CN114797997A - Regeneration method of composite modified molecular sieve catalyst for aromatic alkylation reaction - Google Patents

Abstract

The invention provides a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which comprises the following steps: sequentially heating and roasting the inactivated composite modified molecular sieve catalyst to obtain a regenerated composite modified molecular sieve catalyst; and introducing mixed gas of inert gas and air in the roasting treatment. The regeneration method is a regeneration method combining heating treatment and roasting treatment, and simultaneously, the oxygen concentration and the mixed gas flow in the regeneration process are adjusted, so that the metal and/or nonmetal active sites on the molecular sieve catalyst are recovered, the catalytic performance of the regenerated molecular sieve catalyst is further improved, and the service cycle of the molecular sieve catalyst is prolonged.

Description

Regeneration method of composite modified molecular sieve catalyst for aromatic alkylation reaction

Technical Field

The invention belongs to the technical field of molecular sieves, and particularly relates to a regeneration method of a composite modified molecular sieve catalyst for an aromatic alkylation reaction.

Background

The molecular sieve is used as a common solid acid catalyst and an active center component in acid catalytic reaction, is widely applied to catalytic conversion reaction of hydrocarbons, such as catalytic cracking, alkylation, hydrocracking and the like, and plays an important role in the catalytic field. In the using process of the molecular sieve catalyst, hydrocarbon molecules undergo reactions such as polymerization, hydrogen transfer and the like to generate polyene species and low-ring aromatic hydrocarbon, and the reactions such as hydrogen transfer, alkylation, cyclization and the like are continuously performed to form coke deposits which are difficult to volatilize and have a multi-ring structure, so that carbon deposition and inactivation of the catalyst are caused.

After the carbon deposition of the catalyst is inactivated, the catalyst can be regenerated by oxidation burning, the activity can be partially or completely recovered, and the catalyst can still be continuously used in industrial production. Some catalysts can be regenerated and used even for a plurality of times, thereby achieving the purposes of saving energy and increasing benefit. CN102151589A discloses an in-situ regeneration method of a molecular sieve catalyst, which comprises the following steps: carrying out in-situ treatment on the inactivated catalyst at the temperature of 30-140 ℃ by using a mixed solution, wherein the mixed solution is a mixture of an aqueous solution containing oxidizing substances and one or more organic solvents; the oxidizing substance in the mixed solution can be tert-butyl peroxide, peracetic acid, performic acid and hydrogen peroxide, and the solvent can be a mixture of one or more of methanol, ethanol, propanol and formic acid and water. The method provides a method which can realize good regeneration effect without high-temperature roasting, but needs a large amount of organic solvent.

CN102836743A discloses a regeneration method of a molecular sieve catalyst, which comprises roasting the molecular sieve catalyst to be regenerated at the temperature of 300-750 ℃ so as to decompose carbon deposit in the molecular sieve catalyst to be regenerated into CO ₂ The roasting method comprises the following steps: in the presence of oxygen-containing gas, the catalyst to be regenerated is roasted at constant temperature in multiple stages, the multiple constant-temperature roasting stages comprise a first roasting stage and a roasting stage after the first roasting stage, the roasting temperature of any roasting stage after the first roasting stage is 5-70 ℃ higher than that of the adjacent previous roasting stage, and the roasting time of each roasting stage is that the roasting is carried out under the roasting condition of the stage until no CO exists ₂ And (4) generating. The regeneration roasting temperature is high and needs to be over 600 ℃, and the high temperature in the regeneration process can affect other components in the catalyst, such as metal sintering, crystal phase transformation and the like. Therefore, how to reduce the impact on other components in the molecular sieve is an important issue in the regeneration process of the molecular sieve.

Disclosure of Invention

The invention aims to provide a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which solves the problem of overhigh catalyst cost caused by the service life of the catalyst and increases the usable times of the catalyst.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which comprises the following steps: sequentially heating and roasting the inactivated composite modified molecular sieve catalyst to obtain a regenerated composite modified molecular sieve catalyst;

and introducing mixed gas of inert gas and air in the roasting treatment.

In the invention, volatile organic small molecules and water adsorbed in the pore passages of the molecular sieve can be removed by heating treatment and introducing nitrogen for purging; and then roasting to eliminate carbon deposition in the molecular sieve catalyst, so that organic matter macromolecules which are difficult to volatilize, such as long-chain aliphatic hydrocarbon, polyalkylbenzene and polycyclic aromatic hydrocarbon, react with oxygen, the carbon deposition species fully react with the oxygen by adjusting the oxygen concentration and the mixed gas flow in the regeneration process, and metal and/or nonmetal active components on the molecular sieve catalyst are retained, so that the activity of the catalyst is recovered, and the catalytic performance of the regenerated molecular sieve catalyst is further improved.

In a preferred embodiment of the present invention, the temperature of the heat treatment is 100-350 ℃, and may be, for example, 100 ℃, 150 ℃, 200 ℃, 250 ℃, 300 ℃ or 350 ℃, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the heating rate of the heating treatment is 1 to 20 ℃/min, and for example, 1 ℃/min, 5 ℃/min, 8 ℃/min, 10 ℃/min, 15 ℃/min, or 20 ℃/min, etc., but not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the heat treatment is carried out for a holding time of 1 to 6 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours, but not limited to the values listed, and other values not listed in the numerical range are also applicable.

As a preferable technical scheme of the invention, inert gas is introduced into the heating treatment.

Preferably, the flow rate of the inert gas is 10 to 50L/min, for example, 10L/min, 15L/min, 20L/min, 25L/min, 30L/min, 35L/min, 40L/min, 45L/min or 50L/min, etc., but not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the inert gas comprises any one of nitrogen, argon or helium or a combination of at least two of these, typical but non-limiting examples being: a combination of nitrogen and argon, a combination of argon and helium, or a combination of nitrogen, argon and helium, and the like.

In a preferred embodiment of the present invention, the temperature of the baking treatment is 450 ℃ and 560 ℃, for example, 450 ℃, 460 ℃, 470 ℃, 480 ℃, 490 ℃, 500 ℃, 510 ℃, 520 ℃, 530 ℃, 540 ℃, 550 ℃ or 560 ℃, but not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the heating rate of the baking treatment is 1-20 ℃/min, for example, 1 ℃/min, 5 ℃/min, 8 ℃/min, 10 ℃/min, 15 ℃/min, or 20 ℃/min, etc., but is not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the heat preservation time of the roasting treatment is 6-10h, for example, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, etc., but not limited to the recited values, and other values not recited in the range of the values are also applicable.

In a preferred embodiment of the present invention, the flow rates of the inert gas and air introduced in the baking treatment are 10 to 50L/min, for example, 10L/min, 15L/min, 20L/min, 25L/min, 30L/min, 35L/min, 40L/min, 45L/min, or 50L/min, but not limited to the above-mentioned values, and other values not listed in the numerical range are also applicable.

Preferably, the volume ratio of the inert gas to air is (2-4):1, and may be, for example, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1 or 4:1, but is not limited to the values recited, and other values not recited within the range of values are also applicable.

In a preferred embodiment of the present invention, the calcination treatment is performed in a medium.

Preferably, the medium comprises an aqueous alkaline solution.

In a preferred embodiment of the present invention, the pH of the basic aqueous solution is 8 to 10, and may be, for example, 8, 8.2, 8.4, 8.6, 8.8, 9, 9.2, 9.4, 9.6, 9.8 or 10, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the basic aqueous solution comprises ammonia.

Preferably, the concentration of the aqueous ammonia is 0.1% to 2.5%, and may be, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, or 2.5%, etc., but is not limited to the values recited, and other values not recited in the numerical range are also applicable.

As a preferable technical scheme of the invention, the modifying elements of the composite modified molecular sieve catalyst comprise metal elements and/or non-metal elements.

Preferably, the metallic elements include any one or a combination of at least two of Mg, Cu, Fe, Cr, Pt, Ni, Pd, Co or Mn, as typical but non-limiting examples: combinations of Mg and Cu, Fe and Cr, Pt and Ni, or Co and Mn, and the like.

Preferably, the non-metallic element includes Si and/or P.

As a preferred embodiment of the present invention, the molecular sieve comprises any one or a combination of at least two of BEA, CHA, MFI, MWW, LTA, AEI, AFX, FAU or RTH, typical but non-limiting examples of which are: combinations of BEA and CHA, MFI and LTA, AEI and AFX, or FAU and RTH, and the like.

As a preferred embodiment of the present invention, the regeneration method comprises:

(1) heating the deactivated composite modified molecular sieve catalyst to 100-350 ℃ at the speed of 1-20 ℃/min for heating treatment, preserving the heat for 1-6h, and simultaneously blowing by adopting inert gas at the flow of 10-50L/min;

(2) continuously heating the catalyst subjected to the heating treatment in the step (1) to 450-560 ℃ at the speed of 1-20 ℃/min for roasting treatment, preserving the heat for 6-10h, and introducing mixed gas of inert gas and air into the catalyst through a medium; the volume ratio of the introduced inert gas to the air is (2-4) to 1, and the medium comprises an alkaline aqueous solution to obtain the regenerated composite modified molecular sieve catalyst.

The numerical ranges set forth herein include not only the recited values but also any values between the recited numerical ranges not enumerated herein, and are not intended to be exhaustive or otherwise clear from the intended disclosure of the invention in view of brevity and clarity.

Compared with the prior art, the invention has the following beneficial effects:

(1) the regeneration method of the composite modified molecular sieve catalyst for the aromatic alkylation reaction, which is provided by the invention, has the advantages of simple process, easy operation and low regeneration cost, and the activity of the regenerated catalyst can be recovered to 80-90% of that of the fresh catalyst, and the selectivity can be recovered to 98-100% of that of the fresh catalyst;

(2) the regeneration method of the invention recovers the activity of metal and/or nonmetal on the molecular sieve catalyst by a regeneration method combining heating treatment and roasting treatment and simultaneously by adjusting the oxygen concentration and the flow rate of mixed gas in the regeneration process, further improves the catalytic performance of the regenerated molecular sieve catalyst, and increases the service cycle of the molecular sieve catalyst.

Detailed Description

The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

The present embodiment provides a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which comprises the following steps:

(1) heating the deactivated Si/P/Pt/MFI catalyst from room temperature to 350 ℃ at the speed of 10 ℃/min, preserving the heat for 3 hours, and simultaneously blowing the catalyst by nitrogen at the flow rate of 50L/min;

(2) and then heating to 540 ℃ at the speed of 10 ℃/min for roasting for 6h, and simultaneously introducing mixed gas with the nitrogen flow of 50L/min and the air flow of 16L/min into the catalyst through a medium, wherein the medium is an ammonia water solution with the pH value of 8, so as to obtain the regenerated composite modified molecular sieve catalyst.

Example 2

The present embodiment provides a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which comprises the following steps:

(1) heating the deactivated Si/P/Pd/MFI catalyst to 300 ℃ from room temperature at the speed of 5 ℃/min, preserving the heat for 5 hours, and simultaneously blowing the catalyst by adopting nitrogen at the flow rate of 50L/min;

(2) and then heating to 550 ℃ at the speed of 10 ℃/min for roasting for 6h, and simultaneously introducing mixed gas with the nitrogen flow of 50L/min and the air flow of 16L/min into the catalyst through a medium, wherein the medium is an ammonia water solution with the pH of 9, so as to obtain the regenerated composite modified molecular sieve catalyst.

Example 3

The present embodiment provides a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which comprises the following steps:

(1) heating the deactivated Si/P/Ni/MFI catalyst from room temperature to 250 ℃ at the speed of 10 ℃/min, preserving the heat for 5 hours, and simultaneously blowing the catalyst by nitrogen at the flow rate of 50L/min;

(2) and then heating to 560 ℃ at the speed of 10 ℃/min for roasting for 5h, and simultaneously introducing mixed gas with the nitrogen flow of 50L/min and the air flow of 16L/min into the catalyst through a medium, wherein the medium is an ammonia water solution with the pH value of 10, so as to obtain the regenerated composite modified molecular sieve catalyst.

Example 4

The present embodiment provides a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which comprises the following steps:

(1) heating the deactivated Si/P/Co/MFI catalyst from room temperature to 250 ℃ at the speed of 5 ℃/min, preserving the heat for 5 hours, and simultaneously blowing the catalyst for 5 hours by adopting nitrogen at the flow rate of 50L/min;

(2) and then heating to 550 ℃ at the speed of 10 ℃/min for roasting for 5h, and simultaneously introducing mixed gas with the nitrogen flow of 50L/min and the air flow of 16L/min into the catalyst through a medium, wherein the medium is an ammonia water solution with the pH of 9, so as to obtain the regenerated composite modified molecular sieve catalyst.

Example 5

The present embodiment provides a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which comprises the following steps:

(1) heating the deactivated Si/P/Pt/MWW catalyst from room temperature to 350 ℃ at the speed of 5 ℃/min, carrying out heat treatment, keeping the temperature for 5 hours, and simultaneously blowing the catalyst for 5 hours by adopting nitrogen at the flow rate of 50L/min;

(2) and then heating to 540 ℃ at the speed of 10 ℃/min for roasting for 5h, and simultaneously introducing mixed gas with the nitrogen flow of 50L/min and the air flow of 16L/min into the catalyst through a medium, wherein the medium is an ammonia water solution with the pH value of 9, so as to obtain the regenerated composite modified molecular sieve catalyst.

Example 6

The present embodiment provides a regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction, which comprises the following steps:

(1) heating the deactivated Si/P/Pt/BEA catalyst from room temperature to 350 ℃ at the speed of 5 ℃/min, preserving the heat for 5 hours, and simultaneously blowing the catalyst for 5 hours by adopting nitrogen at the flow rate of 50L/min;

(2) and then heating to 540 ℃ at the speed of 10 ℃/min for roasting for 5h, and simultaneously introducing mixed gas with the nitrogen flow of 50L/min and the air flow of 16L/min into the catalyst through a medium, wherein the medium is an ammonia water solution with the pH value of 9, so as to obtain the regenerated composite modified molecular sieve catalyst.

Example 7

This example is different from example 1 only in that it is the same as example 1 except that the firing temperature in step (2) is 600 ℃.

Example 8

This example is different from example 1 only in that it is the same as example 1 except that the firing temperature in step (2) is 400 ℃.

Example 9

This example is different from example 1 only in that it is the same as example 1 except that nitrogen gas is purged at a flow rate of 5L/min in step (1).

Example 10

This example is different from example 1 only in that the same procedure as in example 1 was repeated except that "a mixed gas having a nitrogen flow rate of 50L/min and an air flow rate of 16L/min" was replaced with "a mixed gas having a nitrogen flow rate of 33L/min and an air flow rate of 33L/min" in step (2).

Example 11

This example is different from example 1 only in that the same procedure as in example 1 was repeated except that "a mixed gas having a nitrogen flow rate of 50L/min and an air flow rate of 16L/min" was replaced with "a mixed gas having a nitrogen flow rate of 55L/min and an air flow rate of 11L/min" in step (2).

Example 12

This example is different from example 1 only in that the same procedure as in example 1 was repeated except that "a mixed gas having a nitrogen flow rate of 50L/min and an air flow rate of 16L/min" was replaced with "a mixed gas having a nitrogen flow rate of 50L/min and an air flow rate of 5L/min" in step (2).

Example 13

This example differs from example 1 only in that it is the same as example 1 except that the deactivated catalyst of step (1) is a Cu/Fe/Pt/MFI catalyst.

Example 14

This example differs from example 1 only in that it is the same as example 1 except that the deactivated catalyst of step (1) is a Cu/Ni/Pt/MFI catalyst.

Comparative example 1

This comparative example differs from example 1 only in that it is the same as example 1 except that the step (1) "purging the catalyst with nitrogen at a flow rate of 50L/min" is replaced with "purging the catalyst with air at a flow rate of 50L/min".

Comparative example 2

This comparative example differs from example 1 only in that it is the same as example 1 except that "the mixed gas having a nitrogen flow rate of 50L/min and an air flow rate of 16L/min" in step (2) is replaced with "the nitrogen flow rate of 50L/min".

The regenerated composite modified molecular sieve catalyst obtained in examples 1-14 and comparative examples 1-2 was reduced and usedToluene and methanol alkylation reaction experiments, the toluene conversion rate evaluation of the regenerated catalyst adopts a fixed bed reactor, an Agilent gas chromatograph is used for analysis, and the experimental conditions are as follows: the raw material feeding ratio n (T/M) is 2:1, the reaction pressure is 0.2Mpa, and n (H) ₂ O/Material) 2:1, n (H) ₂ Material is 2:1, and the space velocity is 1h ^-1 . The toluene conversion and para-xylene selectivity of the regenerated composite modified molecular sieve catalyst are shown in table 1.

TABLE 1

As can be seen from Table 1:

(1) the regenerated composite modified molecular sieve catalyst obtained by the regeneration method provided by the invention is applied to the alkylation reaction of toluene and methanol, has higher selectivity of p-xylene, the selectivity is 91.5-95.0%, and the conversion rate of toluene is 17.4-19.5%, which shows that the regenerated molecular sieve catalyst maintains higher selectivity of p-xylene, and carbon deposition species on the catalyst are eliminated and the activity is recovered;

(2) as can be seen from the comparison of example 1 with examples 7-8, when the calcination treatment temperature is too high, the molecular sieve framework structure collapses; when the roasting treatment temperature is too low, the toluene conversion rate and the selectivity of paraxylene of the regenerated molecular sieve catalyst are reduced because carbon deposit species cannot be completely eliminated;

(3) comparing example 1 with example 9, it can be seen that when the nitrogen gas introduction amount is too low during the heat treatment process, the toluene conversion rate and the selectivity of paraxylene of the regenerated molecular sieve catalyst are reduced because water vapor and small organic molecules adsorbed in the molecular sieve pore channels cannot be rapidly removed;

(4) as can be seen from the comparison between example 1 and examples 10-12, when the volume ratio of the nitrogen gas and the air introduced during the roasting treatment is lower than 2:1, the carbon deposit is burnt too violently due to the higher air concentration, so that the metal species are agglomerated; when the volume ratio of the introduced nitrogen to the air in the roasting treatment process is higher than 4:1, the carbon deposit can not be fully combusted due to lower air concentration, so that the toluene conversion rate and the selectivity of p-xylene of the regenerated molecular sieve catalyst are reduced;

(5) as can be seen from the comparison between example 1 and examples 13-14, when the modifying elements of the composite modified molecular sieve catalyst are all metal elements, the catalytic performance of the regenerated catalyst is slightly reduced, which indicates that the regeneration method is more suitable for the molecular sieve catalyst loaded with both metal elements and nonmetal elements;

(6) comparing example 1 with comparative example 1, it can be seen that when air is introduced during the heating process, organic matters and moisture adsorbed in the molecular sieve pore channels cannot be sufficiently removed due to a certain amount of water vapor and impurities contained in the air, which results in the reduction of toluene conversion rate and selectivity of p-xylene of the regenerated molecular sieve catalyst; as can be seen from the comparison of example 1 with comparative example 2, when only nitrogen gas was introduced during the second heating process, the toluene conversion and the selectivity to p-xylene of the regenerated molecular sieve catalyst were reduced because the carbon deposit was not sufficiently reacted with oxygen.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are all within the protection scope of the present invention.

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims (10)

1. A regeneration method of a composite modified molecular sieve catalyst for aromatic alkylation reaction is characterized by comprising the following steps: sequentially heating and roasting the inactivated composite modified molecular sieve catalyst to obtain a regenerated composite modified molecular sieve catalyst;

and introducing mixed gas of inert gas and air in the roasting treatment.

2. The regeneration method as claimed in claim 1, wherein the temperature of the heating treatment is 100-350 ℃;

preferably, the heating rate of the heating treatment is 1-20 ℃/min;

preferably, the heat treatment is carried out for 1-6 h.

3. Regeneration process according to claim 1 or 2, characterized in that the heating treatment is fed with an inert gas;

preferably, the flow rate of the introduced inert gas is 10-50L/min;

preferably, the inert gas comprises any one of nitrogen, argon or helium or a combination of at least two thereof.

4. The regeneration method as claimed in any one of claims 1 to 3, wherein the temperature of the roasting treatment is 450-560 ℃;

preferably, the heating rate of the roasting treatment is 1-20 ℃/min;

preferably, the heat preservation time of the roasting treatment is 6-10 h.

5. The regeneration method according to any one of claims 1 to 4, wherein the flow rates of the inert gas introduced for the roasting treatment and the air are respectively 10 to 50L/min independently;

preferably, the volume ratio of the introduced inert gas to the air is (2-4): 1.

6. Regeneration process according to any one of claims 1 to 5, characterised in that the calcination treatment is carried out in a medium;

preferably, the medium comprises an aqueous alkaline solution.

7. The regeneration process according to claim 6, characterized in that the pH value of the aqueous alkaline solution is between 8 and 10;

preferably, the basic aqueous solution comprises ammonia;

preferably, the concentration of the ammonia water is 0.1% -2.5%.

8. The regeneration process of any one of claims 1 to 7, wherein the modifying elements of the composite modified molecular sieve catalyst comprise metallic elements and/or non-metallic elements;

preferably, the metal element includes any one or a combination of at least two of Mg, Cu, Fe, Cr, Pt, Ni, Pd, Co, or Mn;

preferably, the non-metallic element includes Si and/or P.

9. The regeneration process of any one of claims 1 to 8, wherein the molecular sieve comprises any one or a combination of at least two of BEA, CHA, MFI, MWW, LTA, AEI, AFX, FAU or RTH.

10. Regeneration method according to any one of claims 1 to 9, characterized in that it comprises:

(1) heating the inactivated composite modified molecular sieve catalyst to 100-350 ℃ at the speed of 1-20 ℃/min for heating treatment, preserving the heat for 1-6 hours, and simultaneously blowing by adopting inert gas at the flow rate of 10-50L/min;

(2) continuously heating the catalyst subjected to the heating treatment in the step (1) to 450-560 ℃ at the speed of 1-20 ℃/min for roasting treatment, preserving the heat for 6-10h, and introducing mixed gas of inert gas and air into the catalyst through a medium; the volume ratio of the introduced inert gas to the air is (2-4) to 1, and the medium comprises an alkaline aqueous solution to obtain the regenerated composite modified molecular sieve catalyst.