Treatment method and treatment device for modulating surface acid properties of molecular sieve catalyst

Abstract

The invention discloses a treatment method and a treatment device for modulating the surface acid property of a molecular sieve catalyst, and the treatment method comprises the following steps: carrying out primary contact on the molecular sieve catalyst and an acid site masking agent, and carrying out secondary contact on the molecular sieve after primary contact and organic silicon surface modifier steam, washing the molecular sieve catalyst after secondary contact, performing solid-liquid separation, drying and roasting to obtain the surface acid-poor molecular sieve catalyst. Wherein the acid site masking agent is ammonia gas or pyridine. The method can effectively reduce the amount of weak acid on the surface of the SAPO-34 molecular sieve, the ZSM-5 molecular sieve or the MTO catalyst, reduce the selectivity of macromolecular hydrocarbon by-products, improve the methanol-to-olefin catalytic reaction performance, and overcome the problem of excessive by-products in the existing methanol-to-olefin reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a method and a device for treating the surface acidity of a molecular sieve catalyst. Background Art

[0002] The MTO (methanol to olefins) reaction usually uses methanol as a raw material, and produces hydrocarbon products mainly composed of ethylene and propylene under the action of a catalyst. By-products include various alkanes and high-carbon molecules such as C4 and C5. SAPO-34 molecular sieve is the main active component of the MTO catalyst. Due to its unique CHA cage structure, it provides a place for the methanol conversion reaction. At the same time, since the pore diameter of the eight-membered ring entering and exiting the cage is 0.38nm, which is close to the molecular dynamics diameter of ethylene and propylene, it exhibits a high selectivity for ethylene and propylene. The carbon-based selectivity of ethylene and propylene in the methanol conversion reaction of the industrial MTO unit is about 80%, the selectivity of C4 hydrocarbons is 10-12%, and the proportion of hydrocarbons above C5 is about 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 factors affecting the selectivity of by-products are mainly acidic properties and shape selectivity. Among them, the shape selectivity is mainly manifested in that the pores in the molecular sieve are limited by the pore size, and the selectivity of ethylene and propylene is high, but the outer surface of the molecular sieve is not restricted by shape selectivity, resulting in high selectivity for macromolecular hydrocarbon by-products, such as carbon four and carbon five. The reason why SAPO-34 molecular sieve has non-selective catalysis on the outer surface is closely related to the acidic properties of its outer surface. The synthesis study of molecular sieves shows (Microporous Mesoporous Mater., 2008, 114, 416-423. Microporous Mesoporous Mater., 2008, 111, 143-149. J. Phys. Chem. C, 2013, 117, 4048-4056.) that SAP0-34 molecular sieve has a silicon content gradient from the crystal core to the shell, which is manifested as surface silicon-rich. The framework Si-O-Al structure in the molecular sieve system requires H + Ions are neutralized, so the molecular sieve appears acidic. Specifically for SAPO-34, the silicon enrichment on the outer surface means that the amount of acid on the outer surface is high, which further aggravates the side reactions in the MTO reaction. Therefore, one of the strategies to inhibit side reactions is to adjust the acid properties of the outer surface. ZSM-5 molecular sieve, as another conventional catalyst for the methanol to olefins reaction, has the same technical problems as the above SAPO-34 molecular sieve.

[0003] Commonly used methods for suppressing the amount of acid on the surface of molecular sieves in the prior art include acid treatment, alkali treatment, chemical deposition, metal modification, etc. For example, CN 102050463 A discloses a mesoporous Beta molecular sieve and its silicification preparation method, wherein the calcined Beta molecular sieve is first subjected to acid treatment for dealumination, and then subjected to surface deposition of liquid silicon source to form a surface silicon-rich layer. ZL200610047961 uses a gas phase / liquid phase deposition method to deposit tetraethoxysilane on the molecular sieve, and removes the organic group by calcination. However, the above treatment methods have no directional selectivity for the modification of the outer surface of the molecular sieve, have an impact on the acidic sites on the outer surface, and cannot directionally treat the weakly acidic sites. Summary of the invention

[0004] In order to solve the above-mentioned problems in the background technology, the main purpose of the present invention is to provide a method and a device for treating the surface acid properties of a molecular sieve catalyst, which can effectively reduce the amount of weak acid on the surface of SAPO-34 molecular sieve, ZSM-5 molecular sieve or MTO catalyst, reduce the selectivity of large molecular hydrocarbon by-products, improve the performance of methanol to olefins catalytic reaction, and overcome the problem of excessive by-products in the existing methanol to olefins reaction.

[0005] In order to achieve one aspect of the above purpose, the present invention adopts the following technical solution: a treatment method for adjusting the surface acid properties of a molecular sieve catalyst, comprising the following steps:

[0006] The molecular sieve catalyst is contacted with the acidic site masking agent once, and the molecular sieve after the first contact is contacted with the steam of the organosilicon surface modifier for a second time, and then the molecular sieve catalyst after the second contact is washed, solid-liquid separated, dried and calcined to obtain a surface acid-poor molecular sieve catalyst;

[0007] Wherein, 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 minutes; the reaction temperature during the second contact is 200-330°C, and the reaction time is 30-60 minutes.

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

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

[0010] Furthermore, the one-time contact includes: loading the molecular sieve catalyst into a closed reaction vessel, heating the interior of the closed reaction vessel to a reaction temperature, and allowing the acidic site masking agent and the inert gas to enter the reaction vessel together to react with the molecular sieve catalyst in one contact.

[0011] Preferably, after the primary contact reaction is completed, the introduction of the acidic site masking agent is stopped, and the introduction of the inert gas continues for a period of time.

[0012] Furthermore, the amount of the acidic site masking agent introduced accounts for 2-10% 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 contacted with the organic silicon surface modifier vapor for a second time, wherein the suitable temperature is 200-330°C.

[0014] Furthermore, the secondary contact comprises: the liquid phase organosilicon surface modifier is vaporized into steam through a preheater, enters a reaction container, and undergoes a secondary contact reaction with the molecular sieve.

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

[0016] Furthermore, the surface modifier vapor enters the reaction container together with the inert gas path, and the inert gas is preferably nitrogen.

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

[0018] The second aspect of the present invention provides a treatment device for adjusting the surface acid properties of a molecular sieve catalyst, comprising:

[0019] A reaction vessel, which is filled with a molecular sieve catalyst and receives the acidic site masking agent and the surface modifier vapor, and is used to provide a place for the molecular sieve catalyst to make a primary contact with the acidic site masking agent and for the molecular sieve catalyst to make a secondary contact with the surface modifier vapor;

[0020] A heater is disposed around the outer wall of the reaction container and is used to heat the internal environment temperature of the reaction container;

[0021] A preheater, used for receiving the liquid surface modifier and vaporizing it into steam, wherein the steam outlet of the preheater is connected to the reaction container;

[0022] The inert gas device is used to provide inert gas into the reaction container.

[0023] Compared with the prior art, the present invention has the following advantages: the weakly acidic sites on the surface of the molecular sieve or catalyst tend to undergo hydrogen transfer reaction and methylation reaction, which is not conducive to the improvement of the selectivity of ethylene and propylene. Therefore, the present invention contacts the molecular sieve catalyst with an acidic site masking agent once, contacts the molecular sieve after the first contact with the steam of the organic silicon surface modifier for a second time, and then washes, solid-liquid separates, dries and roasts the molecular sieve catalyst after the second contact to obtain a surface acid-poor molecular sieve catalyst. Among them, the acidic sites on the surface of the molecular sieve come from the surface skeleton Si-O-Al. When an acidic site masking agent such as ammonia is adsorbed on the acidic site, the greater the acid strength of the acidic site, the more stable the ammonia adsorption. Under high temperature environment, ammonia desorbs from the weakly acidic site, exposing the acidic site, and ammonia does not desorb from the strongly acidic site, and the acidic site is still masked. Afterwards, a macromolecular surface modifier is used to react with the molecular sieve. Since the macromolecular surface modifier cannot enter the interior of the molecular sieve empty island, the weakly acidic sites exposed on the surface will be covered by the replaced or deposited Si species, thereby achieving the purpose of reducing the proportion of weakly acidic sites. The treatment method and treatment device of the present invention can effectively reduce the amount of weak acid on the surface of SAPO-34 molecular sieve, ZSM-5 molecular sieve or MTO catalyst, and the amount of weak acid on the outer surface of the molecular sieve can be reduced by more than 50% without destroying or changing other physical and chemical properties. The surface acid-poor molecular sieve obtained by the present invention is applied to methanol conversion reaction, the catalytic life is extended, the diene selectivity is improved, and the selectivity of large molecular hydrocarbon by-products can be reduced.

[0024] Other features and advantages of the present invention will be described in detail through the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a treatment device for modulating the surface acid properties of a molecular sieve catalyst provided in an embodiment of the present invention.

[0026] Figure 2 A schematic diagram of another treatment device for adjusting the surface acid properties of a molecular sieve catalyst provided in an embodiment of the present invention.

[0027] Marking instructions: 1-nitrogen bottle, 2-surface modifier storage tank, 3-plunger pump, 4-preheating furnace, 5-ammonia bottle, 6-electric heating jacket, 7-molecular sieve or catalyst, 8-metal reaction tube, 9-stirring paddle, 10-kettle reactor. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the concept of the present application and the technical effects produced in combination with the embodiments, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of them. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present application.

[0029] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

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

[0031] The molecular sieve catalyst is contacted with the acidic site masking agent once, and the molecular sieve after the first contact is contacted with the steam of the organosilicon surface modifier for a second time, and then the molecular sieve catalyst after the second contact is washed, solid-liquid separated, dried and calcined to obtain a surface acid-poor molecular sieve catalyst;

[0032] Wherein, 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 30-60min; the reaction temperature during the second contact is 200-330°C, and the reaction time is 30-60min. When the reaction is carried out according to the above parameters, the effect of reducing the surface acidic sites is more obvious.

[0033] In some specific embodiments, the chemical formula of the organosilicon surface modifier is R m1 SiX m2 or Y n1 Yj Y n2, wherein X and R are selected from chloro, methoxy, ethoxy, methoxyethoxy, acetoxy, vinyl, phenyl, amino, epoxy, methacryloxy, mercapto or urea, m1, m2 = 1 to 3, m1 + m2 = 4, U is a nitrogen group or an oxygen group, Y is a methyl group, and n1, n2 = 1 to 3. The effects of using the above-mentioned surface modifiers are: first, the organic silicon molecules contact the molecular sieve framework structure at high temperature, and the group can fall off to provide a silicon-based group of a single molecular sieve. The silicon-based group is adsorbed on the defective site or acidic site of the molecular sieve framework, and silicon filling or silicon replacing the aluminum of the framework occurs at high temperature to eliminate the acidic site, or physical deposition occurs and is converted into SiO2 to cover the acidic site; second, the organic silicon containing macromolecular groups can avoid diffusion into the molecular sieve pores, ensuring that it acts on the acidic site 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 may be an MTO catalyst with SAPO-34 molecular sieve or ZSM-5 molecular sieve as an active component.

[0035] In some specific embodiments, the one-time contact includes: loading the molecular sieve catalyst into a closed reaction vessel, heating the interior of the closed reaction vessel to a reaction temperature, and introducing the acidic site masking agent into the reaction vessel together with an inert gas to react with the molecular sieve catalyst in one contact.

[0036] Preferably, after the primary contact reaction is completed, the introduction of the acidic site masking agent is stopped, and the introduction of the inert gas is continued for a period of time. The purpose of such 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 introducing the inert gas is to remove the acidic site masking agent adsorbed by the acidic sites with weak chemical binding ability, so as to expose the weak acidic sites in a directionally manner.

[0037] In some specific embodiments, the amount of acidic site masking agent introduced is 2-10% of the total mass of the molecular sieve catalyst. The above parameters are set so that the surface of the molecular sieve accounts for about 10% of the total specific surface area, of which the strong acidic sites account for about 20% of the total acidic sites. The amount of acidic site masking agent introduced must be controlled to cover the strong acidic sites as much as possible. Therefore, the amount introduced is controlled not to be lower than the estimated proportion of strong acidic sites on the external surface. When it is higher than 10%, the amount introduced is seriously excessive and the effect does not change much.

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

[0039] In some specific embodiments, the molecular sieve after the first contact is lowered to a suitable temperature and then contacted with the organosilicon surface modifier vapor for a second time. The suitable temperature is 200-330°C. The molecular sieve strongly acidic sites chemically adsorb the acidic site masking agent. As the temperature rises, the acidic site masking agent is easier to desorb. At high temperatures, only the strong acidic sites can adsorb the acidic site masking agent, and the acidic site masking agent at the weakly acidic site has no adsorption capacity. When the acidic site masking agent is introduced for a period of time at high temperature, it can be ensured that only the strong acidic sites adsorb the acidic site masking agent. After that, the temperature is lowered to ensure that the acidic site masking agent adsorbed on the strong acidic site will not desorb, ensuring that only the weakly acidic sites are exposed. The molecular sieve in this state is contacted with the organosilicon surface modifier vapor for a second time to ensure that the organosilicon surface modifier only acts on 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, enters a reaction container, and undergoes a secondary contact reaction with the molecular sieve.

[0041] In some specific embodiments, the surface modifier is preheated to 100-300° C. by 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 increase the linear velocity. The inert gas is preferably nitrogen.

[0043] Preferably, after the secondary contact reaction is completed, the introduction of steam is stopped and the introduction of inert gas is continued for a period of time. The purpose of such operation is to purge the excess physically adsorbed organosilicon surface modifier.

[0044] In some specific embodiments, the amount of surface modifier vapor introduced accounts for 2-20% of the total mass of the molecular sieve catalyst. The above parameter settings can ensure that the purpose of reducing the number of weakly acidic sites is achieved, and increasing the introduction amount will not change the effect.

[0045] The second aspect of the present invention provides a treatment device for adjusting the surface acid properties of a molecular sieve catalyst, comprising:

[0046] A reaction vessel, which is filled with a molecular sieve catalyst and receives the acidic site masking agent and the surface modifier vapor, and is used to provide a place for the molecular sieve catalyst to make a primary contact with the acidic site masking agent and for the molecular sieve catalyst to make a secondary contact with the surface modifier vapor;

[0047] A heater is disposed around the outer wall of the reaction container and is used to heat the internal environment temperature of the reaction container;

[0048] A preheater, used for receiving the liquid surface modifier and vaporizing it into steam, wherein the steam outlet of the preheater is connected to the reaction container;

[0049] The inert gas device is used to provide inert gas into the reaction container.

[0050] In some specific embodiments, the reaction container may be a columnar or tubular metal container or a quartz container comprising a gas inlet and a gas outlet, or may be a reactor having only one gas inlet and outlet.

[0051] In some specific embodiments, when the reaction container is a columnar or tubular metal container or a quartz container comprising an air inlet and an air outlet, the surface modifier is fed continuously, that is, introduced from the air inlet and released from the air outlet; when the reaction container is a reactor with only one gas inlet and outlet, a certain amount of surface modifier is introduced into the reactor through the inlet and outlet, and then the reactor is closed, and the surface modifier is fed discontinuously.

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

[0053] In some specific embodiments, the processing device of the present invention also includes a surface modifier storage tank and a facility for conveying the liquid surface modifier to a preheater. Exemplarily, the logistics in the surface modifier storage tank is conveyed to the preheater for preheating by a delivery pump. It can be understood that the present invention can adjust the flow rate of the surface modifier entering the preheater as needed.

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

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

[0056] In the present invention, the flow rate of the logistics entering the reaction vessel can be adjusted as needed, such as the flow rate of the acidic site masking agent, the inert gas, or the steam feed rate of the surface modifier.

[0057] The present invention is further described below by way of examples:

[0058] The raw material information is as follows:

[0059] Pseudo-boehmite: specification dry basis 70%, China Aluminum New Materials Co., Ltd.;

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

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

[0062] Triethylamine: Specification 99.9%, 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: Specification 98%, Shanghai MacLean Biochemical Technology Co., Ltd.

[0067] Ammonia: Specification 99.999%, Beijing Hepu North Gas Industry Co., Ltd.

[0068] Vinyltrimethoxysilane: Specification 98%, Shanghai MacLean Biochemical Technology Co., Ltd.

[0069] Dichlorodimethylsilane: specification 99%, Shanghai MacLean Biochemical Technology Co., Ltd.

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

[0071] Homemade conventional SAPO-34 molecular sieve. Pseudo-boehmite was used as aluminum source, phosphoric acid as phosphorus source, silica sol as silicon source, triethylamine as organic template, aluminum source as Al2O3, silicon source as SiO2, phosphorus source as P2O5, and the initial mixed gel was prepared according to the molar ratio of each substance, aluminum source: phosphorus source: silicon source: organic template: water = 1:1:0.3:3.5:50. After uniform dispersion, it was transferred to a high-pressure reactor for crystallization reaction at 200°C for 24h, and the SAPO-34 molecular sieve raw powder was obtained after cooling, separation, washing, and drying, and the SAPO-34 molecular sieve D1 was obtained after calcination at 650°C for 5h.

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

[0073] Homemade conventional ZSM-5 molecular sieve. 25% TPAOH aqueous solution, sodium hydroxide, sodium aluminate, 30% silica sol and water were mixed in a certain order and stirred for 24 hours to form a gel. The molar ratio of each substance in the gel was: 100SiO2:Al2O3:10TPAOH:3.8Na2O:1350H2O. The gel aged for 24 hours was transferred to a hydrothermal crystallization reactor and dynamically crystallized for 72 hours at 125°C and its own pressure. After the crystallization was completed, the ZSM-5 molecular sieve was obtained by cooling, separation, washing, drying and calcination. The hydrogen-type ZSM-5 molecular sieve D2 was obtained by ion exchange three times at 80°C with 0.5mol / L ammonium nitrate solution, drying at 80°C for 12 hours, and calcining at 650°C for 5 hours. The SiO2 / Al2O3 molar ratio was 88.

[0074] Comparative Example 3 (MTO catalyst)

[0075] The SAPO-34 molecular sieve powder, aluminum sol and kaolin in Comparative Example 1 were uniformly mixed according to the dry weight percentage of 40%:25%:35%, the mixture was spray-formed after rubber grinding, and calcined at 650° C. for 5 h to obtain methanol to olefins catalyst D3.

[0076] Example 1

[0077] The experimental process is as follows Figure 1 The reaction vessel is a metal reaction tube, the outside of which is heated by an electric heating jacket, the molecular sieve bed temperature is 300° C., and the total loading of SAPO-34 molecular sieve is 40 g. First, ammonia and nitrogen are introduced, with an ammonia flow rate of 50 ml / min and a nitrogen flow rate of 10 ml / min. The reaction lasts for 30 minutes, the ammonia valve is closed, and the nitrogen is continuously purged for 30 minutes. After that, the molecular sieve bed temperature is reduced to 260°C, and the surface modifier hexamethyldisilazane is introduced, and the material is fed at a rate of 0.05 ml / min through a plunger pump. The liquid surface modifier passes through a preheating furnace with a preheating furnace temperature of 120°C. The surface modifier vaporized into a gas is heated and merged with the nitrogen pipeline. The nitrogen flow rate is maintained at 10 ml / min. The mixed gas of nitrogen and the surface modifier enters the metal reaction tube from the bottom, fully contacts with the SAPO-34 molecular sieve D1, passes through the molecular sieve bed, and exits from the top of the reaction tube. After the above contact process with the surface modifier is continuously carried out for 90 minutes, the surface modifier is stopped, and the nitrogen is continuously purged for 30 minutes. After cooling, the molecular sieve is unloaded, washed, filtered, dried, and roasted to obtain the SAPO-34 molecular sieve S1 with poor acid on the outer surface.

[0078] Example 2

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

[0080] The obtained outer surface acid-poor ZSM-5 molecular sieve is recorded as S2.

[0081] Example 3

[0082] The difference from Example 1 is that the SAPO-34 molecular sieve D1 is replaced by the 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 obtained external surface acid-poor MTO catalyst is recorded as S3.

[0084] Example 4

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

[0086] The SAPO-34 molecular sieve S4 with poor external surface acid is obtained.

[0087] Example 5

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

[0089] The SAPO-34 molecular sieve S5 with poor external surface acid was obtained.

[0090] Example 6

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

[0092] The SAPO-34 molecular sieve S6 with poor external surface acid was obtained.

[0093] Example 7

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

[0095] The external surface acid-poor SAPO-34 molecular sieve S7 was obtained.

[0096] Example 8

[0097] The experimental process is as follows Figure 2. The reaction vessel was changed to an autoclave reactor, with a total loading of 40g of SAPO-34 molecular sieve in the autoclave, and a stirring paddle was connected to the autoclave to stir the molecular sieve powder. First, 1.1L of ammonia was introduced, the air inlet of the autoclave reactor was closed, the temperature was raised to 300°C, the reaction was carried out for 30min, the pressure reducing valve of the reactor was opened, the pressure was released, and nitrogen was continuously introduced for 30min, with a nitrogen flow rate of 50ml / min, and then the reactor temperature was lowered to 260°C. The nitrogen valve was closed, and the surface modifier hexamethyldisilazane was introduced, and the feed rate was 0.10ml / min through a plunger pump. The liquid surface modifier passed through a preheating furnace with a preheating furnace temperature of 150°C. The surface modifier vaporized into a gas by heating entered the autoclave reactor from the top, and the hexamethyldisilazane was fully in contact with the SAPO-34 molecular sieve D1. After hexamethyldisilazane was continuously introduced for 20 minutes, the plunger pump was stopped, the air inlet of the autoclave reactor was closed, and the autoclave reactor was heated by an external oil bath, the temperature in the autoclave was raised to 150°C, and the reaction was maintained for 20 minutes. After cooling, the molecular sieve was unloaded, washed, filtered, dried, and calcined to obtain the SAPO-34 molecular sieve S8 with poor external surface acid.

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

[0099] Ammonia molecules are smaller than the pores of SAPO-34 or ZSM-5 molecular sieves and can enter the internal pores of the molecular sieves. Therefore, NH3-TPD is used to analyze the total acid content (including internal acid content and surface acid content) of the molecular sieve sample to be tested. Instrument model: Micromeritics ASAP 2920 fully automatic chemical adsorption instrument. First, the sample to be tested is pressed into tablets, crushed, sieved, and 40-60 mesh particles are taken and dried for use. Accurately weigh 0.1g of the dried sample to be tested and put it into a quartz tube. The sample is heated to 600℃ in a He atmosphere for activation for 0.5h, cooled to room temperature, and adsorbed with NH3 (1.vol%)-He mixed gas for 15min. After the baseline is stable, the temperature is raised to 600℃ at a heating rate of 10℃ / min and the ammonia desorption signal in the 100-600℃ region is collected.

[0100] The pyridine molecule size exceeds the pore size of the SAPO-34 molecular sieve and cannot enter the internal pores of the molecular sieve. It can only be adsorbed by the acid sites on the surface. Therefore, the pyridine infrared method is used to characterize the surface acid content of the SAPO-34 molecular sieve sample. Instrument model: Thermo Fisher Nicolet IS10 infrared spectrometer, resolution 0.5cm -1 First, the sample to be tested was dried at 120°C for 2 hours, and the sample was made into a self-supporting disc with a diameter of 12 mm under a pressure of 5 MPa. The pretreated sample was adsorbed with pyridine vapor for 1 minute, balanced for 20 minutes, and then vacuum desorbed at 200°C (vacuum degree 10 -4Pa) for 1 h, then cooled to room temperature and the corresponding infrared absorption spectrum was collected. The collection range was 1300-1700 cm -1 The total acid content of pyridine infrared is calculated 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) is the number of B or L acid centers per gram of sample, and the unit of acid amount is mmol / g; I A (B / L) is the integrated area of ​​the absorption peak of B 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 raised to 350°C and vacuum desorption (vacuum degree 10 -4 Pa) for 1h, then cool to room temperature and collect the corresponding infrared absorption spectrum. Collect data again to obtain the strong acid amount determined by pyridine infrared.

[0106] The molecular size of 2,6-di-tert-butylpyridine exceeds the pore size of ZSM-5 molecular sieve and cannot enter the internal pores of ZSM-5 molecular sieve. It can only be adsorbed by the acid sites on the surface. Therefore, the infrared method of 2,6-di-tert-butylpyridine is used to characterize the surface acidity of ZSM-5 molecular sieve samples. Instrument model: Thermo Fisher Nicolet IS10 infrared spectrometer, resolution 0.5cm -1 First, the sample to be tested was dried at 120°C for 2h, and the sample was made into a self-supporting disc with a diameter of 12mm under a pressure of 5MPa. The pretreated sample was adsorbed with 2,6-di-tert-butylpyridine vapor for 1min, and after balancing for 20min, vacuum desorption was performed at 200°C (vacuum degree 10 -4 Pa) for 1 h, cooled to room temperature, and collected the corresponding infrared absorption spectrum. The collection range was 1615 cm -1 The calculation formula of the acid amount of 2,6-di-tert-butylpyridine infrared is as follows:

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

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

[0109] After collecting the above data, the temperature was raised to 350°C and vacuum desorption (vacuum degree 10 -4 Pa) for 1h, then cooled to room temperature and collected the corresponding infrared absorption spectrum. The data were collected again to obtain the strong acid amount of 2,6-di-tert-butylpyridine by infrared determination.

[0110] Table 1 Acid properties of Examples and Comparative Examples

[0111]

[0112] Compared with the comparative example, the ratio of the surface weak acid amount to the surface acid amount in the embodiments is reduced.

[0113] The catalyst performance evaluation in the present invention adopts a fixed bed reactor, the feed is a methanol aqueous solution with a concentration of 80%, the reaction temperature is 480°C, and the space velocity is 3.0h -1 , molecular sieve / catalyst loading amount 1.0g. Specific steps: the sample to be tested is loaded into the stainless steel reaction tube, heated to 500℃ for activation for 1h, cooled to 480℃, methanol aqueous solution is introduced, online sampling is adopted, the product is separated by condensation, and the gas phase components enter the gas chromatograph (Agilent, 7890A model) for composition analysis, equipped with HP-PLOT Al2O3 / KCl chromatographic column (50m×0.53mm×15μm) (separation of C1-C6 hydrocarbons), HP-PLOT Q chromatographic column (30m×320μm×20μm) (separation of alcohols and ethers), Hayesep Q column and X molecular sieve column (separation of permanent gases such as CO, CO2, H2, N2), 2 FID detectors and 1 TCD detector.

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

[0115]

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

[0117] When the methanol conversion rate in the test component is lower than 99%, the catalyst is considered to be deactivated, and the catalyst life is the time during which the methanol conversion rate is maintained above 99%. The test results are as follows.

[0118] Table 2 Methanol conversion reaction life and product selectivity of Examples and Comparative Examples

[0119]

[0120]

[0121] Compared with the comparative example, the examples of the present invention have excellent catalytic performance, long reaction life, high selectivity for ethylene and propylene, and low selectivity for C4.

[0122] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as limiting the present invention. Those skilled in the art will appreciate that, under the guidance of this specification, some modifications or adjustments may be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for modifying the surface acidity of a molecular sieve catalyst, characterized in that: The steps include: The molecular sieve catalyst is contacted with the acidic site masking agent once, and the molecular sieve after the first contact is contacted with the steam of the organosilicon surface modifier for a second time, and then the molecular sieve catalyst after the second contact is washed, solid-liquid separated, dried and calcined to obtain a surface acid-poor molecular sieve catalyst; Wherein, 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 minutes; the reaction temperature during the second contact is 200-330°C, and the reaction time is 30-60 minutes.

2. The processing method according to claim 1, characterized in that: The chemical formula of the organosilicon surface modifier is R m1 SiX m2 or Y n1 Yj Y n2 , wherein X and R are selected from chloro, methoxy, ethoxy, methoxyethoxy, acetoxy, vinyl, phenyl, amino, epoxy, methacryloxy, mercapto or urea, m1, m2=1 to 3, m1+m2=4, U is nitrogen or oxy, Y is methyl, and n1, n2=1 to 3.

3. The processing method according to claim 1 or 2, characterized in that: 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 an active component.

4. The processing method according to any one of claims 1 to 3, characterized in that: The one-time contact comprises: loading the molecular sieve catalyst into a sealed reaction container, heating the inside of the sealed reaction container to a reaction temperature, and allowing the acidic site masking agent and the inert gas to enter the reaction container together to react with the molecular sieve catalyst in one-time contact.

5. The processing method according to claim 1 or 4, characterized in that: The amount of the acidic site masking agent introduced accounts for 2-10% of the total mass of the molecular sieve catalyst.

6. The processing method according to any one of claims 1 to 5, characterized in that: The secondary contact comprises: vaporizing the liquid phase organosilicon surface modifier into steam through a preheater, and entering the reaction container to conduct a secondary contact reaction with the molecular sieve catalyst; Preferably, the molecular sieve after the first contact is cooled to a suitable temperature and then contacted with the organic silicon surface modifier vapor for a second time, and the suitable temperature is 200-330°C.

7. The processing method according to claim 6, characterized in that: The surface modifier is preheated to 100-300°C by a preheater.

8. The processing method according to claim 6, characterized in that: The surface modifier vapor enters the reaction vessel together with an inert gas, preferably nitrogen.

9. The processing method according to any one of claims 1 to 9, characterized in that: The amount of surface modifier steam introduced accounts for 2-20% of the total mass of the molecular sieve catalyst.

10. A treatment device for adjusting the surface acidity of a molecular sieve catalyst, characterized in that: include: A reaction vessel, which is filled with a molecular sieve catalyst and receives acidic site masking agent and surface modifier vapor, and is used to provide a place for the molecular sieve catalyst to make a primary contact with the acidic site masking agent and for the molecular sieve catalyst to make a secondary contact with the surface modifier vapor; A heater is disposed around the outer wall of the reaction container and is used to heat the internal environment temperature of the reaction container; A preheater, used for receiving the liquid surface modifier and vaporizing it into steam, wherein the steam outlet of the preheater is connected to the reaction container; The inert gas device is used to provide inert gas into the reaction container.

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