Synthesis of zsm-5 molecular sieve and zsm-5 molecular sieve with high hydrothermal stability

Abstract

The application belongs to the technical field of material synthesis, and relates to a synthesis method of ZSM-5 molecular sieve and high hydrothermal stability nanometer size ZSM-5 molecular sieve. The synthesis method comprises forming a crystallization liquid containing less weak acid amount of seeds; and stepwise crystallization under certain conditions and recovery of the ZSM-5 molecular sieve. The high hydrothermal stability nanometer size ZSM-5 molecular sieve still has relatively high crystallization retention and acid amount retention after very harsh hydrothermal aging. The ZSM-5 molecular sieve method can synthesize nanometer size ZSM-5 molecular sieve, the synthesis method is green and environment-friendly, and the synthesized molecular sieve has higher hydrothermal stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material synthesis, and relates to synthesis of ZSM-5 molecular sieve. BACKGROUND

[0002] Due to the limitation of the micropore channel of the conventional molecular sieve, diffusion and reaction can be enhanced by optimizing the length and width of the channel. The grain size of the molecular sieve affects the diffusion performance of the reactant and product molecules, and further affects the re-conversion and coking capacity of the target product such as low-carbon olefin. The size of the industrial molecular sieve is mainly between 2-5 microns. In order to improve the diffusion, researchers have developed nanoscale molecular sieves, and the size of the particles of these molecular sieves is generally between 50 nm and 1 micron. When the same mass is used, the number of nanoparticle molecular sieve orifices is more, and the channel is shorter, so that the reactant molecules can have more opportunities to enter the channel for reaction, and the product molecules can diffuse out of the channel more smoothly, avoiding the occurrence of re-conversion reaction, and thus the selectivity of the target product such as low-carbon olefin can be improved, and the selectivity of coke can be reduced when used for cracking of hydrocarbon oil.

[0003] At present, the synthesis of nanoscale ZSM-5 molecular sieves mainly includes a template method and a template-free method. The synthesis of ZSM-5 molecular sieves using a template has a high cost. The nanoscale ZSM-5 molecular sieves synthesized by the template-free method have poor size uniformity, poor crystallization, and are prone to produce impurity crystal phases. Moreover, the nanoscale molecular sieves synthesized at present have a low hydrothermal stability.

[0004] A method for synthesizing nanoscale ZSM-5 molecular sieves is to add seeds in a crystallization mother liquor, but a template is often still needed to be used, and a directing agent, a surfactant, microwave, ultrasonic treatment and the like are also needed to be added. The synthesis of ZSM-5 molecular sieves using a template has a high cost, and the addition of a directing agent, a surfactant, microwave, ultrasonic treatment and the like also increase the cost. It is difficult to synthesize nanoscale ZSM-5 molecular sieves with higher hydrothermal stability, and the obtained molecular sieves have problems of poor size uniformity, poor crystallization and being prone to produce impurity crystal phases. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a method for synthesizing nanoscale ZSM-5 molecular sieves, which does not use a template, a microwave, ultrasonic treatment and a directing agent.

[0006] Another technical problem to be solved by the present application is to provide nanoscale ZSM-5 molecular sieves with higher hydrothermal stability.

[0007] The nanoscale refers to that the average particle size of the molecular sieve particles is less than 1 micron, for example, greater than 0.01 micron and less than 1 micron.

[0008] The present application provides a method for synthesizing ZSM-5 molecular sieve, comprising the following steps:

[0009] (1) mixing alkali, optional aluminum source, silicon source, water and seeds uniformly to form a crystallization solution; wherein the seeds have a weak acid amount of no more than 35 ml / g;

[0010] (2) performing stepwise crystallization on the crystallization solution; the first step crystallization temperature is 5-90℃, and the crystallization time is more than 0.5h, for example, 0.5-48h, and the second step crystallization temperature is more than 120℃;

[0011] (3) recovering the ZSM-5 molecular sieve.

[0012] The present application also provides a ZSM-5 molecular sieve obtained by the above method.

[0013] The present application further provides a nano-sized ZSM-5 molecular sieve with high hydrothermal stability, wherein the ZSM-5 molecular sieve is subjected to phosphorus modification to obtain a modified molecular sieve, and the modified molecular sieve after aging at 800℃ under 100% water vapor for 30h has a crystalline retention degree of no less than 90% and / or an acid amount retention degree of no less than 30% relative to the unaged modified molecular sieve. The phosphorus modification comprises: impregnating phosphorus at a molar ratio of P / Al=1. The acid amount retention degree=(acid amount of the modified molecular sieve after aging) / (acid amount of the unaged modified molecular sieve)×100%; and the acid amount is measured by NH3-TPD method.

[0014] The crystalline retention degree=(relative crystallinity of the modified molecular sieve after aging) / (relative crystallinity of the unaged modified molecular sieve)×100%.

[0015] The method for synthesizing ZSM-5 molecular sieve provided by the present application does not use template agent, does not need to add directing agent and surfactant, and does not need to use microwave and ultrasonic treatment, etc., and can synthesize small crystal grain ZSM-5 molecular sieve at a lower cost, and is a green, simple and efficient method for preparing nano-sized ZSM-5 molecular sieve. The synthesis method has good repeatability and high stability. The synthesized ZSM-5 molecular sieve has higher hydrothermal stability, and the hydrothermal stability is obviously better than that of existing large crystal grain ZSM-5 molecular sieve. In an optimal case, the nano-sized ZSM-5 molecular sieve with more uniform secondary particle size distribution can be synthesized.

[0016] The ZSM-5 molecular sieve obtained by the method for synthesizing ZSM-5 molecular sieve provided by the application is an aggregate of nano ZSM-5 molecular sieve grains, is formed by aggregation and / or growth of grains with an average grain size of not more than 100 nm, has small secondary particles, for example, the size of the secondary particles can be less than 900 nm, has uniform particle size, high crystallinity, and no other molecular sieve impurities, and has higher hydrothermal stability. The hydrothermal stability is obviously better than that of existing small-grain ZSM-5 molecular sieves and that of existing large-grain ZSM-5 molecular sieves.

[0017] The ZSM-5 molecular sieve provided by the application can be used for preparing a gas adsorbent, a hydrocarbon catalytic cracking catalyst, a hydrocracking catalyst, an aromatic hydrocarbon alkylation catalyst, an alkane isomerization catalyst, a toluene disproportionation catalyst, a xylene isomerization catalyst, a dewaxing reaction catalyst, a methanol-to-olefin catalyst, a methanol-to-aromatic hydrocarbon catalyst, an esterification catalyst, or an acylation reaction catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The XRD spectrum of the molecular sieve Z-1 synthesized in Example 1.

[0019] Figure 2 The SEM electron microscope image of the Z-1 molecular sieve synthesized in Example 1.

[0020] Figure 3 The SEM electron microscope image of the Z-2 molecular sieve synthesized in Example 2.

[0021] Figure 4 The SEM electron microscope image of the D-1 molecular sieve synthesized in Comparative Example 1. DETAILED DESCRIPTION

[0022] According to the method for synthesizing ZSM-5 molecular sieve provided by the application, in step (1), the base, the optional aluminum source, the silicon source, water, and the seed crystals are mixed to form a crystallization liquid. The seed crystals can be one or more of ZSM-5 molecular sieves or a catalyst containing ZSM-5 molecular sieves, wherein the content of the ZSM-5 molecular sieves in the catalyst containing ZSM-5 molecular sieves is preferably not less than 8 wt%, for example, 8-99 wt%, for example, 35-70 wt%.

[0023] Preferably, the volume of particles with a particle diameter of not more than 80 microns in the catalyst seed crystal containing ZSM-5 molecular sieves accounts for more than 95% of the total particle volume, and the particle size is measured by a laser particle size method, see the standard NB / SH / T 0951-2017.

[0024] According to the method for synthesizing ZSM-5 molecular sieve provided by the application, the specific surface area of the seed crystals is preferably not less than 180 m 2 / g, for example, 180-500 m 2 / g,

[0025] According to the method for synthesizing ZSM-5 molecular sieve, the weak acid amount of the seed crystal is not more than 35 ml / g, for example, 0-30 ml / g or 0-25 ml / g or 0-20 ml / g or 0.5-30 ml / g or 0.5-20 ml / g; wherein the weak acid amount is the 120-300 ℃ acid amount measured by the NH3-TPD method, and the acid amount value is the volume of ammonia gas desorbed at 120-300 ℃ converted into the volume of ammonia gas under standard state.

[0026] According to the method for synthesizing ZSM-5 molecular sieve, the amount of the alkali, the silicon source and the aluminum source is such that the molar ratio of the oxides of the mineralizer metal, the silicon source SiO2, the aluminum source Al2O3 and H2O in the crystallization solution is (0.01-0.15):1:(0.000-0.025):(5-100), wherein the molar amount of the silicon source SiO2 is obtained by converting the silicon source into SiO2 in terms of the molar amount of silicon element, the molar amount of the aluminum source Al2O3 is obtained by converting the aluminum source into Al2O3 in terms of the molar amount of aluminum element, and the molar amount of the oxide of the mineralizer metal is the total amount of the molar amount of the mineralizer metal element in the alkali, the aluminum source and the silicon source converted into the molar amount of the oxide of the mineralizer metal, the mineralizer metal being alkali metal (denoted as M) and / or alkaline earth metal (denoted as M'), preferably alkali metal, the oxide of the alkali metal being M2O, and the oxide of the alkaline earth metal being M'O.

[0027] According to the method for synthesizing ZSM-5 molecular sieve, generally, the amount of the seed crystal added is not more than 30 wt% of the amount of the silicon source SiO2, for example, 0.5-30 wt% or 5-15 wt%, the amount of the silicon source SiO2 being the amount of SiO2 converted from silicon element in the silicon source.

[0028] In an embodiment, the mineralizer metal is alkali metal, the alkali metal is denoted as M, the molar ratio of M2O:SiO2 is 0.05-0.15:1, the molar ratio of Al2O3:SiO2 is 0-0.04:1, and the molar ratio of H2O:SiO2 is 10-30:1, the SiO2 being the silicon source SiO2 and the Al2O3 being the aluminum source Al2O3. The weight ratio of the seed crystal / SiO2 is preferably 0.05-0.15:1.

[0029] Preferably, the pH value of the crystallization solution obtained in step (1) is preferably 11.0-13.5.

[0030] According to the method for synthesizing ZSM-5 molecular sieve, in step (1), the aluminum source can be one or more of aluminum hydroxide, pseudoboehmite, sodium metaaluminate, aluminum isopropoxide, aluminum sulfate, aluminum acetate, elemental aluminum, aluminum nitrate, aluminum sol, aluminum oxide and aluminum chloride.

[0031] According to the method for synthesizing ZSM-5 molecular sieve, in step (1), the silicon source can be one or more of silica sol, white carbon black, tetramethyl orthosilicate, tetraethyl orthosilicate, sodium silicate, water glass, solid silica gel and sodium fluorosilicate.

[0032] According to the method for synthesizing ZSM-5 molecular sieve, in step (1), the base can be one or more of alkali metal and / or alkaline earth metal and / or nitrogen basic compounds such as sodium carbonate, sodium hydroxide, sodium bicarbonate, potassium carbonate, potassium bicarbonate, potassium hydroxide, ammonia, calcium hydroxide.

[0033] In one embodiment, the base includes a first base and / or a second base, for example, a first base and an optional second base, wherein the first base is a mineralizer base such as one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, potassium carbonate, potassium bicarbonate or potassium hydroxide, and the second base is a pH adjusting base such as ammonia, and the pH of the crystallization solution can be adjusted to preferably 11-13.5 by adding the second base.

[0034] According to the method for synthesizing ZSM-5 molecular sieve, the water can be one or more of cation exchange water, anion exchange water, deionized water and distilled water.

[0035] According to the method for synthesizing ZSM-5 molecular sieve, in step (2), the crystallization solution is subjected to stepwise crystallization; in the first step of crystallization, the crystallization temperature is 5-90°C, and the crystallization time is 0.5-48h. In the second step of crystallization, the crystallization temperature is greater than 120°C.

[0036] According to the method for synthesizing ZSM-5 molecular sieve, the crystallization temperature in the first step of crystallization is preferably 25-90°C, for example, 25-80°C or 25-70°C.

[0037] According to the method for synthesizing ZSM-5 molecular sieve, the crystallization time in the first step of crystallization is preferably 0.5-24h, for example, 0.5-20h or 8-20h.

[0038] According to the method for synthesizing ZSM-5 molecular sieve, the crystallization temperature in the second step of crystallization is preferably greater than 120°C and not more than 200°C.

[0039] The crystallization time of the second step crystallization is preferably 3-72 hours.

[0040] The crystallization temperature of the second step crystallization is preferably 150-180°C, for example 160-175°C, and the crystallization time of the second step crystallization is preferably 10-60 hours, for example 20-60 hours or 20-48 hours.

[0041] The temperature is raised to the crystallization temperature of the second step crystallization after the first step crystallization, and the temperature raising rate is preferably 2-10°C / min.

[0042] The first step crystallization can be crystallization under stirring or crystallization under static state, and the stirring speed under stirring is 1-1000 rpm.

[0043] The second step crystallization is preferably under stirring, and the stirring speed is 1-1000 rpm, and the crystallization product liquid is obtained after the second step crystallization.

[0044] The step (3) recovers the molecular sieve, and the recovery generally includes separation, optional washing, optional drying and optional calcination.

[0045] The separation can be separated by filtration or centrifugation, and the conventional filtration or centrifugation method known by those skilled in the art can be used. The ZSM-5 molecular sieve is obtained by separation.

[0046] The separated ZSM-5 molecular sieve can be further washed to wash away the unreacted raw materials and other impurities. The washing can refer to the washing method in the prior art, for example, water washing can be used, and then filtration or centrifugation is performed.

[0047] The washed ZSM-5 molecular sieve can be further exchanged, and the exchange method is known by those skilled in the art, for example, ammonium salt aqueous solution is used for exchange.

[0048] The calcination can use conventional calcination, for example, calcination can be performed at 400-600°C for 1-5 hours.

[0049] The method for synthesizing ZSM-5 molecular sieve according to the present application, in one embodiment, comprises the following steps:

[0050] (1) dissolving the base and the aluminum source into water, then adding the silicon source, mixing uniformly, and then adding the seed crystal to obtain a crystallization liquid;

[0051] (2) the crystallization solution is pre-crystallized (first step crystallization) at 5-90°C, for example 25-80°C, for 0.5-48h, with a stirring speed of 0-1000rpm (it is meant that the stirring speed can be greater than 0-1000rpm or no stirring); then crystallized (second step crystallization) at greater than 120°C and not more than 200°C, for example 150-180°C, for 3-72h;

[0052] (3) after the crystallization, the ZSM-5 molecular sieve is obtained by filtration or centrifugation, washing, drying and calcination. In this embodiment, the ZSM-5 molecular sieve obtained has a more uniform particle size distribution.

[0053] The present application further provides the ZSM-5 molecular sieve obtained by the method for synthesizing ZSM-5 molecular sieve.

[0054] The present application further provides a nano-sized ZSM-5 molecular sieve with high hydrothermal stability, wherein the ZSM-5 molecular sieve is modified by phosphorus to obtain a modified molecular sieve, and after the modified molecular sieve is aged at 800°C under 100% water vapor for 30h, the crystallinity retention is not less than 90% and / or the acid amount retention measured by NH3-TPD is not less than 30% compared with the unaged modified molecular sieve. The phosphorus modification includes impregnating phosphorus at a molar ratio of P / Al=1, and optionally further includes drying and / or calcination.

[0055] According to any one of the above technical solutions, the particles of the ZSM-5 molecular sieve are secondary particles formed by aggregation of primary particles, and the average particle size of the secondary particles is preferably 100-900nm.

[0056] According to any one of the above technical solutions, the secondary particles have good uniformity in particle size distribution. Preferably, the variance of the particle size of the secondary particles is not more than 0.03, for example not more than 0.015μm 2 or not more than 0.01μm 2 or 0.001-0.0012μm 2 . The ZSM-5 molecular sieve has good hydrothermal stability.

[0057] According to any one of the above technical solutions, the primary particles are ZSM-5 molecular sieve crystals, and the average crystal size of the primary particles is not more than 100nm, for example the average crystal size of the primary particles is 10-100nm, for example 35-95nm.

[0058] According to any one of the above technical solutions, in an embodiment, the average particle size of the ZSM-5 molecular sieve secondary particles is 100-900 nm, and the secondary particles are formed by growth and / or accumulation of crystals with an average crystal grain size of not more than 100 nm in a close and / or loose manner.

[0059] According to any one of the above technical solutions, the modified molecular sieve obtained after the ZSM-5 molecular sieve is modified by phosphorus has a crystallinity retention of not less than 90%, for example, 90-99% or 91-98% after aging at 800°C under 100% water vapor for 30 hours, relative to the modified molecular sieve without aging, indicating that the ZSM-5 molecular sieve has good hydrothermal stability. The phosphorus modification includes impregnating phosphorus according to P / Al = 1 (molar ratio), optionally drying, and optionally calcining to obtain the modified molecular sieve; the impregnation of phosphorus can be performed by using phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or ammonium phosphate by equal volume impregnation or excess impregnation, and the impregnation makes the P / Al molar ratio in the molecular sieve equal to 1. In an embodiment, the phosphorus modification includes equal volume impregnation of phosphorus according to P / Al = 1, drying, and calcination at 550°C for 3 hours.

[0060] According to any one of the above technical solutions, the modified molecular sieve obtained after the ZSM-5 molecular sieve is modified by phosphorus has an acid retention of not less than 30%, for example, 32-45% or 35-42% after aging at 800°C under 100% water vapor for 30 hours, relative to the modified molecular sieve without aging, as determined by NH3-TPD. This indicates that the ZSM-5 molecular sieve has good hydrothermal stability. The phosphorus modification includes impregnating phosphorus according to P / Al = 1 (molar ratio), optionally drying, and optionally calcining to obtain the modified molecular sieve; the impregnation of phosphorus can be performed by using phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or ammonium phosphate by equal volume impregnation or excess impregnation, and the phosphorus modification makes the P / Al molar ratio in the molecular sieve equal to 1. In an embodiment, the phosphorus modification includes equal volume impregnation of phosphorus according to P / Al = 1, drying, and calcination at 550°C for 3 hours.

[0061] According to any one of the above technical solutions, in an embodiment, the ZSM-5 molecular sieve has abundant intercrystalline mesoporous structures, in which the mesopore volume ratio is more than 35%, for example, the mesopore volume ratio is not less than 35% and not more than 86%, for example, 42-65% or 40-60%. The mesopore volume ratio refers to the ratio of the mesopore volume to the total pore volume. The mesopore volume and the total pore volume are determined by the nitrogen adsorption capacity method, the specific surface area is calculated according to the BET equation, and the pore size distribution is calculated by the BJH method. The measurement method is described in NB / SH / T0959-2017.

[0062] The following examples are used to further illustrate the present application, but should not be construed as limiting the practical scope of the present application.

[0063] ZSM-5 as seed crystals was purchased from Nankai Catalyst Co., Ltd.

[0064] The ZSM-5-containing catalyst was purchased from Sinopec Catalyst Qilu Branch Co., Ltd., sieved, and particles with a particle diameter less than 80 microns were collected.

[0065] The reagents used are as follows:

[0066] Silica sol (SiO2 content 30 wt%, pH 9.8),

[0067] Water glass (Na2O content 80 g / L, modulus 3.3),

[0068] Tetraethyl orthosilicate (TEOS, analytical pure, concentration 99 wt%),

[0069] The other raw materials are analytical pure reagents.

[0070] In the examples and comparative examples, in order to compare the hydrothermal stability, the synthesized molecular sieve was modified with phosphorus, the phosphorus-modified molecular sieve was hydrothermally aged, the acid amount and the relative crystallinity of the phosphorus-modified molecular sieve before and after the hydrothermal aging were measured, and the acid amount retention and the crystallinity retention were calculated; wherein:

[0071] The phosphorus modification method is as follows: the molecular sieve is impregnated with diammonium hydrogen phosphate in equal volume according to P / Al = 1 (amount of substance), then dried and calcined at 550°C for 3h to obtain the modified molecular sieve (also referred to as “unaged molecular sieve (after phosphorus modification) ”); the hydrothermal aging conditions are as follows: the modified molecular sieve is treated at 800°C under 100% water vapor for 30h, and is named “aged molecular sieve (after phosphorus modification)”;

[0072] The acid amount is measured by the NH3-TPD method, and the testing method is as follows: 0.1g of the sample is pretreated by heating to 550°C under a helium atmosphere, and maintained for 1h, with a helium flow rate of 50ml / min. Then, the temperature is lowered to 120°C, and a NH3 / He mixed gas with a NH3 content of 10% (volume content) is introduced, with a flow rate of 50ml / min, which is changed to He after 10min, and the helium flow rate is 50ml / min for 60min. Then, the temperature is raised to 550°C at a rate of 10°C / min for desorption. The flow rate of the gas is the flow rate under standard conditions;

[0073] The relative crystallinity was measured by XRD. The powder X-ray diffraction (XRD) was measured on an X-ray diffractometer with Cu-Ka radiation (λ = 1.5406 Å) at 2θ of 5°-50°, the scanning speed was 2° min -1 . Refer to NB / SH / T6024-2021.

[0074] The acid retention degree = the acid amount of the aged molecular sieve (after phosphorus modification) / the acid amount of the non-aged molecular sieve (after phosphorus modification) x 100%

[0075] The crystallinity retention degree = the relative crystallinity of the aged molecular sieve (after phosphorus modification) / the relative crystallinity of the non-aged molecular sieve (after phosphorus modification) x 100%

[0076] The molecular sieve crystal and aggregate particle size was measured by SEM, and the measurement method was as follows: the maximum size (referred to as particle length or particle size) of 10 aggregates (referred to as molecular sieve particles or secondary particles) was randomly measured, and the average value was the average particle size. The maximum size (referred to as crystal particle size or primary particle size) of 10 crystal particles was randomly measured, and the average value was the average crystal particle size or average particle size. The uniformity of particle size was characterized by variance, and the calculation formula of variance was as follows:

[0077]

[0078] S 2 is the sample variance, X is the variable, is the sample mean, and n is the number of samples.

[0079] Example 1

[0080] In the crystallization solution, the alkali, silicon source and aluminum source were configured in the following ratio (molar ratio): 0.11 M2O:SiO2:0.01 Al2O3:20 H2O; wherein M represents Na, the silicon source is silica sol, the aluminum source is aluminum sulfate, and the alkali is sodium hydroxide. The above ratio does not calculate the seed crystal. The seed crystal is ZSM-5 molecular sieve seed crystal, the specific surface area of the seed crystal is 320 m 2 / g, the weak acid amount is 15 ml / g, and the seed crystal / SiO2 is 0.1 (weight ratio).

[0081] Sodium hydroxide and aluminum sulfate were added into water in sequence, and after being uniformly mixed, silica sol was added. After stirring for 1 h, ZSM-5 molecular sieve seed crystal was added to obtain a crystallization solution. Then, the crystallization solution was placed at 25℃ for 8 h, and then heated to 175℃ at a heating rate of 5℃ / min for crystallization for 28 h, and the stirring speed was 300 rpm. After crystallization, solid-liquid separation, washing (using deionized water to leach according to a solid-liquid weight ratio of 1:10), drying, and calcination (calcination at 550℃ for 3 h, same below) were performed to obtain nano-sized ZSM-5 molecular sieve Z-1.

[0082] XRD (attached Figure 1 ) measurement showed that the crystal of Z-1 was ZSM-5 molecular sieve, and SEM (attached Figure 2 ) scanning electron microscope image showed that the average particle size (secondary particle average particle size) of Z-1 was 650 nm, which was formed by aggregation / growth of nanocrystals with an average crystal grain size of 92 nm.

[0083] As can be seen from Table 1, the crystallization retention and acid retention of the ZSM-5 molecular sieve Z-1 synthesized according to the present application were 97% and 38% respectively, while the results of the comparative ZSM-5 molecular sieve (conventional crystal grain molecular sieve, named C (provided by SINOPEC Qilu Catalyst Branch, with a silicon-aluminum ratio of 25)) measured under the same conditions were 81% and 31% respectively. Compared with the comparative molecular sieve, the crystallization retention and acid retention of the ZSM-5 molecular sieve prepared according to the present application were obviously higher, and the hydrothermal stability was excellent.

[0084] Example 2

[0085] The crystallization materials (silicon source, aluminum source and alkali) in the crystallization liquid were configured according to the following molar ratio: 0.13 Na2O:SiO2:0.014 Al2O3:20 H2O, and the seed crystal was not calculated in the above ratio; the silicon source was water glass, the aluminum source was sodium aluminate (caustic ratio was 1.4), and the alkali was sodium hydroxide. The seed crystal was ZSM-5 molecular sieve seed crystal, the specific surface area of the seed crystal was 275 m 2 / g, the weak acid amount was 10 ml / g, and the seed crystal / SiO2 was 0.2 (weight). The sodium hydroxide and sodium aluminate were added into water in sequence, and after being mixed uniformly, the water glass was added. After being stirred for 1 h, the seed crystal ZSM-5 molecular sieve was added. Then, the temperature was increased (temperature increasing rate was 5 ℃ / min) to 160 ℃, and the crystallization was carried out for 48 h at a stirring speed of 300 rpm. After the crystallization, the solid-liquid separation, washing (the same below), drying and calcination (the same below) were carried out to obtain the nanometer-sized ZSM-5 molecular sieve Z-2. The SEM (attached Figure 3 ) scanning electron microscope image showed that the average particle size was 350 nm, which was formed by aggregation / growth of nanocrystals with an average crystal grain size of about 50 nm.

[0086] Example 3

[0087] The crystallization materials (silicon source, aluminum source and alkali) in the crystallization liquid were configured according to the following molar ratio: 0.08 M2O:SiO2:0.04 Al2O3:30 H2O; wherein, M represented alkali metal, the silicon source was water glass, the aluminum source was aluminum nitrate, and the alkali was potassium hydroxide. The seed crystal was ZSM-5 molecular sieve, and the specific surface area was 350 m 2 / g, weak acid amount 16 ml / g, and seed / SiO2=0.15 (weight). The potassium hydroxide and aluminum nitrate were added to water in sequence, and after being mixed uniformly, the water glass was added. After being stirred for 1 h, the seed ZSM-5 molecular sieve was added. Then, the mixture was stirred at 70°C for 20 h at a stirring speed of 200 rpm, and then the temperature was increased (temperature increasing rate 5°C / min) to 170°C for crystallization for 20 h, and the stirring speed was not changed. After crystallization, the nano-sized ZSM-5 molecular sieve Z-3 was obtained by solid-liquid separation, washing, drying, and calcination.

[0088] Example 4

[0089] The crystallization material was configured into a crystallization liquid in the following molar ratio: 0.09 M2O:SiO2:10H2O; wherein M represents an alkali metal, the silicon source was TEOS, and the base was sodium hydroxide. The seed was a catalyst containing ZSM-5 molecular sieve (50 wt% ZSM-5, other components being kaolin and aluminum sol, based on dry basis) with a specific surface area of 220 m 2 / g, weak acid amount 8 ml / g, and 100% of the particle diameter was not more than 80 microns, and seed / SiO2=0.08 (weight). The sodium hydroxide was added to water, and after being mixed uniformly, the TEOS was added. After being stirred for 1 h, the seed was added. Then, the mixture was stirred at 80°C for 0.5 h at a stirring speed of 300 rpm, and then the temperature was increased to 150°C for crystallization for 60 h, and the stirring speed was not changed. After crystallization, the ZSM-5 molecular sieve Z-4 was obtained by solid-liquid separation, washing, drying, and calcination. The average particle size of Z-4 was 400 nm, and the average crystal grain size was 55 nm.

[0090] Example 5

[0091] The crystallization material (referring to the silicon source, the aluminum source, the base, and water) was configured into a crystallization liquid in the following molar ratio: 0.1 Na2O:SiO2:0.02 Al2O3:10 H2O; wherein the silicon source was silica sol, the aluminum source was sodium aluminate, and the base was sodium hydroxide. The seed was ZSM-5 molecular sieve, and the specific surface area of the seed was 302 m 2 / g, weak acid amount 0.9 ml / g, and seed / SiO2=0.12 (weight). The sodium hydroxide and sodium aluminate were added to water in sequence, and after being mixed uniformly, the silica sol was added. After being stirred for 1.5 h, the seed ZSM-5 was added. Then, the mixture was stirred at 70°C for 24 h at a stirring speed of 200 rpm, and then the temperature was increased to 170°C for crystallization for 30 h, and the stirring speed was not changed. After crystallization, the nano-sized ZSM-5 molecular sieve Z-5 was obtained by solid-liquid separation, washing, drying, and calcination. The average particle size of Z-5 was 590 nm, and the average crystal grain size was 82 nm.

[0092] Example 6

[0093] The method of Example 1 was followed, except that the sodium hydroxide solution and the aluminum sulfate solution were added to the silica sol in succession, and after mixing well, the ZSM-5 seed crystals were added after stirring for 1 h to obtain a crystallization liquid. After crystallization, solid-liquid separation, washing, drying, and calcination were performed to obtain the nano-sized ZSM-5 molecular sieve Z-6.

[0094] The properties of Z-6 molecular sieve were as follows: the average particle size was 680 nm, and the average crystal grain size was 89 nm.

[0095] Comparative Example 1

[0096] The crystallization liquid was prepared by mixing the following crystallization materials (molar ratio) : 0.11 M2O: SiO2: 0.01 Al2O3: 20 H2O; wherein M represents an alkali metal, the silicon source was silica sol, the aluminum source was aluminum sulfate, and the base was sodium hydroxide. The specific surface area of the ZSM-5 molecular sieve seed crystals was 301 m 2 / g, the weak acid amount was 37 ml / g, and the seed crystal / SiO2 ratio was 0.1 (by weight). The sodium hydroxide and the aluminum sulfate were added to water in succession, and after mixing well, the silica sol was added, and after stirring for 1 h, the ZSM-5 seed crystals were added. Then, the mixture was allowed to stand at 25 °C for 8 h, and then the temperature was increased to 175 °C, and the mixture was crystallized for 28 h at a stirring speed of 300 rpm. After crystallization, solid-liquid separation, washing, drying, and calcination were performed to obtain the small crystal grain ZSM-5 molecular sieve D-1. The SEM scanning electron microscope image (attached Figure 4 ) showed that the average particle size of the synthesized ZSM-5 was about 1820 nm, which was significantly larger than that of Z-1. The modified molecular sieve was obtained by phosphorus modification of D-1, and the crystallization retention and the acid amount retention of the modified molecular sieve after hydrothermal aging were 90% and 30%, respectively. Compared with Z-1, the crystallization retention and the acid amount retention of the comparative molecular sieve were both significantly lower, indicating that the hydrothermal stability of the comparative molecular sieve was not as good as that of Z-1.

[0097] Comparative Example 2

[0098] The method of Example 1 was followed, except that one-step crystallization was used, and the mixture was crystallized at 175 °C for 28 h.

[0099] The crystallization liquid was prepared by mixing the following crystallization materials (molar ratio) : 0.11 M2O: SiO2: 0.01 Al2O3: 20 H2O; wherein M represents Na, and the seed crystal was not included in the ratio. The specific surface area of the ZSM-5 molecular sieve seed crystals was 320 m 2 / g, weak acid amount is 15 ml / g, and the ratio of the seed crystal to SiO2 is 0.1 (by weight). The sodium hydroxide and aluminum sulfate are added into water in sequence, and then the silica sol is added after being uniformly mixed. After stirring for 1 h, the seed crystal ZSM-5 is added. Then, the temperature is increased to 175°C at a rate of 5°C / min, and the crystallization is performed for 28 h at a stirring speed of 300 rpm. After the crystallization, the solid-liquid separation, washing (using deionized water to elute according to a solid-liquid weight ratio of 1:10), drying, and calcination (calcination at 550°C for 3 h) are performed to obtain the ZSM-5 molecular sieve D-2.

[0100] Comparative Example 3

[0101] The crystallization material is configured into a crystallization liquid according to the following molar ratio: 0.11 M2O:SiO2:0.01 Al2O3:20 H2O; wherein M represents an alkali metal, the silicon source is silica sol, the aluminum source is aluminum sulfate, and the base is sodium hydroxide. The seed crystal is ZSM-5 molecular sieve seed crystal, and the specific surface area of the seed crystal is 320 m 2 / g, and the ratio of the seed crystal to SiO2 is 0.1 (by weight).

[0102] The sodium hydroxide and aluminum sulfate are added into water in sequence, and then the silica sol is added after being uniformly mixed. After stirring for 1 h, the seed crystal ZSM-5 is added. Then, the temperature is increased to 175°C at a rate of 5°C / min, and the crystallization is performed for 28 h at a stirring speed of 300 rpm. After the crystallization, the solid-liquid separation, washing, drying, and calcination are performed to obtain the small-crystal ZSM-5 molecular sieve D-3. The average particle size of the synthesized ZSM-5 is about 1000 nm, which is obviously larger than that of Z-1, and the crystallinity is only 16.5%. The modified molecular sieve is obtained by phosphorus modification of D-3. The crystallinity retention and acid amount retention of the modified molecular sieve after hydrothermal aging are 83% and 28%, respectively. Compared with Z-1, the crystallinity retention and acid amount retention of the comparative molecular sieve are obviously lower, which indicates that the hydrothermal stability of the comparative molecular sieve is not as good as that of Z-1.

[0103] The properties of the molecular sieves synthesized in the above Examples 1-6 and Comparative Examples are shown in Table 1.

[0104] Table 1

[0105]

[0106] As shown in Table 1, the molecular sieve provided by the application has a smaller particle size, which is less than 0.9 microns. The length variance of the particle is small, which indicates that the particle size distribution is more uniform. The ZSM-5 molecular sieve provided by the application has higher hydrothermal stability.

Claims

1. A ZSM-5 molecular sieve, characterized in that, The modified molecular sieve obtained by phosphorus modification of the ZSM-5 molecular sieve is aged at 800℃ and 100% water vapor for 30 hours. The crystal retention is not less than 90% and / or the acid retention measured by NH3-TPD is not less than 30% relative to the modified molecular sieve. The phosphorus modification includes impregnation with phosphorus at a P / Al molar ratio of 1.

2. The ZSM-5 molecular sieve according to claim 1, characterized in that, The ZSM-5 molecular sieve particles are secondary particles formed by the aggregation of primary particles, and the average particle size of the secondary particles is 100-900 nm.

3. The ZSM-5 molecular sieve according to claim 1 or 2, characterized in that, The variance of the size of the secondary particles does not exceed 0.03 μm. 2 .

4. The ZSM-5 molecular sieve according to claim 1, characterized in that, The average grain size of the primary particles in the ZSM-5 molecular sieve does not exceed 100 nm.

5. The ZSM-5 molecular sieve according to claim 1, characterized in that, The modified molecular sieve obtained by phosphorus modification of the ZSM-5 molecular sieve was aged at 800℃ and 100% volume water vapor for 30 hours. Compared with the unaged modified molecular sieve, the crystal retention was 90-99% and / or the acid retention determined by NH3-TPD was 32-45%. The phosphorus modification included impregnation with phosphorus according to the molar ratio of P / Al = 1.

6. The ZSM-5 molecular sieve according to claim 1, characterized in that, The ZSM-5 molecular sieve has a mesopore volume ratio of 35% to 86% or 40% to 60%.

7. The ZSM-5 molecular sieve according to claim 3, characterized in that, The variance of the size of the secondary particles does not exceed 0.01 μm. 2 .

8. The ZSM-5 molecular sieve according to claim 4, characterized in that, The average grain size of the primary particles is 10-100 nm.

9. The ZSM-5 molecular sieve according to claim 5, characterized in that, The phosphorus modification involves impregnating phosphorus in equal volumes according to a P / Al molar ratio of 1, drying, and calcining at 550°C for 3 hours.

10. A method for synthesizing ZSM-5 molecular sieves, comprising the following steps: (1) A crystallization solution is formed by mixing alkali, silicon source, water, and seed crystals, or by mixing alkali, aluminum source, silicon source, water, and seed crystals; wherein, The amount of weak acid in the seed crystal is no more than 35 ml / g; the amount of weak acid is the volume of ammonia gas desorbed by NH3-TPD at 120-300℃ converted to ammonia gas under standard conditions. (2) The crystallization solution is subjected to step-by-step crystallization; wherein, the first step crystallization temperature is 5℃~90℃, the first step crystallization time is more than 0.5h, and the second step crystallization temperature is greater than 120℃; (3) Recover ZSM-5 molecular sieve.

11. The method according to claim 10, characterized in that, In step (1), the aluminum source is one or more of aluminum hydroxide, boehmite, sodium aluminate, aluminum isopropoxide, aluminum sulfate, aluminum acetate, elemental aluminum, aluminum nitrate, aluminum sol, aluminum oxide, and aluminum chloride. In step (1), the silicon source is one or more of the following: silica sol, silica fume, tetramethyl orthosilicate, tetraethyl orthosilicate, sodium silicate, water glass, solid silica gel, and sodium fluorosilicate. The alkali is one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, potassium carbonate, potassium bicarbonate, potassium hydroxide, ammonia, and calcium hydroxide.

12. The method according to any one of claims 10 to 11, characterized in that, The pH value of the crystallization solution obtained in step (1) is 11 to 13.

5.

13. The preparation method according to claim 10, characterized in that, The weak acid content of the seed crystal is 0.5-30 ml / g or 0-20 ml / g.

14. The preparation method according to claim 10, characterized in that, The specific surface area of ​​the seed crystal is not less than 180m². 2 / g.

15. The method according to claim 10, characterized in that, In step (1), the seed crystal is one or more of ZSM-5 molecular sieve or catalyst containing ZSM-5 molecular sieve, and the content of ZSM-5 molecular sieve in the catalyst containing ZSM-5 molecular sieve is not less than 8% by weight. In the catalyst seed crystals containing ZSM-5 molecular sieve, particles with a diameter not exceeding 80 micrometers account for more than 95% of the total particle volume.

16. The method according to claim 10, characterized in that, In the crystallization solution, the molar ratio of the mineralizing agent metal oxide, silicon source SiO2, aluminum source Al2O3, and H2O is (0.01-0.15):1:(0.000-0.025):(5-100). The amount of silicon source SiO2 is obtained by converting the amount of silicon in the silicon source to the amount of SiO2. The amount of aluminum source Al2O3 is obtained by converting the amount of aluminum in the aluminum source to the amount of Al2O3. The amount of mineralizing agent metal oxide is the total amount of mineralizing agent metal elements in the alkali, aluminum, and silicon sources converted to the amount of mineralizing agent metal oxide. The mineralizing agent metal is an alkali metal and / or an alkaline earth metal. The alkali metal oxide is calculated as M2O, and the alkaline earth metal oxide is calculated as M'O. The amount of seed crystal added shall not exceed 30% by weight of the amount of silicon source SiO2, where the amount of silicon source SiO2 is the amount of silicon element in the silicon source converted into SiO2.

17. The method according to claim 10 or 16, characterized in that, The mineralizing agent metal is an alkali metal, represented by M. The molar ratio of M2O:SiO2 is 0.05–0.15:1, the molar ratio of Al2O3:SiO2 is 0–0.04:1, and the molar ratio of H2O:SiO2 is 10–30:1; the weight ratio of seed crystal to SiO2 is 0.05–0.15:

1.

18. The method according to claim 10, characterized in that, The second step crystallization temperature is greater than 120℃ and not more than 200℃, and the crystallization time is 3 to 72 hours; the first step crystallization is carried out under stirring or by static crystallization, and the stirring speed for crystallization under stirring is 1 to 1000 rpm.

19. The method according to claim 10, characterized in that, The first crystallization temperature is 25℃~90℃ and the first crystallization time is 0.5~24h. The second crystallization temperature is 150℃~180℃ and the second crystallization time is 10~60h.

20. The method according to claim 10, characterized in that, After the first crystallization step is completed, the heating rate to the second crystallization temperature is 2–10 °C / min.

21. The method according to claim 10, characterized in that, The recovered molecular sieve in step (3) includes separation.

22. The method according to claim 10, characterized in that, Includes the following steps: (1) Dissolve the alkali and aluminum source in water, then add the silicon source, mix evenly, add seed crystals to obtain crystallization solution; (2) Precrystallize the crystallization solution at 5℃~90℃ for 0.5-48h with a stirring speed of 0-1000rpm; then crystallize at 120℃ and not exceeding 200℃ for 3~72 hours. (3) After crystallization, the ZSM-5 molecular sieve is obtained by filtration or centrifugation, washing, drying and calcination.

23. The method according to claim 10, characterized in that, The first crystallization step takes 0.5-48 hours.

24. The preparation method according to claim 14, characterized in that, The specific surface area of ​​the seed crystal is 180–500 m². 2 / g.

25. The preparation method according to claim 16, characterized in that, The amount of seed crystal added is 0.5 to 30% by weight of the silicon source SiO2.

26. The preparation method according to claim 18, characterized in that, The second crystallization step is carried out under stirring at a speed of 1-1000 rpm.

27. The method according to claim 19, characterized in that, The crystallization temperature of the first step is 25–80°C.

28. The method according to claim 21, characterized in that, The recovered molecular sieve in step (3) includes washing, drying and calcination.

29. The ZSM-5 molecular sieve obtained by the method according to any one of claims 10-28.

30. The application of the ZSM-5 molecular sieve according to any one of claims 1 to 9 or claim 29 in the preparation of gas adsorbents, hydrocarbon catalytic cracking catalysts, hydrocracking catalysts, aromatic alkylation catalysts, alkane isomerization catalysts, toluene disproportionation catalysts, xylene isomerization catalysts, dewaxing catalysts, methanol-to-olefins catalysts, methanol-to-aromatics catalysts, esterification catalysts or acylation catalysts.

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