchased from the following manufacturers:

[0043] Bacillus subtilis (strain number: CICC 10732) was purchased from China Industrial Microbiology Culture Collection Center.

[0044] Pseudomonas aeruginosa (strain number: CICC 24649) was purchased from China Industrial Microbiological Culture Collection Center.

[0045] Rhodococcus ruber, strain number: CICC 21900, was purchased from China Industrial Microbiological Culture Collection Center.

[0046] Example 1

[0047] This embodiment provides a method for preparing low-condensation biodiesel, comprising the following steps:

[0048] (1) Acid reduction process: waste oil from which mechanical impurities have been removed, ethanol with a mass of 3.6 times that of the waste oil, water with a mass of 2.5% that of the waste oil, and mixed bacteria are added to a reactor and reacted aerobically at 42°C for 2.5 hours. After the reaction is completed, the heavy phase and light phase containing bacteria are separated after static stratification, and the light phase is evaporated to remove water and ethanol to obtain pretreated waste oil. The mixed bacteria include Bacillus subtilis, Pseudomonas aeruginosa, and Rhodococcus erythrorhizium, and the amount of Bacillus subtilis is 10 5 CFU / g waste oil; the amount of Pseudomonas aeruginosa is 10 3 CFU / g waste oil; the amount of the red coccus is 10 6 CFU / g waste oil;

[0049] (2) Pre-hydrogenation process: The pre-treated waste oil is subjected to the pre-hydrogenation process using an upflow hydrogenation reactor, with a reaction temperature of 220°C, a pressure of 12 MPa, and a volume ratio of hydrogen to waste oil of 120:1;

[0050] (3) Deep hydrotreating process: The product of the pre-hydrotreating process is subjected to a deep hydrotreating process at a reaction temperature of 380°C, a pressure of 12 MPa, and a volume ratio of hydrogen to waste oil of 1100:1;

[0051] (4) Hydroisomerization process: The product of deep hydrorefining is subjected to the hydroisomerization process to reduce the freezing point. The reaction temperature is 355°C, the pressure is 27 MPa, the volume ratio of hydrogen to waste oil is 550:1, and the volume space velocity of the isomerization hydrogenation catalyst is 1 h -1 ;

[0052] The preparation method of the isomerization hydrogenation catalyst comprises the following steps:

[0053] a. Mix a microporous molecular sieve with a weight ratio of 1:25 and a NaOH aqueous solution with a mass concentration of 27%, reflux and stir at 82°C for 7 hours, cool, filter, wash with water until neutral, and dry to obtain a pretreated molecular sieve;

[0054] The preparation method of the microporous molecular sieve comprises the following steps:

[0055] Step 1, mixing mica powder and sodium hydroxide in a weight ratio of 1:1.7 and calcining them at a calcination temperature of 640°C for 2.5 hours to obtain clinker; the mica powder includes the following components in mass percentage: 49.8% SiO2, 37.8% Al2O3, 1.2% Fe2O3, 2.3% K2O, 2.0% Na2O, 2.1% CaO, and 4.8% H2O;

[0056] Step 2: adding deionized water and n-propylamine to the clinker, wherein the amount of deionized water added is 20 mL / g mica powder, and the molar ratio of n-propylamine to deionized water is 1:140, and stirring is performed for 5.6 hours to obtain a silica-alumina gel;

[0057] Step 3: Place the silica-alumina gel in a crystallization kettle for crystallization at a temperature of 182° C. for 32 h to obtain a microporous molecular sieve.

[0058] b. Mix the pretreated molecular sieve and H2PtCl6 in a weight ratio of 1:0.07, stir until a paste, let stand at 27°C for 5 hours, and then dry at 72°C for 27 hours to obtain a catalyst precursor;

[0059] c. The catalyst precursor was heated to 280°C at a heating rate of 1.4°C / min, and then kept warm and calcined for 4 hours to obtain an isomerization hydrogenation catalyst;

[0060] (5) Deep hydrogenation refining process again: The reaction products of the hydroisomerization process are further refined through a deep hydrogenation refining process at a reaction temperature of 380°C, a pressure of 12 MPa, and a volume ratio of hydrogen to waste cooking oil of 1100:1 to obtain low-condensation biodiesel.

[0061] Example 2

[0062] This embodiment provides a method for preparing low-condensation biodiesel, comprising the following steps:

[0063] (1) Acid reduction process: waste oil from which mechanical impurities have been removed, ethanol with a mass of 3 times that of the waste oil, water with a mass of 2% that of the waste oil, and mixed bacteria are added to a reactor and reacted aerobically at 45°C for 3 hours; after the reaction is completed, the heavy phase and light phase containing bacteria are separated after static stratification, and the light phase is evaporated to remove water and ethanol to obtain pretreated waste oil; the mixed bacteria include Bacillus subtilis, Pseudomonas aeruginosa, and Rhodococcus erythrorhizium, and the amount of Bacillus subtilis is 10 5 CFU / g waste oil; the amount of Pseudomonas aeruginosa is 10 4 CFU / g waste oil; the amount of the red coccus is 10 6 CFU / g waste oil;

[0064] (2) Pre-hydrogenation process: The pre-treated waste oil is subjected to the pre-hydrogenation process using an upflow hydrogenation reactor at a reaction temperature of 200°C, a pressure of 10 MPa, and a volume ratio of hydrogen to waste oil of 100:1;

[0065] (3) Deep hydrotreating process: The product of the pre-hydrotreating process is subjected to a deep hydrotreating process at a reaction temperature of 350°C, a pressure of 10 MPa, and a volume ratio of hydrogen to waste oil of 1000:1;

[0066] (4) Hydroisomerization process: The product of deep hydrogenation refining is reduced in freezing point through the hydroisomerization process. The reaction temperature is 350°C, the pressure is 25 MPa, the volume ratio of hydrogen to waste oil is 500:1, and the volume space velocity of the isomerization hydrogenation catalyst is 0.5-1.5h -1 ;

[0067] The preparation method of the isomerization hydrogenation catalyst comprises the following steps:

[0068] a. Mix a microporous molecular sieve with a weight ratio of 1:20 and a NaOH aqueous solution with a mass concentration of 25%, reflux and stir at 80°C for 6 hours, cool, filter, wash with water until neutral, and dry to obtain a pretreated molecular sieve;

[0069] The preparation method of the microporous molecular sieve comprises the following steps:

[0070] Step 1, mixing mica powder and sodium hydroxide in a weight ratio of 1:1.6 and calcining them at a calcination temperature of 630°C for 2 hours to obtain clinker; the mica powder includes the following components in mass percentage: 49.8% SiO2, 37.8% Al2O3, 1.2% Fe2O3, 2.3% K2O, 2.0% Na2O, 2.1% CaO, and 4.8% H2O;

[0071] Step 2: adding deionized water and n-propylamine to the clinker, wherein the amount of deionized water added is 10 mL / g mica powder, and the molar ratio of n-propylamine to deionized water is 1:120, stirring for 5 hours to obtain a silica-alumina gel;

[0072] Step 3: Place the silica-alumina gel in a crystallization kettle for crystallization at a temperature of 180° C. for 30 h to obtain a microporous molecular sieve.

[0073] b. Mix the pretreated molecular sieve and H2PtCl6 in a weight ratio of 1:0.05, stir until a paste, let stand at 25°C for 4 hours, and then dry at 70°C for 25 hours to obtain a catalyst precursor;

[0074] c. The catalyst precursor was heated to 250°C at a heating rate of 1.2°C / min, and then kept warm for 3 hours to obtain an isomerization hydrogenation catalyst;

[0075] (5) Deep hydrogenation refining process again: The reaction products of the hydroisomerization process are further refined through a deep hydrogenation refining process at a reaction temperature of 350°C, a pressure of 10 MPa, and a volume ratio of hydrogen to waste cooking oil of 1000:1 to obtain low-condensation biodiesel.

[0076] Example 3

[0077] This embodiment provides a method for preparing low-condensation biodiesel, comprising the following steps:

[0078] (1) Acid reduction process: waste oil from which mechanical impurities have been removed, ethanol with a mass of 3-4 times that of the waste oil, water with a mass of 3% that of the waste oil, and mixed bacteria are added to a reactor and reacted aerobically at 40°C for 3 hours; after the reaction is completed, the heavy phase and light phase containing bacteria are separated after static stratification, and the light phase is evaporated to remove water and ethanol to obtain pretreated waste oil; the mixed bacteria include Bacillus subtilis, Pseudomonas aeruginosa, and Rhodococcus erythrorhizium, and the amount of Bacillus subtilis is 10 4 CFU / g waste oil; the amount of Pseudomonas aeruginosa is 10 4 CFU / g waste oil; the amount of the red coccus is 10 5 CFU / g waste oil; (2) Pre-hydrogenation process: The pre-treated waste oil is subjected to the pre-hydrogenation process using an upflow hydrogenation reactor, with a reaction temperature of 250°C, a pressure of 15 MPa, and a volume ratio of hydrogen to waste oil of 150:1;

[0079] (3) Deep hydrotreating process: The product of the pre-hydrotreating process is subjected to a deep hydrotreating process at a reaction temperature of 400°C, a pressure of 15 MPa, and a volume ratio of hydrogen to waste oil of 1200:1;

[0080] (4) Hydroisomerization process: The product of deep hydrorefining is subjected to the hydroisomerization process to reduce the freezing point. The reaction temperature is 360°C, the pressure is 30 MPa, the volume ratio of hydrogen to waste oil is 600:1, and the volume space velocity of the isomerization hydrogenation catalyst is 1.5 h -1 ;

[0081] The preparation method of the isomerization hydrogenation catalyst comprises the following steps:

[0082] a. Mix a microporous molecular sieve with a weight ratio of 1:30 and a NaOH aqueous solution with a mass concentration of 30%, reflux and stir at 85°C for 8h, cool, filter, wash with water until neutral, and dry to obtain a pretreated molecular sieve;

[0083] The preparation method of the microporous molecular sieve comprises the following steps:

[0084] Step 1, mixing mica powder and sodium hydroxide in a weight ratio of 1:1.8 and calcining them at a calcination temperature of 650°C for 3 hours to obtain clinker; the mica powder includes the following components in mass percentage: 49.8% SiO2, 37.8% Al2O3, 1.2% Fe2O3, 2.3% K2O, 2.0% Na2O, 2.1% CaO, and 4.8% H2O;

[0085] Step 2: adding deionized water and n-propylamine to the clinker, wherein the amount of deionized water added is 30 mL / g mica powder, and the molar ratio of n-propylamine to deionized water is 1:150, stirring for 6 hours to obtain a silica-alumina gel;

[0086] Step 3: Place the silica-alumina gel in a crystallization kettle for crystallization at a temperature of 185° C. for 35 h to obtain a microporous molecular sieve.

[0087] b. Mix the pretreated molecular sieve and H2PtCl6 in a weight ratio of 1:0.1, stir until a paste, let stand at 30°C for 6 hours, and then dry at 75°C for 30 hours to obtain a catalyst precursor;

[0088] c. The catalyst precursor was heated to 300°C at a heating rate of 1.5°C / min, and then kept at this temperature for 5 hours to obtain an isomerization hydrogenation catalyst;

[0089] (5) Deep hydrogenation refining process: The reaction products of the hydroisomerization process are further refined through a deep hydrogenation refining process at a reaction temperature of 400°C, a pressure of 15 MPa, and a volume ratio of hydrogen to waste cooking oil of 1200:1 to obtain low-condensation biodiesel.

[0090] Comparative Example 1

[0091] The difference between this comparative example and Example 1 is that the isomerization hydrogenation catalyst was purchased from Liaoning Haitai Technology Development Co., Ltd., model SKI-110 isomerization catalyst.

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 1 is that the microporous molecular sieve is a commercially available product purchased from Shanghai MacLean Biochemical Technology Co., Ltd., model: Z875520 ZSM-5 molecular sieve.

[0094] Comparative Example 3

[0095] The difference between this comparative example and Example 1 is that the mica powder is replaced by white mud, and the white mud includes the following components in mass percentage: 67% SiO2, 15% Al2O3, 1.58% TiO2, 0.63% Fe2O3, 0.27% K2O, 0.12% Na2O, 2.5% CaO, and the balance is water.

[0096] Comparative Example 4

[0097] The difference between this comparative example and Example 1 is that the heating rate of the catalyst precursor in step c is 0.8° C. / min.

[0098] Comparative Example 5

[0099] The difference between this comparative example and Example 1 is that the heating rate of the catalyst precursor in step c is 2.0° C. / min.

[0100] Comparative Example 6

[0101] The difference between this comparative example and Example 1 is that the mixed bacteria include Bacillus subtilis, Pseudomonas aeruginosa and Rhodococcus erythrorhizium, and the amount of Bacillus subtilis is 10 6 CFU / g waste oil; the amount of Pseudomonas aeruginosa is 10 5 CFU / g waste oil; the amount of the red coccus is 10 3 CFU / g waste oil.

[0102] Comparative Example 7

[0103] The difference between this comparative example and Example 1 is that no acid reduction process is performed.

[0104] Comparative Example 8

[0105] The difference between this comparative example and Example 1 is that the mixed bacteria is replaced by Aspergillus oryzae, strain number: CICC 2012 purchased from China Industrial Microbiological Culture Collection Administration Center. The dosage of Aspergillus oryzae is 10 6 CFU / g waste oil.

[0106] Performance Testing

[0107] With reference to NB / T10897-2021, the performance of the low-condensing biodiesel prepared in Examples 1-3 and Comparative Examples 1-8 was tested.

[0108] The yield of low-condensing biodiesel = the mass of low-condensing biodiesel / the mass of waste cooking oil × 100%.

[0109] The service life of isomerization hydrogenation catalyst: The stability of ZSM-5 molecular sieve is measured based on the feedstock conversion rate (conversion rate = total amount of feedstock consumed by the reaction / total amount of initial feedstock × 100%) being less than 90%. This means that under continuous operation conditions, the catalyst can maintain its activity and selectivity, and the length of time that the feedstock conversion rate reaches or exceeds 90%. During this time, the catalyst can effectively promote the reaction, ensuring that most of the feedstock can be converted into the target product, and the conversion rate will not be less than 90%. The test results are shown in Table 1.

[0110] Table 1 Low-condensation biodiesel performance test results

[0111] Yield % Condensation point ℃ Acidity (in terms of potassium hydroxide, mg / 100mL) <![CDATA[Density kg / m 3 > 95% recovery temperature ℃ Cetane number Flash point℃ Catalyst life h Example 1 94.8 -18.3 4.0 784.9 352.5 79 66 1432 Example 2 94.2 -18.7 4.2 787.3 354.3 77 65 1414 Example 3 94.5 -18.9 4.1 790.2 353.2 78 64 1405 Comparative Example 1 93.9 -16.9 4.5 806.5 362.6 71 59 - Comparative Example 2 93.0 -17.1 4.6 791.1 364.8 73 57 1378 Comparative Example 3 93.1 -16.8 4.4 795.9 352.4 72 63 1312 Comparative Example 4 93.6 -16.7 4.1 783.9 354.3 74 62 1381 Comparative Example 5 93.3 -17.4 4.2 785.7 357.4 73 61 1367 Comparative Example 6 93.0 -16.2 5.3 790.5 360.2 76 63 1397 Comparative Example 7 93.8 -16.8 6.5 784.6 352.3 78 65 1354 Comparative Example 8 92.4 -15.7 6.0 780.2 350.6 70 60 1305

[0112] Note: - stands for not determined.

[0113] It can be seen from the above performance test results that the yield of the low-condensing biodiesel of Examples 1-3 is high, >90%. The isomerization hydrogenation catalyst can be recycled many times. The 95% recovery temperature refers to the temperature when 95% of the diesel has evaporated and been collected in the standard distillation process. This indicator reflects the content of heavy components in the diesel. A lower 95% recovery temperature means that the diesel contains fewer heavy components. Such diesel usually has better combustion performance and lower fuel consumption, because the heavy components are difficult to completely burn, which may lead to higher emissions and lower thermal efficiency. The low-condensing biodiesel of Examples 1-3 can maintain a low condensing point and a lower 95% recovery temperature at the same time, which meets the standard of the relevant standard NB / T10897-2021 that the 95% recovery temperature is not higher than 365°C, and is a high-quality biodiesel. However, because the comparative example did not adopt the necessary technical solutions, it was significantly worse than the embodiment in the corresponding performance test. Through comparative example 6, it was found that when different proportions of strains were used for deacidification, the acidity exceeded the range in standard NB / T10897-2021, and the freezing point also increased, indicating that the strains played a synergistic role and affected the acidity and freezing point of the product. However, in comparative example 7, no deacidification was performed, and the acidity did not meet the standard NB / T10897-2021. In comparative example 8, Aspergillus oryzae was used for deacidification, and the performance parameters of the low-freezing biodiesel produced varied greatly, indicating that the components in the waste oil treated with Aspergillus oryzae had a great influence on the quality of subsequent products.

[0114] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing biodiesel, characterized in that: The following steps are involved: (1) Acid reduction process: waste oil from which mechanical impurities have been removed, ethanol with a mass of 3-4 times that of the waste oil, water with a mass of 2-3% that of the waste oil, and mixed bacteria are added to a reactor and reacted aerobically at 40-45°C for 2-3 hours; after the reaction is completed, the heavy phase and light phase containing bacteria are separated after static stratification, and the light phase is evaporated to remove water and ethanol to obtain pretreated waste oil; the mixed bacteria include Bacillus subtilis, Pseudomonas aeruginosa, and Rhodococcus erythrorhizium, and the amount of Bacillus subtilis is 10 4 -10 5 CFU / g waste oil; the amount of Pseudomonas aeruginosa is 10 3 -10 4 CFU / g waste oil; the amount of the red coccus is 10 5 -10 6 CFU / g waste oil; (2) Pre-hydrogenation process: The pre-treated waste oil is subjected to the pre-hydrogenation process in a hydrogenation reactor, with a reaction temperature of 200-250°C, a pressure of 10-15 MPa, and a volume ratio of hydrogen to waste oil (100-150): 1; (3) Deep hydrotreating process: The product of the pre-hydrotreating process is subjected to a deep hydrotreating process at a reaction temperature of 350-400°C, a pressure of 10-15 MPa, and a volume ratio of hydrogen to waste oil (1000-1200): 1; (4) Hydroisomerization process: The product of deep hydrorefining is subjected to the hydroisomerization process to reduce the freezing point. The reaction temperature is 350-360°C, the pressure is 25-30 MPa, the volume ratio of hydrogen to waste oil is (500-600):1, and the volume space velocity of the isomerization hydrogenation catalyst is 0.5-1.5 h-1; The preparation method of the isomerization hydrogenation catalyst comprises the following steps: a. Mix the microporous molecular sieve and NaOH aqueous solution in a weight ratio of 1: (20-30), reflux and stir at 80-85°C for 6-8h, cool, filter, wash with water until neutral, and dry to obtain the pretreated molecular sieve; b. Mix the pretreated molecular sieve and H2PtCl6 in a weight ratio of 1: (0.05-0.1), stir until a paste, let stand at 25-30°C for 4-6 hours, and then dry at 70-75°C for 25-30 hours to obtain a catalyst precursor; c. Raise the temperature of the catalyst precursor to 250-300°C and calcine for 3-5 hours to obtain an isomerization hydrogenation catalyst; (5) Deep hydrogenation refining process again: The reaction products of the hydroisomerization process are further refined through a deep hydrogenation refining process at a reaction temperature of 350-400°C, a pressure of 10-15 MPa, and a volume ratio of hydrogen to waste cooking oil (1000-1200): 1 to obtain biodiesel.

2. The method for preparing biodiesel according to claim 1, characterized in that: In step c, the heating rate of the catalyst precursor is 1.2-1.5° C. / min.

3. The method for preparing biodiesel according to claim 1, characterized in that: The mass concentration of the NaOH aqueous solution is 25-30%.

4. The method for preparing biodiesel according to claim 1, characterized in that: The preparation method of the microporous molecular sieve comprises the following steps: step 1, mixing mica powder and sodium hydroxide and calcining them to obtain clinker; step 2, adding deionized water and n-propylamine to the clinker and stirring to obtain silica-alumina gel; step 3, placing the silica-alumina gel in a crystallization kettle for crystallization at a crystallization temperature of 180-185° C. and a crystallization time of 30-35 hours to obtain a microporous molecular sieve.

5. The method for preparing biodiesel according to claim 4, characterized in that: The mica powder comprises the following components in percentage by mass: 46-50% SiO2, 35-39% Al2O3, 0.5-1.5% Fe2O3, 1-2.5% K2O, 0.5-2.5% Na2O, 1-3% CaO, and 3-6% H2O.

6. The method for preparing biodiesel according to claim 4, characterized in that: The weight ratio of the mica powder to sodium hydroxide is 1:(1.6-1.8).

7. The method for preparing biodiesel according to claim 4, characterized in that: The calcination temperature is 630-650° C., and the calcination time is 2-3 hours.

8. The method for preparing biodiesel according to claim 4, characterized in that: The amount of deionized water added is 10-30 mL / 1 g of mica powder, and the stirring time is 5-6 hours.

9. The method for preparing biodiesel according to claim 4, characterized in that: The molar ratio of n-propylamine to deionized water is 1:(120-150).

10. Biodiesel produced according to the preparation method according to any one of claims 1 to 9.