An oxide catalyst for dehydrating ethanol to produce ethylene and its preparation and application

Abstract

The present invention relates to an oxide catalyst for the dehydration of ethanol to produce ethylene. The preparation method thereof comprises the following steps: (1) loading and (2) reduction. The present invention uses common silicon oxide as a carrier, introduces a composite oxide, and partially reduces the catalyst to prepare the catalyst under mild conditions and a stable and controllable process. The Lewis acid centers generated after the partial reduction can promote the adsorption of oxygen-containing functional groups, thereby improving the reaction activity. The prepared catalyst has the advantages of low reaction temperature, high activity, and strong resistance to carbon deposition.

Description

Technical Field

[0001] The present invention relates to a catalytic method for preparing ethylene by dehydrating ethanol, in particular to a catalytic dehydration method for ethanol on a composite metal oxide. Background Art

[0002] Ethylene is an important bulk commercial chemical and monomer, and has become a key indicator of the development level of a country or region's petrochemical industry. Petroleum-based ethylene is primarily produced through the cracking of petroleum distillates, relying heavily on petroleum resources and requiring large-scale production facilities. In recent years, with the increasing depletion of fossil resources like petroleum and the expansion of the small- and medium-scale ethylene production and consumption market, the production of ethylene from renewable bioethanol through dehydration has attracted widespread attention. Bioethanol dehydration to ethylene technology offers a simple reaction process, easily separable reaction products, and is environmentally friendly, making it suitable for small-scale production. It can partially or completely replace petroleum-based ethylene and holds significant economic value and strategic energy significance.

[0003] The key to ethanol dehydration to ethylene is the development of efficient catalysts. Heterogeneous catalysts used for ethanol dehydration to ethylene primarily include activated alumina, molecular sieves, and heteropolyacids. Activated alumina offers low cost, high mechanical strength, and good selectivity, but it also suffers from high reaction temperatures, low space velocity, high specific energy consumption, and low equipment utilization. Patent CN 101244971 A reports a method for preparing a nanomolecular sieve catalyst for bioethanol dehydration to ethylene. While this method offers low reaction temperatures, high ethanol conversion rates, and high ethylene selectivity, the process requires the introduction of a carrier gas and still suffers from poor catalyst stability, demanding preparation conditions, and difficulty controlling crystallinity, limiting further industrial application. Patents CN 105709822A and CN 106944139 A disclose a method for ethanol dehydration to ethylene catalyzed by heteropolyacid ammonium salts.

[0004] The present invention develops a new method for preparing a catalyst for the dehydration of ethanol to ethylene. In the process of preparing a supported metal oxide, the catalyst precursor is partially reduced to generate a Lewis acidic Mo δ+ species, promoting the adsorption of oxygen-containing groups, and the Mo-OH and / or P-OH provided The acid centers synergistically catalyze dehydration, thereby enhancing reaction activity. This method is simple to operate and can be applied to acid catalysis fields such as alcohol dehydration. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a method for preparing a catalyst for ethanol dehydration to ethylene with mild reaction conditions, a controllable preparation process and simple steps. The prepared catalyst has the advantages of mild reaction conditions, high activity and good stability, can be applied to acid-catalyzed alcohol dehydration reactions, and has broad application prospects.

[0006] The technical solution is:

[0007] The method for preparing a catalyst for producing ethylene oxide by dehydrating ethanol of the present invention comprises the following steps:

[0008] (1) Loading: The mixed solution of raw salts is impregnated onto a silica carrier, and after aging, drying, and calcination, a catalyst precursor is obtained.

[0009] (2) Reduction: In a reducing atmosphere, the catalyst precursor is moderately reduced to obtain a catalyst for the dehydration of ethanol to ethylene. This step is a key step of the present invention, and its function is to obtain a Lewis acid center (Mo) with appropriate acid amount and acid strength through reduction. δ+ ), which is beneficial to the adsorption of oxygen-containing groups in alcohol molecules, and the adsorption of oxygen-containing groups provided by Mo-OH and / or P-OH The acid sites act synergistically to catalyze dehydration, thereby enhancing the reaction activity.

[0010] Preferably, in step (1), the carrier is silicon oxide with the following properties: specific surface area 350±100m 2 / g, pore volume 0.8±0.4mL / g, average pore diameter 12±6nm.

[0011] Preferably, in step (1), the active component is a composite oxide MPO, wherein M is Mo; the molar ratio of metal to phosphorus is 0.8-1.2; the active component content is 10-40 wt%; and the carrier content is 60-90 wt%.

[0012] Preferably, in step (1), the metal source in the raw salt is (NH4)6Mo7O 24 4H2O or (NH4)6H2W 12 O 40 xH2O, the phosphorus source is (NH4)2HPO4; the mixed liquid is impregnated into the carrier by an equal volume impregnation method, aged for 8-16 hours, dried at 110-130°C for 6-12 hours, and calcined at 400-650°C for 4-8 hours to obtain a catalyst precursor.

[0013] Preferably, the reducing atmosphere in step (2) is hydrogen or a mixture of hydrogen and nitrogen (or argon, or helium), the volume proportion of hydrogen in the mixture is 10-90%; the reduction temperature is 300-450° C.; and the reduction time is 2-4 h.

[0014] The invention discloses an oxide catalyst for producing ethylene by dehydrating ethanol. The oxide catalyst is used in the reaction of producing ethylene by dehydrating ethanol.

[0015] Preferably, a fixed bed reactor is used, the raw material is anhydrous ethanol or an ethanol aqueous solution with a water content of less than 25wt%, the reaction temperature is 220-280℃; the reaction pressure is 0.5-1.5MPa; the mass space velocity is 1-20h in terms of ethanol-1 The ethanol dehydration reaction is sensitive to operating conditions such as temperature, pressure, and space velocity. Operating conditions should be maintained in the vapor phase and meet the following requirements: the operating temperature should be at least 10°C above the dew point, and the operating pressure should be at least 0.1 MPa below the dew point. Therefore, the preferred reaction temperature for this invention is 220-280°C and the reaction pressure should be 0.5-1.5 MPa.

[0016] The present invention uses common silicon oxide as a carrier, introduces a composite oxide, and then partially reduces it to prepare a catalyst. The conditions are mild and the process is stable and controllable. The Lewis acid centers generated after the partial reduction promote the adsorption of oxygen-containing functional groups, thereby enhancing reaction activity. The resulting catalyst has the advantages of low reaction temperature, high activity, and strong resistance to carbon deposition.

[0017] Beneficial technical effects

[0018] 1. The present invention prepares an ethanol dehydration catalyst by loading and partial reduction, which has simple steps, mild conditions and controllable process. The obtained catalyst has both suitable Lewis acid centers and Acid centers help adsorption of oxygen-containing compounds and improve reaction activity;

[0019] 2. The catalyst has the advantages of low reaction temperature and good stability. The reaction process is simple, controllable and easy to operate, and has broad application prospects. DETAILED DESCRIPTION

[0020] In order to further illustrate the present invention in detail, several specific implementation cases are given below, but the present invention is not limited to these embodiments.

[0021] Example 1

[0022] (1) Weigh 50g of silica carrier and add it to a mixture containing 17.66g of (NH4)6Mo7O 24 · The catalyst was prepared by adding a mixed aqueous solution of 4H2O and 13.21g (NH4)2HPO4 and aging at room temperature for 12h. The obtained material was dried at 120℃ for 12h and calcined at 500℃ for 4h to obtain a catalyst precursor.

[0023] (2) Reduction: The catalyst precursor prepared in step (1) was placed in a quartz tube furnace and reduced at 350° C. for 3 h in a H 2 atmosphere (flow rate 50 mL / min) to obtain a catalyst, which was determined to be a partially reduced oxide by XRD and was recorded as Catalyst 1. The content of the active component was 30 wt % based on the oxide.

[0024] (3) Catalyst evaluation: The catalyst was evaluated in a fixed-bed tubular reactor with anhydrous ethanol as the raw material, reaction temperature of 240°C, reaction pressure of 1.0 MPa, and mass space velocity of 1.0 h -1After gas-liquid separation, the products were subjected to gas chromatography analysis for composition and content. The tail gas flow rate was monitored and counted using a flow meter. The conversion rate of ethanol and the selectivity of ethylene and ether were calculated based on the comprehensive gas-liquid phase reaction results.

[0025] Comparative Example 1

[0026] The process and conditions are the same as those in Example 1. Compared with Example 1, Comparative Example 1 differs in that step (2) is omitted, and the rest is exactly the same as Example 1. The prepared catalyst is recorded as Catalyst 3, and the content of active components is 30 wt% in terms of oxide.

[0027] Example 2: Types of active ingredients

[0028] Weigh 50g of silica carrier and add it to a mixture containing 17.43g (NH4)6H2W 12 O 40 A mixed aqueous solution of 1 x HO and 9.35 g (NH₄)₂HPO₄ was stirred at 70°C until the solution evaporated to dryness. The resulting material was dried at 120°C for 12 h and calcined at 500°C for 4 h to obtain a catalyst precursor. The catalyst precursor was then reduced in a quartz tube furnace at 350°C for 3 h under a H₂ atmosphere (flow rate 50 mL / min) to obtain a catalyst, designated Catalyst 4, having an active component content of 30 wt % (calculated as oxide). The catalyst evaluation conditions and procedures were the same as those in Example 1.

[0029] Example 3: Increased active ingredient loading

[0030] Weigh 50g of silica carrier and add it to a mixture containing 27.38g of (NH4)6Mo7O 24 A mixed aqueous solution of 4H2O and 20.48 g (NH4)2HPO4 was stirred at 70°C until the solution evaporated to dryness. The resulting material was dried at 120°C for 12 h and calcined at 500°C for 4 h to obtain a catalyst precursor. The catalyst precursor was reduced in a quartz tube furnace at 350°C for 3 h under a H2 atmosphere (flow rate 50 mL / min) to obtain a catalyst, designated Catalyst 5, with an active component content of 40 wt% (calculated as oxide). The catalyst evaluation conditions and procedures were the same as those in Example 1.

[0031] Example 4: Reduction of active ingredient loading

[0032] Weigh 50g of silica carrier and add it to a mixture containing 4.56g of (NH4)6Mo7O 24A mixed aqueous solution of 4H2O and 3.41 g (NH4)2HPO4 was stirred at 70°C until the solution evaporated to dryness. The resulting material was oven-dried at 120°C for 12 h and calcined at 500°C for 4 h to obtain a catalyst precursor. The catalyst precursor was reduced in a quartz tube furnace at 350°C for 3 h under a H2 atmosphere (flow rate 50 mL / min) to obtain a catalyst, designated Catalyst 6, with an active component content of 10 wt% (calculated as oxide). The catalyst evaluation conditions and procedures were the same as those in Example 1.

[0033] Example 5: Increase in the Mo / P molar ratio of the active component

[0034] Weigh 50g of silica carrier and add it to a mixture containing 18.64g (NH4)6Mo7O 24 A mixed aqueous solution of 4H2O and 11.61 g (NH4)2HPO4 was stirred at 70°C until the solution evaporated to dryness. The resulting material was oven-dried at 120°C for 12 h and calcined at 500°C for 4 h to obtain a catalyst precursor. The catalyst precursor was reduced in a quartz tube furnace at 350°C for 3 h under a H2 atmosphere (flow rate 50 mL / min) to obtain a catalyst, designated Catalyst 7. The active component content, calculated as oxide, was 30 wt%. The catalyst evaluation conditions and procedures were the same as those in Example 1.

[0035] Example 6: Reduction of the Mo / P molar ratio of the active component

[0036] Weigh 50g of silica carrier and add it to a mixture containing 16.17g (NH4)6Mo7O 24 A mixed aqueous solution of 4H2O and 15.12 g (NH4)2HPO4 was stirred at 70°C until the solution evaporated to dryness. The resulting material was dried at 120°C for 12 h and calcined at 500°C for 4 h to obtain a catalyst precursor. The catalyst precursor was reduced in a quartz tube furnace at 350°C for 3 h under a H2 atmosphere (flow rate 50 mL / min) to obtain a catalyst, designated Catalyst 8, with an active component content of 30 wt% (calculated as oxide). The catalyst evaluation conditions and procedures were the same as those in Example 1.

[0037] Example 7: Reduction conditions, reducing atmosphere, reducing temperature, reducing time

[0038] Weigh 50g of silica carrier and add it to a mixture containing 17.66g of (NH4)6Mo7O 24A mixed aqueous solution of 4H2O and 13.21 g (NH4)2HPO4 was stirred at 70°C until the solution evaporated to dryness. The resulting material was dried at 120°C for 12 h and calcined at 500°C for 4 h to obtain a catalyst precursor. The catalyst precursor was reduced in a quartz tube furnace at 350°C for 6 h in a H2 / N2 mixed atmosphere (flow rate 50 mL / min) (H2 volume ratio 10%) to obtain a catalyst, designated as Catalyst 9. The active component content, calculated as oxide, was 30 wt%. The catalyst evaluation conditions and procedures were the same as those in Example 1.

[0039] Example 8: Reduction conditions, reducing atmosphere, reducing temperature, reducing time

[0040] Weigh 50g of silica carrier and add it to a mixture containing 17.66g of (NH4)6Mo7O 24 A mixed aqueous solution of 4H2O and 13.21 g (NH4)2HPO4 was stirred at 70°C until the solution evaporated to dryness. The resulting material was dried at 120°C for 12 h and calcined at 500°C for 4 h to obtain a catalyst precursor. The catalyst precursor was reduced in a quartz tube furnace at 300°C for 6 h in a H2 / N2 mixed atmosphere (flow rate 50 mL / min) (H2 volume ratio 50%) to obtain a catalyst, designated as Catalyst 10. The active component content, calculated as oxide, was 30 wt%. The catalyst evaluation conditions and procedures were the same as those in Example 1.

[0041] Example 9: Reduction conditions, reducing atmosphere, reducing temperature, reducing time

[0042] Weigh 50g of silica carrier and add it to a mixture containing 17.66g of (NH4)6Mo7O 24 A mixed aqueous solution of 4H2O and 13.21 g (NH4)2HPO4 was stirred at 70°C until the solution evaporated to dryness. The resulting material was dried at 120°C for 12 h and calcined at 500°C for 4 h to obtain a catalyst precursor. The catalyst precursor was reduced in a quartz tube furnace at 400°C for 2 h in a H2 / N2 mixed atmosphere (flow rate 50 mL / min) (H2 volume ratio 90%) to obtain a catalyst, designated as Catalyst 11. The active component content, calculated as oxide, was 30 wt%. The catalyst evaluation conditions and procedures were the same as those in Example 1.

[0043] Example 10: Reaction conditions, raw materials, temperature, pressure, space velocity

[0044] Catalyst 1 was used in a fixed bed tubular reactor. The raw material was 20 wt% ethanol aqueous solution. The reaction temperature was 240 ° C. The reaction pressure was 1.0 MPa and the mass space velocity was 1.0 h -1 ; Product analysis conditions and process are the same as in Example 1.

[0045] Example 11: Reaction conditions, raw materials, temperature, pressure, space velocity

[0046] Catalyst 1 was used in a fixed bed tubular reactor. The raw material was anhydrous ethanol. The reaction temperature was 280°C, the reaction pressure was 1.0 MPa, and the mass space velocity was 1.0 h -1 ; Product analysis conditions and process are the same as in Example 1.

[0047] Example 12: Reaction conditions, raw materials, temperature, pressure, space velocity

[0048] Catalyst 1 was used in a fixed bed tubular reactor. The raw material was anhydrous ethanol. The reaction temperature was 220°C, the reaction pressure was 1.0 MPa, and the mass space velocity was 1.0 h -1 ; Product analysis conditions and process are the same as in Example 1.

[0049] Example 13: Reaction conditions, raw materials, temperature, pressure, space velocity

[0050] Catalyst 1 was used in a fixed bed tubular reactor. The raw material was anhydrous ethanol. The reaction temperature was 240°C, the reaction pressure was 0.5 MPa, and the mass space velocity was 1.0 h -1 ; Product analysis conditions and process are the same as in Example 1.

[0051] Example 14: Reaction conditions, raw materials, temperature, pressure, space velocity

[0052] Catalyst 1 was used in a fixed bed tubular reactor. The raw material was anhydrous ethanol. The reaction temperature was 240°C, the reaction pressure was 1.5 MPa, and the mass space velocity was 1.0 h -1 ; Product analysis conditions and process are the same as in Example 1.

[0053] Example 15: Reaction conditions, raw materials, temperature, pressure, space velocity

[0054] Catalyst 1 was used in a fixed-bed tubular reactor. The raw material was anhydrous ethanol. The reaction temperature was 240°C, the reaction pressure was 1.0 MPa, and the mass space velocity was 20.0 h -1 ; Product analysis conditions and process are the same as in Example 1.

[0055] Table 1 below lists the reaction evaluation results of the catalyst prepared by the method of the present invention

[0056]

[0057] From Example 1 and Comparative Example 1, it can be seen that partial reduction is beneficial to improving the conversion rate of ethanol and the selectivity of ethylene; from Examples 1 and 2, it can be seen that the reactivity of Mo-PO is slightly higher than that of WPO; from Examples 1, 3, and 4, it can be seen that the reaction activity gradually increases with the increase of the active component content; from Examples 1, 5, and 6, it can be seen that the M / P molar ratio in the active component has little effect on the reaction activity within a certain range; from Examples 1, 7-9, it can be seen that the reducing atmosphere, reduction temperature, and reduction time have a great influence on the activity of the catalyst, and suitable reaction conditions are required; from Examples 1 and 10, it can be seen that the addition of water to the reaction raw materials leads to a slightly lower reaction activity, but the change is not large, indicating that the prepared catalyst has good water resistance; from Examples 1, 11-15, it can be seen that under the conditions of ensuring gas phase operation, the higher the reaction temperature, the lower the reaction pressure, and the lower the ethanol mass space velocity, the higher the ethanol conversion rate, and under low temperature and high space velocity conditions, the selectivity of ethylene is lower.

Claims

1. A method for producing ethylene by dehydrating ethanol, characterized in that: The invention adopts an oxide catalyst to catalyze the dehydration of ethanol to produce ethylene. The oxide catalyst comprises an active component and a carrier, wherein the active component is a partially reduced composite oxide and the carrier is silicon oxide; the active component content is 5-50wt%, the carrier content is 50-95wt%, the active component is a composite oxide MPO, wherein M is Mo and / or W, and the molar ratio of metal to phosphorus is 0.5-2. The preparation of the catalyst comprises the following steps: (1) Loading: The raw salts of the active components M and P are prepared into a mixed solution, impregnated onto a silica support, and then left to mature, dried, and calcined to obtain a catalyst precursor; (2) Reduction: In a reducing atmosphere, the catalyst precursor is partially reduced to obtain an ethanol dehydration to ethylene catalyst; In step (1), the metal source in the raw salt is (NH4)6Mo7O 24 4H2O and / or (NH4)6H2W 12 O 40 xH2O, the phosphorus source is (NH4)2HPO4; the mixed liquid is impregnated onto the support by the impregnation method, left to mature for 8-16 hours, dried at 110-130°C for 6-12 hours, and calcined at 400-650°C for 2-8 hours to obtain a catalyst precursor; The reducing atmosphere in step (2) is hydrogen or a mixture of hydrogen and nitrogen, argon or helium, the volume proportion of hydrogen in the mixture is 10-90%, the reduction temperature is 250-450 ° C, and the reduction time is 1-8 h. A fixed bed reactor is used, the raw material is anhydrous ethanol or an ethanol aqueous solution with a water content of less than 25wt%, the reaction temperature is 220-280℃, the reaction pressure is 0.1-1.5MPa, and the mass space velocity is 1-20h -1 .

2. The method according to claim 1, characterized in that: The carrier content in the oxide catalyst is 60-90wt%, the active component is the composite oxide MPO, wherein M is Mo; and the molar ratio of the metal to phosphorus is 0.8-1.2; In step (2), the reduction temperature is 300-400°C; and the reduction time is 2-4 h.

3. The method according to claim 1, wherein: In step (1), the carrier is common silicon oxide with the following properties: specific surface area 350±100 m 2 / g, pore volume 0.8±0.4mL / g, average pore diameter 12±6 nm.

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