CN102898266A - Method for selectively hydrogenating acetylene in ethylene under normal pressure - Google Patents

Abstract

The invention discloses a method for selectively hydrogenating acetylene in ethylene under normal pressure. Ethylene mixed gas containing the acetylene is subjected to gas phase hydrogenation under normal pressure by using bimetallic A-B/TiO2 as a catalyst, the acetylene is selectively hydrogenated and reduced into ethylene, and the catalyst is an A-B/TiO2 catalyst obtained by a continuous bimetal photo-deposition method, wherein A is Pd, Pt, Au or Rh, and B is Ag, Cu or Ni. The A-B/TiO2 catalyst is used for selectively hydrogenating the acetylene under normal pressure, the ethylene can be reduced under the mild condition to form a hydrocarbon using the ethylene as a main product, and the selectivity of the catalyst is 80 to 97 percent. The method has technical feasibility, does not have secondary pollution, has a remarkable effect of selectively hydrogenating the acetylene in the ethylene, and has high economic and environmental benefits.

Description

A method for selective hydrogenation of acetylene in ethylene under normal pressure

technical field

The invention relates to a method for removing acetylene in ethylene, in particular to a method for realizing selective hydrogenation of acetylene in ethylene under normal pressure.

Background technique

With the development of the economy, the importance of ethylene in industrial production has become increasingly prominent, and its output has become an important symbol to measure the development level of a country's oil industry. Ethylene mainly participates in chemical production in the form of monomers. During the reaction process of synthesizing high polymers, since ethylene comes from hydrocarbon steam cracking method, the outlet gas of cracking furnace contains 0.1%~0.5% acetylene, which is used in the production of polyolefins. Ziegler-Natta catalysts are easily deactivated, and the presence of acetylene can also lead to poor performance of polymerization products, so the removal of small amounts of acetylene in ethylene has attracted attention.

The methods used to remove acetylene in ethylene units mainly include solvent absorption method and catalytic hydrogenation method. The solvent absorption method uses organic solvents such as acetone as the extraction agent, and the process is complex and will cause environmental pollution. Catalytic hydrogenation has become the main method for removing acetylene due to its simple process and low energy consumption.

Due to the better activity and certain selectivity of Pd catalysts, Pd-loaded catalysts are widely used in industry for selective hydrogenation of acetylene. The research results show that the supported Pd catalyst can be further optimized by adding appropriate additives and adjusting the pretreatment conditions to improve the selectivity to ethylene. Substantial improvement in the selectivity of ethylene in the product can be observed by impregnating bimetallic and other methods , but the methods are all realized under pressurized conditions.

Since the selective hydrogenation of acetylene is mostly realized under pressurized conditions, higher requirements are placed on the high-pressure resistance of the reaction equipment, and the pressurized process increases economic investment and increases safety hazards in production operations. Therefore, it is necessary to invent a method capable of selectively hydrogenating acetylene under normal pressure. The catalyst used in the method of the invention can realize the purpose of selectively hydrogenating acetylene to generate ethylene under normal pressure, and the method can realize the purpose of economy, environmental protection and easy operation.

Contents of the invention

The object of the present invention is to provide a method for the selective hydrogenation of acetylene in ethylene under normal pressure.

For realizing the purpose of the present invention, adopt following technical scheme:

A method for the selective hydrogenation of acetylene in ethylene under normal pressure, characterized in that, using bimetallic AB/ _TiO as a catalyst, under normal pressure conditions, gas-phase hydrogenation is carried out to ethylene mixed gas containing acetylene, and the selective hydrogenation of acetylene Hydrogenation reduction to ethylene, the catalyst uses titanium dioxide as a carrier, sequentially photodeposits binary metals to obtain an AB/TiO ₂ catalyst, wherein A is noble metal Pd, Pt, Au or Rh, and B is Cu, Ag or Ni.

Described method specifically comprises the following steps:

1) Use the photodeposition method to load metals A and B on the surface of titanium dioxide in sequence to obtain a titanium dioxide-supported bimetallic AB/TiO ₂ catalyst;

2) Using AB/TiO ₂ as a catalyst, after mixing acetylene, ethylene, hydrogen and inert gas, the mixed gas is catalytically hydrogenated. The reaction temperature is 40~120℃, and acetylene is selectively hydrogenated and reduced to ethylene.

In the catalyst, the loaded precious metal A accounts for 0.5-1.5% of the total catalyst mass, and the molar ratio of metal A to metal B is between 1:0.5 and 1:3, preferably between 1:1.0 and 1:3 between.

The catalyst deposits two kinds of metal elements on titanium dioxide by a continuous photodeposition method, the surface of which forms the core of noble metal Pd or Pt, etc., and forms shells of elements such as Ag or Cu on the outer surface of the noble metal core, thereby adjusting the two metals. The number of exposed sites can achieve the purpose of enhancing the adsorption of acetylene and weakening the adsorption of ethylene, so as to prevent the further hydrogenation of ethylene to form ethane. The effective adjustment of Pd or Pt exposed sites keeps the catalysts with good activity and selectivity during the reaction.

Described catalyst adopts the method preparation of light deposition, and specific method comprises the following steps:

1) Add TiO ₂ , metal A salt solution and methanol into the photoreactor, remove O ₂ by passing N ₂ gas under the condition of avoiding light, react for 3-6 hours under continuous ultraviolet light irradiation, filter and wash with distilled water until the pH is neutral, dry;

Then, according to the above method, metal B was loaded onto the carrier _TiO2 , namely:

2) Add the product obtained in step 1), metal B salt solution and methanol into the photoreactor, pass _N2 to remove _O2 under light-proof conditions, react under continuous ultraviolet light for 3 to 6 hours, filter and use Wash with distilled water until the pH is neutral, and dry to obtain the catalyst.

Described metal A salt is the chloride, nitrate or sulfate of metal A; Described metal B salt is the chloride, nitrate or sulfate of metal B. The concentration of metal A salt or B salt is 0.0001~0.01g/ml.

The AB/TiO ₂ type supported bimetallic catalyst prepared by the above photodeposition method can be used for the selective hydrogenation of acetylene in ethylene under normal pressure. The selectivity of ethylene varies with the molar ratio of the two metals, and the selectivity can reach ≥95%.

The selective catalytic hydrogenation of acetylene adopts the method of in-situ reduction. The catalyst can be reduced at 250-350°C for 1-2 hours first, and then the selective hydrogenation of acetylene can be carried out after cooling down to 40-120°C.

In the catalytic hydrogenation reaction, usually when the amount of the catalyst is 50 mg, the flow rate of the mixed gas is 40-180 ml/min; in terms of volume concentration, H ₂ accounts for 1-2%, ethylene accounts for 50-55%, and acetylene It accounts for 0.1-1%, and the rest is inert gas.

According to the present invention, the AB/TiO ₂ -type supported bimetallic catalyst is prepared by the photodeposition method, which shows remarkable effect on the selective hydrogenation of acetylene under normal pressure. The conversion rate of the catalyst to acetylene is stable, and the selectivity of the target product ethylene is stable and high. The catalyst and the method for selective hydrogenation of acetylene in ethylene under normal pressure are technically feasible, have no secondary pollution, remarkable treatment effect, good economic benefits and are environmentally friendly.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The protection scope of the present invention is not limited by the specific embodiments, but by the claims.

Example 1

The Pd-Ag/TiO ₂ catalyst was prepared by photodeposition method, in which the Pd loading was about 1%, and the molar ratio of Pd and Ag was about 1:1. Using the above-mentioned Pd-Ag/ _TiO2 as a catalyst, the selective hydrogenation reaction of acetylene is carried out under normal pressure, and the acetylene is converted into ethylene and ethane after hydrogenation. The amount of catalyst used is about 50mg, the reaction temperature is 40~120°C, H ₂ accounts for 1.455%, ethylene accounts for 52.605%, acetylene accounts for 0.731%, and helium is used to balance. The flow rate of the mixed gas is 40~180ml/min. React at normal pressure for 2-10 hours, and use a gas chromatograph equipped with an FID detector for on-line detection. The results show that the selectivity to the target product ethylene is 80~89.0%.

×100%。 In the description of the present invention, in the present embodiment and the following examples and comparative examples, the catalyst selectivity is defined as:

×100%.

Comparative example 1

Pd/TiO ₂ with a Pd loading of about 1% prepared by photodeposition was used as a catalyst for the selective hydrogenation of acetylene under normal pressure. The amount of catalyst used is about 50mg, the reaction temperature is 40~120°C, H ₂ accounts for 1.455%, ethylene accounts for 52.605%, acetylene accounts for 0.731%, and helium is used to balance. The flow rate of the mixed gas is 40~180ml/min. Normal pressure reaction 2~10h, catalyst selectivity -180~-140%.

It can be seen that the Pd-supported catalyst prepared by the photodeposition method not only failed to achieve the selective hydrogenation of acetylene, but caused the loss of ethylene in the feed gas.

Comparative example 2

Ag/TiO ₂ with an Ag loading of about 1% prepared by photodeposition was used as a catalyst. Selective hydrogenation of acetylene under atmospheric pressure. The amount of catalyst used is about 50mg, the reaction temperature is 40~120°C, H ₂ accounts for 1.455%, ethylene accounts for 52.605%, acetylene accounts for 0.731%, and helium is used to balance. The flow rate of the mixed gas is 40~180ml/min. Normal pressure reaction 2 ~ 10h, did not show any activity and selectivity.

It can be seen that the Ag-only catalyst prepared by photodeposition method has no activity to acetylene.

Comparative example 3

The Pd-Ag/TiO ₂ catalyst was prepared by the impregnation method, in which the Pd loading was about 1%, and the molar ratio of Pd and Ag was about 1:1. Using this Pd-Ag/TiO ₂ as a catalyst, the selective hydrogenation reaction of acetylene was carried out under normal pressure. The amount of catalyst used is about 50mg, the reaction temperature is 40~120°C, H ₂ accounts for 1.455%, ethylene accounts for 52.605%, acetylene accounts for 0.731%, and helium is used to balance. The flow rate of the mixed gas is 40~180ml/min. Normal pressure reaction 2~10h, catalyst selectivity -100~-20%.

It can be seen that the bimetallic catalyst prepared by the impregnation method not only failed to realize the selectivity to ethylene, but caused the loss of ethylene in the raw material instead.

Example 2

The Pd loading amount prepared by photodeposition is about 1%, and Pd-Ag/TiO ₂ with an atomic molar ratio of Pd and Ag of about 1:0.5 is used as a catalyst for the selective hydrogenation of acetylene under normal pressure. The amount of catalyst used is about 50mg, the reaction temperature is 40~120°C, H ₂ accounts for 1.455%, ethylene accounts for 52.605%, acetylene accounts for 0.731%, and helium is used to balance. The flow rate of the mixed gas is 40~180ml/min. Normal pressure reaction 2~10h, catalyst selectivity -10~10%.

It can be seen that compared with the single Pd catalyst, the addition of Ag effectively changed the selectivity of the catalyst to ethylene.

Example 3

The Pd loading amount prepared by photodeposition is about 1%, and Pd-Ag/TiO ₂ with an atomic molar ratio of Pd and Ag of about 1:1.5 is used as a catalyst for the selective hydrogenation of acetylene under normal pressure. The amount of catalyst used is about 50mg, the reaction temperature is 40~120°C, H ₂ accounts for 1.455%, ethylene accounts for 52.605%, acetylene accounts for 0.731%, and helium is used to balance. The flow rate of the mixed gas is 40~180ml/min. Normal pressure reaction 2~10h, the selectivity of the catalyst is 90~97%.

It can be seen that as the content of Ag increases, the selectivity of the catalyst to ethylene increases.

Example 4

Pd-Ag/TiO ₂ with a Pd loading of about 1% prepared by photodeposition and an atomic molar ratio of Pd and Ag of about 1:3 was used as a catalyst for the selective hydrogenation of acetylene under normal pressure. The amount of catalyst used is about 50mg, the reaction temperature is 40~120°C, H ₂ accounts for 1.455%, ethylene accounts for 52.605%, acetylene accounts for 0.731%, and helium is used to balance. The flow rate of the mixed gas is 40~180ml/min. Normal pressure reaction 2~10h, the selectivity of the catalyst is 95~97%.

It can be seen that when the ratio of Pd and Ag reaches 1:1.5, the selectivity of the catalyst to ethylene remains basically stable with the increase of the content of Ag in the catalyst.

Claims (10)

1. a method for the selective hydrogenation of acetylene in ethylene under normal pressure, is characterized in that, with binary metal AB/TiO ₂ as catalyst, under normal pressure conditions, carry out gas-phase hydrogenation to the ethylene mixed gas containing acetylene, Acetylene is selectively hydrogenated and reduced to ethylene. The catalyst uses titanium dioxide as a carrier, and sequentially photodeposits binary metals to obtain an AB/TiO ₂ catalyst, wherein A is noble metal Pd, Pt, Au or Rh, and B is Cu, Ag or Ni. 2. the method for selective hydrogenation of acetylene according to claim 1, is characterized in that, described method comprises the following steps: 1) Use the photodeposition method to load metals A and B on the surface of titanium dioxide in sequence to obtain a titanium dioxide-supported bimetallic AB/TiO ₂ catalyst; 2) Using AB/TiO ₂ as a catalyst, after mixing acetylene, ethylene, hydrogen and inert gas, the mixed gas is catalytically hydrogenated. The reaction temperature is 40~120℃, and acetylene is selectively hydrogenated and reduced to ethylene. 3. according to the method for the described acetylene selective hydrogenation of claim 1 or 2, it is characterized in that, described catalyst AB/ _TiO In, the noble metal A of load accounts for 0.5～1.5% of total catalyst mass, metal A and The molar ratio of metal B is 1:0.5~1:3. 4. The method for selective hydrogenation of acetylene according to claim 3, characterized in that, in the catalyst AB/ _TiO2 , the molar ratio of metal A to metal B is 1:1.0 to 1:3. 5. according to the method for the selective hydrogenation of acetylene described in claim 1 and 2, it is characterized in that, the method for preparing catalyst by described light deposition method comprises the following steps: 1) Add TiO ₂ , metal A salt solution and methanol into the photoreactor, pass N ₂ to remove O ₂ under the condition of avoiding light, react under continuous ultraviolet light for 3-6 hours, filter and wash with distilled water until the pH is neutral, dry; 2) Add the product obtained in step 1), metal B salt solution and methanol into the photoreactor, pass _N2 to remove _O2 under the condition of avoiding light, react under continuous ultraviolet light for 3 to 6 hours, filter and washed with distilled water until the pH is neutral, and dried to obtain the catalyst. 6. the method for the selective hydrogenation of acetylene according to claim 5 is characterized in that described A salt is the nitrate, sulfate or chloride of metal A; Described B salt is the nitrate of metal B, sulfates or chlorides. 7. The method for selective hydrogenation of acetylene according to claim 5, characterized in that the concentration of the A salt or the B salt is 0.0001 ~ 0.01g/ml. 8. The method for selective hydrogenation of acetylene according to claim 2, characterized in that, in step 2) in the catalytic hydrogenation reaction, in the mixed gas by volume, _H accounts for 1 to 2%, and ethylene accounts for 50-55%, acetylene accounts for 0.1-1%, and the rest is inert gas. 9. The method for selective hydrogenation of acetylene according to claim 2, characterized in that, in step 2) in the catalytic hydrogenation reaction, the flow rate of the mixed gas is 40-180ml/min. 10. The method for selective hydrogenation of acetylene according to claim 2, characterized in that the catalytic hydrogenation reaction time of step 2) is 2 to 10 hours.