Method for preparing ethylene from ethanol

Abstract

The invention discloses a method for preparing ethylene from ethanol. The method comprises the following steps: by taking ethanol as a raw material and benzene as a diluent, in a fixed bed reactor, contacting a mixture of the raw materials ethanol and benzene with a modified ZSM-5 molecular sieve catalyst to generate ethylene and co-produce a small amount of ethylbenzene and diethylbenzene. According to the method, the isothermal fixed bed reactors and the adiabatic fixed bed reactors are connected in series in a multi-stage manner to perform the reaction of preparing ethylene from ethanol, and the method has the remarkable advantages of high catalyst use efficiency, low energy consumption and good product selectivity.

Description

Technical Field

[0001] The present application relates to a method for producing ethylene from ethanol, and belongs to the field of chemistry and chemical engineering. Background Art

[0002] As the most important basic chemical raw material, ethylene can be used in synthetic fibers, synthetic rubber, and synthetic plastics. In recent years, with the continuous advancement and maturity of technologies such as coal-to-ethanol and biomass-to-ethanol, the price and production cost of ethanol have shown a clear downward trend, which makes the application prospects of ethanol promising. Among them, ethanol dehydration to ethylene has become an important direction for the high-value utilization of ethanol.

[0003] A large number of patents disclose the process technology of ethanol dehydration to ethylene, such as:

[0004] Patent CN101219920A discloses a highly efficient ethanol dehydration process using a molecular sieve catalyst, which uses ethanol as a raw material and a modified molecular sieve as a catalyst to prepare ethylene through a dehydration reaction. The specific steps are: connect two or more tubular fixed bed reactors in series, load the catalyst into the reactor, and heat the reactor at a temperature of 150 to 400°C for 0.4 to 4.5 hours. -1 The liquid hourly space velocity is converted into ethylene through the ethanol in the reactor. The present application can effectively improve the ethylene yield and the conversion rate of the raw material, save energy, and has flexible reaction conditions. The catalyst has high efficiency, high reaction activity, long life, high strength, low reaction temperature, and great industrial application value. Patent CN102372566A discloses a method for dehydrating ethanol to produce ethylene, which mainly solves the problem of small single-unit production capacity of the reactor in the previous production method of dehydrating ethanol to produce ethylene. The present application adopts a molten salt external circulation method, and an annular molten salt channel is arranged at both ends of the reactor shell. The upper and lower molten salt channels are opened at the corresponding parts in contact with the shell wall. The upper and lower molten salt channels are respectively provided with a molten salt inlet and a molten salt outlet, and a baffle is arranged inside the reactor shell. The technical solution of the channel for the molten salt to flow through is well solved, and can be used in the industrial production of ethanol dehydration to produce ethylene. Patent CN116217323B discloses a method for dehydrating ethanol to produce ethylene. In an adiabatic fixed bed reactor, ethanol is used as raw material, benzene is used as diluent, the reaction temperature is 200-500°C, the reaction pressure is 0.0-0.6MPa, and the ethylene weight space velocity is 0.1-5.0h 1 Under the condition of benzene alcohol molar ratio of 0.5:1 to 6:1, the mixture of raw ethanol and benzene contacts with the modified ZSM5 molecular sieve catalyst to mainly produce ethylene products and co-produce a small amount of ethylbenzene and diethylbenzene. This method can be used for large-scale production in an adiabatic fixed bed reactor, and has the significant advantages of simple reactor, easy scale-up, low energy consumption in the reaction process, and good product selectivity.

[0005] The above-mentioned public patents mainly adopt tubular fixed bed reactors in series, molten salt external circulation heating fixed bed reactors, and adiabatic fixed bed reaction process methods using benzene as diluent, which effectively solve the problems of low catalyst utilization efficiency, difficulty in reactor amplification, and high energy consumption in the production process in the previous technology. However, in the actual production process of ethanol to ethylene, it is still faced with problems such as low production efficiency and high energy consumption. The reason is that the existing process cannot combine low energy consumption and high catalyst utilization efficiency. When only an isothermal fixed bed reactor reaction process is used, the energy consumption is usually high, and when only an adiabatic fixed bed reactor reaction process is used, the catalyst utilization efficiency is usually not high. Therefore, it is urgent to develop relevant new processes or technologies to solve the above-mentioned problems. Summary of the invention

[0006] The technical problem to be solved by this application is the high energy consumption and low production efficiency of the existing fixed bed process technology for ethanol dehydration to ethylene, and a new process method for ethanol dehydration to prepare ethylene is provided. The process method has the significant advantages of low production energy consumption, high catalyst utilization efficiency, and good product selectivity, and a small amount of high value-added products ethylbenzene and diethylbenzene are co-produced while obtaining ethylene.

[0007] According to one aspect of the present application, there is provided a method for preparing ethylene from ethanol, comprising the following steps:

[0008] In a reactor, ethanol and benzene are contacted with a catalyst to react to obtain ethylene and co-produce ethylbenzene and diethylbenzene;

[0009] The reactor is composed of n fixed bed reactors connected in series;

[0010] Among them, 2≤n≤10;

[0011] The fixed bed reactor is selected from an isothermal fixed bed reactor or an adiabatic fixed bed reactor;

[0012] The reactors include at least one isothermal fixed bed reactor;

[0013] The ethanol and benzene are fed from the feed port of the first fixed bed reactor, and then the ethanol and benzene can continue to be fed from the feed ports of other fixed bed reactors.

[0014] That is, the first fixed bed reactor must be fed, and the subsequent fixed bed reactors may or may not be fed. If the subsequent fixed bed reactors are also fed, the overall segmented feeding can be equal or unequal.

[0015] The reaction temperature is 200-500°C

[0016] Optionally, the reaction temperature is 320-450°C.

[0017] Optionally, the upper limit of the reaction temperature is selected from 500°C, 460°C, 450°C, 400°C, 350°C, 300°C, 250°C; the lower limit is selected from 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 460°C.

[0018] The reaction pressure is 0-1 MPa;

[0019] Optionally, the reaction pressure is 0-0.5 MPa.

[0020] Optionally, the upper limit of the reaction pressure is selected from 1.0 MPa, 0.9 MPa, 0.8 MPa, 0.7 MPa, 0.6 MPa, 0.5 MPa, 0.4 MPa, 0.3 MPa, 0.2 MPa, 0.1 MPa; the lower limit is selected from 0 MPa, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa.

[0021] The molar ratio of benzene to ethanol is 0.1 to 6:1;

[0022] Optionally, the molar ratio of benzene to ethanol is 0.5 to 3:1.

[0023] Optionally, the upper limit of the molar ratio of benzene to ethanol is selected from 3:1 or 3:2; the lower limit is selected from 0.5:1 or 1:1.

[0024] The mass space velocity of the ethanol is 0.1 to 6.0 h -1 ;

[0025] Optionally, the mass space velocity of ethanol is 0.5 to 3.0 h -1 .

[0026] Optionally, the upper limit of the mass air velocity of ethanol is selected from 6.0h -1 , 5.0h -1 , 4.0h -1 , 3.0h -1 , 2.0h -1 , 1.0h -1 , 0.5h -1 ; The lower limit is selected from 0.1h -1 , 0.5h -1 , 1.0h -1 , 2.0h -1 , 3.0h -1 , 4.0h -1 , 5.0h -1 .

[0027] The catalyst is a modified ZSM-5 molecular sieve, which is obtained by the following steps:

[0028] (1) treating HZSM-5 molecular sieve with phosphoric acid to obtain phosphorus-modified ZSM-5 molecular sieve;

[0029] (2) steam treating the phosphorus-modified ZSM-5 molecular sieve to obtain a treated ZSM-5 molecular sieve;

[0030] (3) reacting a mixed solution containing the treated ZSM-5 molecular sieve and ammonium fluoride to obtain a modified ZSM-5 molecular sieve.

[0031] The catalyst is uniformly loaded or unequally loaded in the reactor.

[0032] The beneficial effects of this application include:

[0033] In the technical scheme described in the present application, ethanol is a reaction raw material, and benzene is a diluent. In addition to the endothermic ethanol dehydration reaction, an exothermic reaction of ethylene and benzene alkylation to generate ethylbenzene will also occur. By endothermic coupling reaction, the heat exchange efficiency between endothermic and exothermic reactions is improved, so that energy consumption can be significantly reduced. In the technical scheme described in the present application, by connecting two or more fixed-bed reactors (including adiabatic reactors and at least one section of isothermal reactors) in series, it is avoided that only the catalyst efficiency of the adiabatic fixed-bed reactor is low and the problem of high heat load required for the isothermal fixed-bed reactor is avoided. Under low energy consumption conditions, the selectivity of the product is ensured and the use efficiency of the catalyst is significantly improved. The ethanol conversion rate of the method is>99.0%, the ethylene selectivity in the gas phase product is>99.0%, and the selectivity of ethylbenzene or / and diethylbenzene in the oil phase product is>99.0%. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0035] In the technical solution described in this application, ethanol is used as the raw material, benzene is used as the diluent, and the modified ZSM-5 molecular sieve catalyst used in the process of dehydrating ethanol to produce ethylene and co-producing a small amount of ethylbenzene and diethylbenzene is prepared by referring to the method in patent 202010796906.4. (1) Preparation of HZSM-5 molecular sieve: Aluminum sulfate, water glass, n-butylamine (C 4 H 11 N), sodium hydroxide and deionized water are mixed and stirred to obtain a gel. SiO 2 :Al 2 O 3:C 4 H 11 N:Na 2 O:H 2 The molar ratio of SiO2 was 1:0.02:0.5:0.1:30; the gel was transferred to a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and nano ZSM-5 seeds (the amount of SiO2 was 1:0.02:0.5:0.1:30) were added. 2 10% of mass), heated to 120℃ for crystallization for 24h, and then heated to 140℃ for crystallization for 120h. The product was filtered and washed, dried at 110℃ for 12h, and calcined at 550℃ for 3h; then exchanged with 1mol / L ammonium nitrate aqueous solution at 60℃ for three times, filtered and washed again, dried at 110℃ for 12h, and calcined at 550℃ for 3h to obtain HZSM-5 molecular sieve with a grain size of about 60nm and a silicon-aluminum ratio of 50. (2) Preparation of HZSM-5 molecular sieve modified with phosphorus and treated with high-temperature steam: 100g of the prepared HZSM-5 molecular sieve was taken and impregnated with 2.5mol / l phosphoric acid aqueous solution at 30℃ for 12h, the weight ratio of phosphoric acid aqueous solution to catalyst was 50:1, then filtered, dried at 110℃ for 12h, and calcined at 500℃ for 6h to obtain phosphorus-modified ZSM-5 molecular sieve. The phosphorus-modified HZSM-5 molecular sieve is pressed into a tablet and placed in a reactor. Water is introduced at 700°C under normal pressure for 2 hours, wherein the mass ratio of water to phosphorus-modified HZSM-5 molecular sieve is 30. Then, nitrogen gas is purged at a flow rate of 20 ml / min for 2 hours to obtain phosphorus-modified and high-temperature steam-treated HZSM-5 molecular sieve. (3) Preparation of phosphorus-modified, high-temperature steam-treated and ammonium fluoride-modified ZSM-5 molecular sieve: 10 g of the phosphorus-modified and high-temperature steam-treated ZSM-5 molecular sieve is taken and immersed in a 0.03 mol / L ammonium fluoride aqueous solution at 100°C for 2 hours. The weight ratio of the ammonium fluoride aqueous solution to the catalyst is 10:1. Then, the mixture is filtered and washed until the pH value is ≈ 7. Then, the mixture is dried at 110°C for 12 hours and calcined at 550°C for 6 hours to obtain phosphorus-modified, high-temperature steam-treated and ammonium fluoride-modified ZSM-5 molecular sieve, referred to as modified ZSM-5 molecular sieve catalyst.

[0036] In the technical solution described in the present application, ethanol is used as the raw material, benzene is used as the diluent, and the dehydration of ethanol to produce ethylene and co-production of a small amount of ethylbenzene and diethylbenzene is carried out in a small isothermal fixed bed reaction device and (or) a small adiabatic fixed bed reaction device.

[0037] The specific evaluation steps on the small isothermal fixed-bed reaction device (section 1) are as follows: 40g of modified ZSM-5 molecular sieve catalyst is pressed into tablets, mixed with quartz sand and installed in a stainless steel reaction tube with an inner diameter of Ф14. The outside of the reaction tube is heated with circulating lava. Under certain experimental conditions, the catalytic performance of the modified ZSM-5 molecular sieve in catalyzing the dehydration of ethanol to produce ethylene and co-producing a small amount of ethylbenzene and diethylbenzene is evaluated.

[0038] The specific evaluation steps on the small-scale adiabatic fixed bed reaction device (stage 1) are as follows: 40g of modified ZSM-5 molecular sieve catalyst is pressed into tablets and placed in a stainless steel reaction tube with an inner diameter of 14, and the reaction tube is insulated with rock wool. The reaction raw materials are preheated to the experimental temperature and passed into the reaction tube. Under the set experimental conditions, the catalytic performance of the modified ZSM-5 molecular sieve in catalyzing the dehydration of ethanol to produce ethylene and co-producing a small amount of ethylbenzene and diethylbenzene is evaluated.

[0039] The specific evaluation steps on the small isothermal fixed bed and small adiabatic fixed bed series evaluation reaction device (multi-stage) are as follows: 40g of modified ZSM-5 molecular sieve catalyst is pressed into tablets and equally loaded into a stainless steel reaction tube with an inner diameter of 14 in a small isothermal fixed bed or a small adiabatic fixed bed. The reaction raw materials are preheated to the experimental temperature and passed into the reaction tube. Under the set experimental conditions, the catalytic performance of the modified ZSM-5 molecular sieve in catalyzing the dehydration of ethanol to produce ethylene and co-producing a small amount of ethylbenzene and diethylbenzene is evaluated.

[0040] Ethanol conversion rate = (mass of ethanol converted / mass of ethanol in feed) x 100%

[0041] Ethylene selectivity in gas phase product = (mass of ethylene in gas phase product / total mass of gas phase product) x 100%

[0042] Ethyl selectivity in oil phase product = (sum of the moles of ethyl in ethylbenzene and diethylbenzene in oil phase product / moles of ethylene alkylated) x 100%

[0043] Ethylene alkylation rate = (alkylated ethylene moles / total ethylene moles generated) x 100% Comparative Example 1

[0044] 40g of the modified ZSM-5 molecular sieve catalyst was evaluated for reaction in a small-scale adiabatic fixed bed reactor (stage 1), and the specific steps were as follows: the catalyst was pressed into tablets and placed in a stainless steel reaction tube with an inner diameter of 14, the reaction tube was insulated with rock wool, the reactor inlet temperature was 410°C, the reaction pressure was 0.1Mpa, the benzene-alcohol molar ratio was 3.0, and the raw material ethanol and the diluent benzene entered from the reactor inlet. The optimized ethanol conversion rate was >99% (actually 99.02%), and the catalytic reaction was continuously operated for 12h. At this time, the ethylene selectivity in the gas phase was 99.38%, and the ethanol mass space velocity was 0.56h -1 , ethylene alkylation rate is 15.23%.

[0045] Comparative Example 2

[0046] According to the steps, operating conditions and catalyst of Comparative Example 1, pure ethanol was fed and the reaction temperature was 420°C. The optimized ethanol conversion rate was > 99% (actually 99.39%), and the catalytic reaction was continuously operated for 12 hours. At this time, the ethylene selectivity in the gas phase was 99.28%, and the ethanol mass space velocity was 0.67h -1 , ethylene alkylation rate is 16.19%.

[0047] Comparative Example 3

[0048] 40g of the modified ZSM-5 molecular sieve catalyst was evaluated for reaction in a small-scale adiabatic fixed bed reactor (4 sections). The specific steps are as follows: the catalyst was pressed into tablets and equally packed in a stainless steel reaction tube with an inner diameter of 14. The reaction tube was insulated with rock wool. The inlet temperature of the first reactor was 430°C, the reaction pressure was 0.1Mpa, the benzene-alcohol molar ratio was 3.0, the diluent benzene entered from the inlet of the first reactor, and the raw material ethanol entered from the inlet of the first, second and third reactors in equal parts. The optimized ethanol conversion rate was >99% (actually 99.02%), and the catalytic reaction was continuously operated for 12h. At this time, the ethylene selectivity in the gas phase was 99.38%, and the mass space velocity of ethanol was 0.81h -1 , ethylene alkylation rate is 17.58%.

[0049] Example 1

[0050] The steps, operating conditions and catalysts of Comparative Example 3 were followed, except that the first stage reactor was an isothermal fixed bed reactor. The optimized ethanol conversion rate was > 99% (actually 99.57%), and the catalytic reaction was continuously operated for 12 hours. At this time, the ethylene selectivity in the gas phase was 99.51%, and the ethanol mass space velocity was 0.91h -1 , ethylene alkylation rate is 18.11, and ethyl selectivity in the oil phase product is >99.0%.

[0051] Example 2

[0052] The steps, operating conditions and catalysts of Example 1 were followed, except that the inlet temperature of the first stage reactor was 410°C. The optimized ethanol conversion rate was > 99% (actually 99.16%), and the catalytic reaction was continuously operated for 12 hours. At this time, the ethylene selectivity in the gas phase was 99.36%, and the ethanol mass space velocity was 0.62 h -1 , ethylene alkylation rate is 16.11%, and ethyl selectivity in the oil phase product is >99.0%.

[0053] Example 3

[0054] The steps, operating conditions and catalysts of Example 1 were followed, except that the inlet temperature of the first stage reactor was 420°C. The optimized ethanol conversion rate was > 99% (actually 99.45%), and the catalytic reaction was continuously operated for 12 hours. At this time, the ethylene selectivity in the gas phase was 99.60%, and the mass space velocity of ethanol was 0.76 h -1 , ethylene alkylation rate is 17.08%, and ethyl selectivity in the oil phase product is >99.0%.

[0055] Example 4

[0056] According to the steps, operating conditions and catalysts of Comparative Example 3, the difference is that the first and third reactors are isothermal fixed bed reactors. The optimized ethanol conversion rate is > 99% (actually 99.19%), and the catalytic reaction is continuously operated for 12 hours. At this time, the ethylene selectivity in the gas phase is 99.31%, and the ethanol mass space velocity is 1.31h -1 , ethylene alkylation rate is 19.11%, and ethyl selectivity in the oil phase product is >99.0%.

[0057] Example 5

[0058] The steps, operating conditions and catalysts of Example 4 were followed, except that the inlet temperature of the first stage reactor was 410°C. The optimized ethanol conversion rate was > 99% (actually 99.39%), and the catalytic reaction was continuously operated for 12 hours. At this time, the ethylene selectivity in the gas phase was 99.25%, and the mass space velocity of ethanol was 0.85 h -1 , ethylene alkylation rate is 17.08%, and ethyl selectivity in the oil phase product is >99.0%.

[0059] Example 6

[0060] The steps, operating conditions and catalysts of Example 4 were followed, except that the inlet temperature of the first stage reactor was 420°C. The optimized ethanol conversion rate was > 99% (actually 99.68%), and the catalytic reaction was continuously operated for 12 hours. At this time, the ethylene selectivity in the gas phase was 99.32%, and the mass space velocity of ethanol was 1.15 h -1 , ethylene alkylation rate is 18.47%, and ethyl selectivity in the oil phase product is >99.0%.

[0061] Example 7

[0062] The steps, operating conditions and catalysts of Example 4 were followed, except that the total molar ratio of benzene to alcohol was 2. The optimized ethanol conversion rate was > 99% (actually 99.12%), and the catalytic reaction was continuously operated for 12 hours. At this time, the ethylene selectivity in the gas phase was 99.47%, and the mass space velocity of ethanol was 1.55 h -1 , ethylene alkylation rate is 19.28%, and ethyl selectivity in the oil phase product is >99.0%.

[0063] Example 8

[0064] The steps, operating conditions and catalysts of Example 4 were followed, except that the reaction pressure was 0.3 MPa. The optimized ethanol conversion rate was > 99% (actually 99.61%), and the catalytic reaction was continuously operated for 12 h. At this time, the ethylene selectivity in the gas phase was 99.39%, and the ethanol mass space velocity was 1.42 h -1 , ethylene alkylation rate is 20.15%, and ethyl selectivity in the oil phase product is >99.0%.

[0065] It can be seen from the experimental data of the comparative examples and the examples that under the experimental conditions of the same temperature and pressure, when the optimized ethanol conversion rate is greater than 99%, the mass space velocity of ethanol in the device using an isothermal fixed bed reactor and an adiabatic fixed bed reactor in series in the present application is greater than the mass space velocity of ethanol in the device using only an adiabatic fixed bed reaction device in the comparative example. It can be seen from Examples 4 to 8 that under the experimental conditions of ethanol as a raw material and benzene as a diluent described in the present application, ethanol dehydration and ethanol alkylation reactions occurred. When the ethanol conversion rate is greater than 99%, the ethanol mass space velocity is between 0.85 and 1.55 h -1 The ethylene selectivity is >99.0%, and the ethyl selectivity in the oil phase product is >99.0%, indicating that the process of the present application is under low energy consumption working conditions (ethanol dehydration and ethanol alkylation coupling reactions can effectively reduce energy consumption), the catalyst utilization efficiency is high (ethanol mass space velocity is large), the product selectivity is good, and the industrial application prospect is good.

[0066] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing ethylene from ethanol, characterized in that: The following steps are involved: In a reactor, ethanol and benzene are contacted with a catalyst to react to obtain ethylene and co-produce ethylbenzene and diethylbenzene; The reactor is composed of n fixed bed reactors connected in series; Among them, 2≤n≤10; The fixed bed reactor is selected from an isothermal fixed bed reactor or an adiabatic fixed bed reactor; The reactors include at least one isothermal fixed bed reactor; The ethanol and benzene are fed from the feed port of the first fixed bed reactor, and then the ethanol and benzene can continue to be fed from the feed ports of other fixed bed reactors.

2. The method according to claim 1, characterized in that: The reaction temperature is 200-500°C Preferably, the reaction temperature is 320-450°C.

3. The method according to claim 1, characterized in that The reaction pressure is 0-1 MPa; Preferably, the reaction pressure is 0-0.5 MPa.

4. The method according to claim 1, characterized in that: The molar ratio of benzene to ethanol is 0.1 to 6:1; Preferably, the molar ratio of benzene to ethanol is 0.5 to 3:

1.

5. The method according to claim 1, characterized in that The mass space velocity of the ethanol is 0.1 to 6.0 h -1 ; Preferably, the mass space velocity of ethanol is 0.5 to 3.0 h -1 .

6. The method according to claim 1, characterized in that The catalyst is a modified ZSM-5 molecular sieve, which is obtained by the following steps: (1) treating HZSM-5 molecular sieve with phosphoric acid to obtain phosphorus-modified ZSM-5 molecular sieve; (2) steam treating the phosphorus-modified ZSM-5 molecular sieve to obtain a treated ZSM-5 molecular sieve; (3) reacting a mixed solution containing the treated ZSM-5 molecular sieve and ammonium fluoride to obtain a modified ZSM-5 molecular sieve.

7. The method according to claim 1, characterized in that The catalyst is uniformly loaded or unequally loaded in the reactor.