Preparation method of low-sodium hydrothermal ultra-stable molecular sieve

Abstract

The invention relates to the technical field of molecular sieve materials and preparation thereof, in particular to a preparation method of a low-sodium hydrothermal ultra-stable molecular sieve, which comprises the following steps: 1, mixing a silicon source and a sodium metaaluminate aqueous solution, and aging to obtain a guiding agent; 2, adding a sodium metaaluminate aqueous solution, a guiding agent and aluminum sulfate into a silicon source to obtain aluminosilicate gel; 3, heating and crystallizing to obtain a NaY type molecular sieve; 4, adding the NaY type molecular sieve into a first cation exchanger to obtain a first-exchange molecular sieve slurry, filtering, carrying out belt exchange, and washing to obtain a first-exchange molecular sieve; 5, carrying out primary flash evaporation and primary roasting to obtain a one-time-exchange and one-time-roasting molecular sieve; and 6, adding the one-time-exchange and one-baking molecular sieve into a first cation exchanger, mixing to obtain a two-time-exchange and one-baking molecular sieve slurry, filtering and washing to obtain the two-time-exchange and one-baking molecular sieve. While the sodium content of the Y-type molecular sieve is reduced, the preparation efficiency of the Y-type molecular sieve is improved.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieve materials and preparation thereof, and in particular to a method for preparing a low-sodium hydrothermal ultrastable molecular sieve. Background Art

[0002] Molecular sieve is a kind of aluminosilicate compound with cubic lattice. Molecular sieve has uniform microporous structure and its pore diameter is uniform. These pores can adsorb molecules smaller than their diameter into the inside of the pore cavity, and have preferential adsorption capacity for polar molecules and unsaturated molecules, so it can separate molecules with different polarity, saturation, molecular size and boiling point, that is, it has the function of "screening" molecules, so it is called molecular sieve. In recent years, molecular sieve has been widely used in organic chemical industry, petrochemical industry, coal gas dehydration and waste gas purification due to its advantages of strong selective adsorption capacity, high internal surface area and good thermal stability.

[0003] Molecular sieves can be divided into A-type molecular sieves, X-type molecular sieves, Y-type molecular sieves and mordenite according to their composition and structure. Among them, Y-type molecular sieves refer to artificially synthesized zeolite molecular sieves with a silicon-aluminum ratio (SiO2 / Al2O3) greater than 3.0. The crystal structure of Y-type molecular sieves contains supercage cavities and a three-dimensional twelve-membered ring channel system, which can be used as an active component of an acidic catalyst in catalytic cracking reactions. NaY-type molecular sieves are precursors of acidic Y-type molecular sieves. This type of molecular sieve itself has no acidity and cracking activity and cannot be used directly as an acidic catalyst. The prior art usually modifies NaY-type molecular sieves by removing sodium ions from them and prepares them into Y-type molecular sieves to improve catalytic activity. Due to the complex structure of NaY-type molecular sieves, sodium ions at different positions have different spatial steric hindrances, and sodium ions located in small cages are difficult to be exchanged out. The catalyst prepared with NaY-type molecular sieves as precursors has the problems of low catalytic activity, poor thermal stability and poor structural stability. Summary of the invention

[0004] In view of the technical problems that the catalyst prepared with NaY type molecular sieve as a precursor has low catalytic activity, poor thermal stability and poor structural stability, the present invention provides a method for preparing a low-sodium hydrothermal ultra-stable molecular sieve, wherein the NaY type molecular sieve is prepared by a directing agent method, and the NaY type molecular sieve is sequentially subjected to a tank exchange, a flash evaporation, a roasting, and a secondary tank exchange treatment, thereby reducing the sodium content of the Y type molecular sieve and improving the preparation efficiency of the Y type molecular sieve.

[0005] The present invention provides a method for preparing a low-sodium hydrothermal ultrastable molecular sieve, comprising the following steps: Step 1: Mix the silicon source and the sodium aluminate aqueous solution, stir evenly, and age at room temperature to obtain a directing agent; Step 2: adding sodium aluminate aqueous solution, a directing agent and aluminum sulfate to the silicon source, and mixing them evenly to obtain an aluminosilicate gel; Step 3: introducing water vapor into the aluminosilicate gel to raise the temperature for crystallization, thereby obtaining a NaY type molecular sieve; Step 4: Add NaY molecular sieve to the first cation exchanger and mix evenly, perform a tank exchange, then adjust the pH to 3.5-4.5, heat to 60-70°C and keep constant for 0.5-1.5h to obtain a cross-molecular sieve slurry. During the tank exchange, the amount of the first cation exchanger is 0.08-0.15g / g NaY molecular sieve; filter the cross-molecular sieve slurry to obtain a cross-molecular sieve crude product, and add the first cation exchanger to the cross-molecular sieve crude product for belt exchange, and then wash with water to obtain a cross-molecular sieve. During the belt exchange, the amount of the first cation exchanger is 0-0.25g / g of the cross-molecular sieve crude product, preferably 0.12-0.25g / g of the cross-molecular sieve crude product; wherein the first cation exchanger is ammonium sulfate solution or lanthanum chloride solution, and the molar concentration of the first cation exchanger is 0.9-1.1mol / L; Step 5: sequentially flashing and calcining the cross-linked molecular sieve mixed slurry to obtain a cross-linked and calcined molecular sieve, wherein the temperature of the flashing is 110-150° C., and the temperature of the calcining is 500-800° C.; Step 6: Add the cross-linked and roasted molecular sieve to the first cation exchanger and mix evenly, perform a secondary tank exchange, then heat to 60-70°C and keep constant for 0.5-1.5h to obtain a cross-linked and roasted molecular sieve slurry, filter and wash the cross-linked and roasted molecular sieve slurry to obtain a cross-linked and roasted molecular sieve, wherein the amount of the first cation exchanger is 0.08-0.15g / g of the cross-linked and roasted molecular sieve, the first cation exchanger is ammonium sulfate solution or lanthanum chloride solution, and the molar concentration of the first cation exchanger is 0.9-1.1mol / L.

[0006] In step 4, filtering and washing the molecular sieve slurry can discharge the chloride ions in the molecular sieve slurry along with the sewage, thereby preventing the chloride ions from entering the first flash evaporation and first roasting steps.

[0007] Further, step 4 also includes: adding a molecular sieve to a second cation exchanger and mixing evenly to obtain a molecular sieve mixed slurry, wherein the dosage of the second cation exchanger is 0.01-0.09 g / g molecular sieve, the second cation exchanger is a lanthanum nitrate solution or a yttrium nitrate solution, and the molar concentration of the second cation exchanger is 1.1-1.3 mol / L. The nitrate ions in the second cation exchanger can enter a flash evaporation and a roasting step, and enter the tail gas recovery device in the form of nitrogen oxides.

[0008] Furthermore, the method further comprises step 7: sequentially performing secondary flash evaporation and secondary calcination on the two-crosslinked and one-calcined molecular sieve to obtain the two-crosslinked and two-calcined molecular sieve, wherein the temperature of the secondary flash evaporation is 110-150° C., and the temperature of the secondary calcination is 500-800° C. The secondary flash evaporation and secondary calcination are beneficial to further improve the thermal stability and structural stability of the Y-type molecular sieve.

[0009] Furthermore, the silicon source is an aqueous solution of sodium silicate, in which the mass percentage of SiO2 is 20wt%, and the mass percentage of Na2O is 7wt%; the aqueous solution of sodium aluminate is a high-alkali aqueous solution of sodium aluminate or a low-alkali aqueous solution of sodium aluminate, the caustic ratio of the high-alkali aqueous solution of sodium aluminate is 10.5mol / mol, and the caustic ratio of the low-alkali aqueous solution of sodium aluminate is 2.4mol / mol.

[0010] Furthermore, in step 1, the silicon source and the sodium aluminate aqueous solution are mixed in a molar ratio of 10.67Na2O:1Al2O3:10SiO2:180H2O, and the aging time is 12-24h, preferably 12-14h.

[0011] Furthermore, in step 2, the silicon source, the sodium aluminate aqueous solution, the directing agent and aluminum sulfate are mixed in a molar ratio of 8Na2O: 1Al2O3: 20SiO2: 320H2O. The addition of aluminum sulfate is conducive to the recycling of silicon and improves the yield of NaY molecular sieve.

[0012] Furthermore, in step three, the crystallization temperature is 92-98° C., and the crystallization time is 20-30 h.

[0013] Further, in step 4, the cross-linked molecular sieve slurry is filtered and washed with water to obtain a cross-linked molecular sieve, and the amount of water used is 3-5g / g of the cross-linked molecular sieve. The solid content of the cross-linked molecular sieve slurry after filtration is 440-460g / L. Washing the cross-linked molecular sieve slurry with water and filtering can remove the crystallized residual liquid remaining in the cross-linked molecular sieve slurry.

[0014] Furthermore, in step 6, the cross-linked calcined molecular sieve slurry is filtered and washed with water to obtain the cross-linked calcined molecular sieve, and the amount of water used is 3-5 g / g of the cross-linked calcined molecular sieve. The solid content of the cross-linked calcined molecular sieve slurry after filtration is 460-480 g / L.

[0015] Further, in step 4, sulfuric acid or hydrochloric acid is used to adjust the pH. The concentration of sulfuric acid is preferably 98wt%, and the concentration of hydrochloric acid is preferably 31wt%; in step 4 and step 6, the filtration is performed on a belt filter. By filtering and washing the molecular sieve slurry with a belt filter, the thickness of the filter cake and the amount of water washing can be flexibly controlled, and the fine-grained Y-type molecular sieve in the molecular sieve slurry can be retained as needed to achieve reuse. The belt filter also has the characteristics of low failure rate, simple operation, and high filtration efficiency, which is conducive to improving the preparation efficiency of the Y-type molecular sieve.

[0016] The beneficial effects of the present invention are: The invention provides a method for preparing a low-sodium hydrothermal ultra-stable molecular sieve. Under hydrothermal conditions, a silicon source and a sodium aluminate aqueous solution are used to prepare a directing agent, and aluminum sulfate is introduced in the process of preparing aluminosilicate gel, thereby improving the yield of a NaY type molecular sieve; a first cation exchanger and a second cation exchanger are used to successively perform two cation exchanges on the NaY type molecular sieve, and the reaction conditions of the two cation exchanges are regulated, so that the cations in the first cation exchanger and the cations in the second cation exchanger are used to replace the sodium ions in the NaY type molecular sieve, thereby reducing the sodium content of the Y type molecular sieve and improving the catalytic activity of the Y type molecular sieve; by flashing and calcining the molecular sieve slurry, water molecules combined with cations in the first cation exchanger are removed, and the dehydrated cations can enter the small cage structure of the Y type molecular sieve to replace the sodium ions, thereby further reducing the sodium content of the Y type molecular sieve. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0018] Example 1 A low sodium hydrothermal ultrastable molecular sieve, the preparation method comprises the following steps: Step 1: Mix 9.6g of sodium silicate aqueous solution and 13.8g of high-alkali sodium aluminate aqueous solution, stir evenly, and age at room temperature for 12 hours to obtain a directing agent. In the sodium silicate aqueous solution, the mass percentage of SiO2 is 20wt%, and the mass percentage of Na2O is 7wt%; the caustic ratio of the high-alkali sodium aluminate aqueous solution is 10.5mol / mol.

[0019] Step 2: Weigh 41.3 g of sodium silicate aqueous solution, and add 10.3 g of low-alkali sodium aluminate aqueous solution, 6.9 g of directing agent and 12.8 g of aluminum sulfate thereto in sequence, and mix well to obtain aluminosilicate gel. The caustic ratio of the low-alkali sodium aluminate aqueous solution is 2.4 mol / mol.

[0020] Step 3: Add water vapor to the aluminosilicate gel to raise the temperature to 98°C and then crystallize at a constant temperature for 28 hours. After the crystallization is completed, a crystallization slurry is obtained. The crystallinity of the crystallization slurry is tested. The crystallization slurry with a crystallinity of 90%-93% is a NaY type molecular sieve. The crystallinity test method of the crystallization slurry is as follows: First, the crystallized slurry was introduced into a vacuum Buchner funnel for filtration to form a filter cake with a thickness of about 2 mm. The filter cake was then washed with water until the pH value was 9.0. The filter cake was taken out of the Buchner funnel and dried in an oven at 140°C for 1 hour to obtain a sample to be tested. After the sample to be tested was prepared, an X-ray diffractometer was used to test the crystallinity of the sample to be tested.

[0021] Step 4: Filter and wash the NaY molecular sieve on a belt filter. The filter cake obtained is the washed NaY molecular sieve. The amount of water used in the washing process is 3-5 L / Kg NaY molecular sieve.

[0022] Step 5: Sampling the washed NaY molecular sieve for content analysis, so as to calculate the total weight of the washed NaY molecular sieve according to the volume of the washed NaY molecular sieve, and then calculating the amount of ammonium sulfate solution added according to the total weight of the washed NaY molecular sieve. In this embodiment, the solid content of the washed NaY molecular sieve sample is 440g / L. Then take 10g of the washed NaY molecular sieve and add it to 8mL of ammonium sulfate solution to mix evenly, perform a tank exchange, obtain a mixed solution, use 98wt% concentrated sulfuric acid to adjust the pH of the mixed solution to 3.5, heat to 60°C and keep constant temperature for 1h, and obtain a molecular sieve slurry, wherein the molar concentration of the ammonium sulfate solution is 0.9mol / L.

[0023] Step 6: Filter the cross-linked molecular sieve slurry on a belt filter, add 15.3 mL of ammonium sulfate solution for belt exchange, and then add 50 g of filtered water for washing. The filter cake obtained is a cross-linked molecular sieve for standby use.

[0024] Step 7: Add 3.5 g of lanthanum nitrate solution to the cross-linked molecular sieve and mix evenly to obtain a cross-linked molecular sieve mixed slurry, wherein the molar concentration of the lanthanum nitrate solution is 1.1 mol / L.

[0025] Step 8: sequentially flash and roast the cross-linked molecular sieve mixed slurry to obtain a cross-linked and roasted molecular sieve. The flash is carried out in a flash tower at a temperature of 110°C and a pressure of 1.2Kpa. The cross-linked and roasted molecular sieve is dried instantly in the flash tower and then enters a roasting furnace for a roasting at a temperature of 800°C and a roasting time of 1.5h.

[0026] Step 9: Add the cross-linked-roasted molecular sieve to 8 mL of ammonium sulfate solution and mix evenly, perform a second tank exchange, and then heat to 60°C and keep constant for 1 hour to obtain a cross-linked-roasted molecular sieve slurry. Filter the cross-linked-roasted molecular sieve slurry on a belt filter, then add 50 g of filtered water for washing, and the filter cake obtained is the cross-linked-roasted molecular sieve.

[0027] Step 10: sequentially perform secondary flash evaporation and secondary calcination on the di-crosslinked molecular sieve slurry to obtain a di-crosslinked and di-calcined molecular sieve, i.e., an ultra-stable Y-type molecular sieve. The secondary flash evaporation is performed in a flash tower, the temperature of the secondary flash evaporation is 110°C, the tower pressure of the flash tower is controlled to be 1.2Kpa, the di-crosslinked and di-calcined molecular sieve is dried instantly in the flash tower, and then enters a calcination furnace for secondary calcination, the temperature of the secondary calcination is 800°C, and the secondary calcination time is 1h.

[0028] Example 2 A low sodium hydrothermal ultrastable molecular sieve, the preparation method comprises the following steps: Step 1: Mix 9.6g of sodium silicate aqueous solution and 13.8g of high-alkali sodium aluminate aqueous solution, stir evenly, and age at room temperature for 12 hours to obtain a directing agent. In the sodium silicate aqueous solution, the mass percentage of SiO2 is 20wt%, and the mass percentage of Na2O is 7wt%; the caustic ratio of the high-alkali sodium aluminate aqueous solution is 10.5mol / mol.

[0029] Step 2: Weigh 41.3 g of sodium silicate aqueous solution, and add 10.3 g of low-alkali sodium aluminate aqueous solution, 6.9 g of directing agent and 12.8 g of aluminum sulfate thereto in sequence, and mix well to obtain aluminosilicate gel. The caustic ratio of the low-alkali sodium aluminate aqueous solution is 2.4 mol / mol.

[0030] Step 3: Add water vapor to the aluminosilicate gel to raise the temperature to 98°C and then crystallize at a constant temperature for 28 hours. After the crystallization is completed, a crystallization slurry is obtained. The crystallinity of the crystallization slurry is tested. The crystallization slurry with a crystallinity of 90%-93% is a NaY type molecular sieve. The crystallinity test method of the crystallization slurry is as follows: First, the crystallized slurry was introduced into a vacuum Buchner funnel for filtration to form a filter cake with a thickness of about 2 mm. The filter cake was then washed with water until the pH value was 9.0. The filter cake was taken out of the Buchner funnel and dried in an oven at 140°C for 1 hour to obtain a sample to be tested. After the sample to be tested was prepared, an X-ray diffractometer was used to test the crystallinity of the sample to be tested.

[0031] Step 4: Filter and wash the NaY molecular sieve on a belt filter. The filter cake obtained is the washed NaY molecular sieve. The amount of water used in the washing process is 3-5 L / Kg NaY molecular sieve.

[0032] Step 5: The washed NaY molecular sieve is sampled for content analysis, and the mass of the washed NaY molecular sieve and the amount of lanthanum chloride solution added are calculated according to the total volume of the washed NaY molecular sieve. In this embodiment, the solid content of the washed NaY molecular sieve sample is 442g / L. Then 10g of the washed NaY molecular sieve is added to 1mL of lanthanum chloride solution and mixed evenly, and a tank exchange is performed to obtain a mixed solution, and the pH of the mixed solution is adjusted to 4.5 using concentrated hydrochloric acid with a concentration of 32wt%, and the temperature is raised to 70°C for 1.5h to obtain a molecular sieve slurry, wherein the molar concentration of the lanthanum chloride solution is 1.0mol / L.

[0033] Step 6: Filter the cross molecular sieve slurry on a belt filter, add 2 mL of lanthanum chloride solution for belt exchange, and then add 50 g of filtered water for washing. The filter cake obtained is a cross molecular sieve for standby use.

[0034] Step 7: sequentially flash and calcine the cross-linked molecular sieve to obtain a cross-linked and calcined molecular sieve. The flash evaporation is carried out in a flash tower at a temperature of 150°C and a pressure of 1.2KPa. The cross-linked and calcined molecular sieve is dried instantly in the flash tower and then enters a calcination furnace for a calcination at a temperature of 500°C and a calcination time of 1h.

[0035] Step 8: Add the cross-linked-roasted molecular sieve to 8 mL of ammonium sulfate solution and mix evenly, perform a second tank exchange, and then heat to 70°C and keep constant for 0.5 h to obtain a cross-linked-roasted molecular sieve slurry. The molar concentration of the ammonium sulfate solution is 0.9 mol / L. The cross-linked-roasted molecular sieve slurry is filtered on a belt filter, and then 50 g of filtered water is added for washing, and the filter cake obtained is a cross-linked-roasted molecular sieve.

[0036] Step 9: The cross-linked and roasted molecular sieve slurry is subjected to secondary flash evaporation and secondary roasting in sequence to obtain the cross-linked and roasted molecular sieve, i.e., the ultra-stable Y-type molecular sieve. The secondary flash evaporation is carried out in a flash tower, the temperature of the secondary flash evaporation is 150°C, the tower pressure of the flash tower is controlled to be 1.2Kpa, the cross-linked and roasted molecular sieve is dried instantly in the flash tower, and then enters the roasting furnace for secondary roasting, the temperature of the secondary roasting is 500°C, and the secondary roasting time is 1.5h.

[0037] Example 3 A low sodium hydrothermal ultrastable molecular sieve, the preparation method comprises the following steps: Step 1: Mix 9.6g of sodium silicate aqueous solution and 13.8g of high-alkali sodium aluminate aqueous solution, stir evenly, and age at room temperature for 12 hours to obtain a directing agent. In the sodium silicate aqueous solution, the mass percentage of SiO2 is 20wt%, and the mass percentage of Na2O is 7wt%; the caustic ratio of the high-alkali sodium aluminate aqueous solution is 10.5mol / mol.

[0038] Step 2: Weigh 41.3 g of sodium silicate aqueous solution, and add 10.3 g of low-alkali sodium aluminate aqueous solution, 6.9 g of directing agent and 12.8 g of aluminum sulfate thereto in sequence, and mix well to obtain aluminosilicate gel. The caustic ratio of the low-alkali sodium aluminate aqueous solution is 2.4 mol / mol.

[0039] Step 3: Add water vapor to the aluminosilicate gel to raise the temperature to 98°C and then crystallize at a constant temperature for 28 hours. After the crystallization is completed, a crystallization slurry is obtained. The crystallinity of the crystallization slurry is tested. The crystallization slurry with a crystallinity of 90%-93% is a NaY type molecular sieve. The crystallinity test method of the crystallization slurry is as follows: First, the crystallized slurry was introduced into a vacuum Buchner funnel for filtration to form a filter cake with a thickness of about 2 mm. The filter cake was then washed with water until the pH value was 9.0. The filter cake was taken out of the Buchner funnel and dried in an oven at 140°C for 1 hour to obtain a sample to be tested. After the sample to be tested was prepared, an X-ray diffractometer was used to test the crystallinity of the sample to be tested.

[0040] Step 4: Filter and wash the NaY molecular sieve on a belt filter. The filter cake obtained is the washed NaY molecular sieve. The amount of water used in the washing process is 3-5 L / Kg NaY molecular sieve.

[0041] Step 5: Sampling the washed NaY molecular sieve for content analysis, so as to calculate the mass of the washed NaY molecular sieve and the amount of the first cation exchanger added according to the total volume of the washed NaY molecular sieve. In this embodiment, the solid content of the washed NaY molecular sieve sample is 445g / L. Then 10g of the washed NaY molecular sieve is added to 3mL of lanthanum chloride solution and mixed evenly, and a tank exchange is performed to obtain a mixed solution, and the pH of the mixed solution is adjusted to 3.0-4.0 using concentrated hydrochloric acid with a concentration of 32wt%, and the temperature is raised to 60-70°C for 1h to obtain a molecular sieve slurry, wherein the molar concentration of the lanthanum chloride solution is 1.0mol / L.

[0042] Step 6: Filter the cross molecular sieve slurry on a belt filter, add 2.3 mL of lanthanum chloride solution for belt exchange, and then add 50 g of filtered water for washing. The filter cake obtained is a cross molecular sieve for standby use.

[0043] Step 7: sequentially flash and calcine the cross-linked molecular sieve to obtain a cross-linked and calcined molecular sieve. The flash evaporation is carried out in a flash tower at a temperature of 123°C and a pressure of 1.2Kpa. The cross-linked and calcined molecular sieve is dried instantly in the flash tower and then enters a calcination furnace for a calcination at a temperature of 700°C and a calcination time of 1h.

[0044] Step 8: Add the cross-linked and roasted molecular sieve to 0.3mL of lanthanum chloride solution and mix evenly, perform a secondary tank exchange, obtain a mixed solution, use 32wt% concentrated hydrochloric acid to adjust the pH of the mixed solution to 4.0, and then heat it to 66°C for 1h to obtain a cross-linked and roasted molecular sieve slurry. Filter the cross-linked and roasted molecular sieve slurry on a belt filter, add 2.3mL of lanthanum chloride solution for belt exchange, and then add 50g of filtered water for washing. The filter cake obtained is a cross-linked and roasted molecular sieve, that is, an ultra-stable Y-type molecular sieve. The molar concentration of the lanthanum chloride solution is 1.0mol / L.

[0045] Comparative Example 1 A hydrothermal ultrastable molecular sieve, the preparation method comprises the following steps: Step 1: Mix 9.6g of sodium silicate aqueous solution and 13.8g of high-alkali sodium aluminate aqueous solution, stir evenly, and age at room temperature for 12 hours to obtain a directing agent. In the sodium silicate aqueous solution, the mass percentage of SiO2 is 20wt%, and the mass percentage of Na2O is 7wt%; the caustic ratio of the high-alkali sodium aluminate aqueous solution is 10.5mol / mol.

[0046] Step 2: Weigh 41.3 g of sodium silicate aqueous solution, and add 10.3 g of low-alkali sodium aluminate aqueous solution, 6.9 g of directing agent and 12.8 g of aluminum sulfate thereto in sequence, and mix well to obtain aluminosilicate gel. The caustic ratio of the low-alkali sodium aluminate aqueous solution is 2.4 mol / mol.

[0047] Step 3: Add water vapor to the aluminosilicate gel to raise the temperature to 98°C and then crystallize at a constant temperature for 28 hours. After the crystallization is completed, a crystallization slurry is obtained. The crystallinity of the crystallization slurry is tested. The crystallization slurry with a crystallinity of 90%-93% is a NaY type molecular sieve. The crystallinity test method of the crystallization slurry is as follows: First, the crystallized slurry was introduced into a vacuum Buchner funnel for filtration to form a filter cake with a thickness of about 2 mm. The filter cake was then washed with water until the pH value was 9.0. The filter cake was taken out of the Buchner funnel and dried in an oven at 140°C for 1 hour to obtain a sample to be tested. After the sample to be tested was prepared, an X-ray diffractometer was used to test the crystallinity of the sample to be tested.

[0048] Step 4: Filter the NaY molecular sieve on a belt filter, and then wash it with water. The filter cake obtained is the water-washed NaY molecular sieve. During the washing process, the amount of water used is 3-5L / KgNaY molecular sieve.

[0049] Step 5: Sampling the washed NaY molecular sieve for content analysis, so as to calculate the mass of the washed NaY molecular sieve and the amount of the first cation exchanger added according to the total volume of the washed NaY molecular sieve. In this comparative example, the solid content of the washed NaY molecular sieve sample is 440g / L. Take 10g of the washed NaY molecular sieve and add it to 2mL of lanthanum chloride solution and mix it evenly to obtain a mixed solution, adjust the pH of the mixed solution to 3.0-4.0 using concentrated hydrochloric acid with a concentration of 32wt%, and then heat it to 60-70℃ for 1h for a tank exchange to obtain a cross molecular sieve slurry, wherein the molar concentration of the lanthanum chloride solution is 1.0mol / L.

[0050] Step 6: Filter the cross-linked molecular sieve slurry on a belt filter, then add 50g of filtered water for washing, and the obtained filter cake is a cross-linked molecular sieve for standby use.

[0051] Step 7: Add 1.7g of lanthanum nitrate solution to the cross-linked molecular sieve for tank exchange, and then perform a flash evaporation and a calcination to obtain a cross-linked and calcined molecular sieve. The flash evaporation is performed in a flash tower, the flash evaporation temperature is 130°C, and the tower pressure of the flash tower is controlled to be 1.2Kpa. The cross-linked and calcined molecular sieve is dried instantly in the flash tower, and then enters the calcination furnace for a calcination, the calcination temperature is 500°C, and the calcination time is 1h.

[0052] Step 8: Add water to the cross-baked molecular sieve to obtain a cross-baked molecular dilution sieve slurry, and the amount of water added is based on the centrifugal pump delivery conditions. Sample the cross-baked molecular sieve dilution slurry for content analysis, calculate the amount of ammonium oxalate added according to the total volume of the cross-baked molecular sieve dilution slurry, and then add solid ammonium oxalate to the cross-baked molecular sieve dilution slurry and stir for 40 minutes to obtain a mixed slurry, wherein the amount of solid ammonium oxalate added is 5wt% of the dry weight of the cross-baked molecular sieve. Use 15wt% ammonia water to adjust the pH of the mixed slurry to 5.5, then heat to 60℃ and keep constant temperature for 1h, and perform secondary belt exchange washing and filtration on a belt filter. The secondary belt exchange uses 15.3mL of ammonium sulfate as a cation exchange liquid to obtain a two-cross-baked molecular sieve. After that, wash the two-cross-baked molecular sieve with water. During the washing process, wash the two-cross-baked molecular sieve with 50g filtered water, and the filter cake obtained is a two-cross-baked molecular sieve. Wherein, the mass fraction of solid ammonium oxalate is ≥99.0wt%, and the molar concentration of the ammonium sulfate solution is 0.9mol / L.

[0053] The Na2O content in the molecular sieves obtained in Examples 1-3 and Comparative Example 1 was tested by X-ray fluorescence intensity analysis. The test results are shown in Table 1.

[0054] Table 1 Na2O content in the molecular sieves obtained in Examples 1-3 and Comparative Example 1

[0055] It can be seen from Table 1 that the Na2O content in the molecular sieves obtained in Examples 1-3 is lower than the Na2O content in the molecular sieve obtained in Comparative Example 1. It can be seen that the preparation method provided by the invention can effectively reduce the Na2O content in the molecular sieve.

[0056] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A method for preparing a low sodium hydrothermal ultrastable molecular sieve, characterized in that: The steps include: Step 1: Mix the silicon source and the sodium aluminate aqueous solution, stir evenly, and age at room temperature to obtain a directing agent; Step 2: adding sodium aluminate aqueous solution, a directing agent and aluminum sulfate to the silicon source, and mixing them evenly to obtain an aluminosilicate gel; Step 3: introducing water vapor into the aluminosilicate gel to raise the temperature for crystallization, thereby obtaining a NaY type molecular sieve; Step 4: Add NaY molecular sieve to the first cation exchanger and mix evenly, perform a tank exchange, then adjust the pH to 3.5-4.5, heat to 60-70°C and keep constant temperature for 0.5-1.5h to obtain a cross-molecular sieve slurry. During the tank exchange, the amount of the first cation exchanger is 0.08-0.15g / g NaY molecular sieve; filter the cross-molecular sieve slurry to obtain a cross-molecular sieve crude product, and add the first cation exchanger to the cross-molecular sieve crude product for belt exchange, and then wash with water to obtain a cross-molecular sieve. During the belt exchange, the amount of the first cation exchanger is 0-0.25g / g of the cross-molecular sieve crude product; wherein the first cation exchanger is ammonium sulfate solution or lanthanum chloride solution, and the molar concentration of the first cation exchanger is 0.9-1.1mol / L; Step 5: sequentially flashing and calcining the cross-linked molecular sieve to obtain a cross-linked and calcined molecular sieve, wherein the temperature of the flashing is 110-150° C., and the temperature of the calcining is 500-800° C.; Step 6: Add the cross-linked and roasted molecular sieve to the first cation exchanger and mix evenly, perform a secondary tank exchange, then heat to 60-70°C and keep constant for 0.5-1.5h to obtain a cross-linked and roasted molecular sieve slurry, filter and wash the cross-linked and roasted molecular sieve slurry to obtain a cross-linked and roasted molecular sieve, wherein the amount of the first cation exchanger is 0.08-0.15g / g of the cross-linked and roasted molecular sieve, the first cation exchanger is ammonium sulfate solution or lanthanum chloride solution, and the molar concentration of the first cation exchanger is 0.9-1.1mol / L.

2. The method for preparing a low-sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: Step four also includes: adding a cross-linked molecular sieve to a second cation exchanger and mixing evenly to obtain a cross-linked molecular sieve mixed slurry, the dosage of the second cation exchanger is 0.01-0.09g / g of the cross-linked molecular sieve, the second cation exchanger is a lanthanum nitrate solution or a yttrium nitrate solution, and the molar concentration of the second cation exchanger is 1.1-1.3mol / L.

3. The method for preparing a low-sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: The method further comprises step seven: sequentially performing secondary flash evaporation and secondary calcination on the di-crosslinked and di-calcined molecular sieve to obtain the di-crosslinked and di-calcined molecular sieve, wherein the secondary flash evaporation temperature is 110-150° C., and the secondary calcination temperature is 500-800° C.

4. The method for preparing a low-sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: The silicon source is a sodium silicate aqueous solution, in which the mass percentage of SiO2 is 20wt% and the mass percentage of Na2O is 7wt%; the sodium aluminate aqueous solution is a high-alkali sodium aluminate aqueous solution or a low-alkali sodium aluminate aqueous solution, the caustic ratio of the high-alkali sodium aluminate aqueous solution is 10.5mol / mol, and the caustic ratio of the low-alkali sodium aluminate aqueous solution is 2.4mol / mol.

5. The method for preparing a low-sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: In step 1, the silicon source and the sodium aluminate aqueous solution are mixed in a molar ratio of 10.67Na2O:1Al2O3:10SiO2:180H2O, and the aging time is 12-24h.

6. The method for preparing a low-sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: In step 2, the silicon source, the sodium aluminate aqueous solution, the directing agent and the aluminum sulfate are mixed in a molar ratio of 8Na2O:1Al2O3:20SiO2:320H2O.

7. The method for preparing a low sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: In step 3, the crystallization temperature is 92-98° C. and the crystallization time is 20-30 h.

8. The method for preparing a low-sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: In step 4, the cross-linked molecular sieve slurry is filtered and washed with water to obtain the cross-linked molecular sieve, and the amount of water used is 3-5 g / g of the cross-linked molecular sieve.

9. The method for preparing a low-sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: In step six, the cross-linked calcined molecular sieve slurry is filtered and washed with water to obtain the cross-linked calcined molecular sieve, and the amount of water used is 3-5 g / g of the cross-linked calcined molecular sieve.

10. The method for preparing a low sodium hydrothermal ultrastable molecular sieve according to claim 1, characterized in that: In step 4, sulfuric acid or hydrochloric acid is used to adjust the pH; in step 4 and step 6, filtration is performed on a belt filter.

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