Method for synthesizing acetylene selective hydrogenation catalyst by liquid phase method

Abstract

The invention belongs to the technical field of catalysts and acetylene selective hydrogenation, and discloses a method for synthesizing an acetylene selective hydrogenation catalyst by a liquid phase method. The preparation method comprises the following steps: introducing C2H2 gas into a mixed solution of CuCl2, CuCl and ammonia water, carrying out low-temperature stirring reaction in a water bath, drying the generated solid precipitate, and reducing in an H2 atmosphere to obtain the acetylene selective hydrogenation catalyst taking copper carbide CuxC as an active phase. The method is simple in step and easy and convenient to operate; low-temperature liquid phase reaction conditions are mild, thermal decomposition of a Cu source can be effectively reduced, more CuxC active phases are generated, and the performance of the catalyst is improved; the catalyst has high low-temperature hydrogenation activity, high ethylene selectivity and high industrial potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and relates to a method for preparing a carbon-containing copper-based acetylene selective hydrogenation catalyst by a liquid phase method, which is particularly suitable for the efficient removal of acetylene impurities in ethylene raw materials. Background Art

[0002] Ethylene is an important basic raw material in the petrochemical industry, mainly used for the production of polyethylene. In industrial production of ethylene, naphtha steam cracking method is mostly used, but the cracked gas often contains a small amount of acetylene impurities (0.5 - 2%), which will poison the downstream polymerization reaction catalyst and affect the quality of the polymer. In industrial ethylene production, catalytic selective hydrogenation method is mostly used to remove a small amount of acetylene in the ethylene raw material, and the commonly used catalyst is a supported Pd - Ag catalyst, whose disadvantages are scarce resources, high cost and poor ethylene selectivity. Therefore, it is imperative to develop high-performance non-precious metal catalysts to replace precious metal catalysts.

[0003] Among the non-precious metal catalysts studied, Cu-based catalysts show excellent ethylene selectivity and stability, but their low-temperature hydrogenation activity is relatively low. At high-temperature reactions, acetylene is prone to oligomerization and polymerization reactions on the Cu surface, resulting in rapid deactivation of the catalyst. Therefore, improving the low-temperature hydrogenation activity of the copper-based catalyst is the key to optimizing the copper-based catalyst. Bridier et al. prepared a ternary Cu-Ni-Fe metal system with Cu as the hydrogenation metal in "Cooperative effects in ternary Cu-Ni-Fe catalysts lead to enhanced alkene selectivity in alkyne hydrogenation". By modifying the microstructure of the catalyst with Ni and Fe, the prepared catalyst has excellent ethylene selectivity and stability, but the required temperature is as high as 250 °C, much higher than the current industrial Pd catalyst (about 100 °C); Shi et al. introduced in "Copper Catalysts in Semihydrogenation of Acetylene: From Single Atoms to Nanoparticles" that on Al 2 O 3Methods for synthesizing Cu-based single-atom catalysts of different sizes on a support. As the size of the Cu particles decreases, both the ethylene selectivity and stability during the catalytic acetylene selective hydrogenation reaction are improved, but the catalyst activity decreases. The prepared single-atom Cu-based catalyst can only achieve a 76% acetylene conversion rate at a reaction temperature of 190 °C. Liu et al. in "Hydrophobic Surface Modification of Cu-Based Catalysts for Enhanced Semihydrogenation of Acetylene in Excess Ethylene" modified the Cu 2 O surface by hexadecyltrimethoxysilane (HDTMS) to promote the enrichment of acetylene gas on the surface by forming a hydrophobic layer on the catalyst surface to enhance its acetylene hydrogenation activity. However, this process has cumbersome operation steps, and the catalyst still needs to reach 100% acetylene conversion rate at a reaction temperature of 190 °C. All in all, catalyst improvement methods such as multi-metal synergy, adding a support, and modifying the surface cannot effectively improve the low-temperature hydrogenation activity of Cu-based catalysts, resulting in the reaction temperature required for the catalyst being still significantly higher than that of industrial Pd-based catalysts. Lu in "Copper-Based Catalysts for Selective Hydrogenation of Acetylene Derived from Cu(OH) 2 " found that treating Cu(OH) 2 with acetylene-containing gas and then reducing it with hydrogen to obtain a catalyst with a special copper carbide Cu x C structure as the active phase, showing low-temperature hydrogenation activity similar to that of noble metals and higher ethylene selectivity. However, this process requires high-temperature gas-phase treatment, and in this process, the intermediate phase polyacetylene copper (Cu-(C≡C) n -Cu) will thermally decompose, resulting in low utilization rate of the copper source in the catalyst and harsh preparation conditions.

[0004] To address the above problems, in order to improve the low-temperature hydrogenation activity of the catalyst while reducing the thermal decomposition of the intermediate phase, the present invention proposes a method for synthesizing polyacetylene copper intermediate phase by a low-temperature liquid phase method, suppressing the ineffective thermal decomposition of the intermediate phase by reducing the preparation temperature, and improving the utilization rate of the copper source during the preparation process, thereby preparing a higher-performance Cu x C-containing copper-based catalyst. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a Cu-based acetylene selective hydrogenation catalyst by co-precipitation method. To solve the problem that the low-temperature hydrogenation activity of Cu-based catalysts at the present stage is low and they cannot effectively replace noble metal catalysts. The catalyst obtained by the present invention can achieve noble metal-like hydrogenation activity at a lower reaction temperature while maintaining a high ethylene selectivity.

[0006] The technical solution of the present invention

[0007] A method for synthesizing an acetylene selective hydrogenation catalyst by liquid phase method, comprising the following steps:

[0008] Step 1: Dissolve CuCl 2 in NH 3 ·H 2 O solution, and control the copper ion concentration in the NH 3 ·H 2 O solution to be 0.04 - 0.16 mol / L; then add CuCl, and control the cuprous ion concentration in the NH 3 ·H 2 O solution to be 0.08 mol / L; stir the above mixed solution at a certain water bath temperature, and then introduce C 2 H 2 gas to gradually form a black solid precipitate; filter the black solid precipitate by suction, wash it with deionized water, and dry it under vacuum at room temperature to obtain the catalyst precursor B;

[0009] Step 2: Take the catalyst precursor B prepared above, add it to a quartz reaction tube, introduce H 2 gas, heat it at a heating rate of 1 °C / min to 150 °C, keep it for 3 h and then cool it to room temperature to obtain the acetylene selective hydrogenation catalyst, denoted as Cu-(C≡C) n -Cu(R150).

[0010] In step 1, the molar ratio of Cu 2+ / Cu + ranges from 0.5 to 2, and the optimal molar ratio of Cu 2+ / Cu + is 1;

[0011] In step 1, the concentration of NH 3 ·H 2 O solution is 2.5 - 10 wt%, and the optimal concentration of NH 3 ·H 2 O solution is 5 wt%;

[0012] In step 1, the certain water bath temperature is 0 - 50 °C, and the optimal temperature is 0 °C;

[0013] In step 1, introduce C 2 H2 The time for the gas is 0.5 - 2 h, and the optimal time is 1 h;

[0014] In step 1, the time for vacuum drying is more than 12 h.

[0015] Advantages of the present invention:

[0016] (1) High hydrogenation activity: The present catalyst synthesizes copper carbide Cu x C is the hydrogenation active phase, which greatly improves the low-temperature hydrogenation activity of the catalyst and at the same time maintains the high ethylene selectivity of the Cu-based catalyst. Under the conditions of 105 °C and 0.1 MPa H 2 , the acetylene conversion rate is 100%, the ethane selectivity is about 15%, and it remains stable within 100 hours.

[0017] (2) Mild preparation conditions: Synthesize the Cu-(C≡C) n -Cu catalyst precursor under low-temperature liquid phase. The whole method is simple to operate, with simple steps and mild preparation conditions. Cu-(C≡C) n -Cu will not decompose thermally during the treatment process.

[0018] (3) Cost advantage: Only inexpensive and readily available Cu salt precursors are used in the preparation process. The catalyst only contains Cu and C elements, and has great potential to replace noble metal catalysts. Description of the drawings

[0019] Figure 1 It is the scanning electron microscope characterization of Example 1.

[0020] Figure 2 It is the XRD characterization of Example 1 and Comparative Example 1.

[0021] Figure 3 It is the catalyst performance diagram of Example 1, Comparative Example 1 and Comparative Example 2.

[0022] Figure 4 It is the performance comparison of the Cu-(C≡C) 2+ / Cu + -Cu(R150) catalysts prepared in Example 2 at different Cu n ratios.

[0023] Figure 5 It is the performance comparison of the Cu-(C≡C) n -Cu(R150) catalysts in Example 3 at different temperatures.

[0024] Figure 6 It is the performance comparison of the Cu-(C≡C) n -Cu(R150) catalysts prepared in Example 4 at different reaction times.

[0025] Figure 7 Cu-(C≡C) prepared in Example 5 at different ammonia water concentrations n -Performance comparison of Cu(R150) catalysts. Detailed implementation manners

[0026] The following further illustrates the detailed implementation manners of the present invention in combination with the accompanying drawings and technical solutions.

[0027] Example 1

[0028] Dissolve 1.08 g of CuCl 2 in 100 mL of 5% NH 3 ·H 2 O solution, and then add 0.8 g of CuCl. Transfer the obtained mixed solution of CuCl 2 and CuCl to a 500 mL round-bottom flask, heat it to the synthesis temperature in a water bath, and introduce N 2 gas at 20 mL / min for 30 min under stirring to remove the dissolved air in the solution. Introduce C 2 H 2 gas (10 mL / min), and a black solid precipitate gradually forms in the solution. After reacting for a certain time, introduce N 2 again (20 mL / min) and purge for 20 min to remove the residual C 2 H 2 in the solution. Filter the black solid precipitate by suction, wash it with deionized water, and dry it under vacuum at room temperature to obtain the catalyst precursor B.

[0029] Weigh 0.1 g of the solid B prepared above, add it to a quartz reaction tube (inner diameter 10 mm), introduce 10 mL / min of H 2 , heat it to 150 °C at a heating rate of 1 °C / min, keep it for 3 h and then cool it to room temperature to obtain an acetylene selective hydrogenation catalyst, denoted as Cu-(C≡C) n -Cu(R150).

[0030] Comparative Example 1

[0031] Comparative Example 1 is a Cu single-component catalyst prepared from a Cu 2 O precursor, and specifically includes the following steps:

[0032] Prepare 100 mL of 0.01 mol / L CuCl 2 solution, denoted as solution C; prepare 100 mL of a mixed solution of 0.28 mol / L NaOH and 0.06 mol / L ascorbic acid, denoted as solution D. Under stirring at room temperature, slowly drop solution D into solution C, and orange-yellow Cu 2O precipitate. The obtained suspension was centrifuged, washed with deionized water, and vacuum dried at room temperature to obtain Cu 2 O sample, denoted as Cu 2 O.

[0033] Weigh 0.1 g of the above-prepared Cu 2 O intermediate and add it to a quartz reaction tube (inner diameter 10 mm) padded with quartz wool. Then, introduce 10 mL / min of H 2 , and heat it to 150 °C at a heating rate of 1 °C / min. After maintaining for 3 h, cool it to room temperature to obtain an acetylene selective hydrogenation catalyst, denoted as Cu(R150).

[0034] Perform XRD characterization on the Cu-(C≡C) n -Cu(R150) and Cu 2 O(R150). The results are as Figure 2 shown. Characteristic diffraction peaks attributed to Cu in Cu-(C≡C) n -Cu(R150) and Cu(R150) can be detected at 2θ = 43.4, 50.4, and 74.1°. Moreover, a characteristic diffraction peak attributed to the Cu n C crystal phase at 37.1° is only observed in Cu-(C≡C) x -Cu(R150).

[0035] Perform catalyst performance testing under reaction conditions of 105 °C and atmospheric pressure (reaction gas: 0.5 vol% CH 4 as the internal standard gas, 0.5 vol% C 2 H 2 , 89.0 vol% C 2 H 4 and 10.0 vol% H 2 ). Since a large amount of ethylene in the industrial simulation gas leads to easy error in the calculation of ethylene selectivity, ethane selectivity is used instead. From Figure 3 the comparison results of the performance of Cu-(C≡C) n -Cu(R150) and Cu 2 O(R150) catalysts, it can be seen that Cu-(C≡C) x with the Cu n C active phase has much higher low-temperature acetylene hydrogenation activity than Cu 2 O(R150).

[0036] Comparative Example 2

[0037] Weigh 4.83 g of Cu(NO 3 ) 2 ·3H 2O was dissolved in 200 mL of deionized water, placed in an ice-water mixture at 0 °C and stirred continuously for 30 min, then 50 mL of 2 mol / L NaOH solution was added dropwise, stirred at 0 °C for 30 min, filtered and washed, and vacuum dried at 30 °C for 12 h to obtain Cu(OH) 2 Solid samples.

[0038] Weigh 0.1g of Cu(OH) 2 Add it into a quartz reaction tube (10 mm in inner diameter) padded with quartz wool, and then introduce 30 mL / min of a mixed gas containing acetylene (0.5% C 2 H 2 / 99.5% Ar), heated to 120°C at a heating rate of 3°C / min, kept for 2h and cooled to room temperature. The obtained sample was recorded as Cu(OH) 2 (T120), then switch to 50 mL / min H 2 , purged at room temperature for 5 min, heated to 150 °C at a heating rate of 3 °C / min, maintained for 3 h and then cooled to room temperature. The obtained sample was recorded as Cu(OH) 2 (T120-R150).

[0039] from Figure 3 Cu-(C≡C) n -Cu(R150) and Cu(OH) 2 (T120-R150) Catalyst performance comparison results show that Cu-(C≡C) n -The low temperature hydrogenation activity of Cu(R150) is better than that of Cu(OH) 2 (T120-R150), Cu-(C≡C) n -Cu(R150) is an acetylene selective hydrogenation catalyst with industrial potential.

[0040] Example 2

[0041] This example is to study the Cu-(C≡C) prepared at different copper ion ratios n -Cu(R150) catalyst activity. Compared with Example 1, by adjusting CuCl 2 The amount of addition was prepared in Cu 2+ / Cu + = Cu-(C≡C) obtained under the conditions of 0.5, 1, 1.5, 2 n -Cu(R150), the rest of the preparation method and application conditions are the same as those in Example 1.

[0042] Experiments show that under normal pressure and reaction temperature of 110°C, there is no Cu 2+ or Cu 2+Less (Cu 2+ / Cu + = 0.5), the acetylene conversion rates are 29.0% and 95.4% respectively; Cu 2+ / Cu + = 1, the acetylene conversion rate of the catalyst can reach 100%. Further increasing the Cu 2+ content (Cu 2+ / Cu + = 2), the acetylene conversion rate drops to 64.8%.

[0043] This result shows that: (1) Too little Cu 2+ cannot fully participate in the polymerization reaction, resulting in insufficient production of Cu-(C≡C) n -Cu, reducing the production of the subsequent active phase Cu x C and decreasing the catalyst activity; (2) Too much Cu 2+ will form a large amount of cupric ammonia complex, reducing the ammonia concentration in the solution, decreasing the stability of the cuprous ammonia complex, resulting in a decrease in the production of Cu-(C≡C) n -Cu, reducing the production of the subsequent active phase Cu x C, and ultimately decreasing the catalyst activity.

[0044] Example 3

[0045] This example is to study the activity of Cu-(C≡C) n -Cu(R150) catalyst prepared at different temperatures. Compared with Example 1, by adjusting the preparation temperature, Cu-(C≡C) n -Cu(R150) obtained under the conditions of 0, 25, 50, 75 °C is prepared, and the remaining preparation methods and application conditions are the same as those in Example 1.

[0046] Experiments show that under normal pressure and a reaction temperature of 110 °C, the acetylene conversion rate is only 13.4% when prepared at -5 °C, and reaches 100.0% when prepared at 0 °C, but the ethane selectivity is relatively high (63.0%), and the obtained catalyst has high hydrogenation activity. The acetylene conversion rate is 100% when prepared at 25 °C, while the ethane selectivity is relatively low (12.7%). The acetylene conversion rate drops significantly when prepared at 50 °C and 75 °C, only 13.4% and 12.5% respectively.

[0047] This result shows that: (1) When the preparation temperature is lower than 0 °C, the ammonia aqueous solution freezes during the reaction process, and acetylene cannot react fully with the solution to form Cu-(C≡C) n -Cu, reducing the production of the subsequent active phase Cu x C and resulting in a decrease in catalytic activity; (2) When the temperature is too high, it will lead to Cu-(C≡C) n- Excessive polymerization of Cu produces polymers and fails to generate the active phase Cu during subsequent hydrogen reduction. x C, resulting in a significant decrease in the hydrogenation activity of the catalyst.

[0048] Example 4

[0049] This example studies the activity of the Cu-(C≡C) n -Cu(R150) catalyst prepared at different acetylene feeding times. Compared with Example 1, by adjusting the gas feeding time, Cu-(C≡C) n -Cu(R150) is prepared under the conditions of acetylene gas feeding times of 0.5, 1, 1.5, and 2 h, and the remaining preparation methods and application conditions are the same as those in Example 1.

[0050] Experiments show that under normal pressure and a reaction temperature of 105 °C, when the gas feeding time is short (0.5 h), the acetylene conversion rate is 99.1%. When the gas feeding time is 1 h, the acetylene conversion rate reaches 100.0%. When the gas feeding time is further increased (1.5 h and 2 h), the acetylene conversion rates are 98.4% and 94.3% respectively, but the ethane selectivities reach 113.0% and 95.3% respectively, showing a relatively serious over-hydrogenation phenomenon.

[0051] This result indicates that: (1) too short a gas feeding time will lead to insufficient formation of Cu-(C≡C) n -Cu, resulting in a decrease in the content of the Cu x C active phase and ultimately a decrease in the hydrogenation activity of the catalyst; (2) an extended gas feeding time will increase the yield of Cu-(C≡C) n -Cu, but due to the excessive content of Cu x C in the catalyst after hydrogen reduction and the relative decrease in the content of Cu, the ethylene selectivity of the catalyst decreases.

[0052] Example 5

[0053] This example studies the activity of the Cu-(C≡C) n -Cu(R150) catalyst prepared at different ammonia concentrations. Compared with Example 1, by adjusting the ammonia concentration, Cu-(C≡C) n -Cu(R150) is prepared in an environment with ammonia concentrations of 2.5, 5, 7.5, and 10 wt%, and the remaining preparation methods and application conditions are the same as those in Example 1.

[0054] Experiments show that under normal pressure and a reaction temperature of 105 °C, the acetylene conversion rate of the catalyst prepared at an ammonia concentration of 2.5 wt% is only 28.4%. When the ammonia concentration is 5 wt%, the acetylene conversion rate reaches 100.0%. When the ammonia concentration is increased to 7.5 wt% and 10 wt%, the acetylene conversion rates are 72.4% and 71.5% respectively.

[0055] This result indicates that: (1) If the ammonia water concentration is too low, Cu + cannot be fully complexed, resulting in a decrease in the amount of Cu-(C≡C) n -Cu formed, and ultimately leading to a decrease in the active phase Cu x C production and a decrease in catalyst activity; (2) If the ammonia water concentration is too high, a large amount of Cu 2+ will form stable cupric ammonia complexes and cannot fully participate in the reaction to form Cu-(C≡C) n -Cu, resulting in a decrease in catalyst activity.

[0056] In summary, the Cu-(C≡C) n -Cu(R150) provided by the present invention has significantly better reaction performance than ordinary Cu-based catalysts, which is specifically reflected in three aspects: simple and mild catalyst preparation conditions, high low-temperature hydrogenation activity, and high ethylene selectivity. This catalyst has high hydrogenation performance similar to noble metals, and the raw materials are cheap and easily available, providing an efficient catalyst to replace noble metals for the acetylene selective hydrogenation reaction.

Claims

1. A method for synthesizing acetylene selective hydrogenation catalyst by liquid phase method, characterized in that: The following steps are involved: Step 1: dissolving CuCl2 in NH3·H2O solution, controlling the copper ion concentration in the NH3·H2O solution to be 0.04-0.16 mol / L; then adding CuCl, controlling the cuprous ion concentration in the NH3·H2O solution to be 0.08 mol / L; stirring the mixed solution at a certain water bath temperature, then introducing C2H2 gas to gradually generate a black solid precipitate; filtering the black solid precipitate, washing with deionized water, and vacuum drying at room temperature to obtain a catalyst precursor B; Step 2: Take the catalyst precursor B prepared above, add it into a quartz reaction tube, introduce H2 gas, heat it to 150°C at a heating rate of 1°C / min, keep it for 3 hours and then cool it to room temperature to obtain an acetylene selective hydrogenation catalyst, denoted as Cu-(C≡C) n -Cu(R150).

2. The method according to claim 1, characterized in that In step 1, the Cu2+ / Cu+ molar ratio is 0.5-2.

3. The method according to claim 1, characterized in that In step 1, the Cu2+ / Cu+ molar ratio is 1.

4. The method according to claim 1, characterized in that: In step 1, the NH3·H2O solution is 2.5-10wt%.

5. The method according to claim 1, characterized in that In step 1, the NH3·H2O solution is 5 wt%.

6. The method according to claim 1, characterized in that In step 1, the water bath temperature is set at 0-50°C.

7. The method according to claim 1, characterized in that In step 1, the time for introducing C2H2 gas is 0.5-2h.

8. The method according to claim 1, characterized in that In step 1, the time for introducing C2H2 gas is 1 h.

9. The method according to claim 1, characterized in that: In step 1, the vacuum drying time is more than 12 hours.

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