Catalyst and method for preparing dimethyl oxalate and dimethyl carbonate from industrial tail gas

Abstract

The invention belongs to the technical field of synthesis of CI chemical and fine chemical intermediates, and particularly relates to a catalyst and a method for preparing dimethyl oxalate and dimethyl carbonate by taking CO-containing industrial tail gas and methyl nitrite as raw materials. The catalyst provided by the invention comprises a carrier, an active component and an auxiliary agent, wherein the carrier is a molecular sieve, the active component is noble metal palladium, the mass fraction of the noble metal palladium in the carrier is 0.1-0.5%, and the auxiliary agent is one or more of Cu, Zn and La, and the mass fraction of the auxiliary agent in the carrier is 0.1-2.0%. According to the catalyst, industrial tail gas such as steel mill tail gas and coal chemical tail gas can be directly utilized to react with methyl nitrite, the CO conversion rate is 80%-95%, the DMO selectivity is 40%-90%, the DMC selectivity is 10%-60%, and the total selectivity is larger than or equal to 99.5%.

Description

Technical Field

[0001] This invention belongs to the field of C1 chemical and fine chemical intermediate synthesis technology, specifically relating to a catalyst and method for preparing dimethyl oxalate and dimethyl carbonate using CO-containing industrial tail gas and methyl nitrite as raw materials. Background Technology

[0002] Dimethyl oxalate and dimethyl carbonate, as important green chemical intermediates, have long been a research hotspot in the field of C1 chemistry. Among them, the gas-phase catalytic coupling reaction of CO with methyl nitrite has become the mainstream route for preparing these ester compounds due to its advantages such as high atom economy and mild reaction conditions. The core of this reaction lies in the design and control of the catalyst. While several patents and research results have been published, significant technical bottlenecks still exist.

[0003] I. Inherent Defects of Traditional Chlorine-Containing Catalysts The traditional industrial catalysts used in this reaction generally contain chlorine. Chloride ions cause severe corrosion to stainless steel reactors in high-temperature environments. Operational data from a large coal chemical enterprise shows that the reactor flange seals are replaced an average of four times a year due to corrosion, increasing direct maintenance costs by more than 35%. Secondly, the active component Pd is rapidly deactivated due to the migration and loss of chlorine, and the catalyst life is usually less than 500 hours, requiring frequent regeneration.

[0004] II. Limitations of Carrier Performance and Product Selectivity Regulation Existing technologies struggle to meet the flexible industrial demands for product selectivity in carrier selection and processing: ① Limited and unoptimized carrier types: Oxide carriers such as Al2O3, SiO2, TiO2, and ZrO2 (e.g., patents CN 106431920A, CN 101190884B, and CN 106518675A) are commonly used. Their surfaces lack regular pores and controllable acid / base sites, making it impossible to significantly adjust the DMO and DMC ratios according to market demands. ② Inadequate acid / base treatment: Precise acid / base treatment of the carriers is lacking, resulting in a chaotic distribution of surface active sites (e.g., Lewis acid / base sites), hindering the targeted activation of key reaction steps (e.g., MN decomposition to generate methoxy groups and CO coupling to form esters). (Patent CN 110227451A).

[0005] 3. Poor adaptability to gas sources, dependent on high-purity CO Existing catalysts have stringent requirements for the purity of feed gas and cannot directly utilize inexpensive industrial tail gas: ① Industrial tail gas is highly sensitive to impurities: Impurities such as CO2 and H2 in steel plant tail gas (containing 10%~30% CO, 5%~15% CO2, and 55%~80% N2) and coal chemical tail gas (containing 20%~30% CO, 5%~10% H2, and 5%~10% CO2) compete for adsorption active sites, resulting in a 20%~30% decrease in CO conversion rate. ② Purification costs are high: To adapt to existing catalysts, industrial tail gas needs to be purified by pressure swing adsorption (removing CO2, H2, etc.), and the purification cost accounts for 15%~20% of the total production cost, significantly reducing the economic efficiency of the process.

[0006] In summary, developing a chlorine-free, flexibly adjustable product selectivity, and highly efficient catalytic system suitable for industrial exhaust gases has become a key issue that urgently needs to be addressed in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the technical problem to be solved by this invention is to provide a catalyst and method for preparing dimethyl oxalate and dimethyl carbonate using industrial tail gas.

[0008] The catalyst provided by the present invention comprises a support, an active component, and an additive; wherein the support is a molecular sieve, the active component is the noble metal palladium, which has a mass fraction of 0.1%-0.5% in the support, and the additive is one or more of Cu, Zn, and La, which has a mass fraction of 0.1%-2.0% in the support.

[0009] Furthermore, the carrier is selected from molecular sieves treated with acid or alkali. And the molecular sieve uses six specific types of molecular sieves, including LTA molecular sieve, 13X type molecular sieve, and calcium Y type molecular sieve (Ca... 2+ The above supports include exchangeability ≥80%, MOR zeolite, ZSM-5 molecular sieve, and SAPO-34 molecular sieve. These supports have regular channels (pore size 0.4~0.8nm), which match the molecular size of DMO (0.62nm) and DMC (0.58nm), and the active sites of the framework can be regulated by acid / base treatment.

[0010] The acid is selected from at least one of nitric acid, hydrochloric acid, citric acid, sulfuric acid, and acetic acid (chlorine-free or low-corrosive acid to avoid introducing impurities). Function: ① Removes extra-skeletal cations (such as Na+). + Fe 3+ ① Unblock the channels; ② Perform appropriate dealuminization to expose high Al content. 3+ The region enhances Lewis acid sites (promoting DMC formation).

[0011] The alkali is selected from at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, and ammonia. Its functions are: ① to etch the Si framework and optimize the pore size distribution (e.g., the mesoporous ratio of 13X molecular sieve increases by 10%~20% after alkali treatment); ② to generate oxygen defect sites and activate moderate-intensity Lewis base sites (promoting DMO formation); ③ to stabilize the framework structure and inhibit dealumination deactivation during the reaction.

[0012] The precursor of the auxiliary agent is one of nitrate, sulfate, or acetate; the Pd source is one of palladium acetate, palladium nitrate, or palladium acetylacetonate. Pd (active component) and the auxiliary agent are loaded using an equal-volume impregnation method, with a chlorine-free metal source to avoid introducing chlorine.

[0013] The preparation process of the above catalyst is as follows: The carrier is immersed in a 0.5M~0.8M acid or alkali solution for 2~12h at a temperature of 25~80℃, washed with deionized water until neutral, dried at 120℃ for 2h after washing, and calcined in air at 500~600℃ for 4~6h to obtain the acid / alkali modified carrier. The additive and Pd source are dissolved in deionized water, mixed with the modified support until the solution is completely adsorbed, dried at 120℃ for 2 hours, calcined in air at 400-500℃ for 3-5 hours, and then reduced at 200-300℃ for 2-4 hours in a mixed H2 / N2 atmosphere (H2 volume fraction 5%-20%) to convert the metal oxide into an active state (e.g., Pd). 0 / Pd 2+ The target catalyst is obtained by ( ).

[0014] H2-TPR spectrum of the catalyst in Example 1 ( Figure 3 A unique reduction peak appeared in the 200–250℃ range. This peak position is significantly different from that of Pd alone. 2+ (100–150℃) with Cu 2+ The reduction temperature is 250–350℃. This phenomenon originates from the interaction between the two to form a nanoscale Pd-Cu alloy, thereby producing a synergistic reduction effect. The inventors speculate that this active structure can preferentially adsorb and activate CO and MN molecules, thus endowing the catalyst with excellent selectivity and anti-interference ability in complex industrial exhaust gases.

[0015] A method for preparing dimethyl oxalate and dimethyl carbonate from industrial tail gas using the catalyst provided by this invention includes the following factors: (1) Composition of raw gas: CO source is selected from industrial tail gas, and the volume fraction of CO in the raw gas is 5%~20%; methyl nitrite: volume fraction 10%~30%; balance gas: nitrogen; (2) Reaction conditions: reaction temperature 100~130℃; reaction pressure 0.1~0.5MPa absolute pressure; gas space velocity 3000~6000h -1 ; (3) Product selectivity regulation: By adjusting the type and concentration of acid / base in the treatment carrier, the selective and directional regulation of the product can be achieved. Alkali treatment generates more moderate-strength Lewis base sites (skeleton oxygen vacancies), promoting the synergistic effect of CO coupling and MN decomposition, with DMO and DMC selectivities of 40%–60% and 40%–60%, respectively. Acid treatment is used to expose more Lewis acid sites (high Al). 3+ (Region), to enhance the CO unimolecular insertion reaction, the selectivity of DMO and DMC is 80%~90% and 10%~20%, respectively.

[0016] In the above-mentioned method for preparing dimethyl oxalate and dimethyl carbonate using industrial tail gas, the industrial tail gas is steel plant tail gas, which contains 10%~30% CO, 5%~15% CO2 and 55%~80% N2 by volume; or coal chemical tail gas, which contains 0%~30% CO2, 5%~10% H2 and 5%~10% CO2 by volume.

[0017] In the above method for preparing dimethyl oxalate and dimethyl carbonate using industrial tail gas, the concentration of the alkali used to treat the carrier is 0.5~0.8 mol / L, and the concentration of the acid used to treat the carrier is 0.5~0.8 mol / L.

[0018] Compared with the prior art, the present invention has the following significant advantages: The chlorine-free system solves the problems of corrosion and deactivation: It adopts chlorine-free precursors (copper nitrate, palladium acetate, etc.) to completely eliminate chlorine. The equipment can be directly made of 316 stainless steel, and the catalyst life is extended to more than 1500 hours (activity decrease ≤5%).

[0019] Product selectivity can be flexibly adjusted: DMO (40%~90%) and DMC (10%~60%) can be directionally adjusted through acid / alkali treatment to meet the needs of different downstream products.

[0020] Adaptable to industrial exhaust gas, reducing raw material costs: It can directly utilize exhaust gas from steel plants and coal chemical plants (no purification required), maintaining a CO conversion rate of 80%~95% and reducing raw material costs by 15%~20%; High activity and selectivity: CO conversion rate 80%~95%, total selectivity ≥99.5%, by-products (such as MF, CO2, methanol) <0.5%, and atom utilization rate close to 100%. Attached Figure Description

[0021] Figure 1 Transmission electron microscope image of the catalyst prepared in Example 1.

[0022] Figure 2 XRD pattern of the catalyst prepared in Example 1.

[0023] Figure 3 H2-TPR spectrum of the catalyst prepared in Example 1. Detailed Implementation Example

[0024] (1) Carrier treatment: Take LTA molecular sieve, soak it in 0.6M nitric acid solution at 60℃ for 8h, wash it with deionized water until neutral, dry it at 120℃ for 2h, and calcine it at 550℃ for 5h to obtain acid-modified LTA carrier.

[0025] (2) Catalyst preparation: Copper nitrate and palladium acetate were dissolved in deionized water with a Cu loading of 1% and a Pd loading of 0.5% (Pd / Cu mass ratio 1:2), and impregnated in the treated LTA support with equal volume. The mixture was dried at 120℃ for 2h and calcined in air at 450℃ for 4h. The catalyst Pd-Cu / LTA was obtained by reduction at 250℃ for 3h in a 10% H2 / N2 atmosphere.

[0026] (3) Reaction evaluation: The feed gas was steel plant tail gas (CO 20%, CO2 10%, N2 70%), which was mixed with MN and N2 in a specific volume ratio to make the volume fractions of CO and MN in the feed gas 15% and 30%, respectively; Reaction conditions: temperature 120℃, pressure 0.3MPa, space velocity 4500h -1 .

[0027] (4) Results: After the reaction stabilized, the CO conversion rate was 95%, the DMO selectivity was 80.5%, the DMC selectivity was 19.2%, and the total selectivity was 99.7%. After continuous operation for 1000 h, the CO conversion rate dropped to 90%, and the selectivity did not change significantly (DMO 83.0%, DMC 16.6%). Example

[0028] (1) Carrier treatment: Take 13X molecular sieve, soak it in 0.5M potassium hydroxide solution at 20℃ for 12h, wash it, dry it at 120℃ for 2h, and calcine it at 500℃ for 6h to obtain alkali-modified 13X carrier.

[0029] (2) Catalyst preparation: Zn loading 2.0%, Pd loading 0.4% (Pd / Zn mass ratio 1:5), zinc sulfate and palladium nitrate were dissolved in deionized water, calcined in air at 400℃ for 5h, and then calcined at 200℃ for 4h in H2 / N2 mixed atmosphere (H2 volume fraction 5%) to obtain catalyst Pd-Na / 13X.

[0030] (3) Reaction evaluation: The feed gas is coal chemical tail gas (CO 25%, H2 8%, CO2 7%, N2 60%). After mixing with MN and N2 in a specific volume ratio, the volume fractions of CO and MN in the feed gas are 5% and 15%, respectively. Reaction conditions: temperature 100℃, pressure 0.5MPa, space velocity 6000h -1 .

[0031] (4) Results: CO conversion rate 85%, DMO selectivity 40.2%, DMC selectivity 59.5%, total selectivity 99.7%. Example

[0032] (1) Carrier treatment: Take calcium Y-type molecular sieve (Ca 2+ The calcium Y-type carrier with an exchangeability of 85% was soaked in 0.7M nitric acid solution at 80℃ for 2 hours, washed, dried at 120℃ for 2 hours, and calcined at 550℃ for 5 hours to obtain the alkali-modified calcium Y-type carrier.

[0033] (2) Catalyst preparation: Zn loading 0.5% and Pd loading 0.5% (Pd / Zn mass ratio 1:1), zinc acetate and palladium acetylacetone were dissolved in deionized water, calcined in air at 500℃ for 3h, and reduced at 300℃ for 2h in H2 / N2 mixed atmosphere (H2 volume fraction 20%) to obtain catalyst Pd-Zn / calcium Y.

[0034] (3) Reaction evaluation: The feed gas was steel plant tail gas (CO 30%, CO2 15%, N2 55%), which was mixed with MN and N2 in a specific volume ratio to make the volume fractions of CO and MN in the feed gas 20% and 20%, respectively; Reaction conditions: temperature 130℃, pressure 0.1MPa, space velocity 3000h -1 .

[0035] (4) Results: CO conversion rate 80%, DMO selectivity 85.5%, DMC selectivity 14.2%, total selectivity 99.7%. Example

[0036] (1) Carrier treatment: Take MOR zeolite molecular sieve, soak it in 0.5M sodium hydroxide solution at 40℃ for 10h, wash it, dry it at 120℃ for 2h, and calcine it at 600℃ for 4h to obtain alkali-modified MOR carrier.

[0037] (2) Catalyst preparation: La loading 1.5%, Pd loading 0.3% (Pd / La mass ratio 1:5), lanthanum nitrate and palladium acetate were dissolved in deionized water, calcined in air at 450℃ for 4h, and reduced at 250℃ for 3h in H2 / N2 mixed atmosphere (H2 volume fraction 15%) to obtain catalyst Pd-Ca / MOR.

[0038] (3) Reaction evaluation: The feed gas is steel plant tail gas (CO 30%, CO2 15%, N2 55%), which is mixed with MN and N2 in a specific volume ratio to make the volume fractions of CO and MN in the feed gas 10% and 25%, respectively; Reaction conditions: temperature 125℃, pressure 0.2MPa, space velocity 5000h -1 .

[0039] (4) Results: CO conversion rate 91%, DMO selectivity 49.6%, DMC selectivity 50.2%, total selectivity 99.8%. Example

[0040] (1) Carrier treatment: Take SAPO-34 molecular sieve, soak it in 0.8M acetic acid solution at 50℃ for 8h, dry it at 120℃ for 2h, and calcine it at 550℃ for 5h.

[0041] (2) Catalyst preparation: 2% La loading, 0.1% Pd loading (Pd / La mass ratio 1:20), the metal source is lanthanum nitrate and palladium nitrate, the remaining steps are the same as in Example 1, and the catalyst Pd-La / SAPO-34 is obtained.

[0042] (3) Reaction evaluation: Three sets of raw material gases were set up: Group 1: Steel plant tail gas (CO 10%, CO2 5%, N2 85%) is mixed with MN and N2 in a specific volume ratio to make the volume fractions of CO and MN in the raw gas 5% and 20%, respectively. Group 2: Coal chemical tail gas (CO 30%, H2 5%, CO2 5%, N2 60%) is mixed with MN and N2 in a specific volume ratio so that the volume fractions of CO and MN in the raw gas are 15% and 25%, respectively. Reaction conditions: temperature 115℃, pressure 0.4MPa, space velocity 3500h⁻¹ -1 .

[0043] (4) Results: Group Raw material gas type CO volume fraction CO conversion rate DMO Selectivity DMC Selectivity Total selectivity Group 1 steel plant exhaust gas 5% 97% 82.2% 17.7% 99.9% Group 2 coal chemical tail gas 15% 82% 88.2% 11.4% 99.6% Comparative Example 1: (1) Carrier treatment: referring to the method of Chinese patent CN 110227451A, 5% ZrO2-A12O3 composite oxide was used as the carrier, calcined at 550℃ for 7 hours, and then cooled to room temperature.

[0044] (2) Catalyst preparation: Magnesium nitrate was used as an auxiliary agent with a loading of 1.2%; PdCl2 was used as the precursor of Pd with a loading of 0.55% Pd; after impregnation, drying (120℃, 5h), calcination (200℃, 4h), and reduction at 180℃ for 4h in a 10% CO / N2 atmosphere, a chlorine-containing catalyst was obtained.

[0045] (3) Reaction evaluation: methyl nitrite concentration 15%, carbon monoxide concentration 40%, reaction conditions: temperature 115℃, space velocity 3000h -1 .

[0046] (4) Results: CO conversion rate 35%, DMO selectivity 94.8%, DMC selectivity 5%, total selectivity 99.8%.

[0047] (1) Catalyst preparation: The modified LTA support of Example 1 was used, with only 0.5% Pd loaded (without additives), and the metal source was palladium acetate. The remaining steps were the same as in Example 1 to obtain the Pd / LTA catalyst.

[0048] (2) Reaction evaluation: The raw material gas and reaction conditions are the same as in Example 1.

[0049] (3) Results: CO conversion rate 75%, DMO selectivity 30%, DMC selectivity 5%, total selectivity 35%; the main byproducts were MF (selectivity 40%), CO2 (selectivity 20%) and methanol (selectivity 5%). Due to the lack of auxiliary agents, MN could not be effectively activated to decompose and generate methoxy intermediates.

[0050] (1) Catalyst preparation: Take 13X molecular sieve that has not been treated with acid / alkali, load Cu 1.0% and Pd 0.5% (chlorine-free precursor), and follow the same steps as in Example 1 to obtain catalyst Pd-Cu / 13X (untreated).

[0051] (2) Reaction evaluation: The raw material gas and reaction conditions are the same as in Example 2.

[0052] (3) Results: CO conversion rate 68%, DMO selectivity 35%, DMC selectivity 25%, total selectivity 60%; byproducts included MF (selectivity 20%), methanol (10%), CO2 (8%), and dimethyl ether (2%). The reaction pathway was disordered due to carrier pore blockage (no acid treatment) or disordered active sites (no alkali treatment).

[0053] (1) Catalyst preparation: The modified LTA support of Example 1 was used, with Cu 3.0% (exceeding the range of 0.1%~2% in claim 3) and Pd 0.5%. The metal source was copper nitrate and palladium acetate. The remaining steps were the same as in Example 1.

[0054] (2) Reaction evaluation: The raw material gas and reaction conditions are the same as in Example 1.

[0055] (3) Results: CO conversion rate was 75%, DMO selectivity was 20%, DMC selectivity was 10%, and total selectivity was 30%. The main byproduct was MF (selectivity 55%). Due to excessive Cu loading, metal agglomeration occurred, the utilization rate of active sites decreased, and MN was excessively decomposed to generate MF.

[0056] The preferred embodiments disclosed above are merely illustrative of this application. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. These embodiments have been selected and specifically described in this specification to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to better understand and utilize this application. This application is limited only by the claims and their full scope and equivalents.

[0057] In the description of this specification, references to terms such as "example" or "some examples" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0058] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A catalyst for preparing dimethyl oxalate and dimethyl carbonate from industrial tail gas, the catalyst comprising a support, an active component, and an additive; characterized in that, The carrier is a molecular sieve, the active component is the noble metal palladium, which has a mass fraction of 0.1%-0.5% in the carrier, and the auxiliary agent is one or more of Cu, Zn and La, which has a mass fraction of 0.1%-2.0% in the carrier.

2. The catalyst according to claim 1, characterized in that, The carrier is selected from molecular sieves that have been treated with acid or alkali, and the molecular sieve is selected from LTA molecular sieve, 13X type molecular sieve, calcium Y type molecular sieve, MOR zeolite, ZSM-5 molecular sieve or SAPO-34 molecular sieve.

3. The catalyst according to claim 2, characterized in that, The acid is selected from at least one of nitric acid, hydrochloric acid, citric acid, sulfuric acid, and acetic acid, and the base is selected from at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, and ammonia.

4. The catalyst according to claim 2, characterized in that, The precursor of the auxiliary agent is one of nitrate, sulfate, or acetate; the Pd source is one of palladium acetate, palladium nitrate, or palladium acetylacetonate.

5. The method for preparing the catalyst according to claim 1, characterized in that: The carrier is immersed in a 0.5M~0.8M acid or alkali solution for 2~12h at a temperature of 25~80℃, washed with deionized water until neutral, dried at 120℃ for 2h after washing, and calcined in air at 500~600℃ for 4~6h to obtain the acid / alkali modified carrier. The additive and Pd source are dissolved in deionized water, mixed with the modified support until the solution is completely adsorbed, dried at 120℃ for 2 hours, calcined in air at 400~500℃ for 3~5 hours, and reduced at 200~300℃ for 2~4 hours in a H2 / N2 mixed atmosphere to convert the metal oxide into an active state, thus obtaining the target catalyst.

6. A method for preparing dimethyl oxalate and dimethyl carbonate using the catalyst according to any one of claims 1-4, characterized in that, Including the following factors: (1) Composition of raw gas: CO source is selected from industrial tail gas, and the volume fraction of CO in the raw gas is 5%~20%; methyl nitrite: volume fraction 10%~30%; balance gas: nitrogen; (2) Reaction conditions: reaction temperature 100~130℃; reaction pressure 0.1~0.5MPa absolute pressure; gas space velocity 3000~6000h -1 ; (3) By adjusting the type and concentration of acid / base in the treatment carrier, the selective and directional regulation of the product can be achieved; Alkali treatment generates more moderate-strength Lewis base sites, promoting the synergistic effect of CO coupling and MN decomposition, with DMO and DMC selectivities of 40%–60% and 40%–60%, respectively. Acid treatment was used to expose more Lewis acid sites, which enhanced the CO unimolecular insertion reaction. The selectivity of DMO and DMC was 80%~90% and 10%~20%, respectively.

7. The method according to claim 6, characterized in that, The industrial exhaust gas is steel plant exhaust gas, which contains 10%~30% CO, 5%~15% CO2, and 55%~80% N2 by volume; or coal chemical exhaust gas, which contains 20%~30% CO, 5%~10% H2, and 5%~10% CO2 by volume.

8. The method according to claim 6, characterized in that, The alkaline concentration of the treatment carrier is 0.5~0.8 mol / L, and the acid concentration of the treatment carrier is 0.5~0.8 mol / L.

Images