阅读说明：本技术 高分散Pd-Ag负载型乙炔氢化催化剂及其制备方法 (High-dispersion Pd-Ag supported acetylene hydrogenation catalyst and preparation method thereof ) 是由 蔡建华 于 2019-12-04 设计创作，主要内容包括：本发明公开了一种高分散Pd-Ag合金催化剂,属于化工催化剂领域。催化剂活性组分为Pd,Ag为助组分,载体为Al<Sub>2</Sub>O<Sub>3</Sub>或含氧化铝的复合氧化物载体,其特征在于：以质量计,催化剂中Pd含量为0.01～0.1％；Ag含量为0.03～1.0％,该催化剂为合金型双金属催化剂,制备过程中采用含羧基的化合物与Pd配合行定点负载,更有利于Pd和高分散和Pd-Ag合金的形成。该方法解决了目前工业中用浸渍法制备催化剂导致活性金属颗粒尺寸大,分散不均匀,导致催化剂活性金属利用率低,活性、选择性不理想,催化剂易结焦、失活速率快的问题。本发明催化剂可用于碳二馏分选择加氢过程。(The invention discloses a high-dispersion Pd-Ag alloy catalyst, belonging to the field of chemical catalysts. The active component of the catalyst is Pd, Ag is an auxiliary component, and the carrier is Al 2 O 3 Or a composite oxide support comprising alumina, characterized in that: the Pd content in the catalyst is 0.01-0.1% by mass; the content of Ag is 0.03-1.0%, the catalyst is an alloy type bimetallic catalyst, and a carboxyl-containing compound and Pd are matched for fixed-point loading in the preparation process, so that Pd and high dispersion and Pd-Ag alloy formation are facilitated. The method solves the problems of large active metal particle size, uneven dispersion, low active metal utilization rate of the catalyst, unsatisfactory activity and selectivity, easy coking of the catalyst and high inactivation rate caused by the preparation of the catalyst by an impregnation method in the industry at present. The catalyst of the present invention can be used for carbonThe second fraction is selected to be hydrogenated.)

1. The high-dispersion Pd-Ag supported acetylene hydrogenation catalyst has Pd as active component, Ag as assistant component and α -Al as carrier₂O₃A base carrier, characterized in that the Pd content in the catalyst is 0.01-0.1% by mass; the content of Ag is 0.01-1.0%; the preparation process of the catalyst comprises the following steps: soaking an additive Ag on a carrier in the same volume, aging, drying and activating; then putting the mixture into polymaleic acid or polymaleic acid-acrylic acid excess solution, carrying out ultrasonic reaction, filtering and drying; and finally, impregnating the active component Pd with the same volume on the macromolecule modified intermediate, and performing ultrasonic reaction, drying and activation to obtain the finished Pd-Ag bimetallic catalyst.

2. The acetylene hydrogenation catalyst according to claim 1, wherein the content of the active component Pd is 0.01-0.1%, and the content of the auxiliary agent Ag is 0.01-0.5%.

3. The acetylene hydrogenation catalyst according to claim 1, wherein the catalyst contains 0.03-0.05% of active component Pd and 0.06-0.15% of auxiliary agent Ag.

4. The acetylene hydrogenation catalyst according to claim 1, wherein the carrier is α -Al₂O₃Or α -Al₂O₃And (3) a composite carrier with other oxides, wherein the other oxides are selected from one or more of alkali metal oxides, silicon oxide and titanium oxide.

5. The acetylene hydrogenation catalyst according to claim 1, wherein the specific surface area of the catalyst is 1 to 30m²Per g, pore volume of 0.15-0.5 mL/g, bulk density of 0.5-1.2 g/cm³。

6. A process for preparing an acetylene hydrogenation catalyst according to any of claims 1 to 5, characterized by comprising the steps of:

i. preparation of a first-impregnation catalyst: preparing an Ag ion solution with a certain concentration, loading the Ag ion solution on a carrier in the same volume, aging at room temperature for 30-60min, drying at 80-120 ℃ for 240min, and activating at 400-600 ℃ for 180-300min to obtain a soaking catalyst;

preparation of organic modified intermediate: placing the first-dipping catalyst in an excessive polymaleic acid or polymaleic acid-acrylic acid solution, carrying out ultrasonic reaction for 10-30min, filtering, and drying at 80-120 ℃ for 120-;

active component Pd loading: pd ion solution with a certain concentration is prepared and dipped on the organic modified intermediate in the same volume, the ultrasonic reaction is carried out for 10-30min, the drying is carried out for 120-120 ℃ for 240min, and the activation is carried out for 180-300min at 400-600 ℃ to obtain the finished Pd-Ag bimetallic catalyst.

7. The method according to claim 6, wherein the Ag ion solution in step i is silver nitrate or other soluble silver salt solution.

8. The method according to claim 6, wherein the solvent of the maleic acid or polymaleic acid-acrylic acid solution in step ii is at least one of water, ethanol and methanol, the solution concentration is 1-20 mmol/L, and the solution pH is 1-8.

9. The method of claim 6, wherein: and in the step ii, the organic matter is loaded by adopting an excess impregnation method.

10. The method of claim 6, wherein: in step iii, the Pd ion solution is an aqueous solution of soluble chloride, nitrate, acetate or ammonium complex of Pd.

Technical Field

The invention belongs to the technical field of chemical catalysts, and relates to a high-dispersion Pd-Ag supported acetylene hydrogenation catalyst and a preparation method thereof, which are particularly suitable for selective hydrogenation conversion of trace acetylene in ethylene material flow into ethylene.

Background

Ethylene is a main mark for measuring the development level of national chemical industry, and ethylene streams prepared by steam cracking and ethane cracking usually contain 0.5-2.5% of acetylene, and can be used in the subsequent polymerization process after being converted into ethylene by selective hydrogenation. The existence of acetylene can cause the increase of side reactions of ethylene polymerization and influence the quality of polymers, and in addition, acetylene is easy to react with a copper-based polymerization catalyst to generate copper acetylide explosive compounds. Therefore, the acetylene content in polymer grade ethylene is required to be below 1 ppm.

At present, acetylene in ethylene materials is usually removed by adopting selective hydrogenation and adsorption methods in the industry, wherein the selective hydrogenation method is simple to operate, the catalyst technology is mature, the economy is excellent, and acetylene catalytic hydrogenation methods are generally adopted for removing acetylene in petrochemical devices at present.

The prior industrialized front hydrogenation catalyst is composed of Pd-Ag bimetal and is prepared by adopting an immersion method, due to the surface tension of liquid and the nonuniformity of the surface of a carrier, active component clusters grow irregularly, the size of the Pd clusters is large, and the utilization rate of the active components is low. Because Pd is expensive, how to improve the dispersion degree of active metals is a hotspot of catalyst research. In addition, the electron energy on the 5s orbit of the auxiliary agent Ag atom is close to the electron energy on the 4d orbit of the Pd atom, after the Pd-Ag forms an alloy, the electron cloud density of the 4d orbit of the Pd atom is increased, the electron empty orbit is reduced, the adsorption capacity to ethylene is reduced, the excessive hydrogenation of the ethylene is inhibited, and the selectivity of the catalyst is improved. In the traditional impregnation method, because Pd and Ag are unevenly distributed, Pd-Ag is difficult to form stable alloy, and the assistant effect is not obvious.

The Chinese patent application 201110086174.0 is characterized in that a specific polymer compound is adsorbed on a carrier, a polymer coating layer is formed on the surface of the carrier in a certain thickness, a compound with a functional group reacts with a polymer to enable the polymer to have the functional group capable of being complexed with an active component, and the active component is ensured to be orderly and highly dispersed by the complexation reaction of the active component on the functional group on the surface of the carrier. By adopting the method, the carrier adsorbs specific high molecular compounds, and chemical adsorption is carried out on the high molecular compounds and the hydroxyl groups of the alumina, so that the amount of the high molecular compounds adsorbed by the carrier is limited by the number of the hydroxyl groups of the alumina; the functional polymer and Pd have weak complexing effect, sometimes the loading capacity of the active component can not meet the requirement, and part of the active component remains in the impregnation liquid, so that the cost of the catalyst is increased.

The Chinese patent application 201710602826.9 discloses a preparation method of Pd-M base metal catalyst for preparing ethylene by hydrogenation of high-purity acetylene and a preparation method of ethylene, wherein the preparation method of the catalyst comprises the following steps: 1) mixing water-soluble palladium salt and an auxiliary agent metal M precursor with water to obtain a mixed solution, wherein the auxiliary agent metal M precursor is water-soluble salt; (2) contacting the carrier with the mixed solution by adopting an isometric impregnation method to load the metal palladium and the auxiliary agent on the carrier; (3) drying the product obtained in the step (2), and then carrying out reduction roasting to obtain the Pd-M-based metal catalyst, wherein the reduction roasting is carried out under the vacuum dilute hydrogen condition: the vacuum degree is 0.04-0.085MPa, and the hydrogen flow is 0.1ml/(gcat.min) -10 ml/(gcat.min). The method can prepare the catalyst with the advantages of high dispersion degree of active metal and no agglomeration of metal microcrystals, thereby greatly prolonging the service life of the catalyst, and the catalyst is particularly suitable for industrial large-scale production of ethylene by hydrogenation of high-concentration acetylene, and the obtained ethylene has higher yield. However, the catalyst activation is carried out in a hydrogen atmosphere, so that great safety risk exists, and the method is not beneficial to large-scale industrial production.

The chinese patent application 201510711449.3 relates to an acetylene hydrogenation catalyst and a preparation method thereof, the preparation method comprises: (1) treating the carrier with an alkaline solution, and then roasting to obtain a carrier Z; (2) loading a main active component palladium precursor on a carrier Z to obtain a catalyst semi-finished product; (3) and mixing and contacting the catalyst semi-finished product with a solution containing a free radical scavenger, and then carrying out ionizing radiation on the catalyst semi-finished product to reduce palladium into a simple substance. The catalyst prepared by the method has good dispersibility and stability, obviously improves the hydrogenation performance of the catalyst, and particularly improves the removal of CO and H rich in₂The capability of trace acetylene in the mixed gas has better industrial application prospect. In addition, the ionizing radiation has high requirements on operating conditions and environment, and does not have industrial production operability.

The Chinese patent application 201410666452.3 discloses a ligand-modified supported acetylene hydrogenation Pd catalyst and a preparation method thereof, and relates to a catalyst and a preparation method thereof, wherein Pd is an active component and accounts for 1-3% by mass; the surface of the carrier silicon dioxide is grafted with organic groups containing N, S; alkyl mercaptan is taken as a ligand, and tetrabutylammonium borohydride is taken as a reducing agent; the method comprises the steps of adopting PdCl2 or palladium nitrate as a palladium salt and a toluene solution as a solvent, dissolving the palladium salt in the toluene solution, adding an alkyl mercaptan ligand, ultrasonically oscillating to obtain a clear colored solution, then adding tetrabutylammonium borohydride, and finally adding organic modified silicon dioxide powder to obtain the catalyst. The catalyst can effectively regulate and control the performance of the loaded Pd catalyst by introducing the alkyl mercaptan ligand, the acetylene conversion rate is 100 percent, the ethylene selectivity is over 90 percent, and the performance is stable under the conditions of lower reaction temperature and high hydrogen alkyne ratio. The mercaptan is used as a ligand, and the active metal Pd is easy to generate sulfur poisoning, so that the activity of the catalyst is influenced.

The prior arts generally have the disadvantages of poor dispersibility of active metals in the catalyst, complex preparation method, high cost, being not beneficial to large-scale production and the like.

Disclosure of Invention

In view of the disadvantages of the prior art, the invention aims to provide a high-dispersion Pd-Ag supported acetylene hydrogenation catalyst and a preparation method thereof. The purpose of the invention is realized by the following technical scheme.

A high-dispersity Pd-Ag supported acetylene hydrogenation catalyst contains Pd as active component, Ag as assistant component, α -Al as carrier₂O₃A base vector characterized by: the catalyst comprises 0.01-0.1% by mass of Pd and 0.01-1.0% by mass of Ag; the preparation process of the catalyst comprises the following steps: soaking an additive Ag on a carrier in the same volume, aging, drying and activating; then placing the mixture into a polymaleic acid (PMA) or polymaleic acid-acrylic acid (MA-AA) excess solution, carrying out ultrasonic reaction, filtering and drying; and finally, impregnating the active component Pd with the same volume on the macromolecule modified intermediate, and performing ultrasonic reaction, drying and activation to obtain the finished Pd-Ag bimetallic catalyst.

Further, the content of an active component Pd in the catalyst is 0.01-0.1%, preferably 0.03-0.05%; the content of the additive Ag is 0.01-0.5%, preferably 0.06-0.15%.

Further, the carrier was α -Al₂O₃Supports or α -Al₂O₃And (3) a composite carrier with other oxides, wherein the other oxides are selected from one or more of alkali metal oxides, silicon oxide and titanium oxide.

Further, the specific surface area of the catalyst is 1-30m²Per g, pore volume of 0.15-0.5 mL/g, bulk density of 0.5-1.2 g/cm³。

The preparation method of the high-dispersion Pd-Ag supported acetylene hydrogenation catalyst comprises the following steps:

i. preparation of a first-impregnation catalyst: preparing an Ag ion solution with a certain concentration, loading the Ag ion solution on a carrier in the same volume, aging at room temperature for 30-60min, drying at 80-120 ℃ for 240min, and activating at 400-600 ℃ for 180-300min to obtain the one-step catalyst.

Preparation of organic modified intermediate: placing the first-dipping catalyst in an excessive polymaleic acid (PMA) or polymaleic acid-acrylic acid (MA-AA) solution, carrying out ultrasonic reaction for 10-30min, filtering, and drying at 80-120 ℃ for 120-240min to obtain an organic modified intermediate.

Active component Pd loading: pd ion solution with a certain concentration is prepared and dipped on the organic modified intermediate in the same volume, the ultrasonic reaction is carried out for 10-30min, the drying is carried out for 120-120 ℃ for 240min, and the activation is carried out for 180-300min at 400-600 ℃ to obtain the finished Pd-Ag bimetallic catalyst.

Further, the Ag ion solution in step i is silver nitrate or other soluble silver salt solution.

Further, in step ii, the solvent of the maleic acid or polymaleic acid-acrylic acid solution is at least one of water, ethanol and methanol, the solution concentration is 1-20 mmol/L, and the pH value of the solution is 1-8. The pH value can be adjusted by ammonia water or dilute nitric acid.

Further, in step ii, the organic matter is loaded by an excess impregnation method.

Further, in step iii, the Pd ion solution is an aqueous solution of soluble chloride, nitrate, acetate or ammonium complex of Pd.

The maleic acid (PMA) or polymaleic acid-acrylic acid (MA-AA) solution is any one solvent of water, ethanol and methanol, the concentration of the solution is 1-20 mmol/L, and the pH value of the solution is 1-8. And loading the organic solution to the pore channels of the carrier by adopting an excess impregnation method. Because the solution has certain viscosity, the loading process is carried out under the ultrasonic condition, so that the solution is fully immersed into the carrier pore channel.

The invention adopts maleic acid (PMA) or polymaleic acid-acrylic acid (MA-AA) modified carrier, disperses chain maleic acid (PMA) or polymaleic acid-acrylic acid (MA-AA) polymer into carrier pore canal, forms complex with Pd ion through rich carboxyl on chain, disperses Pd ion directionally, is surrounded by a plurality of Ag particles on the carrier, and obtains the Pd highly dispersed bimetallic catalyst after high temperature activation. The catalyst prepared by the method has the advantages that Pd is adjacent to a plurality of silver atoms, and the Pd-Ag alloy is easier to form, so that the catalyst has more excellent selectivity and coking resistance. In the invention, Pd is matched with carboxyl groups on a polymer chain in a fixed point manner, the dispersity is higher, and the activity is higher under the same load rate. Solves the problems that the size of an active metal cluster is difficult to control, the active metal cluster is not uniformly dispersed, the active metal is easy to agglomerate, the activity and the selectivity of the catalyst are low, and the catalyst is easy to coke when the catalyst is prepared by the existing industrial impregnation method.

The catalyst provided by the invention is used for acetylene hydrogenation reaction, and has good activity, selectivity and coking resistance. The preparation method provided by the invention can realize fixed-point loading of the active metal Pd, the Pd atoms are surrounded by the Ag atoms, the highly dispersed Pd atoms are favorable for forming stable alloy with Ag, and the synthesis method is simple, low in cost and easy to realize mass production.

Drawings

FIG. 1 is a schematic diagram of the loading of polymer modified Pd.

Figure 2 is the XRD spectrum of the catalyst of example 1.

FIG. 3 is a comparison of the reaction performance of example 1 and comparative example 1.

FIG. 4 is a comparison of the reaction performance of example 2 and comparative example 2.

FIG. 5 is a comparison of the reaction performance of example 3 and comparative example 3.

FIG. 6 is a comparison of the reaction performance of example 4 and comparative example 4.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

The analytical test method related by the invention is as follows:

specific surface area: GB/T-5816;

pore diameter: GB/T-5816;

the content of active components in the catalyst is as follows: atomic absorption method;

catalyst active component dispersity: hydrogen-oxygen titration;

particle size of catalyst active component: a high-resolution transmission electron microscope;