Method for regulating and controlling acid site structure of ultra-stable Y-type molecular sieve through post-treatment of esterification reaction

Abstract

The invention belongs to the field of petroleum processing and petrochemical engineering catalyst application, and particularly relates to a method for regulating and controlling an acid site structure of an ultra-stable Y-type molecular sieve through esterification reaction aftertreatment. According to the method, an esterification reaction system constructed by lactic acid and alcohol is used as a post-treatment solution to treat an ultra-stable Y-type molecular sieve containing non-framework aluminum, and a low-pH-value environment is created at the initial stage of the reaction to promote dealumination of the ultra-stable Y-type molecular sieve containing non-framework aluminum; along with the esterification reaction, acid is consumed step by step, a mild pH environment is created, aluminum removed in the initial stage of the reaction is promoted to be inserted into a Y-type molecular sieve framework again, and the molecular sieve which is high in crystallinity and silica-alumina ratio, only contains tetra-coordinated framework aluminum, is high in B acid / L acid ratio and is of an open mesoporous structure is prepared. The acid strength is ensured while the acid density is reduced, that is, the ratio of B acid to L acid is increased while the silica-alumina ratio of the molecular sieve is increased, and the molecular sieve shows high activity and good recycling performance in an esterification reaction.

Description

Technical Field

[0001] The invention belongs to the field of petroleum processing and petrochemical catalyst application, and specifically is a method for regulating the acidic site structure of an ultra-stable Y-type molecular sieve through post-esterification reaction treatment. Background Art

[0002] In recent years, ultrastable Y molecular sieve (USY) has attracted much attention in experimental research and industrial applications due to its excellent hydrothermal stability and catalytic activity. Usually, USY is prepared by high-temperature dealumination treatment of Y-type molecular sieves, in which framework aluminum atoms are removed to form non-framework aluminum species. However, due to the difficulty in controlling its silicon-aluminum ratio and the large number of lattice defects, the removed aluminum is still retained in the molecular sieve cage, resulting in a decrease in the diffusion capacity of macromolecular reactants in its pores and poor accessibility to active centers. In addition, the enrichment of a large amount of non-framework aluminum in the pores of the molecular sieve will also promote coking and overreaction, thereby affecting the further improvement of its selectivity.

[0003] With the rapid development of petrochemical industry, traditional USY molecular sieves can no longer meet industrial needs. Therefore, USY molecular sieves are usually required to be dealuminated to increase the secondary pores of the molecular sieve, increase the contact area between the reactants and the active center, and improve the catalytic performance of the catalyst. In recent years, research on dealumination modification of USY molecular sieves has received widespread attention, and a variety of methods have been used to improve it.

[0004] Ultrastable Y-type molecular sieve is used for catalytic reactions, mainly relying on the acid sites formed by its tetracoordinated framework aluminum and its characteristic mesoporous structure. Therefore, its modification is mainly to increase its tetracoordinated framework aluminum content, so that it has high acid strength (i.e. high B acid content), low acid density (i.e. high silicon-aluminum ratio) and mesoporous structure after modification. Improving the acid strength of molecular sieves, reducing acid density and introducing mesopores are mainly achieved by chemical post-treatment of USY for dealumination.

[0005] The chemical dealumination modification methods of ultra-stable Y-type molecular sieves mainly include high-temperature gas phase method, ammonium fluorosilicate liquid phase reaction method, EDTA coordination dealumination method, organic acid coordination method and inorganic acid dealumination method.

[0006] 1. High temperature hydrothermal method:

[0007] The process is relatively mature. However, the silicon-aluminum ratio of the molecular sieve obtained after modification is not high and difficult to control, there are many lattice defects, the removed aluminum is still retained in the molecular sieve cage, the migration of the sub-outer layer aluminum to the outer layer aluminum leads to uneven distribution of bulk aluminum, and the surface enrichment of amorphous aluminum promotes coking and overreaction, affecting selectivity. In addition, since the modified molecular sieve contains a large amount of non-framework aluminum, its L acid ratio is too high, which is not conducive to improving the catalytic reaction activity. Therefore, it is necessary to further modify the Y-type molecular sieve treated by high-temperature hydrothermal method by other methods to improve its performance.

[0008] 2. High temperature gas phase crystallization replacement dealumination method:

[0009] This method can dealuminate molecular sieves over a wide range, and the resulting samples have high crystallinity. However, the chlorine-oxygen species formed during the dealumination process are difficult to completely remove, and the emission of chlorides will cause environmental pollution. At the same time, the crystallinity of the sample decreases significantly under high temperature conditions. Therefore, this method is still difficult to be widely industrialized.

[0010] 3. Ammonium fluorosilicate liquid phase reaction method:

[0011] By (NH 4 ) 2 SiF 6 Liquid phase replaces dealumination, dealumination is uniform and has few defects. As the reaction conditions deepen, the unit cell constant of the product decreases and the silicon-aluminum ratio increases. However, excessive ammonium fluorosilicate and a large amount of Na 3 AlF 6 and (NH 4 ) 2 AlF 6 The solubility of species such as ions in the aqueous phase is low and difficult to wash clean, which reduces the thermal stability and catalytic performance of the dealuminated molecular sieve. At the same time, since the dealumination and silicon replenishment rates are relatively close, fewer mesopores are formed, which is not conducive to the contact of macromolecular reactants with the active sites in the molecular sieve crystals. In addition, the reaction requires the maintenance of a buffer system, which makes industrial operation more difficult.

[0012] 4. Organic coordination reaction method:

[0013] Organic coordination reaction method uses organic compounds (such as H 4 The principle of EDTA) forming a stable complex with aluminum ions, reacting with Y-type molecular sieves in buffered or non-buffered solutions, removing and removing aluminum from the molecular sieve framework, and replacing the formed vacancies with silicon atoms, thereby increasing the silicon-aluminum ratio of the molecular sieve. However, the process has harsh reaction conditions in the buffer system, and the pH value of the system is too small to be controlled, which is not conducive to industrialization.

[0014] In summary, the existing chemical treatment methods for ultra-stable Y-type molecular sieves will cause the USY molecular sieve skeleton structure to be destroyed, resulting in a decrease in the crystallinity of the ultra-stable Y-type molecular sieve obtained by post-treatment, a significant decrease in the amount of B acid, a significant increase in the amount of L acid, and poor recycling performance. Therefore, it is a difficult problem to develop a new post-treatment method to reduce the acid density while ensuring the acid strength, that is, to increase the ratio of B acid and L acid while increasing the silicon-aluminum ratio of the molecular sieve. Summary of the invention

[0015] In order to overcome the shortcomings of the existing chemical post-treatment USY technology, the present invention aims to provide a method for regulating the acidic site structure of an ultra-stable Y-type molecular sieve by post-esterification reaction treatment, modifying USY during the esterification reaction of lactic acid and alcohol, and increasing the ratio of B acid and L acid while improving the silicon-aluminum ratio of the molecular sieve.

[0016] The technical solution of the present invention is:

[0017] A method for regulating the acidic site structure of an ultra-stable Y-type molecular sieve by post-treatment of an esterification reaction. The method uses an esterification reaction system constructed by lactic acid and alcohol as a post-treatment solution to treat an ultra-stable Y-type molecular sieve containing non-framework aluminum, and promotes dealumination of the ultra-stable Y-type molecular sieve containing non-framework aluminum by creating a low pH environment at the beginning of the reaction; as the esterification reaction proceeds, the acid is gradually consumed to create a mild pH environment, which promotes the aluminum removed at the beginning of the reaction to be reinserted into the Y-type molecular sieve framework, thereby preparing a molecular sieve with high crystallinity, high silicon-aluminum ratio, only tetracoordinated framework aluminum, high B acid / L acid ratio and open mesoporous structure, and the molecular sieve exhibits high activity and good recycling performance in the esterification reaction.

[0018] The method for regulating the acidic site structure of the ultra-stable Y-type molecular sieve through post-esterification reaction treatment, the post-treatment solution consists of lactic acid and alcohol, the molar ratio of lactic acid to alcohol is 1:5 to 5:1, and the alcohol includes methanol, ethanol, isopropanol, propylene glycol or n-butanol; 0.1 to 1.5 grams of ultra-stable Y-type molecular sieve are treated with each mole of lactic acid in the solution.

[0019] In the method for regulating the acidic site structure of the ultrastable Y-type molecular sieve by post-esterification treatment, preferably, the molar ratio of lactic acid to alcohol is 1:2 to 3:1, and 0.2 to 0.6 grams of the ultrastable Y-type molecular sieve is treated with each mole of lactic acid.

[0020] The method for regulating the acidic site structure of an ultra-stable Y-type molecular sieve by post-esterification reaction treatment comprises the following steps: the ultra-stable Y-type molecular sieve contains non-framework aluminum, the content of the non-framework aluminum accounts for 10 to 80 wt% of the total aluminum content in the molecular sieve, and the silicon-aluminum atomic ratio of the ultra-stable Y-type molecular sieve is in the range of 2 to 10; wherein the non-framework aluminum is an aluminum species remaining in the pores during the preparation process of the ultra-stable Y-type molecular sieve.

[0021] In the method for regulating the acidic site structure of the ultrastable Y-type molecular sieve by post-esterification reaction treatment, preferably, the content of non-framework aluminum accounts for 20-40wt% of the total aluminum content in the molecular sieve, and the silicon-aluminum atomic ratio of the ultrastable Y-type molecular sieve is in the range of 3-8.

[0022] The method for regulating the acidic site structure of the ultra-stable Y-type molecular sieve by post-esterification reaction is that the temperature of post-esterification reaction of lactic acid and alcohol to treat the ultra-stable Y-type molecular sieve is 50-100°C and the treatment time is 3-12 hours.

[0023] The method for regulating the acidic site structure of the ultra-stable Y-type molecular sieve by post-esterification reaction, preferably, the temperature of post-esterification reaction of lactic acid and alcohol to treat the ultra-stable Y-type molecular sieve is 60-90°C, and the treatment time is 4-8 hours.

[0024] The method for regulating the acidic site structure of the ultra-stable Y-type molecular sieve by post-esterification treatment, wherein the molecular sieve prepared by post-esterification treatment has a silicon-aluminum atomic ratio greater than 26 and does not contain non-framework aluminum; the molecular sieve has a high acid content, which is greater than 0.46 mmol·g -1 ; Higher ratio of B acid to L acid, the B acid amount / L acid amount is greater than 2.8.

[0025] The method for regulating the acidic site structure of the ultra-stable Y-type molecular sieve by post-esterification reaction treatment, through the post-esterification reaction treatment, the relative crystallinity of the molecular sieve is significantly improved compared with the original ultra-stable Y-type molecular sieve, and the relative crystallinity is greater than 100%; after the post-esterification reaction treatment, the molecular sieve has a higher micropore volume and a higher mesopore volume, and the micropore volume is greater than 0.32cm 3 ·g -1 , the mesopore volume is greater than 0.2 cm 3 ·g -1 .

[0026] The design idea of ​​the present invention is:

[0027] USY containing non-framework aluminum is post-treated using a mixed solution of lactic acid and alcohol under suitable temperature conditions. Lactic acid and alcohol undergo esterification reaction under the action of USY until chemical equilibrium is reached. In the initial stage of the reaction, the pH of the solution is low, and the non-framework aluminum and part of the framework aluminum in the molecular sieve are dissolved and removed. As the reaction time increases, lactic acid and alcohol continue to undergo esterification reaction, consuming lactic acid, gradually increasing the pH value of the solution, creating a mild acidic environment, and allowing the removed aluminum to be partially reinserted into the molecular sieve framework. Changes in aluminum coordination in the molecular sieve directly affect its acidic site structure. Compared with the original USY molecular sieve with a low silicon-to-aluminum ratio, the treated molecular sieve has a higher silicon-to-aluminum ratio and a higher ratio of B acid to L acid.

[0028] The present invention promotes the dealumination of the ultra-stable Y-type molecular sieve containing non-framework aluminum by creating a low pH environment at the initial stage of the reaction; as the esterification reaction proceeds, lactic acid is gradually consumed to form a mild pH environment, which promotes the aluminum part removed in the initial stage to be reinserted into the Y-type molecular sieve framework. Different from the traditional ultra-stable Y-type molecular sieve post-treatment method, the present method not only involves the removal of non-framework aluminum, but also includes the process of first dealumination and then aluminum insertion to reinsert aluminum into the molecular sieve framework, thereby preparing a molecular sieve with high crystallinity, high silicon-aluminum ratio, only four-coordinated framework aluminum, no non-framework aluminum, high B acid / L acid ratio and open mesoporous structure. The technical feature of the present invention is: utilizing the gradual consumption of acid during the esterification reaction and the characteristics of the kinetic equilibrium of the esterification reaction to create an environment of first dealumination and then aluminum insertion, thereby preparing an ultra-stable Y-type molecular sieve that does not contain non-framework aluminum, has high crystallinity, strong hydrothermal stability and can be recycled.

[0029] The transformation mechanism of the physical and chemical properties of USY molecular sieve during the esterification reaction is as follows: During the esterification reaction, non-framework aluminum and part of the framework aluminum are removed under the action of acid to form Al 3+ Cations and Due to the presence of alcohol, lactic acid is continuously consumed, creating a mild acidic environment. 3+ Cations in H + Hydrolysis by ions produces The aluminum content of the framework was increased by isomorphous substitution, and the ratio of Br to L acid was improved. This study provides a new strategy for regulating the acidic structure of USY, that is, post-treating USY through esterification reaction to promote the conversion of non-framework aluminum into framework aluminum, thereby increasing the molecular sieve silicon-aluminum ratio and improving its crystallinity and Br / L acid ratio.

[0030] The present invention has the following advantages and beneficial effects:

[0031] 1. Innovative esterification reaction system:

[0032] The present invention proposes a method for modifying an ultrastable Y-type molecular sieve using an esterification reaction system of lactic acid and alcohol. This method promotes the removal of non-framework aluminum and part of the framework aluminum in the molecular sieve by creating a low pH environment at the beginning of the reaction. As the reaction proceeds, lactic acid is gradually consumed to form a mild pH environment, so that the removed aluminum is partially reinserted into the Y-type molecular sieve framework. This innovative reaction design is significantly different from traditional post-treatment methods.

[0033] 2. Combine dealumination and aluminum insertion process:

[0034] The present invention not only involves the removal of non-framework aluminum, but also includes the process of reinserting aluminum into the molecular sieve framework. Through the reaction mechanism of first dealumination and then aluminum insertion, a molecular sieve with high crystallinity, high silicon-aluminum ratio, high B acid / L acid ratio and open mesoporous structure is prepared.

[0035] 3. Significantly improve the physical and chemical properties of molecular sieves:

[0036] The present invention improves the crystallinity, silicon-aluminum ratio, B acid content and B acid / L acid ratio of the molecular sieve by adjusting the aluminum coordination structure in the molecular sieve, thereby enhancing the acid strength and stability of the molecular sieve. The treated molecular sieve has a higher relative crystallinity, a silicon-aluminum atomic ratio (greater than 26) and does not contain non-framework aluminum; the acid content (greater than 0.46 mmol·g -1 ); B acid / L acid ratio (greater than 2.8); micropore volume (greater than 0.32cm 3 ·g -1 ) and mesopore volume (greater than 0.2 cm 3 ·g -1 ).

[0037] 4. Improve catalytic performance:

[0038] The treated molecular sieves showed high activity and excellent recycling performance in the esterification reaction, and had significant performance improvements compared to the traditional USY molecular sieve post-treatment method.

[0039] 5. Green production concept:

[0040] The method of the invention regulates the acidic site structure of the molecular sieve while catalyzing the esterification reaction, embodies the concept of green production, and improves production efficiency and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The XRD patterns of USY molecular sieves containing non-framework aluminum after post-treatment with lactic acid and ethanol solutions at different times are shown. It can be seen from the figure that when the post-treatment time is short, the sample is amorphous; as the treatment time increases, the crystallinity of the sample gradually increases, and finally recovers to 150% of the original USY crystallinity.

[0042] Figure 2(a) and Figure 2(b) show the solid NMR spectra of USY molecular sieve containing non-framework aluminum after post-treatment with lactic acid and ethanol solutions at different times. 27 Al spectrum, Figure 2(b) is 29 Si spectrum. It can be seen from the figure that when the post-treatment time is short, the sample contains a large amount of non-framework aluminum; as the treatment time increases, the content of non-framework aluminum gradually decreases until it disappears completely.

[0043] Figure 3 The XRD patterns of USY molecular sieves containing non-framework aluminum after post-treatment with lactic acid and methanol, lactic acid and ethanol, and lactic acid and isopropanol solutions for 5 hours are shown. It can be seen from the figure that the samples treated with these different solution systems all maintain a high degree of crystallinity.

[0044] Figures 4(a) and 4(b) show the solid NMR spectra of USY molecular sieve containing non-framework aluminum after post-treatment with lactic acid and methanol, lactic acid and ethanol, and lactic acid and isopropanol solutions for 5 hours, respectively. 27 Al spectrum, Figure 4(b) is 29 Si spectrum. The figure shows that these treatment systems can also achieve the transformation of dealumination and aluminum insertion.

[0045] Figure 5 The XRD patterns of USY molecular sieve containing non-framework aluminum after post-treatment with lactic acid alone at different times are shown. It can be seen from the figure that the treated USY is amorphous, and extending the treatment time does not improve the crystallinity of the molecular sieve.

[0046] Figures 6(a) and 6(b) show the solid NMR spectra of USY molecular sieve containing non-framework aluminum after post-treatment with lactic acid solution at different times. 27 Al spectrum, Figure 6(b) is 29 Si spectrum. Compared with before treatment, a large amount of non-framework aluminum was produced in the treated USY molecular sieve, and extending the treatment time could not reduce the content of non-framework aluminum.

[0047] Figure 7 The change of solution pH value with reaction time of lactic acid-ethanol system, lactic acid-methanol system, lactic acid-isopropanol system and pure lactic acid system is shown. As can be seen from the figure, for the reaction system of lactic acid and alcohol, the solution pH value increases significantly with the extension of reaction time; while for the pure lactic acid system, the solution pH value does not change much.

[0048] The above XRD and solid NMR characterization results show that the use of lactic acid and ethanol solution to post-treat USY can reinsert the removed framework aluminum and non-framework aluminum into the molecular sieve framework, thereby preparing a mesoporous Y-type molecular sieve with high crystallinity, high silicon-aluminum ratio, and no non-framework aluminum. Post-treating low silicon-aluminum ratio molecular sieves with lactic acid alone will only produce a large amount of non-framework aluminum and destroy the molecular sieve framework structure. Figure 7 It can be seen that the reason for this result is that in the initial stage of the reaction, the pH of the solution is low, and the non-framework aluminum and part of the framework aluminum in the molecular sieve are dissolved and removed. As the reaction time increases, lactic acid and alcohol continue to undergo esterification, consuming lactic acid, gradually increasing the pH value of the solution, creating a mild acidic environment, and allowing the removed aluminum to be partially reinserted into the molecular sieve framework.

[0049] The above experimental results indicate that the post-treatment of the ultra-stable Y-type zeolite with the lactic acid and ethanol esterification reaction system can achieve the dealumination and aluminum insertion transformation of the zeolite, and improve the crystallinity and silicon-aluminum ratio of the zeolite; this is essentially different from the post-treatment of the ultra-stable Y-type zeolite with the traditional chemical method. DETAILED DESCRIPTION

[0050] In the specific implementation process, the present invention proposes a method for regulating the acidic site structure of ultra-stable Y-type molecular sieves through post-esterification reaction treatment, wherein a low silicon-aluminum ratio USY molecular sieve containing non-framework aluminum is placed in a mixed solution of lactic acid and alcohol, and post-treated at a specific temperature. By controlling the type of alcohol, the ratio of lactic acid to alcohol, and the treatment time, the aluminum removed from USY is partially reinserted into the molecular sieve framework, thereby preparing a mesoporous molecular sieve catalyst with high crystallinity, high silicon-aluminum ratio, high B acid / L acid ratio, and high stability.

[0051] Below, the present invention is further described in detail by examples.

[0052] Example 1

[0053] In this embodiment, 1.5 g of USY molecular sieve containing non-framework aluminum was slowly added to a mixed solution of lactic acid (0.4 mol) and ethanol (0.4 mol), stirred at 500 rpm, treated at 65°C for 1 to 7 hours, then centrifuged, washed with deionized water until the centrifuge was neutral, dried at 100°C for 12 hours, moved to a muffle furnace, and calcined at 550°C for 2 hours to obtain the USY molecular sieve treated after the esterification reaction. The XRD spectrum of the obtained USY molecular sieve is as follows: Figure 1 As shown, the solid NMR spectrum is shown in Figure 2. As shown in Tables 1 and 2, the acidic site structure of the molecular sieve and the atomic ratio of silicon to tetracoordinate framework aluminum.

[0054] from Figure 1 It can be seen that during the post-treatment of the esterification reaction, the crystallinity of the molecular sieve decreases at the beginning of the reaction; as the esterification reaction proceeds, the crystallinity of the molecular sieve gradually increases, and the crystallinity of the sample prepared by the 7-hour reaction is 50% higher than that of the original ultra-stable Y-type molecular sieve. From the analysis results of solid NMR in Figure 2, it can be seen that the change in the crystallinity of the molecular sieve is directly related to the change in aluminum coordination in the molecular sieve crystal. At the beginning of the reaction, the non-framework aluminum and part of the framework aluminum in the molecular sieve are removed, resulting in a decrease in the crystallinity of the molecular sieve; as the reaction proceeds, the non-framework aluminum is reinserted into the molecular sieve framework, resulting in an increase in the crystallinity of the molecular sieve. It can be seen that the molecular sieve silicon-aluminum ratio increases in the initial stage of the reaction, and as the reaction proceeds, the molecular sieve silicon-aluminum ratio first reaches a peak and then decreases slightly. The reaction mechanism of the molecular sieve first dealumination and then aluminum insertion during the post-treatment of the esterification reaction is proved.

[0055] It can be seen from Table 1 and Table 2 that the acidic site structure of the molecular sieve is directly related to the aluminum coordination. The original ultra-stable Y-type molecular sieve contains a large amount of non-framework aluminum, resulting in a large proportion of L acid in the molecular sieve; after the esterification reaction post-treatment, the non-framework aluminum is removed, resulting in a significant increase in the proportion of B acid in the molecular sieve. In short, through the above-mentioned esterification reaction post-treatment, the silicon-aluminum ratio of the molecular sieve is increased, the B acid / L acid ratio is increased, and the modified molecular sieve has a higher acid strength, lower acid density and higher crystallinity, which will significantly improve the catalytic activity and stability of the molecular sieve catalyst.

[0056] Example 2

[0057] In this embodiment, 1.5 grams of USY molecular sieve containing non-framework aluminum is slowly added to a mixed solution of lactic acid (0.4 mol) and methanol (0.4 mol), the stirring speed is 500 rpm, and the mixture is treated at 65°C for 5 hours, then centrifuged, washed with deionized water until the centrifuge is neutral, dried at 100°C for 12 hours, moved to a muffle furnace, and calcined at 550°C for 2 hours to obtain a lactic acid and methanol system post-treatment modified USY molecular sieve. As shown in Table 3, the acidic site structure of the obtained molecular sieve.

[0058] Example 3

[0059] In this embodiment, 1.5 grams of USY molecular sieve containing non-framework aluminum is slowly added to a mixed solution of lactic acid (0.4 mol) and propanol (0.4 mol) at a stirring speed of 500 rpm, treated at 65°C for 5 hours, then centrifuged, washed with deionized water until the centrifuge is neutral, dried at 100°C for 12 hours, transferred to a muffle furnace, and calcined at 550°C for 2 hours to obtain a lactic acid and propanol system post-treatment modified USY molecular sieve.

[0060] The XRD patterns of the USY molecular sieves obtained in Examples 3 and 4 are as follows: Figure 3 As shown, the solid NMR spectrum is shown in Figure 4. As shown in Tables 3 and 4, the acidic site structure of the molecular sieve and the atomic ratio of silicon to tetracoordinate framework aluminum.

[0061] from Figure 3 It can be seen that the USY samples containing non-framework aluminum after post-treatment with lactic acid and methanol, lactic acid or isopropanol solution system can also maintain a high degree of crystallinity. As can be seen from Figure 4, USY molecular sieves containing non-framework aluminum after post-treatment with lactic acid and methanol, lactic acid and ethanol, lactic acid and isopropanol solution can also undergo dealumination and aluminum insertion transformation. It can be seen from Tables 3 and 4 that USY molecular sieves post-treated with these solution systems can also increase the B acid / L acid ratio of the molecular sieve.

[0062] Comparative Example 1

[0063] In this comparative example, 1.5 g of USY molecular sieve containing non-framework aluminum was slowly added to a mixed solution of lactic acid (0.4 mol) and acetone (0.4 mol) at a stirring speed of 500 rpm, treated at 65°C for 1 to 7 hours, then centrifuged, washed with deionized water until the centrifuge was neutral, dried at 100°C for 12 hours, transferred to a muffle furnace, and calcined at 550°C for 2 hours to obtain the lactic acid post-treated USY molecular sieve.

[0064] The XRD pattern of the obtained USY molecular sieve is as follows: Figure 5 As shown in Figure 6, the solid NMR spectrum is shown in Figure 6. As shown in Table 5, the acidic site structure and the atomic ratio of silicon to framework aluminum. Figure 5 It can be seen from the figure that the crystallinity of the ultra-stable Y-type molecular sieve is greatly reduced by the lactic acid treatment alone, and it will not recover with the extension of reaction time. It can be seen from Figure 6 that a large amount of non-framework aluminum is produced in the molecular sieve by the lactic acid treatment alone, and the non-framework aluminum will not be reinserted into the molecular sieve framework as the reaction time increases. It can be seen from Table 5 that the total acid content of the molecular sieve is greatly reduced by the lactic acid treatment alone. The above results show that the lactic acid treatment alone will cause the ultra-stable Y-type molecular sieve framework structure to collapse and the total acid content to be greatly lost.

[0065] The physical adsorption results of the samples obtained by post-treatment of USY by different methods are shown in Table 6. As can be seen from Table 6, the samples obtained by the lactic acid-alcohol system treatment maintained a high micropore volume and mesopore volume, while the micropore volume and mesopore volume of the samples treated with lactic acid alone were greatly reduced.

[0066] From the above results, it can be seen that the use of lactic acid and alcohol system to post-treat the ultra-stable Y-type molecular sieve can achieve the transformation of molecular sieve dealumination and aluminum insertion; while the use of lactic acid treatment alone will only cause dealumination and crystal structure destruction of the molecular sieve. Figure 7 It can be seen that the reason for this result is that in the initial stage of the reaction, the pH of the solution is low, and the non-framework aluminum and part of the framework aluminum in the molecular sieve are dissolved and removed. As the reaction time increases, lactic acid and alcohol continue to undergo esterification, consuming lactic acid, gradually increasing the pH value of the solution, creating a mild acidic environment, and allowing the removed aluminum to be partially reinserted into the molecular sieve framework.

[0067] Application Examples

[0068] This application example uses the lactic acid and alcohol system post-treatment USY molecular sieve in Examples 1-3 and the comparative example of the USY molecular sieve post-treatment with lactic acid alone to catalyze the synthesis of ethyl lactate. The experimental process is as follows: 0.3 mol of ethanol and 0.3 mol of lactic acid are added to a three-necked flask equipped with a thermometer and a reflux condenser, the catalyst dosage is 1.5 grams, the reaction is carried out at 65°C for 5 hours, and sampling is performed. The results are shown in Table 7.

[0069] It can be seen from Table 7 that the samples prepared by post-treatment with lactic acid and alcohol system, especially lactic acid and ethanol system, showed excellent catalytic activity and recycling performance in the synthesis reaction of ethyl lactate. However, the USY samples prepared by post-treatment with lactic acid for different time periods alone had lower catalytic activity in the ethyl lactate reaction than the original USY.

[0070] Table 1 Ammonia temperature-programmed desorption (NH 3 -TPD) data

[0071]

[0072] a Weakness: 100~350℃; b strongacid:350~500℃

[0073] Table 2 NH 2 of samples obtained by treating USY with lactic acid-ethanol system at different times 3 -TPD, Py-FTIR and Si-Al ratio data

[0074]

[0075]

[0076] (Brønsted acidity), L: Lewis acidity; Py-FTIR is pyrolysis-Fourier transform infrared spectroscopy, and NMR is nuclear magnetic resonance.

[0077] Table 3 NH 2 O values ​​of samples obtained by treating USY with lactic acid-ethanol, lactic acid-methanol and lactic acid-isopropanol for different time periods 3 -TPD data

[0078]

[0079] a Weakness: 100~350℃; b strongacidity:350~500℃

[0080] Table 4 NH of samples obtained by treating USY with lactic acid-ethanol, lactic acid-methanol and lactic acid-isopropanol for different time periods 3 -TPD and Py-FTIR data

[0081]

[0082] L: Lewis acidity

[0083] Table 5 NH of samples obtained from USY treated with lactic acid at different times 3 -TPD data

[0084]

[0085] a Weakness: 100~350℃; b strongacid:350~500℃

[0086] Table 6 Physical adsorption results of samples prepared by different methods

[0087]

[0088]

[0089] Table 7 Catalytic ethyl lactate synthesis reaction results of samples prepared by different methods

[0090] Catalyst First reaction Second reaction The third reaction Original USY 21.5 24.3 24.5 Lactic acid-ethanol system treatment for 1 hour 21.2 20.3 20.0 Lactic acid-ethanol system treatment for 3 hours 25.3 25.0 24.9 Lactic acid-ethanol system treatment for 5 hours 26.9 26.2 26.0 Lactic acid-ethanol system treatment for 7 hours 26.5 26.0 25.8 Lactic acid-methanol system treatment for 5 hours 23.6 23.8 23.7 Lactic acid-isopropanol system treatment for 5 hours 25.2 25.5 25.7 Lactic acid treatment for 1 hour 20.2 20.3 20.0 Lactic acid treatment for 3 hours 20.5 20.2 20.4 Lactic acid treatment for 5 hours 20.5 20.3 20.4 Lactic acid treatment for 7 hours 20.8 20.2 20.1

[0091] The results of the embodiments, comparative examples and application examples show that, compared with the traditional USY post-treatment method, the present invention utilizes a mixed solution of lactic acid and alcohol to post-treat USY containing non-framework aluminum under suitable temperature conditions. Alcohol and lactic acid undergo an esterification reaction under the action of USY until chemical equilibrium is reached. In the initial stage of the reaction, the pH of the solution is low, and the non-framework aluminum and part of the framework aluminum in the molecular sieve are dissolved and removed. As the reaction time increases, lactic acid and alcohol continue to undergo an esterification reaction, consuming lactic acid, gradually increasing the pH value of the solution, creating a mild acidic environment, and allowing the removed aluminum to be partially reinserted into the molecular sieve framework. Changes in aluminum coordination in the molecular sieve directly affect its acidic site structure. Compared with the original USY molecular sieve with a low silicon-to-aluminum ratio, the treated molecular sieve has a higher silicon-to-aluminum ratio and a higher ratio of B acid to L acid.

Claims

1. A method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment, characterized in that: The method uses an esterification reaction system constructed by lactic acid and alcohol as a post-treatment solution to treat an ultra-stable Y-type molecular sieve containing non-framework aluminum, and promotes dealumination of the ultra-stable Y-type molecular sieve containing non-framework aluminum by creating a low pH environment at the initial stage of the reaction; as the esterification reaction proceeds, the acid is gradually consumed to create a mild pH environment, which promotes the aluminum removed at the initial stage of the reaction to be reinserted into the Y-type molecular sieve framework, thereby preparing a molecular sieve with high crystallinity, high silicon-aluminum ratio, only tetracoordinated framework aluminum, high B acid / L acid ratio and open mesoporous structure, and the molecular sieve exhibits high activity and good recycling performance in the esterification reaction.

2. The method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment according to claim 1, characterized in that: The post-treatment solution is composed of lactic acid and alcohol, the molar ratio of lactic acid to alcohol is 1:5 to 5:1, and the alcohol includes methanol, ethanol, isopropanol, propylene glycol or n-butanol; 0.1 to 1.5 grams of ultra-stable Y-type molecular sieve is treated per mole of lactic acid in the solution.

3. The method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment according to claim 2, characterized in that: Preferably, the molar ratio of lactic acid to alcohol is 1:2 to 3:1, and 0.2 to 0.6 grams of ultrastable Y-type molecular sieve is treated per mole of lactic acid.

4. The method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment according to claim 1, characterized in that: The ultra-stable Y-type molecular sieve used contains non-framework aluminum, and the content of the non-framework aluminum accounts for 10 to 80 wt% of the total aluminum content in the molecular sieve. The silicon-aluminum atomic ratio of the ultra-stable Y-type molecular sieve ranges from 2 to 10; wherein the non-framework aluminum is the aluminum species remaining in the pores during the preparation process of the ultra-stable Y-type molecular sieve.

5. The method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment according to claim 4, characterized in that: Preferably, the content of non-framework aluminum accounts for 20-40 wt% of the total aluminum content in the molecular sieve, and the silicon-aluminum atomic ratio of the ultra-stable Y-type molecular sieve is in the range of 3-8.

6. The method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment according to claim 1, characterized in that: The temperature of post-treatment of the ultra-stable Y-type molecular sieve by esterification reaction of lactic acid and alcohol is 50-100° C., and the treatment time is 3-12 hours.

7. The method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment according to claim 6, characterized in that: Preferably, the temperature of post-treatment of the ultra-stable Y-type molecular sieve by esterification reaction of lactic acid and alcohol is 60-90° C., and the treatment time is 4-8 hours.

8. The method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment according to any one of claims 1 to 7, characterized in that: The molecular sieve prepared by post-esterification reaction has a silicon-aluminum atomic ratio greater than 26 and does not contain non-framework aluminum; the molecular sieve has a high acid content, which is greater than 0.46 mmol·g -1 ; Higher ratio of B acid to L acid, the B acid amount / L acid amount is greater than 2.

8.

9. The method for regulating the acidic site structure of ultrastable Y-type molecular sieve by post-esterification treatment according to any one of claims 1 to 7, characterized in that: After esterification reaction, the relative crystallinity of the molecular sieve is significantly improved compared with the original ultra-stable Y-type molecular sieve, and the relative crystallinity is greater than 100%. After esterification reaction, the molecular sieve has a higher micropore volume and a higher mesopore volume, and the micropore volume is greater than 0.32cm 3 ·g -1 , the mesopore volume is greater than 0.2 cm 3 ·g -1 .

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