CN102206131B - Selective hydrogenation method for carbon-dioxide fraction - Google Patents

Abstract

The invention relates to a selective hydrogenation method of carbon dioxide fraction, which is used for post-hydrogenation, wherein carbon dioxide feeding materials from a front deethanizer in an ethylene device enter a fixed bed reactor for selective hydrogenation after pressurization and hydrogen distribution, and the method is characterized in that: the fixed bed reactor is filled with Pd-Ag series catalyst and Al₂O₃Or Al₂O₃The mixture of the catalyst and other oxides is used as a carrier, and the organic polymer metal complex is formed in the preparation process of the catalyst; the reaction conditions are as follows: the inlet temperature of the fixed bed reactor is 40-100 ℃, the reaction pressure is 1.5-2.5 MPa, and the gas space velocity is 2000-10000 h^-1. The hydrogenation reaction activity and selectivity of the method are greatly superior to those of the traditional hydrogenation method, and the generation amount of green oil in the hydrogenation process is greatly reduced, so that the activity and selectivity of the catalyst are well maintained.

Description

A method for selective hydrogenation of carbon distillates

technical field

The invention relates to a method for selective hydrogenation, in particular to a method for selective hydrogenation of carbon distillates to remove acetylene.

Background technique

The production of polymer grade ethylene is the leader of the petrochemical industry, and polymer grade ethylene and propylene are the most basic raw materials for downstream polymerization units. Among them, the selective hydrogenation of acetylene has an extremely important impact on the ethylene processing industry. In addition to ensuring that the acetylene content at the outlet of the hydrogenation reactor reaches the standard, the selectivity of the catalyst is excellent, which can make ethylene generate as little ethane as possible, which is beneficial to improving the entire process. It is of great significance to improve the ethylene yield of the process and improve the economic benefits of the device.

The cracked carbon distillate contains acetylene with a mole fraction of 0.5% to 2.5%. When producing polyethylene, a small amount of acetylene in ethylene will reduce the activity of the polymerization catalyst and deteriorate the physical properties of the polymer. Therefore, the acetylene in ethylene must be Only when the acetylene content is reduced to a certain limit can it be used as a monomer for the synthesis of high polymers. Therefore, the separation and conversion of acetylene is one of the important processes in the flow of ethylene plants.

Catalytic selective hydrogenation in ethylene units includes pre-hydrogenation and post-hydrogenation. Pre-hydrogenation and post-hydrogenation of acetylene refer to the position of the acetylene hydrogenation reactor relative to the demethanizer. The hydrogenation reactor is located before the demethanizer. Pre-hydrogenation, the hydrogenation reactor is located after the demethanizer for post-hydrogenation. The advantage of the post-hydrogenation process is that there are many control methods in the hydrogenation process, it is not easy to overheat, and it is easy to operate, but the disadvantage is that the catalyst is easy to coke and the regeneration of the catalyst is relatively frequent. The reason is that in the hydrogenation process, due to the small amount of hydrogen added, the hydrogenation dimerization of acetylene is prone to occur, and 1,3-butadiene is generated, and further oligomers with wider molecular weights are formed, commonly known as " green oil". The green oil is adsorbed on the surface of the catalyst, and further forms coke, blocks the pores of the catalyst, and reduces the activity and selectivity of the catalyst.

At present, C2 post-hydrogenation mainly adopts two-stage or three-stage reactor series process, and devices with low space velocity or low alkyne content can use two-stage reactor series series. At present, the industrial installations are mainly based on the three-stage reactor series process.

The general composition of post-hydrogenation materials is: 1.0-2.2% (v/v) of acetylene, 65-85% of ethylene, the rest is ethane, and hydrogen is added after metering.

The reaction is an exothermic reaction, but the temperature rise is relatively low. According to the space velocity, the maximum temperature rise of a single reactor ranges from 30 to 60, so an adiabatic reactor is basically used.

For two-stage reactors, the first-stage reactor is required to convert more than 70% of acetylene, and the second-stage reactor converts the remaining acetylene to a content of less than 5×10 ^-6 (V/V).

For devices with high space velocity or high acetylene content, a three-stage reactor process is generally adopted. The first stage converts about 50%, and the remaining two stages convert the remaining acetylene. The acetylene content at the outlet of the three-stage reactor is less than 5×10 ^-6 (V/V).

The amount of hydrogen added is related to the content of acetylene and the process used. For the three-stage reactor process, the hydrogen/acetylene ratio of the first-stage reactor is generally 0.8-1.2, the hydrogen/acetylene ratio of the second-stage reactor is 1-1.5, and the hydrogen/acetylene ratio of the third-stage reactor is 1.5-3.

For the two-stage reactor process, generally, the hydrogen/acetylene ratio of the first-stage reactor is 1-1.5, and the hydrogen/acetylene ratio of the second-stage reactor is 2-4.

The reaction mechanism is as follows:

Main reaction C ₂ H ₂ +H ₂ →C ₂ H ₄ ΔH=-175.7kJ/mol (1)

side effects

C ₂ H ₄ +H ₂ →C ₂ H ₆ ΔH=-138.1kJ/mol (2)

C ₂ H ₂ +2H ₂ →C ₂ H ₆ (3)

2C ₂ H ₂ +H ₂ →C ₄ H ₆ (4)

C ₂ H ₂ +nC ₂ H ₂ +H ₂ →C _2n+2 H _2n+4 (5)

Of these reactions, reaction (1) is the hydrogenation of acetylene, and reactions (2) and (3) are the hydrogenation of ethylene. Reaction (4) is the hydrogenation dimerization of acetylene, which has an important contribution to the formation of green oil, and reaction (5) is a general reaction formula for the formation of green oil.

Among these reactions, only reaction (1) is the desired reaction, and the rest are undesired reactions.

US5856262 reported the method of preparing low-acid palladium catalyst with silicon oxide modified by potassium hydroxide (or the hydroxide of barium, strontium, rubidium, etc.) as ^the carrier. Under the conditions of 0.71% mole fraction and 1.43 hydrogen-alkyne mole ratio, the outlet acetylene mole fraction is less than 1×10 ^-7 , and the ethylene selectivity reaches 56%. The patent US 4404124 uses alumina as a carrier and adds co-catalyst silver and palladium to prepare a carbon dioxide hydrogenation catalyst with excellent performance. The catalyst has the functions of reducing the amount of ethane generated, inhibiting the partial hydrogenation dimerization of acetylene adsorbed on the surface of the catalyst, inhibiting the generation of 1,3-butadiene, reducing the generation of green oil, improving the selectivity of ethylene, and reducing the generation of oxygen-containing compounds Quantity characteristics, has been widely used in the ethylene industry. However, the above-mentioned catalysts are all prepared by the impregnation method. Due to the limitation of the preparation method, the metal dispersion is only about 30%, and there are many shortcomings in the performance of the catalyst, which still needs further improvement.

Traditional Pd-Ag bimetallic selective hydrogenation catalysts are all prepared by aqueous solution impregnation method. When the separate leaching method is used, one component will be more enriched on the surface of the carrier, while the other component will be enriched on the outer surface, and only part of the metal atoms will penetrate each other to form an alloy structure. When using the co-impregnation method, due to the different interactions between the precursors of the two metal ions and the carrier, as well as surface tension and solvation, it is difficult to form a uniform loading of the two components, and only a partial alloy structure can be formed. When this catalyst is used in the selective hydrogenation of carbon distillates, the selectivity is often good at the initial stage of the reaction, but the selectivity decreases continuously with the prolongation of the operation time. Generally, it needs to be regenerated after 3 to 6 months of operation, and the economic loss is relatively large.

Contents of the invention

The purpose of the present invention is to provide a method for post-hydrogenation of carbon distillate, by selecting a Pd-Ag catalyst with a high alloy structure, the selectivity of hydrogenation is improved, the increase of ethylene is increased, and the economic benefits of device operation are improved .

The inventors found that when Pd and Ag in the catalyst form an alloy, Pd is separated by Ag, so that the distance between the active centers is widened, and the probability of hydrogenation dimerization of two acetylene molecules is greatly reduced. The production of 1,3-butadiene is greatly reduced, the surface coking rate of the catalyst is also greatly reduced, the operation period of the catalyst is prolonged, and the economic effect is obvious.

The invention provides a method for selective hydrogenation of carbon distillates. The adiabatic bed reactor used for hydrogenation is located behind the demethanizer, and the carbon dihydrogenation materials from the front deethanizer in the ethylene plant are distributed under pressure. After hydrogenation, it enters the adiabatic bed reactor for selective hydrogenation, which is characterized in that: the adiabatic bed reactor is equipped with a Pd-Ag catalyst, with Al ₂ O ₃ or a mixture of Al ₂ O ₃ and other oxides as the carrier, with The mass of the catalyst is 100%, wherein the Pd content is 0.03-0.06%, the Ag content is 0.06-0.2%, the specific surface area of the catalyst is 15-50m ² /g; the pore volume is 0.25-0.8ml/g; the catalyst is in The organic polymer metal complex is formed during the preparation process; the reaction conditions are: the inlet temperature of the adiabatic bed reactor is 40-100°C, the reaction pressure is 1.5-2.5MPa, and the gas space velocity is 2000-10000h ^-1 .

The characteristic of the Pd-Ag series catalyst used in the present invention is that the catalyst is prepared by the method of the present invention using the metal-organic polymer complex precursor.

The recommended preparation method of the catalyst is: make palladium and silver and organic polymers form an organic polymer metal complex through a complexing agent to obtain a Pd-Ag-polymer/Al ₂ O ₃ precursor; The Pd-Ag-polymer/Al ₂ O ₃ precursor is calcined for 2-6 hours to obtain the desired catalyst.

The complexing agent of the present invention is a complexing agent that can carry out functionalization reaction with the side chain group of the macromolecule, and can complex the ions of Pd and Ag after the reaction. The functional group of the complexing agent can be an amine group or a di Amino.

The side chain of the organic polymer of the present invention contains a group that can react with a complexing agent, and the group can be one or more of halogen and cyano groups.

The present invention is a post-hydrogenation process. The composition of the imported raw material is mainly carbon distillate, wherein acetylene is 1.0-2.5 (v/v)%, ethane is 11.2-30.3 (v/v)%, and ethylene is 68.8-88.9 (v/v). v) %. The present invention does not particularly limit the hydrogen-alkyne ratio of each reactor, and the usual hydrogen-alkyne ratio (V/V) can be used, which is generally 0.8-4. For the three-stage reactor process, the hydrogen/acetylene ratio of the first-stage reactor is generally 0.8-1.2, the hydrogen/acetylene ratio of the second-stage reactor is 1-1.5, and the hydrogen/acetylene ratio of the third-stage reactor is 1.5-3. For the two-stage reactor process, generally, the hydrogen/acetylene ratio of the first-stage reactor is 1-1.5, and the hydrogen/acetylene ratio of the second-stage reactor is 2-4.

The type of catalyst used is limited in the present invention, and the selectivity of this type of catalyst is quite different from that of traditional catalysts.

The principle of the present invention is: in the selective hydrogenation reaction, as the active components of the catalyst Pd and Ag form an alloy, the amount of hydrogen adsorbed by the bulk phase of the catalyst is greatly reduced, and the tendency of deep hydrogenation of acetylene is greatly reduced , the selectivity of the catalytic reaction was significantly improved.

The acquisition of the catalyst preferably includes the following steps: loading the organic polymer on the catalyst carrier by a complexing agent, grafting functional groups on the loaded polymer chain, preparing a palladium-silver solution, and loading the functionalized polymer The precursor is immersed in the prepared palladium-silver solution for reaction, so that palladium and silver are complexed to the loaded polymer chains, and palladium and silver form organic polymer metal complexes with organic polymers to obtain Pd-Ag-polymer/Al ₂ O ₃ precursor; the (Pd-Ag)-polymer/Al ₂ O ₃ precursor is calcined at 380-550° C. for 2-6 hours to obtain the desired catalyst. During the roasting process, the palladium-silver atoms will undergo an oxidation reaction in situ, and the distribution of palladium-silver in the final crystal phase is uniform. The catalyst prepared by this method is an alloy-type bimetallic catalyst with excellent selectivity. sex.

The Al ₂ O ₃ carrier refers to Al ₂ O ₃ or the mixture of Al ₂ O ₃ and other oxides as the carrier, and Al ₂ O ₃ is preferably γ, δ, θ, α or a mixed crystal form of several of them . The carrier can be in the shape of spherical, strip, clover, four-leaf or toothed ball, etc.

The catalyst preparation of the present invention can adopt the following process to implement, and this process can be divided into 3 steps to carry out.

1. First prepare the functionalized-polymer (polymer)/Al ₂ O ₃ precursor.

2. Prepare the (Pd-Ag)-polymer/Al ₂ O ₃ precursor again.

3. Calcining the precursor prepared in step 2 at 450-550° C. for 2-6 hours.

The hydrogenation method of the present method is limited to the use of catalysts defined in the present invention.

The preparation method of this catalyst comprises the steps:

A. Preparation of functionalization-polymer/Al ₂ O ₃ precursor

An organic polymer (such as PVC) is completely dissolved in an organic solvent such as THF (tetrahydrofuran) to form a polymer solution, the carrier is immersed in the above solution, and the organic polymer (polymer) is deposited on the surface of Al ₂ O ₃ after standing, Drying; add complexing agent containing functional groups, reflux for 30-300 minutes, cool to room temperature, wash with deionized water until neutral, and obtain functionalized-polymer/Al ₂ O ₃ precursor.

A more specific method is as follows: at 20-35°C, dissolve the polymer with reactive groups on the side chain in an organic solvent, immerse the carrier in the above solution, and let it stand for 2-6 hours to make the high Molecules are deposited on the surface of Al ₂ O ₃ , and after drying, a complexing agent is added at 20-35°C. The complexing agent can not only perform a functional reaction with the side chain Combine Pd and Ag ions, reflux the above solution for 1-4 hours, cool to 20-35°C, wash with deionized water, and dry.

The macromolecules with reactive groups on the side chains refer to macromolecules whose side chains contain halogen, cyano and other groups, such as polyvinyl chloride (PVC), polystyrene acrylonitrile (SAN), etc. , the complexing agent is a small molecular compound that can provide amine or diamine functional groups, it can be dicyandiamide, ethanolamine, ethylenediamine or hydroxylamine hydrochloride, it can be one or more of them; in moles Calculated, the number of moles of the complexing agent/the number of moles of the reactive groups in the polymer is preferably 100-1.

B. Preparation of (Pd-Ag)-polymer/Al ₂ O ₃ precursor

Prepare a mixed solution of Pd(NO ₃ ) ₂ and Ag NO ₃ , adjust the pH value to 1-4 with inorganic acid, weigh the prepared functionalized-polymer/Al ₂ O ₃ precursor, and mix the Pd(NO ₃ ) _2. Add the mixed solution of Ag NO ₃ to the precursor, stir for 5-60 minutes, pour out the residual liquid, wash and dry the above product with deionized water, and obtain the (Pd-Ag)-polymer/Al ₂ O ₃ precursor The number of moles of functional groups on the polymer chain after functionalization/the number of moles of (Pd+Ag) is preferably 100-1.

C. Preparation of catalyst

The precursor prepared above is calcined at 450-550° C. for 4-8 hours in an air atmosphere to obtain a Pd—Ag/Al ₂ O ₃ catalyst.

The catalyst prepared above can also be reduced by using H ₂ in a reactor to obtain (Pd—Ag)/Al ₂ O ₃ . The above-mentioned roasting can be carried out in an oxygen atmosphere, and the effect is better.

When the catalyst is used, the catalyst prepared by the above method can be reduced by using _H in a reactor to obtain a reduced catalyst.

The macromolecules used in the present invention are macromolecules with reactive groups on the side chains, and the reactive groups are preferably cyano groups or chlorine atoms.

The complexing agent is a molecule that can carry out grafting reaction with the above-mentioned reactive groups, and can carry out complexation reaction with palladium and silver ions. Specifically, it can be dicyandiamide, ethanolamine, ethylenediamine, hydroxylamine hydrochloride and the like.

The number of moles of functional groups on the polymer chain after functionalization/the number of moles of (Pd+Ag) is preferably 100 to 1, for example, the number of moles of reactive groups in SAN -CN (cyanide)/the number of moles of (Pd+Ag) Preferably 100-1. The number of moles of the complexing agent/the number of moles of (Pd+Ag) is preferably 10000-1.

The purpose of adding solvent in step A is to dissolve the macromolecule completely, so as to facilitate the adsorption of the macromolecule on the carrier. The solvent can be tetrahydrofuran (THF), toluene, dimethylformamide (DMF) and other solvents. The amount of solvent to be added is mainly to control that the added solvent can completely dissolve the polymer.

The reactor in the present invention refers to an adiabatic bed reactor. It can be single bed or multiple beds, preferably 2-3 beds.

The inventors also found that when the method is used for selective hydrogenation, the selectivity of the catalytic reaction is also improved. Increased ethylene gain.

Description of drawings

Figure 1 is a flow chart of the C2 post-hydrogenation process.

In the figure: 1-oil washing tower; 2-water washing tower; 3-alkali washing tower; 4-dryer; 5-demethanizer; 6-front deethanizer; 7-carbon two hydrogenation reactor; Heat Exchanger.

Detailed ways

Example 1

Catalyst preparation:

A, the preparation of functionalized polyvinyl chloride (PVC)/Al ₂ O ₃

Weigh 250g of a columnar Al ₂ O ₃ carrier with a diameter of 4.5mm, a length of 4.5mm, a specific surface area of 15.m ² /g, a pore volume of 0.25ml/g, and a bulk density of 1.1g/cm ³ .

Completely dissolve 4.450g of PVC in 400ml of THF (tetrahydrofuran), dip the above-mentioned carrier into the above-mentioned solution, let the PVC adsorb on the surface of Al ₂ O ₃ after standing for 2 hours, and dry. 205 g of PVC/Al ₂ O ₃ product were obtained.

Add 59.64g of dicyandiamide and 2.0g of Na ₂ CO ₃ , add 205g of PVC/Al ₂ O ₃ to reflux for 1 hour, cool to room temperature, wash with deionized water until neutral, and dry for later use. A functionalized PVC/Al ₂ O ₃ is obtained.

B. Preparation of (Pd-Ag)-polymer/Al ₂ O ₃ precursor

Weigh 0.165g of Pd(NO ₃ ) ₂ , 0.8g of AgNO ₃ , and 0.5ml of nitric acid to prepare a 1200ml mixed solution. Weigh 255g of the prepared functionalized-PVC/Al ₂ O ₃ precursor and add it to the Pd (NO ₃ ) ₂ , AgNO ₃ mixed solution, stirred for 30 min, poured out the raffinate, washed the above product with deionized water until neutral to obtain (Pd-Ag)-PVC/Al ₂ O ₃ precursor.

C. Preparation of catalyst

The precursor prepared above was calcined at 550° C. for 2 h in an air atmosphere to obtain an oxidized (Pd—Ag)/Al ₂ O ₃ catalyst. Place it in a fixed bed reaction device before use, use a mixed gas with a molar ratio of N ₂ : H ₂ =0.1:1, and perform a reduction treatment for 12 hours at a temperature of 120°C and a space velocity of 100h ^-1 to obtain a highly dispersed palladium- silver catalyst. The Pd content of the catalyst was measured to be 0.03%, and the Ag content was 0.2%.

The post-hydrogenation process is adopted, and the raw material composition is shown in Table 1.

Table 1 hydrogenation raw material composition

Hydrogenation raw material C ₂ H ₄ C ₂ H ₂ C ₂ H ₆ content (mol%) 75.5 1.5 twenty three

The technological reaction conditions are as follows: two-stage adiabatic bed reactors are used.

Material space velocity: 2000h ^- 1, operating pressure: 1.5MPa, catalyst filling volume: 300ml. The inlet temperature of the reactor is 45°C, H ₂ /C ₂ H ₂ =1:1 (V/V) at the inlet of the first-stage reactor; H ₂ /C 2 H _{2 =} 2:1 (V/V) at the inlet of the second-stage reactor, The results are shown in Table 2.

Comparative example 1

Catalyst preparation

Weigh 250 g of a columnar Al ₂ O ₃ carrier with a diameter of 4.5 mm, a length of 4.5 mm, a specific surface area of 15 m ² /g, a pore volume of 0.25 ml/g, and a bulk density of 1.1 g/cm ³ .

Weigh 0.165g Pd(NO ₃ ) ₂ , 0.8g Ag NO ₃ , measure 0.5ml nitric acid, and prepare 180ml solution. Add the above-mentioned carrier into the prepared solution, stir for 30 minutes, pour out the residue, dry and calcinate at 550°C for 8 hours to obtain (Pd-Ag)/Al ₂ O ₃ catalyst. Place it in a fixed-bed reaction device before use, use a mixed gas with a molar ratio of N ₂ :H ₂ =0.1:1, and perform a reduction treatment at 120° C. for 12 hours to obtain a highly dispersed palladium-silver catalyst. The Pd content of the catalyst was measured to be 0.03%, and the Ag content was 0.2%.

Carbon two hydrogenation flow process and processing conditions are identical with embodiment 1. After 500 hours of assessment, the results are shown in Table 2.

Table 2 500-hour post-assessment reaction results

Example 2

Catalyst preparation

A. Preparation of functionalized polystyrene acrylonitrile (SAN)/Al ₂ O ₃

Weigh 250g of a spherical Al ₂ O ₃ carrier with a diameter of 2.5mm, a specific surface area of 50m ² /g, a pore volume of 0.8ml/g, and a bulk density of 0.65g/cm ³

Weigh 1.1g of SAN resin, dissolve it in 300ml of DMF (dimethylformamide) solvent, stir at room temperature to completely dissolve the SAN resin, add the above-mentioned weighed carrier in this solution, leave it to stand for 6 hours after fully stirring, separate Solvent post-drying yields SAN/Al ₂ O ₃ .

Add the SAN/Al ₂ O ₃ obtained above into 500ml of deionized water, add 28.8g of ethylenediamine, reflux for 4h, take out the product after cooling, wash until neutral, and dry to obtain functionalized-SAN/Al ₂ O ₃ .

B. Preparation of (Pd-Ag)-SAN/Al ₂ O ₃ precursor

Weigh 0.47gPd(NO ₃ ) ₂ , 0.4gAgNO ₃ , measure 0.5ml nitric acid, and prepare a mixed solution of 1200ml, weigh 251.1g of the prepared functionalized-SAN/Al ₂ O ₃ precursor, and functionalize- SAN/Al ₂ O ₃ was added to the mixed solution of Pd(NO ₃ ) ₂ and AgNO ₃ , stirred for 5 minutes, and the raffinate was poured out, and the above product was washed with deionized water until neutral to obtain (Pd-Ag)-SAN /Al ₂ O ₃ precursor.

C. Preparation of catalyst

The precursor prepared above was calcined in an air atmosphere at 450° C. for 4 h to obtain a (Pd—Ag)/Al ₂ O ₃ catalyst. The Pd content of the catalyst was measured to be 0.06%, and the Ag content was 0.1%.

Comparative example 2

Catalyst preparation

Weigh 250 g of a spherical θ-Al ₂ O ₃ carrier with a diameter of 2.5 mm, a specific surface area of 50 m ² /g, a pore volume of 0.8 ml/g, and a bulk density of 0.65 g/cm ³ .

Weigh 0.47g Pd(NO ₃ ) ₂ and dissolve it in 300ml deionized water, adjust the pH value of the solution to 2.8 with dilute hydrochloric acid, immerse the carrier in the prepared solution, stir for 5min, pour out the raffinate, and C and dried for 10 hours to obtain catalyst A.

Weigh 0.4g AgNO ₃ and 0.5ml nitric acid to prepare 300ml solution. Add the above-mentioned carrier to the prepared solution, stir for 5 minutes, pour out the residual liquid, dry and roast at 450°C for 2 hours to obtain a (Pd-Ag)/Al ₂ O ₃ catalyst. The Pd content of the catalyst is measured to be 0.06 %, the Ag content is 0.1%.

Catalyst reduction:

Reducing gas: hydrogen, reducing space velocity: 100h ^-1 , temperature 80°C, keep for 8h.

Adopt post-hydrogenation process, its process flow chart is as shown in accompanying drawing 1 raw material composition is:

_C2H2 : 1.5% (V _% ) _{C2H4 80} % (V%), _C2H6 18.5% (V _% ).

Reaction conditions: Two-stage adiabatic bed reactors react in series, that is, the outlet material of the first-stage reactor enters the second-stage reactor. Each reactor has an independent gas distribution system.

Material gas space velocity: 5000h ^-1 , operating pressure: 1.9MPa, loading amount of catalyst in each reactor: 300ml. The inlet temperature of the first stage reactor is 40°C, H ₂ /C ₂ H ₂ =3:1 (V/V); the inlet temperature of the second stage reactor is 50°C, H ₂ /C ₂ H ₂ =2:1 (V/V) , the results after 500 hours of assessment are shown in Table 3.

Table 3 500-hour post-assessment reaction results

Example 3

Catalyst preparation

Weigh 250g of a columnar Al ₂ O ₃ carrier with a diameter of 4.5mm, a length of 4.5mm, a specific surface area of 25.m ² /g, a pore volume of 0.35ml/g, and a bulk density of 0.75g/cm ³ .

A, the preparation of functionalized chlorinated polyethylene (CPE)

Completely dissolve 8.0 g of CPE in 400 ml of THF, add 240 g of dicyandiamide and 2.0 g of Na ₂ CO ₃ , add CPE and reflux for 2 hours, cool to room temperature, wash with deionized water until neutral, and obtain functionalized CPE for use.

B. Preparation of (Pd-Ag)-polymer/Al ₂ O ₃ precursor

Weigh 0.22g of Pd(NO ₃ ) ₂ , 0.28g of Ag NO ₃ , and 0.5ml of nitric acid, add them into the above functionalized CPE solution, and stir for 60min to obtain (Pd—Ag)—CPE.

250g of carrier was added into the mixed solution, stirred thoroughly and left to stand for 4h, and the above product was washed with deionized water until neutral to obtain a (Pd-Ag)-CPE/Al ₂ O ₃ precursor.

C. Preparation of catalyst

The precursor prepared above was calcined at 500° C. for 4 h in an air atmosphere to obtain an oxidized (Pd—Ag)/Al ₂ O ₃ catalyst. Place it in a fixed-bed reaction device before use, use a mixed gas with a molar ratio of N ₂ :H ₂ =0.1:1, and perform a reduction treatment at 120° C. for 12 hours to obtain a highly dispersed palladium-silver catalyst. The Pd content of the catalyst was measured to be 0.04%, and the Ag content was 0.06%.

Comparative example 3

Catalyst preparation

Weigh 250 g of a columnar Al ₂ O ₃ carrier with a diameter of 4.5 mm, a length of 4.5 mm, a specific surface area of 25 m ² /g, a pore volume of 0.35 ml/g, and a bulk density of 0.75 g/cm ³ .

Weigh 0.22g Pd(NO ₃ ) ₂ , 0.28g AgNO ₃ , add 0.5ml nitric acid to prepare 87.5ml solution, spray the solution onto the above carrier and shake for 0.5 hours, after drying, bake at 500°C for 4h in air atmosphere to obtain (Pd—Ag)/Al ₂ O ₃ catalyst. The Pd content of the catalyst was measured to be 0.04%, and the Ag content was 0.06%.

Catalyst reduction: reducing gas: hydrogen, reduction space velocity: 200h ^-1 , temperature 180°C, keep for 8h.

The post-hydrogenation process is adopted, and the reaction raw materials are:

C ₂ H ₂ : 2.5 (V%) C ₂ H ₄ 80 (V %), C ₂ H ₆ 17.5 (V %).

Reaction conditions: Three-stage adiabatic bed reactor series process, that is, the outlet material of the first-stage reactor enters the second-stage reactor, and the outlet material of the second-stage reactor enters the third-stage reactor. Each reactor has an independent gas distribution system.

Material space velocity: 10000h ^-1 , operating pressure: 2.5MPa, catalyst filling volume: 300ml. The inlet temperature of the first stage reactor is 50°C, H ₂ /C ₂ H ₂ =1:1 (V/V); the inlet temperature of the second stage reactor is 80°C, H ₂ /C ₂ H ₂ =2:1 (V/V) ; The inlet temperature of the three-stage reactor is 100° C., and the H ₂ /C ₂ H ₂ =3:1 (V/V) test results after 500 hours are shown in Table 4.

Table 4 500-hour post-assessment reaction results

It can be seen that with the hydrogenation method of the present invention, the activity and selectivity of the hydrogenation reaction are much better than the traditional hydrogenation method, and the amount of green oil produced during the hydrogenation process is also greatly reduced. Due to the reduction of green oil, the active center of the catalyst is not covered by by-products, and the activity and selectivity of the catalyst are well maintained.

Claims (16)

1. A carbon distillate selective hydrogenation method, the fixed-bed reactor used for hydrogenation is located after the demethanizer, and the carbon dihydrogenation material from the front deethanizer in the ethylene unit is pressurized and hydrogenated Finally, it enters the adiabatic bed reactor for selective hydrogenation, which is characterized in that: the fixed bed reactor is equipped with a Pd-Ag catalyst, with Al ₂ O ₃ or a mixture of Al ₂ O ₃ and other oxides as the carrier, and the catalyst The mass of the catalyst is 100%, wherein the Pd content is 0.03-0.06%, the Ag content is 0.06-0.2%, the specific surface area of the catalyst is 15-50m ² /g; the pore volume is 0.25-0.8ml/g; the catalyst is prepared During the process, an organopolymer metal complex is formed; the reaction conditions are: fixed-bed reactor inlet temperature 40-100°C, reaction pressure 1.5-2.5MPa, gas volume space velocity 2000-10000h ^-1 ; catalyst acquisition includes the following steps : The organic macromolecule is grafted with a functional group by a complexing agent and loaded onto a catalyst carrier to obtain a functionalized-polymer/Al ₂ O ₃ precursor; prepare a palladium-silver solution, and load a functionalized-polymer/Al 2 O 3 precursor; _{The 2} O ₃ precursor is impregnated into the prepared palladium-silver solution for reaction, so that palladium and silver are complexed to the functionalized polymer chains, and palladium and silver form organic polymer metal complexes with organic polymers to obtain Pd-Ag-polymer/Al ₂ O ₃ precursor; roasting the Pd-Ag-polymer/Al ₂ O ₃ precursor at 380-550° C. for 2-6 hours. 2. The hydrogenation method according to claim 1, characterized in that the complexing agent can carry out a functionalization reaction with the side chain group of the macromolecule, and can complex the ions of Pd and Ag after the reaction. agent. 3. The hydrogenation method according to claim 2, characterized in that the functional group contained in the complexing agent is an amine group. 4. The hydrogenation method according to claim 1, characterized in that the side chain of the organic polymer contains a group that can react with a complexing agent. 5. The hydrogenation method according to claim 4, characterized in that the side chain of the organic polymer contains one or more of halogen and cyano groups that can react with complexing agents. 6. The hydrogenation method according to claim 1, characterized in that the crystal form of Al ₂ O ₃ is γ, δ, θ, α or a mixed crystal form of several of them. 7. The hydrogenation method according to claim 1, characterized in that when the catalyst is prepared, the organic polymer is grafted with a functional group by a complexing agent and loaded onto the catalyst carrier, which means: loading the organic polymer onto the catalyst carrier , and then graft functional groups on the loaded polymer chains through a complexing agent. 8. The hydrogenation method according to claim 1, wherein when the catalyst is prepared, the organic macromolecule is grafted with a functional group by a complexing agent and loaded onto the catalyst carrier, which means: firstly, the organic polymer is grafted by a complexing agent After grafting and functionalization, it is then loaded on a catalyst carrier to prepare a functionalized-polymer/Al ₂ O ₃ precursor. 9. The hydrogenation method according to claim 1, characterized in that the obtaining of the catalyst comprises the steps: the preparation method of the catalyst comprises the steps: A. Functionalization - Preparation of Polymer/Al ₂ O ₃ Precursor Dissolve the organic polymer in an organic solvent to form a polymer solution, then impregnate the carrier into the above solution, let the organic polymer deposit on the surface of Al ₂ O ₃ and dry it; then add a complexing agent containing functional groups Reflux for 0.5-300 minutes to prepare a functionalized-polymer/Al ₂ O ₃ precursor; B. Preparation of Pd-Ag-polymer complex/Al ₂ O ₃ precursor Prepare a palladium-silver solution, and adjust the pH value to 1-4 with inorganic acid, weigh the prepared functionalized-polymer/Al ₂ O ₃ precursor, and add the prepared palladium-silver solution to the precursor, 20-35 Immerse at ℃ for 5-60 minutes, wash and dry to obtain the Pd-Ag-polymer complex/Al ₂ O ₃ precursor; C. Catalyst Preparation The precursor prepared above is calcined at 380-550° C. for 2-6 hours to obtain a Pd-Ag/Al ₂ O ₃ catalyst. 10. The hydrogenation method according to claim 9, characterized in that the number of moles of functional groups on the polymer chain after functionalization/the number of moles of (Pd+Ag) is 100-1. 11. The hydrogenation method according to claim 9, characterized in that the number of moles of the complexing agent/the number of moles of reactive groups in the polymer is 100-1 in terms of moles. 12. The hydrogenation method according to claim 9, characterized in that the number of moles of the complexing agent/the number of moles of (Pd+Ag) is 10000-1. 13. The hydrogenation method according to claim 1, characterized in that the hydrogen/acetylene volume ratio is 0.8-4. 14. The hydrogenation method according to claim 1, characterized in that the number of reaction bed layers in the adiabatic bed reactor is two-stage or three-stage beds. 15. The hydrogenation method according to claim 14, characterized in that when the number of reaction bed layers in the adiabatic bed reactor is two stages, the hydrogen/acetylene volume ratio in the first stage reactor is 1 to 1.5, and the hydrogen gas in the second stage reactor The /acetylene volume ratio is 2-4. 16. The hydrogenation method according to claim 14, characterized in that when the number of reaction bed layers in the adiabatic bed reactor is three stages, the hydrogen/acetylene volume ratio of the first stage reactor is 0.8 to 1.2, and the second stage reactor hydrogen The hydrogen/acetylene volume ratio is 1-1.5, and the third-stage reactor hydrogen/acetylene volume ratio is 1.5-3.