Molecular sieves and their preparation methods and applications

Abstract

The application discloses a molecular sieve, characterized in that the ratio of B value to T value of the molecular sieve is 1.5-6, wherein the B value represents the mass fraction of Al2O3 on the surface of the molecular sieve, the T value represents the mass fraction of Al2O3 in the bulk phase of the molecular sieve, the mesopore volume accounts for 15-35% of the total pore volume, and the total acid amount is higher than 2500 mu mol / g. 26 In a reaction method for preparing linear alkylbenzene by alkylation of linear olefins, the monoalkylbenzene selectivity is more than 99%, the linearity of alkylbenzene reaches more than 92%, and the 2-LAB proportion reaches more than 25% when the conversion is 100%.

Description

Technical Field

[0001] The present invention relates to a molecular sieve, a preparation method and application thereof, and more specifically, to a molecular sieve with surface aluminum-rich and hierarchical pore structure characteristics, a preparation method thereof and application thereof in the alkylation of long-chain olefins. Background Art

[0002] Long-chain alkylbenzenes are an important raw material for the production of sodium alkylbenzene sulfonate, a synthetic detergent. Long-chain alkylbenzenes are primarily produced by the alkylation of long-chain olefins with benzene. Currently, commercial catalysts for this reaction are primarily HF or AlCl₃. However, these two catalytic systems pose significant safety and environmental risks and are being phased out as safety and environmental standards continue to rise. The development of a new, corrosion-free, and pollution-free solid acid alkylation method as an alternative is an inevitable trend in long-chain alkylbenzene production technology.

[0003] Currently, the industrial solid acid process uses the fluorine-containing SiO2-Al2O3 solid acid catalyst (ZL93104573.8) jointly developed by UOP of the United States and Petresa of Spain. Since the catalyst itself contains fluorine, it is corrosive to equipment and still has certain safety and environmental risks.

[0004] Zeolite molecular sieve catalyst systems have received extensive research both domestically and internationally. Because long-chain alkylbenzene molecules are relatively large, they are unable to access pores with ten-membered rings or less. Only molecular sieves with pores with twelve or more rings, such as MOR, Y, and Beta, exhibit good catalytic performance in the alkylation of benzene with long-chain olefins (Catal Surv Asia (2014) 18:1-12; Catal Today (2017) 298:109-116). The biggest challenge with molecular sieve-catalyzed long-chain alkylbenzene synthesis is its short service life or low linearity. Y molecular sieve is widely used in the petrochemical industry and is the most widely used molecular sieve in the petrochemical industry. The acid distribution and diffusion properties of Y molecular sieve are key factors affecting the alkylation life and product linearity of linear long-chain olefins.

[0005] CN107867699A discloses a Y zeolite containing regular ultra-large micropores. By subjecting the selected Y zeolite to template and acid-base treatment, a Y zeolite with regular ultra-large micropores of 1 to 2 nm is constructed. Due to the abundant acid centers and suitable reaction channels provided by the regular ultra-large micropores, higher conversion rate and selectivity are achieved.

[0006] CN110562995A discloses a method for synthesizing nano Y zeolite and its application in the synthesis of linear alkylbenzenes. Due to the catalyst crystals, the diffusion resistance is small, and the activity and stability of the alkylation of long-chain olefins are improved. Summary of the Invention

[0007] After extensive research, the inventors discovered that Y molecular sieves, obtained through a special preparation process, possess a unique acid distribution and pore structure, which significantly influences the activity and selectivity for the alkylation of benzene with long-chain olefins. When the molecular sieve acid is distributed on the surface and the pore structure is optimally distributed, the alkylation activity and 2-LAB selectivity are excellent. This discovery led to the present invention.

[0008] The purpose of the present invention is to address the problem that the pore structure and acid distribution in the prior art are difficult to simultaneously control, and to provide a preparation method to prepare a Y molecular sieve with acid distributed on the surface and a reasonable pore distribution, and further apply the Y molecular sieve to the alkylation reaction of benzene with long-chain olefins.

[0009] In order to achieve the purpose of the present invention, the first aspect of the present invention provides a molecular sieve, characterized in that the ratio of the B value to the T value of the molecular sieve is 1.5 to 6, wherein the B value represents the mass fraction of Al2O3 on the surface of the molecular sieve, the T value represents the mass fraction of Al2O3 in the bulk phase of the molecular sieve, the mesopore volume accounts for 15% to 35% of the total pore volume, and the total acid content is higher than 2500 μmol / g.

[0010] The molecular sieve is preferably a silicon-aluminum molecular sieve, more preferably a molecular sieve selected from Y, MCM-22, beta or MOR, and the most preferred molecular sieve is Y molecular sieve.

[0011] The molecular sieve, the acid content of medium-strong acid accounts for preferably not less than 40% of the total acid content, more preferably 40-60%. The acid content is determined by NH3-TPD, wherein the desorption amount at 250-450°C is defined as the medium-strong acid content, and the total desorption amount is defined as the total acid content.

[0012] The molecular sieve has the characteristic of being aluminum-rich on the surface. Preferably, the ratio of the molecular sieve's B value to its T value is 2 to 4. The Al2O3 mass fraction in the molecular sieve bulk is determined by XRF, and the Al2O3 mass fraction on the molecular sieve surface is determined by XPS.

[0013] The molecular sieve preferably has a mesopore volume of 17% to 25% of the total pore volume. The ratio of the mesopore volume to the total pore volume is determined by BET.

[0014] In order to achieve the purpose of the present invention, the second aspect of the present invention provides a method for preparing a molecular sieve, which is characterized by comprising the following steps: calcining a sodium-type molecular sieve under a slightly positive pressure in an alkaline atmosphere; performing a first ammonium exchange on the calcined molecular sieve; performing cation adsorption on the molecular sieve after the first ammonium exchange; performing an acid treatment on the molecular sieve after the cation adsorption; performing a second ammonium exchange on the molecular sieve after the acid treatment and recovering the product.

[0015] In the preparation method, the sodium molecular sieve is preferably NaY molecular sieve, with a silicon-aluminum molecular ratio of 4 to 8, a relative crystallinity greater than 95%, and a sodium oxide mass fraction of 2 to 5%.

[0016] In the preparation method, the alkaline atmosphere is preferably an ammonia atmosphere with a concentration of 0.05 to 0.5M.

[0017] In the preparation method, the calcination under slightly positive pressure is preferably carried out at a gauge pressure of 0.01 to 0.1 MPa and a temperature of 400 to 600°C.

[0018] In the preparation method, the first ammonium exchange is performed using an ammonium salt solution, the ammonium salt is selected from one or more of ammonium nitrate, ammonium chloride or ammonium sulfate, the concentration of the ammonium salt solution is 50-200 g / L, the ammonium exchange temperature is 50-90° C., and the ammonium exchange time is 0.5-2 h.

[0019] In the preparation method, in the cation adsorption, the cation is selected from the group consisting of cations with an ion radius of 1 to For example, the cation is selected from NH4 + 、Ag + , K + 、Cs + The compound used for the cation adsorption can be selected from but not limited to one or more of ammonium nitrate, silver nitrate, potassium nitrate or cesium chloride.

[0020] In the preparation method, the cation concentration is 1-5 mmol / g molecular sieve, the mass ratio of the cation solution volume to the molecular sieve is 2-10 ml / g, and the adsorption temperature is 50-80°C.

[0021] In the preparation method, the acid treatment is performed with one or more of hydrochloric acid, nitric acid, fluorosilicic acid, ammonium fluoride, ammonium hexafluorosilicate, and ammonium bifluoride, preferably one or more of fluorosilicic acid, ammonium fluoride, ammonium hexafluorosilicate, and ammonium bifluoride. The acid concentration is 1 to 50 g / L, the mass ratio of the acid solution to the molecular sieve is 1 to 10:1, and the acid treatment temperature is 40 to 80°C.

[0022] In the preparation method, the second ammonium exchange is carried out using an ammonium salt solution, the ammonium salt is selected from one or more of ammonium nitrate, ammonium chloride or ammonium sulfate, the concentration of the ammonium salt solution is 50-200 g / L, the ammonium exchange temperature is 50-90° C., and the ammonium exchange time is 0.5-2 h.

[0023] In order to achieve the purpose of the present invention, the third aspect of the present invention provides a molecular sieve obtained by the above-mentioned preparation method.

[0024] In order to achieve the purpose of the present invention, the fourth aspect of the present invention provides a C8~C 26 The invention relates to a reaction method for preparing linear alkylbenzene by alkylation of linear olefins, which is characterized in that the molecular sieve of the invention or the molecular sieve obtained by the preparation method of the invention is used as the active component of the catalyst.

[0025] In the reaction method for preparing linear alkylbenzenes, the linear olefin can be a linear olefin having double bonds at terminal and internal positions, or a mixture of linear alpha olefins having double bonds at terminal positions. The linear olefin preferably has 8 to 28 carbon atoms, preferably 8 to 15 carbon atoms, and more preferably 10 to 14 carbon atoms. For ease of description, the present invention will refer to substantially linear olefins as simply olefins, and aromatic hydrocarbons will be described using benzene as an example.

[0026] The reaction method provided by the present invention is to carry out an alkylation reaction between olefins and benzene under reaction conditions in the presence of a catalyst having the Y molecular sieve of the present invention or the Y molecular sieve prepared by the preparation method of the present invention as an active component. The reaction conditions of the reaction method provided by the present invention minimize the isomerization of the alkyl group and minimize the polyalkylation of benzene (or the aromatic structure of other aromatic compounds), while simultaneously maximizing the consumption of olefins to maximize the product. The conditions of the alkylation reaction include a reaction temperature of 50 to 250°C, typically 70 to 200°C, a pressure in the reactor of 0.1 to 7 MPa, typically 2 to 4 MPa, a benzene-olefin ratio of 3:1 to 60:1, typically 4:1 to 40:1, and a feed olefin space velocity of 0.1 to 5 h -1 , preferably 0.3 to 3 hours -1 The alkylation reaction is carried out in the liquid phase and the pressure is always sufficient to ensure that the reaction is carried out in a single liquid phase. The feed olefins can be obtained from various sources, such as olefins obtained by dehydrogenation of paraffins, cracking, and oligomerization of small molecule olefins, which can be used in the present invention.

[0027] The alkylation of benzene with linear olefins presents significant challenges to the activity and selectivity of the reaction due to the long length of the olefins, resulting in activation and skeletal isomerization of the linear olefins. The molecular sieve provided by the present invention, on the one hand, features an aluminum-rich surface, with the acid primarily distributed on the outer surface, thereby improving the accessibility of the acid centers of the linear olefins and alkylbenzenes. On the other hand, the high acid content (particularly a high proportion of medium-strong acids) ensures high alkylation activity. Combined with a suitable pore structure including mesopores, this facilitates the alkylation reaction and suppresses side reactions such as skeletal isomerization. Therefore, the reaction method of the present invention achieves significant improvements in monoalkylbenzene selectivity, 2-LAB selectivity, and linearity while maintaining high stability and high olefin conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawing is an operating diagram of the molecular sieve provided by the present invention in the reaction of preparing linear alkylbenzene with benzene and dodecene. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials used can be obtained from commercial channels.

[0030] In the embodiments, the mass fraction of Al2O3 in the bulk phase of the molecular sieve is determined by XRF, the mass fraction of Al2O3 on the surface of the molecular sieve is determined by XPS, the ratio of the mesopore volume to the total pore volume is determined by BET, and the acid amount is determined by NH3-TPD, wherein the desorption amount at 250°C to 450°C is defined as the medium-strong acid amount, the total desorption amount is defined as the total acid amount, and the proportion of the medium-strong acid amount is the percentage of the medium-strong acid amount to the total acid amount.

[0031] Example 1

[0032] This example illustrates the Y molecular sieve and its preparation method of the present invention.

[0033] (1) Calcination: NaY molecular sieve (n(SiO2) / n(Al2O3)=5, relative crystallinity 96%, w(Na2O)=4%) was calcined at 550°C for 1 h under a pressure of 0.02 MPa while introducing 1 M ammonia solution at 0.1 ml / min during the calcination process;

[0034] (2) First ammonium exchange: the calcined molecular sieve was subjected to ammonium exchange using ammonium chloride solution at a concentration of 150 g / L, an exchange temperature of 80°C, an exchange time of 1 h, a solution to molecular sieve mass ratio of 4, and three exchanges using the same method, with w(Na2O) = 0.2%;

[0035] (3) Cation adsorption, the cation is NH4NO3, the ratio of ammonium nitrate solution to catalyst is 5 ml / g, and the cation concentration is 3 mmol / g;

[0036] (4) Acid treatment: (NH4)2SiF6 was used to treat the cationic adsorption molecular sieve with acid, the acid concentration was 10 g / L, the mass ratio of the acid solution to the catalyst was 5, and the acid treatment temperature was 60°C;

[0037] (5) Second ammonium exchange: ammonium exchange is performed on the acid-treated molecular sieve. Use ammonium chloride solution with a concentration of 150 g / L, an exchange temperature of 80°C, an exchange time of 1 h, a solution to molecular sieve mass ratio of 4, and exchange once using the same method, with w(Na2O) = 0.05%;

[0038] (6) The slurry is filtered, washed and dried to obtain the finished molecular sieve.

[0039] The molecular sieve Y1 was subjected to XRF, XPS, BET and NH3-TPD analysis, and the results of bulk Al2O3 mass fraction, surface Al2O3 mass fraction, mesopore volume ratio and acid content were shown in Table 1.

[0040] In Table 1, the bulk Al2O3 mass fraction is represented by T value, the surface Al2O3 mass fraction is represented by B value, and the mesopore volume is represented by V value. 介 The ratio of mesopore volume to total pore volume is expressed as V 介 / V 总 express.

[0041] Comparative Example 1

[0042] This comparative example illustrates the XRF, XPS, BET and NH3-TPD analysis results of commercially purchased USY molecular sieves, as shown in Table 1.

[0043] Comparative Example 2

[0044] The same as Example 1, except that (3), (4), and (5) are omitted, i.e., there is no cation adsorption, acid treatment, and second ammonium exchange step. The resulting comparative molecular sieve is numbered DY1-1. Molecular sieve DY1-1 was subjected to XRF, XPS, BET, and NH3-TPD analysis, and the results of the bulk Al2O3 mass fraction, surface Al2O3 mass fraction, mesopore volume fraction, and acid content are shown in Table 1.

[0045] Comparative Example 3

[0046] The same as Example 1, except that step (3) is omitted, i.e., the cation adsorption step is omitted. The comparative molecular sieve obtained is numbered DY1-2. Molecular sieve DY1-2 was subjected to XRF, XPS, BET, and NH3-TPD analysis, and the results of bulk Al2O3 mass fraction, surface Al2O3 mass fraction, mesopore volume fraction, and acid content are shown in Table 1.

[0047] Comparative Example 4

[0048] The same as Example 1, except that step (4), i.e., the acid treatment step, is omitted. The resulting comparative molecular sieve is numbered DY1-3. Molecular sieve DY1-3 was subjected to XRF, XPS, BET, and NH3-TPD analysis, and the results of bulk Al2O3 mass fraction, surface Al2O3 mass fraction, mesopore volume fraction, and acid content are shown in Table 1.

[0049] Comparative Example 5

[0050] The same as Example 1, except that Cu(NO3)2 was used as the cation in the cation adsorption step in step (3). The resulting comparative molecular sieve was numbered DY1-4. XRF, XPS, BET, and NH3-TPD analyses of molecular sieve DY1-4 yielded the bulk Al2O3 mass fraction, surface Al2O3 mass fraction, mesopore volume fraction, and acid content, as shown in Table 1.

[0051] Table 1

[0052]

[0053] As can be seen from Table 1, the method of Example 1 can simultaneously achieve the adjustment of aluminum distribution and pore structure while ensuring that the catalyst has a high acid content.

[0054] Example 2

[0055] Same as Example 1, except that the cation in (3) cation adsorption is Cs + (CsCl), numbered Y2.

[0056] Example 3

[0057] Same as Example 1, except that the cation in (3) cation adsorption is Ag + (AgNO3) is numbered Y3.

[0058] Example 4

[0059] Same as Example 1, except that the cation in (3) cation adsorption is K + (KNO3), numbered Y4.

[0060] Example 5

[0061] Same as Example 1, except that the acid used in (4) acid treatment is HNO3. Serial number: Y5.

[0062] Table 2

[0063]

[0064] Example 6

[0065] This example illustrates the MCM-22 molecular sieve and its preparation method of the present invention.

[0066] (1) Calcination: MCM-22 molecular sieve (n(SiO2) / n(Al2O3)=3.2, relative crystallinity 91%, w(Na2O)=2%) was calcined at 400°C under a pressure of 0.01 MPa for 1 h, while 0.05 M ammonia solution was introduced at 0.1 ml / min during the calcination process;

[0067] (2) First ammonium exchange: the calcined molecular sieve was subjected to ammonium exchange using ammonium chloride solution at a concentration of 50 g / L, an exchange temperature of 50°C, an exchange time of 0.5 h, a solution to molecular sieve mass ratio of 4, and three exchanges using the same method, with w(Na2O) = 0.5%;

[0068] (3) Cation adsorption, the cation is AgNO3, the ratio of cationic silver nitrate solution to catalyst is 2 ml / g, and the cation concentration is 5 mmol / g;

[0069] (4) Acid treatment: the cationic adsorption molecular sieve is treated with fluorosilicic acid, the acid concentration is 1 g / L, the mass ratio of the acid solution to the catalyst is 10, and the acid treatment temperature is 40°C;

[0070] (5) Second ammonium exchange: the acid-treated molecular sieve is subjected to ammonium exchange. An ammonium chloride solution with a concentration of 50 g / L, an exchange temperature of 50°C, an exchange time of 0.5 h, a solution to molecular sieve mass ratio of 4, and one exchange using the same method, with w(Na2O) = 0.08%;

[0071] (6) The slurry is filtered, washed and dried to obtain the finished molecular sieve.

[0072] The molecular sieve MCM-22 was subjected to XRF, XPS, BET and NH3-TPD analysis, and the results of bulk Al2O3 mass fraction, surface Al2O3 mass fraction, mesopore volume ratio and acid content were shown in Table 3.

[0073] Example 7

[0074] This example illustrates the beta molecular sieve and its preparation method of the present invention.

[0075] (1) Calcination, β molecular sieve (n(SiO2) / n(Al2O3)=15, relative crystallinity 88%, w(Na2O)=5%), calcined at 600°C under 0.1 MPa pressure for 1 h, while simultaneously introducing 0.5 M ammonia solution at 0.1 ml / min during the calcination process;

[0076] (2) First ammonium exchange: the calcined molecular sieve was subjected to ammonium exchange using ammonium chloride solution at a concentration of 200 g / L, an exchange temperature of 90°C, an exchange time of 2 h, a solution to molecular sieve mass ratio of 4, and three exchanges using the same method, with w(Na2O) = 0.3%;

[0077] (3) Cation adsorption, the cation is KNO3, the ratio of cationic potassium nitrate solution to catalyst is 10 ml / g, and the cation concentration is 1 mmol / g;

[0078] (4) Acid treatment: the cationic adsorption molecular sieve is treated with ammonium fluoride, the acid concentration is 50 g / L, the mass ratio of the acid solution to the catalyst is 1, and the acid treatment temperature is 40°C;

[0079] (5) Second ammonium exchange: ammonium exchange is performed on the acid-treated molecular sieve. Use ammonium chloride solution with a concentration of 200 g / L, an exchange temperature of 90°C, an exchange time of 2 h, a solution to molecular sieve mass ratio of 4, and exchange once using the same method, with w(Na2O) = 0.05%;

[0080] (6) The slurry is filtered, washed and dried to obtain the finished molecular sieve.

[0081] The molecular sieve β was subjected to XRF, XPS, BET and NH3-TPD analysis, and the results of bulk Al2O3 mass fraction, surface Al2O3 mass fraction, mesopore volume ratio and acid content were shown in Table 3.

[0082] Example 8

[0083] This example illustrates the MOR molecular sieve and preparation method of the present invention.

[0084] (1) Calcination: MOR molecular sieve (n(SiO2) / n(Al2O3)=10, relative crystallinity 100.3%, w(Na2O)=2.1%) was calcined at 500°C for 1 h under a pressure of 0.02 MPa, while 0.1 M ammonia solution was introduced at 0.1 ml / min during the calcination process;

[0085] (2) First ammonium exchange: the calcined molecular sieve was subjected to ammonium exchange using ammonium chloride solution at a concentration of 100 g / L, an exchange temperature of 70°C, an exchange time of 1 h, a solution to molecular sieve mass ratio of 4, and three exchanges using the same method, with w(Na2O) = 0.4%;

[0086] (3) Cation adsorption, the cation is CsCl, the ratio of cationic cesium chloride solution to catalyst is 5 ml / g, and the cation concentration is 2 mmol / g;

[0087] (4) Acid treatment: the cationic adsorption molecular sieve is treated with ammonium fluoride, the acid concentration is 20 g / L, the mass ratio of the acid solution to the catalyst is 5, and the acid treatment temperature is 80°C;

[0088] (5) Second ammonium exchange: ammonium exchange is performed on the acid-treated molecular sieve. Use ammonium chloride solution with a concentration of 100 g / L, an exchange temperature of 70°C, an exchange time of 1 h, a solution to molecular sieve mass ratio of 4, and exchange once using the same method, with w(Na2O) = 0.06%;

[0089] (6) The slurry is filtered, washed and dried to obtain the finished molecular sieve.

[0090] The molecular sieve MOR was subjected to XRF, XPS, BET and NH3-TPD analysis, and the results of bulk Al2O3 mass fraction, surface Al2O3 mass fraction, mesopore volume ratio and acid content were obtained as shown in Table 3.

[0091] Table 3

[0092]

[0093] Example 9

[0094] This example illustrates the use of the molecular sieve sample provided by the present invention in the preparation reaction of linear alkylbenzene.

[0095] The molecular sieve sample Y1 of Example 1 was used to carry out the alkylation reaction of benzene with dodecene at 120°C and 3 MPa, with a hydrocarbon feed space velocity of 0.354 h -1 , the molar ratio of feed benzene to olefin was 60. The conversion rate and product selectivity under the reaction conditions are shown in Table 4.

[0096] The molecular sieve of Example 1 was subjected to stability evaluation. The results are shown in the accompanying drawings. As can be seen from the accompanying drawings, the molecular sieve prepared in Example 1 has stable performance in the alkylation of dodecene with benzene. In the 100-h evaluation, the selectivity of monoalkylbenzene has been close to 100%, and the linearity of alkylbenzene has been above 92%.

[0097] Comparative Example 6-Comparative Example 10

[0098] Comparative Examples 6 to 10 illustrate the use of comparative molecular sieve samples in linear alkylbenzene preparation reactions.

[0099] The method is the same as that of Example 10, except that Y1 is replaced by comparative samples USY, DY1-1, DY1-2, DY1-3, and DY1-4, respectively. The results are shown in Table 4.

[0100] Table 4

[0101]

[0102] As can be seen from Table 4, due to its high acid content and suitable acid distribution and pore structure, the activity, stability and selectivity of molecular sieve Y1 in the alkylation of dodecene and benzene are much higher than those of the comparative sample, among which the selectivity of monoalkylbenzene is over 99%, the linearity of alkylbenzene reaches over 92%, and the proportion of 2-LAB reaches over 25% at 100% conversion.

[0103] Examples 10-13

[0104] The molecular sieve samples Y2-Y5 of Examples 2-5 were used to carry out the alkylation reaction of benzene with dodecene at 120°C and 3 MPa, respectively. The hydrocarbon feed space velocity was 0.354 h -1 , the molar ratio of feed benzene to olefin was 60. The conversion rate and product selectivity under the reaction conditions are shown in Table 5.

[0105] Table 5

[0106]

[0107] Examples 14-16

[0108] The molecular sieve samples MCM-22, Beta, and MOR of Examples 6-8 were used to carry out the alkylation reaction of benzene with dodecene at 120°C and 3 MPa, respectively. The hydrocarbon feed space velocity was 0.354 h -1 , the molar ratio of feed benzene to olefin was 60. The conversion rate and product selectivity under the reaction conditions are shown in Table 6.

[0109] Table 6

[0110]

Claims

1. A method for preparing a molecular sieve, characterized in that The method comprises the following steps: calcining a sodium molecular sieve under a slightly positive pressure in an alkaline atmosphere; performing a first ammonium exchange on the calcined molecular sieve; performing cation adsorption on the molecular sieve after the first ammonium exchange; performing an acid treatment on the molecular sieve after the cation adsorption; performing a second ammonium exchange on the molecular sieve after the acid treatment and recovering the product; wherein the sodium molecular sieve is selected from Y, MCM-22, beta or MOR; the calcination under the slightly positive pressure is performed at a gauge pressure of 0.01 to 0.1 MPa and a temperature of 400 to 600° C.; the cation is selected from NH4 + 、Ag + , K + 、Cs + One or more of the following, the cation concentration is 1 to 5 mmol / g molecular sieve, the mass ratio of the cation solution volume to the molecular sieve is 2 to 10 ml / g, the adsorption temperature is 50 to 80 ° C, the acid treatment, the acid treatment liquid is selected from one or more of hydrochloric acid, nitric acid, fluosilicic acid, ammonium fluoride, ammonium hexafluorosilicate, and ammonium bifluoride, the acid treatment liquid concentration is 1 to 50 g / L, the mass ratio of the acid treatment liquid to the molecular sieve is 1 to 10:1, and the acid treatment temperature is 40 to 80 ° C.

2. The preparation method according to claim 1, wherein The sodium type molecular sieve is a NaY molecular sieve, with a silicon-aluminum molecular ratio of 4 to 8, a relative crystallinity greater than 95%, and a sodium oxide mass fraction of 2 to 5%.

3. The preparation method according to claim 1, wherein The alkaline atmosphere is an ammonia atmosphere with a concentration of 0.05 to 0.5M.

4. The preparation method according to claim 1, wherein The first ammonium exchange is performed using an ammonium salt solution, the ammonium salt is selected from one or more of ammonium nitrate, ammonium chloride or ammonium sulfate, the concentration of the ammonium salt solution is 50-200 g / L, the ammonium exchange temperature is 50-90° C., and the ammonium exchange time is 0.5-2 h.

5. The preparation method according to claim 1, wherein The second ammonium exchange is performed using an ammonium salt solution, the ammonium salt is selected from one or more of ammonium nitrate, ammonium chloride or ammonium sulfate, the concentration of the ammonium salt solution is 50-200 g / L, the ammonium exchange temperature is 50-90° C., and the ammonium exchange time is 0.5-2 h.

6. The molecular sieve obtained by the preparation method according to any one of claims 1 to 5.

7. The molecular sieve according to claim 6, characterized in that The ratio of the B value to the T value of the molecular sieve is 1.5 to 6, wherein the B value represents the mass fraction of Al2O3 on the surface of the molecular sieve, and the T value represents the mass fraction of Al2O3 in the bulk phase of the silica-alumina molecular sieve. The mesopore volume accounts for 15% to 35% of the total pore volume, and the total acid content is higher than 2500 μmol / g.

8. The molecular sieve according to claim 7, characterized in that The ratio of the B value to the T value is 2-4.

9. The molecular sieve according to claim 6, characterized in that The acidity of the medium-strong acid in the molecular sieve accounts for no less than 40% of the total acidity. The acidity is determined by NH3-TPD, wherein the desorption amount at 250-450°C is defined as the medium-strong acidity.

10. The molecular sieve according to claim 9, characterized in that The proportion of the medium-strong acid in the total acid content is 40-60%.

11. The molecular sieve according to claim 6, characterized in that The molecular sieve is a Y-type molecular sieve.

12. The molecular sieve according to claim 7, characterized in that The volume of the mesopores accounts for 17% to 25% of the total pore volume.

13. A C8~C 26 A reaction method for preparing linear alkylbenzene by alkylation of linear olefins, characterized in that The molecular sieve according to claim 6 is used as the active component of the catalyst.

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