A method for preparing a low-set biodiesel

Abstract

This invention provides a method for preparing low-pour-point biodiesel, belonging to the field of bio-oil technology, including the following steps: (1) After removing mechanical impurities, waste cooking oil is mixed with hydrogen and a solid catalyst and then fed into a slurry bed hydrotreating reactor for hydrotreating pretreatment; (2) The tailings obtained from the hydrocyclone after hydrotreating are partially recycled to the inlet of the slurry bed hydrotreating reactor, and a small amount of tailings are discharged; (3) The liquid product obtained by the hydrocyclone separator is fed into a gas-liquid separator for gas-liquid separation, and the liquid product is fed into a solid-liquid separator; (4) The liquid product separated by the solid-liquid separator is fed into a fixed-bed hydrorefining reactor, a fixed-bed hydroisocyanate reactor, and a fixed-bed post-refining reactor connected in series for hydrotreating; (5) The hydrotreating product is fed into a gas-liquid separation unit for gas-liquid separation, and the obtained liquid product is fed into a fractionation unit to obtain low-pour-point biodiesel. The product of this invention has a low pour point and a high yield.

Description

Technical Field

[0001] This invention belongs to the field of bio-oil technology, specifically relating to a method for preparing low-pour-point biodiesel. Background Technology

[0002] Low-pour-point biodiesel is a modified type of biodiesel with improved low-temperature performance. It maintains good fluidity at lower temperatures, preventing waxy deposits that can clog filters or malfunction fuel systems in cold weather. This type of biodiesel is particularly suitable for use in winter or cold regions. Currently, the main production process for biodiesel is fixed-bed hydrotreating.

[0003] Patent application CN202310606126.2 discloses a method for producing biodiesel from waste cooking oil via hydrogenation. This method efficiently converts non-ideal components such as oxygen-containing compounds in waste cooking oil through slurry-bed hydrogenation pretreatment, and obtains low-pour-point biodiesel fractions through deep supplemental hydrogenation treatment. The method involves preparing a solution of soluble salts of active metals and impregnating a carbon support using an equal-volume impregnation method to obtain an activated carbon-supported metal catalyst. However, the high temperatures of long-term drying and heat treatment processes on commercially available carbon supports can damage the pore structure of the activated carbon, reducing its specific surface area and thus affecting the catalyst's performance.

[0004] Therefore, in the preparation of low-pour-point biodiesel, how to obtain a highly efficient, reusable, low-cost, and environmentally friendly supported heterogeneous carbon-based catalyst is a highly promising yet challenging problem. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing low-pour-point biodiesel.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing low-pour-point biodiesel, the method comprising the following steps:

[0008] (1) After removing mechanical impurities, waste cooking oil is mixed with hydrogen and solid catalyst and then fed into a slurry bed hydrogenation reactor for hydrogenation pretreatment.

[0009] The preparation method of the solid catalyst is as follows:

[0010] S1: Mix phenolic resin, self-made epoxy resin, and polyester resin in a mass ratio of 1:(0.3-0.5):(1.5-1.8) to obtain a mixed resin. Add a curing accelerator and mix evenly. Place the mixture in a kneader, then add deionized water and knead for 10-20 minutes. Then extrude the mixture and age it in room temperature air for 13-15 hours. Then dry it at 80-85℃ for 8-10 hours, cure it at 150-160℃ for 15-17 hours, and carbonize it at 600-650℃ for 3-4 hours in a nitrogen atmosphere to obtain a carbon carrier.

[0011] The structure of the homemade epoxy resin is shown below:

[0012] n is a positive integer greater than 1;

[0013] S2: Prepare ammonia water solution and ammonium metatungstate water solution of nickel nitrate respectively, mix them in equal volumes to obtain a mixed solution, impregnate the carbon support by equal volume impregnation method, dry at 150-170℃ for 4-6 hours, heat to 650-670℃ under nitrogen atmosphere, and calcine for 2.5-3 hours to obtain carbon-supported metal catalyst.

[0014] S3: Add carbon-supported metal catalyst and ammonium sulfide to a reactor for hydrothermal treatment at a temperature of 120-140℃ for 3-5 hours to obtain a solid catalyst.

[0015] (2) After hydrogenation, the tailings obtained by the hydrocyclone separator are partially recycled to the inlet of the slurry bed hydrogenation reactor, and a small amount of tailings are discharged.

[0016] (3) The liquid product obtained by the hydrocyclone separator enters the gas-liquid separator for gas-liquid separation, and the liquid product enters the solid-liquid separator.

[0017] (4) The liquid phase product separated by the solid-liquid separator enters a fixed-bed hydrorefining reactor, a fixed-bed hydroisomerization reactor and a fixed-bed post-refining reactor connected in series for hydrorefining treatment;

[0018] (5) The hydrogenation product enters the gas-liquid separation unit for gas-liquid separation, and the resulting liquid product enters the fractionation unit to obtain low-pour-point biodiesel.

[0019] Furthermore, the phenolic resin contains 10-14% free phenol by mass. It was purchased from Hebei Zetian Chemical Co., Ltd., brand name 2127-1.

[0020] Furthermore, the method for preparing the self-made epoxy resin is as follows:

[0021] (1) Add 1.5-2.0 mol of dehydrated polytetrahydrofuran diol to 1 mol of naphthalene diisocyanate, heat to 80-85℃ and react for 1-2 h, then cool to 60-65℃, add 0.5-1 mol of dehydrated polytetrahydrofuran diol, heat to 80-85℃ and react for 2-3 h to obtain polyurethane prepolymer;

[0022] Polytetrahydrofuran diol, PTMG2000, CAS: 25190-06-1. Shandong Weishang Chemical Co., Ltd.

[0023] (2) The polyurethane prepolymer and glycidol were mixed in anhydrous dichloromethane solvent at a molar ratio of 1:1.5-1.7 and reacted at 60-65℃ for 7-9 hours under a nitrogen atmosphere to obtain the self-made epoxy resin.

[0024] Furthermore, the polyester resin is a saturated polyester resin with a number-average molecular weight of 15,000, an acid value of 3-5 KOH mg / g, and a hydroxyl value of 5-10 KOH mg / g. It was purchased from SK Korea as SKYBONEW-312 saturated polyester resin.

[0025] In existing technologies, single organic polymers are typically used to prepare carbon supports. However, these carbon supports have low strength, which negatively impacts catalyst stability over long-term use. Furthermore, the small specific surface area of ​​the carbon support hinders uniform loading of active materials, affecting catalyst activity. This invention uses a specific ratio of phenolic resin, a self-made epoxy resin, and polyester resin to prepare a carbon support, improving both its strength and specific surface area, thus enhancing catalyst activity and stability. The carbon support prepared in this invention contains phenolic hydroxyl and carboxyl groups on its surface, which facilitates the dispersion and refinement of active components. Simultaneously, the use of phenolic resin, self-made epoxy resin, and polyester resin with specific structures allows the self-made epoxy resin, with its longer molecular chains, to decompose and recombine during high-temperature carbonization, forming a three-dimensional carbon network structure. This structure determines the porosity, specific surface area, and pore size distribution of the carbon support, resulting in a highly porous carbon support that improves catalyst activity and stability, and extends its service life. The carbon support also affects the dispersion and stability of the metal catalyst, thereby influencing its activity and the catalytic hydrogenation reaction.

[0026] Furthermore, the carbon support was impregnated at 65-70℃ using an equal-volume impregnation method.

[0027] Furthermore, the temperature is increased to 650-670℃ at a heating rate of 4℃ / min-6℃ / min.

[0028] During the experiment, it was found that the impregnation temperature had a significant impact on the impregnation effect of the carbon support prepared by this invention. When the carbon support of this invention was impregnated at a temperature of 65-70℃, the adsorption of active substances by the carbon support was more pronounced, resulting in a catalyst with good catalytic effect. When the impregnation temperature exceeded 75℃, the adsorption of active substances by the support began to decrease, leading to a decline in activity. Analysis suggests that within this temperature range, the solution containing active substances has good fluidity, which helps the active substances to distribute evenly and penetrate deeply into the pores of the carbon support, helping to maintain adsorption equilibrium and establish a stable adsorption relationship between the active substances and the carbon support. Excessively high temperatures may accelerate the diffusion process, leading to rapid deposition of active substances on the support surface without sufficient time for deep penetration, thereby reducing the overall adsorption efficiency.

[0029] Furthermore, in S1, the mass of deionized water accounts for 20-22% of the mass of the mixed resin.

[0030] Furthermore, the curing accelerator is trimethylhexanediamine.

[0031] Furthermore, the curing accelerator in S1 accounts for 7-9% of the mass of the mixed resin.

[0032] Furthermore, the concentrations of both the ammonia-water aqueous solution and the ammonium metatungstate aqueous solution of nickel nitrate are 0.8-1 mol / L.

[0033] Furthermore, the molar ratio of sulfur in ammonium sulfide to the active metal in the carbon-supported metal catalyst is 3-5:1, and the active metals are nickel and tungsten.

[0034] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0035] 1. The method of the present invention uses less catalyst, has lower operating costs, milder conditions, higher raw material utilization, and produces products with lower pour points and higher yields, making it suitable for industrial-scale promotion.

[0036] 2. This invention uses a specific ratio of phenolic resin, self-made epoxy resin and polyester resin to prepare a carbon support, which improves the strength and specific surface area of ​​the carbon support and enhances the activity and stability of the catalyst.

[0037] 3. During the experiment, it was found that the impregnation temperature has a significant impact on the impregnation effect of the carbon support prepared by this invention. When the carbon support of this invention is impregnated at a temperature of 65-70℃, the adsorption effect of the carbon support on the active substances is more obvious, the resulting catalyst has a good catalytic effect, and the biodiesel yield is high. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of the present invention;

[0039] In the diagram: 1-Waste cooking oil, 2-Hydrogen, 3-Hydrolysis pretreatment catalyst, 4-Slurry bed hydrotreating reactor, 5-Hydrolysis pretreatment reaction product, 6-Hydrocyclone separator, 7-Hydrocyclone separation of solid tailings, 8-Hydrocyclone separation of liquid product, 9-Gas-liquid separator, 10-Hydrogen-rich gas, 11-Solid-liquid separator, 12-Hydrolysis pretreatment product, 13-Solid tailings, 14-Fixed bed hydrorefining reactor, 15-Fixed bed hydrorefining isomerization reactor, 16-Fixed bed post-refining reactor, 17-Gas-liquid separation unit, 18-Friction unit. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for preparing low-pour-point biodiesel, including the following steps:

[0043] (1) The waste cooking oil 1 from the pipeline is thoroughly mixed with hydrogen 2 and solid catalyst 3 and then enters the slurry bed hydrogenation reactor 4 for hydrogenation pretreatment. The reaction conditions are: hydrogen partial pressure in the reactor is 10 MPa, reaction temperature is 350℃, and liquid hourly space velocity is 1 h⁻¹. -1 The volume ratio of hydrogen to waste cooking oil is 500 Nm3 / m3;

[0044] The preparation method of solid catalyst is as follows:

[0045] S1: Phenolic resin, self-made epoxy resin, and polyester resin in a mass ratio of 1:0.4:1.7 are mixed to obtain a mixed resin. A curing accelerator is added and mixed evenly. The mixture is placed in a kneader, and then deionized water is added and kneaded in the kneader for 15 minutes. The mixture is then extruded and molded, aged in room temperature air for 14 hours, dried at 82°C for 9 hours, cured at 155°C for 16 hours, and carbonized at 620°C for 3.5 hours in a nitrogen atmosphere to obtain a carbon carrier.

[0046] Phenolic resin, with a free phenol content of 10-14% by mass; purchased from Hebei Zetian Chemical Co., Ltd., grade 2127-1.

[0047] The method for preparing homemade epoxy resin is as follows:

[0048] (1) Add 1.7 mol of dehydrated polytetrahydrofuran diol to 1 mol of naphthalene diisocyanate, heat to 82°C and react for 1.5 h, then cool to 62°C, add 0.8 mol of dehydrated polytetrahydrofuran diol, heat to 82°C and react for 2.5 h to obtain polyurethane prepolymer;

[0049] Polytetrahydrofuran diol, PTMG2000, CAS: 25190-06-1. Shandong Weishang Chemical Co., Ltd.

[0050] (2) The polyurethane prepolymer and glycidol were mixed in anhydrous dichloromethane solvent at a molar ratio of 1:1.6 and reacted at 62°C for 8 hours under a nitrogen atmosphere to obtain the self-made epoxy resin.

[0051] The polyester resin is a saturated polyester resin with a number-average molecular weight of 15,000, an acid value of 3-5 KOH mg / g, and a hydroxyl value of 5-10 KOH mg / g; it was purchased from SK SKYBONEW-312 saturated polyester resin from South Korea.

[0052] The mass of deionized water accounts for 21% of the mass of the mixed resin. The curing accelerator is trimethylhexanediamine, which accounts for 8% of the mass of the mixed resin.

[0053] S2: Prepare ammonia-water aqueous solution of nickel nitrate and ammonium metatungstate aqueous solution separately, mix them in equal volumes to obtain a mixed solution, impregnate the carbon support at 68℃ using the equal volume impregnation method, dry at 160℃ for 5 hours, heat to 660℃ at a heating rate of 5℃ / min under nitrogen atmosphere, and calcine for 2.8 hours to obtain a carbon-supported metal catalyst; the concentrations of both the ammonia-water aqueous solution of nickel nitrate and the ammonium metatungstate aqueous solution are 0.9mol / L.

[0054] S3: Carbon-supported metal catalyst and ammonium sulfide are added to a reactor for hydrothermal treatment. The molar ratio of sulfur in ammonium sulfide to active metal in carbon-supported metal catalyst is 4:1. The active metals are nickel and tungsten. The reaction temperature is 130℃ and the reaction time is 4h to obtain a solid catalyst.

[0055] (2) The product 5 of the slurry bed hydrogenation pretreatment reaction is separated by the hydrocyclone 6 to obtain the hydrocyclone-separated solid tailings 7. Part of the tailings is recycled to the inlet of the slurry bed hydrogenation reactor 6, and the rest of the tailings are discharged.

[0056] (3) The liquid product 8 obtained by the hydrocyclone separator 6 enters the gas-liquid separator 9 for gas-liquid separation. The hydrogen-rich gas 10 obtained is purified and recycled. The liquid product enters the solid-liquid separator 11.

[0057] (4) The liquid product separated by the solid-liquid separator 11 is the pre-hydrogenated product 12, and the solid tailings 13 are discharged from the device. The pre-hydrogenated product 12 enters the series of fixed-bed hydrorefining reactor 14, fixed-bed hydroisomerization reactor 15 and fixed-bed post-refining reactor 16 for hydrogenation reaction. The reaction conditions of the fixed-bed hydrorefining reactor 14 are: hydrogen partial pressure in the reactor 10 MPa, reaction temperature 300 °C, and liquid hourly space velocity 2 h⁻¹. -1 The hydrogen-to-material volume ratio entering the reactor is 500 Nm³ / m³. The reaction conditions of the fixed-bed hydroisomerization reactor are: hydrogen partial pressure in the reactor 10 MPa, reaction temperature 360 ​​°C, and liquid hourly space velocity 2 h⁻¹. -1 The hydrogen-to-material volume ratio entering the reactor is 600 Nm³ / m³. The reaction conditions in the fixed-bed refining reactor are: hydrogen partial pressure 10 MPa, reaction temperature 300 °C, and liquid hourly space velocity 2 h⁻¹. -1 The volume ratio of hydrogen to the material entering the reactor is 600 Nm3 / m3;

[0058] (5) The hydrogenation product enters the gas-liquid separation unit 17 for gas-liquid separation, and the resulting liquid product enters the fractionation unit 18 to finally obtain low-pour-point biodiesel.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that the self-made epoxy resin was replaced with a commercially available product.

[0061] The epoxy resin is a glycidyl ether epoxy resin with an epoxy equivalent of 180-190 g / eq and a viscosity of 11000-15000 cps at 25°C. It was purchased from Wanqing Chemical Technology Co., Ltd., model number NPEL-128.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 1 is that the polyester resin used is a saturated polyester resin with a number-average molecular weight of 6 × 10³ Da, an acid value of 5 KOH mg / g, and a hydroxyl value of 619 KOH mg / g. It was purchased from Dongguan Haosheng Plastic Raw Materials Co., Ltd., and the model number is TOYOBOGK810.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that the phenolic resin has a free phenol content of ≤4.5% by mass. It is manufactured by Hebei Zetian Chemical Co., Ltd., and its grade is 4123B.

[0066] Comparative Example 4

[0067] The difference between this comparative example and Example 1 is that it is a mixture of phenolic resin, self-made epoxy resin, and polyester resin in a mass ratio of 1:1:1.

[0068] Comparative Example 5

[0069] The difference between this comparative example and Example 1 is that the carbon carrier was impregnated at 60°C using an equal-volume impregnation method.

[0070] Comparative Example 6

[0071] The difference between this comparative example and Example 1 is that the carbon carrier was impregnated at 80°C using an equal-volume impregnation method.

[0072] Comparative Example 7

[0073] The difference between this comparative example and Example 1 is that the carbon carrier is commercially available activated carbon with a specific surface area of ​​360-600 g / cm3. (Source: Henan Bize New Materials Co., Ltd.)

[0074] Performance testing

[0075] 1. The main indicators of low-pour-point biodiesel are as follows:

[0076] Yield of low-pour-point biodiesel = mass of low-pour-point biodiesel / mass of waste cooking oil * 100%.

[0077] Table 1. Performance test results of low-pour-point biodiesel

[0078] Yield % Pour point ℃ <![CDATA[Density, 20 °C, kg / m 3 > 95% recovery temperature ℃ Example 1 83.8 -16.1 781.6 352.3 Comparative Example 1 83.6 -15.7 785.4 356.8 Comparative Example 2 80.8 -14.9 782.4 359.9 Comparative Example 3 81.9 -14.8 780.2 360.6 Comparative Example 4 81.3 -13.4 781.4 361.6 Comparative Example 5 82.1 -15.2 782.8 356.3 Comparative Example 6 82.5 -15.0 784.2 357.2 Comparative Example 7 80.5 -12.2 781.4 363.4

[0079] 2. When the yield of low-pour-point biodiesel drops below 80%, the cycle test should be stopped. The number of cycles at this point is the number of cycles the catalyst can be recycled.

[0080] Table 2 Number of cycles

[0081] Number of cycles Example 1 15 Comparative Example 1 12 Comparative Example 2 8 Comparative Example 3 7 Comparative Example 4 5 Comparative Example 5 8 Comparative Example 6 9 Comparative Example 7 3

[0082] The performance test results above show that the low-pour-point biodiesel of Example 1 has a high yield and a high number of catalyst recycling cycles. The 95% recovery temperature refers to the temperature at which 95% of the diesel fuel has evaporated and been collected during a standard distillation process. This indicator reflects the content of heavy components in the diesel fuel. A lower 95% recovery temperature means that the diesel fuel contains fewer heavy components, which typically results in better combustion performance and lower fuel consumption. This is because heavy components are difficult to burn completely, potentially leading to higher emissions and lower thermal efficiency. The biodiesel of Example 1 of this invention can simultaneously maintain a low pour point and a low 95% recovery temperature, meeting the standard of GB19147-2016 regarding a 95% recovery temperature not exceeding 365°C, making it a high-quality biodiesel. Comparative Examples 1-7, however, did not employ the necessary technical solutions, resulting in significantly worse performance than the Example 1 in the corresponding tests. The above experimental results further demonstrate the importance of the technical solutions defined in this invention for its technical effectiveness.

[0083] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing low-pour-point biodiesel, characterized in that, The preparation method includes the following steps: (1) After removing mechanical impurities, waste cooking oil is mixed with hydrogen and solid catalyst and then fed into a slurry bed hydrogenation reactor for hydrogenation pretreatment. The preparation method of the solid catalyst is as follows: S1: Mix phenolic resin, self-made epoxy resin, and polyester resin in a mass ratio of 1:(0.3-0.5):(1.5-1.8) to obtain a mixed resin. Add a curing accelerator and mix evenly. Place the mixture in a kneader, then add deionized water and knead for 10-20 minutes. Then extrude the mixture and age it in room temperature air for 13-15 hours. Then dry it at 80-85℃ for 8-10 hours, cure it at 150-160℃ for 15-17 hours, and carbonize it at 600-650℃ for 3-4 hours in a nitrogen atmosphere to obtain a carbon carrier. The structure of the homemade epoxy resin is shown below: n is a positive integer greater than 1; S2: Prepare ammonia water solution and ammonium metatungstate water solution of nickel nitrate respectively, mix them in equal volumes to obtain a mixed solution, impregnate the carbon support by equal volume impregnation method, dry at 150-170℃ for 4-6 hours, heat to 650-670℃ under nitrogen atmosphere, and calcine for 2.5-3 hours to obtain carbon-supported metal catalyst. S3: Add carbon-supported metal catalyst and ammonium sulfide to a reactor for hydrothermal treatment at a temperature of 120-140℃ for 3-5 hours to obtain a solid catalyst. (2) After hydrogenation, the tailings obtained by the hydrocyclone separator are partially recycled to the inlet of the slurry bed hydrogenation reactor, and a small amount of tailings are discharged. (3) The liquid product obtained by the hydrocyclone separator enters the gas-liquid separator for gas-liquid separation, and the liquid product enters the solid-liquid separator. (4) The liquid phase product separated by the solid-liquid separator enters a fixed-bed hydrorefining reactor, a fixed-bed hydroisomerization reactor and a fixed-bed post-refining reactor connected in series for hydrorefining treatment; (5) The hydrogenation product enters the gas-liquid separation unit for gas-liquid separation, and the resulting liquid product enters the fractionation unit to obtain low-pour-point biodiesel; The free phenol content of phenolic resin is 10-14% by mass; The polyester resin is a saturated polyester resin with a number-average molecular weight of 15,000, an acid value of 3-5 KOH mg / g, and a hydroxyl value of 5-10 KOH mg / g. The carbon support was impregnated at 65-70℃ using the equal volume impregnation method.

2. The method for preparing low-pour-point biodiesel according to claim 1, characterized in that, The method for preparing homemade epoxy resin is as follows: (1) Add 1.5-2.0 mol of dehydrated polytetrahydrofuran diol to 1 mol of naphthalene diisocyanate, heat to 80-85℃ and react for 1-2 h, then cool to 60-65℃, add 0.5-1 mol of dehydrated polytetrahydrofuran diol, heat to 80-85℃ and react for 2-3 h to obtain polyurethane prepolymer; (2) The polyurethane prepolymer and glycidol were mixed in anhydrous dichloromethane solvent at a molar ratio of 1:1.5-1.7 and reacted at 60-65℃ for 7-9 hours under a nitrogen atmosphere to obtain the self-made epoxy resin.

3. The method for preparing low-pour-point biodiesel according to claim 1, characterized in that, In S1, the mass of deionized water accounts for 20-22% of the mass of the mixed resin.

4. The method for preparing low-pour-point biodiesel according to claim 1, characterized in that, The curing accelerator is trimethylhexanediamine.

5. The method for preparing low-pour-point biodiesel according to claim 4, characterized in that, The curing accelerator in S1 accounts for 7-9% of the mass of the mixed resin.

6. The method for preparing low-pour-point biodiesel according to claim 1, characterized in that, The concentrations of both the ammonia-water and ammonium metatungstate aqueous solutions of nickel nitrate are 0.8-1 mol / L.

7. The method for preparing low-pour-point biodiesel according to claim 6, characterized in that, The molar ratio of sulfur to active metal in the carbon-supported metal catalyst of ammonium sulfide is 3-5:1, and the active metals are nickel and tungsten.

Images