CA1190249A

CA1190249A - Process for producing linear hydrocarbons with more than l8 carbon atoms

Info

Publication number: CA1190249A
Application number: CA000422651A
Authority: CA
Inventors: Carl-Dieter Frohning; Klaus Moraw
Original assignee: Ruhrchemie AG
Current assignee: Ruhrchemie AG
Priority date: 1982-03-04
Filing date: 1983-03-01
Publication date: 1985-07-09
Also published as: DE3207743A1; EP0088294B1; ZA831307B; AU556070B2; SU1295995A3; DE3360183D1; AU1189183A; EP0088294A1

Abstract

Abstract of Disclosure Waxy hydrocarhons with more than 18 carbon atoms are obtained by converting carbon monoxide and hydrogen, in the presence of catalysts containing iron and, in addition, a readily reducible metal oxide, a difficultly reducible metal oxide, SiO2, and an alkali metal oxide.

Description

The present invention relates to a process for producing linear hydrocarbons having more than 18 carbon atoms from synthesis gas; i.e. a mixture of carbon monoxide and hydrogen.
The hydrocarbons are waxy and are widely used in industrial technology.

It is known that a whole range of valuable organic compounds caa be obtained by catalytic hydrogenation under pressure of carbon oxides, especially carbon monoxide. For this purpose, a number of catalysts are used which have qualitatively and quantitatively different compositions and which provide various products depending on their composit;on.
Normally, the carbon oxide hydrogenation processes produce, as the main products, hydrocarbons and oxygen-containing organic compounds and contain molecules of different sizes which have complex compositions.

According to a prior art method, carbon monoxide and hydrogen are converted with an alkalinized iron-copper catalyst at temperatures above 220C and pressuYes of 20 to 30 bars in order to produce higher hydrocarbons. Another process for converting synthesis gas into ~-olefins containing 2 to approximately 22 carbon atoms uses iron titanate catalysts containing alkali hydroxide (of. U.S. Patent 4,261,865?.

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The known methods suffer from certain defects in the light of current technical requirements, in particular, their selectivity still needs to be considerably improved.

An object of the invention is, thereEore, to increase the selectlvity of the carbon monoxide/hydrogen reaction; i.e. to improve waxy hydrocarbons so that the molecular size of the hydrocarbons formed is as uniform as possible.

It is also an object of the invention to improve the reaction 80 that the formation of compounds other than hydrocarbons -~ especially oxygen containing substances -- is prevented or minimized.

The invention achieves these objectives in the production of linear hydrocarbons with more than 18 carbon atoms by converting gas mixtures containing carbon monoxide and hydrogen in the presence of iron-containing catalysts at 150 to 350C
and 5 to 50 bars, and incorporating into the catalysts a readily reducible metal oxide, a difficultly reducible metal oxide, SiO2, and an alkali metal oxide.

An important feature of the present invention is the use of a catalyst which contains, in addition to iron, two metal oxides of different reducibility. Cupric oxide, silver oxide, or a mixture of the two oxides is successfully used as the readily reducible metal oxide. In addition, however, oxides of ruthenium and palladium, alone or mixed with one another or with one or more of the afore-mentioned oxides, are also suitable.
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_ _ Titanium dioxide has proved particularly sui~able as the difficultly reducible metal oxide. It~can be used, not only in the form of the commercially available TiO2, but also as the oxide hydrate such as occurs, for example, in converting water-soluble Ti(IV) compounds with alkaline reacting reagents. In addition to titanium dioxide, vanadium pentoxide and chromium (III) oxide are suitable as the difficultly reducible oxide constituents of the catalyst. The difficultly reducible metal oxides can be contained in the catalyst alone, or in the form of a mixture of two or more constituents.

The composition of the catalysts used according to the method of the invention may vary within wide limits. A common feature of the catalysts is, however, the fact that their principal constituent is iron. The preferred catalysts contain 0.1 to 10 parts by weight of the readily reducible metal oxide per 100 parts by weight of iron. More preferably, they should contain 0.5 to 6 parts by weight of the oxide per 100 parts of iron.

It has proved particularly convenient to use catalysts containing 1 to 25 parts by weight and, in particular, 5 ~o 15 parts by weight, of the difficultly reducible metal oxide per 100 parts by weight of iron. The catalyst also advantageously contains 5 to 35 parts by weight and, in particular, 10 to 30 parts by weight, of silicon dioxide per 100 parts by weight of iron. Widely different forms of the compound SiO2 can be used, including those modifications ''`''`'' ~ ~9(~
which contsin water in a bound form; as well as silicates, of which the alkali silicates have proved to be particularly suitable.

Finally, the catalysts are also characterized by the presence of alkali metal oxide, preferably contain 1 to 30 parts by ~eight and, more preferably, l to 15 parts by weight, of alkali metal oxide per 100 parts by weight of iron. The alkali metal oxide need not be added as such to the catalyst, but can be introduced, for example, in the form of hydroxide, carbonate or silicate. The use of sodium and/or potassium compounds is preferred~

Various methods can be used to prepare the catalysts. One procedure starts from soluble iron compounds and the compounds which form the readily reducible and difficultly reducible metal oxides. The corresponding carbonates or hydroxides are precipitated by the action of alkaline reagents; e.g., alkali carbonate or alkali hydroxide. The catalyst mass is then filtered off, washed, and impregnated with alkali silicate.

Another procedure is to start with TiO2, precipitate the remaining components onto this solid, and impregnate it with alkali silicate. According to yet another method, one starts with TiO2 and SiO2 together, and precipitates the remaining components onto the mixture of the oxides. The catalyst is then impregnated with alkali silicate and/or with alkali carbonate and/or alkali hydroxide. The impregnation of SiO2 (and optionally TiO2) with aqueous solutions of an iron salt, as well as a salt of the metal which produces a readily reducible oxide, has also proved suitable for preparing the cata:Lysts.
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The catalyst mass obtained according to one of the described methods is shaped in the usual manner; e.g. by extrusion or by producing broken granules, tablets or pellets.

The reduction of the catalyst is carried out using hydrogen, carbon monoxide, or mixtures thereof at temperatures of 150 to 350C. It has proved convenient to carry out the reduction of the catalyst at linear gas velocities of 10 to 500 cm/sec. (calculated for normal conditions and referred to the empty reactor) and, in particular, at 50 to 250 cm/sec. In this connection, a pressure of 1 to 50 bars, preferably 1 to 25 bars,and most preferably 1 to lO bars, is maintained. The treatment of the catalyst with carbon monoxide, hydrogen or a mixture thereof is continued until the catalyst contains 10 to 50% by weight, preferably 20 to 35% by weight, of metallic iron based on the total iron content of the catalyst.

The conversion can be carried out under the temperature, pressure, gas composition and space velocity conditions normal for the Fischer-Tropsch reaction and, accordingly, the conversion can be carried out in conventional equipment. Of course, it should be borne in mind that the selectivity of the conversion can be increased still further by maintaining strict pressure and temperature ranges, as well as specific space velocities. By the term "selectivity" is meant the proportion of carbon monoxide converted into the desired compounds.

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~ --The conversion is carried out at temperatures of 150 to 35CC and pressures of 5 to 50 bars. It has proved expedient to employ temperatures of 180 to 280C and, in particular, 200 to 250C. The pressures are preferably in the range from 20 to 5 40 bars. Higher temperatures result in a reduced formation of gaseous and liquid hydrocarbons, while higher pressures improve the selectivity with regard to the formation of the desired hydrocarbons. The use of higher pressures is, however, limited by economic factors resulting, for example, from the requirements of pressure tightness of the apparatus. The synthesis gas is led over the catalyst at a fresh gas space velocity of 100 to 300Q VtVh, preferably 500 to 1500 V/Vh.

The ratio of hydrogen to carbon monoxide in the synthesis gas may vary from about 1 : 0.1 to about 1 : 10, preferably from about 3 : 1 to about 1 : 3. In general, an increase in the hydrogen fraction in the gas mixture leads to an increased proportion of low molecular weight hydrocarbons.

In a special embodiment of the process according to the invention, up to 50% by volume based on the total mixture, of -an inert gas or inert gas mixture such as nitrogen and/or earbon dioxide and/or noble gas, is added to the synthesis gas.

The gas can be passed directly over the catalyst. It is, however, expedient to recycle part of the gas after separating the reaction products and replenish the converted hydrogen and carbon monoxide with fresh gas. It has proved particularly advantageous to adjust the volume ratio of fresh gas to cycle gas to values of 1 : 1 to 1 : 10 and in particular to values of 1 : 1 to 1 : 5.

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The catalyst is arranged in the form of a fixed bed or a fixed bed of enlarged volume, iOe. expanded bed. According to a particular embodiment of the invention, organic liqu;d product of the same type is led continuously or discontinuously over the catalyst during the synthesis. Hydrocarbons with 5 to 20 carbon atoms, consisting of up to 10 ~o 90% by weight of olefins, have proved particularly suitable as liquid products.
~he treatment of the catalyst with the organic liquid product of the same type leads to an increased yield of long-chain hydrocarbons.

The synthesis product obtained according to the new process consists of at least 70% by weight of hydrocarbons with more than 18 carbon atoms. Of these hydrocarbons, more than 95% are linear. Gaseous hydrocarbons with 2 to 4 carbon atoms are formed in a proportion of less than 5% by weight.

Example 1 Preparation of Catalyst 1.

4078 g Fe ~NO3)3 . 9 H20 and 107 g Cu(NO3~ . 3 H2O are dissolved in 11 liters of water, heated to 100C, and added during a period of about 2 minutes to a boiling potassium carbonate solution (11.5% by weight K2CO3) containing 225 ml of titanium oxychloride solution (250 g TiO2/1). The conversion product has a pH value of 6.9. The product is filtered off and washed with 65 to 75C warm water until the `' .

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electrical conductivity of the wash water is less than lOOf~ S. The filter cake is made into a slurry with water in a ratio of 1 : 1 and a potassium silicatè solution [150 g K2SiO3 (58% SiO2) / 500 ml H20] is added. The pH is adjusted to 6.9 with concentrated nitric acid, and the solution is heated to 85C and refiltered.

The moist filter cake is dried at about 50C. The prepared catalyst has the following composition (in parts by weight):

100 Fe : 4 Cu : 7 TiO2 : 15 SiO2 : 8 K20 Example 2 Preparation of the Catalyst 2.

4078 g Fe(N03)3 . 9 H20 and 107 g Cu(N03)2 O 3 H20 are dissolved in 11 liters of water, heated to~lO0C, and added during 2 period of about 2 minutes to a boiling potassium carbonate solution (11.5% by weight K2C03) containing 56~3 g titanium oxide. The conversion product has a pH value of 6.9. The product is filtered off and washed with 65 to 75C -warm water until the electrical conductivity of ~he wash water is about 200 ~ S. The filter cake is made into a slurry with water in a ratio of 1 : 1 and potassium silicate solution [150 g K2SiO3 (58% SiO2) / 500 ml H20] is added. The pH
value is adjusted to 6.9 with concentrated nitric acid and the solution is heated to 85C and refiltered. The filter cake is then dried at about 50C. The prepared catalyst has the following composition (in parts by weight):

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100 Fe : 6 Cu : 8 T;02 : 18 SiO2 : 6 K20 In the catalyst, copper may be partially or completely replaced by silver with similar results.

Example 3 Preparation of the Catalyst 3.

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4078 g Fe(N03)3 r 9 H20 and 107 g Cu(N03)2 . 3 H20 are dissolved in 11 liters of water, heated ~o 100C, and added during a period of about 2 minutes to a boiling soda solution (11.5% by weight Na2C03) containing 225 ml titanium oxychloride solution (250 g TiO2/1). The conversion product has a pH value of 6.9. The product is filtered off and washed with 65 to 75C warm water until the electrical conductivity of the wash water is about 100 ~S. The filtrate ia made into a slurry with water in a ratio of 1 : 1 and potassium silicate solution [250 g K2SiO3 (58% SiO2~ /
600 ml H20] is added. The pH value is adjusted to 6.9 with concentrated nitric acid, and the solution is heated to 85C
and refiltered. The moist filter cake is dried at about 50C.
The resultant catalyst has the following composition (in parts by weight):

100 Fe : 5 Cu : 8 TiO2 : 30 SiO~ : 5 K20 In the catalyst, copper can be partially or completely replaced by silver with similar results.

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~ ~ Preparation of ~he Ca~alyst 4 t ; '' ,t, ~ 4078 g Fe(N03)3 . 9 H20 and 107 g Cu(N03)2 . 3 ;~ , ~ H20 are dissolved in 11 liters H20, heated to 100C, and ` ,~ , 5 added over a period of about 2 minutes to a boiling soda solution (11.5% by weight Na2C03) containing 225 ml titanium oxychloride solution (250 g TiO2/1). The conversion product has a pH value of 6.9. The product is filtered off and washed with 65 to 75C warm water until the electrical conductivity of the wash water is about 150~S. The filter cake is made into a slurry with water in thè ratio 1 : 1 and potassium silicate solution [150 g K2SiO3 ~58% SiO2~ /
`i! 500 ml H20] is added. The pH value is adjusted to 6.9 with ¦ concentrated nitric acid and the solution is heated to B5C and refiltered. The moist filter cake is dried at about 50C. The prepared catalyst has the following composition (in parts by weight):

100 Fe : 5 Cu : 9 TiO2 : 15 SiO2 : 3 K20 ~.~
Reduction of the catalyst~ an~ thesis The catalysts produced according to Examples 1 to 4 are reduced with hydrogen which is passed downwards over the ! catalyst. The heating is carried out in an H2 atmosphere until the reduction temperature is reached. The reduction takes place under the following conditions:

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Duration : 1 h Temperature (C) : 240C.
H2 gas velocity : 150 cmtsecO = 650 V/Vh After the end of the reduction, the reaction mixture is S cooled to about 16a to 170C and hydrogen is added up 20 bars pressure. The gas circulation is then started, the CO/H2 metering i6 commenced, and the catalyst is brough~ very slowly to the synthesis temperature. The synthesis results are given in the following Table.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for producing linear hydrocarbons having more than 18 carbon atoms by converting a gas mixture containing carbon monoxide and hydrogen in the presence of iron-containing catalysts at 150 to 350°C and 5 to 50 bars, the improvement which comprises said catalysts containing a readily reducible metal oxide, a difficultly reducible metal oxide, SiO2, and an alkali metal oxide.

2. The process of Claim 1, wherein the readily reducible metal oxide is cupric oxide and/or silver oxide.

3. The process of Claim 1, wherein the difficultly reducible metal oxide is titanium dioxide.

4. The process of Claim 1 wherein the catalyst contains 0.1 to 10 parts by weight of the readily reducible metal oxide per 100 parts by weight of iron.

5. The process of Claim 4 wherein said catalyst contains 0.5 to 6 parts by weight of said readily reducible metal oxide per 100 parts by weight of iron.

6. The process of Claim 1 wherein the catalyst contains 1 to 25 parts by weight of the difficultly reducible metal oxide per 100 parts by weight of iron.

7. The process of Claim 6 wherein said catalyst contains 5 to 15 parts by weight of said difficultly reducible metal oxide per 100 parts by weight of iron.

8. The process of Claim 1 wherein the catalyst contains 5 to 35 parts by weight of SiO2 per 100 parts by weight of iron.

9. The process of Claim 8 wherein said catalyst contains 10 to 30 parts by weight of SiO2 per 100 parts by weight of iron.

10. The process of Claim 1 wherein the catalyst contains 1 to 30 parts by weight of alkali metal oxide per 100 parts by weight of iron.

11. The process of Claim 1 wherein said catalyst contains 1 to 15 parts by weight of alkali metal oxide per 100 parts by weight of iron.

12. The process of Claim 1 wherein unconverted gas is recycled and passed over said catalyst.

13. The process of Claim 12 wherein said unconverted gas is admixed with said gas mixtures.

14. The process of Claim 13 wherein the ratio of said gas mixtures to said unconverted gas is 1 : 1 to 1 : 10.

15. The process of Claim 14 wherein said ratio is 1 : 1 to 1 : 5.