Method for preparing second-generation biodiesel with low freezing point by using nano SAPO-31 molecular sieve-based bifunctional catalyst

Abstract

The application discloses a method for preparing low-freezing-point second-generation biodiesel by using a nano SAPO-31 molecular sieve-based bifunctional catalyst, and aims at solving the problems of low isomerization selectivity and poor low-temperature fluidity of the second-generation biodiesel prepared by hydrogenating and isomerizing the Jatropha oil deoxygenated oil. The method for preparing low-freezing-point second-generation biodiesel comprises the following steps: loading the bifunctional catalyst into a tubular reactor, activating the catalyst under a hydrogen atmosphere, continuously pumping the Jatropha oil deoxygenated oil into the reactor, and collecting liquid-phase products under the control of reaction conditions to obtain the low-freezing-point second-generation biodiesel. The bifunctional catalyst is prepared by loading Pt-Pd bimetal on a composite carrier formed by extruding nano SAPO-31 molecular sieve and gamma-alumina by using a vacuum-assisted impregnation method. The catalyst improves the mass transfer performance of the molecular sieve channel, inhibits the cracking reaction of long-chain normal alkanes in the deoxygenated oil during the hydrogenation and isomerization reaction process, and improves the yield of the second-generation biodiesel.

Description

Technical Field

[0001] This invention relates to a method for producing second-generation biodiesel using a bifunctional catalyst. Background Technology

[0002] With the rapid development of modern industry, the demand for energy is constantly increasing. The shortage of non-renewable fossil fuels and the environmental pollution caused by incomplete combustion during their use as fuels are becoming increasingly serious, making the development of renewable and clean energy sources urgently needed. Biodiesel, as one of the main biofuels, has advantages such as wide availability of raw materials, resource renewability, and environmentally friendly combustion emissions. It is of great significance for addressing my country's energy strategy issues such as oil shortages, petroleum feedstock substitution, and cleaner oil products.

[0003] Jatropha curcas is a representative renewable oilseed crop, with jatropha oil (whose main component is carbon) being the most abundant oil. 15 ~C 18 Produced using vegetable oils as raw materials, such as fatty acid triglycerides, etc., with C 15 ~C 18 Second-generation biodiesel, with isoalkanes as its main component, is an environmentally friendly green and clean energy source. The CO2 emitted after its combustion can promote plant growth through photosynthesis, and the resulting plant oil can be further converted into biodiesel through catalytic conversion. This is of great significance to achieving the "dual carbon" strategic goal of carbon neutrality.

[0004] The production of second-generation biodiesel from inedible jatropha oil is achieved through a two-step reaction. The first step involves catalytic hydrodeoxygenation of jatropha oil to obtain C24. 15 ~C 18 The first step involves producing deoxygenated oil with n-alkanes as the main component. The second step is to produce isomerized C2C2 oil through a hydroisomerization reaction. 15 ~C 18 This is a second-generation biodiesel with excellent low-temperature fluidity as its main component. (Compared to C...) 15 ~C 18 Compared to first-generation biodiesel, which primarily consists of fatty acid methyl esters, second-generation biodiesel exhibits superior low-temperature fluidity, higher energy density, and the ability to be blended with petroleum-based diesel in any proportion at low temperatures, making it one of the main future development directions for biofuel production technology. Currently, research on the hydrodeoxygenation reaction of vegetable oils is relatively mature. The main technical bottlenecks currently hindering the large-scale production of second-generation biodiesel are the high cost of catalysts for the hydroisomerization reaction of deoxygenated oils, low biodiesel product yield, and poor low-temperature fluidity.

[0005] The hydroisomerization reaction of deoxygenated vegetable oils such as jatropha oil is carried out on a bifunctional catalyst with both hydrotreating-dehydrogenation and skeletal isomerization functions. The preparation of bifunctional catalysts with high activity, high isomerization selectivity and catalytic stability is a key technology for producing second-generation biodiesel with excellent low-temperature fluidity.

[0006] Patent CN 115970750A discloses a molecular sieve-based catalyst and its preparation method for the one-step hydrodeoxygenation-hydroisomerization of fatty acid methyl esters to produce biodiesel. The method involves mixing an aluminum source, a transition metal nitrate solution, and a phosphorus source, and mixing a silicon source with a template / inducer (di-n-propylamine, dodecyltrimethylammonium bromide, or F-127 surfactant). A metal-substituted SAPO-11 molecular sieve is obtained through a hydrothermal synthesis reaction. The SAPO-11 molecular sieve is then impregnated (still or stirred) with an aqueous solution of a Pt-containing soluble salt to obtain a Pt-containing molecular sieve-based catalyst for the one-step hydrodeoxygenation-isomerization reaction of fatty acid methyl esters. The deoxygenation rate of the oil reaches over 94%. 15 -C 18 The selectivity for hydrocarbons reached over 91%, but C 15 -C 18 The selectivity of isomeric hydrocarbons is low, ranging from 19.3% to 39.8%, and the loading of the precious metal Pt in the catalyst is as high as 1% to 3 wt.%, which significantly increases the cost of the catalyst.

[0007] Patent CN 111135859 B discloses a long-chain n-alkane hydroisomerization catalyst and its preparation method. The method involves extruding ZSM-22, ZSM-23, ZSM-48, ZSM-12, SSZ-32, and SSZ-32X zeolite molecular sieves (which have been treated with matrine solution to form mesoporous structures with a high silica-to-alumina ratio) with structural aids, and then loading Group VIII metals using an equal-volume impregnation method to prepare a bifunctional catalyst for the hydroisomerization reaction of long-chain n-alkanes. When the Pt loading in the bifunctional catalyst is 0.5 wt.%, the yield of the isomerized product in the hydroisomerization reaction is the highest, reaching 78.5%. However, due to the low metal dispersion of the bifunctional catalyst prepared by the equal-volume impregnation method, it is difficult to effectively suppress the cracking reaction, resulting in a low yield of isododecane.

[0008] Patent CN 109833906 A discloses a bifunctional catalyst for producing low-pour-point biodiesel from deoxygenated vegetable oil via hydroisomerization, its preparation method, and its application. The bifunctional catalyst (containing 0.05–0.5 wt.% Pd and 1.0–5.0 wt.% Ni2P) prepared by supporting Pd-Ni2P bimetals on hierarchical porous SAPO-31 molecular sieves is used in the hydroisomerization reaction of deoxygenated vegetable oil. The maximum pour point reduction after producing biodiesel from deoxygenated vegetable oil is 29.4°C. Although electron transfer between the Pd-Ni2P bimetals and synergistic catalytic activity with acidic sites improves the hydroisomerization reaction activity, the total liquid yield of biodiesel with boiling points above 160°C (160°C+) is 96.1%, and the pour point is reduced to -9.4°C. However, the catalyst disclosed in this invention is insufficient to further reduce the pour point of biodiesel and improve its low-temperature fluidity.

[0009] SAPO-31 is a mildly acidic aluminosilicate phosphate molecular sieve with an ATO topology, composed of one-dimensional circular open-cell twelve-membered ring channels with a channel size of 0.54 nm × 0.54 nm. It is a suitable acidic support for preparing bifunctional catalysts for the hydroisomerization reaction of n-alkane. While micron-sized SAPO-31 molecular sieves possess a suitable channel structure, the single microporous structure and large grain size result in poor mass transfer performance within the sieve channels. The excessive diffusion distance of reaction intermediates and products within the channels exacerbates side reactions. Hierarchical SAPO-31 molecular sieves, possessing both microporous and mesoporous structures, can overcome the mass transfer limitations of the single microporous channels in micron-sized molecular sieves when used as acidic supports for preparing bifunctional catalysts, thus improving the catalytic performance of the catalyst in the hydroisomerization reaction. On the other hand, published methods for preparing bifunctional catalysts typically employ the traditional equal-volume impregnation method, which suffers from problems such as low metal dispersion, low active site density, and poor synergistic catalytic effect between metal and acidic sites. Therefore, establishing a new method for preparing hierarchical porous nanomolecular sieves with intercrystalline mesopores composed of SAPO-31 nanocrystals, and employing effective methods to improve metal dispersion when preparing bifunctional catalysts supported on noble metals, is key to enhancing the synergistic effect between metal sites and acidic sites, improving the hydroisomerization reaction performance of jatropha oil deoxygenated oil, thereby increasing the yield of second-generation biodiesel and improving its low-temperature fluidity. Summary of the Invention

[0010] This invention aims to address the problems of low isomerization selectivity, poor stability, easy carbon deposition and deactivation, and poor low-temperature fluidity of biodiesel in existing bifunctional catalysts for the hydroisomerization of deoxygenated jatropha oil. It provides a method for preparing a highly dispersed Pt-Pd bimetallic catalyst on hierarchical porous nano-SAPO-31 molecular sieve using a vacuum-assisted impregnation method, and for using this catalyst for the hydroisomerization of deoxygenated jatropha oil to produce low-pour-point second-generation clean biodiesel.

[0011] This invention utilizes a nano-SAPO-31 molecular sieve-based bifunctional catalyst to produce low-pour-point second-generation biodiesel, which is achieved through the following steps:

[0012] A bifunctional catalyst was loaded into a tubular reactor and activated at 350–450°C for 5–12 hours under a hydrogen atmosphere. Then, deoxygenated jatropha oil was continuously pumped into the tubular reactor using a feed pump. The reaction temperature was controlled at 260–420°C, the pressure at 1.0–6.0 MPa, and the volume hourly space velocity (VHSV) of the deoxygenated jatropha oil at 0.5–5.0 h⁻¹. -1 The hydrogen-to-oil ratio (volume ratio) is 300-800:1. After the reaction, the liquid phase product is collected to obtain a second-generation biodiesel with a low pour point.

[0013] The bifunctional catalyst is a Pt-Pd bimetallic catalyst supported on a composite support formed by extruding hierarchical porous nano-SAPO-31 molecular sieve and γ-alumina using a vacuum-assisted impregnation method, and then activated under a hydrogen atmosphere. The sum of the weight percentages of Pd and Pt supported in the bifunctional catalyst is 0.1 to 0.6 wt.%.

[0014] The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst of the present invention has the following beneficial effects:

[0015] 1. This invention provides a novel method for synthesizing nano-SAPO-31 molecular sieves with a hierarchical pore structure possessing both micropores and intercrystalline mesopores using a bottom-up strategy, by adding the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) as a crystal growth inhibitor. The synthesized molecular sieve, acting as an acidic support for a bifunctional catalyst, significantly shortens the diffusion path of intermediates and products in the hydroisomerization reaction of long-chain n-alkanes within the molecular sieve pores, effectively increasing the yield of isomer products. Furthermore, due to the improved selectivity of multi-branched isomerization products, it significantly improves the low-temperature flowability of second-generation biodiesel.

[0016] 2. This invention provides a method for preparing a highly efficient bifunctional catalyst (Pt-Pd / S31-A) by vacuum-assisted impregnation of Pt-Pd bimetallic materials onto a composite support formed by extrusion of nano-SAPO-31 molecular sieve and γ-alumina. This method allows Pt and Pd to accumulate at the pores of the molecular sieve, improving metal dispersion, enhancing the interaction between the metal and the molecular sieve support, and better stabilizing the metal nanoclusters.

[0017] 3. This invention provides a novel method for producing low-pour-point second-generation biodiesel by hydroisomerization of jatropha oil deoxygenated oil using a nano-SAPO-31 molecular sieve-based bifunctional catalyst. The catalyst exhibits high reactivity, isomerization selectivity, and catalytic stability even with low noble metal loading. The liquid yield of biodiesel is as high as 99%, and the pour point is reduced to -18 to -32°C. The liquid yield and pour point of biodiesel remain unchanged after 1000 hours of continuous use of the catalyst. Attached Figure Description

[0018] Figure 1 This is the X-ray diffraction pattern of the hierarchical porous nano-SAPO-31 molecular sieve described in Example 1;

[0019] Figure 2 These are scanning electron microscope images of the hierarchical porous nano-SAPO-31 molecular sieve described in Example 1;

[0020] Figure 3 These are transmission electron microscope images of the hierarchical porous nano-SAPO-31 molecular sieve described in Example 1;

[0021] Figure 4 This is the N2 adsorption-desorption isotherm diagram of the nano-SAPO-31 molecular sieve described in Example 1;

[0022] Figure 5 This is a pore size distribution curve of the nano-SAPO-31 molecular sieve described in Example 1;

[0023] Figure 6 This is the NH3-TPD spectrum of the composite support formed by extruding nano-SAPO-31 molecular sieve and γ-alumina as described in Example 1;

[0024] Figure 7 This is the Py-IR spectrum of the composite carrier formed by extruding nano-SAPO-31 molecular sieve and γ-alumina as described in Example 1.

[0025] Figure 8 This is a TEM mapping image of the Pt-Pd bimetallic catalyst supported on a composite support formed by extruding nano-SAPO-31 molecular sieve and γ-alumina as described in Example 1. Detailed Implementation

[0026] Specific Implementation Method 1: This implementation method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst is carried out according to the following steps:

[0027] A bifunctional catalyst was loaded into a tubular reactor and activated at 350–450°C for 5–12 hours under a hydrogen atmosphere. Then, deoxygenated jatropha oil was continuously pumped into the tubular reactor using a feed pump. The reaction temperature was controlled at 260–420°C, the pressure at 1.0–6.0 MPa, and the volume hourly space velocity (VHSV) of the deoxygenated jatropha oil at 0.5–5.0 h⁻¹. -1 The hydrogen-to-oil ratio (volume ratio) is 300-800:1. After the reaction, the liquid phase product is collected to obtain a second-generation biodiesel with a low pour point.

[0028] The bifunctional catalyst is prepared by vacuum-assisted impregnation of 0.1–0.6 wt.% Pt-Pd bimetallic material onto a composite support (simplified as S31-A) formed by extrusion of hierarchical porous nano-SAPO-31 molecular sieve and γ-alumina, followed by activation under hydrogen atmosphere for 2–20 h to obtain the bifunctional catalyst xPd-Pt / S31-A, where x represents the sum of the weight percentages of Pd and Pt supported in the bifunctional catalyst, x = 0.1–0.6 wt.%.

[0029] In this embodiment, the bifunctional catalyst is cloverleaf shaped, with a diameter of 2 mm and a length of 3–5 mm. The catalyst packing density in the isothermal tubular reactor is 0.74–0.78 g / cm³. 3 .

[0030] The hierarchical porous SAPO-31 molecular sieve in this embodiment of the bifunctional catalyst not only has mild acidity, but also smaller nanoparticles with more open pores. When Pt-Pd bimetals are supported by vacuum-assisted impregnation, they can be enriched at the pores of the molecular sieve. This not only effectively "anchors" the metal nanoclusters, promoting their dispersion and improving catalytic stability, but also significantly shortens the diffusion distance of isomeric olefin intermediates and reaction products within the molecular sieve channels, enhancing the accessibility of metal and acidic sites and the synergistic catalytic effect of the two active sites. Therefore, it significantly improves the liquid yield of biodiesel and enhances its low-temperature fluidity.

[0031] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the preparation method of the hierarchical porous nano-SAPO-31 molecular sieve is as follows:

[0032] Boehmite, phosphoric acid, di-n-butylamine (DBA), silica sol, crystal growth inhibitor cetyltrimethylammonium bromide (CTAB), and deionized water were mixed in a molar ratio of Al2O3:P2O5:DBA:SiO2:CTAB:H2O = 1.0:1.0:(1.4~1.5):(0.4~0.8):(0.02~1.2):(50~60). The mixture was stirred until homogeneous to obtain an initial gel. The initial gel was then transferred to a stainless steel crystallization vessel with a polytetrafluoroethylene liner and crystallized at 160~190℃ for 12~72h. The crystallized product was cooled to room temperature and then centrifuged, washed, dried, and calcined to obtain nano-SAPO-31 molecular sieves with a multi-level porous structure.

[0033] In this embodiment, cetyltrimethylammonium bromide (CTAB) is used as a crystal growth inhibitor in the synthesis of nano-SAPO-31 molecular sieves. The cationic surfactant CTAB adsorbs onto the surface of the SAPO-31 precursor through electrostatic interactions and forms hydrophobic micelles, which inhibits the aggregation of the precursor and the growth of crystals during the crystallization process.

[0034] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 2 in that it involves crystallization at 170–180°C for 24–48 hours.

[0035] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Two in that the crystal size of the nano-SAPO-31 molecular sieve is 10-40 nm.

[0036] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the preparation method of the composite carrier is as follows:

[0037] Nano-SAPO-31 molecular sieves and γ-alumina binder were mixed in a mass ratio of 2 to 6:1. Then, a prepared dilute nitric acid solution (6.0%) and guar gum powder were added as extrusion aids. The mixture was extruded using a twin-screw extruder and dried and calcined to obtain a composite carrier (denoted as S31-A).

[0038] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that after molding, the material is dried at 70-120°C (12-24 hours) and then placed in a muffle furnace and calcined at 550-600°C for 8-12 hours.

[0039] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method One or Five in that it employs a vacuum-assisted impregnation method to prepare a bifunctional catalyst for Pt-Pd bimetallic support, as follows:

[0040] The composite support was cut into a column and placed in a suction flask. After evacuation (1-5 h), a mixed solution of dinitro-tetraaminoplatinum (Pd(NH3)4(NO3)2) and dinitro-tetraaminopalladium (Pt(NH3)4(NO3)2) was added dropwise while maintaining the vacuum. After the composite support was fully impregnated in the mixed solution, it was removed, dried, and calcined to obtain a bifunctional catalyst supported on Pt-Pd bimetallic materials.

[0041] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the composite carrier is fully impregnated in the mixed solution, removed, vacuum dried at 60-80°C, and then calcined at 400-500°C for 10-20 hours.

[0042] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Seven in that the solid-liquid ratio (mass ratio) of the composite carrier and the mixed solution of dinitro-tetraaminoplatinum (Pd(NH3)4(NO3)2) and dinitro-tetraaminopalladium (Pt(NH3)4(NO3)2) (the concentrations of the two solutions are 0.038 mol / L and 0.021 mol / L, respectively) is 1:1.5 to 3.

[0043] Specific Implementation Method 10: This implementation method differs from Specific Implementation Method 7 in that the total loading of metals Pt and Pd in ​​the bifunctional catalyst is 0.2 to 0.45 wt.%, and the mass ratio of Pt to Pd is 1:2 to 2:1.

[0044] Specific Implementation Method Eleven: This implementation method differs from Specific Implementation Method One in that the reaction temperature is controlled at 300–400°C, the pressure at 3.0–5.0 MPa, and the volume hourly space velocity (VHSV) of the deoxygenated jatropha oil at 0.5–5.0 h⁻¹. -1 The hydrogen-to-oil ratio (volume ratio) is 500–700:1, and the liquid product is collected after the reaction.

[0045] Example 1: This example describes a method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst, implemented according to the following steps:

[0046] The bifunctional catalyst was loaded into a 20 mL isothermal tubular reactor and maintained at 400 °C for 6 h under a hydrogen atmosphere. After the bifunctional catalyst was reduced, jatropha oil deoxygenated oil was continuously pumped into the reactor using a liquid feed pump. The reaction temperature was controlled at 370 °C, the pressure at 4.0 MPa, and the volume hourly space velocity (VHSV) of the jatropha oil deoxygenated oil at 1.0 h⁻¹. -1 The hydrogen-to-oil ratio (by volume) was 600:1. The liquid phase products were collected to obtain a second-generation biodiesel with a low pour point.

[0047] The preparation method of the bifunctional catalyst is as follows:

[0048] The synthesis method of nano-SAPO-31 molecular sieve with hierarchical pore structure is as follows: Boehmite, phosphoric acid, di-n-butylamine, silica sol, crystal growth inhibitor CTAB, and deionized water are mixed in a molar ratio of Al2O3:P2O5:DBA:SiO2:CTAB:H2O = 1.0:1.0:1.4:0.6:0.05:50. After stirring for a period of time, the resulting uniform initial gel is transferred to a stainless steel crystallization kettle with a polytetrafluoroethylene liner and crystallized at 180℃ for 48 hours. The crystallized product is cooled to room temperature, and then centrifuged, washed, dried, and calcined to obtain nano-SAPO-31 molecular sieve with hierarchical pore structure.

[0049] II. The preparation method of nano-SAPO-31 molecular sieve and γ-alumina composite carrier is as follows: The nano-SAPO-31 molecular sieve synthesized according to the method described in step one is mixed with γ-alumina binder at a mass ratio of 3:1, and a certain amount of dilute nitric acid solution and guar gum powder are added as extrusion aids. The clover-shaped carrier with a diameter of 2 mm is extruded using a twin-screw extruder. After drying and calcination, the shaped nano-SAPO-31 molecular sieve and γ-alumina composite carrier (denoted as S31-A) is obtained.

[0050] III. The specific method for preparing a bifunctional catalyst supported on Pt-Pd bimetallic material using a vacuum-assisted impregnation method is as follows: First, the shaped composite support prepared according to step II is cut into 3-5 mm cylindrical pieces and placed in a suction flask. After evacuating for 2 hours, a mixed solution of dinitro-tetraaminoplatinum (Pd(NH3)4(NO3)2) and dinitro-tetraaminopalladium (Pt(NH3)4(NO3)2) of a certain concentration is added dropwise while maintaining the vacuum. After the shaped support is fully impregnated in the solution, it is removed, dried, and calcined to obtain a bifunctional catalyst 0.44Pd-Pt / S31-A supported on a composite support of nano-SAPO-31 molecular sieve and γ-alumina, containing 0.44 wt.% Pt-Pd. The results of using this catalyst to catalyze the hydroisomerization reaction of jatropha oil deoxygenated oil are shown in Table 1. The liquid yield of biodiesel is 98-99%, the pour point is -18℃, and the pour point drop is 44℃ (the pour point of deoxygenated oil feedstock is 26℃).

[0051] The molecular sieve sample synthesized according to the method described in Example 1 was characterized by XRD, and the XRD spectrum ( Figure 1 All characteristic diffraction peaks in the sample were consistent with the standard card, indicating that the sample was a pure-phase SAPO-31 molecular sieve. This was confirmed by scanning electron microscopy and transmission electron microscopy images. Figure 2 and Figure 3 As can be seen, the individual particle size of SAPO-31 molecular sieve nanocrystals is only ~30 nm. The N2 adsorption-desorption isotherm of SAPO-31 molecular sieve (…) Figure 4The presence of both Type I and Type IV isotherms indicates that the sample contains both micropores and intergranular mesopores formed by the accumulation of nanocrystals. The pore size distribution curve obtained from the BJH model ( Figure 5 As can be seen, the mesopore distribution is concentrated in the range of 5–10 nm. This indicates that, according to the method described in Example 1, introducing the growth inhibitor CTAB into the initial gel for synthesizing SAPO-31 molecular sieves can effectively suppress crystal growth, resulting in the synthesis of a pure-phase, hierarchical porous nano-SAPO-31 molecular sieve with both micropores and intercrystalline mesopores.

[0052] The composite support formed by extruding nano-SAPO-31 molecular sieve and γ-alumina as described in Example 1 was characterized by NH3-TPD. Figure 6 ).Depend on Figure 6 As can be seen, three NH3 desorption peaks appeared on the NH3-TPD curve, indicating the presence of three acidic sites of different strengths in the composite support. Among them, the stronger acidic sites are usually formed by... Acid sites are provided.

[0053] The composite support formed by extruding nano-SAPO-31 molecular sieve and γ-alumina described in Example 1 was characterized by pyridine adsorption using infrared spectroscopy (Py-IR), and the spectrum is shown below. Figure 7 As shown. In the Py-IR spectrum, the value is around 1545 cm⁻¹. -1 and 1455cm -1 Adsorption peaks appeared nearby, corresponding to pyridine adsorbed on the sample. The characteristic absorption peaks of acid sites and Lewis acid sites indicate that the composite support still contains relatively abundant... Acidic sites (density 21.6 μmol / g). Bifunctional catalysts. Acidic sites are active sites in the hydroisomerization of n-alkane intermediates, where they undergo protonation to form carbocations, carbocation skeletal isomerization (rearrangement), and deprotonation of isomeric carbocations. Sufficient acidic site density effectively enhances the reactivity of the hydroisomerization reaction.

[0054] The Pt-Pd bimetallic catalyst supported on the composite support formed by extruding nano-SAPO-31 molecular sieve and γ-alumina as described in Example 1 was characterized by TEM mapping. Figure 8 ).Depend on Figure 8 It is evident that Pt and Pd in ​​the catalyst are highly dispersed, providing more abundant metal sites, which promotes the dehydrogenation of n-alkanes and the hydrogenation of isoalkene intermediates to obtain isoalkane products. This is beneficial for improving the isomerization rate and liquid yield of the hydroisomerization dewaxing reaction of deoxygenated oil.

[0055] Example 2: This example differs from Example 1 in that the reaction conditions for the isomerization and pour point depletion of jatropha oil are: pressure 2.0 MPa, reaction temperature 325°C, and feedstock volume hourly space velocity 2.0 h⁻¹. -1 The hydrogen-to-oil ratio (by volume) is 500:1. Everything else is the same as in Example 1.

[0056] In this embodiment, the yield of the deoxygenated oil after the reaction was 99-100%, the pour point was 15°C, and the pour point drop was 11°C.

[0057] Example 3: This example differs from Example 1 in that the reaction conditions for the isomerization and pour point depletion of jatropha oil are: pressure 2.0 MPa, reaction temperature 340℃, and volumetric void fraction 1.5 h. -1 The hydrogen-to-oil ratio (by volume) is 600:1. Everything else is the same as in Example 1.

[0058] In this embodiment, the yield of the deoxygenated oil after the reaction was 98-99%, the pour point was 10°C, and the pour point drop was 16°C.

[0059] Example 4: This example differs from Example 1 in that the reaction conditions for the isomerization and pour point depletion of jatropha oil are: pressure 2.0 MPa, reaction temperature 350°C, and volumetric void fraction 1.0 h⁻¹. -1 The hydrogen-to-oil ratio (by volume) is 600:1. Everything else is the same as in Example 1.

[0060] In this embodiment, the yield of the deoxygenated oil after the reaction was 98-99%, the pour point was 2°C, and the pour point drop was 24°C.

[0061] Example 5: This example differs from Example 1 in that the reaction conditions for the isomerization and pour point depletion of jatropha oil are: pressure 2.0 MPa, reaction temperature 360°C, and volumetric void fraction 1.0 h⁻¹. -1 The hydrogen-to-oil ratio (by volume) is 600:1. Everything else is the same as in Example 1.

[0062] In this embodiment, the yield of the deoxygenated oil after the reaction was 98-99%, the pour point was -1℃, and the pour point drop was 27℃.

[0063] Examples 1 to 5 present the results of investigating the process conditions for the isomerization and pour point depletion reaction of jatropha oil deoxygenated on a nano-SAPO-31 molecular sieve-based bifunctional catalyst under different reaction conditions.

[0064] Table 2 shows the long-term stability evaluation results of the isomerization and pour point degradation of jatropha oil deoxygenated oil on a nano-SAPO-31 molecular sieve-based bifunctional catalyst. The reaction conditions were 370℃, 4MPa, and 1.0 h⁻¹. -1Under the reaction conditions of a hydrogen-to-oil ratio (v:v) of 600:1, the product liquid yield and pour point depreciation did not decrease significantly after 1000 h of reaction time, indicating that the catalyst can still maintain good catalytic reaction stability.

[0065] Table 1. Optimization of process conditions for evaluating the isomerization and pour point depressing performance of jatropha oil deoxygenated oil.

[0066]

[0067] Table 2. Evaluation results of long-term stability of deoxygenated jatropha oil isomerization dewaxing oil.

[0068]

[0069]

Claims

1. A method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst, characterized in that... The method for producing low-pour-point second-generation biodiesel is implemented according to the following steps: A bifunctional catalyst was loaded into a tubular reactor and activated at 350–450°C for 5–12 hours under a hydrogen atmosphere. Then, deoxygenated jatropha oil was continuously pumped into the tubular reactor using a feed pump. The reaction temperature was controlled at 260–420°C, the pressure at 1.0–6.0 MPa, and the volume hourly space velocity (VHSV) of the deoxygenated jatropha oil at 0.5–5.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 300-800:

1. After the reaction, the liquid phase product is collected to obtain a second-generation biodiesel with a low pour point. The bifunctional catalyst is a Pt-Pd bimetallic catalyst supported on a composite support formed by extruding hierarchical porous nano-SAPO-31 molecular sieve and γ-alumina using a vacuum-assisted impregnation method, and then activated under a hydrogen atmosphere. The sum of the weight percentages of Pd and Pt supported in the bifunctional catalyst is 0.1 to 0.6 wt.%. The preparation method of hierarchical porous nano-SAPO-31 molecular sieve is as follows: Boehmite, phosphoric acid, di-n-butylamine, silica sol, crystal growth inhibitor cetyltrimethylammonium bromide, and deionized water were mixed in a molar ratio of Al2O3:P2O5:DBA:SiO2:CTAB:H2O = 1.0:1.0:(1.4~1.5):(0.4~0.8):(0.02~1.2):(50~60). The mixture was stirred until homogeneous to obtain an initial gel. The initial gel was then transferred to a stainless steel crystallization vessel with a polytetrafluoroethylene liner and crystallized at 160~190℃ for 12~72h. The crystallized product was cooled to room temperature and then centrifuged, washed, dried, and calcined to obtain nano-SAPO-31 molecular sieves with a multi-level porous structure.

2. The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst according to claim 1, characterized in that... In the preparation method of hierarchical porous nano-SAPO-31 molecular sieve, crystallization is carried out at 170-180℃ for 24-48h.

3. The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst according to claim 1, characterized in that... In the preparation method of hierarchical porous nano-SAPO-31 molecular sieve, the crystal size of nano-SAPO-31 molecular sieve is 10-40 nm.

4. The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst according to claim 1, characterized in that... The preparation method of the composite carrier is as follows: Nano-SAPO-31 molecular sieves and γ-alumina binders were mixed in a mass ratio of 2 to 6:

1. Then, a prepared dilute nitric acid solution and guar gum powder were added as extrusion aids. The mixture was extruded using a twin-screw extruder and then dried and calcined to obtain a composite carrier.

5. The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst according to claim 1, characterized in that... The preparation method of Pt-Pd bimetallic bifunctional catalyst supported by vacuum-assisted impregnation is as follows: The composite support was cut into a column and placed in a suction flask. After evacuation, a mixed solution of dinitro-tetraaminoplatinum and dinitro-tetraaminopalladium was added dropwise while maintaining the vacuum. After the composite support was fully impregnated in the mixed solution, it was removed and dried and calcined to obtain a bifunctional catalyst supported on Pt-Pd bimetallic materials.

6. The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst according to claim 5, characterized in that... After the composite carrier is fully impregnated in the mixed solution, it is removed, vacuum dried at 60–80°C, and then calcined at 400–500°C for 10–20 hours.

7. The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst according to claim 5, characterized in that... The solid-liquid ratio of the composite carrier to the mixed solution of dinitro-tetraaminoplatinum and dinitro-tetraaminopalladium is 1:1.5 to 3.

8. The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst according to claim 5, characterized in that... The total loading of metals Pt and Pd in ​​the bifunctional catalyst is 0.2 to 0.45 wt.%, and the mass ratio of Pt to Pd is 1:2 to 2:

1.

9. The method for producing low-pour-point second-generation biodiesel using a nano-SAPO-31 molecular sieve-based bifunctional catalyst according to claim 1, characterized in that... The reaction temperature was controlled at 300–400℃, the pressure at 3.0–5.0 MPa, and the volume hourly space velocity (VHSV) of the deoxygenated jatropha oil at 0.5–5.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 500–700:1, and the liquid product is collected after the reaction.

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