RU2641299C1 - Method for obtaining nanosized fisher-tropsh synthesis catalyst and method of fisher-tropsh synthesis with its application - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: method for obtaining a nanosized catalyst of the three-phase Fischer-Tropsch synthesis comprising catalytically active iron nanoparticles involves dissolving the precursors - iron and potassium salts, in water, introducing the resulting solution into molten paraffin at a rate of 20-60 ml/h, forming the catalyst in situ directly in the reaction zone during the heat treatment of the catalyst components in an inert gas stream at a temperature higher than the decomposition temperature of the catalyst precursors and cooling for 1-6 hours in an inert current gas. The heat treatment time is not more than 15 minutes. The ratio of the catalyst components is, wt %: Fe - 0.5-1.0, K - 0.01-0.02, paraffin - the rest. Three-phase Fischer-Tropsch synthesis method includes obtaining aliphatic hydrocarbons from carbon oxide and hydrogen in the three-phase flowing slurry-reactor at an elevated temperature and a pressure in the presence of nanosized catalyst with a particle size of 0.7 to 4 nm, obtained in this way, when the molar ratio of carbon monoxide and hydrogen of 1:(0.5-3), a temperature of 240-400°C, a pressure of 20-30 ATM with the load on gas from 2 to 20 nl/hCatc⋅.EFFECT: when using the proposed composition and method of preparing a Fe-containing catalyst, a sharp increase in its activity is observed, as a result of which high process values can be achieved in smaller reactors, lower iron and potassium content in the catalyst, and a reduction in the heat treatment time, preventing of coarsening and agglomeration of the catalyst particles, higher catalyst productivity, higher selectivity for the formation of hydrocarbons.2 cl, 4 dwg, 1 tbl, 4 ex

Description

Technical field

The invention relates to the petrochemical industry, and in particular to methods for producing aliphatic hydrocarbons from carbon monoxide and hydrogen, and can be used in oil refining and petrochemicals.

State of the art

Oil is the main raw material for the production of motor fuels and a huge number of chemical compounds. But oil reserves are very limited, oil production is becoming more and more laborious, and oil prices fluctuate on the world market every year with a larger amplitude. Meanwhile, the reserves of natural gas, coal and other combustible minerals are more significant. On this basis, promising and relevant is the creation of new alternative methods for producing fuel and valuable chemical compounds based on non-petroleum feedstocks.

Since a mixture of carbon monoxide and hydrogen (synthesis gas) can be obtained from any carbon-containing raw material, and hydrocarbons or other organic compounds can be synthesized from it, the widespread use of syntheses based on carbon oxides and other single-carbon molecules is considered one of the most realistic ways to replace oil and gas raw materials in energy and chemistry [Peter M. Maitlis, Arno de Klerk. Greener Fischer-Tropsch Processes for Fuels and Feedstocks 2013 Wiley-VCH Verlag & Co. KGaA 372 pages]. Fischer-Tropsch synthesis (synthesis of hydrocarbons from carbon monoxide and hydrogen) is the second stage of most processes of processing alternative raw materials (coal, natural or associated gas, peat, etc.) into components of motor fuels [Arno de Klerk. Fischer-Tropsch Refining, 2011, Wiley-VCH Verlag & Co. KGaA, Boschstr. 622 pages] Traditional Fischer-Tropsch synthesis catalysts are a Group VIII bulk metal (mainly iron) or a metal distributed over the surface of a highly porous support (iron or cobalt) [E.V. Slivinsky, G.A. Kliger, A.E. Kuzmin, A.V. Abramova, E.A. Kulikova // Ross. Chem. journal 2003. V. 17. No. 6. S. 12.]. Their catalytic activity, stability and selectivity are largely determined by the shape and particle size of the used active component [G.L. Bezemer, J.N. Bitter, N. Kuipers, N. Oosterbeek, J.E. Holewijn, X.D. Xu, F. Kapteijn, A.J. van Dillen, K.P. de Jong // Am. Chem. Soc. 2006, V. 128. P. 3956.].

Fischer-Tropsch synthesis (the synthesis of hydrocarbons from CO and H ₂ ) is a process that proceeds with a large release of heat. Carrying out the reaction under the conditions of a three-phase gas-liquid-solid system (i.e., a system in which the catalyst is suspended in a liquid) allows one to balance thermal effects and reduce diffuse restrictions. In the traditional version of the process, micrometer granules of a ready-made activated catalyst are distributed in the liquid phase, which are kept in the reaction zone in the flow of the reaction gas. Maintaining the stability of such a system is difficult, given its complex hydrodynamic characteristics and tendency to stratification. It is known [Guettel R., Kunz U., Turek T. // Chem. Eng. Technol. 2008. 31. No. 5. P.746., Dragomir Dr., Bukur B. // First Annual Technical Progress Report. Period: 09/01 / 00-08 / 31/01 // http://www.osti.gov/bridge/servlets/purl/807156-C0WUS6/native/807156.PDF. Davis B. // Catalysis Today. 2002. V. 71. No. 3-4. P. 249.] that the optimal content of the metal component in the classical three-phase systems used in the Fischer-Tropsch synthesis does not exceed 20%. Ultrafine suspensions with such a concentration of solid particles easily agglomerate. As a result, the search for active and selective catalytic systems with a reduced content of the metal component is relevant.

It is known [Khadzhiev S.N., Krylova A.YU.// Petrochemistry. 2011.Vol. 51. No. 2. S. 84 Petrol. Chemistry. 2011. V. 51. No. 2. R. 74., Khadzhiev S.N., Sagitov S.A., Lyadov A.S., Kulikova M.V., Krylova A.Yu.// Petrochemistry. 2014.V. 54. No. 2. S. 88 // Petrol. Chemistry. 2014. V. 54. No. 2. P. 88.] that a decrease in the particle size of the solid phase of the suspension noticeably reduces the tendency of the system to stratify and leads to a significant increase in the specific activity of the Fischer-Tropsch synthesis catalyst. Ultrafine catalysts can be formed and activated directly in a dispersion medium. Moreover, their properties differ from those of traditional larger catalysts, since in essence they are colloidal solutions - an intermediate state between the suspension and the true solution. The formation of ultrafine Fischer-Tropsch synthesis catalysts in the liquid phase remains little studied at present.

As the closest analogue of the invention (prototype), a method was used to obtain a nanoscale Fischer-Tropsch synthesis catalyst composition, wt. %: 87-95 Fe, 2-9, K ₂ O, 1-8 Al ₂ O ₃ (calculated on the active part), which is obtained and activated directly in the reactor (see, RF patent No. 2443471, IPC B01J 23 / 745, B82B 1/00, B01J 23/78, B01J 21/04, C07C 1/04, publ. 02.27.2012). The catalyst was formed in situ directly in the reaction zone during the heat treatment of the catalyst components in a stream of hydrogen or carbon monoxide in molten paraffin. The components of the catalyst are introduced into molten petroleum paraffin either in the form of a mechanical mixture of salts, or in the form of their solution in a solvent that is not miscible with the liquid phase, for example, alcohol, water, ether. The resulting colloidal solution contains particles of a solid phase with a size of 10-30 nm, associated in aggregates with a size of 500-700 nm. In this case, the conversion of CO reaches 90%, and the yield of C ₅₊ hydrocarbons is about 100 g / m ³ with a productivity of more than 430 g / g _Fe / h for these products. The same patent describes a Fischer-Tropsch synthesis method using this catalyst, hydrogen in a three-phase slarry reactor at a temperature of 200-350 ° C and a pressure of 20-30 atm, which is the closest analogue of the claimed synthesis method. The selectivity of the catalyst in relation to the formation of C ₅₊ hydrocarbons is quite high and reaches 45%. The synthesis is carried out in an autoclave type slarry reactor at a temperature of 200-350 ° C and a pressure of 20-30 atm.

However, the prototype used has several disadvantages:

- high metal content in the catalyst (per 100 ml of paraffin in example 1 accounts for 45.32 g of the specified active part);

- low productivity of the target product;

- low reaction speed;

- agglomeration of catalyst nanoparticles.

Description of the invention

The objective of the invention is to eliminate these disadvantages by creating an effective catalyst with a reduced content of the active component, characterized by the presence in its composition of only finely dispersed iron particles.

The use of nanosized iron particles as a component of the catalyst developed by the authors of the catalyst makes it possible to sharply increase the activity and, as a result, the productivity of the catalyst by increasing the activity of the active component due to the occurrence of nanoscale effects with a decrease in the content of catalytically active metals in it.

The invention also includes the development of a method for producing aliphatic hydrocarbons, mainly C ₅₊ , from CO and H ₂ in the presence of the above-described catalyst.

The technical result that can be achieved using the proposed invention is

- reducing capital costs of production, since when using the proposed composition and method of preparation of the Fe-containing catalyst, a sharp increase in its activity is observed, as a result of which high process performance can be achieved in smaller reactors. In addition, the high activity of the proposed catalyst will reduce production capital costs due to the first catalyst loading, since high process performance can be achieved with a smaller catalyst volume;

- reduction of operating costs of production due to the low content of iron and potassium in the catalyst and the time of heat treatment;

- prevention of aggregation and agglomeration of catalyst particles by minimizing the heat treatment time;

- higher catalyst productivity;

- higher selectivity for the formation of C ₅₊ hydrocarbons.

The problem is solved in that in the method for producing a nanoscale three-phase Fischer-Tropsch synthesis catalyst containing catalytically active iron nanoparticles, including dissolving precursors of iron and potassium salts in water, introducing the resulting solution into molten paraffin and forming the catalyst in situ directly in the reaction zone in the process of heat treatment of the catalyst components in an inert gas stream at a temperature higher than the decomposition temperature of the catalyst precursors salt solution in molten paraffin is 20-60 ml / hour, the specified heat treatment time is not more than 15 minutes, and after the specified heat treatment, cooling is carried out for 1-6 hours in an inert gas stream, and the ratio of catalyst components is, wt%:

Fe - 0.5-1,

K - 0.01-0.02,

paraffin - the rest.

The problem is also solved by the fact that in the three-phase Fischer-Tropsch synthesis method, which includes the production of aliphatic hydrocarbons from carbon monoxide and hydrogen in a three-phase flow through slarry reactor at elevated temperature and pressure in the presence of a nanoscale catalyst containing nanosized iron particles, the synthesis is carried out at a molar ratio carbon monoxide and hydrogen 1: (0.5-3) at a temperature of 240-400 ° C and a pressure of 20-30 atm in the presence of a catalyst obtained by the claimed method, the particle size of which is 0 .7-4 nm, with a gas load of 2-20 nl / gKat⋅ch.

The components of the catalyst are introduced into molten petroleum paraffin in the form of an aqueous solution at temperatures above the decomposition temperature of the salts of the precursors. At the initial stage, a low-concentration catalytic ultrafine system is formed with the content of the active component not exceeding 0.5-1% wt.

Minimizing the processing time of the synthesized ultrafine system to 3-15 minutes prevents the enlargement of the dispersed phase. According to transmission electron microscopy and dynamic light scattering data, the particle size of the obtained catalyst system is 0.7-4.0 nm.

A nanosized catalyst with a low content of the active component is prepared by the method of drop thermolysis of a solution of precursors - iron salts and promoter (potassium salts) in P-2 brand paraffin.

Precursor solutions are introduced into a four-necked flask when heated at a given speed in an inert gas stream with stirring. After adding the entire volume of the salt solution, the sample is kept in a stream of inert gas, and then cooled.

The particle size of the Fe-containing catalyst in the resulting solution was determined by dynamic light scattering on a NanoZetasizer ZS instrument. As salts of iron and potassium can use nitrates, acetates, acetylacetonates.

As a result of the described method for preparing a nanosized catalyst with a low content of the active component, an ultrafine system is formed in which nanosized catalytically active iron particles are finely dispersed and uniformly distributed in the dispersion medium of the slarry reactor - P-2 paraffin.

The proposed method for producing nanoscale iron catalysts with a reduced content of the active component of the catalysts includes the following stages:

- the preparation of a solution of iron salts and potassium salts in water at the rate of 0.5-1% wt. Fe on the weight of a portion of P-2 paraffin;

- heating the dispersion medium (P-2 paraffin) to a temperature exceeding the decomposition temperature of the salts of the precursors in an inert gas stream

- the introduction of a solution of salts of iron and potassium in paraffin - a dispersion medium with a given speed (20-60 ml / h) with stirring in a stream of inert gas - heat treatment for 3-15 minutes;

- Cooling the resulting ultrafine system in an inert gas stream for 1-6 hours.

The synthesized nanosized iron catalyst with a low content of the active component is placed in an autoclave-type flow catalytic reactor. The installation operates in gas flow mode. Effective dispersion of gas bubbles is achieved by sparging the synthesis gas through a layer of the liquid phase, as well as by forced mixing of the suspension with a mechanical rotating mixer. Fischer-Tropsch synthesis is carried out, passing a mixture of carbon monoxide and hydrogen taken in a molar ratio of 1: (0.5-2), at a temperature of 200-360 ° C and a pressure of 20-30 atm with a bulk velocity of 1000 h ^-1 .

The following examples illustrate the invention, but in no way limit its scope.

Example 1 (comparative)

43.3 g of dehydrated iron nitrate are dissolved in 20 ml of distilled water. The resulting solution was injected into 100 ml of molten P-2 paraffin at a rate of 22 ml / hour at a temperature of 280 ° C with constant stirring in a stream of inert gas. After the introduction of the entire volume of the precursor solution, the system is cooled to 80 ° C in an inert gas stream.

The catalyst thus obtained has a composition,% wt .: 8% Fe: 92% P-2 paraffin. The particle size of the obtained catalyst was determined by dynamic light scattering and is 7-9 nm.

The catalyst c is placed in an autoclave type flow catalytic reactor and Fischer-Tropsch synthesis is carried out by passing a mixture of carbon monoxide and hydrogen taken in a molar ratio of 1: 1 at a temperature of T _syn 360 ° C and a pressure of 20 atm with a catalyst load of 2 nl / gKat⋅ch.

The experimental results are shown in the table.

Example 2

7.2 g of dehydrated iron nitrate and 0.05 g of potassium nitrate are dissolved in 3.3 ml of distilled water. The resulting solution was introduced into 100 ml of molten P-2 paraffin at a rate of 22 ml / h at a temperature of 280 ° C with constant stirring in a stream of inert gas. The heat treatment time is 10 minutes. After the introduction of the entire volume of the precursor solution, the system is cooled to 80 ° C in an inert gas stream for 2.5 hours.

Thus obtained catalyst has a composition,% mass .: 1% Fe: 0.02% K: 98.98% P-2 paraffin. The particle size of the obtained catalyst was determined by dynamic light scattering and is 1-1.5 nm.

The catalyst c is placed in an autoclave-type flow catalytic reactor and Fischer-Tropsch synthesis is carried out by passing a mixture of carbon monoxide and hydrogen taken in a 1: 1 molar ratio at a temperature of 335 ° C and a pressure of 20 atm with a catalyst load of 10 nl / gKat⋅ hours

The experimental results are shown in the table.

Example 3

3.6 g of dehydrated iron nitrate and 0.03 g of potassium nitrate are dissolved in 1.7 ml of distilled water. The resulting solution was introduced into 100 ml of molten P-2 paraffin at a rate of 22 ml / h at a temperature of 280 ° C with constant stirring in a stream of inert gas. The heat treatment time is 5 minutes. After the introduction of the entire volume of the precursor solution, the system is cooled to 80 ° C in an inert gas stream for 1.5 hours.

The catalyst thus obtained has a composition,% wt .: 0.5% Fe: 0.01% K: 99.49% P-2 paraffin. The particle size of the obtained catalyst was determined by dynamic light scattering and is 1-1.5 nm.

The catalyst c is placed in the reactor of an autoclave-type flow catalytic unit and Fischer-Tropsch synthesis is carried out by passing a mixture of carbon monoxide and hydrogen taken in a molar ratio of 1: 1 at a temperature of 335 ° C and a pressure of 20 atm with a catalyst load of 20 nl / gKat⋅ hours

The experimental results are shown in the table.

Example 4 (comparative)

43.3 g of dehydrated iron nitrate and 0.3 g of potassium nitrate are dissolved in 20.0 ml of distilled water. The resulting solution is injected into 100 ml of molten P-2 paraffin at a rate of 30 ml / hour at a temperature of 280 ° C with constant stirring in a stream of inert gas. The heat treatment time is 210 min. After the introduction of the entire volume of the precursor solution, the system is cooled to 80 ° C in an inert gas stream for 1 hour.

The catalyst thus obtained has a composition,% wt .: 8.0% Fe: 0.3% K: 91.70% P-2 paraffin. The particle size of the obtained catalyst was determined by dynamic light scattering and is 7-9 nm.

The catalyst c is placed in the reactor of an autoclave-type flow catalytic unit and Fischer-Tropsch synthesis is carried out by passing a mixture of carbon monoxide and hydrogen taken in a molar ratio of 1: 1 at a temperature of 320 ° C and a pressure of 20 atm with a catalyst load of 4 nl / gKat⋅ hours

The experimental results are shown in the table.

Description of drawings

In FIG. Figures 1 and 2 show typical photographs of transmission electron microscopy of nanoscale catalysts with different contents of the active component. It can be seen that the contacts are agglomerates of nanosized particles of the active phase. The particle size distribution was built based on an analysis of at least three fields of view, and the total number of measured particles was from 80 to 100. The data are presented in FIG. 3-4. It was shown that a decrease in the concentration of the active component leads to a narrowing of the particle size distribution, however, for systems with different active phase contents, the average particle size is 4 nm.

Claims (3)

1. A method of producing a nanoscale three-phase Fischer-Tropsch synthesis catalyst containing catalytically active iron nanoparticles, including dissolving precursors of iron and potassium salts in water, introducing the resulting solution into molten paraffin and forming the catalyst in situ directly in the reaction zone during the heat treatment of the catalyst components in inert gas flow at a temperature exceeding the decomposition temperature of the catalyst precursors, characterized in that the rate of introduction of the specified salt solution minutes in molten paraffin is 20-60 ml / hr, while said heat treatment - no more than 15 minutes, and after cooling said heat treatment is carried out for 1-6 hours under an inert gas stream, and the ratio of the catalyst components,% wt .: Fe 0.5-1.0 TO 0.01-0.02 paraffin rest 2. A method of three-phase Fischer-Tropsch synthesis, including the production of aliphatic hydrocarbons from carbon monoxide and hydrogen in a flow-through three-phase slurry reactor at elevated temperature and pressure in the presence of a nanoscale catalyst containing nanoscale iron particles, characterized in that the synthesis is carried out at a molar ratio of carbon monoxide and hydrogen 1: (0.5-3) at a temperature of 240-400 ° C and a pressure of 20-30 atm in the presence of a catalyst obtained by the method according to claim 1, the particle size of which is 0.7-4 nm, with a gas load of 2- 20 n l / gKat · h.

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