Preparation method and application of catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzeneTechnical Field
The invention belongs to the technical field of ethylbenzene preparation, and particularly relates to a preparation method and application of a catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzene.
Background
Ethylbenzene is an important chemical raw material, and is mainly used for producing styrene by catalytic dehydrogenation. Styrene is an important synthetic material for the production of polystyrene, engineering plastics, styrene-butadiene rubber, etc. In recent years, the market demand and the production capacity of styrene show a remarkable rising trend, china has the largest styrene market in the world, and the styrene in China is expected to have new production capacity of 686.2 ten thousand tons in 2018-2022. At present, ethylbenzene is mainly produced in a mode of alkylation reaction of benzene and ethylene/ethanol in industry, and the main processes are two main types of liquid-phase alkylation and gas-phase alkylation.
The traditional ethylbenzene production method mainly adopts a mode of alkylation reaction of benzene and ethylene or ethanol to produce ethylbenzene, and the main processes are two main types of AlCl3 liquid-phase alkylation method and molecular sieve alkylation method.
The AlCl3 liquid phase alkyl method has simple process, mild operation condition and high ethylene conversion rate, but has the problems of equipment corrosion, environmental pollution, high maintenance cost and the like, and the selectivity of ethylbenzene in the product can reach more than 95 percent.
The molecular sieve alkylation method is mainly to prepare ethylbenzene by molecular sieve gas phase alkylation, and the alkylation method has the advantages of no corrosion, no pollution, simple flow, high heat energy recycling rate and the like.
Patent CN102274746a reports a nano ZSM-5 catalyst after rare earth modification, water vapor and phosphoric acid treatment. Under the conditions of 390 ℃ and 1.2MPa, n (benzene)/n (ethanol) =6.5 and WHSV Ethanol=0.8h-1, the ethanol conversion rate reaches 99.9%, the ethyl selectivity reaches 99.9%, the xylene content in the ethylbenzene product is below 800ppm, and the catalyst regeneration period reaches half a year.
Patent CN101450888a reports a high silica alumina ratio ZSM-5 catalyst modified with rare earth. Under the conditions of 400 ℃, 2MPa, n (benzene)/n (ethanol) =6 and WHSV Ethanol=2h-1, the conversion rate of the raw material benzene of 16.58% and the selectivity of ethylbenzene of 96.76% are achieved at the highest.
The vapor phase alkylation catalysts reported above are primarily ZSM-5 molecular sieves, and in addition ZSM-11, MCM-22, beta, Y-type molecular sieves, and the like, are also disclosed.
Patent CN110465326a discloses a process for preparing ethylbenzene from benzene and ethanol by vapor phase alkylation using a modified ZSM-11 molecular sieve, which realizes 98% ethanol conversion and better ethylbenzene selectivity.
The alkylation of benzene and ethylene/ethanol to ethylbenzene is catalyzed mainly by AlCl3、 FeCl3 or by catalysts with strong Lewis acids such as ZSM-5, ZSM-11, beta molecular sieves, etc. Because the alkylation reaction is a reversible reaction, the reaction process is not stopped in the primary alkylation stage, the generated ethylbenzene is more active than raw material benzene, and the secondary alkylation and the like can be continuously carried out to generate diethylbenzene, triethylbenzene and the like. In general experiments and industries, excessive benzene is generally added to inhibit the formation of diethylbenzene and triethylbenzene so as to improve the yield of ethylbenzene, but the excessive benzene-alcohol ratio can bring about the improvement of the operation load of the device. In order to increase ethylbenzene selectivity without increasing the operating load on the unit, efficient use of polyethylbenzene in the product is required.
The current catalyst can inhibit side reaction to make the selectivity of ethyl benzene in the product reach more than 99% whether it is a gas phase process or a liquid phase process, but 5-7% of diethylbenzene in the product is still present. In the industrial process, polyethylbenzene (mainly diethylbenzene, small amount of triethylbenzene) is generally subjected to transalkylation reaction with benzene by using a transalkylation reactor to continuously produce ethylbenzene as a target product.
The patents CN1096025A, CN1199727a and USP5030786 report a process for producing ethylbenzene by transalkylation of benzene and polyethylbenzene using a Y-type molecular sieve, respectively, under a liquid phase process.
Patent CN10956025A, USP4891456 et al reports that the conversion rate of diethylbenzene reaches 57% in the process of preparing ethylbenzene from benzene and diethylbenzene by using Beta molecular sieve under the conditions of 260 ℃ and 3.5 MPa.
Patent CN1207960a reports a Beta molecular sieve modified by rare earth or alkaline earth metals. The polyethylbenzene conversion rate is about 45% under the conditions of 230-280 ℃, 2.3-4.3 MPa, n (benzene)/n (ethylbenzene) =8-12 and WHSV Mixed liquid=6~10h-1.
Patent CN1597110a reports that benzene and diethylbenzene are transalkylation process by MCM-22 molecular sieve, and the modified molecular sieve can achieve diethylbenzene conversion rate and ethylbenzene selectivity up to 70% and 99% respectively.
The process for preparing polyethylbenzene by benzene and polyethylbenzene transalkylation is a liquid phase process, and the adopted catalyst is mostly the same as the catalyst for preparing ethylbenzene by benzene liquid phase alkylation, and is mostly Y-type, beta-type and MWW (MCM-22, MCM-49 and the like). The liquid phase process has the advantages of low operating temperature, small content of diethylbenzene byproduct, but higher pressure ratio.
A significant commercial process has been achieved at present by vapor phase transalkylation of benzene and polyethylbenzene using a solid acid catalyst. U.S. Pat. Nos. 3751504, 3965364 and 4016218 report the use of unmodified ZSM-5, phosphorus modified ZSM-5, and steam treated ZSM-5 to catalyze the vapor phase transalkylation of benzene and polyethylbenzene, respectively.
Patent CN1310051a reports a ZSM-5 catalyst after treatment with water vapor and organic acid to catalyze the reaction of benzene and polyethylbenzene. At a reaction temperature t=435 ℃, 0.6MPa, a weight space velocity of benzene and polyethylbenzene of 28h-1, n (benzene)/n (polyethylbenzene) =5.0, a polyethylbenzene conversion of 60%, an ethylbenzene selectivity of 96% or more and a xylene content of 750ppm in the product was achieved.
Zhao Xuesong et al [ Zhao Xuesong, liu Chenglin, chen Fucun et al, ZSM-5/ZSM-11 co-crystallized molecular sieve, journal of Nature sciences of the university of Heilongjiang, 2006, 23 (3): 6] studied the transalkylation performance of 3884A catalyst on a fixed bed, and realized polyethylbenzene conversion of 28.43% and ethylbenzene selectivity of 95.15% under conditions of a reaction temperature of 420 ℃, a pressure of 0.7MPa, a polyethylbenzene weight space velocity of 1h-1, n (benzene/polyethylbenzene) =5.0.
Disclosure of Invention
The invention provides a preparation method and application of a catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzene, which are used for the transalkylation of benzene and polyethylbenzene, and have high polyethylbenzene conversion rate and good stability.
A method for preparing a catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzene, which comprises the following steps:
(1) Mixing ZSM-11 molecular sieve raw powder with a binder, tabletting and forming, carrying out ammonium exchange treatment on the obtained molecular sieve mixed with the binder by using an ammonium solution, and roasting to obtain an H-ZSM-11 molecular sieve;
(2) Carrying out steam treatment for 1-8h at the treatment temperature of 400-800 ℃;
(3) Adding the molecular sieve obtained in the step (2) into a metal element-containing impregnating solution, stirring and impregnating for 4-12h at 80-95 ℃, and then standing for 3-5h to remove upper-layer liquid, wherein the metal is alkali metal, alkaline earth metal, rare earth metal or Zn;
(4) Drying and roasting to obtain the catalyst.
Preferably, the alkali metal is Cs, the alkaline earth metal is Mg, and the rare earth metal is La or Ce.
Preferably, in the step (3), the ratio of the impregnating solution to the molecular sieve mixed with the binder in the impregnation in the step (3) is (10-20) mL/1 g.
Preferably, the impregnating solution is an aqueous solution of soluble carbonate, nitrate, chloride and acetate corresponding to alkali metal or alkaline earth metal, and the concentration of the impregnating solution is 0.5-2mol/L.
Preferably, in the step (1), the total weight of the molecular sieve mixed with the binder is calculated as 100%, the content of ZSM-11 molecular sieve raw powder is 50-90%, and the balance is the binder. More preferably, the ZSM-11 molecular sieve raw powder is 50-70%.
Preferably, the ammonium exchange is specifically carried out by mixing molecular sieve mixed with binder with ammonium solution, stirring and refluxing at 80-90 ℃ for 5-6h, centrifuging, filtering, drying, repeating the above operation for 2 times, wherein the mass ratio of the molecular sieve mixed with binder to the ammonium solution is 1 (20-25), and the ammonium solution is 1-3mol/L NH4 Cl solution or NH4NO3 solution.
Preferably, the binder is a mixture of SiO2 and Al2O3.
Preferably, the silicon-aluminum ratio of the ZSM-11 molecular sieve raw powder is 30-100. More preferably, the ZSM-11 molecular sieve raw powder has a silica-alumina ratio of 30 to 50.
Preferably, the steam treatment is specifically carried out by placing molecular sieve in a fixed bed reactor, heating to the treatment temperature under inert gas atmosphere, closing inert gas, and introducing liquid water according to the flow rate of 0.05-1 mL/min.
Preferably, the drying conditions are drying at 105-120 ℃ for 5-8 hours and the firing at 550-650 ℃ for 5-6 hours.
The catalyst prepared by the preparation method is used for preparing ethylbenzene by benzene and polyethylbenzene gas phase transalkylation, and the preparation method comprises the following steps of crushing the catalyst, sieving the crushed catalyst by 20-40 meshes, loading the crushed catalyst into a fixed bed catalyst, activating the catalyst for 4-5 hours at 450-500 ℃, taking nitrogen as carrier gas, and reacting the benzene and polyethylbenzene as raw materials at 400-450 ℃ and 1-2MPa, wherein the molar ratio of benzene to polyethylbenzene is 6-8:1, and the weight airspeed of polyethylbenzene mixed solution is 1-2h-1, and the polyethylbenzene is diethylbenzene or a mixture of diethylbenzene and triethylbenzene.
The invention has the advantages that:
(1) According to the preparation method, after the ZSM-11 molecular sieve raw powder is treated by water vapor and treated by metal together, the distribution of B acid and L acid on the catalyst and the acid strength can be effectively regulated, and the acid strength of the catalyst can be obviously changed after the treatment, especially the acid strength of strong acid is reduced.
(2) Compared with the conventional ZSM-11 molecular sieve, the catalyst prepared by the invention has the advantages that the acidity of the catalyst is reduced, the catalytic activity and stability are improved, and the ethylbenzene selectivity is high.
Drawings
FIG. 1 is an XRD pattern of the catalyst obtained in example 1;
FIG. 2 is a graph comparing NH3 -TPD for various catalysts.
Detailed Description
Example 1
A method for preparing a catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzene, which comprises the following steps:
(1) Mixing ZSM-11 molecular sieve raw powder with a silicon-aluminum ratio of 50 and a binder according to a mass ratio of 80:20, tabletting and forming to obtain a molecular sieve mixed with the binder, mixing 20g of the molecular sieve with 1mol/L NH4 Cl solution according to a mass ratio of 1:25, stirring and refluxing for 6 hours at 90 ℃, centrifuging, filtering, drying for 6 hours at 105 ℃, repeating the operations of mixing with NH4 Cl solution, stirring, centrifuging, filtering and drying for 2 times, and roasting for 6 hours at 550 ℃ to obtain an H-ZSM-11 molecular sieve, wherein the binder is a mixture of SiO2 and Al2O3 with equal mass ratio;
(2) Placing the molecular sieve obtained in the step (1) in a fixed bed reactor, heating to 500 ℃ under nitrogen atmosphere, closing inert gas, introducing liquid water according to the flow of 1mL/min, and performing steam treatment for 5 hours at 500 ℃;
(3) Adding 200mL of the molecular sieve obtained in the step (2) into 1mol/L of Mg (CH3COO)2 aqueous solution, stirring and soaking for 10 hours at the temperature of 85 ℃ and the rotating speed of 300rpm, and then standing for 3 hours to remove the upper liquid;
(4) Drying at 105 ℃ for 8 hours and roasting at 550 ℃ for 6 hours to obtain the catalyst, which is marked as Cat-1.
Example 2
A method for preparing a catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzene, which comprises the following steps:
(1) Mixing ZSM-11 molecular sieve raw powder with a silicon-aluminum ratio of 50 and a binder according to a mass ratio of 80:20, tabletting and forming to obtain a molecular sieve mixed with the binder, mixing 20g of the molecular sieve with 1mol/L NH4 Cl solution according to a mass ratio of 1:20, stirring and refluxing for 6 hours at 90 ℃, centrifuging, filtering, drying for 6 hours at 105 ℃, repeating the operations of mixing with NH4 Cl solution, stirring, centrifuging, filtering and drying for 2 times, and roasting for 6 hours at 550 ℃ to obtain an H-ZSM-11 molecular sieve, wherein the binder is a mixture of SiO2 and Al2O3 with equal mass ratio;
(2) Placing the molecular sieve obtained in the step (1) in a fixed bed reactor, heating to 550 ℃ under nitrogen atmosphere, closing inert gas, introducing liquid water according to the flow of 1mL/min, and performing steam treatment for 5h at 550 ℃;
(3) Adding 400mL of Zn (NO3)2·6H2 O solution with the concentration of 1mol/L into the molecular sieve obtained in the step (2), stirring and soaking for 10 hours at the temperature of 85 ℃ and the rotating speed of 400rpm, and then standing for 5 hours to remove the upper liquid;
(4) Drying at 120deg.C for 5h, and calcining at 650deg.C for 5h to obtain catalyst, labeled Cat-2.
Example 3
A method for preparing a catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzene, which comprises the following steps:
(1) Mixing ZSM-11 molecular sieve raw powder with a silicon-aluminum ratio of 50 and a binder according to a mass ratio of 80:20, tabletting and forming to obtain a molecular sieve mixed with the binder, mixing 20g of the molecular sieve with 1mol/L NH4 Cl solution according to a mass ratio of 1:25, stirring and refluxing for 6 hours at 90 ℃, centrifuging, filtering, drying for 6 hours at 105 ℃, repeating the operations of mixing with NH4 Cl solution, stirring, centrifuging, filtering and drying for 2 times, and roasting for 6 hours at 550 ℃ to obtain an H-ZSM-11 molecular sieve, wherein the binder is a mixture of SiO2 and Al2O3 with equal mass ratio;
(2) Placing the molecular sieve obtained in the step (1) in a fixed bed reactor, heating to 550 ℃ under nitrogen atmosphere, closing inert gas, introducing liquid water according to the flow of 1mL/min, and performing steam treatment for 5h at 550 ℃;
(3) Adding 200mL of the molecular sieve obtained in the step (2) into 2mol/L of Mg (CH3COO)2 solution, stirring and soaking for 10 hours at the temperature of 85 ℃ and the rotating speed of 250rpm, and then standing for 3 hours to remove the upper liquid;
(4) Drying at 120deg.C for 5h, and calcining at 650deg.C for 5h to obtain catalyst, labeled Cat-3.
Example 4
A method for preparing a catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzene, which comprises the following steps:
(1) Mixing ZSM-11 molecular sieve raw powder with a silicon-aluminum ratio of 30 and a binder according to a mass ratio of 50:50, tabletting and forming to obtain a molecular sieve mixed with the binder, mixing 20g of the molecular sieve with 3mol/L NH4NO3 solution according to a mass ratio of 1:25, stirring and refluxing for 5 hours at 80 ℃, centrifuging, filtering, drying for 5 hours at 120 ℃, repeating the operations of mixing, stirring, centrifuging, filtering and drying with the NH4NO3 solution for 2 times, and roasting for 5 hours at 650 ℃ to obtain an H-ZSM-11 molecular sieve, wherein the binder is a mixture of SiO2 and Al2O3 with equal mass ratio;
(2) Placing the molecular sieve obtained in the step (1) in a fixed bed reactor, heating to 400 ℃ under nitrogen atmosphere, closing inert gas, introducing liquid water according to the flow of 1mL/min, and performing steam treatment for 8 hours at 400 ℃;
(3) Adding 200mL of La (NO3)3·6H2 O) solution with the concentration of 0.5mol/L into the molecular sieve obtained in the step (2), stirring and soaking for 12h at the temperature of 80 ℃ and the rotating speed of 1000rpm, and then standing for 3h to remove upper liquid;
(4) Drying at 120deg.C for 5h, and calcining at 650deg.C for 5h to obtain catalyst, labeled Cat-4.
Example 5
A method for preparing a catalyst for preparing ethylbenzene by gas phase transalkylation of benzene and polyethylbenzene, which comprises the following steps:
(1) Mixing ZSM-11 molecular sieve raw powder with a silicon-aluminum ratio of 100 with a binder according to a mass ratio of 90:10, tabletting and forming to obtain a molecular sieve mixed with the binder, mixing 20g with 3mol/L NH4NO3 solution according to a mass ratio of 1:25, stirring and refluxing for 5 hours at 80 ℃, centrifuging, filtering, drying for 8 hours at 105 ℃, repeating the operations of mixing with NH4NO3 solution, stirring, centrifuging, filtering and drying for 2 times, and roasting for 5 hours at 650 ℃ to obtain an H-ZSM-11 molecular sieve, wherein the binder is a mixture of SiO2 and Al2O3 with equal mass ratio;
(2) Placing the molecular sieve obtained in the step (1) in a fixed bed reactor, heating to 800 ℃ under nitrogen atmosphere, closing inert gas, introducing liquid water according to the flow of 0.05mL/min, and performing steam treatment for 1h at 800 ℃;
(3) Adding the molecular sieve obtained in the step (2) into 200mL of 0.5mol/L CsCl solution, stirring and soaking for 4 hours at the temperature of 95 ℃ and the rotating speed of 200rpm, and then standing for 3 hours to remove the upper liquid;
(4) Drying at 105 ℃ for 8 hours and roasting at 650 ℃ for 5 hours to obtain the catalyst, which is marked as Cat-5.
Comparative example 1
The molecular sieve obtained in step (1) of example 1.
Comparative example 2
The ZSM-11 molecular sieve raw powder is replaced by the ZSM-5 molecular sieve raw powder with the same silica-alumina ratio, and the other steps are the same as those in example 1.
Acid quantity distribution
The acid amount distribution of the molecular sieve catalyst obtained in example 1 and comparative example 1 was examined, and the results are shown in Table 1. The B acid and L acid amounts of the molecular sieve are obtained by the pyridine desorption amounts measured after 200 ℃ and 350 ℃ desorption, wherein the total acid amount at 200 ℃ corresponds to the total acid amount of the catalyst, and the total acid amount at 350 ℃ corresponds to the acid amounts of the strong acid and the medium strong acid of the catalyst.
TABLE 1 acid quantity distribution
As is clear from Table 1, the distribution of B acid and L acid and the acid strength on the catalyst can be effectively adjusted by treating the oxide MgO with water vapor. Although the total acid amount on the modified catalyst does not change much, the acid B on the modified catalyst is significantly increased.
XRD detection
XRD measurements were performed on the catalyst obtained in example 1, and the results are shown in FIG. 1.
As shown in FIG. 1, the diffraction peak of ZSM-11 is a single peak at the angle of 45.20 degrees 2 theta, and 2 characteristic peaks at the angles of 22.5 degrees to 25.5 degrees are respectively attributed to the characteristic diffraction peaks of (501) crystal faces and (303) crystal faces of the ZSM-11 molecular sieve, which indicates that the synthesized molecular sieve is a typical MEL configuration molecular sieve. In addition, after the water vapor treatment and MgO loading, the position and the intensity of the characteristic diffraction peak of the ZSM-11 are not changed, which indicates that the molecular sieve modified by MgO still maintains the framework structure of the ZSM-11.
Three NH3 -TPD detection
The NH3 -TPD test was performed on the catalysts of examples 1-3 and comparative example 1, and the results are shown in FIG. 2.
As can be seen from FIG. 2, the weak acid peak intensity of the catalyst provided by the invention is smaller and the strong acid peak is obviously weakened compared with untreated ZSM-11.
Fourth, catalyst Performance detection
The catalyst prepared by the preparation method is used for preparing ethylbenzene by benzene and polyethylbenzene gas phase transalkylation, and the preparation method comprises the following steps of crushing the catalyst, sieving the catalyst by 20-40 meshes, loading the catalyst into a fixed bed catalyst, activating the catalyst for 5 hours at 500 ℃, taking nitrogen as carrier gas, and reacting the benzene and polyethylbenzene as raw materials at 420 ℃ and 1MPa, wherein the molar ratio of the benzene to the polyethylbenzene is 6:1, and the weight airspeed of polyethylbenzene mixed solution is 1h-1, wherein the polyethylbenzene is diethylbenzene or a mixture of diethylbenzene and triethylbenzene;
the specific reaction conditions and results are shown in Table 2.
TABLE 2 reaction conditions and results
As can be seen from Table 2, the direct use of unmodified ZMS-11 as a catalyst for the vapor phase transalkylation of benzene and polyethylbenzene in comparative example 1 has three disadvantages, namely low polyethylbenzene conversion and high content of xylenes in the by-products, which results in a relatively low selectivity to ethylbenzene as the main product. The invention provides a modified ZSM-11 catalyst, which can realize higher raw material conversion and high selectivity and purity of ethylbenzene product. In comparative example 2, although ZSM-5 molecular sieve is also a two-dimensional pore system, the oval pore structure of the ZSM-5 molecular sieve is longer than the two-dimensional straight pore of ZSM-11 molecular sieve, and the generated C7-C10 aromatic hydrocarbon is not easy to desorb and is easy to cause more side reactions, so that the selectivity of the aromatic hydrocarbon is lower than that of ZSM-11, and the aim of the invention cannot be met when ZSM-5 is adopted for substitution.