Preparation of a modified heteropolyacid catalyst and its application in dehydration of bioethanol to bioethylene

Abstract

The present invention relates to an additive-modified heteropolyacid catalyst and its use in the dehydration of bioethanol to bioethylene. The catalyst additive is a highly active metal phosphide, and the additive and active components are prepared by a step-by-step impregnation method. The catalyst is prepared by an impregnation method using common silicon oxide as a carrier, resulting in mild reaction conditions and a stable and controllable process. The metal center in the additive promotes the migration of carbon deposit precursors from the acidic sites that catalyze ethanol dehydration, and the phosphorus hydroxyl groups regulate the acidity of the catalyst, thereby extending the catalyst's service life. The resulting catalyst exhibits high reaction activity, resistance to carbon deposits, and long stable operation at low temperatures and high space velocities.

Description

Technical Field

[0001] The present invention relates to a catalytic method for dehydrating bioethanol to produce bioethylene, and in particular to a preparation and modification method of a bioethanol dehydration supported heteropolyacid catalyst, and a method for catalytic dehydration of bioethanol on the catalyst. Background Art

[0002] Ethylene is an important basic chemical raw material. The ethylene industry is the core of the petrochemical industry and represents the level of a country's petrochemical industry. However, petroleum ethylene is large in scale and requires high investment. Due to transportation and cost issues, it cannot meet the demand for decentralized small- and medium-scale ethylene use. Ethanol dehydration to ethylene is a new technology that is different from traditional technologies and can serve as an effective supplement to existing petroleum ethylene production technologies. Raw material ethanol can be obtained from a wide range of sources, not only from coal resources but also from biomass resources. With the continuous advancement of bio-fermentation technology, the output of non-grain bioethanol is increasing. The production of ethylene through bioethanol dehydration has a simple production process, a small number of products that are easy to separate, can be prepared on a small scale, has flexible production, and has strong market competitiveness.

[0003] The development of efficient catalysts is crucial for the production of ethylene from bioethanol dehydration. Heterogeneous catalysts used for ethanol dehydration to ethylene primarily include activated alumina, molecular sieves, and heteropolyacids. Activated alumina offers high mechanical strength and good selectivity, but it also results in 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 faces challenges such as poor catalyst stability, demanding preparation conditions, and difficulty controlling crystallinity, limiting further industrial application. Patents CN 105709822 A and CN 106944139 A disclose a method for ethanol dehydration to ethylene catalyzed by heteropolyacid ammonium salts. Currently, low-temperature, high-efficiency ethanol dehydration to ethylene technology has yet to be fully commercialized, and the development of highly stable catalysts remains a key challenge.

[0004] This invention develops a novel method for preparing a metal phosphide-modified heteropolyacid catalyst and catalyzing the dehydration of bioethanol to bio-ethylene. The metal center in the catalyst promotes the migration of carbon deposit precursors away from the acidic sites involved in catalyzing ethanol dehydration, while the phosphorus hydroxyl groups modulate the acidity of the catalyst, thereby extending its service life. This method is simple to operate, and the resulting catalyst exhibits high reactivity, resistance to carbon deposits, and long stable operation at low temperatures and high space velocities. It is suitable for acid catalysis applications in bio-based alcohol dehydration and other fields. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a method for preparing an auxiliary-modified supported heteropolyacid catalyst. The catalyst preparation process is simple and the process is controllable. The prepared catalyst has high reaction activity and good stability under low temperature and high space velocity conditions, and has broad application prospects in the field of dehydration of bio-based alcohols to olefins.

[0006] The technical solution is:

[0007] The preparation of the metal phosphide-modified heteropolyacid catalyst of the present invention and its application in the dehydration of bioethanol to bioethylene, the auxiliary agent and the active component are prepared by a step-by-step impregnation method:

[0008] (1) The raw salt is prepared into a mixed solution, impregnated onto a silica support, and then subjected to aging, drying, calcination, and reduction to obtain a metal phosphide-modified catalyst precursor. This step is a key step of the present invention, and its function is to obtain a suitable content of metal phosphide additive by loading, and the metal center in the additive promotes the desorption of the precursor that generates carbon deposits from the acid center, thereby protecting the active center for catalyzing the dehydration of bioethanol. The phosphorus hydroxyl group can adjust the acidity of the catalyst, inhibit the formation of carbon deposits, and thus improve the stability of the catalyst.

[0009] (2) preparing a solution of the heteropoly acid raw material, impregnating the solution onto the catalyst precursor obtained in step 1, and then aging, drying, and calcining to obtain a metal phosphide-modified heteropoly acid catalyst.

[0010] Preferably, in step (1), the carrier is silicon oxide, and the properties are: 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 auxiliary agent is a metal phosphide, and the content thereof is 1-5 wt%.

[0012] Preferably, the crystal phase of the metal phosphide is Ni3P.

[0013] Preferably, in step (1), the metal source in the raw salt is Ni(NO3)2·6H2O, and the phosphorus source is (NH4)2HPO4. A mixed solution of nickel and phosphorus is prepared according to a stoichiometric ratio, and the mixed solution is impregnated onto the support by an impregnation method. The mixture is aged for 10-12 hours, dried at 110-130°C for 6-12 hours, calcined at 450-550°C for 4-6 hours, and reduced in hydrogen at 450-550°C for 4-6 hours to obtain a catalyst precursor loaded with an additive.

[0014] Preferably, the active component in step (2) is silicotungstic acid, and the active component content is 10-40 wt%; the carrier content is 55-89 wt%.

[0015] Preferably, in step (2), the active component solution is impregnated into the catalyst precursor by an impregnation method, aged for 10-12 hours, dried at 110-130° C. for 6-12 hours, and calcined at 250-350° C. for 4-6 hours to obtain the catalyst.

[0016] The invention discloses an application of a metal phosphide-modified heteropolyacid catalyst in the dehydration reaction of bioethanol to bioethylene.

[0017] As a preferred method, a fixed bed reactor is used, the raw material is bioethanol, the reaction temperature is 220-280°C, the reaction pressure is 0.5-1.5 MPa, and the mass space velocity is 1-10 h -1 .

[0018] The catalyst prepared in this invention uses common silicon oxide as a carrier and an impregnation method, resulting in mild reaction conditions and a stable and controllable process. The metal centers in the additive promote the migration of carbon deposit precursors away from the acidic sites that catalyze ethanol dehydration, while the phosphorus hydroxyl groups modulate the acidity of the catalyst, thereby extending its service life. The resulting catalyst exhibits high reactivity, resistance to carbon deposits, and long stable operation at low temperatures and high space velocities.

[0019] Beneficial technical effects

[0020] 1. The present invention obtains a metal phosphide-modified heteropolyacid-based bioethanol dehydration catalyst through a step-by-step impregnation method. The catalyst preparation conditions are mild and the reaction process is controllable. The metal center in the additive helps promote the migration of carbon deposit precursors from the acidic sites that catalyze ethanol dehydration, protecting the heteropolyacid used for dehydration. The phosphorus hydroxyl groups can regulate the acidity of the catalyst, inhibiting the formation of carbon deposits, thereby extending the service life of the catalyst.

[0021] 2. The prepared additive-modified heteropolyacid catalyst has a low reaction temperature and long stable operation time in the process of catalyzing the dehydration of bio-based ethanol to produce ethylene, and has a broad application space. DETAILED DESCRIPTION

[0022] 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.

[0023] The properties of the silicon oxide carrier used in the following examples are: specific surface area 285m 2 / g, pore volume 0.79mL / g, pore diameter 5.2-13.8nm.

[0024] Example 1

[0025] (1) Loading auxiliary agent: 10 g of silica carrier was weighed and added to 10 mL of dilute nitric acid solution (concentration of 0.5 mol / L) containing 1.53 g of Ni(NO3)2·6H2O and 0.23 g of (NH4)2HPO4. The catalyst was aged (placed) at room temperature for 12 h, dried at 120°C for 12 h, calcined at 500°C in air for 4 h, and reduced at 500°C in H2 atmosphere (flow rate 50 mL / min) for 3 h. XRD results showed that the auxiliary agent crystalline phase was Ni3P, and a catalyst precursor loaded with auxiliary agent was obtained, in which the auxiliary agent content calculated based on the metal was 3 wt%.

[0026] (2) Loading active components: The catalyst precursor prepared in step (1) was added to 10 mL of a mixture containing 4.29 g H4SiW 12 O 40 ·24H2O aqueous solution, aged at room temperature for 12h, dried at 120℃ for 12h, and calcined in air at 250℃ for 4h to obtain a catalyst, which is designated as catalyst 1. XRD results show that the active phase is heteropoly acid H4SiW 12 O 40 , the content of active components is 30wt%.

[0027] (3) Catalyst evaluation: The catalyst was evaluated in a fixed-bed tubular reactor using bioethanol as the raw material, at a reaction temperature of 240°C, a reaction pressure of 1.0 MPa, and a mass space velocity of 10 h -1 After 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.

[0028] Example 2: Different types of additive raw material salts - Co(NO3)2·6H2O and Na2HPO4

[0029] Compared with Example 1, Example 2 differs in that in step (1), 10 mL of the impregnation solution contains 1.53 g of Co(NO3)2·6H2O and 0.37 g of Na2HPO4, and the remaining processes and conditions are exactly the same as those in Example 1; XRD results show that the auxiliary agent crystal phase is Co2P; the prepared catalyst is recorded as Catalyst 2.

[0030] Example 3: Different types of additive raw material salts - Fe(NO3)3·9H2O and NaH2PO4

[0031] Compared with Example 1, Example 3 differs in that in step (1), 10 mL of the impregnation solution contains 2.23 g of Fe(NO3)3·9H2O and 0.33 g of NaH2PO4, and the rest of the process and conditions are exactly the same as Example 1; XRD results show that the auxiliary agent crystal phase is Fe2P; the prepared catalyst is recorded as Catalyst 3.

[0032] Example 4: Different types of additive raw material salts - Cu(NO3)2·3H2O and NH4H2PO4

[0033] Compared with Example 1, Example 4 differs in that in step (1), 10 mL of the impregnation solution contains 1.17 g of Cu(NO3)2·3H2O and 0.28 g of NH4H2PO4, and the rest of the process and conditions are exactly the same as those in Example 1; XRD results show that the auxiliary agent crystal phase is Cu3P; the prepared catalyst is recorded as Catalyst 4.

[0034] Example 5: Increased additive loading - 5 wt%

[0035] 10 g of silica support was weighed and added to 10 mL of a dilute nitric acid solution (concentration: 0.5 mol / L) containing 2.61 g of Ni(NO3)2·6H2O and 0.39 g of (NH4)2HPO4. The mixture was aged at room temperature for 16 h, dried at 130°C for 6 h, calcined at 650°C in air for 2 h, and reduced at 600°C in a H2 atmosphere (flow rate: 50 mL / min) for 2 h to obtain a catalyst precursor loaded with a promoter, wherein the promoter content was 5 wt% based on the metal.

[0036] The catalyst precursor was added to 10 mL of a mixture containing 4.29 g of H4SiW 12 O 40 The catalyst was aged in a 24H2O aqueous solution at room temperature for 12 h, dried at 120°C for 12 h, and calcined in air at 250°C for 4 h to obtain a catalyst, designated as Catalyst 5, with an active component content of 30 wt %. The catalyst evaluation conditions were the same as those in Example 1.

[0037] Example 6: Reduced additive loading - 1 wt%

[0038] 10 g of silica support was weighed and added to 10 mL of a dilute nitric acid solution (concentration: 0.5 mol / L) containing 0.5 g of Ni(NO3)2·6H2O and 0.08 g of (NH4)2HPO4. The mixture was aged at room temperature for 8 h, dried at 110°C for 12 h, calcined at 400°C in air for 8 h, and reduced at 300°C in a H2 atmosphere (flow rate: 50 mL / min) for 8 h to obtain a catalyst precursor loaded with a promoter, wherein the promoter content was 1 wt% based on the metal.

[0039] The catalyst precursor was added to 10 mL of a mixture containing 4.29 g of H4SiW 12 O 40 The catalyst was prepared by aging in a 24H2O aqueous solution at room temperature for 12 h, drying at 120°C for 12 h, and calcining in air at 250°C for 4 h to obtain a catalyst, designated as Catalyst 6, with an active component content of 30 wt%.

[0040] The catalyst evaluation conditions were the same as in Example 1.

[0041] Example 7: Different active phases of additives - Ni2P

[0042] Compared with Example 1, Example 7 differs in that in step (1), 10 mL of the impregnation solution contains 1.53 g of Ni(NO3)2·6H2O and 0.35 g of (NH4)2HPO4, and the rest of the process and conditions are exactly the same as those in Example 1; XRD results show that the auxiliary agent crystal phase is Ni2P; the prepared catalyst is recorded as Catalyst 7.

[0043] Example 8: Different active phases of additives - Ni 12 P5

[0044] Compared with Example 1, Example 8 is different in that in step (1), 10 mL of the impregnation solution contains 1.53 g Ni(NO3)2·6H2O and 0.29 g (NH4)2HPO4, and the rest of the process and conditions are exactly the same as those in Example 1; XRD results show that the auxiliary crystal phase is Ni 12 P5; the prepared catalyst is recorded as catalyst 8.

[0045] Example 9: Increased active ingredient loading - 40 wt%

[0046] (1) 10 g of silica support was weighed and added to 10 mL of a dilute nitric acid solution (concentration: 0.5 mol / L) containing 1.53 g of Ni(NO3)2·6H2O and 0.23 g of (NH4)2HPO4. The mixture was aged at room temperature for 12 h, dried at 120°C for 12 h, calcined in air at 500°C for 4 h, and reduced in a H2 atmosphere (flow rate: 50 mL / min) at 500°C for 3 h to obtain a catalyst precursor loaded with a promoter, wherein the promoter content was 3 wt% based on the metal.

[0047] (2) Add the catalyst precursor to 10 mL of 6.67 g H4SiW 12 O 40 The catalyst was prepared by aging in a 24H2O aqueous solution at room temperature for 16 h, drying at 130°C for 6 h, and calcining in air at 400°C for 2 h to obtain a catalyst, designated as catalyst 9, with an active component content of 40 wt%.

[0048] (3) The catalyst evaluation conditions were the same as those in Example 1.

[0049] Example 10: Active ingredient loading reduction - 10 wt%

[0050] (1) 10 g of silica support was weighed and added to 10 mL of a dilute nitric acid solution (concentration: 0.5 mol / L) containing 1.53 g of Ni(NO3)2·6H2O and 0.23 g of (NH4)2HPO4. The mixture was aged at room temperature for 12 h, dried at 120°C for 12 h, calcined in air at 500°C for 4 h, and reduced in a H2 atmosphere (flow rate: 50 mL / min) at 500°C for 3 h to obtain a catalyst precursor loaded with a promoter, wherein the promoter content was 3 wt% based on the metal.

[0051] (2) Add the catalyst precursor to 10 mL of 1.11 g H4SiW 12 O 40 The catalyst was prepared by aging in a 24H2O aqueous solution at room temperature for 8 h, drying at 110°C for 12 h, and calcining in air at 200°C for 8 h to obtain a catalyst, designated as catalyst 10, with an active component content of 10 wt%.

[0052] (3) The catalyst evaluation conditions were the same as those in Example 1.

[0053] Comparative Example 1

[0054] Comparative Example 1 is different from Example 10 in that step (1) of loading the auxiliary agent on the carrier is omitted, and the remaining steps and conditions are exactly the same as those of Example 10 (loading the active component heteropoly acid H4SiW on the silica carrier). 12 O 40 ); The catalyst obtained is recorded as catalyst 11. The active component in the catalyst (heteropoly acid H4SiW 12 O 40 ) content is 10wt%.

[0055] Example 11: Different active ingredients - phosphotungstic acid

[0056] Example 11 is different from Example 1 in that in step (2), 10 mL of the impregnation solution contains 4.29 g of H3PW 12 O 40 ·xH2O, and the rest of the process and conditions were exactly the same as in Example 1; the obtained catalyst was recorded as catalyst 12.

[0057] Example 12: Different active ingredients - phosphomolybdic acid

[0058] Example 12 is different from Example 1 in that in step (2), 10 mL of the impregnation solution contains 4.29 g of H3PMo 12 O 40 ·xH2O, and the rest of the process and conditions were exactly the same as in Example 1; the obtained catalyst was recorded as catalyst 13.

[0059] Table 1 below lists the reaction evaluation results of the catalyst prepared by the method of the present invention

[0060]

[0061] From Example 10 and Comparative Example 1, it can be seen that loading the auxiliary agent nickel phosphide is beneficial to improving the stability of ethanol dehydration to ethylene at high space velocity; from Examples 1 and 2, 3, 4, 7, and 8, it can be seen that the effect is best when the nickel phosphide crystal form is Ni3P; from Examples 1, 5, and 6, it can be seen that with the increase of the auxiliary agent content, the ethanol conversion rate and ethylene selectivity decrease slightly after 24 hours of reaction, but the stability of the catalyst increases with the increase of the auxiliary agent content after 800 hours of reaction. Considering the initial activity and stability, Example 1 is the best; from Examples 1, 9, and 10, it can be seen that the catalyst activity increases with the increase of the loading amount; from Examples 1, 11, and 12, it can be seen that after adding the auxiliary agent Ni3P, the activity and stability of phosphotungstic acid and phosphomolybdic acid increase, which is not much different from silicotungstic acid.

Claims

1. A method for preparing an additive-modified heteropolyacid catalyst, comprising an additive, an active component, and a carrier, wherein the additive is a metal phosphide, the active component is a heteropolyacid, and the carrier is silicon oxide; based on the metal content, the additive content in the catalyst is 0.5-10wt%; the active component content is 5-50wt%; and the remainder is the carrier; the additive and active component are prepared by a step-by-step impregnation method: (1) Slowly adding the silica carrier to a mixed solution containing a phosphate salt and a metal salt, and impregnating the raw salt mixed solution onto the carrier under continuous stirring, and then aging at room temperature, drying, calcining, and reducing to obtain a catalyst precursor modified with an additive; (2) adding the catalyst precursor obtained in step (1) into the heteropoly acid solution, and impregnating the raw material heteropoly acid solution onto the catalyst precursor under continuous stirring, and obtaining a metal phosphide modified heteropoly acid catalyst after aging, drying and roasting; in step (1), the crystal phase of the auxiliary metal phosphide is Ni3P, Ni 12 One or more of P5, Ni2P, Fe2P, FeP, Co2P, CoP, and Cu3P.

2. The preparation method according to claim 1, characterized in that: 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±6nm.

3. The method according to claim 1, wherein: Based on the metal content, the content of the promoter in the catalyst is 1-5wt%; the content of the active component is 10-40wt%.

4. The preparation method according to claim 1, characterized in that: In step (1), the crystal phase of the auxiliary metal phosphide is Ni3P.

5. The method according to claim 1, characterized in that: In step (1), the metal salt in the raw material salt is one or more of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O or Cu(NO3)2·3H2O; the phosphorus source is one or more of (NH4)2HPO4, NH4H2PO4, Na2HPO4, and NaH2PO4; a mixed solution of the metal source and the phosphorus source is prepared according to the stoichiometric ratio required for the active phase crystal form, and the mixed solution of the metal and phosphorus is impregnated onto the support by an impregnation method, and the mixture is left to mature for 8-16 h, dried at 110-130 ° C for 6-12 h, calcined at 400-650 ° C for 2-8 h, and reduced in hydrogen at 300-600 ° C for 2-8 h to obtain M x P y / SiO2 catalyst precursor, where x and y represent the number of atoms in the metal phosphide crystal phase.

6. The preparation method according to claim 5, characterized in that: In step (1), the metal salt in the raw salt is Ni(NO3)2·6H2O; the phosphorus source is (NH4)2HPO4; a mixed solution of the metal source and the phosphorus source is prepared according to the stoichiometric ratio required for the active phase crystal form, and the mixed solution of the metal and phosphorus is impregnated onto the support by an impregnation method, and then left to mature for 10-12 h, dried at 110-130 ° C for 6-12 h, calcined at 450-550 ° C for 4-6 h, and reduced in hydrogen at 450-550 ° C for 4-6 h to obtain M x P y / SiO2 catalyst precursor, where x and y represent the number of atoms in the metal phosphide crystal phase.

7. The preparation method according to claim 1, characterized in that: In step (2), the active component is one or more of silicotungstic acid, phosphotungstic acid and phosphomolybdic acid.

8. The preparation method according to claim 1, characterized in that: In step (2), the active component solution is impregnated into the M x P y / SiO2, place it on the sintered silica gel, mature it for 8-16 h, dry it at 110-130 °C for 6-12 h, and calcine it at 200-400 °C for 2-8 h to obtain the catalyst.

9. The preparation method according to claim 8, characterized in that: In step (2), the active component solution is impregnated into the M x P y / SiO2, place it on the molten metal ore and mature it for 10-12 h, dry it at 110-130 °C for 6-12 h, and calcine it at 250-350 °C for 4-6 h to obtain the catalyst.

10. Use of an adjuvant-modified heteropolyacid catalyst prepared by the preparation method according to any one of claims 1 to 9 in an ethanol dehydration reaction.

11. The use according to claim 10, characterized in that: A fixed bed reactor is used, the raw material is bioethanol, the reaction temperature is 200-350 ℃; the reaction pressure is 0.1-2 MPa; the mass space velocity is 0.5-20 h-1 in terms of ethanol. -1 .

12. The use according to claim 11, characterized in that: A fixed bed reactor is used, the raw material is bioethanol, the reaction temperature is 220-280 ℃; the reaction pressure is 0.5-1.5 MPa; the mass space velocity is 1-10 h ... -1 .

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