A method for selectively regulating the acidity of a molecular sieve

Abstract

The application discloses a method for selectively regulating the acidity of a molecular sieve, which comprises the following steps: (1) performing first calcination on a molecular sieve containing an organic template agent in an air atmosphere, wherein the first calcination temperature is 200-450 DEG C; (2) performing ion exchange reaction on the solid obtained in the step (1) with a solution containing metal ions, and then performing washing, filtering and drying; and (3) performing second calcination on the solid obtained in the step (2) in an air atmosphere, wherein the second calcination temperature is 450-600 DEG C. The method can regulate the ratio of the strong acid amount to the weak acid amount of the molecular sieve, and the strong acid amount of the molecular sieve can be selectively regulated under the condition that the weak acid amount of the molecular sieve is less affected, and the process is simple and convenient to operate.

Description

Technical Field

[0001] The present invention relates to the field of molecular sieve preparation, and in particular to a method for selectively regulating the acidity of a molecular sieve. Background Art

[0002] Molecular sieve is a natural or synthetic aluminosilicate with [SiO4] and [AlO4] tetrahedron as basic structural units. It has a regular pore structure and cavity system. Molecular sieve also has flexibly adjustable acidity and high hydrothermal stability. Therefore, it is widely used in various catalytic reactions, such as catalytic cracking, alkylation, isomerization, disproportionation and transalkylation, reforming and other catalytic reaction processes.

[0003] Different catalytic reactions require different acidic properties from the molecular sieve. For example, catalytic cracking requires a molecular sieve with strong acidity, while for xylene isomerization, strong acidity can increase side reactions such as disproportionation and transalkylation, leading to increased xylene losses. Therefore, the acidic properties of the molecular sieve need to be tailored to the specific catalytic reaction. Common methods for controlling the acidic properties of molecular sieves include ion exchange, acid treatment, alkaline treatment, and hydrothermal treatment.

[0004] CN103623617B prepares hydrogen-type molecular sieves by ion exchange for catalytic cracking reactions. CN110665538B adjusts the acidity and pore structure of CHA molecular sieves by ammonium exchange, acid treatment and alkali treatment for ammonia selective catalytic reduction reaction. CN106669774B uses ammonium exchange and hydrothermal treatment to adjust the acidity and pore structure of Y-type molecular sieves for catalytic cracking reactions. The above-mentioned method for adjusting the acid properties of molecular sieves is usually an overall treatment of the acid properties of molecular sieves, that is, changing the weak acid and strong acid properties of the molecular sieve at the same time. It is difficult to selectively change the strong acidity without affecting the weak acid properties of the molecular sieve. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for selectively regulating the acidity of a molecular sieve, which can regulate the ratio of the strong acid content to the weak acid content of the molecular sieve. Under conditions where the weak acid content of the molecular sieve is less affected, the strong acid content of the molecular sieve can be selectively adjusted. The process is simple and easy to operate.

[0006] The method for selectively controlling the acidity of a molecular sieve provided by the present invention comprises:

[0007] (1) calcining the molecular sieve containing the organic template in an air atmosphere at a temperature of 200 to 450° C.;

[0008] (2) subjecting the solid obtained in step (1) to an ion exchange reaction with a solution containing metal ions, followed by washing, filtering and drying;

[0009] (3) The solid obtained in step (2) is subjected to a second calcination in an air atmosphere, wherein the second calcination temperature is 450-600°C.

[0010] The method provided by the present invention selectively adjusts the strong acid content of the molecular sieve by controlling the roasting temperature in step (1) and the concentration of metal ions in the metal ion-containing solution in step (2), while having little effect on the weak acid content. DETAILED DESCRIPTION

[0011] In the prior art, a molecular sieve containing a template is directly calcined at high temperature to remove the template, and a molecular sieve with unregulated acidity can be obtained. The inventors of the present invention have found that a molecular sieve containing an organic template is first calcined at a lower temperature. While removing part of the organic template, only part of the strong acid sites are exposed, and the remaining organic template still occupies part of the strong acid sites and all the weak acid sites; the molecular sieve obtained by the first calcination is then ion exchanged with a solution containing metal ions, so that the metal ions partially or completely occupy these exposed strong acid sites, thereby reducing the strong acidity of the molecular sieve; the molecular sieve after ion exchange is then calcined for a second time at a higher temperature to completely remove the organic template in the molecular sieve, exposing all the remaining acid sites including strong and weak acids, and thus a molecular sieve with a small change in weak acidity and regulated strong acidity can be obtained. The present invention can simply adjust the number of strong acid sites occupied by metal ions by controlling the temperature of the first roasting and the concentration of metal ions in the metal ion solution, thereby selectively adjusting the amount of strong acid reduction, thereby obtaining a molecular sieve with a small change in weak acid amount and an adjustable strong acid amount, that is, a ratio of strong acid to weak acid.

[0012] The method for selectively controlling the acidity of a molecular sieve provided by the present invention comprises:

[0013] (1) calcining the molecular sieve containing the organic template in an air atmosphere at a temperature of 200 to 450° C.;

[0014] (2) subjecting the solid obtained in step (1) to an ion exchange reaction with a solution containing metal ions, followed by washing, filtering and drying;

[0015] (3) The solid obtained in step (2) is subjected to a second calcination in an air atmosphere, wherein the second calcination temperature is 450-600°C.

[0016] Optionally, the organic template-containing molecular sieve has an organic template content of 2 to 20% by mass based on the total mass of the molecular sieve and the template. The molecular sieve is selected from one of EU-1, ZSM-5, beta, MOR, and MCM-22, and the SiO2 / Al2O3 molar ratio of the molecular sieve is 10 to 200.

[0017] In the method of the present invention, the higher the temperature and the longer the time of the first calcination in step (1), the more strong acid sites are exposed. However, the temperature of the first calcination should not be too high and the time should not be too long, otherwise weak acid sites will be exposed, resulting in an increase in the amount of weak acid that has been reduced. Preferably, the first calcination in step (1) is performed at a temperature of 250 to 400° C. and for a time of 0.5 to 2 hours, more preferably 1 to 1.5 hours.

[0018] In the method of the present invention, step (2) can adjust the number of strong acid sites occupied by metal ions by controlling conditions such as the concentration of metal ions in the metal ion solution, the mass ratio of the metal ion solution to the solid, the temperature and time of the ion exchange reaction. The solution containing metal ions is a salt solution containing metal ions or an alkaline solution containing metal ions. The salt solution containing metal ions is selected from one of lithium chloride solution, sodium chloride solution, and potassium chloride solution, and the metal ion concentration in the salt solution containing metal ions is 0.05 to 0.5 mol / L; the alkaline solution containing metal ions is selected from one of lithium hydroxide solution, sodium hydroxide solution, and potassium hydroxide solution, and the metal ion concentration in the alkaline solution containing metal ions is 0.05 to 0.3 mol / L. The mass ratio of the metal ion solution to the solid is 1 to 5:1, the temperature of the ion exchange reaction is 60 to 95°C, the time is 0.5 to 2 hours, and the drying temperature is 90 to 130°C, and the time is greater than 4 hours.

[0019] In the method of the present invention, the temperature and time of the second calcination in step (3) are suitable for removing all the organic templates. The preferred second calcination temperature is 480-580° C. and the time is 2-6 hours.

[0020] The method of the present invention is suitable for regulating the acid content of the molecular sieve containing the organic template. The preparation method of the molecular sieve containing the organic template is a conventional method in the art and will not be described in detail here.

[0021] The present invention uses an AUTOCHEM II 2920 chemical adsorption instrument produced by Micromeritics, USA, and the ammonia temperature-programmed desorption (NH3-TPD) method to determine the acid properties of the molecular sieve. The specific steps are as follows:

[0022] (1) The dried molecular sieve was pelletized, crushed, and sieved into 20-40 mesh particles. 0.2 g was weighed using an analytical balance and placed in a U-shaped quartz tube for measurement.

[0023] (2) Fix the U-shaped quartz tube on the chemical adsorption instrument and program the temperature to 600 °C in a helium atmosphere to remove the impurities adsorbed in the molecular sieve. After purging for 30 minutes, cool it down to room temperature;

[0024] (3) Ammonia-helium mixture (5% ammonia by volume) was introduced at a rate of 20 ml / min for 10 min. After stopping the introduction of ammonia, the temperature was raised to 100°C and helium was continued to be purged for 30 min until the TCD signal of the instrument stabilized.

[0025] (4) Heating to 550°C at a rate of 10°C / min while recording the TCD signal;

[0026] (5) According to the TCD signal, the ammonia concentration is converted into the instrument parameters, and the acid content of the molecular sieve is obtained by integration calculation. The peak at 100-80°C is a weak acid, and the peak at 280-550°C is a strong acid.

[0027] The signal value directly measured by the TCD detector is usually in mV. It needs to be calibrated regularly (introducing ammonia of a certain concentration and flow rate and recording its signal value) to convert the mV value into the corresponding ammonia concentration mmol / s according to a certain ratio. Then, by integrating it with time, the peak area is calculated to obtain the actual acid amount mmol, which is divided by the mass of the sample to obtain the acid amount mmol / g. The entire calculation process can be completed automatically by the instrument.

[0028] The present invention is further described below by way of examples, but the present invention is not limited thereto.

[0029] Example 1

[0030] 100.14 g of silica sol (SiO2 mass fraction of 30%), 9.75 g of low-alkalinity sodium aluminate aqueous solution (Al2O3 mass fraction of 13.1%, Na2O mass fraction of 20.01%), 0.48 g of sodium hydroxide, 18.11 g of hexamethylammonium bromide (CAS: 55-97-0) and 193.52 g of deionized water were mixed to obtain a molecular sieve synthesis gel, and then the molecular sieve synthesis gel was transferred to a reactor and dynamically crystallized at 170° C. for 96 hours to obtain a crystallized product, and the crystallized product was washed and dried to obtain EU-1 molecular sieve A containing the template agent hexamethylammonium bromide.

[0031] (1) 10 g of EU-1 molecular sieve A (containing 12.3% by mass of an organic template and a SiO2 / Al2O3 molar ratio of 34.27) was placed in a muffle furnace and calcined at 250°C for 2 h to obtain molecular sieve A1;

[0032] (2) 4.4 g of molecular sieve A1 was placed in 20 g of 0.1 mol / L sodium hydroxide solution and subjected to an ion exchange reaction under stirring at 65°C for 0.5 h. After the ion exchange reaction, the product was filtered and washed, and the solid product was dried at 120°C for 8 h to obtain molecular sieve A2.

[0033] (3) The solid obtained in step (2) was placed in a muffle furnace and calcined at 550℃ for 4h to obtain molecular sieve A3.

[0034] The NH3-TPD results of molecular sieve A3 are shown in Table 1.

[0035] Comparative Example 1

[0036] 10g of EU-1 molecular sieve A (containing 12% by mass of organic template, SiO2 / Al2O3 molar ratio of 34.27) of Example 1 was placed in a muffle furnace, without first calcination and exchange reaction, and directly calcined at 550℃ for 4h to completely remove the template in the molecular sieve, to obtain comparative molecular sieve DA1, which is an EU-1 molecular sieve without acid amount regulation.

[0037] The NH3-TPD results of molecular sieve DA1 are shown in Table 1.

[0038] Comparative Example 2

[0039] The molecular sieve A was treated according to the method described in Example 1, except that the first calcination temperature in step (1) was 480℃, to obtain comparative molecular sieve DA2.

[0040] The NH3-TPD results of molecular sieve DA2 are shown in Table 1.

[0041] Comparative Example 3

[0042] The molecular sieve A was treated according to the method described in Example 1, except that the first calcination temperature in step (1) was 150℃, to obtain molecular sieve DA3.

[0043] The NH3-TPD results of molecular sieve DA3 are shown in Table 1.

[0044] As shown in Table 1, by the method of Example 1, after first calcination and exchange reaction, part of the exposed strong acid sites were occupied by metal cations, the strong acid amount of molecular sieve A3 was reduced, and compared with the reduction of strong acid amount, the weak acid amount changed little, and the ratio of strong acid amount to weak acid amount was reduced from 0.63 to 0.51.

[0045] As shown in Table 1, the comparative molecular sieve DA1 prepared in Comparative Example 1 was not regulated in acid amount, the weak acid amount was 0.530mmol / g, the strong acid amount was 0.332mmol / g, and the ratio of strong acid amount to weak acid amount was 0.63.

[0046] As shown in Table 1, the comparative molecular sieve DA2 prepared in Comparative Example 2 had more exposed strong acid sites and weak acid sites due to the first calcination temperature exceeding the range defined in the present application, the weak acid amount was 0.450mmol / g, the strong acid amount was 0.276mmol / g, and the ratio of strong acid amount to weak acid amount was 0.61.

[0047] After ion exchange reaction, the amount of strong acid and weak acid of the molecular sieve DA2 is obviously reduced compared with that of the molecular sieve DA1, and the ratio of the amount of strong acid to the amount of weak acid is not obviously reduced.

[0048] It can also be seen from Table 1 that the comparative molecular sieve DA3 prepared in Comparative Example 3 has a small change in the amount of strong acid and almost no change in the amount of weak acid compared with the molecular sieve DA1, i.e. compared with the molecular sieve product without treatment after the treatment of steps (1)-(3), because the first calcination temperature is lower than the range of the present application, and the template removed by the first calcination is too little, and the strong acid sites exposed are too few.

[0049] Example 2

[0050] The EU-1 molecular sieve was treated according to the method described in Example 1, except that the calcination temperature in step (1) was 300°C, and finally the molecular sieve B3 was obtained.

[0051] The NH3-TPD results of the molecular sieve B3 are shown in Table 1. It can be seen that the strong acid sites exposed are increased compared with Example 1 when the first calcination temperature is increased to 300°C, the amount of strong acid of the treated molecular sieve is further reduced, the amount of weak acid changes little compared with the reduction amplitude of the amount of strong acid, and the ratio of the amount of strong acid to the amount of weak acid is further reduced to 0.37.

[0052] Example 3

[0053] The EU-1 molecular sieve was treated according to the method described in Example 1, except that the calcination temperature in step (1) was 350°C, and finally the molecular sieve C3 was obtained.

[0054] The NH3-TPD results of the molecular sieve C3 are shown in Table 1. It can be seen that the strong acid sites exposed are increased compared with Example 2 when the first calcination temperature is increased to 350°C, the amount of strong acid of the treated molecular sieve is further reduced, the amount of weak acid changes little compared with the reduction amplitude of the amount of strong acid, and the ratio of the amount of strong acid to the amount of weak acid is further reduced to 0.16.

[0055] Example 4

[0056] The EU-1 molecular sieve was treated according to the method described in Example 1, except that the calcination temperature in step (1) was 400°C, and finally the molecular sieve D3 was obtained.

[0057] The NH3-TPD results of the molecular sieve D3 are shown in Table 1. It can be seen that the strong acid sites exposed are increased compared with Example 3 when the first calcination temperature is increased to 400°C, the amount of strong acid of the treated molecular sieve is further reduced, the amount of weak acid changes little compared with the reduction amplitude of the amount of strong acid, and the ratio of the amount of strong acid to the amount of weak acid is significantly reduced to 0.07.

[0058] Example 5

[0059] The EU-1 molecular sieve was treated according to the method of Example 4, except that the calcination time in step (1) was 1 h, and finally molecular sieve G3 was obtained.

[0060] The NH3-TPD results of molecular sieve G3 are shown in Table 1.

[0061] Example 6

[0062] The EU-1 molecular sieve was treated according to the method of Example 4, except that the concentration of the sodium hydroxide solution in step (2) was 0.06 mol / L, and finally molecular sieve H3 was obtained.

[0063] The NH3-TPD results of molecular sieve H3 are shown in Table 1.

[0064] Example 7

[0065] The EU-1 molecular sieve was treated according to the method of Example 1, except that the ion exchange in step (2) was performed using a sodium chloride solution with a concentration of 0.3 mol / L, and finally molecular sieve I3 was obtained.

[0066] The NH3-TPD results of molecular sieve I3 are shown in Table 1.

[0067] Example 8

[0068] 100.14 g of silica sol (30% by mass of SiO2), 5.97 g of an aqueous aluminum sulfate solution (20% by mass of Al2(SO4)3), 1.00 g of sodium hydroxide, 8.13 g of an aqueous tetrapropylammonium hydroxide (TPAOH) solution (25% by mass of TPAOH), and 344.94 g of deionized water were mixed to obtain a molecular sieve synthesis gel, which was then transferred to a reaction kettle and subjected to dynamic crystallization at 140°C for 36 h to obtain a crystallization product, and the crystallization product was washed and dried to obtain a ZSM-5 molecular sieve E containing the template TPAOH.

[0069] (1) 10 g of the ZSM-5 molecular sieve E (containing 8.53% by mass of organic template, SiO2 / Al2O3 molar ratio of 119.36) was placed in a muffle furnace and calcined at 300°C for 2 h to obtain a molecular sieve E1;

[0070] (2) The molecular sieve E1 was placed in 20 g of a 0.05 mol / L potassium hydroxide solution and subjected to an ion exchange reaction under stirring at a reaction temperature of 65°C for 0.5 h. After the ion exchange reaction, the solid product was filtered, washed, and dried at 120°C for 8 h to obtain a molecular sieve E2;

[0071] (3) The solid obtained in step (2) was placed in a muffle furnace and calcined at 550°C for 4 h to obtain a molecular sieve E3.

[0072] The NH3-TPD results of molecular sieve E3 are shown in Table 1.

[0073] Comparative Example 4

[0074] Take 10g of ZSM-5 molecular sieve E from Example 8, place it in a muffle furnace, and directly calcine at 550°C for 4h without undergoing the first calcination and exchange reaction to completely remove the template in the molecular sieve to obtain molecular sieve DE1, which is a ZSM-5 molecular sieve with unregulated acid content.

[0075] The NH3-TPD results of molecular sieve DE1 are shown in Table 1.

[0076] Comparative Example 5

[0077] Molecular sieve E was treated according to the method described in Example 8, except that the temperature of the first calcination in step (1) was 500°C, to obtain molecular sieve DE2.

[0078] The NH3-TPD results of molecular sieve DE2 are shown in Table 1.

[0079] As can be seen from Table 1, according to the method of Example 8, after the first calcination and exchange reaction, some of the exposed strong acid sites are occupied by metal cations, and the strong acid content of molecular sieve E3 is reduced. Compared with the magnitude of the reduction in the strong acid content, the change in the weak acid content is small, and the ratio of the strong acid content to the weak acid content is reduced from 1.08 to 0.83.

[0080] Table 1 also shows that the molecular sieve DE1 prepared in Comparative Example 4 has an unregulated acid content, a weak acid content of 0.150 mmol / g, a strong acid content of 0.162 mmol / g, and a ratio of strong acid content to weak acid content of 1.08.

[0081] Table 1 also shows that the molecular sieve DE2 prepared in Comparative Example 5 has a higher first calcination temperature than the range specified in the present invention, resulting in more strong acid sites and weak acid sites exposed during the calcination process. After the ion exchange reaction, the amount of strong acid and weak acid in the molecular sieve DE2 is significantly reduced compared with DE1, and the ratio of strong acid to weak acid is not significantly reduced.

[0082] Example 9

[0083] ZSM-5 molecular sieve was treated according to the method described in Example 8, except that the calcination temperature in step (1) was 350° C., and molecular sieve F3 was finally obtained.

[0084] The NH3-TPD results of molecular sieve F3 are shown in Table 1. It can be seen that when the first calcination temperature is increased to 350°C, the exposed strong acid sites increase compared with Example 8, and the strong acid content of the molecular sieve is further reduced after treatment. Compared with the magnitude of the reduction in the strong acid content, the change in the weak acid content is small, and the ratio of the strong acid content to the weak acid content is further reduced to 0.58.

[0085] Table 1

[0086] Molecular sieve number Weak acid content mmol / g Strong acid content mmol / g Ratio of strong acid to weak acid Example 1 A3 0.530 0.272 0.51 Comparative Example 1 DA1 0.530 0.332 0.63 Comparative Example 2 DA2 0.450 0.276 0.61 Comparative Example 3 DA3 0.530 0.331 0.62 Example 2 B3 0.529 0.195 0.37 Example 3 C3 0.527 0.084 0.16 Example 4 D3 0.523 0.037 0.07 Example 5 G3 0.525 0.061 0.12 Example 6 H3 0.523 0.042 0.08 Example 7 I3 0.519 0.031 0.06 Example 8 E3 0.149 0.124 0.83 Comparative Example 4 DE1 0.150 0.162 1.08 Comparative Example 5 DE2 0.117 0.123 1.05 Example 9 F3 0.147 0.085 0.58

[0087] The above examples illustrate that the method of the present invention can selectively control the amount of strong acid in the molecular sieve and the ratio of the strong acid to weak acid amount in the molecular sieve while having little effect on the amount of weak acid in the molecular sieve.

Claims

1. A method for selectively regulating the acidity of a molecular sieve, characterized in that: The method includes: (1) calcining the molecular sieve containing the organic template in an air atmosphere at a temperature of 200 to 450° C.; (2) subjecting the solid obtained in step (1) to an ion exchange reaction with a solution containing metal ions, followed by washing, filtering and drying; (3) The solid obtained in step (2) is subjected to a second calcination in an air atmosphere, wherein the second calcination temperature is 450-600°C.

2. The method according to claim 1, characterized in that Based on the total mass of the molecular sieve and the template, the content of the organic template is 2 to 20 mass %.

3. The method according to claim 1, characterized in that The molecular sieve is selected from one of EU-1, ZSM-5, beta, MOR, and MCM-22.

4. The method according to claim 1, wherein The SiO2 / Al2O3 molar ratio of the molecular sieve is 10-200.

5. The method according to claim 1, wherein The first calcination in step (1) is performed at a temperature of 250-400°C.

6. The method according to claim 1, characterized in that The metal ion-containing solution in step (2) is a metal ion-containing salt solution or a metal ion-containing alkaline solution.

7. The method according to claim 6, characterized in that The metal ion-containing salt solution described in step (2) is selected from one of lithium chloride solution, sodium chloride solution, and potassium chloride solution, and the metal ion concentration in the metal ion-containing salt solution is 0.05 to 0.5 mol / L; the metal ion-containing alkaline solution described in step (2) is selected from one of lithium hydroxide solution, sodium hydroxide solution, and potassium hydroxide solution, and the metal ion concentration in the metal ion-containing alkaline solution is 0.05 to 0.3 mol / L.

8. The method according to claim 1, characterized in that The mass ratio of the metal ion solution to the solid in step (2) is 1 to 5:

1.

9. The method according to claim 1, characterized in that The temperature of the ion exchange reaction in step (2) is 60-95° C., and the time is 0.5-2 h.

10. The method according to claim 1, characterized in that The drying temperature in step (2) is 90-130° C. and the drying time is greater than 4 hours.

11. The method according to claim 1, wherein The first calcination in step (1) takes 0.5 to 2 hours.

12. The method according to claim 1, characterized in that The second roasting in step (2) takes 2 to 8 hours.