A method and device for modifying the acid properties of the surface of a molecular sieve catalyst

Abstract

The application discloses a treatment method and device for modulating the surface acidity of a molecular sieve catalyst, and the treatment method comprises the following steps: one-time contact of the molecular sieve catalyst with an acid site masking agent, secondary contact of the molecular sieve after the one-time contact with organic silicon surface modifier vapor, and then washing, solid-liquid separation, drying and calcination of the molecular sieve catalyst after the secondary contact to obtain a surface-impoverished acid molecular sieve catalyst; wherein the acid site masking agent is ammonia or pyridine. The application can effectively reduce the weak acid content on the surface of SAPO-34 molecular sieve, ZSM-5 molecular sieve or MTO catalyst, reduce the selectivity of macromolecular hydrocarbon by-products, improve the catalytic reaction performance of methanol to olefin, and overcome the problem of excessive by-products in the existing methanol to olefin reaction.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and more specifically, to a method and apparatus for modifying the acid properties of the surface of a molecular sieve catalyst. Background Technology

[0002] Methanol-to-olefins (MTO) reactions typically use methanol as a raw material to produce hydrocarbon products, primarily ethylene and propylene, under the action of a catalyst. Byproducts include various alkanes and high-carbon molecules such as C4 and C5 hydrocarbons. SAPO-34 molecular sieves are the main active component of MTO catalysts. Due to their unique CHA cage structure, they provide a site for methanol conversion reactions. Furthermore, because the pore size of the eight-membered rings entering and exiting the cage is 0.38 nm, close to the molecular dynamic diameter of ethylene and propylene, they exhibit high selectivity for ethylene and propylene. In industrial MTO units, the carbon-based selectivity for ethylene and propylene in the methanol conversion reaction is around 80%, the selectivity for C4 hydrocarbons is 10–12%, and the proportion of C5 and higher hydrocarbons is around 5%. To improve the selectivity of the target products ethylene and propylene, it is necessary to suppress the occurrence of side reactions. For the active component SAPO-34 molecular sieve, the main factors affecting the selectivity of byproducts are acid properties and shape selectivity. Shape selectivity is primarily manifested in the fact that the pore size within the molecular sieve is limiting, resulting in high selectivity for ethylene and propylene. However, the outer surface of the molecular sieve has no shape selectivity, leading to high selectivity for large hydrocarbon byproducts, such as C4 and C5. The non-shape-selective catalysis of the outer surface of SAPO-34 molecular sieve is closely related to the acid properties of its outer surface. Synthetic studies of molecular sieves (Microporous Mesoporous Mater., 2008, 114, 416-423. Microporous Mesoporous Mater., 2008, 111, 143-149. J. Phys. Chem. C, 2013, 117, 4048-4056.) show that SAPO-34 molecular sieves exhibit a silicon content gradient from the crystal core to the shell, resulting in a silicon-rich surface. The framework Si-O-Al structure in the molecular sieve system requires H₂O. + Ion neutralization causes the molecular sieve to exhibit acidity. Specifically, SAPO-34 has silica enrichment on its outer surface, meaning a high acidity that exacerbates side reactions in the MTO reaction. Therefore, one strategy to suppress side reactions is to modulate the acidity of the outer surface. ZSM-5 molecular sieve, another conventional catalyst for methanol-to-olefins (MTO) reactions, faces similar technical challenges as SAPO-34.

[0003] Commonly used methods for suppressing the acidity on the surface of molecular sieves include acid treatment, alkali treatment, chemical deposition, and metal modification. For example, CN 102050463 A discloses a mesoporous Beta molecular sieve and its silanization preparation method, which involves first acid-treating the calcined Beta molecular sieve to remove aluminum, and then depositing a liquid-phase silicon source on the surface to form a silicon-rich layer. ZL200610047961 uses a vapor-phase / liquid-phase deposition method to deposit tetraethoxysilane on the molecular sieve, and then removes the organic groups by calcination. However, the above methods lack directional selectivity in modifying the outer surface of the molecular sieve, affecting all acidic sites on the outer surface, and cannot directionally treat weakly acidic sites. Summary of the Invention

[0004] To address the aforementioned problems in the background art, the main objective of this invention is to provide a method and apparatus for modifying the surface acidity of molecular sieve catalysts. This method can effectively reduce the amount of weak acid on the surface of SAPO-34 molecular sieves, ZSM-5 molecular sieves, or MTO catalysts, reduce the selectivity of macromolecular hydrocarbon byproducts, improve the catalytic performance of methanol-to-olefins reaction, and overcome the problem of excessive byproducts in existing methanol-to-olefins reactions.

[0005] To achieve one aspect of the above objectives, the present invention employs the following technical solution: a method for treating the surface acidity of a molecular sieve catalyst, comprising the following steps:

[0006] The molecular sieve catalyst is contacted with an acidic site masking agent once, and then the molecular sieve after the first contact is contacted with the vapor of an organosilicon surface modifier a second time. After the second contact, the molecular sieve catalyst is washed, separated into solid and liquid, dried and calcined to obtain a surface-depleted acid molecular sieve catalyst.

[0007] The acidic site masking agent is ammonia or pyridine. The reaction temperature during the first contact is 300–450°C and the reaction time is 30–60 min. The reaction temperature during the second contact is 200–330°C and the reaction time is 30–60 min.

[0008] Furthermore, the chemical formula of the organosilicon surface modifier is R. m1 SiX m2 Or Y n1 SiUSiY n2 X and R are selected from chloro, methoxy, ethoxy, methoxyethoxy, acetoxy, vinyl, phenyl, amino, epoxy, methacryloyloxy, mercapto, or urea; m1 and m2 = 1 to 3; m1 + m2 = 4; U is nitrogen or oxygen; Y is methyl; and n1 and n2 = 1 to 3.

[0009] Furthermore, the molecular sieve catalyst is SAPO-34 molecular sieve or ZSM-5 molecular sieve, or it can be an MTO catalyst with SAPO-34 molecular sieve or ZSM-5 molecular sieve as the active component.

[0010] Furthermore, the primary contact includes: filling the molecular sieve catalyst into a sealed reaction vessel, heating the inside of the sealed reaction vessel to the reaction temperature, and introducing the acidic site masking agent and inert gas into the reaction vessel for a primary contact reaction with the molecular sieve catalyst.

[0011] Preferably, after the initial contact reaction is complete, the flow of the acidic masking agent is stopped, and the flow of inert gas continues for a period of time.

[0012] Furthermore, the amount of acidic site masking agent introduced accounts for 2 to 10% of the total mass of the molecular sieve catalyst.

[0013] Furthermore, the molecular sieve after the first contact is cooled to a suitable temperature and then subjected to a second contact with organosilicon surface modifier vapor, wherein the suitable temperature is 200-330℃.

[0014] Furthermore, the secondary contact includes: the liquid-phase organosilicon surface modifier is vaporized into steam through a preheater and enters the reaction vessel to undergo a secondary contact reaction with the molecular sieve.

[0015] Furthermore, the surface modifier is preheated to 100–300°C using a preheater for vaporization.

[0016] Furthermore, the surface modifier vapor enters the reaction vessel together with the inert gas, preferably nitrogen.

[0017] Furthermore, the amount of surface modifier vapor introduced accounts for 2 to 20% of the total mass of the molecular sieve catalyst.

[0018] A second aspect of the present invention provides a treatment apparatus for modulating the acid properties of the surface of a molecular sieve catalyst, comprising:

[0019] The reaction vessel is filled with molecular sieve catalyst and receives vapors of acidic site masking agent and surface modifier, providing a place for primary contact between the molecular sieve catalyst and the acidic site masking agent and secondary contact between the molecular sieve catalyst and the surface modifier vapor.

[0020] A heater, arranged around the outer wall of the reaction vessel, is used to heat the internal environment of the reaction vessel.

[0021] The preheater is used to receive the liquid surface modifier and vaporize it into steam. The steam outlet of the preheater is connected to the reaction vessel.

[0022] An inert gas supply device is used to supply inert gas into the reaction vessel.

[0023] Compared with existing technologies, this invention has the following advantages: Weakly acidic sites on the surface of molecular sieves or catalysts tend to undergo hydrogen transfer and methylation reactions, which are detrimental to improving the selectivity of ethylene and propylene. Therefore, this invention involves a primary contact between the molecular sieve catalyst and an acidic site masking agent, followed by a secondary contact between the molecular sieve and organosilicon surface modifier vapor. The resulting molecular sieve catalyst is then washed, subjected to solid-liquid separation, dried, and calcined to obtain a surface-depleted acid molecular sieve catalyst. The acidic sites on the molecular sieve surface originate from the Si-O-Al surface framework. When acidic site masking agents such as ammonia are adsorbed onto these sites, the stronger the acidity of the acidic sites, the more stable the ammonia adsorption. Under high-temperature conditions, ammonia desorbs from weakly acidic sites, exposing the acidic sites, while ammonia does not desorb from strongly acidic sites, leaving the acidic sites still masked. Subsequently, a macromolecular surface modifier reacts with the molecular sieve. Since the macromolecular surface modifier cannot penetrate the interior of the molecular sieve islands, the exposed weakly acidic sites are masked by replaced or deposited Si species, thus reducing the proportion of weakly acidic sites. The processing method and apparatus of this invention can effectively reduce the amount of weak acid on the surface of SAPO-34 molecular sieve, ZSM-5 molecular sieve, or MTO catalyst, reducing the amount of weak acid on the outer surface of the molecular sieve by more than 50% without damaging or changing other physicochemical properties. When the surface-depleted molecular sieve obtained by this invention is applied to methanol conversion reaction, the catalytic life is extended, the diene selectivity is improved, and the selectivity of macromolecular hydrocarbon byproducts can be reduced.

[0024] Other features and advantages of the present invention will be described in detail through the following specific embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a device for treating the surface acidity of a molecular sieve catalyst, provided in an embodiment of the present invention.

[0026] Figure 2 A schematic diagram of another device for treating the surface acidity of a molecular sieve catalyst, provided in an embodiment of the present invention.

[0027] Labeling instructions: 1-Nitrogen cylinder, 2-Surface modifier storage tank, 3-Plunger pump, 4-Preheating furnace, 5-Ammonia cylinder, 6-Heating mantle, 7-Molecular sieve or catalyst, 8-Metal reaction tube, 9-Agitator, 10-Stirred reactor. Detailed Implementation

[0028] The following will describe the concept and technical effects of this application clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application.

[0029] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0030] The first aspect of this invention provides a method for modifying the acid properties of the surface of a molecular sieve catalyst, comprising the following steps:

[0031] The molecular sieve catalyst is contacted with an acidic site masking agent once, and then the molecular sieve after the first contact is contacted with the vapor of an organosilicon surface modifier a second time. After the second contact, the molecular sieve catalyst is washed, separated into solid and liquid, dried and calcined to obtain a surface-depleted acid molecular sieve catalyst.

[0032] The acidic site masking agent is ammonia or pyridine. The reaction temperature during the first contact is 300-450℃ and the reaction time is 30-60 min. The reaction temperature during the second contact is 200-330℃ and the reaction time is 30-60 min. When the reaction is carried out according to the above parameters, the effect of reducing the acidic sites on the surface is more obvious.

[0033] In some specific embodiments, the chemical formula of the organosilicon surface modifier is R. m1 SiX m2 Or Y n1 SiUSiY n2Where X and R are selected from chloro, methoxy, ethoxy, methoxyethoxy, acetoxy, vinyl, phenyl, amino, epoxy, methacryloyloxy, mercapto, or urea groups, m1 and m2 = 1–3, m1 + m2 = 4, U is a nitrogen group or an oxygen group, Y is a methyl group, and n1 and n2 = 1–3. The effects of using the above-mentioned surface modifiers are: firstly, when organosilicon molecules come into contact with the molecular sieve framework structure at high temperatures, group detachment can occur, providing silicon-based groups for the monomolecular sieve. These silicon-based groups adsorb onto defect sites or acidic sites in the molecular sieve framework, undergoing silicon filling or silicon substitution of the aluminum framework at high temperatures to eliminate acidic sites, or undergoing physical deposition to transform into SiO2, masking the acidic sites; secondly, organosilicon containing macromolecular groups can prevent diffusion into the molecular sieve channels, ensuring that it acts on the acidic sites on the outer surface of the molecular sieve.

[0034] In some specific embodiments, the molecular sieve catalyst is SAPO-34 molecular sieve or ZSM-5 molecular sieve, or it can be an MTO catalyst with SAPO-34 molecular sieve or ZSM-5 molecular sieve as the active component.

[0035] In some specific embodiments, the primary contact includes: filling a molecular sieve catalyst into a sealed reaction vessel, heating the inside of the sealed reaction vessel to the reaction temperature, and introducing an acidic site masking agent and an inert gas into the reaction vessel for a primary contact reaction with the molecular sieve catalyst.

[0036] Preferably, after the initial contact reaction is complete, the flow of the acidic site masking agent is stopped, and the flow of inert gas is continued for a period of time. The purpose of this operation is that the acidic site masking agent is alkaline and will chemically combine with the acidic sites after contacting the molecular sieve. The purpose of the inert gas is to remove the acidic site masking agent adsorbed on the weakly chemically bonded acidic sites, so that the weakly acidic sites can be directionally exposed.

[0037] In some specific embodiments, the amount of acidic site masking agent introduced accounts for 2-10% of the total mass of the molecular sieve catalyst. With the parameters set as described above, the surface of the molecular sieve accounts for about 10% of the total specific surface area, of which strong acidic sites account for about 20% of the total acidic sites. The amount of acidic site masking agent introduced should be controlled to cover the strong acidic sites as much as possible. Therefore, the amount introduced should be controlled to be no less than the estimated proportion of strong acidic sites on the outer surface. If it is higher than 10%, the amount introduced is seriously excessive and the effect is not significantly changed.

[0038] In some specific implementations, the acidic site masking agent is pyridine, which is a liquid at room temperature and easily volatilizes. The pyridine is heated to the reaction temperature and then brought into contact with the molecular sieve once.

[0039] In some specific embodiments, the molecular sieve, after its initial contact, is cooled to a suitable temperature before being subjected to a second contact with organosilicon surface modifier vapor. This suitable temperature is 200-330°C. The molecular sieve chemically adsorbs the acidic masking agent at its strongly acidic sites; as the temperature increases, the masking agent at these sites desorbs more easily. At high temperatures, only strongly acidic sites can adsorb the masking agent; masking agents at weakly acidic sites have no adsorption capacity. When the masking agent is introduced at high temperatures for a period of time, it ensures that only strongly acidic sites adsorb the masking agent. Lowering the temperature afterwards ensures that the masking agent adsorbed at the strongly acidic sites will not desorb, ensuring that only the weakly acidic sites are exposed. Subsequent contact of the molecular sieve in this state with organosilicon surface modifier vapor ensures that the organosilicon surface modifier interacts only with the weakly acidic sites.

[0040] In some specific embodiments, the secondary contact includes: the liquid-phase organosilicon surface modifier is vaporized into steam through a preheater and enters the reaction vessel to undergo a secondary contact reaction with the molecular sieve.

[0041] In some specific implementations, the surface modifier is preheated to 100–300°C using a preheater for vaporization.

[0042] In some specific embodiments, the surface modifier vapor enters the reaction vessel together with the inert gas path, which can improve the linear velocity. The inert gas is preferably nitrogen.

[0043] Preferably, after the secondary contact reaction is complete, the steam is stopped, and the inert gas is continued to be introduced for a period of time. The purpose of this operation is to purge the excess organosilicon surface modifier that has been physically adsorbed.

[0044] In some specific implementations, the amount of surface modifier vapor introduced accounts for 2 to 20% of the total mass of the molecular sieve catalyst. Setting the parameters as described above can ensure that the number of weak acid sites is reduced, and further increasing the amount introduced will not change the effect.

[0045] A second aspect of the present invention provides a treatment apparatus for modulating the acid properties of the surface of a molecular sieve catalyst, comprising:

[0046] The reaction vessel is filled with molecular sieve catalyst and receives vapors of acidic site masking agent and surface modifier, providing a place for primary contact between the molecular sieve catalyst and the acidic site masking agent and secondary contact between the molecular sieve catalyst and the surface modifier vapor.

[0047] A heater, arranged around the outer wall of the reaction vessel, is used to heat the internal environment of the reaction vessel.

[0048] The preheater is used to receive the liquid surface modifier and vaporize it into steam. The steam outlet of the preheater is connected to the reaction vessel.

[0049] An inert gas supply device is used to supply inert gas into the reaction vessel.

[0050] In some specific embodiments, the reaction vessel can be a cylindrical or tubular metal container or quartz container with an inlet and an outlet, or it can be a reaction vessel with only one gas inlet and outlet.

[0051] In some specific embodiments, when the reaction vessel is a cylindrical or tubular metal or quartz container with an inlet and an outlet, the surface modifier is continuously fed, that is, it is introduced through the inlet and released through the outlet; when the reaction vessel is a reactor with only one gas inlet and outlet, the surface modifier is introduced through the inlet and outlet in a certain amount and then the reactor is sealed, and the surface modifier is discontinuously fed.

[0052] In some specific embodiments, the molecular sieve catalyst inside the reaction vessel is either in a static or dynamic state. When the molecular sieve catalyst is in a dynamic state, it can be driven by mechanical stirring, magnetic stirring, or by a surface modifier and inert gas blowing through the molecular sieve catalyst bed. It is understood that a stirring device can be installed inside the reaction vessel.

[0053] In some specific embodiments, the processing apparatus of the present invention further includes a surface modifier storage tank and a means for conveying the liquid surface modifier to a preheater. For example, the material in the surface modifier storage tank is conveyed to the preheater for preheating by a transfer pump. It is understood that the present invention can adjust the flow rate of the surface modifier entering the preheater as needed.

[0054] In some specific implementations, the feed rate of the delivery pump is 0.02-0.2 ml / min.

[0055] In some specific implementations, the heater may be a heat-conducting oil pipe or an electric heating jacket arranged around the outer wall of the reaction vessel.

[0056] In this invention, the flow rate of the material entering the reaction vessel can be adjusted as needed, such as the flow rate of gases like acidic site masking agents and inert gases, or the steam feed rate of surface modifiers.

[0057] The present invention will be further illustrated by the following examples:

[0058] The raw material information is as follows:

[0059] Boehmite: Specifications 70% dry basis, China Aluminum New Materials Co., Ltd.;

[0060] Phosphoric acid: 85% specification, Sinopharm Chemical Reagent Co., Ltd.

[0061] Silica sol: 30% specification, Qingdao Haiwan Fine Chemical Co., Ltd.

[0062] Triethylamine: 99.9% purity, Sinopharm Chemical Reagent Co., Ltd.

[0063] TPAOH: Specifications, Sinopharm Chemical Reagent Co., Ltd.

[0064] Sodium hydroxide: Specifications, Sinopharm Chemical Reagent Co., Ltd.

[0065] Sodium aluminate: Specifications, Sinopharm Chemical Reagent Co., Ltd.

[0066] Hexamethyldisilazane: 98% purity, Shanghai Maclean Biochemical Technology Co., Ltd.

[0067] Ammonia: 99.999% purity, Beijing Helium North Branch Gas Industry Co., Ltd.

[0068] Vinyltrimethoxysilane: 98% purity, Shanghai Maclean Biochemical Technology Co., Ltd.

[0069] Dichlorodimethylsilane: 99% purity, Shanghai Maclean Biochemical Technology Co., Ltd.

[0070] Comparative Example 1 (SAPO-34 molecular sieve)

[0071] A self-made conventional SAPO-34 molecular sieve was prepared. Using boehmite as the aluminum source, phosphoric acid as the phosphorus source, silica sol as the silicon source, and triethylamine as the organic template agent, with aluminum source calculated as Al2O3, silicon source as SiO2, and phosphorus source as P2O5, an initial mixed gel was prepared according to the molar ratio of aluminum source:phosphorus source:silicon source:organic template agent:water = 1:1:0.3:3.5:50. After uniform dispersion, the mixture was transferred to a high-pressure reactor and crystallized at 200℃ for 24 hours. After cooling, separation, washing, and drying, SAPO-34 molecular sieve raw powder was obtained. Calcination at 650℃ for 5 hours yielded SAPO-34 molecular sieve D1.

[0072] Comparative Example 2 (ZSM-5 molecular sieve)

[0073] A conventional ZSM-5 molecular sieve was prepared. A 25% TPAOH aqueous solution, sodium hydroxide, sodium aluminate, 30% silica sol, and water were mixed in a specific order and stirred for 24 hours to form a gel. The molar ratio of the substances in the gel was 100SiO2:Al2O3:10TPAOH:3.8Na2O:1350H2O. After aging for 24 hours, the gel was transferred to a hydrothermal crystallization reactor and dynamically crystallized at 125℃ and its own pressure for 72 hours. After crystallization, the ZSM-5 molecular sieve was obtained by cooling, separation, washing, drying, and calcination. It was then subjected to three ion exchanges with a 0.5 mol / L ammonium nitrate solution at 80℃, dried at 80℃ for 12 hours, and calcined at 650℃ for 5 hours to obtain the hydrogen-form ZSM-5 molecular sieve D2, with a SiO2 / Al2O3 molar ratio of 88.

[0074] Comparative Example 3 (MTO catalyst)

[0075] SAPO-34 molecular sieve powder, alumina sol, and kaolin from Comparative Example 1 were mixed evenly at a dry weight percentage of 40%:25%:35%. The mixture was then spray-molded after being ground and calcined at 650℃ for 5 hours to obtain methanol-to-olefins catalyst D3.

[0076] Example 1

[0077] The experimental procedure is as follows Figure 1 The reaction vessel is a metal reaction tube, which is heated externally by an electric heating mantle. The molecular sieve bed temperature is 300℃, and the total filling weight of SAPO-34 molecular sieve is 40g. First, ammonia and nitrogen are introduced at a flow rate of 50 ml / min and 10 ml / min, respectively, and the reaction is allowed to proceed for 30 minutes. The ammonia valve is then closed, and nitrogen purging continues for another 30 minutes. Afterward, the molecular sieve bed temperature is lowered to 260°C, and the surface modifier hexamethyldisilazane is introduced via a plunger pump at a rate of 0.05 ml / min. The liquid surface modifier passes through a preheating furnace at 120°C, where it vaporizes and merges with the nitrogen gas. The nitrogen flow rate is maintained at 10 ml / min. The mixture of nitrogen and surface modifier enters the metal reaction tube from the bottom, ensuring full contact with the SAPO-34 molecular sieve D1, and passes through the molecular sieve bed, exiting from the top of the reaction tube. This contact process with the surface modifier continues for 90 minutes. Then, the surface modifier is stopped, and nitrogen purging continues for another 30 minutes. After cooling, the molecular sieve is discharged, washed, filtered, dried, and calcined to obtain the SAPO-34 molecular sieve S1, which has a low-acid outer surface.

[0078] Example 2

[0079] The difference from Example 1 is that SAPO-34 molecular sieve D1 is replaced with ZSM-5 molecular sieve D2;

[0080] The resulting ZSM-5 molecular sieve with a poor outer surface acidity is designated as S2.

[0081] Example 3

[0082] The difference from Example 1 is that SAPO-34 molecular sieve D1 is replaced with MTO catalyst D3, and the continuous reaction time of the contact process with the surface modifier is changed from 90 min to 60 min;

[0083] The resulting MTO catalyst with a poor outer surface acidity is designated as S3.

[0084] Example 4

[0085] The difference from Example 1 is that the surface modifier is replaced with vinyltrimethoxysilane, the preheating temperature is changed to 170°C, and the reaction temperature between the surface modifier and the molecular sieve is changed to 200°C.

[0086] SAPO-34 molecular sieve S4 with a poor outer surface acidity was obtained.

[0087] Example 5

[0088] The difference from Example 1 is that the feed rate of the surface modifier plunger pump is changed to 0.10 ml / min;

[0089] SAPO-34 molecular sieve S5 with a poor outer surface acidity was obtained.

[0090] Example 6

[0091] The difference from Example 1 is that the feed rate of the surface modifier plunger pump is changed to 0.02 ml / min, and the reaction temperature of the surface modifier and molecular sieve is changed to 250°C.

[0092] SAPO-34 molecular sieve S6 with a poor outer surface acidity was obtained.

[0093] Example 7

[0094] The difference from Example 1 is that the surface modifier is changed to dichlorodimethylsilane, and the reaction temperature between the surface modifier and the molecular sieve is changed to 300°C.

[0095] SAPO-34 molecular sieve S7 with a poor outer surface acidity was obtained.

[0096] Example 8

[0097] The experimental procedure is as follows Figure 2The reaction vessel was changed to a high-pressure autoclave reactor, with a total of 40g of SAPO-34 molecular sieve inside. A stirring paddle was connected inside the reactor to agitate the molecular sieve powder. First, 1.1L of ammonia gas was introduced, and the gas inlet of the autoclave reactor was closed. The temperature was raised to 300℃, and the reaction was carried out for 30 minutes. Then, the pressure relief valve of the reactor was opened to release the pressure, and nitrogen gas was continuously introduced for 30 minutes at a flow rate of 50ml / min. After that, the reactor temperature was lowered to 260℃. The nitrogen valve was closed, and the surface modifier hexamethyldisilazane was introduced. It was fed through a plunger pump at a rate of 0.10ml / min. The liquid surface modifier passed through a preheating furnace at a temperature of 150℃. The surface modifier, which was heated and vaporized into gas, entered the autoclave reactor from the top, and the hexamethyldisilazane came into full contact with SAPO-34 molecular sieve D1. After hexamethyldisilazane was continuously introduced for 20 minutes, the plunger pump feed was stopped, and the gas inlet of the batch reactor was closed. The batch reactor was heated by an external oil bath, and the internal temperature was raised to 150°C and maintained for 20 minutes. After cooling, the molecular sieve was discharged, washed, filtered, dried, and calcined to obtain SAPO-34 molecular sieve S8 with a poor outer surface acidity.

[0098] The acid content of the molecular sieve or catalyst in this invention is determined by the following method.

[0099] Ammonia molecules are smaller than the pore size of SAPO-34 or ZSM-5 molecular sieves, allowing them to enter the internal channels of the sieves. Therefore, NH3-TPD was used to analyze the total acid content (including internal and surface acid content) of the molecular sieve sample. Instrument model: Micromeritics ASAP 2920 fully automated chemisorption analyzer. First, the sample was pressed into tablets, crushed, sieved, and 40-60 mesh particles were dried for later use. 0.1 g of the dried sample was accurately weighed and placed in a quartz tube. The sample was activated at 600℃ for 0.5 h under a He atmosphere, then cooled to room temperature. An NH3 (1.vol%)-He mixture was adsorbed for 15 min. After baseline stabilization, the temperature was increased to 600℃ at a rate of 10℃ / min, and the ammonia desorption signal in the 100-600℃ range was collected.

[0100] Pyridine molecules are larger than the pore size of SAPO-34 molecular sieves and cannot enter the internal channels; they can only be adsorbed by acid sites on the surface. Therefore, the surface acidity of SAPO-34 molecular sieve samples is characterized using the pyridine infrared method. Instrument model: Thermo Fisher Nicolet IS10 infrared spectrometer, resolution 0.5 cm⁻¹. -1 First, the sample was dried at 120℃ for 2 hours, and then formed into a self-supporting disc with a diameter of 12 mm under a pressure of 5 MPa. The pretreated sample was then adsorbed with pyridine vapor for 1 min, equilibrated for 20 min, and then desorbed under vacuum at 200℃ (vacuum degree 10). -4After 1 hour at 1000°C, the sample was cooled to room temperature, and the corresponding infrared absorption spectra were collected. The sampling range was 1300–1700 cm⁻¹. -1 The formula for calculating the total acidity of pyridine using infrared spectroscopy is as follows:

[0101] C B =1.88 I A (B)*R 2 / M (1)

[0102] C L =1.42 I A (L)*R 2 / M (2)

[0103] C = C B +C L (3)

[0104] In the formula, C (B,L) The number of Brønsted or Lewis acid centers per gram of sample; the acid content is measured in mmol / g. A (B / L) is the integral area of ​​the absorption peak of Brønsted acid in the infrared spectrum; R is the radius of the sample pellet in cm; M is the mass of the sample pellet in g.

[0105] After collecting the above data, the temperature was further increased to 350℃, and vacuum desorption was performed (vacuum degree 10). -4 After 1 hour of cooling to room temperature, the corresponding infrared absorption spectra were collected. Data were collected again to determine the strong acid content of pyridine by infrared spectroscopy.

[0106] 2,6-Di-tert-butylpyridine molecules are larger than the pore size of ZSM-5 molecular sieves and cannot enter the internal channels. They can only be adsorbed by acid sites on the surface. Therefore, the surface acidity of ZSM-5 molecular sieve samples was characterized using an infrared method. Instrument model: Thermo Fisher Nicolet IS10 infrared spectrometer, resolution 0.5 cm⁻¹. -1 First, the sample was dried at 120℃ for 2 hours, and then formed into a self-supporting disc with a diameter of 12 mm under a pressure of 5 MPa. The pretreated sample was then adsorbed onto 2,6-di-tert-butylpyridine vapor for 1 min, equilibrated for 20 min, and then desorbed under vacuum at 200℃ (vacuum degree 10). -4 After 1 hour at 1000 ppm, the sample was cooled to room temperature, and the corresponding infrared absorption spectra were collected. The sampling range was 1615 cm⁻¹. -1 The formula for calculating the acidity of 2,6-di-tert-butylpyridine using infrared spectroscopy is as follows:

[0107] C = 6280 I*R 2 / M (1)

[0108] In the formula, C is the number of acid centers per gram of sample, and the acid content is in mmol / g; I is the absorption peak height of the acidic site in the infrared spectrum; R is the radius of the sample pellet, in cm; and M is the mass of the sample pellet, in g.

[0109] After collecting the above data, the temperature was further increased to 350℃, and vacuum desorption was performed (vacuum degree 10). -4 After 1 hour of cooling to room temperature, the corresponding infrared absorption spectra were collected. Data were collected again for the strong acid content of 2,6-di-tert-butylpyridine determined by infrared spectroscopy.

[0110] Table 1. Acid properties of the examples and comparative examples.

[0111]

[0112] In the examples, the proportion of weak acid to total surface acid was reduced compared to the comparative examples.

[0113] In this invention, the catalyst performance was evaluated using a fixed-bed reactor with an 80% methanol-water solution as the feed, a reaction temperature of 480°C, and a space velocity of 3.0 h⁻¹. -1 The molecular sieve / catalyst loading amount is 1.0 g. Specific steps: The sample to be tested is loaded into a stainless steel reaction tube, heated to 500℃ for 1 h for activation, cooled to 480℃, and methanol-water solution is introduced. Online sampling is used. The product is separated by condensation, and the gaseous components are analyzed by gas chromatography (Agilent, 7890A type). The chromatography system is equipped with an HP-PLOT Al2O3 / KCl column (50 m × 0.53 mm × 15 μm) (for separating C1-C6 hydrocarbons), an HP-PLOT Q column (30 m × 320 μm × 20 μm) (for separating alcohols and ethers), a Hayesep Q column and an X molecular sieve column (for separating permanent gases such as CO, CO2, H2, and N2), two FID detectors, and one TCD detector.

[0114] Methanol conversion rate (X) and product selectivity (Si is expressed in moles of carbon, based on carbon-based selectivity) are calculated by the following equations:

[0115]

[0116] Wherein, X - methanol conversion rate; S - product selectivity; i - species entering the reactor; o - species exiting the reactor; CxHy - olefin (x - number of carbon atoms in hydrocarbon species, y - number of hydrogen atoms in hydrocarbon species); m - number of carbon atoms in the corresponding substance CxHy; n - number of moles of the corresponding substance; MeOH - methanol; DME - dimethyl ether.

[0117] When the methanol conversion rate in the tested component is below 99%, the catalyst is considered deactivated. The catalyst lifetime is the time during which the methanol conversion rate remains above 99%. The test results are as follows.

[0118] Table 2. Methanol conversion reaction lifetime and product selectivity of the examples and comparative examples.

[0119]

[0120]

[0121] Compared with the comparative example, the embodiments of the present invention exhibit superior catalytic performance, longer reaction lifetime, high selectivity for ethylene and propylene, and low selectivity for C4.

[0122] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as limiting the present invention. Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for treating the surface acidity of a molecular sieve catalyst, characterized in that, The process includes the following steps: a molecular sieve catalyst is contacted once with an acidic site masking agent; the molecular sieve after the first contact is then contacted a second time with organosilicon surface modifier vapor; subsequently, the molecular sieve catalyst after the second contact is washed, subjected to solid-liquid separation, dried, and calcined to obtain a surface-depleted acid molecular sieve catalyst; wherein the acidic site masking agent is ammonia or pyridine; the reaction temperature during the first contact is 300-450℃, and the reaction time is 30-60 min; the reaction temperature during the second contact is 200-330℃, and the reaction time is 30-60 min. The chemical formula of the organosilicon surface modifier is R. m1 SiX m2 Or Y n1 SiUSiY n2 X and R are selected from chloro, methoxy, ethoxy, methoxyethoxy, acetoxy, vinyl, phenyl, amino, epoxy, methacryloyloxy, mercapto or urea, m1 and m2 = 1~3, m1+m2 = 4, U is nitrogen or oxygen, Y is methyl, and n1 and n2 = 1~3. The molecular sieve catalyst is SAPO-34 molecular sieve, ZSM-5 molecular sieve, or an MTO catalyst containing SAPO-34 molecular sieve or ZSM-5 molecular sieve as the active component.

2. The processing method according to claim 1, characterized in that, The first contact includes: filling the molecular sieve catalyst into a sealed reaction vessel, heating the inside of the sealed reaction vessel to the reaction temperature, and introducing the acidic site masking agent and inert gas into the reaction vessel for a first contact reaction with the molecular sieve catalyst.

3. The processing method according to claim 1 or 2, characterized in that, The amount of acidic site masking agent introduced accounts for 2-10% of the total mass of the molecular sieve catalyst.

4. The processing method according to claim 1, characterized in that, The secondary contact includes: vaporizing the liquid-phase organosilicon surface modifier into steam through a preheater, and then entering the reaction vessel to undergo a secondary contact reaction with the molecular sieve catalyst.

5. The processing method according to claim 4, characterized in that, After the molecular sieve has been contacted once, it is cooled to a suitable temperature and then contacted a second time with organosilicon surface modifier vapor. The suitable temperature is 200-330℃.

6. The processing method according to claim 4, characterized in that, The surface modifier is preheated to 100~300℃ using a preheater.

7. The processing method according to claim 4, characterized in that, The surface modifier vapor enters the reaction vessel together with an inert gas, namely nitrogen.

8. The processing method according to claim 4, characterized in that, The amount of surface modifier vapor introduced accounts for 2-20% of the total mass of the molecular sieve catalyst.

9. A device for treating the surface acidity of a molecular sieve catalyst, characterized in that, include: A reaction vessel, internally filled with a molecular sieve catalyst, and receiving vapors of an acidic site masking agent and a surface modifier, is provided for primary contact between the molecular sieve catalyst and the acidic site masking agent and secondary contact between the molecular sieve catalyst and the surface modifier vapor, wherein the molecular sieve catalyst is a surface-depleted acid molecular sieve catalyst obtained by the processing method according to any one of claims 1-8. A heater, arranged around the outer wall of the reaction vessel, is used to heat the internal environment of the reaction vessel. The preheater is used to receive the liquid surface modifier and vaporize it into steam. The steam outlet of the preheater is connected to the reaction vessel. An inert gas supply device is used to supply inert gas into the reaction vessel.

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