Method for preparing low polyethylene glycol through ethylene glycol intermolecular dehydration

Abstract

The device comprises an ethylene glycol storage tank (1), a nitrogen storage tank (2), a mixed gas storage tank (3), a high-pressure plunger pump (4), a preheater (7), a mass flow meter (8), a fixed bed reactor (9), a condenser (10), a phase splitter (11), a liquid collection tank (12), a gas chromatograph (14), a back pressure valve (16), a liquid chromatograph (17) and a plurality of valves. The ethylene glycol storage tank (1) is sequentially connected with the high-pressure plunger pump (4), the preheater (7), the fixed bed reactor (9), the condenser (10) and the phase splitter (11); and the nitrogen storage tank (2) is sequentially connected with a valve (5), the mass flow meter (8) and the preheater (7). By regulating and controlling the acidity and pore channel structure of the molecular sieve, efficient synthesis of the low polyethylene glycol is realized, and the problem of low product selectivity in similar catalysts is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, and particularly relates to a method for preparing oligoglycol by intermolecular dehydration of ethylene glycol. BACKGROUND

[0002] Oligoglycol, including diethylene glycol, triethylene glycol, etc., is a main by-product in the production of ethylene glycol from ethylene oxide. Oligoglycol has hydroxyl and ether bonds and is widely used in various fields: it can be used as a component of lubricants to provide good lubricating performance; it can be used as a solvent in the resin, ink and paint industries, and has good solubility; diethylene glycol and triethylene glycol can be used in automobile antifreeze to help reduce the freezing point and prevent the cooling system from freezing at low temperatures; it can be used as a dehydrating agent in natural gas treatment; and it can be used as a moisturizing ingredient in cosmetics to balance the moisture of the product.

[0003] Currently, diethylene glycol is mainly prepared by chlorohydrination and ethylene oxidation. The former uses chloroethylene and sodium hydroxide as raw materials, and the latter uses ethylene and oxygen as raw materials to synthesize ethylene glycol, and then diethylene glycol is prepared by chlorination of ethylene glycol. These two methods have risks in terms of raw material sources, process safety and environmental protection due to the use of halogen, strong base and oxidizing atmosphere. Therefore, it is necessary to develop a green and efficient catalytic synthesis method. High-efficiency solid acid catalysts have the advantages of high catalytic efficiency, easy recovery, small pollution and convenient regeneration, and have been applied in the synthesis of oligoglycol. CN109053395A discloses a method for continuously preparing diethylene glycol and triethylene glycol from ethylene glycol in a fixed bed reactor. Under the reaction conditions of 200-320 ℃, 0.3-5.0 MPa, and liquid space velocity of 1.2-6.0 L -1 / min, one of HZSM-5, mordenite, Y zeolite, and Hβ or a molecular sieve loaded with metal oxide as a carrier can be used as a catalyst. The conversion rate of ethylene glycol can reach 59.7%. The total selectivity of diethylene glycol and triethylene glycol reaches 73.9%. CN114621061A uses ethylene glycol as a raw material and modified ion exchange resin as a catalyst to realize the synthesis of diethylene glycol, and the selectivity of diethylene glycol reaches 90%.

[0004] Compared with ion exchange resins, molecular sieve-based solid acid catalysts have significantly improved temperature resistance and wear resistance, and the catalyst regeneration process is easy, so they become the preferred catalysts for catalyzing the preparation of oligoglycol from ethylene glycol. In addition to intermolecular dehydration, ethylene glycol is also prone to cyclization to form 1,4-dioxane and dioxolane products under the catalysis of solid acid, which reduces the utilization efficiency of ethylene glycol. According to the differences in molecular size and required acid sites between oligoglycol and cyclic products, oligoglycol can be selectively prepared by regulating the pore and acidity of the molecular sieve catalyst, thereby improving the utilization rate of ethylene glycol. SUMMARY

[0005] In order to solve the problems of high content of cyclic products and low selectivity of oligoglycol in the preparation of oligoglycol by intermolecular dehydration of ethylene glycol by using the existing molecular sieve, the application provides a method for preparing oligoglycol by intermolecular dehydration of ethylene glycol, which improves the utilization rate of ethylene glycol by regulating the pore and acidity of the HY molecular sieve, and the molecular sieve catalyst has the advantages of small pollution, convenient preparation, high yield, easy regeneration and the like.

[0006] According to one aspect of the application, a device for preparing oligoglycol by intermolecular dehydration of ethylene glycol is provided, which comprises an ethylene glycol storage tank (1), a nitrogen storage tank (2), a mixed gas storage tank (3), a high-pressure plunger pump (4), a preheater (7), a mass flow meter (8), a fixed bed reactor (9), a condenser (10), a phase separator (11), a liquid collection tank (12), a gas chromatograph (14), a back pressure valve (16), a liquid chromatograph (17), and a plurality of valves. The ethylene glycol storage tank (1) is connected with the high-pressure plunger pump (4), the preheater (7), the fixed bed reactor (9), the condenser (10), and the phase separator (11) in sequence. The nitrogen storage tank (2) is connected with a valve (5), the mass flow meter (8), and the preheater (7) in sequence.

[0007] According to the above technical solution, the mixed gas storage tank (3) is connected with a valve (6) and the mass flow meter (8) in sequence. The phase separator (11) is connected with a valve (18), the back pressure valve (16), a valve (15), and the gas chromatograph (14) in sequence. The back pressure valve (16) is further connected with a valve (13). The phase separator (11) is further connected with a valve (19), the liquid collection tank (12), and the liquid chromatograph (17) in sequence. The phase separator (11) is further provided with a valve (20).

[0008] According to the second aspect of the application, a method for preparing oligoglycol from ethylene glycol is provided, which comprises: using a device for preparing oligoglycol by intermolecular dehydration of ethylene glycol, using a high-pressure plunger pump (4) to pump raw material ethylene glycol into a preheater (7), mixing nitrogen with ethylene glycol by passing nitrogen, heating to 150-300 ℃, reacting under the action of a modified catalyst, and obtaining polyglycol. The modified catalyst comprises an organic acid modified molecular sieve, an inorganic acid modified molecular sieve, an ammonium salt modified molecular sieve, an alkali modified molecular sieve, and a metal salt supported modified molecular sieve, and the molecular sieve is a HY type molecular sieve with a silicon-aluminum ratio of 4-200.

[0009] According to the above technical solution, the feed space velocity of the raw material ethylene glycol is 0.5-5.0 h-1 ; The pressure of the reaction is 0.1-7.0 Mpa; The time of the reaction is 1-5h.

[0010] According to the technical scheme, the modified catalyst is prepared by impregnation method, and the specific process is as follows: the impregnation solution is impregnated into the HY molecular sieve, and then the HY molecular sieve is placed at room temperature, dried, and calcined to obtain the modified catalyst.

[0011] According to the technical scheme, the impregnation solution comprises an inorganic acid solution, an organic acid solution, a metal salt solution, a base solution, and an ammonium salt solution. The organic acid in the organic acid solution is at least one selected from oxalic acid and citric acid, and the concentration is 0.1-1.0 mol / L. The inorganic acid in the inorganic acid solution is at least one selected from hydrochloric acid and boric acid. The ammonium salt in the ammonium salt solution is at least one selected from diammonium hydrogen phosphate and ammonium fluoride, and the concentration is 0.1-1.0 mol / L, preferably 0.2-0.5 mol / L. The base in the base solution is at least one selected from sodium hydroxide, and the concentration is 0.1-1.0 mol / L, preferably 0.3-0.6 mol / L. The metal in the metal salt solution is at least one selected from La, Co, Cu, and Zr. The metal salt is at least one selected from lanthanum nitrate, cobalt nitrate, copper nitrate, zirconium nitrate, and zirconyl nitrate.

[0012] According to the technical scheme, the amount of the acid in the organic acid modified molecular sieve and the inorganic acid modified molecular sieve is 1.0-10.0wt% of the mass of the molecular sieve, preferably 1.5-3.0wt%. The amount of the ammonium salt in the ammonium salt modified molecular sieve is 1.0-10.0wt% of the mass of the molecular sieve, preferably 1.5-3.5wt%. According to the technical scheme, the loading amount of the metal in the metal salt modified molecular sieve is 0.1-5.0% of the mass of the HY molecular sieve. The precursor of the metal modified molecular sieve comprises a commercial HY molecular sieve, and the HY molecular sieve is modified by an organic acid, an inorganic acid, an ammonium salt, and a base.

[0013] Compared with the prior art, the present application has the following advantages: (1) The technical scheme disclosed by the application controls the pore and acidity of the HY type molecular sieve through an acid solution, an alkali solution, a metal salt solution and an ammonium salt solution, and obtains the modified HY type molecular sieve; the modified HY type molecular sieve and the device provided with a preheater are used for preparing oligoglycol by intermolecular dehydration of ethylene glycol, and it is found that the catalyst performance of the HY molecular sieve is significantly improved after modification by diammonium hydrogen phosphate, and after physical adsorption characterization of the catalyst before and after modification, it is found that the specific surface area of the catalyst after modification is reduced, the pore volume is reduced, the pore size is increased, ethylene glycol is more easily diffused in the pores to contact the acid sites, so that the conversion rate of ethylene glycol is increased, and due to the reduction of the specific surface area, the density of the acid sites is reduced, the possibility of further catalytic dehydration of diethylene glycol molecules into dioxane is reduced, and the selectivity of diethylene glycol is further improved.

[0014] (2) The modified molecular sieve obtained by the technical scheme disclosed by the application has a pore size of 2.68 nm, and when the modified molecular sieve is used for catalyzing intermolecular dehydration of ethylene glycol to prepare oligoglycol, the conversion rate of ethylene glycol can reach 35.64%, and the total selectivity of oligoglycol can reach 81.27%. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The reaction device for preparing oligoglycol used in the embodiment of the application is shown in the figure (component description: 1, ethylene glycol storage tank, 2, nitrogen storage tank, 3, air or nitrogen-oxygen mixed gas storage tank, 4, high-pressure plunger pump, 7, preheater, 8, mass flow meter, 9, fixed bed reactor, 10, condenser, 11, phase separator, 12, liquid collection tank, 5, 6, 13, 15, 18, 19, 20 are valves, 14, gas chromatograph, 16, back pressure valve, 17, liquid chromatograph); Figure 2 The nitrogen adsorption-desorption curve of the HY molecular sieve catalyst before and after modification described in embodiment 3 is shown in the figure; Figure 3 The pore size distribution curve of the HY molecular sieve catalyst before and after modification described in embodiment 3 is shown in the figure. DETAILED DESCRIPTION

[0016] The application will be further described below in combination with specific embodiments, but the application is not limited in any way by the embodiments.

[0017] Unless otherwise specified, the raw materials and commercial HY molecular sieves in the embodiments of the application are purchased through commercial channels, and in addition, the metal modified molecular sieve precursor can be a commercial HY molecular sieve (silicon aluminum ratio of 5.5-200, pore size of 2.58 nm), an HY molecular sieve (silicon aluminum ratio of 5.5-200, pore size of 2.68, self-made) modified by acid / ammonium salt or solution treatment.

[0018] The analysis method in the embodiments of the application is as follows: The ethylene glycol dehydration product is quantitatively analyzed by SH-WAX chromatographic column of Shimadzu 2014 gas chromatograph.

[0019] The calculation formula of the ethylene glycol single-pass conversion (formula 1) and the oligoglycol selectivity (formula 2) in the embodiment of the application is as follows:

[0020] Formula 1;

[0021] Formula 2.

[0022] Example 1 A hydrochloric acid solution with a mass fraction of 5% is configured, 5.0 g of the solution is weighed, and then dripped into 12.0 g of HY with a silicon-aluminum ratio of 5.5 for impregnation, and then left to stand for 8 h, dried in an oven at 100 DEG C for 10 h, and then calcined in a muffle furnace at 550 DEG C for 5 h, to obtain a hydrochloric acid modified HY molecular sieve catalyst, which is recorded as 1#.

[0023] Example 2 A boric acid solution with a mass fraction of 3% is configured, 5.0 g of the solution is weighed, and then dripped into 12.0 g of HY with a silicon-aluminum ratio of 6.5 for impregnation, and then left to stand for 10 h, dried in an oven at 80 DEG C for 10 h, and then calcined in a muffle furnace at 600 DEG C for 4 h, to obtain a boric acid modified HY molecular sieve catalyst, which is recorded as 2#.

[0024] Example 3 A diammonium hydrogen phosphate solution with a mass fraction of 7% is configured, 5.0 g of the solution is weighed, and then dripped into 12.0 g of HY with a silicon-aluminum ratio of 50 for impregnation, and then left to stand for 10 h, dried in an oven at 100 DEG C for 12 h, and then calcined in a muffle furnace at 550 DEG C for 8 h, to obtain a diammonium hydrogen phosphate modified HY molecular sieve catalyst, which is recorded as 3#. The nitrogen adsorption-desorption curves of the HY molecular sieve catalyst samples before and after modification are shown in Figure 2 It is found that the adsorption-desorption curves of the molecular sieve before and after modification are consistent, and there is a clear hysteresis loop, which is caused by capillary condensation, and presents mesoporous characteristics. The diammonium hydrogen phosphate modification does not cause obvious damage to the framework. Due to the generated phosphorus species, the pore size is slightly increased, and the ethylene glycol is more easily contacted with the acid sites. The pore size distribution curves are shown in Figure 3 It is found that The curves before and after modification are consistent, and there are two peaks at about 2.5 nm and 20 nm. The first one is caused by the pore size of the molecular sieve, and the second one is probably the intercrystalline mesopore of the molecular sieve, which further indicates that the modification does not cause obvious damage to the framework of the molecular sieve.

[0025] Example 4 The ammonium fluoride solution with a mass fraction of 5% was prepared, 5.0 g of the solution was weighed and dropped into 12.0 g of HY with a silicon-aluminum ratio of 100 for impregnation, and then was left to stand for 14 h, dried in an oven at 100 ℃ for 8 h, and calcined in a muffle furnace at 550 ℃ for 7 h to obtain an ammonium fluoride modified HY molecular sieve catalyst, which was marked as 4#.

[0026] Example 5 A 200 mL triangular flask was charged with 120 mL of oxalic acid solution with a concentration of 0.2 mol / L, and then 10.0 g of HY molecular sieve with a silicon-aluminum ratio of 6.5 was added thereto, and then was subjected to magnetic stirring treatment at 60 oC for 12 h. After stirring, it was filtered and washed until the filtrate was neutral. It was dried in a 100 ℃ drying oven for 12 h, and then was transferred into a 500 ℃ muffle furnace for calcination for 5 h. The obtained catalyst was marked as 5#. Example 6 A lanthanum nitrate solution with a mass fraction of 3% was prepared, 10.0 g of the solution was weighed and dropped into 5.0 g of boric acid modified HY molecular sieve with a silicon-aluminum ratio of 6.5 for impregnation, and then was left to stand for 20 h, dried in an oven at 120 ℃ for 10 h, and calcined in a muffle furnace at 550 ℃ for 4 h to obtain a La and B modified HY molecular sieve catalyst, which was marked as 6#.

[0027] Example 7 A cobalt nitrate solution with a mass fraction of 2.5% was prepared, 10.0 g of the solution was weighed and dropped into 5.5 g of HY with a silicon-aluminum ratio of 55 for impregnation, and then was left to stand for 24 h, dried in an oven at 100 ℃ for 12 h, and calcined in a muffle furnace at 450 ℃ for 5 h to obtain a Co modified HY molecular sieve catalyst, which was marked as 7#.

[0028] Example 8 A copper nitrate solution with a mass fraction of 3% was prepared, 10.0 g of the solution was weighed and dropped into 5.0 g of HY with a silicon-aluminum ratio of 5.5 for impregnation, and then was left to stand for 12 h, dried in an oven at 80 ℃ for 20 h, and calcined in a muffle furnace at 550 ℃ for 7 h to obtain a Cu modified HY molecular sieve catalyst, which was marked as 8#.

[0029] Example 9 A zirconium nitrate solution with a mass fraction of 5% was prepared, 10.0 g of the solution was weighed and dropped into 5.5 g of HY with a silicon-aluminum ratio of 140 for impregnation, and then was left to stand for 14 h, dried in an oven at 100 ℃ for 16 h, and calcined in a muffle furnace at 550 ℃ for 5 h to obtain a Zr modified HY molecular sieve catalyst, which was marked as 9#.

[0030] Example 10 A copper nitrate solution with a mass fraction of 3% was configured, 3.5 g of the solution was weighed, and was dropped into 6.3 g of HY molecular sieve treated by oxalic acid to perform impregnation, was placed for 12 h, was dried in an oven at 100°C for 16 h, and was calcined in a muffle furnace at 550°C for 5 h to obtain a Cu and oxalic acid modified HY molecular sieve catalyst, which was recorded as 10#.

[0031] Test Example An apparatus as shown in Figure 1 was used, which included an ethylene glycol storage tank 1, a nitrogen storage tank 2, a mixed gas storage tank 3, a high-pressure plunger pump 4, a preheater 7, a mass flow meter 8, a fixed bed reactor 9, a condenser 10, a phase separator 11, a liquid collection tank 12, valves 5, 6, 13, 15, 18, 19, 20, a gas chromatograph 14, a back pressure valve 16, and a liquid chromatograph 17; the ethylene glycol storage tank 1 was connected in sequence with the high-pressure plunger pump 4, the preheater 7, the fixed bed reactor 9, the condenser 10, and the phase separator 11; the nitrogen storage tank 2 was connected in sequence with valve 5, the mass flow meter 8, and the preheater 7; the mixed gas storage tank 3 was connected in sequence with valve 6 and the mass flow meter 8; the phase separator 11 was connected in sequence with valve 18, the back pressure valve 16, valve 15, and the gas chromatograph 14; the back pressure valve 16 was also connected with valve 13; the phase separator 11 was also connected in sequence with valve 19, the liquid collection tank 12, and the liquid chromatograph 17; the phase separator 11 was also provided with valve 20; by adding the preheater 7 before the ethylene glycol storage tank 1, the ethylene glycol raw material was gasified by the preheater 7, and the gaseous ethylene glycol and the carrier gas entered the reactor together; if there was no vaporizer, the ethylene glycol would be gasified in the reactor, and the heat absorption would cause the bed temperature to change, which would affect the results, and would not cause the local ethylene glycol concentration on the catalyst to be too high, which would affect the reaction; that is, the catalysts #1-#10 prepared in Examples 1-8 were subjected to ethylene glycol dehydration reaction by using the apparatus provided with a vaporizer, and the specific performance evaluation process of the catalyst was as follows: first, valve 6 and valve 20 were closed; nitrogen 2 and valve 5 were opened, and the system was purged by the mass flow meter; after the purging was completed, the plunger pump 4 was opened, and the ethylene glycol in the ethylene glycol storage tank 1 was pumped into the preheater 7; the nitrogen was mixed with the ethylene glycol in 7 by the mass flow meter 8, and then entered the fixed bed reactor 9; the reaction product passed through the condenser 10 and the phase separator 11; the gas phase was connected with the back pressure valve 16 through valve 18, and the liquid phase was stored in the storage tank 12 through valve 19; the gas phase composition was analyzed by the chromatograph 14; during the analysis, valve 15 was opened, and after the sampling was completed, valve 15 was closed, and valve 13 was opened to empty the gas; the liquid phase product was sampled and analyzed for its composition by the chromatograph 17; after the analysis was completed, the product separation operation could be performed.

[0032] a) ethylene glycol was pumped into the preheater 7 by using the plunger pump 4, was preheated to the reaction temperature by the preheater 7, and then was introduced into the fixed bed reactor 9 to react, and the feed liquid space velocity was 0.5-5.0 h-1 The preheater can be connected with nitrogen gas before the reaction, and the flow rate of the nitrogen gas is 0-60 mL / min, and the nitrogen gas needs to be mixed with the ethylene glycol uniformly.

[0033] b) The mixed gasification material is reacted with the molecular sieve catalyst in the fixed bed reactor 9, and the temperature range is 150-300 DEG C, and the reaction pressure is 0.1-7.0 Mpa.

[0034] c) The reaction product is condensed, and the liquid phase product is collected by phase separation, and the composition of the liquid phase and the gas phase is analyzed by gas chromatography, and the conversion rate of the ethylene glycol and the total selectivity of the oligomerization glycol are calculated.

[0035] After the reaction parameters are changed and the reaction is stable, the reaction product and the raw material are analyzed by using the online chromatography. The Shimadzu 2014 gas chromatography (FID detector, SH-WAX chromatographic column) is used to analyze the composition of the ethylene glycol dehydration reaction product, and the reaction parameters and the reaction results of examples 1-8 and the commercial HY molecular sieve are shown in table 1.

[0036] Table 1 is the reaction parameters and the reaction results of examples 1-8

[0037] Through the above technical scheme, the modified HY molecular sieve is used as the catalyst, and the reaction is carried out in the improved reaction device, the conversion rate of the ethylene glycol can reach 35.64%, and the total selectivity of the glycol can reach 81.27%, and the oligomerization glycol yield of the unmodified molecular sieve is increased by 3 times.

[0038] The above is only a few embodiments of the present application, and does not limit the present application in any form, although the present application is disclosed as above, however, it is not used to limit the present application, any skilled person in the art, without departing from the scope of the technical scheme of the present application, using the above disclosed technical content makes some changes or modifications, which are equivalent to equivalent embodiments, and are within the scope of the technical scheme.

Claims

1. An apparatus for the intermolecular dehydration of ethylene glycol to produce oligomeric glycols, characterized in that, The device comprises an ethylene glycol storage tank (1), a nitrogen storage tank (2), a mixed gas storage tank (3), a high-pressure plunger pump (4), a preheater (7), a mass flow meter (8), a fixed bed reactor (9), a condenser (10), a phase separator (11), a liquid collection tank (12), a gas chromatograph (14), a back pressure valve (16), a liquid chromatograph (17) and several valves. The ethylene glycol storage tank (1) is connected with the high-pressure plunger pump (4), the preheater (7), the fixed bed reactor (9), the condenser (10) and the phase separator (11) in sequence. The nitrogen storage tank (2) is connected with a valve (5), the mass flow meter (8) and the preheater (7) in sequence.

2. The apparatus of claim 1, wherein, The mixed gas storage tank (3) is connected with a valve (6) and the mass flow meter (8) in sequence. The phase separator (11) is connected with a valve (18), the back pressure valve (16), a valve (15) and the gas chromatograph (14) in sequence. The back pressure valve (16) is also connected with a valve (13). The phase separator (11) is also connected with a valve (19), the liquid collection tank (12) and the liquid chromatograph (17) in sequence. The phase separator (11) is also provided with a valve (20).

3. A process for the preparation of oligomeric glycols from ethylene glycol, characterized in that, The method comprises: using the device for preparing oligoglycol by intermolecular dehydration of ethylene glycol, using the high-pressure plunger pump (4) to pump the raw material ethylene glycol into the preheater (7), mixing the nitrogen and ethylene glycol by nitrogen, heating to 150-300 ℃, reacting under the action of a modified catalyst to obtain polyglycol. The modified catalyst comprises organic acid modified molecular sieve, inorganic acid modified molecular sieve, ammonium salt modified molecular sieve, alkali modified molecular sieve and metal salt supported modified molecular sieve, and the molecular sieve is HY type molecular sieve with a silicon-aluminum ratio of 4-200. The device for preparing oligoglycol by intermolecular dehydration of ethylene glycol is the device according to any one of claims 1-2.

4. The method of claim 3, wherein, The feed space velocity of the raw material ethylene glycol is 0.5-5.0 h -1 ; The pressure of the reaction is 0.1-7.0 Mpa. The reaction time is 1-5 h.

5. The method of claim 3, wherein, The modified catalyst is prepared by an impregnation method, and the specific process is: impregnating a HY molecular sieve with an impregnation solution, standing at room temperature, drying, and calcining to obtain the modified catalyst.

6. The method of claim 5, wherein, The impregnation solution comprises inorganic acid solution, organic acid solution, metal salt solution, alkali solution and ammonium salt solution. The organic acid in the organic acid solution is at least one selected from oxalic acid and citric acid, and the concentration is 0.1-1.0 mol / L. The inorganic acid in the inorganic acid solution is at least one selected from hydrochloric acid and boric acid. The ammonium salt in the ammonium salt solution is at least one selected from diammonium hydrogen phosphate and ammonium fluoride, and the concentration is 0.1-1.0 mol / L, preferably 0.2-0.5 mol / L. The alkali in the alkali solution is at least one selected from sodium hydroxide, and the concentration is 0.1-1.0 mol / L, preferably 0.3-0.6 mol / L. The metal in the metal salt solution is at least one selected from La, Co, Cu and Zr. The metal salt is at least one selected from lanthanum nitrate, cobalt nitrate, copper nitrate, zirconium nitrate and zirconyl nitrate.

7. The method of claim 3, wherein, The acid in the organic acid modified molecular sieve and the inorganic acid modified molecular sieve is 1.0-10.0wt% of the mass of the molecular sieve, preferably 1.5-3.0wt%; The amount of the ammonium salt in the ammonium salt modified molecular sieve is 1.0-10.0wt% of the mass of the molecular sieve, preferably 1.5-3.5wt%.

8. The method of claim 3, wherein, The metal loading in the metal salt modified molecular sieve is 0.1-5.0% of the mass of the HY molecular sieve; The precursor of the metal modified molecular sieve includes commercial HY molecular sieve, and the HY molecular sieve modified by organic acid, inorganic acid, ammonium salt, and alkali.

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