A method for preparing multi-branched isohexadecane by using a bifunctional catalyst with spatial separation of Pd metal sites and acid sites of hierarchical pore ZSM-12 molecular sieve

Abstract

A method for preparing multi-branched isohexadecane by using a bifunctional catalyst with spatial separation of Pd metal sites and acid sites of hierarchical pore ZSM-12 molecular sieve, the present application solves the problems of existing bifunctional catalyst, such as single pore channel limiting the generation and diffusion of long-chain isoparaffin, and reducing the isoparaffin yield, etc. The preparation method is as follows: the bifunctional catalyst is loaded into a fixed bed reactor, after activation, n-hexadecane is continuously injected, the reaction temperature and pressure are controlled, and isoparaffin mainly composed of multi-branched isohexadecane is obtained. The catalyst used in the present application is prepared by loading metal Pd on mesoporous gamma-Al2O3 by a vacuum-assisted impregnation method, and then mixed with hierarchical pore ZSM-12 molecular sieve, the Pd metal sites are spatially separated from the acid sites of the hierarchical pore ZSM-12 molecular sieve, the catalyst inhibits the cracking side reaction in the process of long-chain n-paraffin hydrogenation isomerization, and improves the isomerization selectivity and the proportion of multi-branched isomers in isoparaffin.

Description

Technical Field

[0001] This invention relates to a method for preparing corresponding multi-branched isoalkanes from long-chain n-alkanes via hydroisomerization using a bifunctional catalyst. Background Technology

[0002] With the rapid development of the global transportation industry and the increasing demands for environmental protection, the production of green biodiesel and sustainable aviation fuel (SAF) from renewable vegetable oil or kitchen waste oil has become one of the most promising technological routes for producing clean fuels using renewable resources.

[0003] Biomass is an organic form produced through photosynthesis. The carbon in biomass originates from atmospheric CO2, hydrogen from water, and oxygen from both CO2 and water. Therefore, converting it into fuel or chemicals can be considered a zero-carbon emission process. my country's annual biomass resource production is close to 10 billion tons, of which the amount usable as energy is equivalent to approximately 460 million tons of standard coal, making it an important renewable energy source. However, its current utilization rate remains low. Compared to traditional petroleum-based diesel and aviation fuel, hydrocarbon-based second-generation biodiesel (HVO) and sustainable aviation fuel (SAF), obtained through the hydroisomerization of deoxygenated vegetable oil and primarily composed of isoalkanes, offer advantages such as high energy density and good low-temperature fluidity. HVO can be blended with petrochemical diesel in any proportion, and the maximum blending ratio of SAF currently certified by ASTM is 50%. SAF's greenhouse gas emissions over its entire life cycle can be reduced by 60%–85% compared to traditional aviation kerosene. Therefore, developing production technologies for clean biofuels such as SAF is of great significance for reducing over-reliance on traditional fossil fuels, achieving carbon emission reduction, and ensuring energy security.

[0004] The synthesis of HVO and SAF typically uses non-edible vegetable oils or waste cooking oils as raw materials, which are then hydrogenated and deoxygenated to obtain C. 15 ~C 18 n-Alkanes are then subjected to hydroisomerization (to produce HVO) or a combination of hydroisomerization and selective cracking (to produce SAF) to prepare C64-carbon-based hydrocarbons. 15 ~C 18 Second-generation biodiesel with isoalkanes as the main component or C8~C4 hydrocarbons as the main component 15 SAFs with isoalkanes as the main component. The hydrodeoxygenation process for vegetable oils is relatively mature, but long-chain n-alkanes are prone to over-cracking during hydroisomerization, leading to a decrease in fuel oil yield. Therefore, improving isomerization selectivity and inhibiting over-cracking by designing catalysts to regulate the synergistic effect of metal and acid sites is a key technology for producing high-quality biofuels.

[0005] Catalysts used in the hydroisomerization of n-alkanes are typically bifunctional catalysts consisting of a metal site with hydrogenation / dehydrogenation activity and an acidic site with isomerization / cracking activity. The metal sites are usually provided by noble metals such as Pt and Pd, or non-noble metals such as Ni and Sn, and transition metal compounds; the acidic sites are usually provided by one-dimensional channel silica-alumina phosphate molecular sieves such as SAPO-11, or zeolite molecular sieves such as ZSM-22, ZSM-23, ZSM-48, and MOR. Among these, SAPO-11 molecular sieves exhibit excellent catalytic performance in hydroisomerization reactions due to their mild acidity, but their synthesis process is complex and generates phosphorus-containing wastewater, thus limiting their large-scale industrial application. ZSM-12 molecular sieves, with their one-dimensional twelve-membered ring channel structure and pore size (approximately 5.6 × 6.1 Å), are slightly larger than ten-membered ring molecular sieves such as ZSM-22 / 23, which facilitates the diffusion of larger molecules. This makes them a promising candidate as acidic supports for bifunctional catalysts in the production of sustainable green biofuels. However, the narrow micropores in microporous ZSM-12 molecular sieves still significantly restrict the diffusion of large molecules, hindering efficient mass transfer in the reaction system and prolonging the residence time of reaction intermediates within the channels, thus increasing the probability of side reactions. Therefore, reducing the diffusion resistance of reaction intermediates is crucial for preparing high-performance catalysts. Hierarchical ZSM-12 molecular sieves combine microporous and mesoporous structures, possessing a large specific surface area, abundant catalytic active centers, and high hydrothermal stability. The abundant mesoporous structure further facilitates the diffusion of reactants, intermediates, and products, reducing coking and carbon deposition, thereby significantly improving their catalytic performance. In addition, when using the traditional equal-volume impregnation method to support metals, it is often difficult to achieve a high degree of metal dispersion, and the accessible metal active sites are limited, which may lead to an unsatisfactory isomerization selectivity of the bifunctional catalyst. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of existing bifunctional catalysts, such as the limitation of single micropore channels on the generation and diffusion of long carbon chain isoalkanes, the aggravation of cracking side reactions, and the reduction of isoalkane yield. The invention provides a method for synthesizing hierarchical ZSM-12 molecular sieves with intercrystalline mesopores using crystal growth inhibitors, and applying it to prepare multi-branched isohexadecane.

[0007] The present invention utilizes a bifunctional catalyst with spatially separated Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieves to prepare multi-branched isohexadecane, which is implemented according to the following steps:

[0008] A bifunctional catalyst, spatially separated from the acidic sites of the Pd metal sites in a hierarchical ZSM-12 molecular sieve, was packed into the isothermal zone of a fixed-bed reactor and subjected to heating at 350–500 °C under a H2 atmosphere. oAfter C activation treatment and cooling to the reaction temperature, n-hexadecane is continuously injected into a fixed-bed reactor via a feed pump to carry out the catalytic reaction, with the reaction temperature controlled at 270~340℃. o C, the reaction pressure is 1.5~3.5 MPa, and the mass hourly space velocity of n-hexadecane is controlled at 2.5~5 h⁻¹. -1 The volume ratio of H2 to n-hexadecane is (300~700):1, yielding multi-branched isohexadecane;

[0009] The bifunctional catalyst in which the Pd metal sites and the acidic sites of the hierarchical ZSM-12 molecular sieve are spatially separated is prepared by mixing xPd / A(V) obtained by supporting Pd on mesoporous γ-Al2O3 using a vacuum-assisted impregnation method with the hierarchical ZSM-12 molecular sieve at a mass ratio of 1:1.

[0010] The present invention provides a method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatially separated Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieves. This method offers the following advantages:

[0011] 1. This invention employs a two-step hydrothermal synthesis method. In the first step, after hydrothermal treatment for a certain time, a certain amount of cetyltrimethylammonium bromide (CTAB) is added to the mixed gel of the ZSM-12 molecular sieve obtained in the first step as a crystal growth inhibitor before crystallization in the second step. By changing the crystallization time in both steps, a series of hierarchical porous ZSM-12 molecular sieves (Z12-S(t1,t2)) composed of stacked nanosheets are synthesized, where t1 and t2 are the crystallization times (in hours) for the first and second stages, respectively. The hierarchical porous ZSM-12 molecular sieve, possessing both micropores and intergranular mesopores, has more open pores and accessible acidic sites than traditional microporous molecular sieves. This facilitates the rapid diffusion of long-chain isomerization products within its pores, inhibits the formation of cracking byproducts, reduces coke deposition, and improves catalytic activity and stability.

[0012] 2. In this invention, a series of samples with varying Pd loadings (xPd / A(V)) (x = 0.05~0.3 wt.%) are prepared by vacuum-assisted impregnation onto mesoporous γ-Al₂O₃. These samples exhibit higher Pd dispersion and expose more Pd active sites compared to samples prepared by the traditional wet impregnation method. This significantly reduces the Pd loading while improving the dehydrogenation activity and isomerization selectivity of n-alkane dehydrogenation and isomerization intermediates.

[0013] 3. In this invention, xPd / A(V) samples prepared by supporting Pd on mesoporous γ-Al₂O₃ are mixed with Z₁₂-S(t₁, t₂) of hierarchical porous ZSM-12 molecular sieve with intergranular mesoporous structures prepared by a two-step crystallization method at a mass ratio of 1:1 to prepare a series of xPd / A(V)-Z₁₂-S(t₁, t₂) bifunctional catalysts with spatially separated Pd metal sites and acidic sites of hierarchical porous ZSM-12 molecular sieve. Due to the higher dispersion of Pd and the more suitable distance between the metal and acidic sites in this series of catalysts, synergistic catalysis of the metal and acidic sites is achieved, significantly improving the isomerization selectivity of the hexadecane hydroisomerization reaction, the yield of isohexadecane products, and the proportion of multi-branched isohexadecane products. Attached Figure Description

[0014] Figure 1 The XRD pattern is shown in Example 1 for the graded pore size Z12-S(36,72) molecular sieve sample.

[0015] Figure 2 These are scanning electron microscope (SEM) images of the graded pore size Z12-S(36,72) molecular sieve sample described in Example 1;

[0016] Figure 3 The N2 adsorption-desorption isotherm of the graded pore size Z12-S(36,72) molecular sieve sample described in Example 1;

[0017] Figure 4 This is the pore size distribution curve of the graded pore size Z12-S(36,72) molecular sieve sample described in Example 1;

[0018] Figure 5 The infrared spectrum (Py-IR) of pyridine adsorption of the graded pore size Z12-S(36,72) molecular sieve sample described in Example 1 is shown.

[0019] Figure 6 The XRD pattern of the graded pore size Z12-S(36,60) molecular sieve sample described in Example 3 is shown.

[0020] Figure 7 These are scanning electron microscope (SEM) images of the graded pore size Z12-S(36,60) molecular sieve sample described in Example 3;

[0021] Figure 8 The N2 adsorption-desorption isotherm of the graded pore size Z12-S(36,60) molecular sieve sample described in Example 3;

[0022] Figure 9 This is the pore size distribution curve of the graded pore size Z12-S(36,60) molecular sieve sample described in Example 3;

[0023] Figure 10 The infrared spectrum (Py-IR) of pyridine adsorption of the graded pore size Z12-S(36,60) molecular sieve sample described in Example 3 is shown.

[0024] Figure 11 The XRD pattern of the graded pore size Z12-S(30,60) molecular sieve sample described in Example 5 is shown.

[0025] Figure 12 The N2 adsorption-desorption isotherm of the graded pore size Z12-S(30,60) molecular sieve sample described in Example 5;

[0026] Figure 13 This is the pore size distribution curve of the graded pore size Z12-S(30,60) molecular sieve sample described in Example 5;

[0027] Figure 14 The infrared spectrum (Py-IR) of pyridine adsorption of the graded pore size Z12-S(30,60) molecular sieve sample described in Example 5 is shown.

[0028] Figure 15 The XRD pattern of the microporous ZSM-12 molecular sieve described in Comparative Example 1 is shown below.

[0029] Figure 16 This is a scanning electron microscope (SEM) image of the microporous ZSM-12 molecular sieve described in Comparative Example 1;

[0030] Figure 17 The N2 adsorption-desorption isotherm of the microporous ZSM-12 molecular sieve described in Comparative Example 1;

[0031] Figure 18 The pore size distribution curve of the microporous ZSM-12 molecular sieve described in Comparative Example 1 is shown.

[0032] Figure 19 The infrared spectrum (Py-IR) of pyridine adsorption on the microporous ZSM-12 molecular sieve described in Comparative Example 1 is shown.

[0033] Figure 20 These are curves showing the relationship between the conversion rate of n-hexadecane and the yield of isohexadecane in the hexadecane hydroisomerization reaction when catalyst A is used in Examples 1 and 2 and catalyst D is used in Comparative Examples 1 and 2, where ● represents catalyst A and ■ represents catalyst D.

[0034] Figure 21 The curves showing the relationship between the conversion rate of n-hexadecane and the yield of isohexadecane in the hexadecane hydroisomerization reaction when catalyst B is used in Examples 3 and 4 and catalyst C is used in Examples 5 and 6 are shown. ■ represents catalyst B, and ● represents catalyst C. Detailed Implementation

[0035] Specific Implementation Method 1: This implementation method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatially separated Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve is carried out according to the following steps:

[0036] A bifunctional catalyst, spatially separated from the acidic sites of the Pd metal sites in a hierarchical ZSM-12 molecular sieve, was packed into the isothermal zone of a fixed-bed reactor and subjected to heating at 350–500 °C under a H2 atmosphere. o After C activation treatment and cooling to the reaction temperature, n-hexadecane is continuously injected into a fixed-bed reactor via a feed pump to carry out the catalytic reaction, with the reaction temperature controlled at 270~340℃. o C, the reaction pressure is 1.5~3.5 MPa, and the mass hourly space velocity of n-hexadecane is controlled at 2.5~5 h⁻¹. -1 The volume ratio of H2 to n-hexadecane is (300~700):1, yielding multi-branched isohexadecane;

[0037] The bifunctional catalyst in which the Pd metal sites and the acidic sites of the hierarchical ZSM-12 molecular sieve are spatially separated is prepared by mixing xPd / A(V) (V represents vacuum-assisted impregnation) prepared by supporting Pd on mesoporous γ-Al2O3 using a vacuum-assisted impregnation method with the hierarchical ZSM-12 molecular sieve at a mass ratio of 1:1.

[0038] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that hexadecane is continuously injected into a fixed-bed reactor for the catalytic reaction, and the reaction temperature is controlled at 290~320°C. o C, the reaction pressure is 1.5~3.0 MPa, and the mass hourly space velocity of n-hexadecane is controlled at 3~4 h⁻¹. -1 The volume ratio of H2 to n-hexadecane is (400~600):1.

[0039] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that xPd / A(V) represents the load of Pd, x = 0.05~0.3 wt.%.

[0040] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method One in that the preparation method of the bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve is as follows:

[0041] 1. Dissolve 0.2–1.4 g NaOH, 0.1–0.8 g sodium aluminate (NaAlO2, of which Al2O3 content is 40.04 wt.%), 60–90 g silica sol (of which SiO2 content is 32.13%), and 5–15 g tetraethylammonium bromide (TEABr, of which TEABr content is 99.0%) in 30–50 g deionized water, stir to obtain an initial gel, and then at 150–180 °C... o A hydrothermal reaction was carried out at C to obtain a ZSM-12 molecular sieve precursor solution.

[0042] 2. Dissolve 10-15 g of hexadecyltrimethylammonium bromide (CTAB) in 30-50 g of water, add it to the ZSM-12 molecular sieve precursor solution, stir to obtain a mixed gel, and then heat at 150-180 °C. o The solid product was obtained by crystallization reaction under C and calcination. The solid product was then subjected to ion exchange with 0.2~1 mol / L NH4NO3 solution to obtain ammonium type ZSM-12 molecular sieve. After calcination, hydrogen type graded porous ZSM-12 molecular sieve (Z12-S(t1, t2)) was obtained.

[0043] 3. Place the pseudo-boehmite in a muffle furnace and heat it to 500-800°C in an air atmosphere. o C, after calcination, mesoporous γ-Al2O3 is obtained. The mesoporous γ-Al2O3 is placed in a vacuum system for 1~3 h, and then completely wetted with Pd(NO3)2 aqueous solution. After calcination, xPd / A(V) is obtained.

[0044] IV. xPd / A(V) was mixed with hydrogen-type hierarchical porous ZSM-12 molecular sieve at a mass ratio of 1:1 to prepare a bifunctional catalyst (xPd / A(V)-Z12-S) with spatial separation between Pd metal sites and acidic sites of hierarchical porous ZSM-12 molecular sieve.

[0045] The hierarchical porous ZSM-12 molecular sieve prepared in step two of this embodiment exhibits a morphology of densely packed aggregates composed of nanosheets with a thickness of 10-40 nm, and the size of the aggregates is approximately 0.8-2 μm. The vacuum treatment in step three serves to remove water and inert gases from the pores of the mesoporous γ-Al₂O₃ support, thereby allowing Pd in ​​the Pd(NO₃)₂ aqueous solution to be released. 2+ It is adsorbed into the pores to promote its dispersion.

[0046] Specific Implementation Method 5: This implementation method differs from Specific Implementation Method 4 in that the hydrothermal reaction time in step one is 12~60 h.

[0047] In this embodiment, the hydrothermal reaction time is preferably 30-36 hours.

[0048] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Four or Five in that the crystallization reaction time in step two is 24~84 h.

[0049] In this embodiment, the crystallization reaction time is preferably 60~72 h.

[0050] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods Four to Six in that the ion exchange time in step two is 1 to 5 hours.

[0051] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods Four to Seven in that the vacuum degree of the vacuum system in step three is 0.08~0.09 MPa.

[0052] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Four to Eight in that step three involves heating the temperature to 500-800°C in an air atmosphere. o C, after calcination for 4-8 h, yields mesoporous γ-Al2O3.

[0053] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 4 to 9 in that the particle size of the bifunctional catalyst with spatially separated Pd metal sites and acidic sites of the graded pore ZSM-12 molecular sieve prepared in step 4 is 1.52~4.46 nm.

[0054] Example 1: This example describes a method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatially separated Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieves. The method is implemented according to the following steps:

[0055] A 20-40 mesh bifunctional catalyst was loaded into the isothermal zone of a stainless steel reaction tube and heated to 400°C under a H2 atmosphere. o The bifunctional catalyst was reduced at C for 1 h. Then, the reaction pressure was controlled at 2 MPa, and n-hexadecane was pumped into the fixed-bed reactor via a feed pump at a mass hourly space velocity (WHSV) of 3.7 h⁻¹. -1 The volume ratio of H2 to n-hexadecane is 500:1, and the reaction temperature is 300°C. o C. After the reactor has been running stably, collect the gaseous product and the liquid product, which is mainly composed of multi-branched isohexadecane.

[0056] The bifunctional catalyst is prepared by mixing a sample with 0.28 wt.% Pd supported on mesoporous γ-Al2O3 and graded porous ZSM-12 molecular sieve at a mass ratio of 1:1.

[0057] The preparation method of the bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve described in this embodiment is as follows:

[0058] 1. At room temperature, dissolve 1.03 g NaOH, 0.48 g sodium aluminate (NaAlO2, of which Al2O3 content is 40.04 wt.%), 71.21 g silica sol (of which SiO2 content is 32.13%), and 10 g tetraethylammonium bromide (of which TEABr content is 99.0%) in 27.1 g deionized water, then add the solution and stir until homogeneous to obtain an initial gel. Transfer the obtained initial gel to a crystallization kettle lined with polytetrafluoroethylene and crystallize at 160°C. o After hydrothermal treatment at C for 36 h, a ZSM-12 molecular sieve precursor solution was obtained.

[0059] 2. Dissolve 11.38 g of cetyltrimethylammonium bromide (CTAB) in 34.3 g of water, and slowly add it to the ZSM-12 molecular sieve precursor solution. Stir vigorously to obtain a mixed gel, and then... (The sentence is incomplete and requires more context to translate accurately.) o After crystallization at C for 72 h, followed by centrifugation, washing, drying and calcination, a solid product was obtained. The product was then subjected to ion exchange treatment with 0.5 mol / L NH4NO3 solution at room temperature (liquid-solid ratio of 30:1) for 3 h to obtain ammonium-type ZSM-12 molecular sieve. After centrifugation, washing, drying and calcination, a hydrogen-type hierarchical porous ZSM-12 molecular sieve (Z12-S(36, 72)) composed of stacked nanosheets was obtained.

[0060] 3. Place the pseudo-boehmite in a muffle furnace and heat it to 650°C in an air atmosphere. o C, calcined for 6 h to obtain mesoporous γ-Al2O3. 3 g of the dried mesoporous γ-Al2O3 was placed in a vacuum system for 2 h (vacuum degree of 0.08 MPa), and then 30 mL of 0.0028 mol / L Pd(NO3)2 aqueous solution was added dropwise to the mesoporous γ-Al2O3 to completely impregnate it. After centrifugation, washing, drying, and calcination, a 0.28 Pd / A(V) sample with an actual Pd loading of 0.28 wt.% was obtained (Pd content was determined by ICP method).

[0061] IV. The 0.28 Pd / A(V) sample and the graded pore size ZSM-12 molecular sieve sample Z12-S(36, 72) were mixed in a 1:1 mass ratio, pressed into tablets, ground, and sieved to 20-40 mesh to prepare a bifunctional catalyst 0.14Pd / A(V)-Z12-S(36, 72), which is spatially separated from the acidic sites of the ZSM-12 molecular sieve. This catalyst is denoted as catalyst A. The pore structure and acidity data of the molecular sieve are shown in Table 1.

[0062] The composition of the gaseous and liquid phase products of the hexadecane hydroisomerization reaction was analyzed by gas chromatography, and the results are shown in Table 2. The conversion rate of hexadecane was 94.6%, and the selectivity and yield of isohexadecane were 88.6% and 83.8%, respectively, of which the selectivity of multi-branched isohexadecane was 70.6%.

[0063] Using catalyst A, the yields of isohexadecane at different conversion rates were obtained by changing the reaction temperature. The results are as follows: Figure 20 As shown.

[0064] Example 2: This example differs from Example 1 in that the reaction temperature of the fixed-bed reactor is 290°C. o C. The composition of the products from the hydrogenation isomerization of n-hexadecane was analyzed by gas chromatography, and the results are shown in Table 2. The conversion rate of n-hexadecane was 75.7%, and the selectivity and yield of isohexadecane were 95.8% and 72.5%, respectively, of which the selectivity of multi-branched isohexadecane was 62.4%.

[0065] Example 3: This example differs from Example 1 in that, in step two of synthesizing the hierarchical ZSM-12 molecular sieve, an aqueous solution of hexadecyltrimethylammonium bromide was added to the ZSM-12 precursor solution obtained in the first step of hydrothermal treatment for 36 hours to form a mixed gel, which was then precipitated at 160°C. o Hydrothermal crystallization at C for 60 h yielded hydrogen-type graded porous ZSM-12 molecular sieve sample Z12-S(36,60), which was obtained after washing, drying, calcination, and ion exchange.

[0066] The bifunctional catalyst was prepared by mixing a 0.28 Pd / A(V) sample prepared by vacuum-assisted impregnation with a graded pore size Z12-S(36,60) molecular sieve at a mass ratio of 1:1 to prepare a 0.14 Pd / A(V)-Z12-S(36,60) bifunctional catalyst, denoted as catalyst B. The pore structure and acidity data of the molecular sieve are shown in Table 1.

[0067] Control the reaction temperature to 300°C o C. The composition of the products from the hydrogenation isomerization of n-hexadecane was analyzed by gas chromatography, and the results are shown in Table 2. The conversion rate of n-hexadecane was 86.4%, and the selectivity and yield of isohexadecane were 83.5% and 71.2%, respectively, of which the selectivity of multi-branched isohexadecane was 55.7%.

[0068] Using catalyst B, the yields of isohexadecane at different conversion rates were obtained by changing the reaction temperature. The results are as follows: Figure 21 As shown.

[0069] Example 4: This example differs from Example 3 in that the reaction temperature in the fixed-bed reactor is 310°C. oC. The composition of the products from the hydrogenation isomerization of n-hexadecane was analyzed by gas chromatography, and the results are shown in Table 2. The conversion rate of n-hexadecane was 95.6%, and the selectivity and yield of isohexadecane were 82.2% and 78.6%, respectively, of which the selectivity of multi-branched isohexadecane was 65.6%.

[0070] Example 5: This example differs from Example 1 in that, in step two of synthesizing the graded porous ZSM-12 molecular sieve, an aqueous solution of hexadecyltrimethylammonium bromide was added to the mixed gel obtained in step one after hydrothermal treatment for 30 hours, and then... o Hydrothermal crystallization at C for 60 h synthesized graded porous molecular sieve Z12-S(30,60). The bifunctional catalyst was prepared by mixing a 0.28 Pd / A(V) sample with a graded porous ZSM-12 molecular sieve sample at a mass ratio of 1:1, resulting in a 0.14 Pd / A(V)-Z12-S(30,60) bifunctional catalyst, denoted as catalyst C. The pore structure and acidity data of the molecular sieve are shown in Table 1.

[0071] Control the reaction temperature to 300°C o C. The composition of the products from the hydrogenation isomerization of n-hexadecane was analyzed by gas chromatography, and the results are shown in Table 2. The conversion rate of n-hexadecane was 41.1%, and the selectivity and yield of isohexadecane were 86.3% and 35.5%, respectively, of which the selectivity of multi-branched isohexadecane was 44.3%.

[0072] Using catalyst C, the yields of isohexadecane at different conversion rates were obtained by changing the reaction temperature. The results are as follows: Figure 21 As shown.

[0073] Example 6: This example differs from Example 5 in that the reaction temperature of the fixed-bed reactor is 320°C. o C. The composition of the products of the hexadecane hydroisomerization reaction was analyzed by gas chromatography, and the results are shown in Table 2. The conversion rate of hexadecane was 91.0%, and the selectivity and yield of isohexadecane were 78.1% and 71.1%, respectively, of which the selectivity of multi-branched isohexadecane was 56.3%.

[0074] Comparative Example 1: This comparative example differs from Example 1 in that it uses the following method to synthesize microporous ZSM-12 molecular sieve:

[0075] 0.48 g of NaAlO2, 71.21 g of silica sol (32.13% SiO2), 1.03 g of NaOH, and 10 g of TEABr were added to the initial gel, and then the mixture was heated to 160 °C. oMicroporous ZSM-12 molecular sieves were synthesized by hydrothermal crystallization at C for 72 h. The bifunctional catalyst was prepared by mixing 0.28 Pd / A(V) with microporous ZSM-12 molecular sieve powder at a mass ratio of 1:1, resulting in a 0.14 Pd / A(V)-Z12 bifunctional catalyst, denoted as catalyst D. The pore structure and acidity data of the molecular sieves are shown in Table 1.

[0076] The reaction temperature of the fixed-bed reactor was controlled at 310°C. o C. The composition of the products from the hydrogenation isomerization of n-hexadecane was analyzed by gas chromatography, and the results are shown in Table 2. The conversion rate of n-hexadecane was 96.1%, and the selectivity and yield of isohexadecane were 76.1% and 73.1%, respectively, of which the selectivity of multi-branched isohexadecane was 61.3%.

[0077] Using catalyst D, the yields of isohexadecane at different conversion rates were obtained by changing the reaction temperature. The results are as follows: Figure 20 As shown.

[0078] Comparative Example 2: This comparative example differs from Comparative Example 1 in that the reaction temperature of the fixed-bed reactor is controlled at 300°C. o C. The composition of the products from the hydrogenation isomerization of n-hexadecane was analyzed by gas chromatography, and the results are shown in Table 2. The conversion rate of n-hexadecane was 82.2%, and the selectivity and yield of isohexadecane were 83.7% and 68.8%, respectively, of which the selectivity of multi-branched isohexadecane was 54.1%.

[0079] Table 1. Pore structure characteristics and acidity of ZSM-12 molecular sieves of different pore sizes.

[0080]

[0081] Table 2 shows the reaction results of hexadecane hydroisomerization to isohexadecane for each example using different catalysts.

[0082]

[0083] As can be seen from the results in Table 2, Example 1 showed the best overall effect in preparing isohexadecane. Not only was the yield of isohexadecane the highest, but the selectivity of multi-branched isohexadecane was also the greatest, which is more conducive to improving the low-temperature fluidity of biodiesel.

Claims

1. A method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve, characterized in that... The method for preparing multi-branched isohexadecane is implemented according to the following steps: A bifunctional catalyst, spatially separated from the acidic sites of the Pd metal sites in a hierarchical ZSM-12 molecular sieve, was packed into the isothermal zone of a fixed-bed reactor and subjected to heating at 350–500 °C under a H2 atmosphere. o After C activation treatment and cooling to the reaction temperature, n-hexadecane is continuously injected into a fixed-bed reactor via a feed pump to carry out the catalytic reaction, with the reaction temperature controlled at 270~340℃. o C, the reaction pressure is 1.5~3.5 MPa, and the mass hourly space velocity of n-hexadecane is controlled at 2.5~5 h⁻¹. -1 The volume ratio of H2 to n-hexadecane is (300~700):1, yielding multi-branched isohexadecane; The bifunctional catalyst in which the Pd metal sites and the acidic sites of the hierarchical ZSM-12 molecular sieve are spatially separated is prepared by mixing xPd / A(V) obtained by supporting Pd on mesoporous γ-Al2O3 using a vacuum-assisted impregnation method with the hierarchical ZSM-12 molecular sieve at a mass ratio of 1:

1.

2. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 1, characterized in that... Hexadecane was continuously injected into a fixed-bed reactor for catalytic reaction, with the reaction temperature controlled at 290–320 °C. o C, the reaction pressure is 1.5~3.0 MPa, and the mass hourly space velocity of n-hexadecane is controlled at 3~4 h⁻¹. -1 The volume ratio of H2 to n-hexadecane is (400~600):

1.

3. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 1, characterized in that... In xPd / A(V), x represents the carrying capacity of Pd, x = 0.05~0.3 wt.%.

4. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 1, characterized in that... The preparation method of a bifunctional catalyst with spatially separated Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve is as follows:

1. Dissolve 0.2–1.4 g NaOH, 0.1–0.8 g sodium aluminate, 60–90 g silica sol, and 5–15 g tetraethylammonium bromide in 30–50 g deionized water, stir to obtain an initial gel, and then... (The sentence is incomplete and requires more context to translate accurately.) o A hydrothermal reaction was carried out at C to obtain a ZSM-12 molecular sieve precursor solution.

2. Dissolve 10-15 g of hexadecyltrimethylammonium bromide in 30-50 g of water, add it to the ZSM-12 molecular sieve precursor solution, stir to obtain a mixed gel, and then heat at 150-180 °C. o The solid product was obtained by crystallization reaction under C and calcination. The solid product was then subjected to ion exchange with 0.2~1 mol / L NH4NO3 solution to obtain ammonium type ZSM-12 molecular sieve. After calcination, hydrogen type graded porous ZSM-12 molecular sieve was obtained.

3. Place the pseudo-boehmite in a muffle furnace and heat it to 500-800°C in an air atmosphere. o C, after calcination, mesoporous γ-Al2O3 is obtained. The mesoporous γ-Al2O3 is placed in a vacuum system for 1~3 h, and then completely wetted with Pd(NO3)2 aqueous solution. After calcination, xPd / A(V) is obtained. IV. xPd / A(V) was mixed with hydrogen-type hierarchical porous ZSM-12 molecular sieve at a mass ratio of 1:1 to prepare a bifunctional catalyst in which the Pd metal sites and the acidic sites of the hierarchical porous ZSM-12 molecular sieve are spatially separated.

5. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 4, characterized in that... The hydrothermal reaction time in step one is 12~60 h.

6. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 4, characterized in that... The crystallization reaction time in step two is 24~84 h.

7. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 4, characterized in that... The ion exchange time in step two is 1 to 5 hours.

8. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 4, characterized in that... In step three, the vacuum level of the vacuum system is 0.08~0.09 MPa.

9. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 4, characterized in that... In step three, the temperature is raised to 500-800°C in air. o C, after calcination for 4-8 h, yields mesoporous γ-Al2O3.

10. The method for preparing multi-branched isohexadecane using a bifunctional catalyst with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve according to claim 4, characterized in that... The bifunctional catalyst prepared in step four, with spatial separation of Pd metal sites and acidic sites of hierarchical ZSM-12 molecular sieve, has a particle size of 1.52~4.46 nm.

Images