Catalyst for preparing butadiene by coupling ethanol, preparation method and application thereof

Abstract

The invention belongs to the technical field of chemical catalysis, and discloses a catalyst, preparation method and application for preparing butadiene by ethanol coupling. The catalyst for preparing butadiene by ethanol coupling is a rare earth phosphate modified by a transition metal. Under the conditions of reaction temperature of 200-500°C and reaction pressure of 1-50 atm, the ethanol raw material is introduced into a reactor loaded with the catalyst by a carrier gas, and the reaction gas flow rate is 20-200 mL·min ‑1 , directly catalyzing the conversion of ethanol to butadiene. The catalyst of the present invention has high butadiene selectivity and excellent stability, and the activity is well maintained within 30 hours of testing, mainly because the rare earth phosphate material surface has abundant Lewis acid sites, which can promote the condensation of acetaldehyde intermediates; at the same time, the transition metal and the phosphate group on the surface of the rare earth phosphate are bonded by chemical bonds, and have strong chemical interaction, which ensures the stability of the transition metal under reaction conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical catalysis, and relates to a catalyst for catalytic conversion of ethanol to butadiene, a preparation method and application thereof, and particularly to a catalyst for preparing butadiene by coupling ethanol under gas phase atmospheric pressure conditions. Background Art

[0002] 1,3-Butadiene (hereinafter referred to as butadiene), molecular formula is C 4 H 6 It is a very important basic chemical raw material. Butadiene is a typical conjugated diene with high reactivity. It is widely used in the production of synthetic resins, synthetic rubber, butanediol, adiponitrile and nylon-66 and other chemical products. At present, the main synthetic routes of butadiene are ethylene by-product C 4 Fraction extraction method, butane and butene oxidative dehydrogenation method. The above-mentioned butadiene production methods rely on the cracking of petrochemical resources, and have a series of problems such as high energy consumption, equipment corrosion and low atomic economy. With the continuous development of bioethanol and coal-based ethanol production technology, the development of a one-step production route for butadiene using ethanol as raw material has the advantages of mild reaction conditions, high atomic economy and easy separation of gas and liquid, which is a direction worthy of vigorous research in the future.

[0003] At present, the catalyst systems for ethanol to butadiene can be roughly divided into two categories: MgO-SiO 2 Mixed oxide system and 4th and 5th group transition metal oxide modified molecular sieve catalyst system. MgO-SiO 2 Mixed oxides have a large number of acid and base active centers and are a hot topic in academic research. Cavani et al. [Green Chem., 2016, 18(6): 1653-1663] prepared MgO-SiO by sol-gel method. 2 The catalyst was used to produce butadiene from ethanol. The results showed that the Mg / Si ratio had a great influence on the surface acidity of the catalyst. The selectivity of butadiene showed a volcanic curve relationship with the MgO content. When the Mg / Si ratio was between 9 and 15, the butadiene selectivity was relatively high. 2 The synthesis method and calcination temperature have a great influence on the activity, among which the Mg-O-Si acid-base pair at the interface structure is the active center [Appl. Catal. A-Gen., 2019, 577: 1-9], but the yield of butadiene in this type of catalyst system does not exceed 25%. In order to improve the selectivity of butadiene, some researchers have used MgO-SiO 2Although the conversion rate has been improved by doping the catalyst with transition metal species, such as Cu[ACS Catal., 2015, 5(10): 6005-6015] and Zn[J. Catal., 2018, 359: 184-197], the stability still needs to be improved.

[0004] The corresponding oxides of transition metal elements of the 4th and 5th groups, such as Zr [Appl. Catal. B-Environ., 2022, 301: 120822], Hf [ACS Catal. 2015, 5, 3393-3397], and Nb [J. Mol. Catal. A-Chem, 2016, 424: 27-36], have strong Lewis acidity and show good reactivity for ethanol to butadiene. However, the space-time yield of butadiene is generally around 0.2 g BD ·g Cat. -1 ·h -1 Therefore, the development of a catalyst with simple synthesis method, high activity, selectivity and stability is expected to realize the industrial production and application of ethanol dehydrogenation to butadiene. Summary of the invention

[0005] The purpose of the present invention is to provide a rare earth phosphate-supported metal catalyst for preparing butadiene by coupling ethanol to address the deficiencies of the prior art. The present invention uses rare earth phosphate (YPO) for the first time. 4 、LaPO 4 、CePO 4 The catalyst precursor was first prepared by an equal volume impregnation method, and then the precursor was treated in an air atmosphere to obtain a catalyst. Compared with traditional catalysts, the prepared catalyst has higher butadiene selectivity and excellent catalytic stability, and has good industrial application prospects.

[0006] The technical solution of the present invention:

[0007] A catalyst for preparing butadiene by coupling ethanol is a rare earth phosphate modified by a transition metal, and contains the following components by weight percentage:

[0008] The rare earth phosphate has the general formula of MPO 4 , M is one or a combination of two or more elements selected from Y, La, Ce, Pr, and Yb;

[0009] The transition metal is selected from one or a combination of two or more of Co, Ni, Cu, Zn, Ag, Pd, Rh, Ru, Pt, and Ir, and the loading amount is 0.01 to 50 wt% of the weight of the rare earth phosphate.

[0010] The transition metal uses nitrate, chloride, acetylacetonate, sulfate or acetate as a precursor.

[0011] A method for preparing a catalyst for preparing butadiene by coupling ethanol, comprising the following steps:

[0012] (1) preparing a transition metal salt aqueous solution and a transition metal salt alcohol solution;

[0013] (2) impregnating the rare earth phosphate with an equal volume of the transition metal salt aqueous solution and / or transition metal salt alcohol solution prepared in step (1); and standing at room temperature for 0.5 to 2 hours after the impregnation;

[0014] (3) drying the mixture after standing in step (2) in an oven at 50° C. for 8 to 20 hours;

[0015] (4) The dried product of step (3) is calcined at 200-500° C. in an oxidizing atmosphere, and then calcined at 300-700° C. in a hydrogen atmosphere (10 vol% H 2 / N 2 ) is reduced for 0.5 to 8 hours, preferably 1 to 2 hours, to obtain a transition metal-modified rare earth phosphate catalyst.

[0016] A method for preparing butadiene by ethanol coupling, wherein the ethanol raw material is introduced into a reactor loaded with a catalyst through a carrier gas at a reaction temperature of 200 to 500°C and a reaction pressure of 1 to 50 atm, and the reaction gas flow rate is 20 to 200 mL min -1 , directly catalyzes the conversion of ethanol into butadiene.

[0017] In step (1), the concentration of the transition metal salt aqueous solution is 0.08 to 1.0 g·mL -1 , the concentration of transition metal salt alcohol solution is 0.08~0.3g·mL -1 ; The alcohol solvent is selected from methanol and / or ethanol.

[0018] In step (5), the reaction temperature is preferably 350-400°C, the reaction pressure is preferably atmospheric pressure, and the reaction gas flow rate is preferably 30 mL min -1 .

[0019] The reactor is preferably a fixed bed and atmospheric pressure reactor.

[0020] The reaction mass space velocity is 0.01~5h -1 , preferably 1.0~2.0h -1 .

[0021] The carrier gas is a reaction inert gas such as nitrogen, argon, helium, etc.

[0022] Beneficial effects of the present invention: The catalyst provided by the present invention has high butadiene selectivity and excellent stability, and the activity is maintained well within 30 hours of testing (Co-YPO 4 This is mainly because the rare earth phosphate material has abundant Lewis acid sites on its surface, which can promote the condensation of acetaldehyde intermediates; at the same time, transition metals such as Co and the phosphate groups on the surface of rare earth phosphates are chemically bonded, which has strong chemical interactions and ensures the stability of transition metals under reaction conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 YPO of Example 1 4 Co-YPO with different cobalt contents 4 XRD pattern of .

[0024] Figure 2 Co-YPO of Example 4 4 The changes in conversion rate and selectivity of the samples within 30 hours. DETAILED DESCRIPTION

[0025] The present invention is described in detail below through some embodiments, but the present invention is not limited to these embodiments.

[0026] Example 1

[0027] Co Load YPO 4 Catalyst preparation process:

[0028] (1) Weigh a certain amount of YPO 4 The samples were dried in an air flow oven at 120 °C for 2 h to remove physically adsorbed water on the surface;

[0029] (2) At 25°C, take Co(NO 3 ) 2 6H 2 The YPO obtained by drying in step (1) was impregnated with an equal volume of aqueous solution of O 4 On, let stand for 2h;

[0030] (3) drying the mixture after standing in step (2) at 50° C. for 10 h to obtain a catalyst precursor;

[0031] (4) The catalyst precursor obtained in step (3) was oxidized in an air atmosphere at 350°C for 2 h, and then reduced in a hydrogen atmosphere at 400°C for 2 h (10 vol% H 2 / N 2 ), to obtain 1Co-YPO 4 (No. 4 in Table 1) Catalyst.

[0032] (5) Modulation of Co(NO 3 ) 2 6H 2 The concentration of O aqueous solution can adjust the Co loading amount. The preparation method is the same as the above steps, corresponding to numbers 2, 3, 5, 6 and 7 in Table 1.

[0033] The XRD pattern of the obtained catalyst is as follows Figure 1 shown.

[0034] The preparation conditions and processes of other catalysts are the same as those in Example 1. The corresponding relationship between the sample numbers and the preparation conditions is shown in Table 1.

[0035] Table 1 Correspondence between sample numbers and preparation conditions of Example 1

[0036]

[0037] Example 2

[0038] Co and Zn bimetallic loaded YPO 4 Catalyst preparation process:

[0039] (1) Weigh a certain amount of YPO 4 The samples were dried in an air flow oven at 120 °C for 2 h to remove physically adsorbed water on the surface;

[0040] (2) At 25°C, take Co(NO 3 ) 2 6H 2 O aqueous solution and Zn(NO 3 ) 2 6H 2 The YPO obtained by drying in step (1) was impregnated with an equal volume of aqueous solution of O 4 On, let stand for 2h;

[0041] (3) drying the mixture after standing in step (2) at 50° C. for 10 h to obtain a catalyst precursor;

[0042] (4) The catalyst precursor obtained in step (3) was oxidized in an air atmosphere at 350°C for 2 h, and then reduced in a hydrogen atmosphere at 400°C for 2 h (10 vol% H 2 / N 2 ), and 0.5Co0.5Zn-YPO was obtained 4 (No. 18 in Table 1) Catalyst.

[0043] Example 3

[0044] Ethanol to butadiene catalyzed by rare earth phosphates modified with different transition metals.

[0045] Using ethanol as raw material, the ethanol to butadiene reaction was carried out in a fixed bed reactor. The reaction conditions were as follows: the catalyst was loaded in a fixed bed reactor with an inner diameter of 8 mm, normal pressure, reaction temperature of 350°C, and ethanol mass space velocity of 2.0 h -1 After the reaction stabilized, the reaction raw materials and products were analyzed by online chromatography. The corresponding relationship between the sample number and the ethanol conversion activity is shown in Table 2.

[0046] Table 2 Correspondence between sample numbers and ethanol activity and butadiene selectivity in Example 2

[0047]

[0048]

[0049] Example 3

[0050] Co-YPO at different temperatures 4 Catalytic production of butadiene from ethanol.

[0051] Using ethanol as raw material, the ethanol to butadiene reaction was carried out in a fixed bed reactor. The reaction conditions are as follows: the catalyst is loaded in a fixed bed reactor with an inner diameter of 8 mm, normal pressure, reaction temperature 200-450℃, and the mass space velocity of ethanol is 2.0h -1 After the reaction stabilized, the reaction raw materials and products were analyzed by online chromatography. The corresponding relationship between the sample number and the ethanol conversion activity is shown in Table 3.

[0052] Table 3 Reaction temperature of Example 3 and 1.0Co-YPO 4 Corresponding relationship of catalytic activity of ethanol to butadiene

[0053] Temperature(℃) Ethanol conversion rate / % Butadiene selectivity / % 200 0.6 40.3 250 1.6 42.2 300 13.6 58.5 350 65.1 68.0 400 96 54.5 450 >99.0 53.6

[0054] Example 4

[0055] 1.0Co-YPO 4 Stability test experiment of catalytic production of butadiene from ethanol.

[0056] Using ethanol as raw material, the ethanol to butadiene reaction was carried out in a fixed bed reactor. The reaction conditions were as follows: the catalyst was loaded in a fixed bed reactor with an inner diameter of 8 mm, normal pressure, reaction temperature of 350°C, and ethanol mass space velocity of 1.0 h -1 After the reaction stabilized, the reaction raw materials and products were analyzed by online chromatography. The change of conversion rate and selectivity within 30h reaction time is shown in the figure Figure 2 shown.

Claims

1. A method for preparing butadiene by coupling ethanol, characterized in that: Under the conditions of reaction temperature of 200-500℃ and reaction pressure of 1-50atm, the ethanol raw material is introduced into the reactor loaded with the catalyst through the carrier gas, and the reaction gas flow rate is 20-200mL·min -1 , directly catalyze the conversion of ethanol to butadiene; The catalyst for preparing butadiene by coupling ethanol is a transition metal-modified rare earth phosphate, and the components included by weight percentage are: The rare earth phosphate has a general formula of MPO4, where M is one or a combination of two or more elements selected from Y, La, Ce, Pr, and Yb; The transition metal is selected from one or a combination of two or more of Co, Ni, Cu, Zn, Ag, Pd, Rh, Ru, Pt, and Ir, and the loading amount is 0.01 to 50 wt% of the weight of the rare earth phosphate.

2. The method according to claim 1, characterized in that The reaction temperature is 350-400°C, the reaction pressure is normal pressure, and the reaction gas flow rate is 30 mL·min -1 .

3. The method according to claim 1, characterized in that The reaction mass space velocity is 0.01~5h -1 .

4. The method according to claim 1, characterized in that: The carrier gas is nitrogen, argon or helium.

5. The method according to claim 1, characterized in that The transition metal uses nitrate, chloride, acetylation, sulfate or acetate as a precursor.

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