RU2432990C2 - Cobalt catalyst for synthesis of c5+ hydrocarbons, synthesis method thereof and method of producing said catalyst - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to petrochemisry, gas chemistry, coal chemistry and a catalyst for synthesis of hydrocarbons containing 5 or more carbon atoms from CO and H₂ (Fischer-Tropsch synthesis), a method for synthesis of C₅₊ hydrocarbons using said catalyst and a method of producing said catalyst. Described is a catalyst for synthesis of C₅₊ hydrocarbons containing a support in form of fluorinated γ-aluminium oxide, 30 wt % cobalt and 0.5 wt % rhenium. Described is a method of producing said catalyst, involving preliminary thermal treatment of the γ-aluminium oxide-based support and then adding cobalt and rhenium via step-by-step saturation with aqueous solutions of cobalt nitrate and ammonium perrhenate and step-by-step thermal treatment, wherein the support used is fluorinated γ-aluminium oxide. The invention also describes a method of producing C₅₊ hydrocarbons via catalytic conversion of CO and H₂ using said catalyst.

EFFECT: high selectivity with respect to formation of desired hydrocarbon products (over 90%) and low selectivity with respect to formation of by-product - methane (less than 4%), wherein the relationship between the output of the desired products and the conversion of carbon oxide (output C₅₊-K_co) is linear in the conversion interval from 0 to 80-90%.

4 cl, 4 ex, 1 tbl, 6 dwg

Description

FIELD OF THE INVENTION

The invention relates to petrochemistry, gas chemistry, coal chemistry and relates to a catalyst for the synthesis of hydrocarbons containing 5 or more carbon atoms from synthesis gas (a mixture of carbon monoxide WITH hydrogen gas H ₂ ) (Fischer-Tropsch synthesis), a method for producing hydrocarbons With ₅₊ with using the specified catalyst and a method for producing a catalyst.

State of the art

Mixtures of aliphatic hydrocarbons containing 5 or more carbon atoms (C ₅₊ ) are valuable intermediates for the production of components of motor fuels and lubricants, which are isolated from these mixtures by simple distillation.

Catalysts that are suitable for Fischer-Tropsch synthesis typically contain one or more catalytically active transition metals of group VIII of the Periodic system of elements supported on oxide carriers (Al ₂ O ₃ , SiO ₂ , TiO ₂ , etc.) . In particular, iron, cobalt, nickel and ruthenium are well known as active metals for such a catalyst. Cobalt is the most optimal catalyst in the conversion of synthesis gas to hydrocarbons containing 5 or more carbon atoms, due to its high selectivity with respect to these products.

Fischer-Tropsch synthesis on cobalt catalysts proceeds at temperatures above 150 ° C. With increasing temperature, there is an increase in the conversion of CO (linear in the ideal case) and the yield of liquid and gaseous synthesis products. A typical temperature dependence of the yield of synthesis products is shown in figure 1

It can be seen that the selectivity of the process with increasing temperature does not remain unchanged: the yield of liquid products initially increases and then decreases, the yield of gases increases over the entire temperature range.

The temperature at which the largest yield of liquid hydrocarbons is observed on the catalyst is called the optimum synthesis temperature. It is determined by the composition of the catalyst and the total pressure in the system (at higher pressures, the optimum temperature is higher). Process indicators are usually compared at the optimum temperature.

The intensification of gas generation, especially at high temperatures, is caused not only by the feature of Fischer-Tropsch synthesis (lower temperature and higher pressure favor polymerization), but also by the intense side reaction of direct hydrogenation of CO to methane (methanation of CO): CO + 3H ₂ = CH ₄ + H ₂ O. The methanation of CO proceeds at the active centers of the catalyst operating at high temperatures. It is this reaction that causes a sharp change in the selectivity of the catalyst during overheating, which arises as a result of poor heat removal.

In the industrial implementation of the process and the creation of industrial catalyst samples, the dependence of the yield of liquid target products on the conversion of CO is of great importance. In the ideal case (100% conversion of CO, the absence of adverse reactions) this dependence has the form of a straight line (dashed line in figure 2).

Under real conditions of the process, an increase in the conversion of CO is achieved by raising the temperature. However, on the surface of FT catalysts, in addition to active polymerization centers, there are usually also CO methanation centers. As a result, at a certain CO conversion (“conversion barrier”), a decrease in the yield of the target products is observed as a result of a marked decrease in the selectivity of the process due to increased gas generation. The conversion barrier determines the region of operation of the catalyst under conditions of constant selectivity, which is extremely important for obtaining stable process performance.

Currently, researchers are focused on the development of catalysts with the ability to polymerize and reduced selectivity for the formation of methane, the main by-product of the synthesis.

The ability to polymerize is evaluated by the value of the alpha index in the Schulz-Flory equation describing the molecular weight distribution of the resulting hydrocarbons:

,

,

where W _{n is the} mass fraction of normal paraffin with the number of carbon atoms n, n is the number of hydrocarbon atoms, α is a constant characterizing the probability of growth of the hydrocarbon chain.

The higher α, the more selective the catalyst is in relation to the formation of heavy products.

Known catalysts for the synthesis of high molecular weight hydrocarbons from CO and H ₂ containing as the active component kolbat and γ-alumina as a carrier (US patent No. 4801573, 5028634, 6271432, European patent application EP 031375). However, in the presence of these catalysts, the synthesis proceeds with relatively high selectivity for methane formation, which reaches 14%.

In most cases, the starting material for the production of γ-alumina (γ-Al ₂ O ₃ ) is boehmite AlO (OH), for example, applications US 2004/0214904 A1, US 2004/0132833 A1, US 2004/0132833 A1. Of all the modifications of alumina, γ-Al ₂ O ₃ is most used in catalysis and, in particular, in the synthesis of hydrocarbons from synthesis gas. Typically, γ-Al ₂ O ₃ -based catalysts are prepared by depositing metals (in particular cobalt) on alumina by impregnation in several steps with metal salt solutions followed by calcination after each step to fix the active metal to the support.

Closest to the catalyst proposed in the invention is a catalyst of 30% Co - 0.5% Re / γ-Al ₂ O ₃ synthesis of C ₅₊ -C ₁₀₀ hydrocarbons from CO and H ₂ , previously developed by the authors of the present invention (RF patent 2279912, publ. . 07.20.2006). The catalyst contains gamma-alumina stable under hydrothermal conditions as a support. A method of producing a catalyst includes heat treatment of a carrier precursor, gibbsite, to produce γ-alumina, onto which cobalt is applied in several stages from an aqueous solution of its nitrate. In addition to cobalt and γ-Al ₂ O ₃ , the known catalyst also contains rhenium, which contributes to the recovery of cobalt from mixed oxides of cobalt and aluminum. The catalyst is highly selective for the formation of C ₅₊ hydrocarbons (about 90%) and low methane selectivity (up to 4%). However, the dependence of the yield of C ₅₊ -K _CO obtained for this catalyst is far from linear, and the conversion barrier is only 50%, which significantly complicates the operation of the catalyst in an industrial environment.

The task was to develop a Co-Re / Al ₂ O ₃ catalyst, which allows to obtain a linear dependence of the yield of C ₅₊ - K _CO with a conversion barrier above 80%.

Disclosure of invention

An object of the present invention is to provide a catalyst for the synthesis of C ₅₊ hydrocarbons from carbon monoxide and hydrogen, which has high selectivity for the formation of target synthesis products (more than 90%) and reduced selectivity for the formation of a by-product methane (up to 4%), which allows to obtain the linear dependence of the yield of C ₅₊ -K _CO with a conversion barrier above 80%.

In accordance with this object of the proposed invention is a catalyst for the synthesis of hydrocarbons C ₅₊ containing a carrier based on γ-alumina, 30 wt.% Cobalt and 0.5 wt.% Rhenium, characterized in that fluorinated γ-oxide is used as a carrier aluminum.

The above fluorinated alumina γ-Al ₂ O _{3 is} produced by domestic enterprises in accordance with TU 2163-025-04610600-2003.

Fluorinated γ-Al ₂ O ₃ is a cylindrical extrudate with the following physico-chemical characteristics:

The bulk density of the catalyst, g / cm ³ within 0.6-0.8 The average coefficient of strength of the catalyst, kg / mm 1,0 Diameter of granules, mm, within 2.6-3.0 Mass fraction of losses during ignition,% no more 6.8 Specific surface, m ² / g, not less 195 Total pore volume, cm ² / g, not less 0.65

Another object of the proposed invention is a method for producing a catalyst for the synthesis of C ₅₊ hydrocarbons, including preliminary heat treatment of a carrier - fluorinated γ-alumina, followed by the introduction of cobalt and rhenium by stage impregnation of an aqueous solution of cobalt nitrate and ammonium perrenate salts and a stage heat treatment by drying and / or annealing.

Another object of the invention is a method for producing C ₅₊ hydrocarbons by converting CO and H ₂ in the presence of the aforementioned catalyst 30% Co - 0.5% Re / γ-Al ₂ O ₃ , which has increased selectivity for the formation of target hydrocarbon synthesis products (more 90%) and reduced selectivity for methane by-product formation (up to 4%). The method is characterized by a linear dependence of the yield of C ₅₊ -K _CO with a conversion barrier above 80%.

The implementation of the invention

A method of producing a cobalt-aluminum catalyst of 30% Co - 0.5% Re / γ-Al ₂ O ₃ , proposed in the present invention, consists in using fluorinated γ-alumina as a carrier, its preliminary heat treatment and the subsequent introduction of cobalt and a promoter by stepwise impregnation of salts of cobalt nitrate and ammonium perrenate salts with aqueous solutions with stepwise heat treatment by drying and / or calcination.

It was found that the use of the catalyst corresponding to the invention in the synthesis of hydrocarbons from CO and H ₂ leads to high selectivity for C ₅₊ hydrocarbons (about 90%) and low selectivity for methane (up to 4%). It should be noted that the yield of C ₅₊ -K _CO with a conversion barrier above 80% is characterized by a linear dependence.

In the first stage of preparation of the catalyst, fluorinated γ-alumina is calcined for 5-10 hours at a temperature of 400-500 ° C. The active component (cobalt) is applied by impregnation in several stages from a solution of cobalt nitrate. At each stage, the sample is dried in a water bath and the resulting catalyst precursor is dried and / or calcined in a stream of air at a temperature of 300-500 ° C for 5-10 hours.

Before synthesis, the catalyst is activated by reduction in a stream of hydrogen at a temperature of 400-500 ° C for 1-3 hours

The synthesis of hydrocarbons from CO and H _{2 is} carried out in a tubular reactor with a stationary catalyst bed at a pressure of 1-30 atm (preferably 20 atm) in the temperature range of 150-300 ° C. The molar ratio of CO: H ₂ in the synthesis gas is 1: 1-3 (preferably 1: 2).

Example 1

A sample of the catalyst composition 30% Co - 0.5% Re / γ-Al ₂ O ₃ is prepared in the following way.

Stage 1: γ-alumina is calcined for 5-10 hours at a temperature of 400-500 ° C.

Stage 2: 21.16 g of cobalt nitrate is dissolved in distilled water and added to 30 g of the carrier obtained in stage 1. The mixture is placed in a porcelain cup and dried in a water bath for 30-60 minutes, after which it is calcined at a temperature of 400 ° C. within 1 hour

Stage 3 is carried out similarly to the second.

Stage 4: 0.22 g of ammonium perrenate is dissolved in distilled water and added to the material obtained in stage 2 (or 3). The mixture is placed in a porcelain cup and dried in a water bath for 30-60 minutes, after which it is calcined at a temperature of 450 ° C for 1 hour.

Stage 5: 21.16 g of cobalt nitrate is dissolved in distilled water and added to the material obtained in stage 3 (or 4). The mixture is placed in a porcelain cup and dried in a water bath for 30-60 minutes.

Before carrying out the synthesis, the sample is activated in a stream of hydrogen at 450 ° С for 1 h.

The synthesis of hydrocarbons from CO and H _{2 is} carried out in a tubular reactor with a stationary catalyst bed at a pressure of 1 atm (preferably 20 atm) in the temperature range of 150-220 ° C. The molar ratio of CO: H ₂ in the synthesis gas is 1: 2.

The main indicators of synthesis are given in the table. Figure 3 shows the dependence of the yield of C ₅₊ -K _CO . You can see that the resulting dependence is different from linear. The conversion barrier is 60%.

Example 2

A catalyst obtained using the method described in Example 1 was used, but fluorinated γ-alumina was used as a carrier.

Activation of the catalyst and Fischer-Tropsch synthesis is carried out similarly to the procedures described in example 1.

The main indicators of synthesis are given in the table. Figure 4 shows the dependence of the yield of C ₅₊ -K _CO . It can be seen that the dependence obtained in the range of 20-80% (from CO conversion) is almost linear. The conversion barrier is 80%.

Example 3

Use the catalyst obtained by the method described in example 1.

The activation of the catalyst is carried out similarly to the procedures described in example 1.

The synthesis of hydrocarbons from CO and H _{2 is} carried out in a tubular reactor with a stationary catalyst bed at a pressure of 20 atm in a temperature range of 150-220 ° C. The molar ratio of CO: H ₂ in the synthesis gas is 1: 2.

The main indicators of synthesis are given in the table. Figure 5 shows the dependence of the yield of C ₅₊ -K _CO . You can see that the resulting dependence is not linear. The conversion barrier is 70%.

Example 4

A catalyst obtained using the method described in Example 1 was used, but fluorinated γ-alumina was used as a carrier.

The activation of the catalyst is carried out similarly to the procedures described in example 1.

The synthesis of hydrocarbons from CO and H _{2 is} carried out in a tubular reactor with a stationary catalyst bed at a pressure of 20 atm in a temperature range of 150-220 ° C. The molar ratio of CO: H ₂ in the synthesis gas is 1: 2

The main indicators of synthesis are given in the table. Figure 6 shows the dependence of the yield of C ₅₊ -K _CO . It can be seen that in the range of 20-90% (by CO conversion), the dependence is almost linear. The conversion barrier is 90%.

The results in the table below show that the proposed method for the preparation of cobalt catalyst leads to the production of catalytic systems characterized by high selectivity for the target product (above 90%) and allowing to obtain hydrocarbons with a high molecular weight (α> 0.9) with a low selectivity of side formation methane product (up to 4%).

The performance of the synthesis of hydrocarbons from CO and H ₂ carried out using samples of the catalysts corresponding to the invention Example T opt, ° C Selectivity for CH ₄ ,% C ₅₊ selectivity,% α one 190 8 84 0.95 2 190 7 91 0.95 3 210 7 86 0.95 four 230 four 93 0.97

Claims (4)

1. The catalyst for the synthesis of hydrocarbons With ₅₊ containing a carrier based on γ-alumina, 30 wt.% Cobalt and 0.5 wt.% Rhenium, characterized in that the carrier is used fluorinated γ-alumina. 2. A method of obtaining a catalyst for the synthesis of hydrocarbons With ₅₊ containing a carrier based on γ-alumina, 30 wt.% Cobalt and 0.5 wt.% Rhenium, including preliminary heat treatment of the carrier based on γ-alumina with the subsequent introduction of cobalt and rhenium by stage-impregnation of aqueous solutions of salts of cobalt nitrate and ammonium perrenate and stage heat treatment, characterized in that fluorinated γ-alumina is used as a carrier. 3. The method according to claim 2, characterized in that the heat treatment is carried out by drying and / or calcination. 4. A method of producing hydrocarbons With ₅₊ by catalytic conversion of CO and H ₂ , characterized in that the catalyst according to claim 1 is used as a catalyst.

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