CN1307134C - Method for removing small amount of acetylene in ethylene fraction - Google Patents

Abstract

A process for removing less acetylene from ethylene fraction by selective hydrogenation features that in magnetically stabilized bed reactor, the ethylene fraction containing less acetylene and magnetic noble metal catalyst are reacted at 25-150 deg.C, 0.5-5.0MPa, the molar ratio of hydrogen to acetylene hydrocarbon is 1-3: 1, and the volume space velocity is 1000-^-1The magnetic noble metal catalyst consists of spherical carrier and one or several noble metal active components selected from Pd, Ru and Rh, the spherical carrier consists of alumina and magnetic particle, and the magnetic particle consists of SiO₂A coating layer and an iron-containing substance core.

Description

A method for removing a small amount of acetylene in ethylene fractions

technical field

The invention relates to a method for selectively hydrogenating and removing a small amount of acetylene in ethylene fractions. More specifically, it relates to a method for selectively hydrogenating ethylene fractions with a magnetic noble metal catalyst in a magnetically stable bed reactor to remove a small amount of acetylene.

Background technique

In the petrochemical industry, ethylene is a monomer for preparing polymers, which can be produced by steam cracking or catalytic cracking. The ethylene fractions produced in this way all contain a small amount of acetylene, which is a poison for further processing of ethylene and affects the stability of the catalyst used in the further processing, so it must be removed. The industry usually adopts the method of selective hydrogenation to remove these small amounts of acetylene. Selective hydrogenation catalysts generally consist of an inert carrier and a Group VIII noble metal supported on it. At present, palladium is mostly used as an active component in industry. Selective hydrogenation is generally carried out in fixed bed reactors.

USP 5,648,576 discloses a method for the gas-phase selective hydrogenation of _C2 or _C3 alkynes to the corresponding alkenes. The method is to process the material containing _C2 or _C3 alkynes in the gas phase on a spherical or strip-shaped catalyst in the presence of hydrogen. The catalyst used comprises palladium and at least one metal of Group IB of the Periodic Table of the Elements (preferably silver) and alumina, wherein the weight ratio of metal of Group IB to palladium is 0.05-0.4, at least 80% of palladium and at least 80% of metal of Group IB Distributed within a catalyst volume bounded by a spherical or cylindrical surface of radius r ₁ (corresponding to the average radius of a spherical or extruded catalyst) and radius r ₂ (r ₂ equal to at least 0.8r ₁ ). The active components palladium and group IB metals are loaded on the carrier by impregnation method.

USP 5,847,250 discloses a catalyst for selective hydrodeacetylene removal from _C2 hydrocarbons. The catalyst uses silicon dioxide as a carrier, palladium with a load of 0.001-1% as an active component, and 0.005-5% of an alkali metal or an alkaline earth metal as an auxiliary active component. The catalyst is suitable for the removal of acetylene in the ethylene-ethane mixture with the acetylene content of 0.01-5% (volume).

Contents of the invention

The object of the present invention is to provide a method for selectively hydrogenating ethylene fractions to remove a small amount of acetylene using a magnetic noble metal catalyst in a magnetically stable bed reactor.

The method provided by the invention is to make the ethylene fraction containing a small amount of acetylene and the magnetic noble metal catalyst in a magnetically stable bed reactor at a reaction temperature of 25-150°C, a reaction pressure ^of 0.5-5.0MPa, and a volume space velocity of 1000-24000 hours- ^1. The molar ratio of hydrogen to acetylene is 1-3:1, and the magnetic field strength is 10-1000 Oersted. The magnetic noble metal catalyst is composed of a spherical carrier and one or Composed of several noble metal active components, the spherical carrier is composed of alumina and magnetic particles, and the magnetic particles are composed of SiO ₂ coating layer and inner core of iron-containing substance.

The applicable ethylene fraction of the method of the present invention is the ethylene fraction of 0.01-5 volume % from the acetylene content of steam cracking or catalytic cracking unit for example, wherein also can contain ethane and a small amount of propylene, methane, hydrogen etc. from industrial equipment.

The magnetically stable bed reactor mentioned in the method of the present invention is a reactor in which there is a uniform magnetic field in the reactor, and the catalyst with ferromagnetism interacts stably in the reactor due to the existence of the magnetic field and does not flow with the reaction materials. . The magnetically stabilized bed reactor is composed of a reactor and an external magnetic field. The external magnetic field is a uniform and stable magnetic field along the axis of the reactor. The uniform magnetic field is composed of a DC power supply and a series of Helmholtz coils coaxial with the reactor or evenly wound Solenoids are provided, and the reactor and other parts of the reactor are made of materials with good magnetic permeability.

The preferred reaction conditions of the inventive method are: reaction temperature is 25-100 DEG C, reaction pressure is 1.0-3.0MPa, volume space velocity is 1000-18000 hours ^-1 , hydrogen and acetylene feed molar ratio is 1-2: 1, The magnetic field strength is 50-800 Oersted.

Said magnetic noble metal catalyst in the method of the present invention is to be selected from palladium, ruthenium, rhodium in one or more noble metals, preferred noble metal palladium and the rest Spherical vector composition. In order to facilitate the use in a magnetically stable bed reactor, the particle size of the catalyst should preferably be between 10 μm and 1 mm.

The spherical carrier is composed of 1-50% by weight of the carrier, preferably 2-15% by weight of magnetic particles and the balance of alumina. The magnetic particles wherein the weight ratio is (0.05-6): 1, preferably (0.3-4.0): 1 SiO ₂ coating layer and uniformly dispersed therein, one or more particles with a particle size of 3-30 nanometers, Its chemical composition is the inner core composition of one or several iron-containing substances selected from Fe ₃ O ₄ , Fe and γ-Fe ₂ O ₃ . The alumina in it can be in any crystal phase, and can be selected from p-, x-, η-, γ-alumina of various low-temperature transition phases, and can also be selected from k-, δ-, θ of various high-temperature transition phases - One or more mixtures of alumina and α-alumina.

In the above-mentioned magnetic particles, the amorphous SiO ₂ cladding layer tightly covering the inner core is firmly combined with the inner core to form magnetic particles. For magnetic particles with multiple particles in the inner core, the particles are uniformly distributed due to the barrier of _SiO2 .

Said spherical carrier is measured by a vibrating sample magnetometer, and its hysteresis loop has no hysteresis; when an external magnetic field exists, it has good magnetic properties; when an external magnetic field H=0, the residual magnetization Mr and The coercive force Hc is zero and has superparamagnetism.

The spherical carrier composed of magnetic particles and alumina has good thermal stability and corrosion resistance, and due to the isolation effect of the _SiO2 coating, it can avoid the formation of iron components at high temperatures between the core iron component and the carrier alumina component. aluminum spinel.

The preparation method of said spherical carrier in the inventive method is as follows:

Step 1—Preparation of carrier core magnetic particles: Add alkali to the aqueous solution containing Fe ²⁺ and Fe ³⁺ salts at 50-100°C, transfer the precipitated Fe ₃ O ₄ particles into sodium silicate aqueous solution, and inert gas Under the protection of , use acid to adjust the pH to ≤ 7 to obtain SiO ₂ coated Fe ₃ O ₄ particles of magnetic particles. Wherein, said alkali is selected from KOH, NaOH, NH ₄ OH, Na ₂ CO ₃ or NaHCO ₃ or a mixture thereof; the molar ratio of Fe ²⁺ to Fe ³⁺ in said iron salt solution is 1 : (0.5-2.5), preferably 1: (1.5-2); the molar ratio of the ^OH- of the base to Σ(Fe ²⁺ +Fe ³⁺ ) is 1: (0.1-1.0); the silicic acid The molar ratio of sodium to _Fe3O4 is 1:(0.04-5), preferably 1:(0.06-1); _said acid is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid or acetic acid mixture of species.

Step 2—Preparation of spherical carrier: at 10-35°C, the aluminum hydroxide sol, the organic amine solution and the magnetic particles obtained in step 1 are mixed according to the volume ratio of the aluminum hydroxide sol and the organic amine solution 1: (0.4-3.5) , Aluminum hydroxide sol and the weight ratio of magnetic particles 1: (0.02-0.2), the three are mixed and dispersed evenly, and then it is 1: (3-20) with kerosene or vegetable oil, preferably 1: ( 4-10) to form water-in-oil droplets, the heating system solidifies the aluminum hydroxide sol in the water phase, and then undergoes the same hydrothermal treatment, aging, drying and The calcination step can be used to obtain the spherical carrier. The organic amine mentioned here refers to the organic nitrogen-containing compound whose pH value is close to neutral at normal temperature, but can release alkaline substances after thermal decomposition, such as urea or hexamethylenetetramine, which can be used alone or in combination , the concentration of the organic amine solution is preferably 12-40% by weight; said dispersing means can be selected from various conventional methods, such as: stirring, shaking, ultrasonic and so on.

The catalyst used in the method of the present invention is obtained by impregnating the spherical carrier prepared above with an impregnation solution containing precious metals, followed by drying, calcining and reduction. The impregnating solution is made of noble metal salts (such as palladium chloride, ruthenium chloride, rhodium chloride, etc.), inorganic acid and deionized water, said inorganic acid is preferably hydrochloric acid, and the pH value of the impregnating solution is 2-6; The drying temperature is room temperature-120°C; the calcination temperature is 150-600°C; the reduction is carried out at 50-500°C in a hydrogen atmosphere, or with reducing agents such as formaldehyde and hydrazine hydrate.

The method for removing acetylene provided by the present invention has the following advantages due to the use of a magnetically stable bed reactor, and the catalyst used has superparamagnetism:

1. Catalysts with superparamagnetism are arranged in a chain in the external magnetic field, the bed is uniform and stable, and there is no channel flow; the external magnetic field can break the bubbles, realize scattered fluidization, and have high mass transfer and heat transfer efficiency.

2. The external magnetic field can prevent the catalyst from being carried out, so fine particle catalysts can be used, which not only helps to accelerate the mass transfer rate, but also prevents further deep hydrogenation of ethylene, thereby obtaining highly selective products.

Detailed ways

The present invention will be further described below by way of examples, but the present invention is not limited thereto.

Example 1

This example illustrates the preparation of spherical supports for catalysts used in the process of the invention.

Dissolve 189g Na ₂ SiO ₃ ·9H ₂ O in 1000mL distilled water, slowly add 3mol/L HCl solution dropwise under stirring condition, adjust the pH value of the solution to 13, filter and set aside.

Add 42.2g FeCl ₃ 6H ₂ O and 20.6g FeCl ₂ 4H ₂ O to a 3L stirred tank with 1200mL of distilled water, raise the temperature to 85-90°C, add 60mL of 25% NH ₃ H ₂ O during high-speed stirring The solution was stirred at high speed for 3 minutes, and the Fe ₃ O ₄ particle product was separated by a magnetic separator. Ultrasonically disperse the cleaned precipitated product in the above-mentioned pretreated Na ₂ SiO ₃ solution, then transfer it into a 3L stirred tank, raise the temperature to 85°C, and slowly add a concentration of about 2mol into the solution under nitrogen protection and stirring conditions. /L of HCl solution, the pH value of the solution will drop from 13 to 6 in about 3 hours. The magnetic particles of SiO ₂ coated Fe ₃ O ₄ particles were obtained. The total weight of the above product magnetic particles is about 60g, which contains about 20g of Fe ₃ O ₄ and about 40g of SiO ₂ coated on the surface of Fe ₃ O ₄ , which is amorphous SiO ₂ . The magnetic hysteresis loop detected by the vibrating sample magnetometer (VSM) shows that the magnetic particles have superparamagnetism. This component is abbreviated as SF.

Weigh 80g of AlCl ₃ 6H ₂ O, dissolve it in 600ml of deionized water, add 44g of high-purity aluminum foil, and keep it at 80-100°C for 60-72 hours to fully dissolve the aluminum foil in the solution, then heat and concentrate the solution volume to 300ml, to obtain a clear translucent sol, wherein the aluminum/chlorine weight ratio is about 1.5: 1.0, and the aluminum in the sol is converted into aluminum oxide and is about 100g. This sol is abbreviated as AL1.

At 10°C, measure 100ml of AL1 aluminum hydroxide sol, mix it with 90ml of organic amine solution (containing 300g/L hexamethylenetetramine and 150g/L urea), stir evenly, and then add 7.3g SF coating type The magnetic component particles were poured into a 3L stirred tank filled with 1600ml of sulfonated kerosene (containing 0.05% by volume of surfactant Span80) after fully stirring. At room temperature, disperse uniformly at a speed of 700 rpm to form a water-in-oil emulsion, then raise the temperature of the system to 85-90°C, keep it for 15 minutes, then cool and separate the product to obtain magnetic spherical Al(OH) ₃ . This spherical product is abbreviated as AL2.

Put _the above-mentioned magnetic spherical Al(OH) product AL2 into a 1L autoclave filled with 0.7L sulfonated kerosene medium, and conduct a hydrothermal treatment at 180°C for 2 hours under the protection of nitrogen. ) in dilute ammonia water at 80°C for 5 hours to remove some of the impurities, and after drying at 60°C, a magnetic spherical Al(OH) ₃ product with a boehmite structure (α-AlOOH) can be obtained. This product is abbreviated as AL3. AL3 is composed of α-AlOOH, Fe ₃ O ₄ and γ-Fe ₂ O ₃ etc. During the hydrothermal treatment, aging and drying process, the Fe ₃ O ₄ in the product is partially oxidized to γ-Fe ₂ O ₃ .

The above-mentioned boehmite product AL3 was sintered at 580° C. in an air atmosphere for 2 hours to obtain about 45 g of spherical γ-Al ₂ O ₃ carriers containing γ-Fe ₂ O ₃ magnetic cores.

The average particle size of the spherical carrier is about 200 μm, and the weight ratio of each component is: γ-Fe ₂ O ₃ : SiO ₂ : Al ₂ O ₃ = 6: 12: 82. The carrier has superparamagnetic characteristics, and the ratio The saturation magnetization was 2.97A·m ² /Kg. The BET specific surface of the carrier is 200m ² /g, and the pore volume is 0.75mL/g.

Example 2

This example illustrates the preparation of the palladium catalyst used in the process of the present invention.

Take 10 g of the spherical carrier prepared in Example 1, add PdCl ₂ and hydrochloric acid to form 30 ml of an impregnating solution with a Pd content of 0.0035 wt % and a pH of 4.5, impregnate the carrier at room temperature for 2 hours, and place the impregnated PdCl ₂ carrier in an oven at 70° C. Dry for 2 hours, dry at 120°C for 2 hours, then bake in a muffle furnace at 300°C for 4 hours, and then reduce it with hydrogen at 100°C for 4 hours. The prepared catalyst is designated as Catalyst-1, and the Pd content in the catalyst is 0.01 wt%.

Example 3

This example illustrates the preparation of the ruthenium catalyst used in the process of the present invention.

Take 10 g of the spherical carrier prepared in Example 1, add RuCl ₃ and hydrochloric acid to form 30 ml of an impregnating solution with a Ru content of 0.105 wt % and a pH of 4.5, impregnate the carrier at room temperature for 2 hours, and place the RuCl _- impregnated carrier in an oven at 70° C. Dry for 2 hours, dry at 120°C for 2 hours, then bake in a muffle furnace at 300°C for 4 hours, and then reduce it with hydrogen at 100°C for 4 hours. The prepared catalyst is designated as Catalyst-2, and the Ru content in the catalyst is 0.3 wt%.

Example 4-11

These examples illustrate the effect of the method of the invention performed at different space velocities.

8 g of Catalyst-1 with a particle size of 60-80 microns were charged into a reactor with an inner diameter of 13.5 mm. Four copper coils with an inner diameter of 65 mm, an outer diameter of 160 mm, a thickness of 60 mm and a number of turns of 400 are arranged along the axis of the reactor to provide a uniform magnetic field, and the distance between the axes of the coils is 70 mm. The reaction material (mixed gas of ethylene and acetylene) enters from the lower part of the reactor and flows out from the upper part, under the conditions of reaction temperature of 75°C, pressure of 1.5MPa, magnetic field strength of 300 Oersted, and hydrogen to acetylene feed molar ratio of 1.2:1 The selective hydrogenation reaction is carried out under the reactor outlet, and the gas chromatography is used for analysis at the outlet of the reactor.

Table 1

Example Acetylene content, volume % Airspeed, hour ^-1 Acetylene conversion rate, % Ethylene selectivity, % 4567891011 0.660.660.660.661.02.03.04.5 6000900012000180007000500030002000   100.099.798.393.6100.0100.096.792.8 82.290.392.593.290.289.190.591.6

Examples 12-17

These examples illustrate the effect of the method of the invention implemented under different reaction conditions (magnetic field strength, reaction temperature, reaction pressure).

Carry out selective hydrogenation reaction according to the said method of embodiment 4-11. The reaction material (mixed gas of ethylene and acetylene) contains 0.66% by volume of acetylene, the space velocity is 9000 h ^-1 , and the molar ratio of hydrogen to acetylene is 1.2:1. The implementation effects under different magnetic field strengths, reaction temperatures, and reaction pressures are listed in Table 2.

Table 2

Example temperature, ℃ Pressure, MPa Magnetic Field Strength, Oersted Acetylene conversion rate, % Ethylene selectivity, % 121314151617 3010075757575 1.51.50.84.01.51.5 30030030030060700 60.210085.410093.889.2 98.363.293.681.291.390.5

Example 18

This example illustrates the implementation effect when using a ruthenium catalyst in the method of the present invention.

According to the method described in Example 4-11, 8 g of catalyst-2 with a particle size of 60-80 microns was added to a magnetically stabilized bed reactor with an inner diameter of 13.5 mm. The reaction material (mixed gas of ethylene and acetylene) containing 3.0% by volume of acetylene enters from the lower part of the reactor and flows out from the ^upper part. 1. The selective hydrogenation reaction is carried out under the condition that the molar ratio of hydrogen to acetylene feed is 1.2:1. The reaction results showed that the conversion rate of acetylene was 99.3%, and the selectivity of ethylene was 66.2%.

Comparative example 1

This comparative example illustrates the comparison of the effect of the selective hydrogenation of acetylene in ethylene with the method provided by the present invention and the industrial catalyst G83-C (commercial product of NGC Corporation, Japan) in a fixed-bed reactor.

The reaction mass had the same composition: an ethylene-acetylene mixture with an acetylene content of 0.66% by volume.

When the method of the present invention is adopted, the reaction conditions in the magnetically stabilized bed reactor are temperature 75° C., pressure 1.5 MPa, volume space velocity 9000 hours ⁻¹ , hydrogen to acetylene feed molar ratio 1.2:1, and magnetic field strength 300 Oersted.

The reaction conditions in the fixed-bed reactor used for comparison are: temperature 75°C, pressure 1.5 MPa, volumetric space velocity 9000 hours ⁻¹ , hydrogen to acetylene feed molar ratio 1.2:1.

Analyzed by gas chromatography at the outlet of the reactor, the results are listed in Table 3.

table 3

Catalyst Acetylene conversion rate, % Ethylene selectivity, % Catalyst-1G83-C 99.799.5 90.386.5

Claims (8)

1. A method for selective hydrogenation to remove a small amount of acetylene in the ethylene fraction, which is to make the ethylene fraction with an acetylene content of 0.01-5% by volume and a magnetic noble metal catalyst in a magnetically stable bed reactor at a reaction temperature of 25-150°C , the reaction pressure is 0.5-5.0MPa, the molar ratio of hydrogen and acetylene feed is 1-3:1, the volume space velocity is 1000-24000 hours ^-1 , and the magnetic field strength is 10-1000 Oersted. The catalyst consists of a spherical carrier and one or more noble metal active components selected from palladium, ruthenium, and rhodium. The spherical carrier is composed of alumina and magnetic particles. The magnetic particles are covered by _SiO2 and contain The inner core of the iron substance. 2. The method according to claim 1, wherein the reaction temperature is 25-100° C., the reaction pressure is 1.0-3.0 MPa, the molar ratio of hydrogen to acetylene is 1-2:1, and the volume space velocity is 1000-3.0 MPa. 18000 hours ^-1 , magnetic field strength 50-800 Oersted. 3. The method according to claim 1, wherein said magnetic noble metal catalyst is composed of one or more noble metal active components selected from palladium, ruthenium, rhodium and the balance spherical Vector composition. 4. The method according to claim 3, wherein the noble metal in the catalyst is palladium, which accounts for 0.01-0.3% by weight of the catalyst. 5. The method according to claim 1, wherein said spherical carrier is composed of magnetic particles in an amount of 1-50% by weight of the carrier and the balance of alumina. 6. The method according to claim 5, wherein the magnetic particles in said spherical carrier account for 2-15% by weight of the carrier. 7. The method according to any one of claims 1, 5 and 6, wherein the magnetic particles in the spherical carrier are composed of a _SiO2 coating with a weight ratio of (0.05-6): 1 and uniformly dispersed therein, One or more single-domain superparamagnetic particles with a particle size of 3-30 nanometers and a chemical composition of one or more iron-containing substances selected from Fe ₃ O ₄ , Fe and γ-Fe ₂ O ₃ Kernel composition. 8. The method according to claim 7, wherein the magnetic particles in the spherical carrier consist of a _SiO2 coating layer and a magnetic particle inner core in a weight ratio of (0.3-4.0):1.