Zsm-48 molecular sieve, method of making and use thereof

Abstract

The application relates to the field of molecular sieves, and discloses a ZSM-48 molecular sieve and a preparation method and application thereof, the method comprising the following steps: concentrating ZSM-48 molecular sieve mother liquor in the presence of an acid solution to obtain concentrated mother liquor; performing first crystallization on a first mixture containing the concentrated mother liquor; after solid-liquid separation, obtaining a first solid product and a first mother liquor; performing second crystallization on a second mixture containing seeds; part of the first solid product is used to provide seeds; performing solid-liquid separation on a mixture obtained through the second crystallization to obtain a second solid product and a second mother liquor; wherein the first mother liquor and the second mother liquor are returned to concentration; and performing washing, drying and calcination on the remaining first solid product and the second solid product to obtain the ZSM-48 molecular sieve. The ZSM-48 molecular sieve obtained through the method has high relative crystallinity, the method is simple to operate, waste liquid discharge is small, post-treatment difficulty is low, production efficiency is high, and the method is beneficial to industrialized continuous production.

Description

Technical Field

[0001] This invention relates to the field of molecular sieves, specifically to a ZSM-48 molecular sieve, its preparation method, and its applications. Background Technology

[0002] ZSM-48 molecular sieve is a novel high-silica molecular sieve developed in the 1980s. It has a one-dimensional ten-membered ring channel structure and is characterized by a high silicon-to-aluminum molar ratio and tubular linear channels, which can accommodate organic molecular reactions with kinetic radii smaller than those of benzene. Current research on the preparation methods of ZSM-48 mainly focuses on the screening and optimization of different template agents. However, the mother liquor from molecular sieve synthesis is difficult to fully recover and reuse, and the discharge of waste liquid may pose a potential environmental pollution hazard.

[0003] Existing research on the recovery and treatment of molecular sieve mother liquor focuses on two main methods. One method involves treating the mother liquor to recover silicon sources, aluminum sources, and template agents. For example, CN108128789A discloses a method combining molecular sieve production and alumina production processes. By removing silicon from the solution, the molecular sieve mother liquor undergoes desilication treatment followed by clinker leaching. The resulting sodium aluminate solution is used as a raw material for molecular sieve synthesis. However, this method does not effectively utilize the silicon source in the mother liquor. CN104030499A discloses a comprehensive treatment method for special molecular sieve synthesis mother liquor, which contains silicate and quaternary ammonium base template agents. After removing and recovering the silicon source, the mother liquor is then fed into a bipolar membrane electrodialysis system to recover quaternary ammonium base template agents such as TPAOH. CN105314757A discloses a method that uses an inorganic polymer composite flocculant to remove Al, Si, P and other ions from SAPO molecular sieve crystallization mother liquor wastewater containing high ion concentration. After deionization, the pH value of the wastewater is adjusted by adding alkali to make the organic amines oleic and freed from the wastewater. The organic amines are then separated by an oil-water separator and reused in the synthesis of SAPO molecular sieves.

[0004] Another approach is to reuse the entire molecular sieve mother liquor. For example, CN108569706A discloses a method where, after molecular sieve crystallization, it is directly connected to a condenser for vacuum distillation. The concentrated product is then added directly to the next crystallization system for recycling after solid-liquid separation. CN105668587A discloses adding a large amount of concentrated SAPO-34 molecular sieve synthesis mother liquor to the semi-crystallized crystallization liquid to prepare a gel mixture for synthesizing SAPO-34 molecular sieve for the next synthesis, thus recycling the molecular sieve mother liquor. CN103979572A discloses mixing and modifying molecular sieve with mother liquor. After solid-liquid separation, the content of SiO2, Al2O3, Na2O, and template agent in the mother liquor is analyzed. Silicon source, aluminum source, alkali source, template agent, and water are added in proportion to prepare a new molecular sieve sol mixture. The new molecular sieve sol mixture is then placed in a hydrothermal reactor and crystallized to obtain a new molecular sieve. CN106044793A discloses a method for flocculating, separating, and drying the mother liquor after crystallizing ZSM-5 molecular sieves, and then using the mother liquor flocculent as a raw material for the synthesis of ZSM-5 molecular sieves. However, the above method may require analysis of the composition of each phase in the mother liquor for raw material preparation when reusing it, or it may require the addition of a large amount of water during the crystallization process, which will further increase the difficulty of mother liquor treatment during the recycling process. Therefore, it is not suitable for industrial continuous production processes.

[0005] In conclusion, there is currently a lack of effective methods for the efficient and clean production of ZSM-48 molecular sieves. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of poor relative crystallinity of ZSM-48 molecular sieves, large wastewater discharge during production, low production efficiency, and high cost in existing technologies. This invention provides a ZSM-48 molecular sieve, its preparation method, and its applications. The preparation method of this ZSM-48 molecular sieve can completely recover and reuse the molecular sieve mother liquor generated during the preparation process. It is simple to operate, has high production efficiency, and is conducive to industrial production. The obtained ZSM-48 molecular sieve has high relative crystallinity and can achieve higher product yields when applied to hydrocarbon hydroisomerization reactions.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing ZSM-48 molecular sieve, comprising the following steps:

[0008] (1) Under acidic conditions, the mother liquor of ZSM-48 molecular sieve was concentrated to obtain concentrated mother liquor;

[0009] (2) Provide a first mixture containing a first silicon source, a first alkali source, a first aluminum source, a first template agent and the concentrated mother liquor, and perform a first crystallization on the first mixture;

[0010] (3) The mixture obtained by the first crystallization in step (2) is subjected to solid-liquid separation to obtain a first solid product and a first mother liquor; wherein the first mother liquor is returned to step (1);

[0011] (4) Provide a second mixture containing a second silicon source, a second alkali source, a second aluminum source, a second template agent, water and seed crystals, and perform a second crystallization on the second mixture;

[0012] A portion of the first solid product is used to provide the seed crystals;

[0013] (5) The mixture obtained by the second crystallization in step (4) is subjected to solid-liquid separation to obtain a second solid product and a second mother liquor; wherein the second mother liquor is returned to step (1);

[0014] (6) The remaining first solid product and the second solid product are washed, dried and calcined to obtain the ZSM-48 molecular sieve.

[0015] The second aspect of the present invention provides a ZSM-48 molecular sieve prepared by the preparation method described in the first aspect above.

[0016] The third aspect of this invention provides the application of the above-mentioned ZSM-48 molecular sieve in the hydroisomerization treatment of hydrocarbon oils.

[0017] Through the above technical solution, the present invention achieves the following beneficial effects:

[0018] The method for preparing ZSM-48 molecular sieve provided by this invention can completely recover and reuse the molecular sieve mother liquor generated during the preparation process, which greatly reduces the discharge of waste liquid and reduces the difficulty of post-treatment. The method is simple to operate, has high production efficiency, and is conducive to continuous industrial production.

[0019] The ZSM-48 molecular sieve prepared by the method provided by this invention has high relative crystallinity, large specific surface area, and high silicon-to-aluminum ratio. When applied to the hydroisomerization reaction of hydrocarbon oils, it can achieve higher product yields. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for preparing ZSM-48 molecular sieve according to one embodiment of the present invention;

[0021] Figure 2 The X-ray diffraction pattern of the ZSM-48 molecular sieve prepared in Example 1 is shown.

[0022] Figure 3 The X-ray diffraction pattern of the ZSM-48 molecular sieve prepared in Comparative Example 1 is shown. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The first aspect of this invention provides a method for preparing ZSM-48 molecular sieve, comprising the following steps:

[0025] (1) Under acidic conditions, the mother liquor of ZSM-48 molecular sieve was concentrated to obtain concentrated mother liquor;

[0026] (2) Provide a first mixture containing a first silicon source, a first alkali source, a first aluminum source, a first template agent and the concentrated mother liquor, and perform a first crystallization on the first mixture;

[0027] (3) The mixture obtained by the first crystallization in step (2) is subjected to solid-liquid separation to obtain a first solid product and a first mother liquor; wherein the first mother liquor is returned to step (1);

[0028] (4) Provide a second mixture containing a second silicon source, a second alkali source, a second aluminum source, a second template agent, water and seed crystals, and perform a second crystallization on the second mixture;

[0029] A portion of the first solid product is used to provide the seed crystals;

[0030] (5) The mixture obtained by the second crystallization in step (4) is subjected to solid-liquid separation to obtain a second solid product and a second mother liquor; wherein the second mother liquor is returned to step (1);

[0031] (6) The remaining first solid product and the second solid product are washed, dried and calcined to obtain the ZSM-48 molecular sieve.

[0032] In this invention, the above-described preparation method can completely recover and reuse the molecular sieve mother liquor generated during the preparation process, reducing the amount of water used, significantly reducing waste liquid discharge, and simplifying post-treatment. Simultaneously, the product of the first crystallization is used as a seed crystal for the second crystallization, greatly improving production efficiency. Compared to ZSM-48 molecular sieves in the prior art, the ZSM-48 molecular sieve prepared using the method provided by this invention has higher relative crystallinity and a higher silicon-to-aluminum ratio, as well as better hydrothermal stability.

[0033] According to the present invention, in order to further improve production efficiency, preferably, the mass percentage of the seed crystal is 20-50 wt%, more preferably 30-40 wt%, based on the mass of the first solid product.

[0034] According to a preferred embodiment of the present invention, the concentration includes: evaporating and concentrating the ZSM-48 molecular sieve mother liquor at 80-99°C under acidic conditions until the volume reduction is 40-60% of the volume of the ZSM-48 molecular sieve mother liquor, preferably 50-60%; by adopting the above preferred embodiment, the concentrated mother liquor has the characteristic of having an appropriate amount of seed crystals, which is further introduced into step (2) to participate in the reaction, which is beneficial to the formation of a high specific surface area molecular sieve.

[0035] In this invention, preferably, the acidic conditions are provided by adding acid or an acidic solution to the ZSM-48 molecular sieve mother liquor to adjust the pH value to 5-8, preferably 6-7.

[0036] In this invention, there is no specific limitation on the type of acid or acidic solution, as long as the pH adjustment effect can be achieved. Preferably, the acid is selected from at least one of hydrochloric acid, nitric acid and sulfuric acid, and the acidic solution is selected from an aqueous solution of at least one of hydrochloric acid, nitric acid, sulfuric acid, ammonium chloride and ammonium nitrate.

[0037] Preferably, the concentration of the acidic solution is 0.01-1 mol / L, and more preferably 0.1-1 mol / L.

[0038] According to a preferred embodiment of the present invention, the source of the ZSM-48 molecular sieve mother liquor includes method one and / or method two.

[0039] Method 1: The preparation method of the ZSM-48 molecular sieve mother liquor includes:

[0040] (1-1) Provide a mixture containing a silicon source, an alkali source, an aluminum source, a template agent, and water;

[0041] (1-2) The mixture is subjected to a crystallization reaction; the conditions for the crystallization reaction include: reacting at 20-50°C for 1-24 h, reacting at 50-80°C for 0.5-36 h, and then reacting at 80-180°C for 0.5-72 h.

[0042] (1-3) The mixture obtained from the crystallization reaction in step (1-2) is subjected to solid-liquid separation to obtain molecular sieve mother liquor;

[0043] Method 2: The ZSM-48 molecular sieve mother liquor is provided by the first mother liquor obtained in step (3) and the second mother liquor obtained in step (5).

[0044] In this invention, those skilled in the art will understand that, during initial preparation, the ZSM-48 molecular sieve mother liquor in step (1) can be provided by the above method one. When the preparation process is running in a cycle, the ZSM-48 molecular sieve mother liquor provided by the above method two can maintain the cyclic operation of the preparation system. During the cyclic preparation process, the molecular sieve mother liquor can also be recycled according to the actual production situation to avoid the discharge of waste liquid.

[0045] According to a preferred embodiment of the present invention, the selection range of the silicon source, alkali source, aluminum source and template agent in Method 1 can be the same as the selection range in the above-described molecular sieve preparation method, which will be described in detail below; preferably, in the process of preparing the ZSM-48 molecular sieve mother liquor in Method 1, the content of each component in the mixture satisfies the following relationship:

[0046] R / SiO2 = 0.01-0.50, more preferably 0.01-0.3;

[0047] H2O / SiO2 = 5-50, more preferably 5-20;

[0048] M + / SiO2 = 0.01-0.50, more preferably 0.01-0.15;

[0049] Al2O3 / SiO2 = 0-0.02; more preferably 0.01-0.017;

[0050] Where R represents the template agent, M + Indicates the alkali source.

[0051] Those skilled in the art will understand that, during the initial preparation, the ZSM-48 molecular sieve mother liquor can be prepared under the same conditions as the first crystallization, by simply replacing the concentrated mother liquor in the first crystallization with water.

[0052] According to a preferred embodiment of the present invention, the conditions for the first crystallization include: crystallization at temperature t1 for 5-24 hours, crystallization at temperature t2 for 0.5-36 hours, and crystallization at temperature t3 for 10-96 hours, wherein 15℃≤t1<50℃, 50℃≤t2<100℃, and 100℃≤t3≤200℃; preferably, crystallization at temperature t1 for 6-15 hours, crystallization at temperature t2 for 5-30 hours, and crystallization at temperature t3 for 20-80 hours, wherein 20℃≤t1≤45℃, 60℃≤t2≤80℃, and 120℃≤t3≤190℃. Using the above preferred embodiment facilitates control of the crystallization reaction progress and temperature. By setting the crystallization reaction process at a low temperature, it helps control grain growth, facilitates full utilization of raw materials, and simultaneously provides a large number of seed crystals for the second crystallization.

[0053] According to a preferred embodiment of the present invention, the first crystallization is carried out under stirring conditions, wherein the stirring rate is preferably 200-800 rpm, and more preferably 300-600 rpm.

[0054] In this invention, the proportions of each raw material in the reactants have a certain influence on the final performance of the molecular sieve. According to a preferred embodiment of this invention, the composition of each component in the first mixture in step (2) according to molar amounts satisfies the following relationship:

[0055] R / SiO2 = 0.01-0.5, preferably 0.01-0.3;

[0056] The ratio of concentrated mother liquor to SiO2 is 5-50, preferably 5-20;

[0057] M + / SiO2 = 0.01-0.5, preferably 0.01-0.15;

[0058] Al2O3 / SiO2 = 0-0.02, preferably 0.01-0.017;

[0059] Wherein, SiO2 refers to SiO2 in the silicon source, R represents the template agent, and M... + The molar amount of the concentrated mother liquor, expressed as pure water, is the mass of the concentrated mother liquor / 18.

[0060] According to a preferred embodiment of the present invention, step (2) of the method does not include the addition of additional water. In the above-described preferred embodiment, it is advantageous to increase the silica-to-alumina ratio of the molecular sieve.

[0061] According to a preferred embodiment of the present invention, compared to the first crystallization, the second crystallization is a rapid crystallization process. Preferably, the conditions for the second crystallization include: a crystallization temperature of 180-200℃, more preferably 180-190℃, a crystallization time of 12-24h, more preferably 15-20h, and a heating rate of not less than 1.5℃ / min, more preferably 2-5℃ / min. Under the combination of the above-mentioned preferred conditions for the first and second crystallization, it is beneficial to further improve the relative crystallinity of the molecular sieve.

[0062] Preferably, the second crystallization is carried out under stirring conditions. The stirring rate is preferably 200-800 rpm, and more preferably 300-600 rpm.

[0063] According to a preferred embodiment of the present invention, the composition of each component in the second mixture in step (4), calculated by molar amount, satisfies the following relationship:

[0064] R / SiO2 = 0.01-0.5, preferably 0.01-0.3;

[0065] H2O / SiO2 = 5-50, preferably 5-20;

[0066] M + / SiO2 = 0.01-0.5, preferably 0.01-0.15;

[0067] Al2O3 / SiO2 = 0-0.02, preferably 0.01-0.017;

[0068] Wherein, SiO2 refers to SiO2 in the silicon source, R represents the template agent, and M... + Indicates the alkali source.

[0069] In this invention, the amount of seed crystals used is relatively large. According to a preferred embodiment of this invention, the mass of the seed crystals added is 20-50% of the mass of the silicon source, preferably 30-50%, where the mass of the silicon source is SiO2. Under these preferred conditions, it is beneficial to form more crystal nuclei and rapidly prepare ZSM-48 molecular sieves with high crystallinity.

[0070] According to a preferred embodiment of the present invention, step (4) of the method does not include the addition of molecular sieve mother liquor.

[0071] In this invention, the selection range of the first silicon source, first alkali source, first aluminum source, first template agent, second silicon source, second alkali source, second aluminum source, and second template agent is relatively wide, and all are conventional choices in the art. The above raw materials are generally mixed into a uniform gel by appropriate means, such as by stirring.

[0072] According to a preferred embodiment of the present invention, the first template agent and the second template agent may be the same or different. Preferably, the first template agent and the second template agent are each independently selected from at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-anetanediamine, hexamethylammonium bromide, hexamethylammonium chloride, and hexamethylammonium hydroxide; more preferably, at least one of 1,6-hexanediamine, hexamethylammonium bromide, hexamethylammonium chloride, and hexamethylammonium hydroxide.

[0073] According to a preferred embodiment of the present invention, the first silicon source and the second silicon source may be the same or different. Preferably, the first silicon source and the second silicon source are each independently selected from at least one of silica sol, silica, fumed silica, water glass and tetraethyl orthosilicate; more preferably, silica sol.

[0074] According to a preferred embodiment of the present invention, the first aluminum source and the second aluminum source may be the same or different. Preferably, the first aluminum source and the second aluminum source are each independently selected from soluble aluminum sources. More preferably, at least one of boehmite, aluminum sulfate, aluminum isopropoxide, sodium aluminate and aluminum nitrate is selected. More preferably, at least one of aluminum sulfate and sodium aluminate is selected.

[0075] According to a preferred embodiment of the present invention, the first alkali source and the second alkali source are each independently selected from at least one of sodium hydroxide, potassium hydroxide and calcium hydroxide, and more preferably at least one of sodium hydroxide and potassium hydroxide.

[0076] According to the present invention, the remaining portion of the first solid product and the second solid product are washed, dried, and calcined to obtain the ZSM-48 molecular sieve. The washing can be performed using conventional methods in the art. Preferably, the washing includes washing for 40-120 minutes in the presence of an alkaline solution or water; preferably, the washing includes washing with an alkaline solution for 30-60 minutes, followed by washing with water for 40-60 minutes; more preferably, the temperature of the alkaline solution is 40-90°C.

[0077] According to a preferred embodiment of the present invention, the alkaline solution is selected from an aqueous solution of at least one of sodium hydroxide, potassium hydroxide and sodium carbonate; preferably, the concentration of the alkaline solution is 0.01-1 mol / L, and more preferably 0.1-1 mol / L.

[0078] To obtain the molecular sieve powder described in this invention, the washed product can be further subjected to solid-liquid separation and drying operations. The methods and conditions for solid-liquid separation and drying are conventional operations in the art. Preferably, the drying conditions include: a drying temperature of 100-160℃, more preferably 120-140℃, and a drying time of 1-10h, more preferably 6-10h.

[0079] According to a preferred embodiment of the present invention, the calcination conditions include: a calcination temperature of 400-600℃, preferably 500-580℃, and a calcination time of 1-10h, preferably 6-8h.

[0080] A second aspect of the present invention provides a ZSM-48 molecular sieve prepared by the above-described preparation method; wherein the molar ratio of silica to alumina in the ZSM-48 molecular sieve is 70-150, preferably 90-130, and the specific surface area is 200-240 cm². 2 / g, preferably 220-240cm 2 / g, with a relative crystallinity of not less than 90%, preferably 100-120%.

[0081] In this invention, the relative crystallinity is calculated by the following method: XRD patterns of the sample to be tested and the standard sample are tested separately, the characteristic peak areas are calculated, and then the relative crystallinity of the sample to be tested is calculated by substituting these values ​​into the following formula.

[0082] Relative crystallinity = S 18-28° (sample to be tested) / S 18-28° (Standard) × 100%;

[0083] Among them, S 18-28° (Sample to be tested) is the area of ​​the characteristic peak of the sample to be tested at 2θ = 18-28°, S 18-28° (Standard) is the area of ​​the characteristic peak of the standard at 2θ = 18-28°.

[0084] In this invention, the specific surface area is tested as follows: the sample is degassed under vacuum at 250℃ and 1.33Pa for 4 hours, with N2 as the adsorbate, and contacted with the adsorbate at 77K until static adsorption equilibrium is reached. The amount of N2 adsorbed by the sample is calculated from the difference between the amount of N2 introduced and the amount remaining in the gas phase after adsorption, and the specific surface area is calculated using the BET formula.

[0085] Currently, the relative crystallinity of ZSM-48 molecular sieves synthesized using existing technologies is relatively poor, generally ranging from 70% to 90%. However, the researchers of this invention have discovered that by employing a specific synthesis method, the relative crystallinity of ZSM-48 molecular sieves can be significantly improved, which is beneficial for their subsequent application in isomer dewaxing catalysts, thereby increasing product yield and selectivity.

[0086] A third aspect of this invention provides the application of the aforementioned ZSM-48 molecular sieve in the hydroisomerization of hydrocarbon oils. The ZSM-48 molecular sieve provided by this invention has a high silica-to-alumina ratio and high relative crystallinity, and when applied to the hydroisomerization reaction of hydrocarbon oils, it can achieve higher product yields.

[0087] The present invention will be described in detail below through embodiments.

[0088] All raw materials used in the following examples are commercially available.

[0089] In the following preparation examples, the samples were characterized by XRD using a Bruker D5005 diffractometer with Cu Kα rays (λ = 0.154 nm), tube voltage 40 kV, tube current 30 mA, scanning range 5°–35°, step size 0.013°, and 1 step per second.

[0090] The composition of the sample was determined using a Rigaku Electric Industries, Ltd. 3271E X-ray fluorescence spectrometer (XRF). The sample was prepared by pellet method, and the measurement conditions were a rhodium target with an end window, a tube voltage of 50 kV, and a tube current of 50 mA.

[0091] The relative crystallinity is calculated as follows: XRD patterns of the sample and standard are measured separately, the characteristic peak areas are calculated, and then the relative crystallinity of the sample is calculated using the following formula.

[0092] Relative crystallinity = S 18-28° (sample to be tested) / S 18-28° (Standard) × 100%;

[0093] Among them, S 18-28° (Sample to be tested) is the area of ​​the characteristic peak of the sample to be tested at 2θ = 18-28°, S 18-28° (Standard) is the area of ​​the characteristic peak of the standard at 2θ = 18-28°.

[0094] Preparation of standard samples

[0095] Aluminum sulfate, hexamethyldiamine chloride (HMOH), sodium hydroxide, and deionized water were mixed in a certain proportion and stirred for 30 minutes. Silica sol was then added. The molar ratio of each substance was n(Al₂O₃):(HMOH):n(Na₂O₃). + The mixture of n(H₂O):n(SiO₂) = 0.01:0.03:0.3:8:1 was transferred to a crystallization vessel and crystallized at room temperature with stirring at 400 rpm for 6 hours; then crystallized at 80℃ for 24 hours, followed by crystallization at 160℃ for 48 hours. After crystallization, the mixture was filtered, and the solid product was dried at 120℃ for 6 hours. The resulting product was defined as a standard. The XRD characteristic peak area of ​​this standard at 2θ = 18-28° was 10⁴, which was used to calculate the relative crystallinity.

[0096] Example 1

[0097] Preparation process as follows Figure 1 As shown.

[0098] (1) Collect the ZSM-48 synthesis mother liquor in a concentration reactor, add NH4Cl until the solution pH is 6.8, heat open to 95°C, and after 18 hours the liquid level drops to 48% of the initial level. Stop heating to obtain the concentrated mother liquor. When preparing the initial solution, use the same conditions as the first crystallization to prepare the ZSM-48 molecular sieve mother liquor, simply replace the concentrated mother liquor in the first crystallization with water.

[0099] (2) Place the concentrated mother liquor obtained in step (1) into the first crystallization kettle, and then add aluminum sulfate, hexamethyldiamine hydroxide (HMBr), and sodium hydroxide into the mixture in a certain proportion. After stirring for 30 minutes, add silica sol. The molar ratio of each substance is n(Al2O3):(HMBr):n(Na) +The molar ratio of n(H₂O):n(SiO₂) was 0.01:0.03:0.3:5:1, and the molar amount of the concentrated mother liquor was calculated as pure water. The mixture was crystallized at room temperature with stirring at 400 rpm for 6 hours; then crystallized at 80℃ for 24 hours, followed by crystallization at 180℃ for 48 hours. After crystallization, the mixture was filtered to obtain the first solid product and the first mother liquor. 30% of the first solid product was used as seed crystals, and the first mother liquor was returned to the concentration reactor for further concentration.

[0100] (3) Sodium aluminate, hexamethyldiamine chloride (HMBr), potassium hydroxide, and deionized water were added to the second crystallization vessel in a certain proportion and mixed. After stirring for 30 minutes, silica sol and seed crystals were added sequentially. The molar ratio of each substance was n(Al2O3):(HMBr):n(Na) + The ratio of n(H2O):n(SiO2) = 0.0125:0.03:0.3:15:1 was used. The amount of silica sol used was such that the mass of the seed crystal was 30% of the mass of SiO2 in the silica sol. The mixture was stirred for 30 minutes, and then heated to 180°C within 1 hour. After crystallization for 18 hours, the mixture was cooled and filtered to obtain the second solid product and the second mother liquor. The second mother liquor was returned to the concentration reactor for further concentration.

[0101] (4) The remaining 70% of the first solid product from step (2) and the second solid product obtained in step (3) were placed on a plate and frame apparatus, then washed with 0.5M NaOH aqueous solution at 80℃ for 30 min, and then washed with deionized water for 1 h. The product was dried at 120℃ for 4 h and calcined at 560℃ for 6 h, and named CP-1. The XRF analysis results, specific surface area and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1, and the XRD pattern is shown in the figure. Figure 2 As shown.

[0102] Example 2

[0103] Preparation process as follows Figure 1 As shown.

[0104] (1) Collect the ZSM-48 synthesis mother liquor in a concentration reactor, add NH4Cl until the solution pH is 6.8, heat open to 95°C, and after 18 hours the liquid level drops to 48% of the initial level. Stop heating to obtain the concentrated mother liquor. When preparing the initial solution, use the same conditions as the first crystallization to prepare the ZSM-48 molecular sieve mother liquor, simply replace the concentrated mother liquor in the first crystallization with water.

[0105] (2) Place the concentrated mother liquor obtained in step (1) into the first crystallization kettle, and then add sodium aluminate, hexamethyldiamine hydroxide (HMBr), and sodium hydroxide into the mixture in a certain proportion. After stirring for 30 minutes, add silica sol. The molar ratio of each substance is n(Al2O3):(HMBr):n(Na) + The molar ratio of n(H₂O):n(SiO₂) was 0.01:0.03:0.3:10:1, and the molar amount of the concentrated mother liquor was calculated as pure water. The mixture was crystallized at room temperature with stirring at 400 rpm for 6 hours; then crystallized at 80℃ for 24 hours, followed by crystallization at 180℃ for 48 hours. After crystallization, the mixture was filtered to obtain the first solid product and the first mother liquor. 30% of the first solid product was used as seed crystals; the first mother liquor was returned to the concentration reactor for further concentration.

[0106] (3) Sodium aluminate, hexamethyldiamine chloride (HMBr), potassium hydroxide, and deionized water are mixed in a certain proportion and stirred for 30 minutes. Then, silica sol and seed crystals are added sequentially. The molar ratio of each substance is n(Al2O3):(HMBr):n(Na) + The ratio of n(H2O):n(SiO2) = 0.0125:0.03:0.3:20:1 was used. The amount of silica sol used was such that the mass of the seed crystal was 30% of the mass of SiO2 in the silica sol. The mixture was stirred for 30 minutes, and then heated to 190°C within 1 hour. After crystallization for 12 hours, the mixture was cooled and filtered to obtain the second solid product and the second mother liquor. The second mother liquor was returned to the concentration reactor for further concentration.

[0107] (4) The remaining 70% of the first solid product from step (2) and the second solid product obtained in step (3) were placed on a plate and frame apparatus, then washed with 0.5M NaOH aqueous solution at 60℃ for 60 min, and then washed with deionized water for 1 h. The product was dried at 120℃ for 4 h and calcined at 560℃ for 6 h and named CP-2. The XRF analysis results, specific surface area and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1.

[0108] Example 3

[0109] Preparation process as follows Figure 1 As shown.

[0110] (1) Collect the ZSM-48 synthesis mother liquor in a concentration reactor, add NH4Cl until the solution pH is 6.8, heat open to 95°C, and after 20 hours the liquid level drops to 42% of the initial liquid level. Stop heating to obtain the concentrated mother liquor. When preparing the initial solution, use the same conditions as the first crystallization to prepare the ZSM-48 molecular sieve mother liquor, and simply replace the concentrated mother liquor in the first crystallization with water.

[0111] (2) Place the concentrated mother liquor obtained in step (1) into the first crystallization kettle, and then add aluminum sulfate, hexamethyldiamine hydroxide (HMBr), and sodium hydroxide into the mixture in a certain proportion. After stirring for 30 minutes, add silica sol. The molar ratio of each substance is n(Al2O3):(HMBr):n(Na) + The molar ratio of n(H₂O):n(SiO₂) was 0.01:0.03:0.3:5:1, and the molar amount of the concentrated mother liquor was calculated as pure water. The mixture was crystallized at room temperature with stirring at 400 rpm for 6 hours; then crystallized at 80℃ for 24 hours, followed by crystallization at 180℃ for 48 hours. After crystallization, the mixture was filtered to obtain the first solid product and the first mother liquor. 35% of the first solid product was used as seed crystals, and the first mother liquor was returned to the concentration reactor for further concentration.

[0112] (3) Sodium aluminate, hexamethyldiamine chloride (HMBr), potassium hydroxide, and deionized water were added to the second crystallization vessel in a certain proportion and mixed. After stirring for 30 minutes, silica sol and seed crystals were added sequentially. The molar ratio of each substance was n(Al2O3):(HMBr):n(Na) + The ratio of 0.0125:0.03:0.3:15:1 for n(H2O):n(SiO2) is 0.0125:0.03:0.3:15:1. The amount of silica sol used is such that the mass of the seed crystal is 35% of the mass of SiO2 in the silica sol. Stirring is continued for 30 minutes, and then the temperature is raised to 190℃ within 1 hour. After crystallization for 20 hours, the temperature is lowered and filtered to obtain the second solid product and the second mother liquor. The second mother liquor is returned to the concentration reactor for further concentration.

[0113] (4) The remaining 70% of the first solid product from step (2) and the second solid product obtained in step (3) were placed on a plate and frame apparatus, then washed with 0.5M NaOH aqueous solution at 80℃ for 30 min, and then washed with deionized water for 1 h. The product was dried at 120℃ for 4 h and calcined at 560℃ for 6 h and named CP-3. The XRF analysis results, specific surface area and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1.

[0114] Example 4

[0115] The method of Example 1 was followed, except that the amount of silica sol used was such that the mass of the seed crystal was 50% of the mass of SiO2 in the silica sol, and the product was named CP-4. The XRF analysis results, specific surface area, and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1.

[0116] Example 5

[0117] The method of Example 1 was followed, except that the amount of silica sol used was such that the mass of the seed crystal was 40% of the mass of SiO2 in the silica sol, and the product was named CP-5. The XRF analysis results, specific surface area, and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1.

[0118] Example 6

[0119] The method of Example 1 was followed, except that the amount of silica sol used was such that the mass of the seed crystal was 15% of the mass of SiO2 in the silica sol, and the product was named CP-6. The XRF analysis results, specific surface area, and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1.

[0120] Example 7

[0121] The method of Example 1 was followed, except that the conditions for the first crystallization were: the reaction mixture was heated to 180°C within 2 hours and crystallized for 48 hours; the conditions for the second crystallization were: the reaction mixture was heated to 180°C within 1 hour and crystallized for 20 hours, and the product was named CP-7. The XRF analysis results, specific surface area, and relative crystallinity data of the obtained ZSM-48 molecular sieve are shown in Table 1.

[0122] Example 8

[0123] The method of Example 1 was followed, except that in step (1), the pH value was adjusted to 4, the concentrated liquid level was reduced to 30% of the initial liquid level, heating was stopped, and a concentrated mother liquor was obtained. The product was named CP-8. The XRF analysis results, specific surface area, and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1.

[0124] Comparative Example 1

[0125] Aluminum sulfate, hexamethyldiamine hydroxide (HMBr), potassium hydroxide, and deionized water were mixed in a certain proportion and stirred for 30 minutes. Silica sol was then added. The molar ratio of each substance was n(Al₂O₃):(HMBr):n(Na₂O₃). + The mixture of n(H2O):n(SiO2) = 0.01:0.03:0.3:5:1 was transferred to a crystallization vessel and crystallized at 80℃ for 24 h, followed by crystallization at 180℃ for 48 h. After crystallization, the mixture was filtered, and the product was dried at 120℃ for 6 h. The sample was calcined at 600℃ for 4 h and identified as ZSM-48 molecular sieve, named DZ-1. The XRF analysis results, specific surface area, and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1. The XRD pattern is shown in the figure. Figure 3 As shown.

[0126] It can be seen that the relative crystallinity of ZSM-48 molecular sieves obtained by conventional preparation methods decreases after calcination.

[0127] Comparative Example 2 did not undergo mother liquor concentration.

[0128] (1) Place the ZSM-48 molecular sieve mother liquor into the first crystallization kettle and weigh it as the weight of H2O. Then add aluminum sulfate, hexamethyldiamine hydroxide (HMBr), and sodium hydroxide into the mixture in a certain proportion. After stirring for 30 minutes, add silica sol. The molar ratio of each substance is n(Al2O3):(HMBr):n(Na) + The ratio of H₂O to SiO₂ was 0.01:0.03:0.3:5:1. The mixture was crystallized at room temperature with stirring at 400 rpm for 6 hours; then at 80°C for 24 hours, followed by crystallization at 180°C for 48 hours. After crystallization, the mixture was filtered to obtain the first solid product and the first mother liquor. 30% of the first solid product was used as seed crystals, and the first mother liquor was recycled as ZSM-48 molecular sieve mother liquor after weighing.

[0129] (2) Sodium aluminate, hexamethyldiamine chloride (HMBr), potassium hydroxide, and deionized water were added to the second crystallization vessel in a certain proportion and mixed. After stirring for 30 minutes, silica sol and seed crystals were added sequentially. The molar ratio of each substance was n(Al2O3):(HMBr):n(Na) + ):n(H2O):n(SiO2)=0.0125:0.03:0.3:15:1, the amount of silica sol used is such that the mass of the seed crystal is 30% of the mass of SiO2 in the silica sol. Stir for 30 min, then heat to 180℃ within 1 h, crystallize for 18 h, cool down and filter to obtain the second solid product and the second mother liquor. The second mother liquor is weighed and returned to step (1) as the ZSM-48 molecular sieve mother liquor.

[0130] (3) The remaining 70% of the first solid product from step (1) and the second solid product obtained in step (2) were placed on a plate and frame apparatus, then washed with 0.5M NaOH aqueous solution at 60℃ for 60 min, and then washed with deionized water for 1 h. The product was dried at 120℃ for 4 h and calcined at 560℃ for 6 h and named DZ-2. The XRF analysis results, specific surface area and relative crystallinity data of the prepared ZSM-48 molecular sieve are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] Test case

[0135] 100g of the molecular sieves from Examples 1-8 and Comparative Examples 1-2 were mixed with 100g of alumina, extruded, dried, and calcined to obtain a carrier. The mass fraction of molecular sieves in the carrier was calculated to be 50%.

[0136] One gram of dichlorotetraammineplatinum (containing 57.3% Pt by mass) was poured into 100 grams of deionized water and stirred until homogeneous. One hundred grams of support was added to the above solution and impregnated at room temperature for 4 hours. Subsequently, the catalyst precursor was dried at 120°C for 4 hours. It was then calcined under an airflow at 450°C for 4 hours. The semi-finished catalyst was then reduced again in a hydrogen atmosphere at 400°C for 4 hours to obtain the final catalyst. The catalysts in Test Examples 1-8 were named IC-1 to IC-8, respectively, and the catalysts obtained in Comparative Test Examples 1-2 were named DIC-1 and DIC-2, respectively.

[0137] The catalysts were evaluated using the following evaluation methods:

[0138] 50g of catalyst was loaded into a high-pressure hydrocracking reactor. Hydrocracking tail oil feedstock was injected into the reactor from top to bottom for reaction. The reaction conditions are shown in Table 2, and the analytical data of the hydrocracking tail oil feedstock are shown in Table 3. After the reaction, the total liquid product was collected, and the liquid yield was calculated. The liquid product was then distilled to remove light components below 420°C, and the components above 420°C were collected for analysis and the product yield was calculated. The results are shown in Table 4.

[0139] Table 2 Reaction conditions

[0140] Reaction conditions numerical values Pressure, MPa 12 <![CDATA[Air speed, h -1 > 1 Reaction temperature, °C 330 Hydrogen-to-oil ratio, v / v 500

[0141] Table 3 Properties of Hydrocracking Tail Oil

[0142] Analysis Project Analyze data Analytical methods <![CDATA[Density at 20°C / (kg / m 3 )]]> 838.9 SH / T 0604-2000 <![CDATA[Kinematic viscosity / (mm 2 ·s -1 )]]> GB / T 265-1988 40℃ 16.4 100℃ 3.8 Pour point / ℃ +40 SH / T 0771-2005 Nitrogen mass fraction (μg / g) 1.2 NB / SH / T 0704-2010 Sulfur mass fraction (μg / g) 2.1 SH / T 0842-2010 Distillation range / ℃ ASTM D-1160 IBP 411 10％ 434 50％ 467 90％ 510 FBP 544

[0143] Table 4 Evaluation results at 330℃

[0144]

[0145]

[0146] As shown in Table 1, the preparation method of this invention can completely recover and reuse the molecular sieve mother liquor generated during the preparation process. It is simple to operate, has high production efficiency, and yields ZSM-48 molecular sieves with high crystallinity. Furthermore, the prepared hydroisomerization catalyst can achieve even higher product yields in hydrocarbon oil hydroisomerization reactions.

[0147] Examples 1 and 6 show that insufficient seed crystal addition may reduce catalyst activity, hindering product yield improvement. Examples 1 and 7 show that a three-stage crystallization process in the first crystallization stage, combined with a rapid crystallization stage in the second stage, can further improve the relative crystallinity of ZSM-48 molecular sieve. The resulting catalyst achieves higher product yield in the hydrocarbon oil hydroisomerization reaction.

[0148] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing ZSM-48 molecular sieve, comprising the following steps: (1) concentrating a ZSM-48 molecular sieve mother liquor under acidic conditions to obtain a concentrated mother liquor; (2) providing a first mixture containing a first silicon source, a first alkali source, a first aluminum source, a first template agent and the concentrated mother liquor, and subjecting the first mixture to a first crystallization; the first crystallization is performed under the following conditions: crystallization at t1 for 5-24 h, crystallization at t2 for 0.5-36 h, and crystallization at t3 for 10-96 h, 15 ℃≤t1<50 ℃, 50 ℃≤t2<100 ℃, and 100 ℃≤t3≤200 ℃; (3) subjecting the mixture obtained from the first crystallization in step (2) to solid-liquid separation to obtain a first solid product and a first mother liquor; wherein the first mother liquor is returned to step (1); (4) providing a second mixture containing a second silicon source, a second alkali source, a second aluminum source, a second template agent, water and seeds, and subjecting the second mixture to a second crystallization; wherein part of the first solid product is used to provide the seeds; the mass of the seeds is 20-50% of the mass of the second silicon source, and the mass of the second silicon source is calculated based on SiO2; (5) subjecting the mixture obtained from the second crystallization in step (4) to solid-liquid separation to obtain a second solid product and a second mother liquor; wherein the second mother liquor is returned to step (1); (6) washing, drying and calcining the remaining part of the first solid product and the second solid product to obtain the ZSM-48 molecular sieve. The mass of the seeds accounts for 20-50 wt% of the mass of the first solid product. The concentration comprises: evaporating and concentrating the ZSM-48 molecular sieve mother liquor at 80-99 ℃ under acidic conditions until the volume reduction is 40-60% of the volume of the ZSM-48 molecular sieve mother liquor. The acidic conditions are provided by adding an acid or an acidic solution to the ZSM-48 molecular sieve mother liquor to adjust the pH value to 5-7. The acidic conditions are provided by adding an acid or an acidic solution to the ZSM-48 molecular sieve mother liquor to adjust the pH value to 6-7. The acidic solution is selected from an aqueous solution of at least one of hydrochloric acid, nitric acid, sulfuric acid, ammonium chloride and ammonium nitrate. The source of the ZSM-48 molecular sieve mother liquor comprises mode one and / or mode two, mode one: the method for preparing the ZSM-48 molecular sieve mother liquor comprises: (1-1) providing a mixture containing a silicon source, an alkali source, an aluminum source, a template agent and water; (1-2) subjecting the mixture to a crystallization reaction; the crystallization reaction is performed under the following conditions: reaction at 20-50 ℃ for 1-24 h, reaction at 50-80 ℃ for 0.5-36 h, and then reaction at 80-180 ℃ for 0.5-72 h; (1-3) subjecting the mixture obtained from the crystallization reaction in step (1-2) to solid-liquid separation to obtain a molecular sieve mother liquor; mode two: the ZSM-48 molecular sieve mother liquor is provided by the first mother liquor obtained from step (3) and the second mother liquor obtained from step (5). ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The production method according to claim 1, wherein ​ 3. The production method according to claim 1 or 2, wherein ​ 4. The production method according to claim 1 or 2, wherein ​ 5. The production method according to claim 4, wherein ​ 6. The production method according to claim 4, wherein ​ 7. The production method according to claim 1 or 2, wherein ​ ​ ​ ​ ​ ​ 8. The production method according to claim 1, wherein The first crystallization conditions include: sequentially crystallizing at t1 for 6-15 h, at t2 for 5-30 h, and at t3 for 20-80 h, 20℃≤t1≤45℃, 60℃≤t2≤80℃, and 120℃≤t3≤190℃.

9. The production method according to claim 1, wherein The first crystallization is performed under stirring, and the stirring rate is 200-800 rpm.

10. The production method according to claim 1, wherein, The components in the first mixture in step (2) satisfy the following relationships in terms of molar amount: R / SiO2 = 0.01-0.5; Concentrated mother liquor / SiO2 = 5-50; M + / SiO2 =0.01-0.5; Al2O3 / SiO2 = 0-0.02; wherein SiO2 refers to SiO2 in the silicon source, R represents a templating agent, M + represents an alkali source, the molar amount of the concentrated mother liquor, calculated as pure water, is the mass of the concentrated mother liquor / 18.

11. The production method according to claim 10, wherein The components in the first mixture in step (2) satisfy the following relationships in terms of molar amount: R / SiO2 = 0.01-0.3; Concentrated mother liquor / SiO2 = 5-20; M + / SiO2 =0.01-0.15; Al2O3 / SiO2 = 0.01-0.017; wherein SiO2 refers to SiO2 in the silicon source, R represents a templating agent, M + represents an alkali source, the molar amount of the concentrated mother liquor, calculated as pure water, is the mass of the concentrated mother liquor / 18.

12. The method of producing according to claim 1, wherein, Step (2) of the method does not include additional addition of water.

13. The method of producing according to claim 1, wherein, The second crystallization conditions include: a crystallization temperature of 180-200℃, a crystallization time of 12-24 h, and a temperature rising rate of no less than 1.5℃ / min.

14. The production method according to claim 13, wherein The second crystallization conditions include: a crystallization temperature of 180-190℃, a crystallization time of 15-20 h, and a temperature rising rate of 2-5℃ / min.

15. The method of producing according to claim 1, wherein, The second crystallization is performed under stirring.

16. The method of producing according to claim 1, wherein, The components in the second mixture in step (4) satisfy the following relationships in terms of molar amount: R / SiO2 = 0.01-0.5; H2O / SiO2 = 5-50; M + / SiO2 =0.01-0.5; Al2O3 / SiO2 = 0-0.02; wherein SiO2 refers to SiO2 in the silicon source, R represents a templating agent, M + represents an alkali source.

17. The method of making according to claim 16, wherein, The components in the second mixture in step (4) satisfy the following relationships in terms of molar amount: R / SiO2 = 0.01-0.3; H2O / SiO2 = 5-20; M + / SiO2 =0.01-0.15; Al2O3 / SiO2 = 0.01-0.017; wherein SiO2 refers to SiO2 in the silicon source, R represents a templating agent, M + represents an alkali source.

18. The method of producing according to claim 1, wherein, The seed crystal is added in an amount of 30-50% of the mass of the second silicon source, and the mass of the second silicon source is calculated based on SiO2.

19. The method of producing according to claim 1, wherein, Step (4) of the method does not include additional addition of molecular sieve mother liquor.

20. The method of producing according to claim 1, wherein, The first template agent and the second template agent are each independently selected from at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, hexamethonium bromide, hexamethonium chloride, and hexamethonium hydroxide.

21. The method of producing according to claim 1, wherein, The first silicon source and the second silicon source are each independently selected from at least one of silica sol, white carbon black, fumed silica, water glass, and tetraethyl orthosilicate.

22. The method of producing according to claim 1, wherein, The first aluminum source and the second aluminum source are each independently selected from at least one of pseudo-boehmite, aluminum sulfate, aluminum isopropoxide, sodium aluminate, and aluminum nitrate.

23. The method of producing according to claim 1, wherein, The first alkali source and the second alkali source are each independently selected from at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

24. The method of producing according to claim 1, wherein, The washing includes: washing in the presence of an alkaline solution or water for 40-120 min.

25. The method of producing according to claim 1, wherein, The washing includes: first washing with an alkaline solution for 30-60 min, and then washing with water for 40-60 min.

26. The method of manufacturing according to claim 25, wherein, The temperature of the alkaline solution is 40-90℃.

27. The method of making according to claim 25, wherein, The basic solution is selected from at least one of an aqueous solution of sodium hydroxide, potassium hydroxide and sodium carbonate.

28. The method of manufacturing according to claim 25, wherein, The concentration of the basic solution is 0.01-1 mol / L.

29. The method of making according to claim 28, wherein, The concentration of the basic solution is 0.1-1 mol / L.

30. The method of producing according to claim 1, wherein, The drying condition includes that the drying temperature is 100-160 ℃ and the drying time is 1-10 h.

31. The method of manufacturing according to claim 30, wherein, The drying condition includes that the drying temperature is 120-140 ℃ and the drying time is 6-10 h.

32. The method of producing according to claim 1, the conditions of said calcining comprising: The calcination temperature is 400-600 ℃ and the calcination time is 1-10 h.

33. The method of claim 21, wherein the conditions of the calcination comprise: The calcination temperature is 500-580 ℃ and the calcination time is 6-8 h.

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