RU2387477C1 - Catalyst, method of preparing said catalyst and method of purifying olefins - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: described is a catalyst which contains 0.01-1.0 wt % palladium in form of particles with controlled size ranging from 1.5 to 20 nm, deposited on bidispersed silica gel. A method of preparing the palladium catalyst is described, which is characterised by that, a dried support which contains an alkali metal in amount of not more than 0.01 wt, bidispersed silica gel with specific surface area of 150-350 m²/g, total pore volume of 0.8-1.2 cm³/g with complete absence of micropores, volume of mesopores with radius of approximately 50 Ǻ 0.60-0.85 cm³/g and volume of macropores with radius of 1000-5500 Ǻ - 0.15-0.30 cm³/g, is impregnated with an aqueous solution of stabilised palladium nitrate at certain pH values, with subsequent drying, calcination in air and reduction. Also described is a method of purifying olefins from impurities of polyunsaturated hydrocarbons through catalytic hydrogenation in the presence of the catalyst described above.

EFFECT: increased degree of purity of olefins from polyunsaturated hydrocarbons up to 0,1 ppm, reduced loss of olefin material and prevention of formation of undesirable oligomers which lead to deactivation of the catalyst.

7 cl, 1 tbl, 4 ex

Description

The invention relates to the purification of olefin streams of various origins from impurities of polyunsaturated hydrocarbons, in particular to catalysts for the purification of olefin raw materials for polymerization processes by the selective hydrogenation of polyunsaturated impurities.

In recent years, for newly developed highly effective olefin polymerization catalysts, restrictions on the concentration of alkynes and polyolefins have become increasingly stringent. For example, for fraction C ₂ after 1980, the acetylene content was limited to 1 ppm or less, and for some processes that have special requirements, such as the production of high density polyethylene, the acetylene content in purified ethylene was limited to 0.1 ppm or less .

Therefore, a common problem is to increase the efficiency of removing polyunsaturated hydrocarbons, such as acetylene, from olefins. Typically, a catalytic selective hydrogenation process is used for this purpose.

During selective hydrogenation to remove polyunsaturated compounds to a residual content of less than 0.1 ppm, excessive hydrogenation should not occur to avoid loss of olefin feed. Therefore, both a high activity in the hydrogenation of polyunsaturated hydrocarbons and an increased selectivity are required from a hydrogenation catalyst. Moreover, acetylene compounds adsorbed on the catalyst surface easily dimerize during hydrogenation to form C ₄ -C ₆ diene hydrocarbons, for example, butadiene-1.3, which, in turn, can subsequently react with acetylenes or olefins to form oligomers, better known as "Green oil". Part of the “green oil” can be retained on the surface of the catalyst and cover the active sites of the catalyst, which leads to a gradual decrease in the activity and selectivity of hydrogenation, to a reduction in the working cycle of the catalyst, which requires more frequent regeneration, which reduces the life of the catalyst and leads to an increase in production costs. Therefore, a selective hydrogenation catalyst having excellent characteristics should have high activity and selectivity, as well as a reduced tendency to form green oil and, especially, its retention at the active sites of the catalyst.

For selective hydrogenation, generally supported heterogeneous catalysts are used from metals of the eighth group of the Periodic Table of the Elements, preferably nickel, palladium and platinum. In most cases, palladium is used.

The support used is generally a porous inorganic oxide, for example silica, aluminosilicate, titanium dioxide, zirconium dioxide, zinc aluminate, zinc titanate, spinel and / or mixed oxide compositions based on these carriers, however, for the most part, oxides are used as the carrier aluminum, preferably low-surface, since the surface centers of the carriers catalyze the side formation of oligomerization products (the so-called green oil), which clog the pores and block the act Willow catalyst sites, resulting in shorter catalyst lifetimes. There are only a few publications that describe catalysts for selective hydrogenation on supports other than alumina, in which metals of the eighth group are supported on titanium dioxide, carbon or silica materials.

The advantage of silicon dioxide is that it has a significantly lower specific gravity in comparison with alumina. Supported catalysts with a low bulk density are generally more economical than catalysts having a large bulk density.

One of the first patents, which showed a lesser tendency of a carrier such as silica gel to form green oil, appeared in 1983. US Pat. No. 4,387,258, B01J 21/08, 06/07/1983, discloses a method for preparing platinum or palladium catalysts with a particle size of the active component of 2-20 nm on crystalline silica gel polymorph with certain diffraction characteristics for the selective hydrogenation of polyunsaturated compounds in olefin feedstock.

Patent RU 2118909, B01J 37/02, 09/20/1998, discloses a method for producing a catalyst for the selective hydrogenation of acetylene and diene compounds, using a palladium catalyst mounted on low-porous supports - alpha-alumina (S _beats = 2-40 m ² / g) or macroporous silica gel (S _beats. = 30-60 m ² / g). The catalyst is promoted with silver or lithium, and palladium is reduced by allylic compounds in the liquid phase, followed by activation in hydrogen. The use of silica gel made it possible to achieve a visible absence of green oil, however, the efficiency of ethylene purification is insufficient - the residual acetylene content in the mixtures at T 100 ° C reaches 5 ppm, and deactivation of the catalyst is also observed.

In later patents, it is noted that when ethylene is purified from acetylene impurities on Pd / SiO ₂ , as well as on lanthanum-modified Pd / SiO ₂ , catalyst deactivation is associated with the formation of green oil (EP 1611072, B01J 23/58, 04.01. 2006; EP 1700836, C07C 5/09, B01J 23/44, 09/13/2006).

The closest is a catalyst for the selective hydrogenation of alkynes and dienes in _C2-C5 + -olefin mixtures, which comprise palladium in an amount of 0.005-1.0 wt.% Of the catalyst in the boundary layer and are uniformly distributed over the silver carrier in an amount of 0.005-1.5 wt.% which are deposited on silica with a BET surface of 20 to 400 m ² / g, preferably 100 to 160 m ² / g, and a pore volume of 0.1 to 1.5 ml / g, preferably 0.7 to 1.2 ml / g. The catalyst is prepared by impregnating the support with a solution of silver nitrate, then the support is calcined, molded and impregnated with a solution of palladium nitrate, dried and calcined (RU 2290258, B01J 23/56, 23/66, C07C 5/03, 5/08, 12/20/2002).

The disadvantage of the known catalyst on silicon dioxide as a carrier is the insufficient depth of purification of ethylene from acetylenes, the formation of a significant amount of ethane and the occurrence of side reactions of the formation of undesirable oligomers.

An object of the present invention is to provide a catalyst for the selective hydrogenation of polyunsaturated compounds in olefin mixtures, having a high activity in the hydrogenation of polyunsaturated compounds and a low degree of formation of complete hydrogenation products and undesired oligomers.

Under the olefin mixtures in the context of the present invention refers mainly to the so-called hydrocarbon products obtained by cracking petroleum distillates or natural gas, which contain mainly olefins. However, the method according to the invention can also be used for the selective hydrogenation of alkynes and dienes in olefin mixtures, which are obtained in other processes. Hydrogenation can be carried out as a pure gas-phase process, and as a gas-liquid-phase process. The reaction parameters, for example, the flow rate of a hydrocarbon stream, the ratio of hydrogen to polyunsaturated hydrocarbons, temperature and pressure, are optimized similarly to known methods.

To solve this problem, a catalyst is proposed that contains

a) palladium in an amount of from 0.01 to 1 wt.%;

b) mounted on a carrier made of bidispersed silicon dioxide, not containing sodium;

c) palladium is in the form of particles with an adjustable average size in the range from 1.5 to 20 nm.

Another object of the invention is a method for producing said catalyst, in which a solution of the precursor of the active component is impregnated on a prepared carrier, the resulting material is dried, calcined and reduced with hydrogen.

A catalyst for the purification of olefins from impurities of polyunsaturated hydrocarbons is described, containing palladium in an amount of 0.01 ÷ 1.0 wt.% With an adjustable particle size of the active component in the range from 1.5 to 20 nm, deposited on bidispersed silica gel. Bidispersed silica gel containing an alkali metal in an amount of no higher than 0.01 wt.% Has the following characteristics: specific surface area 150 ÷ 350 m ² / g, total pore volume 0.8 ÷ 1.2 cm ³ / g, no micropores, mesopore volume s with a radius of about 50 Ǻ is 0.60 ÷ 0.85 cm ³ / g, and the volume of macropores with a radius of 1000-5500 Ǻ is 0.15 ÷ 0.30 cm ³ / g.

A method for preparing a palladium catalyst for the purification of olefins from impurities of polyunsaturated hydrocarbons is described, characterized in that the pre-dried carrier containing an alkali metal in an amount of not higher than 0.01 wt.%, Bidispersed silica gel with a specific surface area of 150 ÷ 350 m ² / g, total pore volume 0 , 8 ÷ 1.2 cm ³ / g in the complete absence of micropores, with a volume of mesopores with a radius of about 50 Ǻ 0.60 ÷ 0.85 cm ³ / g and a volume of macropores with a radius of 1000-5500 Ǻ 0.15 ÷ 0.30 cm ³ / g, impregnated with an aqueous solution of stabilized palladium nitrate when determined pH, after which the catalyst is dried, calcined in air and then reduced in a stream of hydrogen-containing gas, the result is a catalyst containing palladium in an amount of 0.01 ÷ 1.0 wt.% with an adjustable particle size of the active component in the range from 1.5 to 20 nm deposited on bidispersed silica gel.

In addition to stabilized palladium nitrate, citric acid is added to the impregnation solutions to prevent agglomeration of palladium-containing particles on the surface of the carrier.

The pH adjustment of the impregnating solutions containing stabilized palladium nitrate is carried out without the introduction of alkali metal cations due to alkalization with an aqueous solution of tetramethylammonium hydroxide.

A method is described for purifying olefins from polyunsaturated hydrocarbon impurities by catalytic hydrogenation at elevated temperatures in the presence of the supported palladium catalyst described above, hydrogenation is carried out at atmospheric pressure, a temperature of 50-200 ° C, and a space velocity of 10000-20000 h ^-1 .

Bidispersed silica gel is obtained by the method of construction from prefabricated structural elements described in the works of the school of Professor Dzisko V.A. [one. V.A.Dzisko, A.P. Karnaukhov, D.V. Tarasova. Physicochemical basis for the synthesis of oxide catalysts. Publishing House "Science" Siberian Branch, Novosibirsk 1978; 2. V.A. Dzysko, D.V. Tarasova, A.S. Tikhov, R.I. Nazarov, G.P. Vishnyakova, M.A. Guseva. The influence of the preparation method on the porous structure and strength of catalysts and carriers. Kinetics and catalysis, vol. 9, issue 3, p. 668, 1968].

The method consists in bonding silica gel particles of a given size with internal porosity using a binder. KSK grade industrial silica gel, purified from sodium, was used as the starting material, and SiO ₂ hydrogel containing sodium in an amount of no higher than 0.01 wt% was used as a binder.

The specific surface area of the carrier used is 150 ÷ 350 m ² / g, the total pore volume is 0.8 ÷ 1.2 cm ³ / g, there are no micropores, the volume of mesopores with a radius of about 50 Ǻ is 0.60 ÷ 0.85 cm ³ / g, and the volume of macropores with a radius of 5500 Ǻ is 0.15 ÷ 0.30 cm ³ / g.

The catalysts are prepared by impregnating the support previously dried at 110-130 ° С with an aqueous solution of stabilized palladium nitrate, taken in a twofold excess relative to the total pore volume of the support, at various pHs (in the slightly acidic region at pH 4 ÷ 5 and the slightly alkaline region at pH 8 ÷ 9). Palladium adsorption is carried out for 1 h, after which the excess solvent is removed at 50 ÷ 60 ° C on a rotary evaporator in a vacuum water-jet pump. An air-dry sample of the supported catalyst is dried at 110–130 ° С for at least 4 hours, after which it is calcined for 4 hours in air at 400 ° С and then reduced in a stream of hydrogen at 300 ± 5 ° С for 3 hours.

The invention is illustrated by the following examples.

Example 1

20 ml of distilled water are poured into a powder flask for drying powders, in which 171 mg of citric acid are dissolved and 280 μl of an aqueous solution of palladium nitrate containing 10.3 wt.% Pd is then added. The resulting slightly acidic solution is thoroughly mixed, with stirring, 4.5 g of a SiO ₂ support _{of a} fraction of 0.25 ÷ 0.50 mm, dried immediately before synthesis at 120 ° C for 4 hours (specific surface area according to BET 296 m ² / g, total pore volume 0, 95 cm ³ / g, micropores are absent, the volume of mesopores is 0.65 cm ³ / g with an average diameter of 10.7 nm, and the volume of macropores with a radius of more than 1000 Ǻ is 0.30 cm ³ / g, containing no more than an alkali metal 0.01 wt.%). After that, the flask-glass is fixed on a rotary evaporator and stirring is continued for 1 h, after which the excess solvent is removed in a vacuum water-jet pump at 50-60 ° C.

Next, the air-dry sample is dried in an oven at 120 ° C for 4 hours, calcined for 4 hours in air at 400 ° C. The calcined sample is placed in a flow reactor and purged with argon, heating to 160 ° C, and maintained at this temperature for 30 minutes. After that, the gas is switched to a nitrogen-hydrogen mixture

(H ₂ / N ₂ = 1: 3), incubated for another 30 min at 160 ° C in this mixture, then brought the temperature to 300 ° C and maintained at 300 ° C for 3 hours. At all stages, the rate of temperature rise is 3 ° / min

The palladium content in the catalyst obtained in this way is 1.0 wt.%, Particle size 2.5 nm, dispersion 27%.

Example 2

In 19.5 ml of distilled water, 280 μl of an aqueous solution of palladium nitrate containing 10.3 wt.% Pd; the resulting solution was thoroughly mixed, then 600 μl of a 25% aqueous solution of tetramethylammonium hydroxide was added to it, adjusting the pH of the impregnation solution to 8. The obtained weakly alkaline solution of palladium nitrate was poured into a flask for drying powders, after which 4.5 g was added with stirring SiO ₂ support, fractions 0.25-0.50 mm, dried immediately before synthesis at 120 ° C for 4 h (BET specific surface area 205 m ² / g, total pore volume 1.10 cm ³ / g, no micropores, mesopore volume 0, 85 cm ³ / g with an average diameter of 11.9 nm, and about the volume of macropores with a radius of more than 1000Å is 0.25 cm ³ / g). The suspension is stirred for 1 h, after which the excess solvent is removed on a rotary evaporator in a vacuum water-jet pump. The sample is dried, calcined and reduced according to the procedure described in Example 1. The palladium content in the catalyst was 0.97 wt.%, The metal particle size was 10 nm, and the dispersion was 8%.

Example 3

Similar to example 1, only the amount of palladium is reduced by 10 times. The palladium content in the catalyst obtained in this way is 0.1 wt.%, The palladium particle size is 1.7 nm, and the dispersion is 60%.

Example 4

Similar to example 2, only the amount of palladium is reduced by 10 times. The palladium content in the catalyst obtained in this way is 0.1 wt.%, The palladium particle size is 3.7 nm, and the dispersion is 30%.

The test of the catalysts is carried out in a laboratory flow reactor at atmospheric pressure, a temperature of 50-200 ° C, space velocity

10000-20000 h ^-1 , which vary by changing the weight of the catalyst.

0.25 ÷ 1.0 g of the catalyst sample is loaded into the reactor and reduced in a hydrogen stream of 3 l / h at 200 ° C for 1 hour. Then, the catalyst is cooled to the desired reaction temperature. Then, at a speed of 10 l / h, the initial reaction mixture of the composition С ₂ Н ₂ 1.0% vol., Н ₂ 1.0 ÷ 3.1% vol., The rest С ₂ Н _{4 is} fed into the reactor.

When testing the catalyst, the composition of the reaction products is determined every 10 minutes. The analysis is carried out on a Crystal-2000M chromatograph with a thermal conductivity detector for determining the concentration of hydrogen and a flame ionization detector for determining the concentration of organic compounds connected in series, which makes it possible to determine all components of the reaction mixture from one sample. The chromatographic system used makes it possible to determine the content of unreacted acetylene up to 0.05 ppm.

The test results of the catalysts during the hydrogenation of acetylene in ethylene are presented in the table.

The test results of the catalysts show that on the studied catalysts the content of unreacted acetylene is less than 0.1 ppm, the formation of ethane does not exceed 2% vol. During an experiment lasting 3 hours, the activity of the catalyst is stable, there are no signs of deactivation, C ₄ dimers and green oil are absent among the products.

Table Selective hydrogenation of acetylene in ethylene on Pd / SiO ₂ catalysts, with different Pd contents and average Pd particle sizes. Reaction conditions: t = 100 ÷ 200 ° С, C _H2 = 3.1% vol., C _C2H2 = 1% vol., In a stream С ₂ Н ₄ 10 l / h, C _H2 / C _C2H2 = 3.1, space velocity = 10000 ÷ 20,000 h ^-1 Sample Pd,% wt. d _Pd , nm t _reaction = 100 ° C t _reaction = 200 ° C C unreacted _C2H2 , ppm C _C2H6 ,% vol. C unreacted _C2H2 , ppm C _C2H6 ,% vol. Pd / SiO ₂ one 1,0 2.5 <0.1 2.05 <0.1 2.10 2 0.97 10 <0.1 1.90 <0.1 2.18 3 0.1 1.7 <0.1 1.72 <0.1 2.07 four 0.1 3,7 <0.1 1.82 <0.1 1.95

Claims (7)

1. The catalyst for the purification of olefins from impurities of polyunsaturated hydrocarbons containing palladium in an amount of 0.01 ÷ 1.0 wt.% With an adjustable particle size of the active component in the range from 1.5 to 20 nm, deposited on bidispersed silica gel. 2. The catalyst according to claim 1, characterized in that bidispersed silica gel containing an alkali metal in an amount of not higher than 0.01 wt.%, Has the following characteristics: specific surface area 150 ÷ 350 m ² / g, total pore volume 0.8 ÷ 1.2 cm ³ / g, micropores are absent, the volume of mesopores with a radius of about 50 Ǻ is 0.60 ÷ 0.85 cm ³ / g, and the volume of macropores with a radius of 1000-5500 Ǻ is 0.15 ÷ 0.30 cm ³ / g 3. A method of preparing a palladium catalyst for the purification of olefins from impurities of polyunsaturated hydrocarbons, characterized in that the pre-dried carrier containing an alkali metal in an amount of not higher than 0.01 wt.%, Bidispersed silica gel with a specific surface area of 150 ÷ 350 m ² / g, total pore volume 0.8 ÷ 1.2 cm ³ / g with a complete absence of micropores, mesopore volume with a radius of about 50 Ǻ 0.60 ÷ 0.85 cm ³ / g and macropore volume with a radius of 1000-5500 Ǻ - 0.15 ÷ 0.30 cm ³ / g, was impregnated with an aqueous solution of palladium nitrate stabilized with certain p after which the catalyst is dried, calcined in air and then restored in a stream of hydrogen-containing gas, the result is a catalyst containing palladium in an amount of 0.01 ÷ 1.0 wt.% with an adjustable particle size of the active component in the range from 1.5 to 20 nm deposited on bidispersed silica gel. 4. The method according to claim 3, characterized in that citric acid is added to the impregnating solutions along with stabilized palladium nitrate to prevent agglomeration of palladium-containing particles on the surface of the carrier. 5. The method according to claim 3, characterized in that the pH adjustment of the impregnating solutions containing stabilized palladium nitrate is carried out without the introduction of alkali metal cations by alkalization with an aqueous solution of tetramethylammonium hydroxide. 6. The method of purification of olefins from impurities of polyunsaturated hydrocarbons by catalytic hydrogenation at elevated temperatures in the presence of a supported palladium catalyst, characterized in that they use the catalyst according to claims 1 and 2 or prepared according to claims 3-5. 7. The method according to claim 6, characterized in that the hydrogenation is carried out at atmospheric pressure, a temperature of 50-200 ° C, a space velocity of 10000-20000 h ^-1 .