CN105903466A - Catalyst for dimethyl oxalate synthesis and preparation method of catalyst for dimethyl oxalate synthesis - Google Patents

Abstract

The invention discloses a catalyst for synthesizing dimethyl oxalate and a preparation method thereof. The catalyst uses palladium as the active component and a-Al ₂ O ₃ as the carrier, wherein the active component Pd has a mass fraction of 0.01-0.5%; there is a small amount of residual Zn, and its mass fraction is 0.01-0.08. It is prepared by dipping-roasting-pickling method, and the auxiliary agent Zn is introduced in the preparation process. The addition of the auxiliary agent can make the active components more dispersed on the surface of the carrier, and at the same time reduce the amount of active components. Then, most of the additives are washed away by pickling treatment, further changing the spatial distribution structure of the active components of the catalyst, and optimizing the performance of the catalyst to a greater extent. Experiments show that the catalyst prepared by the present invention shows better catalytic activity in CO gas-phase oxidative coupling synthesis of dimethyl oxalate, its CO single-pass conversion rate is as high as 63%, and the selectivity of dimethyl oxalate is greater than 96%. The space-time yield of methyl ester is greater than 1100g. L ^-1 . h ^‑1 (the airspeed is 3000h ^‑1 ).

Description

Catalyst for synthesizing dimethyl oxalate and preparation method thereof

technical field

The invention relates to a method for preparing a catalyst for oxidative coupling of carbon monoxide to synthesize dimethyl oxalate, mainly including related technologies of Pd/Al ₂ O ₃ loaded catalyst prepared by an acid washing method.

technical background

Dimethyl oxalate is an important chemical raw material, a solvent, extractant and intermediate for various important fine chemical dyes and medicines. In particular, ethylene glycol, an extremely important chemical raw material, is prepared under the action of a hydrogenation catalyst.

According to the resource situation of more coal and less oil in our country, the route of producing dimethyl oxalate and ethylene glycol by using the synthetic method of coal chemical industry is gradually carried out in an all-round way in the country. The dependence and the pressure of insufficient supply of ethylene. The dimethyl oxalate synthesis process in the "coal to ethylene glycol" route realizes the transformation of inorganic C ₁ (carbon monoxide) to organic C ₂ (dimethyl oxalate), which is an atom-economical reaction, and the synthesis catalyst is in It plays a key role in the whole reaction, so the research on the catalyst for the synthesis of dimethyl oxalate is of great significance.

At present, domestic and foreign reports on the preparation method of CO gas-phase oxidative coupling synthesis of dimethyl oxalate catalysts are constantly emerging. Patent CN102962060A discloses a kind of adopting precious metal palladium supported catalyst, obtains optimal catalyst performance by changing the kind of auxiliary agent and the content of auxiliary agent, wherein the loading of palladium is 1% (by carrier weight), CO and The space-time yield when methyl nitrite is synthesized into dimethyl oxalate is 977g. L ^-1 . h ^-1 (the space velocity condition is 3000h ^-1 ), the catalyst shows good stability in the lifetime test. Other relevant patents have also reported different catalyst preparation methods and improved catalyst selectivity and space-time yield by adding different additives, but these catalysts mainly have the following two problems:

1. The loaded amount of noble metal Pd (in terms of carrier mass) is relatively high, such as the Pd-La-Re/a _{- Al2O3} catalyst Pd loaded amount reported by patent CN101791555A reaches 1.5%; the Pd-Zr/ The content of Pd in the a- _Al2O3 catalyst reaches ₁ %. Pd is a noble metal with limited reserves and high price. The high loading of Pd leads to high cost of the catalyst, which is not conducive to the economics of industrialization.

2. The space-time yield of CO gas-phase oxidative coupling to synthesize dimethyl oxalate product is low, such as the catalyst space-time yield reported in patent CN1148589 is 450g. L ^-1 . About h ^-1 , the space-time yield of Pd-Mo/Al ₂ O ₃ and Pd-Ni/Al ₂ O ₃ catalysts reported in the patent US4384433 is only 400g. L ^-1 . h ^-1 .

Therefore, how to prepare a suitable catalyst for CO gas-phase oxidative coupling synthesis of dimethyl oxalate is of great importance to further improve the space-time yield of dimethyl oxalate, reduce the loading of noble metal Pd and further optimize the composition of the product. meaning.

Contents of the invention

The object of the present invention is to provide a kind of catalyst and preparation method thereof for synthesizing dimethyl oxalate, the catalyst provided by the invention has better catalytic performance in CO gas-phase oxidative coupling synthesizing dimethyl oxalate reaction.

The catalyst for synthesizing dimethyl oxalate provided by the present invention uses palladium as an active component and a _{- Al2O3} as a carrier, wherein the mass fraction of the active component Pd is 0.01-0.5%, preferably The fraction is 0.2-0.4%; the specific surface area of the carrier a-Al ₂ O ₃ is 1-10m ² /g, the specific pore volume is 0.01-1cm ³ /g, and the average pore diameter is 5-30nm; there is a small amount of residual additives , and its mass fraction is 0.01-0.08%.

The preparation method of catalyst of the present invention, concrete steps are as follows:

A. Soluble palladium salt and zinc salt are dissolved in the solution to make impregnating liquid, and palladium ion concentration is 0.001-0.025mol/L in the impregnating liquid, and zinc ion concentration is 0.002-0.1mol/L; Described solution is hydrochloric acid, nitric acid , acetic acid or sulfuric acid solution, and the pH of the solution is 0-6.

The soluble palladium salt is any one or both of palladium acetate, palladium chloride, palladium nitrate, palladium ammonium chlorate or palladium acetylacetonate; the soluble zinc salt is zinc nitrate, zinc chloride, zinc acetate or zinc sulfate any of the.

B. Add the a-Al ₂ O ₃ carrier to the impregnation solution in step A, let it stand for 1-2 days, filter off the solution, and dry at 70-80°C for 12-24h; then fully dry at 140-150°C ; and then baked in a muffle furnace at 250-300°C for 5-6h; the amount of a-Al ₂ O ₃ added is determined according to the concentration of palladium ions in the impregnation solution and the mass fraction of palladium in the prepared catalyst.

The a-Al ₂ O ₃ carrier has a specific surface area of 1-10m ² /g, a specific pore volume of 0.01-1 cm ³ /g, and an average pore diameter of 5-30nm.

C. reducing the dried catalyst precursor in a reducing atmosphere for 2-10 hours, the reduction temperature is 200-600°C, the reducing gas space velocity is 500-6000h ^-1 , and then cooled to room temperature in a reducing atmosphere to obtain a catalyst, Wherein the mass fraction of Pd is 0.01-0.5%, and the mass fraction of zinc is 0.1-0.6%; the reducing gas is pure hydrogen or carbon monoxide-nitrogen mixed gas.

D Place the catalyst in step C in an acidic solution with a concentration of 1-5% and soak for 1-4 hours, then wash the catalyst with deionized water at 60-80°C until it is neutral, and then put it in an oven at 140-150°C to fully After drying, the catalyst after zinc removal is obtained, wherein the mass fraction of Pd is 0.01-0.5%, and the mass fraction of zinc is 0.01-0.08%. The solution is one of hydrochloric acid, nitric acid, acetic acid or sulfuric acid solution.

The present invention introduces auxiliary agents in the preparation process, and the addition of the auxiliary agents can make the active components more dispersed on the surface of the carrier, while reducing the dosage of the active components. Then, most of the additives are washed away by pickling, which further changes the spatial distribution structure of the active components of the catalyst and optimizes the performance of the catalyst to a greater extent.

Test the catalytic performance of the catalyst obtained above for CO gas-phase oxidative coupling synthesis of dimethyl oxalate: the catalyst is packed in a fixed-bed reactor (test device), the amount of catalyst is 2ml, raw gas CO and methyl nitrite The flow ratio is 1.5, the gas phase space velocity is 3000h ^-1 , the raw material gas is contacted with the catalyst under the condition of normal pressure and 140°C, and the dimethyl oxalate product is obtained. Feed gas and products are monitored and analyzed online by gas chromatography. The results showed that the catalytic performance of the acid-treated catalyst samples was significantly better than that of the untreated catalysts.

Fig. 1～6 has provided the TEM photograph situation of each embodiment and comparative example catalyst sample, as seen from the figure, the size of the Pd particle of the catalyst after acid treatment is obviously smaller than the catalyst without acid treatment, and the catalyst of acid treatment The Pd dispersion is more uniform.

Figure 7 shows the composition of the product after the catalytic reaction and the ratio of each component. The single-pass conversion rate of CO, selectivity of oxalate and space-time yield of oxalate can be calculated through the change of each component before and after the reaction.

Compared with the prior art, the present invention has the following remarkable effects:

1. Compared with the traditional impregnation method, the catalyst of the present invention introduces the auxiliary agent due to the preparation process, and then removes the auxiliary agent by pickling, so that the catalyst with lower loading of noble metal palladium and higher catalytic performance is prepared.

2. The catalyst prepared by the catalyst of the present invention has a CO single-pass conversion rate of up to 63%, a selectivity of dimethyl oxalate greater than 96%, and a space-time yield of dimethyl oxalate greater than 1100g in the gas-phase oxidative coupling of CO to synthesize dimethyl oxalate. ﹒ L ^-1 . h ^-1 (airspeed is 3000h ^-1 ). Much higher than similar catalysts prepared by the traditional impregnation method.

Description of drawings

Figure 1 is a transmission electron micrograph of the catalyst prepared in Example 1.

FIG. 2 is a transmission electron micrograph of the catalyst prepared in Comparative Example 1.

3 is a transmission electron micrograph of the catalyst prepared in Example 2.

FIG. 4 is a transmission electron micrograph of the catalyst prepared in Comparative Example 2.

FIG. 5 is a transmission electron micrograph of the catalyst prepared in Example 3.

FIG. 6 is a transmission electron micrograph of the catalyst prepared in Comparative Example 3.

Fig. 7 is the chromatogram of the catalyst of Example 1 in the test example.

Specific implementation examples

Example 1:

1. Preparation steps: 0.075g of palladium chloride and 0.48g of auxiliary agent zinc nitrate are dissolved in a hydrochloric acid buffer solution with a volume of 15ml at pH=1.3, and 15g of alumina balls (diameter 2mm, rotating disc type rolling) (obtained by ball method) was added to the buffer solution; firstly, let it stand at 60°C for 12h, put it into an oven and dry it at 80°C for 24h, fully dry it in the oven at 150°C, and finally put it into a muffle furnace and bake it at 300°C for 6h; The catalyst precursor was reduced at 200° C. for 6 h in a reducing gas (nitrogen-carbon monoxide mixed gas) atmosphere, wherein the space velocity of the reducing gas was 3000 h ⁻¹ . Through the ICP test, the content of Pd is 0.29% of the weight of the carrier, and the content of zinc as an auxiliary agent is 0.57% of the weight of the carrier.

2. pickling step: the gained Pd-Zn/Al ₂ O ₃ catalyst is placed in a volume of 15ml and soaked in a 1% hydrochloric acid solution with a mass fraction of 2h, and then the catalyst is washed 8 times with deionized water at 60°C. At intervals of 3 hours, until the pH test paper shows neutrality, put it into an oven at 150°C to fully dry to obtain the desired catalyst. Through the ICP test, the content of Pd is 0.28% of the weight of the carrier, and the content of zinc as an auxiliary agent is 0.04% of the weight of the carrier.

Comparative example 1:

Catalyst prepared according to "step one" in Example 1.

Example 2:

1. Preparation steps: 0.098g of palladium nitrate and 0.48g of auxiliary zinc nitrate are dissolved in 15ml of nitric acid buffer solution with pH=1.2, and 15g of alumina balls (diameter 2mm, rotating disc rolling ball method) roasted at 1300°C (obtained) was added to the buffer solution; first, let it stand at 60°C for 12h, put it into an oven and dry it at 80°C for 24h, fully dry it in the oven at 150°C, and finally put it into a muffle furnace for 300°C roasting for 6h; the dried catalyst The precursor was reduced at 200° C. for 6 h in a reducing gas (nitrogen-carbon monoxide mixed gas) atmosphere, wherein the space velocity of the reducing gas was 3000 h ⁻¹ . Through the ICP test, the content of Pd is 0.29% of the weight of the carrier, and the content of zinc as an auxiliary agent is 0.57% of the weight of the carrier.

2. pickling step: the gained Pd-Zn/Al ₂ O ₃ catalyst is placed in a volume of 15ml and soaked in a nitric acid solution with a mass fraction of 1.5% for 2h, and then the catalyst is washed 8 times with deionized water at 60°C, each The time interval is 3 hours, until the pH test paper shows neutrality, and then placed in an oven at 150°C to fully dry to obtain the required Pd/Al ₂ O ₃ catalyst. Through the ICP test, the content of Pd is 0.29% of the weight of the carrier, and the content of zinc as an auxiliary agent is 0.05% of the weight of the carrier.

Comparative example 2:

Catalyst prepared according to "step one" in Example 2.

Example 3:

1. Preparation steps: Dissolve 0.095g of palladium acetate and 0.48g of zinc nitrate as an auxiliary agent in 15ml of acetic acid buffer at pH = 1, and place 15g of alumina balls (diameter 2mm, rotating disk type rolling ball) that have been roasted at 1300°C method) was added to the buffer solution; first, let it stand at 60°C for 12h, put it in an oven and dry it at 80°C for 24h, then fully dry it in the oven at 150°C, and finally put it in a muffle furnace and roast it at 300°C for 6h; the dried The catalyst precursor was reduced at 200° C. for 6 h in a reducing gas (nitrogen-carbon monoxide mixed gas) atmosphere, wherein the space velocity of the reducing gas was 3000 h ⁻¹ . Through the ICP test, the content of Pd is 0.29% of the weight of the carrier, and the content of zinc as an auxiliary agent is 0.57% of the weight of the carrier.

2. pickling step: place the gained Pd-Zn/Al ₂ O ₃ catalyst in a volume of 15ml and soak it in an acetic acid solution with a mass fraction of 2.0% for 2h, then wash the catalyst 8 times with deionized water at 60°C, each The time interval is 3 hours, until the pH test paper shows neutrality, and then placed in an oven at 150°C to fully dry to obtain the required Pd/Al ₂ O ₃ catalyst. Through the ICP test, the content of Pd is 0.29% of the weight of the carrier, and the content of zinc as an auxiliary agent is 0.06% of the weight of the carrier.

Comparative example 3:

Catalyst prepared according to "step one" in Example 3.

Test case:

The catalyst is packed in a fixed-bed reaction device for testing, the amount of catalyst is 2ml, the flow ratio of raw material gas CO and methyl nitrite is 1.5, the gas phase space velocity is 3000h ^-1 , the raw material gas is at a reaction pressure of 0.1Mpa, 140℃ Contact with the catalyst under the conditions to obtain the dimethyl oxalate product. On-line monitoring and analysis of product and feed gas composition changes by gas chromatography, and calculation of catalyst performance indicators such as CO single-pass conversion rate, oxalate selectivity, and oxalate space-time yield.

The catalyst performance of embodiment 1, comparative example 1, embodiment 2, comparative example 2, embodiment 3 and comparative example 3 is evaluated respectively according to the above-mentioned method, and the results are shown in Table 1

Table 1: Catalytic performance of example catalysts in CO gas-phase oxidative coupling reaction to produce dimethyl oxalate

From Table 1, after pickling treatment, there is a slight loss of precious metal Pd, and the additive Zn is basically removed. Compared with the catalyst without acid washing treatment, the catalyst of the present invention exhibits better catalytic activity in CO gas-phase oxidative coupling synthesis of dimethyl oxalate.

Claims (3)

1. a catalyst for synthesizing dimethyl oxalate, this catalyst is to be active component with palladium, a-Al ₂ O ₃ is carrier, wherein the massfraction of active component Pd is 0.01-0.5%; Carrier a-Al ₂ The specific surface area of O ₃ is 1-10m ² /g, the specific pore volume is 0.01-1cm ³ /g, and the average pore diameter is 5-30nm; there is a small amount of residual Zn in it, and its mass fraction is 0.01-0.08%. 2. the synthetic dimethyl oxalate catalyst according to claim 1 is characterized in that the massfraction of active component Pd is 0.2-0.4% in the catalyst. 3. a method for preparing the synthetic dimethyl oxalate catalyst described in claim 1, concrete steps are as follows: A. Soluble palladium salt and zinc salt are dissolved in the solution to make impregnating solution, palladium ion concentration is 0.001-0.025mol/L in the impregnating solution, and zinc ion concentration is 0.002-0.1mol/L; Described solution is hydrochloric acid, nitric acid , acetic acid or sulfuric acid solution, and the pH of the solution is 0-6; The soluble palladium salt is any one or both of palladium acetate, palladium chloride, palladium nitrate, palladium ammonium chlorate or palladium acetylacetonate; the soluble zinc salt is zinc nitrate, zinc chloride, zinc acetate or zinc sulfate any of the B. Add the a-Al ₂ O ₃ carrier to the impregnation solution in step A, let it stand for 1-2 days, filter off the solution, and dry at 70-80°C for 12-24h; then fully dry at 140-150°C ; put it into a muffle furnace and bake at 250-300°C for 5-6h; wherein the amount of a-Al ₂ O ₃ added is determined according to the concentration of palladium ions in the impregnation solution and the mass fraction of palladium in the prepared catalyst; The specific surface area of the a-Al ₂ O ₃ carrier is 1-10m ² /g, the specific pore volume is 0.01-1cm ³ /g, and the average pore diameter is 5-30nm; C. reducing the dried catalyst precursor in a reducing atmosphere for 2-10 hours, the reduction temperature is 200-600°C, the reducing gas space velocity is 500-6000h ^-1 , and then cooled to room temperature in a reducing atmosphere to obtain a catalyst, Wherein the mass fraction of Pd is 0.01-0.5%, and the mass fraction of zinc is 0.1-0.6%; the reducing gas is pure hydrogen or carbon monoxide-nitrogen mixed gas; D Place the catalyst in step C in an acidic solution with a concentration of 1-5% and soak for 1-4 hours, then wash the catalyst with deionized water at 60-80°C until it is neutral, and then put it in an oven at 140-150°C to fully After drying, the catalyst after zinc removal is obtained, wherein the mass fraction of Pd is 0.01-0.5%, and the mass fraction of zinc is 0.01-0.08%. The solution is one of hydrochloric acid, nitric acid, acetic acid or sulfuric acid solution.