Method for controlling the acid strength distribution of solid acids and solid acids and applications

Abstract

The application relates to the field of solid acid, and discloses a method for regulating acid strength distribution of solid acid, solid acid and application. The method for regulating acid strength distribution of solid acid comprises the following steps: (1) in the presence of ammonium cations, reversibly adsorbing the solid acid on the ammonium cations, and then performing first desorption; and (2) in the presence of metal cations, performing directional adsorption of the product after the first desorption in step (1) on the metal cations, and then performing second desorption. The method combines the reversible adsorption of ammonium cations and the directional adsorption of metal cations, can regulate the acid strength distribution conveniently while keeping the acid amount of the solid acid, and meets different application environments.

Description

Technical Field

[0001] This invention relates to the technical field of solid acids, specifically to a method for regulating the acid strength distribution of a solid acid, as well as the solid acid and its applications. Background Technology

[0002] Solid acid catalysts are commonly used in petrochemical processes, such as alkylation, isomerization, catalytic cracking, and catalytic pyrolysis. Due to the inherent structure of solid acids, the strength of acidic sites on their surface varies, resulting in a wide acid strength distribution. Furthermore, controlling the acid strength of solid acids is more difficult than with liquid acids, which allow for the convenient control of acid density and strength using proton concentration. However, different catalytic reactions have varying requirements for acid strength; for example, alkylation requires high acid strength. The acid strength of molecular sieve-type solid acids is generally achieved by controlling the silica-alumina ratio of the molecular sieve. However, unlike liquid acids where acid strength and density increase synchronously with proton concentration, a higher silica-alumina ratio in molecular sieves leads to higher acid strength, but a significant decrease in acid density. This presents a considerable challenge for reactions requiring both high acid strength and density simultaneously.

[0003] In the literature, the acid strength distribution of molecular sieve catalysts is generally controlled by adjusting the silica-to-alumina ratio (S / A ratio). For example, Xu Ruren et al. pointed out that the S / A ratio of molecular sieves is closely related to their acidity and catalytic activity, and adjusting the S / A ratio of the molecular sieve framework is a common method for controlling the acid strength of molecular sieves (Molecular Sieves and Porous Materials Chemistry (Second Edition), Science Press, 2014.8, 345-359). Bao et al. used dealumination and re-alumination to control the S / A ratio of HZSM-5 molecular sieves, successfully modulating the acid content and acid strength of the molecular sieve (J. Phys. Chem. B 2006, 110, 15411-15416). For other types of solid acids, there are methods to suppress strong acids by alkali adsorption, but no method to precisely control the acid strength of the desired catalyst. Therefore, how to conveniently control the acid strength of solid acid catalysts has important theoretical and practical significance. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that existing technologies cannot simultaneously achieve both strong and abundant acid in solid acids. This invention provides a method for regulating the distribution of acid strength in solid acids, as well as the application of solid acids. This method combines reversible adsorption of ammonium cations with directional adsorption of metal cations, which can conveniently regulate the distribution of acid strength while maintaining the abundance of solid acids, in order to meet different application environments.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for regulating the distribution of acid strength in a solid, wherein the method includes the following steps:

[0006] (1) In the presence of ammonium cations, solid acid is reversibly adsorbed by ammonium cations, and then subjected to a first desorption.

[0007] (2) In the presence of metal cations, the product after the first desorption in step (1) is subjected to directional adsorption of metal cations, and then a second desorption is performed.

[0008] Preferably, the directional adsorption temperature of the metal cation is 5-30°C higher than that of the reversible adsorption temperature of the ammonium cation, and more preferably 10-25°C higher.

[0009] Preferably, in step (2), the metal ion exchange degree of the second desorption product is 15-80%, more preferably 30-50%.

[0010] The second aspect of the present invention provides a solid acid prepared by the control method described in the first aspect.

[0011] A third aspect of the present invention provides the application of the solid acid described in the second aspect in the alkylation reaction of low-carbon olefins.

[0012] Through research, the inventors of this invention discovered that the alternation of reversible adsorption of ammonium cations with the directional adsorption (irreversible adsorption) of other cations can selectively cover acid centers of different intensities, thereby achieving the goal of conveniently controlling the distribution of solid acid strength while maintaining the amount of solid acid.

[0013] The method of the present invention can control the catalyst to have only a certain acid strength, such as a moderately strong acid, based on the reaction requirements. The method is simple, convenient, and highly applicable, and has significant advantages over the prior art. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] The first aspect of this invention provides a method for regulating the distribution of acid strength in a solid, wherein the method includes the following steps:

[0016] (1) In the presence of ammonium cations, solid acid is reversibly adsorbed by ammonium cations, and then subjected to a first desorption.

[0017] (2) In the presence of metal cations, the product after the first desorption in step (1) is subjected to directional adsorption of metal cations, and then a second desorption is performed.

[0018] Through research, the inventors of this invention discovered that the alternation of reversible adsorption of ammonium cations with the directional adsorption (irreversible adsorption) of other cations can selectively cover acid centers of different intensities, thereby achieving the goal of conveniently controlling the distribution of solid acid strength while maintaining the amount of solid acid.

[0019] The method of the present invention can control the catalyst to have only a certain acid strength, such as a moderately strong acid, based on the reaction requirements. The method is simple, convenient, and highly applicable, and has significant advantages over the prior art.

[0020] This invention utilizes the reversible adsorption of ammonium cations, followed by desorption at a certain temperature to expose acidic sites of a certain intensity. Then, it utilizes the directional irreversible adsorption of metal cations to occupy these sites. Finally, all or part of the reversibly adsorbed cations are removed, thereby exposing some acidic sites. This allows for convenient and simple control of acid distribution, making it suitable for different industrial scenarios.

[0021] In this invention, by controlling the conditions for the reversible adsorption of ammonium cations and the directional adsorption of metal cations in steps (1) and (2), the various reaction conditions interact to obtain a solid acid with a high amount and distribution of moderately strong acids. Preferably, the amount of moderately strong acid in the solid acid is 450-1400 μmol / g, more preferably 950-1200 μmol / g, for example, it can be 950 μmol / g, 1000 μmol / g, 1050 μmol / g, 1100 μmol / g, 1150 μmol / g, 1200 μmol / g, or any value between any two groups. Preferably, the proportion of the medium-strong acid in the solid acid to the total acid content is 40-85%, more preferably 65-80%, for example, it can be 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, and any value between any two groups.

[0022] In this invention, reversible adsorption refers to the ability of a medium adsorbed at low temperatures to be completely desorbed at high temperatures.

[0023] In this invention, the directional adsorption of metal cations refers to the directional adsorption of metal ions onto a portion of the acidic sites.

[0024] In this invention, preferably, the directional adsorption temperature of the metal cation is 5-30°C higher than the reversible adsorption temperature of the ammonium cation, more preferably 10-25°C higher. For example, it can be 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, or any value between two groups. The advantage of this preferred embodiment is that the migration of cations during the high-temperature desorption process may lead to changes in the coverage of acidic sites. Since the temperature is higher than the reversible adsorption temperature, better stability of the metal cations can be ensured.

[0025] In this invention, step (1) is carried out in the presence of ammonium cations to expose acidic sites on the solid acid, providing acidic sites for subsequent directional adsorption of metal cations and facilitating acid intensity control. This invention does not particularly limit the source of the ammonium cations, as long as the required ammonium cations can be provided. Preferably, the ammonium cations are provided by an ammonia-containing atmosphere and / or a compound containing ammonium cations.

[0026] In this invention, the concentration of ammonia in the ammonia-containing atmosphere is not particularly limited, as long as the required ammonium cations can be provided. Preferably, the volume concentration of ammonia in the ammonia-containing atmosphere is 5-100%. By selecting ammonium cations within the above preferred range, the liquid filtration and drying processes are avoided, making adsorption convenient and efficient.

[0027] In this invention, there is no particular limitation on the specific type of compound containing ammonium cations, as long as the required ammonium cations can be provided. Preferably, the compound containing ammonium cations is provided by a solution of the compound containing ammonium cations.

[0028] In this invention, preferably, the concentration of the solution containing the ammonium cation is 1-5 mol / L.

[0029] In this invention, there is no particular limitation on the type of solid acid; any solid acid conventionally defined in the art can be applied to the control method of this invention. Preferably, in step (1), the solid acid is selected from at least one of heteropoly acids, solid superacids, mixed oxides, supported solid acids, and molecular sieves, and is more preferably a molecular sieve.

[0030] In this invention, preferably, the molecular sieve is selected from at least one of Y-type molecular sieves, Beta-type molecular sieves, ZSM-5 type molecular sieves, MOR type molecular sieves, and MCM-22 type molecular sieves, and more preferably, Y-type molecular sieves. The method provided by this invention is particularly suitable for acid intensity control of molecular sieves, making the molecular sieves applicable to different application scenarios.

[0031] In this invention, by controlling the conditions for reversible adsorption of ammonium cations, acidic sites are sufficiently exposed, providing more acidic sites for subsequent directional cation adsorption and facilitating the control of acid strength. According to a preferred embodiment of the invention, the ammonium cations are provided by an ammonia-containing atmosphere, and the conditions for reversible adsorption of the ammonium cations include: an adsorption temperature of 20-100℃, a time of 0.5-3 h, and a flow rate of 5-50 mL / min relative to 1 g of solid acid.

[0032] According to another preferred embodiment of the present invention, the ammonium cation is provided by a compound containing ammonium cations, and the reversible adsorption of the ammonium cations is performed by ion exchange. The advantage of this preferred embodiment is that the ion exchange method allows the ammonium cations to be exchanged only to acidic sites, without affecting the pores or the outer surface.

[0033] In this invention, the selection range of conditions for ammonium cation exchange by ion exchange method is relatively wide. Preferably, the ammonium cation is provided by a compound containing ammonium cation, and the conditions for reversible adsorption of the ammonium cation include: an adsorption temperature of 50-90℃, a time of 1-5 h, and an amount of solution of the compound containing ammonium cation of 2-10 g relative to 1 g of solid acid.

[0034] In this invention, by controlling the conditions for the first desorption, the requirements of different application environments for the acid strength distribution of solid acids can be met. The operation process is simple and highly adaptable. Preferably, in step (1), the conditions for the first desorption include: a temperature of 200-350℃ and a time of 2-8h.

[0035] In this invention, preferably, in step (1), the first desorption is carried out in the presence of an inert atmosphere, preferably the inert atmosphere is selected from at least one of nitrogen, argon and helium.

[0036] In this invention, preferably, in step (1), the conditions for the first desorption further include: the flow rate of the inert atmosphere is 5-50 mL / min relative to 1 g of solid acid.

[0037] In this invention, preferably, step (1) further includes drying the solid acid followed by reversible adsorption of ammonium cations. In this invention, the method and conditions of the drying process are not particularly limited, and those skilled in the art can adjust them according to actual circumstances.

[0038] In this invention, preferably, in step (2), the metal ion exchange degree of the second desorption product is 15-80%, more preferably 30-50%, for example, it can be 30%, 35%, 40%, 45%, 50% and any value between any two groups.

[0039] In this invention, the metal ion exchange degree refers to the ratio of the amount of cations (amount of substance) exchanged into the molecular sieve to the amount of Al atoms in the molecular sieve. The exchange degree is determined by performing compositional tests on the final molecular sieve (XRF or ICP can be used to determine the relative amounts of exchanged metals and Al atoms in the molecular sieve).

[0040] In this invention, step (2) selectively covers the acidic sites of the solid acid in the presence of metal cations, thereby achieving convenient control over the acid strength of the solid acid. This invention does not particularly limit the source of the metal cations, as long as the required metal cations can be provided. Preferably, the metal cations are provided by compounds containing metal cations, more preferably by at least one of compounds containing Group IIA metals, compounds containing Group VIIB metals, and compounds containing Group IB metals, and even more preferably by compounds containing Ca... 2+ Compounds containing Ag + Compounds and Re-containing 2+ At least one of the compounds is provided. Preferably, in this invention, the metal cation-containing compound is provided by a solution of the metal cation-containing compound. In this invention, there is no particular limitation on the concentration of the solution of the metal cation-containing compound; preferably, the concentration of the solution of the metal cation-containing compound is 1-10% by weight, which can be selected by those skilled in the art according to actual needs.

[0041] In this invention, there is no particular limitation on the method of metal cation adsorption, as long as the metal cations can cover the acidic sites of the solid. Preferably, in step (2), the metal cation adsorption is selected from at least one of ion exchange, equal volume impregnation, and vacuum impregnation, with ion exchange being preferred. By using ion exchange to achieve the directional adsorption of metal cations, excessive metal ion residue can be avoided from affecting pore diffusion.

[0042] In this invention, preferably, in step (2), the conditions for the directional adsorption of the metal cations include: a temperature of 40-95℃, a time of 1-10h, and the amount of the compound containing the metal cations is 0.05-3g relative to 1g of the product after the first desorption; more preferably, in step (2), the conditions for the directional adsorption of the metal cations include: a temperature of 60-90℃, a time of 2-6h, and the amount of the compound containing the metal cations is 0.1-1.3g relative to 1g of the product after the first desorption.

[0043] In this invention, by controlling the conditions for the second desorption, the requirements of different application environments for the acid strength distribution of solid acids can be met. The operation process is simple and highly adaptable. Preferably, in step (2), the conditions for the second desorption include: a temperature of 400-650℃ and a time of 1-8h; more preferably, in step (2), the conditions for the second desorption include: a temperature of 450-600℃ and a time of 1-6h.

[0044] In this invention, preferably, in step (2), the second desorption is carried out in the presence of an inert atmosphere, preferably the inert atmosphere is selected from at least one of nitrogen, argon and helium.

[0045] In this invention, preferably, in step (2), the conditions for the second desorption further include: the flow rate of the inert atmosphere is 5-50 mL / min relative to 1 g of the product after the first desorption.

[0046] The second aspect of the present invention provides a solid acid prepared by the control method described in the first aspect.

[0047] The present invention provides a solid acid with a high medium-strong acid content. Preferably, the medium-strong acid content of the solid acid is 450-1400 μmol / g, more preferably 950-1200 μmol / g.

[0048] The present invention provides a solid acid with a high proportion of moderately strong acids. Preferably, the proportion of moderately strong acids in the solid acid is 40-85% of the total acid content, more preferably 65-80%.

[0049] A third aspect of the present invention provides the application of the solid acid described in the second aspect in the alkylation reaction of low-carbon olefins.

[0050] In this invention, preferably, the low-carbon olefin is selected from C3-C6 low-carbon olefins. This invention does not particularly limit the specific type of low-carbon olefin; for example, it can be butene.

[0051] The solid acid provided by this invention has a specific ratio of medium-strong acid content and separation, provides alkylation performance of low-carbon olefins, and improves the selectivity of the target product C8.

[0052] In this invention, the acid strength and acid content are determined using the NH3-TPD method, specifically as follows: A chemisorption analyzer is used. 0.15 g of sample with a particle size of 20-40 mesh is weighed and placed in a quartz sample tube, which is then placed in a thermal conductivity cell furnace. First, He gas at a flow rate of 50 mL / min is used as the carrier gas to raise the temperature to 250 °C and purge for 2 hours to remove adsorbed impurities from the sample surface. Then, the temperature is lowered to 100 °C and held for 30 minutes. The mixture is then switched to an NH3 / He mixture (10 vol% NH3 + 90 vol% He) for saturated adsorption for 30 minutes, followed by purging with He gas for 90 minutes until the baseline stabilizes, thus removing NH3 physically adsorbed on the sample surface. The temperature is then raised to 250 °C at a rate of 10 °C / min and held for 30 minutes to remove ammonia that can be desorbed below 250 °C. A TCD detector is used to detect changes in gas composition. The temperature is then raised to 350, 450, and 550 °C, and the above steps are repeated. A TCD detector was used to detect gas changes. The adsorption curves obtained at different temperature ranges were integrated to automatically calculate the acid content distribution at different temperatures. The desorption amount at 250℃ represents the amount of weak acid, the desorption amounts at 350℃ and 450℃ represent the amount of medium-strong acid, and the desorption amount at 550℃ represents the amount of strong acid.

[0053] The present invention will be described in detail below through embodiments. In the following embodiments, unless otherwise specified, the raw materials used are all commercially available products.

[0054] In Examples 1-4, 6 and the Comparative Example below, the solid acid used was a Y-type molecular sieve (n Si / n Al =3.5, Na2O mass fraction 0.1%, crystallinity 95%.

[0055] Example 1

[0056] (1) After the HY molecular sieve was vacuum dried at 150℃ for 24h, an atmosphere containing ammonia was introduced at room temperature for reversible adsorption of ammonium cations. The volume concentration of ammonia in the atmosphere was 5%, and the flow rate of the atmosphere containing ammonia was 5mL / min relative to 1g of HY molecular sieve. The conditions for reversible adsorption of ammonium cations were: 50℃ for 2h. After adsorption saturation, the temperature was raised to 350℃ and held for 2h for the first desorption under nitrogen. The flow rate of nitrogen was 5mL / min relative to 1g of HY molecular sieve. Nitrogen was introduced into the water, and the first desorption was completed when the pH change of the water was less than 0.1.

[0057] (2) The molecular sieve after the first desorption was subjected to ion exchange with silver nitrate solution (temperature 75℃, mass ratio of AgNO3:H2O:molecular sieve after the first desorption = 1:60:6, exchange time 1h). When the pH change of the solution was less than 0.1, the Ag ion exchange was completed. +The catalyst was then subjected to directional adsorption. The directionally adsorbed catalyst was then heated to 450℃ and subjected to a second desorption under nitrogen for 1 hour. The nitrogen flow rate was 5 mL / min relative to 1 g of the molecular sieve after the first desorption. Nitrogen was introduced into water, and the second desorption was completed when the pH change of the water was less than 0.1. The metal ion exchange capacity of the second desorption product was 45%. The acid strength and acid content of the obtained catalyst were determined by NH3-TPD characterization, and the results are shown in Table 1.

[0058] Example 2

[0059] (1) After the HY molecular sieve was vacuum dried at 150℃ for 24h, an atmosphere containing ammonia was introduced at room temperature for reversible adsorption of ammonium cations. The volume concentration of ammonia in the atmosphere was 100%, and the flow rate of the atmosphere containing ammonia was 15mL / min relative to 1g of HY molecular sieve. The conditions for reversible adsorption of ammonium cations were: 80℃ for 0.5h. After adsorption saturation, the temperature was raised to 200℃ and held for 8h for the first desorption under nitrogen. The flow rate of nitrogen was 15mL / min relative to 1g of HY molecular sieve. Nitrogen was introduced into the water, and the first desorption was completed when the pH change of the water was less than 0.1.

[0060] (2) The molecular sieve after the first desorption was subjected to ion exchange with silver nitrate solution (temperature 95℃, mass ratio of AgNO3:H2O:molecular sieve after the first desorption = 0.6:60:6, exchange time 1h). When the pH change of the solution was less than 0.1, the Ag ion exchange was completed. + The catalyst was then subjected to directional adsorption. The directionally adsorbed catalyst was then heated to 600℃ and subjected to a second desorption under nitrogen for 6 hours. The nitrogen flow rate was 15 mL / min relative to 1 g of the molecular sieve after the first desorption. Nitrogen was introduced into water, and the second desorption was completed when the pH change of the water was less than 0.1. The metal ion exchange capacity of the second desorption product was 30%. The acid strength and acid content of the obtained catalyst were determined by NH3-TPD characterization, and the results are shown in Table 1.

[0061] Example 3

[0062] (1) After the HY molecular sieve was vacuum dried at 150℃ for 24h, an atmosphere containing ammonia was introduced at room temperature for reversible adsorption of ammonium cations. The volume concentration of ammonia in the atmosphere was 20%, and the flow rate of the atmosphere containing ammonia was 50mL / min relative to 1g of HY molecular sieve. The conditions for reversible adsorption of ammonium cations were: 20℃ for 3h. After adsorption saturation, the temperature was raised to 300℃ and held for 1h for the first desorption under nitrogen. The flow rate of nitrogen was 50mL / min relative to 1g of HY molecular sieve. Nitrogen was introduced into the water, and the first desorption was completed when the pH change of the water was less than 0.1.

[0063] (2) The molecular sieve after the first desorption was subjected to ion exchange with silver nitrate solution (temperature 40℃, AgNO3:H2O:molecular sieve mass ratio = 1.2:60:6, exchange time 1h). When the pH change of the solution was less than 0.1, the Ag ion exchange was completed. + The catalyst was then subjected to directional adsorption. The directionally adsorbed catalyst was then heated to 500℃ and subjected to a second desorption under nitrogen for 3 hours. The nitrogen flow rate was 50 mL / min relative to 1 g of the molecular sieve after the first desorption. Nitrogen was introduced into water, and the second desorption was completed when the pH change of the water was less than 0.1. The metal ion exchange rate of the second desorption product was 50%. The acid strength and acid content of the obtained catalyst were determined by NH3-TPD characterization, and the results are shown in Table 1.

[0064] Example 4

[0065] (1) After the HY molecular sieve was vacuum dried at 150℃ for 24h, an atmosphere containing ammonia was introduced at room temperature for reversible adsorption of ammonium cations. The volume concentration of ammonia in the atmosphere was 5%, and the flow rate of the atmosphere containing ammonia was 5mL / min relative to 1g of HY molecular sieve. The conditions for reversible adsorption of ammonium cations were: 100℃ for 2h. After adsorption saturation, the temperature was raised to 350℃ and held for 2h for the first desorption under nitrogen. The flow rate of nitrogen was 5mL / min relative to 1g of HY molecular sieve. Nitrogen was introduced into the water, and the first desorption was completed when the pH change of the water was less than 0.1.

[0066] (2) The molecular sieve after the first desorption was subjected to ion exchange with silver nitrate solution (temperature 75℃, mass ratio of AgNO3:H2O:molecular sieve after the first desorption = 1:60:6, exchange time 1h). When the pH change of the solution was less than 0.1, the Ag ion exchange was completed. + The catalyst was then subjected to directional adsorption. The directionally adsorbed catalyst was then heated to 450℃ and subjected to a second desorption under nitrogen for 1 hour. The nitrogen flow rate was 5 mL / min relative to 1 g of the molecular sieve after the first desorption. Nitrogen was introduced into water, and the second desorption was completed when the pH change of the water was less than 0.1. The metal ion exchange capacity of the second desorption product was 40%. The acid strength and acid content of the obtained catalyst were determined by NH3-TPD characterization, and the results are shown in Table 1.

[0067] Example 5

[0068] The method of Example 1 was followed, except that the molecular sieve used was Hβ molecular sieve (nSi / nAl = 10, Na2O mass fraction 0.08%, crystallinity 90%), and all other conditions were the same, with a final metal ion exchange ratio of 35%. The acid strength and acid content were determined by NH3-TPD characterization, and the results are shown in Table 1.

[0069] Example 6

[0070] (1) After the HY molecular sieve was vacuum dried at 150℃ for 24h, an atmosphere containing ammonia was introduced at room temperature for reversible adsorption of ammonium cations. The volume concentration of ammonia in the atmosphere was 5%, and the flow rate of the atmosphere containing ammonia was 5mL / min relative to 1g of HY molecular sieve. The conditions for reversible adsorption of ammonium cations were: 50℃ for 2h. After adsorption saturation, the temperature was raised to 350℃ and held for 2h for the first desorption under nitrogen. The flow rate of nitrogen was 5mL / min relative to 1g of HY molecular sieve. Nitrogen was introduced into the water, and the first desorption was completed when the pH change of the water was less than 0.1.

[0071] (2) The molecular sieve after the first desorption was subjected to ion exchange with silver nitrate solution (temperature 25℃, mass ratio of AgNO3:H2O:molecular sieve after the first desorption = 0.3:60:6, exchange time 1h). When the pH change of the solution was less than 0.1, the Ag ion exchange was completed. + The catalyst was then subjected to directional adsorption. The directionally adsorbed catalyst was then heated to 450℃ and subjected to a second desorption under nitrogen for 1 hour. The nitrogen flow rate was 5 mL / min relative to 1 g of the molecular sieve after the first desorption. Nitrogen was introduced into water, and the second desorption was completed when the pH change of the water was less than 0.1. The metal ion exchange capacity of the second desorption product was 15%. The acid strength and acid content of the obtained catalyst were determined by NH3-TPD characterization, and the results are shown in Table 1.

[0072] Example 7

[0073] Following the method of Example 1, except that step (2) employed a vacuum impregnation method with the solution ratio remaining unchanged, conducted in a rotary evaporator for 1 hour. After impregnation, the solution was heated and vacuumed to remove water, then dehydrated at 75°C and 0.08 MPa for 3 hours, followed by drying in an oven at 110°C for 4 hours, and then undergoing the corresponding desorption process. The final ion exchange capacity was 60%. The acid strength and acid content were determined by NH3-TPD characterization, and the results are shown in Table 1.

[0074] Comparative Example 1

[0075] The HY molecular sieve from Example 1 was selected. After vacuum drying at 150℃ for 24h, ammonia gas was introduced at room temperature for adsorption. After adsorption saturation, the molecular sieve was heated to 350℃ and held for 1h for the first step of desorption. The resulting catalyst was characterized by NH3-TPD (note that NH3-TPD only desorbed to 350℃) and its acid strength and acid content were determined. The results are shown in Table 1.

[0076] Comparative Example 2

[0077] The HY molecular sieve from Example 1 was selected and treated with ammonium fluorosilicate solution (0.25 mol / L, 1 g molecular sieve = 30 mL solution) at 80 °C for 2 h. After washing with a large amount of water, drying at 110 °C for 12 h, and then calcining at 450 °C for 3 h, a HY molecular sieve with nSi / nAl = 9.5, Na₂O mass fraction of 0.08%, and crystallinity of 85% was obtained. This was used as a comparative example to obtain catalysts using conventional post-treatment methods. Its acid strength and acid content were determined by NH₃-TPD characterization (note that NH₃-TPD desorption was performed at 550 °C), and the results are shown in Table 1.

[0078] Table 1

[0079]

[0080]

[0081] As can be seen from the table above, the molecular sieve prepared by the method of the present invention can conveniently control the distribution of medium-strong acids in the catalyst, and the total acid content is not significantly affected. Compared with the catalyst prepared by conventional post-treatment method, the amount of medium-strong acid can be more than twice as high.

[0082] Test case

[0083] The solid acids prepared in the above examples and comparative examples were used for alkylation reactions involving isoparaffins and olefins in a fixed-bed reactor. The reaction conditions were as follows: the molar ratio of isobutane to mixed butenes (1-butene and 2-butene) was 220, the reaction temperature was 75°C, the reaction pressure was 2.5 MPa, and the feed flow rate of isobutane and mixed butenes was 200 mL / h. The detection of butene in the product indicated catalyst deactivation. The reaction time before catalyst deactivation was defined as the catalyst cycle life. The results are shown in Table 2.

[0084] Table 2

[0085]

[0086]

[0087] As can be seen from the table above, the solid acid prepared by the method of the present invention has a high acid content and acid strength distribution, and a low amount of weak acid, thus exhibiting better alkylation reaction cycle life and target product selectivity.

[0088] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for controlling the distribution of acid strength in a solid acid, characterized in that, The method includes the following steps: (1) In the presence of ammonium cations, solid acid is reversibly adsorbed by ammonium cations, and then a first desorption is performed; the conditions for the first desorption include: a temperature of 200-350℃; (2) In the presence of metal cations, the product after the first desorption in step (1) is subjected to directional adsorption of metal cations, and then subjected to a second desorption; the conditions for directional adsorption of metal cations include: a temperature of 25-95℃; the conditions for the second desorption include: a temperature of 400-650℃. The directional adsorption temperature of the metal cation is 5-30°C higher than that of the reversible adsorption temperature of the ammonium cation. In step (2), the metal ion exchange degree of the second desorption product is 15-80%; the metal ion exchange degree refers to the ratio of the amount of cations exchanged into the molecular sieve to the amount of Al atoms in the molecular sieve. In step (1), the solid acid is a molecular sieve; the molecular sieve is selected from at least one of Y-type molecular sieve, Beta-type molecular sieve, ZSM-5 type molecular sieve, MOR type molecular sieve and MCM-22 type molecular sieve. In step (2), the metal cation is provided by a compound containing a metal cation; the metal cation is provided by at least one of a compound containing a Group IIA metal element, a compound containing a Group VIIB metal element, and a compound containing a Group IB metal element.

2. The method according to claim 1, wherein, The directional adsorption of the metal cations is 10-25°C higher than the reversible adsorption of the ammonium cations.

3. The method according to claim 1 or 2, wherein, The ammonium cation is provided by an atmosphere containing ammonia and / or a compound containing an ammonium cation.

4. The method according to claim 3, wherein, In the ammonia-containing atmosphere, the volume concentration of ammonia is 5-100%.

5. The method according to claim 3, wherein, The ammonium-containing compound is provided by selecting at least one of ammonia and ammonium salts.

6. The method according to claim 5, wherein, The ammonium-containing compound is provided by ammonia water.

7. The method according to claim 3, wherein, The ammonium-containing cation is provided by a solution of the ammonium-containing cation.

8. The method according to claim 7, wherein, The concentration of the solution containing the ammonium cation is 1-5 mol / L.

9. The method according to claim 1, wherein, The molecular sieve is a Y-type molecular sieve.

10. The method according to claim 3, wherein, The ammonium cations are provided by an ammonia-containing atmosphere, and the conditions for reversible adsorption of the ammonium cations include: an adsorption temperature of 20-80℃, a time of 0.5-3h, and a flow rate of 5-50mL / min of the ammonia-containing atmosphere relative to 1g of solid acid.

11. The method according to claim 3, wherein, The ammonium cation is provided by a compound containing ammonium cations, and the reversible adsorption of the ammonium cation is performed by ion exchange.

12. The method according to claim 11, wherein, The ammonium cation is provided by a compound containing an ammonium cation, and the conditions for reversible adsorption of the ammonium cation include: an adsorption temperature of 50-90℃, a time of 1-5h, and an amount of 2-10g of the solution containing the ammonium cation relative to 1g of solid acid.

13. The method according to claim 1, wherein, In step (1), the conditions for the first desorption include a time of 1-8 hours.

14. The method according to claim 1, wherein, In step (2), the metal ion exchange degree of the second desorption product is 30-50%.

15. The method according to claim 1, wherein, In step (2), the metal cation is composed of Ca... 2+ Compounds containing Ag + Compounds and Re-containing 2+ At least one of the compounds is provided.

16. The method according to claim 1, wherein, In step (2), the directional adsorption of metal cations is selected from at least one of ion exchange, equal volume impregnation and vacuum impregnation.

17. The method according to claim 16, wherein, In step (2), the directional adsorption of metal cations is performed by ion exchange.

18. The method according to claim 1, wherein, In step (2), the conditions for the directional adsorption of the metal cations include: a time of 1-10 h, and an amount of 0.05-3 g of the compound containing the metal cation relative to 1 g of the first desorption product.

19. The method according to claim 1 or 18, wherein, In step (2), the conditions for the directional adsorption of the metal cations include: a temperature of 60-90℃, a time of 2-6h, and an amount of the compound containing the metal cations of 0.1-1.3g relative to 1g of the product after the first desorption.

20. The method according to claim 1, wherein, In step (2), the conditions for the second desorption include a time of 1-8 hours.

21. The method according to claim 1 or 20, wherein, In step (2), the conditions for the second desorption include: a temperature of 450-600℃ and a time of 1-6h.

22. A solid acid prepared by the control method according to any one of claims 1-21.

23. The application of the solid acid prepared by the control method according to any one of claims 1-21 in the alkylation reaction of low-carbon olefins.

24. The application according to claim 23, wherein, The low-carbon olefins are selected from C3-C6 low-carbon olefins.

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