Ethylene synthesis method

Abstract

The invention discloses an ethylene synthesis method, and belongs to the technical field of organic chemical industry and catalysis. According to the technical scheme, ethanol is in contact with an alkali metal type mordenite catalyst which is not subjected to ion exchange treatment for a gas-phase dehydration reaction, ethylene is generated in a high-selectivity mode, no ion exchange post-treatment step is carried out in the preparation process of the catalyst, the technological process of the prior art is shortened, and the production cost is reduced. And a wastewater treatment step can be omitted.

Description

Technical Field

[0001] This application relates to a method for synthesizing ethylene, belonging to the field of organic chemical engineering and catalysis technology. Background Technology

[0002] Ethylene is one of the most important basic raw materials in the petrochemical industry, widely used in the production of a range of bulk chemicals such as polyethylene, ethylene oxide, ethylene glycol, and polyvinyl chloride. Traditional ethylene production is highly dependent on petroleum routes such as naphtha steam cracking. With the transformation of the energy structure, developing technologies for producing ethylene from renewable biomass ethanol (i.e., "bioethylene" technology) is of great strategic significance. It not only reduces dependence on fossil resources but also aligns with the trend of green and low-carbon development.

[0003] The development of efficient catalysts is crucial for the production of ethylene from bioethanol via dehydration. Heterogeneous catalysts used for ethylene production from ethanol dehydration mainly include activated alumina, molecular sieves, and heteropoly acids. Patent CN101244971A reports a method for preparing a nano-molecular sieve catalyst for ethylene production from bioethanol dehydration, which achieves low reaction temperature, high ethanol conversion rate, and high ethylene selectivity; however, the catalyst has poor stability and requires stringent preparation conditions, limiting further industrial application. Patents CN105709822A and CN106944139A disclose a method for ethylene production from ethanol via heteropoly acid ammonium salt catalysis. Currently, low-temperature, high-efficiency ethylene production from ethanol dehydration technology has not yet been truly industrialized, and the catalyst preparation process is complex. Applications CN102625788A, CN107108394A, CN107108395A, and CN107108396A disclose a series of catalysts using mixed oxides, primarily silica, as supports to support heteropoly acid compounds for ethylene production from ethanol dehydration. These heteropolyacid catalysts have attracted widespread attention due to their advantages such as achieving ultra-high ethylene selectivity (ethylene selectivity greater than 99%) at relatively mild temperatures, but they also have problems such as weak support of active components and poor water stability. Summary of the Invention

[0004] To address at least one of the following problems in existing technologies for the dehydration of bioethanol to ethylene: complex catalyst preparation, high wastewater treatment costs, and low ethylene selectivity, this application provides an ethylene synthesis technology that utilizes an alkali metal mordenite catalyst that has not undergone ion exchange treatment. The key aspect is its application to a high-temperature range for the gas-phase dehydration of ethanol. At this high temperature, the reaction pathway undergoes a fundamental shift, reversing the traditional intermolecular dehydration that tends to produce diethyl ether to a highly selective intramolecular dehydration that produces ethylene. This simplifies the process while significantly improving the ethylene yield. The technical solution adopted in this application is as follows: A method for synthesizing ethylene includes: contacting ethanol with a solid catalyst to carry out a dehydration reaction to obtain ethylene; The solid catalyst is an alkali metal zeolite molecular sieve that has not undergone ion exchange treatment.

[0005] Optionally, the alkali metal zeolite molecular sieve is a sodium-type zeolite molecular sieve and / or a potassium-type zeolite molecular sieve.

[0006] Optionally, the framework topology of the alkali metal zeolite molecular sieve is at least one of MOR, MFI, FAU, BEA or FER.

[0007] Optionally, the alkali metal zeolite molecular sieve is prepared by hydrothermal synthesis.

[0008] Optionally, the alkali metal zeolite molecules are screened from at least one of K-ZSM-5, K-ZSM-35, Na-ZSM-35, Na-Y, Na-Beta, and Na-MOR.

[0009] Optionally, the solid catalyst is in particulate form.

[0010] Optionally, the solid catalyst may be activated by heating it to 500-600°C under a nitrogen atmosphere before the dehydration reaction.

[0011] Optionally, the conditions for the dehydration reaction include: The reaction is carried out under gas-phase conditions at a temperature of 250–350 °C and a pressure of 0.1–5.0 MPa.

[0012] Optionally, the contact conditions include: an ethanol mass hourly space velocity of 0.5–2.5 h⁻¹. -1 .

[0013] Optionally, the reaction apparatus used in the process of dehydrating ethanol by contacting it with a solid catalyst to obtain ethylene is selected from a fixed-bed reactor, a fluidized-bed reactor, or a moving-bed reactor.

[0014] The catalyst of this application eliminates the need for complex ion exchange processes, simplifying the preparation process, reducing production costs, and preventing the generation of ammonia-nitrogen-containing wastewater at the source. Furthermore, the Na-type molecular sieve of this application, with its unique crystal structure and acidic characteristics, effectively solves the technical challenges of easy loss of active components and poor water resistance.

[0015] The beneficial effects of this application include: The method for synthesizing ethylene from bioethanol dehydration provided in this application utilizes a specific alkali metal mordenite catalyst in a high-temperature range for gas-phase ethanol dehydration. This high-temperature reaction pathway fundamentally transforms the process, overcoming existing technical biases. It reverses the traditional understanding of intermolecular dehydration, which tends to produce diethyl ether, to intramolecular dehydration, which highly selectively produces ethylene. This simplifies the process while significantly increasing ethylene yield. In terms of preparation, this method eliminates the need for ion exchange post-treatment and completely avoids the generation of ammonia-nitrogen-containing wastewater. Regarding operational performance, under the aforementioned catalyst, this method achieves >99% ethanol conversion and >99% ethylene selectivity at 300-350℃. Furthermore, the catalyst exhibits no performance degradation after continuous operation for over 500 hours, demonstrating superior resistance to carbon buildup and extended service life compared to traditional hydrogen-type zeolites. Therefore, it achieves the dual advantages of simplified process flow and long-term stable operation. Detailed Implementation

[0016] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0017] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased commercially. The molecular sieve raw materials used in this application can be purchased commercially or synthesized according to existing technology. The molecular proportions of the molecular sieve raw materials are shown in Table 1. Table 1

[0018] The preparation steps of Na-MOR (Si / Al = 35) are as follows: NaOH, sodium silicate, aluminum isopropoxide, and water are used as raw materials, and the mixture is prepared in a molar ratio of SiO2:Al2O3:Na2O:H2O = 1:0.0143:0.2:40. The mixture is stirred evenly and aged at 25℃ for 12 h to prepare a silica-alumina sol. Subsequently, seed crystals equivalent to 2% of the mass of SiO2 are added to the sol, and the mixture is stirred for a period of time. Then, the mixture is heated to 170℃ and held at that temperature for 72 h. After the reaction is completed, the resulting sample is washed with deionized water until neutral, and then dried at 120℃ for 12 h to finally obtain Na-MOR molecular sieve.

[0019] The preparation steps of the hydrogen-form molecular sieve sample in the examples are as follows: Sodium-form molecular sieves are subjected to NH4NO3 ion exchange, followed by drying and calcination to obtain hydrogen-form molecular sieves. A typical preparation process for the hydrogen-form molecular sieve Na-ZSM-5 is as follows: Na-ZSM-5 molecular sieve powder is added to a pre-prepared 1 mol·L⁻¹ solution. -1In an aqueous solution of NH4NO3, with a solid-liquid mass ratio of 1:10, the exchange reaction was carried out at 80℃ for 2 h under stirring. The mixture was then vacuum filtered and washed with water. After three consecutive exchange reactions, the mixture was dried overnight at 120℃ and calcined at 550℃ for 4 h to obtain the desired catalyst sample Na-ZSM-5 (Si / Al = 23). The parameters for preparing hydrogen-form molecular sieves for the remaining samples were the same as above, except for the molecular sieve raw materials, yielding H-MOR (Si / Al = 35), HY (Si / Al = 12), and H-Beta (Si / Al = 30), respectively.

[0020] The preparation steps of the metal-modified zeolite molecular sieve in the examples are as follows: the hydrogen-form molecular sieve is impregnated, dried and calcined to obtain the metal-modified zeolite molecular sieve. The typical preparation process of the Na-ZSM-5 sample is as follows: the pre-prepared Zn(NO3)2 solution is added dropwise to the H-ZSM-5 (Si / Al=23) molecular sieve powder, the Zn / H-ZSM-5 (mass ratio) is 0.05, the mixture is stirred at room temperature for 15 min, ultrasonically treated for 15 min, allowed to stand at room temperature for 12 h, then dried in an oven at 80℃ for 24 h, and finally calcined at 550℃ in air atmosphere for 4 h to obtain the desired catalyst sample H-Zn-ZSM-5. The parameters for preparing metal-modified zeolite molecular sieves for the remaining samples are the same as those above, except for the different metal selections (Fe, Cu, Zn, Ni) and the different hydrogen-type molecular sieve raw materials (H-ZSM-5 (Si / Al = 35, HY (Si / Al = 12)), resulting in H-Zn-ZSM-35 (Si / Al = 65), H-Cu-Y (Si / Al = 30), H-Fe-ZSM-5 (Si / Al = 35), H-Cu-ZSM-5 (Si / Al = 35), and H-Ni-ZSM-5 (Si / Al = 35).

[0021] Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.

[0022] The reacted gas is introduced into an online chromatograph via a heated pipeline for online analysis. The chromatograph is an Agilent 7890A, equipped with an FFAP capillary column and a TDX-1 packed column. The FFAP capillary column outlet is connected to an FID detector, and the TDX-1 packed column outlet is connected to a TCD detector.

[0023] In the embodiments of this application, the conversion rate and selectivity are calculated as follows: =

[0024]

[0025] X CHCH2OH : Ethanol conversion rate; n CH3CH2OH, in : Molar flow rate of ethanol at the reactor inlet (mol·min) -1 or mol·h -1 ); n CH3CH2OH, out : Molar flow rate of ethanol at the reactor outlet; S CH3CH2OH : Selectivity of ethanol; n CH3CH2OH : The number of moles of ethanol in the product; n CH3CH2OH, CH2=CH2 The number of moles of ethanol consumed in the production of ethylene; Example 1: Application of alkali metal zeolite molecular sieves in the synthesis of ethylene. The process of synthesizing ethylene: 1.5 g of different solid catalysts were compressed into tablets and sieved into 20-40 mesh particles. These particles were then placed into a stainless steel reaction tube with an inner diameter of 10 mm and reacted under a nitrogen atmosphere at 5 °C / min. -1 The temperature was raised to 550℃ and maintained for 4 h. The reaction was carried out under the following conditions: reaction temperature (T) = 320℃, reaction pressure (P) = 2.0 MPa, N2, and WHSV of ethanol = 1.0 h. -1 The catalytic dehydration reaction of bioethanol to ethylene was run for 20 h.

[0026] Based on the aforementioned ethylene synthesis process, the effects of different alkali metal zeolite molecular sieves (1# to 6#) as solid catalysts in the preparation of ethylene were tested. The results of the catalytic reactions are shown in Table 2.

[0027] Example 2: Using hydrogen-form molecular sieves for ethylene synthesis The ethylene synthesis process was the same as in Example 1, except that the alkali metal zeolite molecular sieve was replaced with a hydrogen molecular sieve. The effects of different alkali metal zeolite molecular sieves (7# to 10#) as solid catalysts in the preparation of ethylene were tested, and the results of the catalytic reaction are shown in Table 2.

[0028] Example 3: Using metal-modified zeolite molecular sieves for ethylene synthesis The ethylene synthesis process was the same as in Example 1, except that the alkali metal zeolite molecular sieve was replaced with a metal-modified zeolite molecular sieve. The effects of different alkali metal zeolite molecular sieves (11# to 16#) as solid catalysts in the preparation of ethylene were tested, and the results of the catalytic reaction are shown in Table 2.

[0029] Table 2

[0030] Other (%) in the table refers to the selectivity of by-products.

[0031] It is evident that the catalyst selection in this application enables the high-selectivity production of ethylene at high temperatures without any modification or exchange.

[0032] Test Example 1 The process of synthesizing ethylene is the same as in Example 1, except that the running time is different. The evaluation results of the catalytic dehydration of ethanol to ethylene of sample 6 at different running times are shown in Table 3.

[0033] Table 3

[0034] Test Example 2 The process of synthesizing ethylene is the same as in Example 1, except that the reaction temperature is different. The evaluation results of the catalytic dehydration of ethanol to ethylene of sample 6 at different reaction temperatures are shown in Table 4.

[0035] Table 4

[0036] Test Example 3 The process of synthesizing ethylene is the same as in Example 1, except that the reaction pressure is different. The evaluation results of the catalytic dehydration of ethanol to ethylene of sample 6# under different reaction pressures are shown in Table 5.

[0037] Table 5

[0038] Test Example 4 The process of synthesizing ethylene is the same as in Example 1, except that the mass hourly space velocity is different. The evaluation results of the catalytic dehydration of ethanol to ethylene of sample 6# at different mass hourly spaces are shown in Table 6.

[0039] Table 6

[0040] Test Example 5 The process for synthesizing ethylene is the same as in Example 1, except that the reactor type is different. The evaluation results of the catalytic dehydration of ethanol to ethylene for sample #6 in different reactor types are shown in Table 7.

[0041] Table 7

[0042] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for synthesizing ethylene, characterized in that, include: Ethylene is obtained by dehydrating ethanol by contacting it with a solid catalyst. The solid catalyst is an alkali metal zeolite molecular sieve that has not undergone ion exchange treatment.

2. The method for synthesizing ethylene according to claim 1, characterized in that, The alkali metal zeolite molecular sieve is a sodium-type zeolite molecular sieve and / or a potassium-type zeolite molecular sieve.

3. The method for synthesizing ethylene according to claim 1, characterized in that, The framework topology of the alkali metal zeolite molecular sieve is at least one of MOR, MFI, FAU, BEA or FER.

4. The method for synthesizing ethylene according to claim 1, characterized in that, The alkali metal zeolite molecular sieve was prepared by hydrothermal synthesis.

5. The method for synthesizing ethylene according to claim 1, characterized in that, The alkali metal zeolite molecules are selected from at least one of K-ZSM-5, K-ZSM-35, Na-ZSM-35, Na-Y, Na-Beta, and Na-MOR.

6. The method for synthesizing ethylene according to claim 1, characterized in that, The solid catalyst is in particulate form.

7. The method for synthesizing ethylene according to claim 1, characterized in that, The dehydration reaction is preceded by activating the solid catalyst by heating it to 500-600°C under a nitrogen atmosphere and holding it thereafter.

8. The method for synthesizing ethylene according to claim 1, characterized in that, The conditions for the dehydration reaction include: The reaction is carried out under gas-phase conditions at a temperature of 250–350 °C and a pressure of 0.1–5.0 MPa.

9. The method for synthesizing ethylene according to claim 1, characterized in that, The contact conditions include an ethanol mass hourly space velocity of 0.5–2.5 h⁻¹. -1 .

10. The method for synthesizing ethylene according to claim 1, characterized in that, The reaction apparatus used to obtain ethylene by dehydrating ethanol by contacting it with a solid catalyst is selected from a fixed-bed reactor, a fluidized-bed reactor, or a moving-bed reactor.

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