RU2361666C1 - Catalyst for producing aliphatic hydrocarbons from co and h2 - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to catalyst production, particularly to catalysts for making aliphatic hydrocarbons from CO and H₂ (Fischer Tropsch synthesis). Described is a catalyst for producing aliphatic hydrocarbons from CO and H₂, containing cobalt and two promoters on a carrier - aluminium oxide. The catalyst contains rhenium and a metal, chosen from a group consisting rhodium, palladium and platinum as promoters, taken in the following ratio, wt %: 0.5:(0.05-0.3) respectively.

EFFECT: increased activity and efficiency of the catalyst.

2 cl, 2 tbl, 11 ex

Description

The present invention relates to the production of catalysts, in particular catalysts for the synthesis of aliphatic hydrocarbons from synthesis gas (Fischer-Tropsch synthesis), which are used as components of motor fuels, as well as raw materials for further processing in the processes of basic organic synthesis.

It is known that the catalytic conversion of synthesis gas to hydrocarbons occurs over heterogeneous catalysts, which are transition metals deposited on substrates with a high specific surface area. It is known that ruthenium is the most active in the Fischer-Tropsch synthesis, followed by iron, cobalt or nickel. The products of Fischer-Tropsch synthesis are a wide hydrocarbon fraction, from methane to paraffin waxes, as well as, on iron catalysts, oxygen-containing products - alcohols, aldehydes, ketones and carboxylic acids. Only iron and cobalt catalysts have found industrial application, and cobalt catalysts are preferred for the synthesis of paraffin hydrocarbons due to their greater selectivity for these products, greater stability and lower activity in the water gas reaction compared to iron. Basic information on the Fischer-Tropsch synthesis process and its catalysts can be found, for example, in reviews (M.E. Dry, Practical and theoretical aspects of the catalytic Fischer-Tropsch process. Applied Catalysis A: General, 138 (1996) 319- 344; AAAdesina, Hydrocarbon synthesis via Fischer-Tropsch reaction: travails and triumphs. Applied Catalysis A: General, 138 (1996) 345-367).

A valuable product obtained on cobalt Fischer-Tropsch synthesis catalysts is the diesel fraction of hydrocarbons. Its cetane number is 75-80 against 40-50 in diesel fuels of petroleum origin. The content of aromatic hydrocarbons does not exceed 2% against 30-35% in modern diesel fuels, nitrogen and sulfur-containing impurities are absent. Cobalt catalysts operating at a temperature not exceeding 250 ° C are particularly suitable for the production of a diesel fraction (M.E. Dry, Fischer-Tropsch reaction and the environment. Applied Catalysis A: General, 189 (1999) 185-190). The performance of the catalyst and the selectivity of the fraction depend, on the one hand, on the process conditions (temperature, pressure, type of reactor), and on the other hand, on the chemical composition and surface properties of the catalyst. It is known that the introduction of promoting additives, such as noble metals and non-reducing oxides, into the composition of cobalt catalysts affects the activity and selectivity of catalysts (AYKhodakov, W. Chu, P. Fongarland, Advances in the Development of Novel Cobalt Fischer-Tropsch Catalysts for Synthesis of Long-Chain Hydrocarbons and Clean Fuels. Chem. Rev. 2007, 107, 1692-1744).

A catalyst is known for use in a Fischer-Tropsch synthesis reaction, which comprises cobalt on an alumina support, said alumina being at least 50% alpha alumina, and optionally further comprising a rhenium, platinum, iridium promoter and / or rhodium (RU Patent No. 2283696 dated 09/20/2006). It is stated that these catalysts have high selectivity for the C5 + fraction, but data on the selectivity for narrower fractions, in particular diesel, are not available.

The closest solution in technical essence is a catalyst for producing aliphatic hydrocarbons from CO and H ₂ (Fischer-Tropsch process) based on cobalt on a carrier - alumina and containing two promoters, the first promoter selected from the group consisting of palladium, platinum, ruthenium, rhenium, rhodium, iridium, and combinations thereof, and the second promoter is selected from the group consisting of potassium, boron, cesium, lanthanum, cerium, strontium, scandium, yttrium, praseodymium, neodymium, promethium, samaria, europium, gadolinium, terbium, dysprosium, holmium, e rbium, thulium, ytterbium, lutetium, palladium, platinum, ruthenium, rhenium, rhodium, iridium, and combinations thereof. The specified catalyst contains components in the following ratio, wt.%:

cobalt 5-60 first promoter 0.0001-1 second promoter 0.01-5 aluminium oxide rest

The objective of the known invention was the creation of a cobalt-based catalyst on a support with a highly developed surface, smooth uniform surface morphology, uniform distribution of the metal throughout the catalyst and a smaller crystallite size of the metal than previously known Fischer-Tropsch synthesis catalysts (RU Patent No. 2292238 from 27.01 .2007). Data on the test results of the above catalyst are not described.

The objective of the present invention is to provide a catalyst based on cobalt, with high activity in the synthesis of aliphatic hydrocarbons from CO and H ₂ and at the same time high performance in relation to the diesel fraction With ₁₁ -C ₁₈ .

The problem is achieved by the proposed catalyst for the production of aliphatic hydrocarbons from CO and H ₂ , containing cobalt and two promoters on a support - alumina, the distinguishing feature of which is that the catalyst contains rhenium and a metal selected from the group consisting of rhodium, palladium as promoters , platinum, taken in the following ratio, wt.%: 0.5: (0.05-0.3), respectively. The proposed catalyst contains components in the following ratio, wt.%:

cobalt 5.0-25.0 rhenium 0.5 rhodium or palladium or platinum 0.05-0.3 aluminium oxide rest

Alumina having a specific surface area of at least 150 m ² / g, preferably at least 190 m ² / g and a specific pore volume of at least 0.5 cm ³ / g, preferably at least 0.68 cm ³ / g, is used as a carrier.

The method of applying cobalt and these promoters to a carrier is not critical and may be selected by one of the methods known to those skilled in the art. One of these methods is impregnation by moisture capacity, when metal compounds are dissolved in such an amount of solvent, which is just enough to fill the pores of the catalyst. The solvent is selected so as to ensure the solubility of the compounds of these metals. When cobalt nitrate is used as the source of cobalt, the preferred solvent is water. In the case of using cobalt carbonyl, it is preferable to use a volatile organic solvent, for example acetone, methanol, ethanol, cyclohexane, toluene, diethyl ether, tetrahydrofuran. As sources of promoter metals, salts such as ammonium perrenate, rhodium chloride, platinum chloride hydrochloride, sodium tetrachloropalladate are suitable. However, the use of these particular compounds is not critical in this invention, and other soluble salts of promoter metals can be used.

When using the impregnation method, cobalt and both promoters can be introduced both by single and multiple impregnation, and the cobalt salt and salts of metal promoters can be applied to the carrier either together or separately. In the case of multiple impregnation, the material at the intermediate stages of preparation is dried in a water bath at a temperature of 60-90 ° C and then calcined in a stream of air at a temperature of 200-500 ° C, preferably 350-400 ° C, keeping at this temperature for 1- 5 o'clock. For proper formation of the surface of the catalyst, the temperature is gradually increased from room temperature to a maximum level at a rate of not more than 5 ° C / min, preferably 2 ° C / min. After applying all the components, the catalyst is also dried and calcined under the indicated conditions.

Before use, the catalyst is reduced in hydrogen, or in a mixture of hydrogen with an inert gas, or in a mixture of hydrogen with carbon monoxide (synthesis gas). The preferred reduction gas is hydrogen. The space velocity of the gas passing through the catalyst bed should be at least 500 h ^-1 , preferably at least 1000 h ^-1 , even more preferably 3000 h ^-1 . The reduction temperature should be in the range of 350-450 ° C, preferably 400 ° C. The recovery time is from 1 to 5 hours. The reduced catalyst contains cobalt metal, easily oxidized by atmospheric oxygen, and therefore must be isolated from it. The catalyst can be stored under nitrogen or argon before its operation in the synthesis of hydrocarbons.

The reactor used for the synthesis of hydrocarbons can be selected from those types of reactors used in the Fischer-Tropsch synthesis that allow the synthesis of high molecular weight hydrocarbons, namely, a fixed-bed reactor or a reactor with a suspension catalyst layer in a high boiling solvent. The size of the granules of the carrier used to prepare the catalyst depends on the type of catalyst. For a fixed bed reactor, large granules are preferred that reduce the resistance to gas flow through the catalyst bed. For a slurry bed reactor, a finely divided catalyst is needed that can form a slurry.

The synthesis gas used as raw material should have a molar ratio of H ₂ : CO from 1 to 3, preferably from 1.5 to 2.5. Inert impurities in the synthesis gas, such as carbon dioxide or nitrogen, are undesirable because they reduce the efficiency of use of the equipment, being essentially ballast. However, they do not adversely affect the activity of the catalyst. In contrast, sulfur-containing compounds are catalytic poison and should, if possible, be removed from the synthesis gas to the lowest possible level, preferably less than 100 ppm.

Suitable pressure in the reactor may be from 1 to 50 atmospheres, preferably from 20 to 25 atmospheres. The load on the catalyst is from 100 to 10,000 h ^-1 , preferably from 1,000 to 2,000 h ^-1 . A high catalyst load is preferred in terms of increasing activity and selectivity for higher hydrocarbons and reducing methane formation. However, with a very large load on the catalyst, the degree of conversion of synthesis gas decreases, which leads to the need to place two or more reactors in series or organize a recycling of the gas leaving the reactor.

A suitable reaction temperature is 180-250 ° C, preferably 200-220 ° C. It is important that the freshly restored catalyst was not immediately heated to the indicated temperature, but would gradually be heated in the synthesis gas stream from 160 ° C to the specified operating temperature for 40-80 hours. In this case, the guideline for the operator should be the degree of synthesis gas absorption ( contraction) and the composition of the gas leaving the reactor. The catalyst, properly brought to operating temperature, maintains high levels of activity and productivity over time.

The technical result of the present invention consists in the unexpected synergism of two promoters deposited on a carrier — alumina of a cobalt catalyst, one of which is rhenium and the other is selected from the group comprising rhodium, palladium, platinum. The simultaneous introduction of these two promoters in the ratio, wt.% 0.5: (0.05-0.3), respectively, leads to an increase in the productivity of the catalyst in relation to the diesel fraction of hydrocarbons C ₁₁ -C ₁₈ , which is the most valuable synthesis product. Data on the activity of the catalyst are given in table.2.

EXAMPLE 1

The catalyst is prepared as follows. A solution of 0.09 g of NH ₄ ReO ₄ and 0.02 g of RhCl ₃ 4H ₂ O in 8 ml of distilled water is poured into 10 g of granular alumina, a fraction of 1-3 mm, with stirring, monitoring the uniformity of the carrier impregnation with a solution. The resulting material was dried in a water bath for 1 h and then calcined in a stream of air at a temperature of 400 ° C for 1 h. A solution of Co (NO ₃ ) ₂ 6H ₂ O in 5 ml of distilled water was prepared. Pour it to the resulting material with stirring. The resulting catalyst was dried in a water bath for 1 h and then calcined in a stream of air at a temperature of 400 ° C for 1 h. After calcination, they are sifted out from the fines. Get the catalyst composition, wt.%:

cobalt 20.0

rhenium 0.5

rhodium 0.1

aluminum oxide the rest

Analogously to example 1 receive the catalysts shown in table. 1. Paragraphs 1-7 relate to the present invention, paragraphs 8-11 are given as an example.

The prepared samples are tested in the synthesis of hydrocarbons in a flow unit with a tubular steel reactor. Immediately prior to testing, the catalysts activate in a stream of hydrogen with a space velocity of 3000 h ^-1 at atmospheric pressure and a temperature of 400 ° C. The synthesis of hydrocarbons is carried out at a pressure of 2.0 MPa, passing through a reactor synthesis gas of the composition CO: H ₂ = 1: 2 with a space velocity of 2000 h ^-1 . The test results are summarized in table 2.

Table 1 Data on the preparation of catalysts. Comparative examples are included for comparison. No. The amount of ingredient, g Structure Co (NO ₃ ) ₂ 6H ₂ O NH ₄ ReO ₄ PhCl ₃ 4H ₂ O Na ₂ PdCl ₄ H ₂ PtCl ₆ 6H ₂ O Al ₂ O ₃ one 12.4 0.09 0.02 - - 10 20% Co-0.5% Re-0.1% Rh 2 12.4 0.09 - 0.02 - 10 20% Co-0.5% Re-0.05% Pd 3 9.9 0.07 - 0.03 - 8 20% Co-0.5% Re-0.1% Pd four 11.2 0.08 - 0.02 - 9 20% Co-0.5% Re-0.05% Pt 5 17.4 0.13 - - 0.05 fourteen 20% Co-0.5% Re-0.1% Pt 6 18.7 0.14 - - 0.15 fifteen 20% Co-0.5% Re-0.3% Pt 7 26.6 0.16 - 0.18 - 16 25% Co-0.5% Re-0.3% Pd Comparative examples 8 14.9 0.09 - 0.17 - 12 20% Co-0.4% Re-0.4% Pd 9 24.8 0.22 0.04 - - twenty 20% Co-0.6% Re-0.1% Rh 10 8.7 0.05 - 0.07 - 7 20% Co-0.4% Re-0.3% Pd eleven 7.5 0.04 - - 0.06 6 20% Co-0.4% Re-0.3% Pt

table 2 Test results of catalysts in the synthesis of hydrocarbons. Conditions: CO / H ₂ = 1 / 2.2000 h ^-1 , P 2.0 MPa, T 210 ° C. No. Structure CO conversion,% Productivity for diesel fraction C ₁₁ -C ₁₈ , kg × h ^-1 × m ^-3 one 20% Co-0.5% Re-0.1% Rh 49 70.0 2 20% Co-0.5% Re-0.05% Pd fifty 69.7 3 20% Co-0.5% Re-0.1% Pd 51 73.9 four 20% Co-0.5% Re-0.05% Pt fifty 72.0 5 20% Co-0.5% Re-0.1% Pt 54 75.8 6 20% Co-0.5% Re-0.3% Pt 54 74.0 7 25% Co-0.5% Re-0.3% Pd 57 78.2 Comparative examples 8 20% Co-0.4% Re-0.4% Pd 45 60.5 9 20% Co-0.6% Re-0.1% Rh 46 62.2 10 20% Co-0.4% Re-0.3% Pd 44 57.4 eleven 20% Co-0.4% Re-0.3% Pt 46 64.1

Claims (2)

1. The catalyst for the production of aliphatic hydrocarbons from CO and H ₂ containing cobalt and two promoters on a carrier - alumina, characterized in that the catalyst contains rhenium and a metal selected from the group consisting of rhodium, palladium, platinum, taken as the following ratio, wt.%: 0.5: (0.05-0.3), respectively. 2. The catalyst according to claim 1, characterized in that it contains components in the following ratio, wt.%:
cobalt 5.0-25.0 rhenium 0.5 rhodium or palladium or platinum 0.05-0.3 aluminium oxide rest.