FIELD

The present invention relates to a catalyst for producing ethylbenzene from ethanol and benzene, preparation method and use thereof.

BACKGROUND

Ethylbenzene is an important and basic organic raw material in industry, mainly used for catalytic dehydrogenation to produce styrene which is further used in the field of polymer materials to produce rubber and plastics. The ethylbenzene can also be used as a solvent or diluent and be used to produce diethylbenzene. With the rapid development of social economy, the market demand and production capacity of ethylbenzene are showing an obvious upward trend. Statistics show that, from 1998 to 2015, the global demand for ethylbenzene increased by 3.7% annually, and our country's annual growth rate reached 5.3%, from 800 kt in 1998 to 2 Mt in 2015.

At present, the industrial production of ethylbenzene is mainly through the alkylation reaction of benzene and ethylene. The main processes include AlCl3liquid-phase alkylation and molecular sieve alkylation. The AlCl3liquid-phase alkylation has advantages of simple process, mild operating conditions, and high ethylene conversion rate, but it has problems such as equipment corrosion, environmental pollution, and high maintenance costs. The molecular sieve alkylation mainly includes the ZSM-5 molecular sieve vapor-phase alkylation (see U.S. Pat. Nos. 3,751,504, 3,751,506, 4,016,218 and 4,547,605) developed by Mobil and Badger companies to produce ethylbenzene, and the Beta molecular sieve and Y-type molecular sieve liquid-phase alkylation (see, U.S. Pat. Nos. 4,891,458, 5,227,558 and ZL02151177) developed by UOP and Lummus companies. These methods have the advantages of no corrosion, no pollution, simple process, high heat recovery and utilization rate and the like. With the depletion of petroleum resources and the soaring price of petroleum, the cost of ethylene alkylation has increased significantly, and thus it has become a trend to seek new raw materials for replacing ethylene to produce ethylbenzene. With the continuous progress and maturity of coal-based ethanol and bio-ethanol technologies in recent years, the price and production costs of ethanol have shown a downward trend, making its application prospects more promising. The use of environmentally friendly renewable ethanol as the alkylation reagent can significantly reduce the production cost of ethylbenzene, and improve the economic efficiency and comprehensive competitiveness of the enterprise, thereby making the process more attractive and have a higher society value.

The process for producing ethylbenzene from ethanol refers to the simultaneous occurrence of ethanol dehydration reaction and the alkylation reaction of ethylene and benzene in a reactor containing ethanol and benzene. The catalyst used therefore not only needs to meet high conversion rate of ethanol and dehydration selectivity, but also has certain requirements for the catalytic efficiency of the alkylation between ethylene and benzene. China Petroleum & Chemical Corporation obtained a series of catalysts based on ZSM-5 by adding binder and modifying the ZSM-5 with rare earth oxides or alkaline earth metal oxides. The treated catalyst was used in the ethylbenzene production reaction. It was found that under the conditions with a temperature of 390° C., a pressure of 1.2 MPa, ethanol weight hourly space velocity of 0.8 h−1and a molar ratio between benzene and ethanol of 6.5, the selectivity of ethylbenzene can be as high as 99%. The period for needing regeneration of the treated catalyst is half a year (see, CN103121909A, CN102872899A, CN102276413A, CN 102875315 and CN102274746A). Zheng Xinyuan et al. used β molecular sieve as a catalyst and obtained the ethanol conversion rate with greater than 99% and the ethylbenzene yield with greater than 80% under the condition that a temperature was in a range from 240 to 260° C., n(benzene):n(ethylene) was in a range from 4 to 6 and a space velocity of benzene was in a range from 3 to 5 h−1(see, Chemical Reaction Engineering and Technology, 2006, 22, 172-175). Similarly, Versalis, Italy, used a zeolite with BEA structure as a catalyst to catalyze the alkylation reaction of bioethanol and benzene (see, WO2011077240). WO2010143043 proposed the use of MTW family zeolite as a catalyst to catalyze the alkylation reaction of benzene and ethanol obtained by fermenting biomass-derived sugar as an alkylating agent to produce ethylbenzene, which greatly improved the economy of the reaction. In addition to the above-mentioned molecular sieve catalysts, Ehsan Rahmani et al. recently used MOF materials, such as Fe-based MIL-110 and Al—Li doped MIL-53, to catalyze the reaction of benzene and ethanol to produce ethylbenzene, under relatively mild reaction conditions (i.e., a temperature in a range from 175 to 200° C.). As a result, a selectivity of ethylbenzene was greater than 75% (see, Microporous and Mesoporous Materials, 2017, 249, 118-127; Ind. Eng. Chem. Res. 2018, 57, 169-178). This research provides a new solution for the selection of reaction catalysts and the control of reaction conditions, but there is still a long way to go before industrialization. Thus, molecular sieve catalysts are still key at present.

In view of the various molecular sieves in the market, the researchers compared their catalytic performance for the reaction of benzene and ethanol. Sun Linping et al. investigated the catalytic performance of ZSM-5, Beta and Y zeolite in the vapor-phase alkylation reaction of coked benzene and ethanol. The results showed that the cage structure in the channels of Beta and Y zeolite easily generates macromolecules, which leads to rapid deactivation of the catalyst, while ZSM-5 molecular sieve showed good resistance to deactivation, see, Acta Petrolei Sinica (Petroleum Processing), 2006, 22, 146-148. Odedairo et al. compared the catalytic reaction performance of MOR and ZSM-5 molecular sieves, and concluded that the selectivity of ethylbenzene over ZSM-5 is higher (see, Catalysis Today, 2013, 204, 73-84). Gao Junhua et al., State Key Laboratory of Coal Conversion, Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, compared the catalytic performance of molecular sieves with different structures in the vapor-phase alkylation of benzene and ethanol to produce ethylbenzene and reached a similar conclusion. The catalytic performance of ZSM-5 molecular sieve was more ideal, the activity thereof was higher and the stability was good. However, if the channel diameter of the ZSM-5 catalyst is too small, the mass transfer of the reaction is easily affected, causing the occurrence of side reactions which in turn results in coking and deactivation of the catalyst. Further, the ZSM-5 catalyst has poor hydrothermal stability, and thus the structure thereof is easy to collapse and the catalyst is easy to deactivate during the reaction. Document Applied Catalysis A: General, 2010, 385, 31-45 compared catalytic performance in alkylation by ethanol of two molecular sieves, i.e., SSZ-33 and TNU-9 molecular sieves, which have similar channel structure to ZSM-5. The alkylation by ethanol was performed under the condition that a ratio of benzene to ethanol was 1:1, and the temperature was in a range from 250 to 300° C. The conversion rate of ethanol over TNU-9 molecular sieve was higher than that over ZSM-5, but the selectivity of ethylbenzene over TNU-9 molecular sieve was low. However, the document lacks detailed descriptions on the synthesis and physicochemical properties of TNU-9 molecular sieve and the conditions for the vapor-phase alkylation of benzene and ethanol are relatively narrow.

SUMMARY

The present invention relates to a catalyst with high activity and high stability for the vapor-phase alkylation of ethanol and benzene to produce ethylbenzene and a preparation method thereof. Specifically, the catalyst used in the present invention is TNU-9 molecular sieve with a composite structure comprising mesopores and micropores. The present invention is mainly aimed to achieve the hydrothermal stability, high alkylation activity and high selectivity of ethylbenzene of the catalyst by synthesizing the mesoporous-microporous composite TNU-9 molecular sieve with high silicon content. The detailed preparation method of the catalyst is as follow: mesoporous silica, MCM-48 or SBA-15 as silicon source, and 1,4-MPB as template are used to synthesize TNU-9 molecular sieve by hydrothermal synthesis. The obtained catalyst is used in the alkylation reaction of ethanol and benzene, wherein the reaction temperature ranges from 300 to 500° C., the reaction pressure ranges from 0.1 to 2 MPa, the weight hourly space velocity of the feed ranges from 3 to 8 h−1, the ratio of benzene to ethanol ranges from 3 to 7, and the main products are ethylbenzene and water. The catalyst of the present invention can be used stably for a long time in the vapor-phase alkylation of ethanol and benzene to directly produce ethylbenzene, and can maintain good catalytic performance of the alkylation reaction of benzene and ethanol. The three-dimensional TNU-9 molecular sieve obtained by hydrothermal synthesis in the present invention, which comprises a 10-ring structure with intersected porous channels and a mesoporous-microporous composite structure, is used in vapor-phase alkylation reaction of ethanol and benzene to produce ethylbenzene in one-step. The catalyst not only has high alkylation activity and high selectivity of ethylbenzene, but also has certain hydrothermal stability and stable catalytic performance. The present invention provides a new catalyst for the reaction of ethanol and benzene to produce ethylbenzene, which has a good application prospect.

According to one aspect of the present application, there is provided a catalyst for vapor-phase alkylation of ethanol and benzene to produce ethylbenzene in one-step. This catalyst performs a high alkylation activity, achieves high selectivity of ethylbenzene in the product of the alkylation, and also has high hydrothermal stability and stable catalytic performance.

The molecular sieve catalyst comprises mesoporous-microporous composite TNU-9 molecular sieve, wherein, the silicon to aluminum molar ratio, i.e., SiO2/Al2O3, of the TNU-9 molecular sieve ranges from 50 to 200.

Optionally, the upper limit of the silicon to aluminum molar ratio, SiO2/Al2O3of the mesoporous-microporous composite TNU-9 molecular sieve is 200, 190, 180, 170, 160, 150, 140, 130, 120, 110 or 100; and the lower limit thereof is 100, 95, 90, 85, 80, 75, 72, 70, 68, 65, 64, 63, 60, 58, 56, 55, 52 or 50.

Optionally, the silicon to aluminum molar ratio, SiO2/Al2O3, of the mesoporous-microporous composite TNU-9 molecular sieve ranges from 50 to 100.

Optionally, the silicon to aluminum molar ratio, SiO2/Al2O3, of the mesoporous-microporous composite TNU-9 molecular sieve ranges from 60 to 100.

Optionally, the silicon to aluminum molar ratio, SiO2/Al2O3, of the mesoporous-microporous composite TNU-9 molecular sieve ranges from 60 to 80.

Optionally, the mesoporous-microporous composite TNU-9 molecular sieve comprises a structure of micropore channel and mesopore channel, and the diameter of the mesopore channel ranges from 3 to 50 nm.

Optionally, the mesoporous-microporous composite TNU-9 molecular sieve is in a form of crystal grain accumulation, and the diameter of a single crystal grain ranges from 100 to 1000 nm.

Optionally, the mesoporous-microporous composite TNU-9 molecular sieve comprises micropores with a pore diameter ranging from 0.3 to 0.8 nm.

Optionally, the mesoporous-microporous composite TNU-9 molecular sieve comprises micropores with a pore diameter ranging from 0.4 to 0.7 nm.

Optionally, the mesoporous-microporous composite TNU-9 molecular sieve comprises mesopores with a pore diameter ranging from 6 to 13 nm.

Optionally, the upper limit of the pore diameter of the mesopores included in the mesoporous-microporous composite TNU-9 molecular sieve is 13 nm, 12 nm, 11 nm or 10 nm and the lower limit thereof is 9 nm, 8 nm, 7 nm or 6 nm.

Specifically, the catalyst is mesoporous-microporous composite TNU-9 molecular sieve with high silicon content, wherein the diameter of mesopore channel of the molecular sieve ranges from 3 to 50 nm, and the silicon to aluminum molar ratio, SiO2/Al2O3, of the molecular sieve ranges from 50 to 200. The catalyst is in a form of small crystal grain accumulation, with a single crystal grain diameter in a range from 100 to 1000 nm.

Optionally, the molecular sieve is used to catalyze the reaction of ethanol and benzene to produce ethylbenzene.

According to another aspect of the present application, there is provided a preparation method of a catalyst for vapor-phase alkylation by ethanol to produce ethylbenzene in one-step, which is simple and reliable and is convenient for industrial production.

The preparation method of the catalyst comprises the following steps:

(1) adding an aluminum source, an alkali source, and a silicon source comprising mesopore structure to an aqueous solution containing a template and then stirring to obtain a gel-like precursor;

(2) crystallizing hydrothermally the gel-like precursor obtained in step (1);

(3) washing the product obtained in step (2) to be neutral and drying the product; and

(4) calcining the product obtained in step (3) to obtain the molecular sieve catalyst.

Optionally, a molar ratio of the aluminum source, alkali source, silicon source comprising mesopore structure, and template in step (1) satisfies: SiO2:Al2O3:M2O:R:H2O=(5˜100):1:(1˜30):(5˜20):(1000˜4000);wherein, R represents the template and is calculated by the molar number of the template itself, the molar number of the aluminum source is calculated by the molar number of Al2O3, the molar number of the alkali source is calculated by the molar number of its corresponding alkali metal oxide M2O, the molar number of silicon source is calculated by the molar number of SiO2, and the molar number of water is calculated by the molar number of H2O itself.

Optionally, the template in step (1) comprises at least one of 1,4-MPB, glucose and activated carbon.

Optionally, the method for preparing 1,4-MPB comprises: subjecting a solution comprising 1,4-dibromobutane and N-methyltetrahydropyrrole to refluxing, recrystallizing and drying to obtain 1,4-MPB.

Optionally, the solution comprising 1,4-dibromobutane and N-methyltetrahydropyrrole is obtained by placing 1,4-dibromobutane and N-methyltetrahydropyrrole in acetone;the refluxing is performed at a temperature ranging from 30 to 80° C. in water bath;a step of extraction by acetone occurs before the recrystallization;a solvent for recrystallization includes a mixed solvent of methanol and diethyl ether; wherein the volume ratio of methanol and diethyl ether is (0.05˜50):(1˜20);the drying is performed at a temperature ranging from 60 to 120° C. for a time ranging from 5 to 20 h.

Optionally, the refluxing is performed in water bath for a time ranging from 6 to 48 h.

Optionally, the silicon source comprising mesopore structure in step (1) is at least one of silica comprising mesopore structure, MCM-48, and SBA-15.

Optionally, the aluminum source in step (1) is at least one of sodium metaaluminate, aluminum powder, aluminum nitrate and aluminum hydroxide, and the alkali source is at least one of sodium hydroxide and potassium hydroxide.

Optionally, the stirring in step (1) is performed for a time ranging from 5 to 24 hours.

Optionally, the hydrothermal crystallization in step (2) refers to hydrothermal dynamic crystallization; and the hydrothermal dynamic crystallization is performed at a temperature ranging from 120 to 260° C. for a time ranging from 100 to 360 hours.

Optionally, the upper limit of the temperature for crystallization is 260° C., 240° C., 220° C., 200° C., 180° C., 160° C., or 140° C., and the lower limit thereof is 140° C., 130° C., or 120° C.

Optionally, the upper limit of the time for crystallization is 360 h, 340 h, 300 h or 280 h, and the lower limit thereof is 280 h, 260 h, 240 h, 200 h, 180 h, 160 h, 140 h, 120 h or 100 h.

Optionally, the dynamic crystallization in step (2) is rotational crystallization, and the rotation speed ranges from 5 to 30 rpm.

Optionally, the upper limit of the rotation speed is 30 rpm, 25 rpm, 20 rpm, or 15 rpm, and the lower limit thereof is 15 rpm, 10 rpm or 5 rpm.

Optionally, the temperature for calcining in step (4) ranges from 200 to 600° C., and the time for calcining ranges from 1 to 20 h.

Optionally, the upper limit of the temperature for calcining is 600° C., 580° C., 550° C., 520° C., 500° C. or 450° C., and the lower limit thereof is 450° C., 400° C., 300° C. or 200° C.

Optionally, the upper limit of the time for calcining is 20 h, 18 h, 15h, 12 h, or 10 h, and the lower limit thereof is 10 h, 8 h, 5 h, 3 h, or 1 h.

Optionally, step (3) comprises filtering and washing the product obtained in step (2) until the washing liquid is neutral, and then drying the product at a temperature ranging from 60 to 110° C.

As an embodiment, the method comprises the following steps:1. Synthesis of 1,4-MPB templatedissolving 1,4-dibromobutane and N-methyltetrahydropyrrole in acetone, heating them to a temperature ranging from 30 to 80° C., refluxing for a time ranging from 6 to 48 h; extracting the obtained reaction solution by acetone, and recrystallizing the obtained product by a mixed solvent of methanol and diethyl ether; drying the recrystallized product in a vacuum drying oven at a temperature ranging from 60 to 120° C. for a time ranging from 5 to 20 h to obtain the template R;2. Preparation of TNU-9 molecular sievedissolving the template R obtained in step 1) in water, and then adding sequentially an aluminum source, an alkali source and a silicon source comprising mesopore structure to obtain a solution I, wherein a molar ratio of raw materials in the solution I was SiO2:Al2O3:M2O:R:H2O=(5˜100):1:(1˜30):(5˜20):(1000˜4000); after stirring for a time ranging from 5 to 24 hours, the solution I will form a gel; putting the gel into a reactor, and performing crystallization for a time ranging from 100 to 360 h under the dynamic and hydrothermal conditions driven by a motor at a temperature ranging from 120 to 260° C.; filtering and washing the obtained product until the washing liquid is neutral, and drying the filter cake at a temperature ranging from 60 to 110° C.; calcining the dried filter cake in a muffle furnace at a temperature ranging from 200 to 600° C. for a time ranging from 1 to 20 h to obtain the molecular sieve catalyst.

As an embodiment, the method comprises the following steps:1. Synthesis of 1,4-MPB templateputting 1,4-dibromobutane and N-methyltetrahydropyrrole in acetone and subjecting them to refluxing in a water bath with a temperature ranging from 30 to 80° C.; extracting excess amine by acetone, and placing the resulting mixture in a mixed solvent of methanol and diethyl ether to perform recrystallization; transferring the recrystallized product to a vacuum drying oven at a temperature ranging from 60 to 120° C. for a time ranging from 5 to 20 h to obtain the template;2. Preparation of TNU-9 molecular sievedissolving the template obtained in step 1 in water, and then adding sequentially an aluminum source, an alkali source and a silicon source comprising mesopore structure therein, wherein all raw materials are respectively calculated according to molar number of SiO2, Al2O3, M2O, R, H2O, and the molar ratio thereof is SiO2:Al2O3:M2O:R:H2O=(5˜100):1:(1-30):(5-20):(1000˜4000), wherein R represents the template in step 1 and M represents the alkali metal; stirring the obtained solution vigorously for a time ranging from 5 to 24 h to form a gel, which is then placed into a stainless steel reactor; performing crystallization under the dynamic and hydrothermal conditions driven by a motor for a time ranging from 100 to 360 h and at a temperature ranging from 120 to 260° C.; filtering and washing the obtained product until the washing liquid is neutral, and transferring the filter cake to an oven at a temperature ranging from 60 to 110° C. for drying; placing the dried filter cake in a muffle furnace and calcining the dried filter cake at a temperature ranging from 200 to 600° C. for a time ranging from 1 to 20 h to obtain the TNU-9 molecular sieve with a composite structure comprising mesopores and micropores.

In step 1, the refluxing is performed for a time ranging from 6 to 48 hours.

In step 2, the aluminum source is at least one of sodium metaaluminate, aluminum powder, aluminum nitrate, and aluminum hydroxide; and the alkali source is at least one of sodium hydroxide and potassium hydroxide; the silicon source used in step 2 is at least one of silica comprising mesopore structure, MCM-48 and SBA-15; the crystallization in step 2 refers to the rotational crystallization driven by a motor, and the rotation speed thereof ranges from 5 to 30 rpm;

The catalyst is used for the reaction of producing ethylbenzene from ethanol. The reaction conditions are as follow: the catalyst is loaded in a reaction tube of a fixed bed reactor for evaluating the catalytic performance of the catalyst, the raw materials are benzene and ethanol, the molar ratio of benzene to ethanol ranges from 3:1 to 7:1, the weight hourly space velocity of the raw materials ranges from 3 to 8 h−1, the reaction temperature ranges from 300 to 500° C., and the reaction pressure ranges from 0.1 to 2 MPa.

According to another aspect of the present disclosure, there is provided the use of the above molecular sieve catalyst, and/or the molecular sieve catalyst obtained by the preparation method described above in the production of ethylbenzene by vapor phase alkylation reaction of ethanol and benzene.

According to another aspect of the present application, there is provided a method for producing ethylbenzene by vapor-phase alkylation of ethanol and benzene, wherein the method comprises the following steps:feeding the raw materials comprising benzene and ethanol to a fixed bed reactor loaded with catalyst to react to obtain ethylbenzene;wherein, the catalyst comprises at least one of the above molecular sieve catalyst and the molecular sieve catalyst prepared by the above method.

Optionally, the reaction temperature ranges from 300 to 500° C., the reaction pressure ranges from 0.1 to 2 MPa, the molar ratio of benzene to ethanol in the raw material ranges from 3:1 to 7:1, and the weight hourly space velocity of the raw materials ranges from 3 to 8 h−1.

The catalyst comprises at least one of the above molecular sieve catalyst and the molecular sieve catalyst prepared by the above preparation method.

Optionally, under the reaction conditions that the molar ration of benzene to ethanol ranges from 4:1 to 7:1, the reaction temperature ranges from 350 to 470° C., and the weight hourly space velocity of the raw materials ranges from 4 to 8 h−1, the selectivity of ethylbenzene is greater than 93%.

In this application, “MCM-48 molecular sieve” belongs to the M41S series of mesoporous molecular sieves, which comprise a uniform pore diameter of about 2.6 nm and two sets of mutually independent three-dimensionally spiral porous channel network structures.

“SBA-15 molecular sieve” is mesoporous molecular sieve belonging to the P3 mm space group, which comprises mesopores with a two-dimensional hexagonal through-hole structure.

1,4-MPB refers to the abbreviation for 1,4-bis(N-methylpyrrole)butane.

The present application achieves the following beneficial effects:

1) The preparation method of the catalyst provided by this application is reliable, simple and has stable repeatability;

2) The catalyst provided in this application can effectively convert ethanol into ethylbenzene in one step, simplifying the process, saving equipment investment, and reducing production costs;

3) The catalyst provided by this application is applied to the process of producing ethylbenzene by the vapor-phase alkylation reaction of ethanol and benzene. Compared with the prior art, the catalyst herein has improved hydrothermal stability and achieves higher selectivity of ethylbenzene in the product. The catalytic evaluation results show that, under the reaction conditions that the molar ratio of benzene to ethanol ranges from 4:1 to 7:1, the reaction temperature ranges from 350 to 470° C. and the weight hourly space velocity of raw materials ranges from 4 to 8 h−1, the selectivity of ethylbenzene is greater than 93%;

4) The catalyst provided by this application has high hydrothermal stability and catalytic reaction stability. After the molecular sieve is calcined at 650° C., the relative crystallinity decreases by about 15%; under the condition that the molecular sieve is subject to saturated water steam treatment at 800° C., the relative crystallinity decreases only about 30%. The catalyst has good application prospects and high application value.

