CN114349018A - MFI molecular sieve, preparation method thereof and preparation method of caprolactam - Google Patents
MFI molecular sieve, preparation method thereof and preparation method of caprolactam Download PDFInfo
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Abstract
The invention provides an MFI molecular sieve, a preparation method thereof and a preparation method of caprolactam. The preparation method of the MFI molecular sieve comprises the following steps: step S1, carrying out hydrothermal synthesis on a mixture of a silicon source, water and a quaternary ammonium template agent to obtain a hydrothermal synthesis system; step S2, filtering, washing and drying the hydrothermal synthesis system to obtain an MFI type molecular sieve precursor; and step S3, carrying out anaerobic roasting on the MFI type molecular sieve precursor to obtain the MFI type molecular sieve catalyst. The crystallized molecular sieve crystal is subjected to anaerobic roasting, so that a quaternary ammonium template agent in a molecular sieve pore channel is subjected to in-situ carbonization, the micropores of the molecular sieve are closed or shortened, the internal diffusion of a substrate and side reactions caused by the internal diffusion are inhibited, nitrogen-containing alkaline gas thermally decomposed by the quaternary ammonium template agent is used for modifying the strong acid sites of the MFI type molecular sieve at high temperature, additional alkali modification is not needed, the selectivity of the catalyst is improved, the preparation process of the catalyst is shortened, and the service life of the catalyst is long.
Description
Technical Field
The invention relates to the field of caprolactam preparation, and in particular relates to an MFI molecular sieve, a preparation method thereof and a preparation method of caprolactam.
Background
Caprolactam is an important intermediate in the industrial production process of nylon, and Beckmann rearrangement of cyclohexanone oxime is one of the key steps in the production process of caprolactam. At present, the traditional liquid phase rearrangement process using concentrated sulfuric acid as a catalyst is mainly adopted in industry. Although the reaction conditions of the process are mild, and the conversion rate and the selectivity are ideal, a large amount of ammonium sulfate is produced as a byproduct, and equipment corrosion and environmental pollution are easily caused. In order to overcome the defects, attention is paid to a gas-phase Beckmann rearrangement process for catalyzing cyclohexanone oxime by using a solid acid such as a molecular sieve in recent years. However, the reaction temperature required by the gas-phase Beckmann rearrangement process is high, the catalyst stability is poor, the deactivation is rapid, and the selectivity of the catalyst is low.
Disclosure of Invention
The invention mainly aims to provide an MFI molecular sieve, a preparation method thereof and a preparation method of caprolactam, and aims to solve the problem that a catalyst is easy to deactivate when caprolactam is prepared by gas phase Beckmann in the prior art.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing an MFI molecular sieve, the method comprising: step S1, carrying out hydrothermal synthesis on a mixture of a silicon source, water and a quaternary ammonium template agent to obtain a hydrothermal synthesis system; step S2, filtering, washing and drying the hydrothermal synthesis system to obtain an MFI type molecular sieve precursor; and step S3, carrying out anaerobic roasting on the MFI type molecular sieve precursor to obtain the MFI type molecular sieve catalyst.
Further, the molar ratio of the silicon source, the water and the quaternary ammonium template agent is 1: 10-50: 0.1 to 1.5.
Further, the mixture also comprises an aluminum source or a titanium source, preferably the aluminum source is selected from one or more of aluminate and metaaluminate, and further preferably the aluminum source is selected from one or more of sodium aluminate, potassium aluminate, metasodium aluminate or potassium metaaluminate; preferably, the titanium source is one or more of titanate, further preferably, the titanium source is one or more of tetraethyl titanate, tetrapropyl titanate or tetrabutyl titanate, and the molar ratio of the silicon source, the aluminum source, the titanium source, the water and the quaternary ammonium template is 1: 0 to 0.001: 0 to 0.002: 10-50: 0.1 to 1.5.
Further, any one of the above silicon source silicates, preferably the silicon source is selected from one or more selected from the group consisting of ethyl orthosilicate, propyl orthosilicate, and butyl orthosilicate.
Further, the quaternary ammonium template is selected from one or more of tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, tetraethyl ammonium bromide, tetrapropyl ammonium bromide, tetraethyl ammonium chloride and tetrapropyl ammonium chloride.
Further, the MFI type molecular sieve is one or more of an all-silica molecular sieve Silicalite-1, a silica-alumina molecular sieve ZSM-5 with a silica-alumina ratio of more than 1000, or a titanium-silica molecular sieve TS-1 with a silica-titanium ratio of more than 500.
Further, the step S1 includes: performing hydrolysis reaction on a mixture of a silicon source, water and a quaternary ammonium template agent to obtain a hydrolysis system, wherein the temperature of the hydrolysis reaction is preferably 20-60 ℃, and the time of the hydrolysis reaction is preferably 2-6 hours; distilling the hydrolysis system to remove alcohol to obtain a glue solution, wherein the preferable distillation temperature is 70-100 ℃, and the preferable distillation time is 1-8 h; and carrying out hydrothermal crystallization on the glue solution to obtain a hydrothermal synthesis system, wherein the temperature of the hydrothermal crystallization reaction is preferably 150-200 ℃, and the time of the crystallization reaction is preferably 36-96 h.
Further, the drying temperature is 60-140 ℃, and the drying time is 2-180 h.
Further, the temperature of the oxygen-free roasting is 600-1000 ℃, preferably the oxygen-free roasting is carried out in protective gas, preferably the protective gas is inert gas or nitrogen, preferably the inert gas is one or more of helium, neon or argon, and preferably the gas space velocity of the protective gas is 0-1.0 h-1The roasting time is 1-8 h.
According to another aspect of the present invention, there is provided an MFI molecular sieve prepared by any of the above-described methods.
According to another aspect of the present invention, there is provided a process for producing caprolactam, the process comprising: gasifying the cyclohexanone oxime solution under the action of carrier gas to obtain a vapor; and conveying the vapor into a reactor for gas phase Beckmann rearrangement reaction to obtain reaction liquid containing caprolactam and carrier gas after reaction, wherein the reactor is loaded with the MFI molecular sieve.
Further, the carrier gas is nitrogen, hydrogen, CO2Preferably, the solvent in the cyclohexanone oxime solution is a saturated aliphatic alcohol having a carbon number of 1 to 6, and more preferably a saturated aliphatic alcohol having a carbon number of 1 to 3.
Further, the preparation method further comprises the following steps: after reaction, the carrier gas is washed by a detergent and then returns to the gasification process of the cyclohexanone-oxime for repeated use; the detergent is any one of water, an organic solvent, an aqueous solution and an organic solution, the organic solvent comprises any one of methanol, ethanol, butanol, cyclohexanol and tert-butanol, the organic solution comprises any one of a methanol trifluoroacetic acid solution and an ethanol benzenesulfonic acid solution, the aqueous solution comprises an acidic solution, an alkaline solution and a neutral solution, and preferably the acidic solution comprises any one or more of a sulfuric acid aqueous solution, a hydrochloric acid aqueous solution, a nitric acid aqueous solution, a phosphoric acid aqueous solution and a phosphate aqueous solution; the alkaline solution comprises one or more of potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, ammonia water and sodium bicarbonate aqueous solution; the neutral solution preferably comprises one or more of a sodium chloride aqueous solution, a sodium sulfate aqueous solution and a polyvinyl alcohol aqueous solution, the washing temperature is preferably 0-50 ℃, and the mass ratio of the detergent to the carrier gas is preferably 0.01-10: 1.
Further, the preparation method further comprises the following steps: distilling the reaction solution to obtain a recovered solvent; adsorbing the recovered solvent by using an adsorbent to obtain a purified solvent; the purified solvent is used as a solvent for the cyclohexanone oxime solution.
Further, the adsorbent is one or more of activated carbon, ion exchange resin and molecular sieve, preferably the ion exchange resin is strong-acid ion exchange resin, preferably the molecular sieve is any one of 4A molecular sieve, 13X molecular sieve and Y molecular sieve, and preferably the mass space velocity of the recovered solvent passing through the adsorbent is 0.5-10 h-1。
By applying the technical scheme of the invention, the crystallized molecular sieve crystal is subjected to anaerobic roasting, so that the quaternary ammonium template agent in the molecular sieve pore channel is carbonized in situ, the molecular sieve micropores are closed or shortened, the substrate internal diffusion and the side reaction caused by the substrate internal diffusion are inhibited, and the nitrogen-containing alkaline gas thermally decomposed by the quaternary ammonium template agent is used for modifying the strong acid sites of the MFI type molecular sieve at high temperature, so that further alkali modification is not needed after roasting, the selectivity of the catalyst is improved, the preparation process of the catalyst is shortened, and the resource consumption is reduced. The preparation method simplifies the preparation process, improves the selectivity of the catalyst, has low production cost and is easy to industrialize. The molecular sieve prepared by the preparation method can be used as an efficient catalyst for synthesizing caprolactam by cyclohexanone-oxime gas phase rearrangement, and the catalyst has the characteristics of good catalytic activity, high selectivity and long service life.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail with reference to examples.
As analyzed in the background of the present application, in order to solve the problem that the catalyst is easily deactivated when the caprolactam is prepared by gas phase beckmann in the prior art, the present application provides an MFI molecular sieve, a preparation method thereof and a preparation method of caprolactam.
In one exemplary embodiment of the present application, there is provided a method of preparing an MFI molecular sieve, the method comprising: step S1, carrying out hydrothermal synthesis on a mixture of a silicon source, water and a quaternary ammonium template agent to obtain a hydrothermal synthesis system; step S2, filtering, washing and drying the hydrothermal synthesis system to obtain an MFI type molecular sieve precursor; and step S3, carrying out anaerobic roasting on the MFI type molecular sieve precursor to obtain the MFI type molecular sieve catalyst.
According to the preparation method, crystallization is carried out through hydrothermal synthesis to obtain an MFI molecular sieve crystal, an MFI molecular sieve precursor containing the MFI molecular sieve crystal is obtained after filtering, washing and drying, the crystallized molecular sieve crystal in the MFI molecular sieve precursor is subjected to anaerobic roasting, so that a quaternary ammonium template in a molecular sieve pore channel is subjected to in-situ carbonization, the molecular sieve pore is sealed or shortened, the internal diffusion of a substrate and a side reaction caused by the internal diffusion are inhibited, and a nitrogen-containing alkaline gas thermally decomposed by the quaternary ammonium template is used for modifying a strong acid site of the MFI molecular sieve at a high temperature, so that the strong acid site is not required to be subjected to further alkali modification after roasting, the selectivity of the catalyst is improved, the preparation process of the catalyst is shortened, and the resource consumption is reduced. The preparation method simplifies the preparation process, improves the selectivity of the catalyst, has low production cost and is easy to industrialize. The molecular sieve prepared by the preparation method can be used as an efficient catalyst for synthesizing caprolactam by cyclohexanone-oxime gas phase rearrangement, and the catalyst has the characteristics of good catalytic activity, high selectivity and long service life.
In order to improve the crystallization efficiency of the molecular sieve, the molar ratio of the silicon source, water and the quaternary ammonium template agent is preferably 1: 10-50: 0.1 to 1.5, for example, 1:10:0.1, 1:20:0.1, 1:30:0.1, 1:40:0.1, 1:50:0.1, 1:10:0.5, 1:10:1.0, 1:10:1.5, 1:20:1, 1:30:1, 1:40:1, 1:20:0.5, 1:30: 0.5. In the above molar ratio, the silicon source is represented by silicon atoms. The silicon source and quaternary ammonium templating agent used in the present application can be selected from the corresponding materials commonly used in the art. For example, the silicon source is selected from any one of silicate esters, such as one or more selected from ethyl orthosilicate, propyl orthosilicate, or butyl orthosilicate. For example, the quaternary ammonium template agent is selected from one or more of tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, tetraethyl ammonium bromide, tetrapropyl ammonium bromide, tetraethyl ammonium chloride and tetrapropyl ammonium chloride
In some embodiments, it is preferred that the mixture further comprises an aluminum source or a titanium source, preferably the aluminum source is selected from one or more of aluminates and metaaluminates, further preferably the aluminum source is selected from one or more of sodium aluminate, potassium aluminate, sodium metaaluminate, or potassium metaaluminate; preferably, the titanium source is one or more of titanate, further preferably, the titanium source is one or more of tetraethyl titanate, tetrapropyl titanate or tetrabutyl titanate, and the molar ratio of the silicon source, the aluminum source, the titanium source, the water and the quaternary ammonium template is 1: 0 to 0.001: 0 to 0.002: 10-50: 0.1 to 1.5. In the above molar ratio, the silicon source is represented by a silicon atom, the aluminum source is represented by an aluminum atom, and the titanium source is represented by a titanium atom.
The molecular sieve synthesized by the method can be an all-silica molecular sieve, and can also be a multi-silica molecular sieve doped with aluminum or titanium, for example, the MFI type molecular sieve is one or more of an all-silica molecular sieve Silicalite-1, a silicon-aluminum molecular sieve ZSM-5 with a silicon-aluminum ratio greater than 1000, or a titanium-silica molecular sieve TS-1 with a silicon-titanium ratio greater than 500.
In order to improve the crystallinity, it is preferable that the step S1 includes: performing hydrolysis reaction on a mixture of a silicon source, water and a quaternary ammonium template agent to obtain a hydrolysis system, wherein the temperature of the hydrolysis reaction is preferably 20-60 ℃, and the time of the hydrolysis reaction is preferably 2-6 hours; distilling the hydrolysis system to remove alcohol to obtain a glue solution, wherein the preferable distillation temperature is 70-100 ℃, and the preferable distillation time is 1-8 h; and carrying out hydrothermal crystallization on the glue solution to obtain a hydrothermal synthesis system, wherein the temperature of the hydrothermal crystallization reaction is preferably 150-200 ℃, and the time of the crystallization reaction is preferably 36-96 h. During hydrolysis, water reacts with the quaternary ammonium template to generate alcohol, the generated alcohol is removed through distillation, and a crystal structure of silicon dioxide is formed through hydrothermal crystallization after the alcohol is removed, wherein a pore structure of the crystal structure of the quaternary ammonium template is utilized. Under the conditions of temperature and time of each step, the reaction efficiency of each stage is improved in the shortest possible time.
In some implementations, the drying temperature is 60-140 ℃ and the drying time is 2-180 hours, so that the water and the alcohol in the water and the alcohol are sufficiently removed.
On the basis of fully carbonizing the quaternary ammonium template agent, in order to improve the structural stability of the formed MFI molecular sieve and the yield of the formed MFI molecular sieve, the anaerobic roasting temperature is preferably 600-1000 ℃, and is too low, so that the quaternary ammonium template agent is easily insufficiently carbonized; the temperature of oxygen-free calcination is too high, which easily causes the formed crystal structure to collapse due to the too high temperature. Further, the temperature of the oxygen-free roasting is preferably 700-800 ℃.
The anaerobic roasting is carried out in a protective atmosphere, preferably in a protective gas, preferably in an inert gas or nitrogen gas, preferably in one or more of helium, neon or argon, and preferably in a protective atmosphere, wherein the gas space velocity is 0-1.0 h-1Preferably 0.2 to 0.5h-1The roasting time is 1-8 h. When the space velocity of the gas is 0, after the replacement with the protective gas, no protective gas needs to be introduced again in the roasting process.
In another exemplary embodiment of the present application, there is provided an MFI molecular sieve prepared by any of the above-described methods of preparation.
According to the preparation method, the crystallized molecular sieve crystal is subjected to anaerobic roasting, so that the quaternary ammonium template agent in a molecular sieve pore channel is subjected to in-situ carbonization, the molecular sieve micropores are closed or shortened, the substrate internal diffusion and the side reaction caused by the substrate internal diffusion are inhibited, and the nitrogen-containing alkaline gas thermally decomposed by the quaternary ammonium template agent is used for modifying the strong acid sites of the MFI type molecular sieve at high temperature, so that the MFI type molecular sieve does not need to be further subjected to alkali modification after roasting, the selectivity of the catalyst is improved, the preparation process of the catalyst is shortened, and the resource consumption is reduced. The MFI molecular sieve prepared by the preparation method can be used as an efficient catalyst for synthesizing caprolactam by cyclohexanone-oxime gas phase rearrangement, and the catalyst has the characteristics of good catalytic activity, high selectivity and long service life.
In another exemplary embodiment of the present application, there is provided a process for producing caprolactam, the process comprising: gasifying the cyclohexanone oxime solution under the action of carrier gas to obtain a vapor; and conveying the vapor into a reactor for gas phase Beckmann rearrangement reaction to obtain reaction liquid containing caprolactam and carrier gas after reaction, wherein the reactor is loaded with the MFI molecular sieve.
The MFI molecular sieve has the characteristics of good catalytic activity, high selectivity and long service life, so that the preparation method of caprolactam can realize longer-time operation on the basis of keeping high selectivity and high yield.
The specific implementation conditions of the gasification and gas phase beckmann rearrangement reaction can be referred to in the prior art, and are not described in detail in the application. That is, when the MFI molecular sieve of the present application is used as a catalyst, the process can maintain longer run times under the same prior art operating conditions.
The carrier gas used in the present application is the same as the common carrier gas of the prior art, such as a gas selected not to participate in the gas phase Beckmann reaction, preferably nitrogen, hydrogen, CO2And argon gas. The solvent in the cyclohexanone oxime solution is preferably a saturated aliphatic alcohol of C1-C6, more preferably a saturated aliphatic alcohol of C1-C3, and the saturated aliphatic alcohol is selected as the solvent, so that the difference between the boiling points of the saturated aliphatic alcohol and the synthesized caprolactam is large, and the saturated aliphatic alcohol and the caprolactam can be conveniently separated.
In the gasification and reaction processes, cyclohexanone oxime undergoes side reactions such as hydrolysis, decomposition, hydrogenation, dehydrogenation and the like to generate impurities such as ammonia, hexenenitrile, hexanenitrile, cyclohexanone, cyclohexanol and the like, and the impurities are inevitably remained in carrier gas and solvent. In order to prolong the service life of the catalyst and maintain a good reaction effect, it is preferable to purify the solvent and/or the carrier gas.
In some embodiments, the above preparation method further comprises: after reaction, the carrier gas is washed by a detergent and then returns to the gasification process of the cyclohexanone-oxime for repeated use; the detergent is any one of water, an organic solvent, an aqueous solution and an organic solution, the organic solvent comprises any one of methanol, ethanol, butanol, cyclohexanol and tert-butanol, the organic solution comprises any one of a trifluoroacetic acid methanol solution and a benzenesulfonic acid ethanol solution, and the aqueous solution comprises an acidic solution, an alkaline solution and a neutral solution. One of the main impurities in the carrier gas is cyclohexanone and hydroxylamine generated by hydrolysis of cyclohexanone oxime, alkaline impurities generated by further decomposition/reaction of hydroxylamine, such as ammonia gas, can be removed by washing with acidic and neutral solutions, and partial alkaline solutions, such as sodium bicarbonate aqueous solution and the like, can also react with ammonia gas and can also play a similar role; in addition, impurities such as cyclohexanone, capronitrile, and hexenenitrile are volatile and easily entrained in the carrier gas, and can be dissolved by water, an organic solvent, and the like to purify the carrier gas.
The acidic solution, the basic solution and the neutral solution used in the present application may be chemically conventional solutions, and preferably the acidic solution contains any one or more of an aqueous sulfuric acid solution, an aqueous hydrochloric acid solution, an aqueous nitric acid solution, an aqueous phosphoric acid solution, and an aqueous phosphate solution; the alkaline solution comprises one or more of potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, ammonia water and sodium bicarbonate aqueous solution; preferably, the neutral solution comprises any one or more of an aqueous sodium chloride solution, an aqueous sodium sulfate solution, and an aqueous polyvinyl alcohol solution. All the substances are conventional substances in the prior art, have stable sources and low cost, and are easy to separate from carrier gas.
The washing is mainly realized by utilizing the solubility and the reactivity of the washing agent to impurities, although the temperature reduction is favorable for reducing the entrainment of the washing agent in the carrier gas and improving the impurity separation effect, particularly the dissolution of ammonia in the washing agent, the freezing or precipitation of the washing agent (particularly water or aqueous solution) is easily caused by the over-low temperature, so that the washing tower is blocked, the balance of the comprehensive cost, the separation effect and the stable degree of the device operation is realized, the washing temperature is preferably 0-50 ℃, and the mass ratio of the washing agent to the carrier gas is preferably 0.01-10: 1. Of course, the washing effect is improved with the increase of the amount of the detergent, but once the ratio exceeds 10:1, the improvement of the washing effect is not obvious, and the requirements on washing equipment are increased, such as high pressure drop of a washing tower, the need of increasing the diameter of the tower to maintain efficient washing, and the increase of the washing cost.
In some embodiments of the present application, the above preparation method further comprises: distilling the reaction solution to obtain a recovered solvent; adsorbing the recovered solvent by using an adsorbent to obtain a purified solvent; the purified solvent is used as a solvent for the cyclohexanone oxime solution. Separating the solvent from caprolactam in the reaction solution by distillation; then the adsorbent is used for adsorbing and removing impurities in the recovered solvent to realize the purification of the solvent.
Since the solvent of the present application is not easily adsorbed by a general adsorbent, the above-mentioned substance for the adsorbent may be selected from adsorptive substances commonly used in the art, and the adsorbent is preferably one or more of activated carbon, ion exchange resin, and molecular sieve, preferably the ion exchange resin is a strongly acidic ion exchange resin, and preferably the molecular sieve is preferably any one of 4A molecular sieve, 13X molecular sieve, and Y molecular sieve. In order to improve the adsorption efficiency and ensure the adsorption effect, the mass space velocity of the recovered solvent passing through the adsorbent is preferably 0.5-10 h-1。
The advantageous effects of the present application will be further described below with reference to examples and comparative examples. Wherein the catalyst life is the run time for cyclohexanone oxime conversion > 98.5% and caprolactam selectivity > 97.5%.
Example 1
Mixing 104.0g of ethyl orthosilicate, 50.8g of 40 wt% tetrapropyl ammonium hydroxide aqueous solution and 60.2g of ultrapure water, hydrolyzing at room temperature for 2h, then distilling to remove alcohol, controlling the distillation temperature to be 70-80 ℃, controlling the distillation time to be 8h, and enabling the alcohol removal rate to be more than 70%, then transferring the colloid into a high-pressure kettle, heating to 170 ℃, and crystallizing for 72h to obtain a molecular sieve precursor; after the crystallization reaction, filtering and washing the reaction liquid, and drying the washed wet filter cake at the temperature of 120 ℃ for 12 hours; grinding the dried solid into powder at a nitrogen air speed of 0.1h-1Roasting for 2 hours at 800 ℃ under the condition to obtain the finished product of the catalyst Silicalite-1.
Fresh usePreparing 20% cyclohexanone-oxime ethanol solution (ethanol is not recycled) by using ethanol, taking fresh nitrogen as carrier gas (nitrogen is not recycled), and setting the space velocity at 0.8h-1The cyclohexanone oxime/ethanol solution is mixed with nitrogen and undergoes rearrangement reaction on a finished product catalyst Silicalite-1 bed layer at 360 ℃ to generate caprolactam. Through detection and calculation, the cyclohexanone-oxime conversion rate is 99.2 percent, the caprolactam selectivity is 98.1 percent, and the operation is stable for 960 h.
Example 2
Mixing 208.1g of ethyl orthosilicate, 82.1mg of sodium metaaluminate, 59.5g of 25 wt% tetraethylammonium hydroxide aqueous solution and 74.6g of ultrapure water, hydrolyzing at room temperature for 6 hours, then distilling to remove alcohol, controlling the distillation temperature to be 70-90 ℃, controlling the distillation time to be 1 hour, and controlling the alcohol removal rate to be more than 70%, then transferring the colloid into a high-pressure kettle, heating to 150 ℃, and crystallizing for 36 hours to obtain a molecular sieve precursor; after the crystallization reaction, filtering and washing the reaction liquid, and drying the washed wet filter cake at the temperature of 120 ℃ for 12 hours; grinding the dried solid into powder at a nitrogen air speed of 0.1h-1Roasting for 2h at 800 ℃ under the condition to obtain the finished product of the catalyst ZSM-5. The process for producing caprolactam of example 1 was repeated using the finished catalyst ZSM-5 as a catalyst for the vapor phase Beckmann reaction, wherein the cyclohexanone oxime conversion and caprolactam selectivity are shown in Table 1.
Example 3
Mixing 104.1g of ethyl orthosilicate, 340.1mg of tetrabutyl titanate, 127.5g of 40 wt% tetrapropyl ammonium hydroxide aqueous solution, 133.2g of tetrapropyl ammonium bromide and 223.3g of ultrapure water, hydrolyzing at room temperature for 3 hours, then distilling to remove alcohol, controlling the distillation temperature to be 70-100 ℃, controlling the distillation time to be 3 hours, the alcohol removal rate to be more than 70%, supplementing 150.2g of water, transferring the colloid into a high-pressure kettle, heating to 200 ℃, and crystallizing for 96 hours to obtain a molecular sieve precursor; after the crystallization reaction, filtering and washing the reaction liquid, and drying the washed wet filter cake at the temperature of 120 ℃ for 12 hours; grinding the dried solid into powder at a nitrogen air speed of 0.1h-1Roasting for 2h at 800 ℃ under the condition to obtain the finished product of the catalyst TS-1. The finished product catalyst TS-1 is used as a catalyst for gas phase Beckmann reaction, and the reaction is repeatedThe caprolactam production process of example 1 wherein the cyclohexanone oxime conversion and caprolactam selectivity are shown in Table 1.
Comparative example 1
The difference from the example 1 is that the cyclohexanone oxime gas phase rearrangement is carried out by completely the same process for preparing caprolactam by using powder calcined at 500 ℃ for 2h as a catalyst under the air atmosphere, the conversion rate of the cyclohexanone oxime is 99.5 percent, the selectivity of the caprolactam is 88.3 percent, after running for 80h, the conversion rate of the cyclohexanone oxime is lower than 98 percent, and the selectivity of the caprolactam is lower than 80 percent.
Examples 4 to 19 drying conditions and calcination conditions, cyclohexanone oxime conversion and caprolactam selectivity were changed on the basis of example 1 as shown in Table 1.
TABLE 1
Furthermore, after a solution with 20% cyclohexanone oxime was gasified with a carrier gas to form a vapor by using the finished catalyst Silicalite-1 of example 1 as a catalyst for the vapor phase Beckmann rearrangement reaction, the reaction mixture was allowed to stand for 0.8h-1The gas and nitrogen are mixed at the airspeed of (1) and undergo rearrangement reaction through a 360 ℃ bed layer to generate reaction liquid containing caprolactam and carrier gas. The carrier gas enters the washing unit, and the solvent recovered by distilling the reaction liquid enters the adsorption unit. The following examples were conducted on carrier gas and solvent recovery processes to verify the effect of different process conditions on catalyst life.
Example 20
This example initially used 99.99% nitrogen as the carrier gas and 99.9% methanol as the solvent.
In the washing unit, carrier gas with the content of 99.96 percent enters the bottom of the washing tower, water is used as a washing agent and enters the washing tower from the top end of the washing tower, the carrier gas and the washing agent are in countercurrent contact, the mass ratio of the washing agent to the carrier gas is 5:1, the washing temperature is 30 ℃, nitrogen with the content of 99.99 percent is extracted from the top of the washing tower, condensed, removed and returned to the reaction unit for recycling.
In the adsorption unit, a solvent (containing 500ppm of ammonia) with the content of 99.6 percent obtained by distilling the reaction liquid passes through an adsorption column filled with strong acid type 732 type cation exchange resin, and the mass space velocity of the solvent is 0.5h-1(ratio of the mass of the solvent passing through the adsorbent to the mass of the adsorbent per hour), the solvent content of the adsorption treatment was 99.8%, and the ammonia content was 0.7ppm, and the reaction mixture was returned as the solvent for cyclohexanone oxime to continue the rearrangement reaction.
The catalyst has a one-way service life of 1314h, an average cyclohexanone oxime conversion rate of 99.4 percent and caprolactam selectivity of 98.1 percent.
Example 21
This example differs from example 20 in that the mass space velocity of the solvent adsorption is 10h-1The carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion rate, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 22
This example differs from example 20 in that the carrier gas for the vapor phase rearrangement is hydrogen, and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 23
This example differs from example 20 in that the adsorbent was activated carbon and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 24
This example differs from example 20 in that the adsorbent was a Y molecular sieve and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 25
This example differs from example 20 in that the adsorbent was a 4A molecular sieve and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 26
This example differs from example 20 in that the adsorbent was a 13X molecular sieve and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 27
This example differs from example 20 in that the carrier gas washing solvent was a 20 wt% aqueous solution of sulfuric acid, and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 28
This example differs from example 20 in that the carrier gas washing solvent was a 5 wt% solution of benzenesulfonic acid in methanol, and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing were as shown in Table 2.
Example 29
This example differs from example 20 in that the washing solvent was a 5 wt% aqueous solution of sodium bicarbonate and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in Table 2.
Example 30
This example differs from example 20 in that the washing solvent was cyclohexanol, and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 31
The difference between the example and the example 20 is that the mass ratio of the washing agent to the carrier gas is 0.01:1, and the carrier gas content, the solvent content, the ammonia content, the cyclohexanone oxime conversion rate, the caprolactam selectivity and the catalyst one-way life after washing are shown in the table 2.
Example 32
The difference between the example and the example 20 is that the mass ratio of the washing agent to the carrier gas is 10:1, and the carrier gas content, the solvent content, the ammonia content, the cyclohexanone oxime conversion rate, the caprolactam selectivity and the catalyst one-way life after washing are shown in the table 2.
Example 33
This example differs from example 20 in that the mass space velocity of the solvent adsorption is 15h-1The carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion rate, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 34
This example differs from example 20 in that the mass space velocity of the solvent adsorption is 0.2h-1The carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion rate, caprolactam selectivity and catalyst one-way life after washing are shown in table 2.
Example 35
The difference between the example and the example 20 is that the mass ratio of the washing agent to the carrier gas is 15:1, and the carrier gas content, the solvent content, the ammonia content, the cyclohexanone oxime conversion rate, the caprolactam selectivity and the catalyst one-way life after washing are shown in the table 2.
Example 36
This example differs from example 20 in that the temperature of washing was 0 ℃ and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in Table 2.
Example 37
This example differs from example 20 in that the temperature of washing was 50 ℃ and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in Table 2.
Example 38
This example differs from example 20 in that the temperature of washing was 80 ℃ and the carrier gas content, solvent content, ammonia content, cyclohexanone oxime conversion, caprolactam selectivity and catalyst one-way life after washing are shown in Table 2.
Comparative example 2
This example differs from example 20 in that only the carrier gas was washed with a detergent and the solvent was returned to the reaction system without adsorption to carry out the rearrangement reaction.
Comparative example 3
This example differs from example 20 in that the carrier gas was not washed and the solvent was returned to the reaction system by adsorption to carry out the rearrangement reaction.
Comparative example 4
This example is different from example 20 in that the carrier gas and the solvent were returned to the reaction system without purification to carry out the rearrangement reaction.
TABLE 2
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:
according to the preparation method, crystallization is carried out through hydrothermal synthesis to obtain an MFI molecular sieve crystal, an MFI molecular sieve precursor containing the MFI molecular sieve crystal is obtained after filtering, washing and drying, then the crystallized molecular sieve crystal in the MFI molecular sieve precursor is subjected to anaerobic roasting, so that a quaternary ammonium template in a molecular sieve pore channel is carbonized in situ, the molecular sieve pore is sealed or shortened, the diffusion in a substrate and the side reaction caused by the diffusion are inhibited, and the strong acid site of the MFI molecular sieve is modified at high temperature by nitrogen-containing alkaline gas thermally decomposed by the quaternary ammonium template, so that the strong acid site of the MFI molecular sieve is not required to be further subjected to alkali modification after roasting, the selectivity of the catalyst is improved, the preparation process of the catalyst is shortened, and the resource consumption is reduced. The MFI molecular sieve prepared by the preparation method can be used as an efficient catalyst for synthesizing caprolactam by cyclohexanone-oxime gas phase rearrangement, and the catalyst has the characteristics of good catalytic activity, high selectivity and long service life.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A preparation method of an MFI molecular sieve, which is characterized by comprising the following steps:
step S1, carrying out hydrothermal synthesis on a mixture of a silicon source, water and a quaternary ammonium template agent to obtain a hydrothermal synthesis system;
step S2, filtering, washing and drying the hydrothermal synthesis system to obtain an MFI type molecular sieve precursor;
and step S3, carrying out anaerobic roasting on the MFI type molecular sieve precursor to obtain the MFI type molecular sieve catalyst.
2. The method according to claim 1, wherein the molar ratio of the silicon source, the water and the quaternary ammonium template agent is 1: 10-50: 0.1 to 1.5;
preferably, the mixture further comprises an aluminum source or a titanium source, preferably the aluminum source is selected from one or more of aluminate and metaaluminate, further preferably the aluminum source is selected from one or more of sodium aluminate, potassium aluminate, sodium metaaluminate or potassium metaaluminate; preferably, the titanium source is one or more of titanate, further preferably, the titanium source is selected from one or more of tetraethyl titanate, tetrapropyl titanate or tetrabutyl titanate, and the molar ratio of the silicon source, the aluminum source, the titanium source, the water and the quaternary ammonium template agent is 1: 0 to 0.001: 0 to 0.002: 10-50: 0.1 to 1.5.
3. The preparation method according to claim 1 or 2, characterized in that the silicon source is selected from any one of silicate esters, preferably the silicon source is selected from one or more of ethyl orthosilicate, propyl orthosilicate or butyl orthosilicate;
and/or the quaternary ammonium template agent is selected from one or more of tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, tetraethyl ammonium bromide, tetrapropyl ammonium bromide, tetraethyl ammonium chloride and tetrapropyl ammonium chloride;
and/or the MFI type molecular sieve is one or more of an all-silicon molecular sieve Silicalite-1, a silicon-aluminum molecular sieve ZSM-5 with a silicon-aluminum ratio of more than 1000 or a titanium-silicon molecular sieve TS-1 with a silicon-titanium ratio of more than 500.
4. The method for preparing a composite material according to claim 1, wherein the step S1 includes:
performing hydrolysis reaction on a mixture of a silicon source, water and a quaternary ammonium template agent to obtain a hydrolysis system, wherein the temperature of the hydrolysis reaction is preferably 20-60 ℃, and the time of the hydrolysis reaction is preferably 2-6 hours;
distilling the hydrolysis system to remove alcohol to obtain a glue solution, wherein the preferable distillation temperature is 70-100 ℃, and the preferable distillation time is 1-8 h;
and carrying out hydrothermal crystallization on the glue solution to obtain the hydrothermal synthesis system, wherein the temperature of the hydrothermal crystallization reaction is preferably 150-200 ℃, and the time of the crystallization reaction is preferably 36-96 h.
5. The preparation method according to claim 1, wherein the drying temperature is 60-140 ℃ and the drying time is 2-180 h;
and/or the temperature of the anaerobic roasting is 600-1000 ℃, the anaerobic roasting is preferably carried out in protective gas, the protective gas is preferably inert gas or nitrogen, the inert gas is preferably one or more of helium, neon or argon, and the gas space velocity of the protective gas is preferably 0-1.0 h-1The roasting time is 1-8 h.
6. An MFI molecular sieve, characterized by being prepared by the preparation method of any one of claims 1 to 5.
7. A process for preparing caprolactam, said process comprising:
gasifying the cyclohexanone oxime solution under the action of carrier gas to obtain a vapor;
the vapor is conveyed into a reactor to carry out gas phase Beckmann rearrangement reaction to obtain reaction liquid containing caprolactam and carrier gas after the reaction,
the reactor is loaded with the MFI molecular sieve of claim 6.
8. The method of claim 7, wherein the carrier gas is nitrogen, hydrogen, CO2And argon, preferably the solvent in the cyclohexanone oxime solution is a saturated aliphatic alcohol of C1-C6, more preferably C1-C3.
9. The production method according to claim 7 or 8, characterized by further comprising: the carrier gas after the reaction is washed by a detergent and then returns to the gasification process of the cyclohexanone oxime for repeated use; the detergent is any one of water, an organic solvent, an aqueous solution and an organic solution, the organic solvent comprises any one of methanol, ethanol, butanol, cyclohexanol and tert-butanol, the organic solution comprises any one of a methanol trifluoroacetic acid solution and an ethanol benzenesulfonic acid solution, the aqueous solution comprises an acidic solution, an alkaline solution and a neutral solution, and preferably the acidic solution comprises any one or more of a sulfuric acid aqueous solution, a hydrochloric acid aqueous solution, a nitric acid aqueous solution, a phosphoric acid aqueous solution and a phosphate aqueous solution; the alkaline solution comprises any one or more of potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, ammonia water and sodium bicarbonate aqueous solution; preferably, the neutral solution comprises any one or more of a sodium chloride aqueous solution, a sodium sulfate aqueous solution and a polyvinyl alcohol aqueous solution, the washing temperature is preferably 0-50 ℃, and the mass ratio of the detergent to the carrier gas is preferably 0.01-10: 1.
10. The production method according to claim 7 or 8, characterized by further comprising:
distilling the reaction solution to obtain a recovered solvent;
adopting an adsorbent to perform adsorption treatment on the recovered solvent to obtain a purified solvent;
the purified solvent is used as a solvent for the cyclohexanone oxime solution,
preferably, the adsorbent is one or more of activated carbon, ion exchange resin and a molecular sieve, preferably, the ion exchange resin is a strong-acid ion exchange resin, preferably, the molecular sieve is any one of a 4A molecular sieve, a 13X molecular sieve and a Y molecular sieve, and preferably, the mass space velocity of the recovered solvent passing through the adsorbent is 0.5-10 h-1。
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| CN114455601A (en) * | 2022-02-24 | 2022-05-10 | 江苏扬农化工集团有限公司 | Preparation method and application of molecular sieve |
| CN114768865A (en) * | 2022-05-24 | 2022-07-22 | 陈天然 | Catalyst for preparing 6-aminocapronitrile from cyclohexanone oxime and application thereof |
| CN115739137A (en) * | 2022-12-21 | 2023-03-07 | 江苏扬农化工集团有限公司 | Preparation method of catalyst for synthesizing caprolactam and synthesis method of caprolactam |
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