GB2050859A

GB2050859A - Process for the manufacture of gaseous olefins from a carbon oxide and hydrogen and catalysts for this process

Info

Publication number: GB2050859A
Application number: GB8016327A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-05-17
Filing date: 1980-05-16
Publication date: 1981-01-14
Also published as: FR2456718A1; JPS5625117A; DE2919921A1; GB2050859B

Abstract

Catalysts for the manufacture of olefins by catalytic hydrogenation of carbon oxides with hydrogen (Fischer- Tropsch process) comprise polycrystalline iron whiskers, especially those that have been obtained by thermal decomposition of gaseous iron pentacarbonyl in a magnetic field. The catalyst may contain promoters, especially potassium oxide, sulphur, gold and cobalt promoters.

Description

SPECIFICATION Process for the manufacture of gaseous olefins from a carbon oxide and hydrogen and catalysts for this process This invention is concerned with novel catalysts for use in a process for the manufacture of hydrocarbons by the catalytic hydrogenation of carbon oxides, especially carbon monoxide, and is also concerned with a process using such a catalyst whereby relatively large quantities of gaseous olefins are formed.

Owing to the price trend of mineral oil and the anticipated decline in mineral oil supplies in the coming decades, there is a need to switch to coal for obtaining chemical raw materials. It is therefore necessary to return to the processes of coal liquefaction used in Germany before and during the war. These processes are the hydrogenation of coal under pressure to produce coal oil and the hydrogenation of carbon monoxide over a cobalt or iron hydrogenation cataylst, the so-called Fischer-Tropsch synthesis.

In the Fischer-Tropsch synthesis, carbon monoxide and hydrogen are passed over a catalyst at a temperature in the range of from 200 to 350 C and at a pressure of from 1 to 50 atmospheres. The synthesis is generally known and has been described comprehensively in the literature (Ullman, Vol. 9, pages 684-748 (1967)).

In the Fischer-Tropsch synthesis aliphatic hydrocarbons from methane to solid paraffin, and oxygencontaining compounds, are produced. The main constituent, in accordance with the needs and objective at that time of producing high yields of petrol fractions, comprises saturated hydrocarbons having chain lengths of C6 - 017.

The catalysts used hitherto contained as catalytically active elements iron or cobalt and were used in the form of precipitation catalysts or melting catalysts.

In addition to activating substances they optionally contained carriers such, for example, as silica gel or diatomaceous earth.

Catalysts of this type that contain iron as the essential constituent yield a product spectrum of predominantly liquid, and partly solid, hydrocarbons.

However, the chemical raw materials required in large quantities are predominantly alkenes with 2 to 4 carbon atoms (ethylene, propylene and butylene).

The new objective of synthetically producing these chemical raw materials from carbon monoxide and hydrogen requires the development of a new catalyst.

Attempts to shift the product spectrum to lower unsaturated hydrocarbons with the hitherto known catalysts described above, for example, by increasing the temperature, were not successful.

Positive results in the desired direction are described in DE-AS 2518964 and DE-AS 25 36 488, which are characterised by the use of titanium, vanadium molybdenum, tungsten and manganese to precipitate the iron. The required long-term stability was not, however, achieved with these catalysts.

According to DE-OS 2507 647, results in the desired direction may be achieved by using electrolytically produced manganese metal or Mn-Fe precipitation catalysts with and without activators.

Surprisingly we have found that polycrystalline iron whiskers, especially with the incorporation of one or more promoters such, for example, as titanium, vanadium, chronium, nickel or especially manganese, cobalt, copper, gold, sulphur and alkali promoters, not only catalyse the carbon monoxide hydrogenation but bring about a high selectivity for the desired products ethylene, propylene and butylene and a-olefins in the liquid phase range (Cg - 020), and at the same time have an excellent long-term activity that can be identified. More than 70% of the C, - C5 hydrocarbons are obtained in the form of olefins and the organic liquid phase consists of approximately 90 % a-olefins.

By polycrystalline whiskers there are to be understood herein fine iron filaments with microscopically small monocrystal ranges. They may be produced, for example, according to the method described in DE-PS 12 24934 by the thermal decomposition of gaseous iron pentacarbonyl in a magnetic field, the monocrystal ranges being aligned filament-like by way of dislocations and grain boundaries by a preferential growth in the direction of the magnetic field. Typical dislocation densities are in the range of approximately 1012 dislocations per cm2.

The present invention therefore provides a catalyst suitable for use in the manufacture of olefins by the hydrogenation of carbon oxides, especially carbon monoxide, with hydrogen, which comprises polycrystalline iron whiskers (as herein before defined). It also provides a process for the manufacture of olefins by catalytic hydrogenation of carbon oxides, especially carbon monoxide, with hydrogen in the presence of an iron catalyst at a raised temperature and preferably superatmospheric pressure, wherein the catalyst comprises polycrystalline iron whiskers which, if desired, may contain one or more promoters and/or carriers.

The process is preferably carried out at 200 to 400"C and 2 to 50 bars.

Preferably the polycrystalline iron whiskers are those obtainable by the thermal decomposition of gaseous iron pentacarbonyl in a magnetic field, advantageously of at least 5000 Gauss, and especially those that have been thermally pretreated at temperatures of 200 to 900"C, especially 300 to 500"C, in a hydrogen or nitrogen atmosphere.

Advantageously, the iron whiskers are in the form of pellets that have been produced from sieved whiskers of a 1.0 to 0.06 mm sieve fraction in compression moulds at pressures of 2 to 2,000 kp/cm2, preferably 10 to 100 kp/cm2.

As suitable promoters the catalysts may contain one or more of the elements titanium, vanadium, chromium, manganese, cobalt, nickel, copper, gold, potassium and sulphur.

An especially preferred catalyst contains, calculated on the iron, 0.05 to 10 % by weight, especially 0.5 to 5 % by weight, of potassium oxide, and 0.01 to 0.5 % by weight of sulphur.

Another especially preferred catalyst contains; in addition, 0.1 to 10 % by weight of gold.

Another especially preferred catalyst contains, calculated on iron, 0.05 to 10% by weight especially 0.5 to 5 by weight, of potassium oxide, 0.01 to 0.5 % by weight of sulphur and 0.1 to 10 % by weight of cobalt.

Even without any additives, however, the iron whiskers have a catalytic activity.

The addition of potassium, cobalt, manganese, copper, sulphur and gold has an advantageous effect regarding activity and selectivity. The activity and selectivity of the whiskers may furthermore be varied by adding further sub-group elements of the 4th period of the Periodic Table (Ti, V, Co, Ni).

We have found that an addition of cobalt enables especially the activity of the catalyst to be considerably increased.

The addition of manganese increases the selectivity and reduces especially the formation of CO2.

The admixtures of cobalt, manganese, potassium, gold and sulphur can be varied within wide limits.

Additions to the iron whiskers of 0.1-10 % in each case of Mn, Co, Cu or Au,0.05-30 of potassium oxide and 0.01 -0.5 % of sulphur are effective. It is especially advantageous, however, to use admixtures in the region of 1-10 % of Mn, 0.1-10 % of Co, 0.5-5 % of K2O, 0.5-5% of gold, and 0.1-0.2% of S.

The process may be carried out in the range of from 200 to 400 C, especially 220 to 3600C, at pressures of 2 to 50 bars, preferably 4 to 15 bars.

Alterations to the parameters of the synthesis, such as to the temperature, pressure, space velocity and H2lCO ratio, lead apparently only to a limited extent to relative shifts within a product spectrum. Marked alterations of the selectivity can be achieved rather by variations of the catalyst.

The application of a different synthesising process technique likewise does not result in a significant alteration of the selectivity. Table 1 below shows a comparison of Fischer-Tropsch synthesis products using a catalyst of the invention in a fixed-bed and in a liquid-phase laboratory reactor. As can be seen, the surprising influence of the catalyst on the product spectra prevails and masks the different processing techniques: the results in the liquid-phase reactor are very similar to those in the fixed-bed reactor when catalysts of the same composition are used.

Synthesis conditions Fixed bed Liquid phase Synthesis gas CO:H2 10:9 10:9 12:7 12:7 12:7 Pressure (bars) 10 10 10.5 10 10 Temperature ("C) 280 300 300 320 340 Space velocity (VNh) 190 230 71 140 160 CO-conversion (%) 98 98 92 91 94 Yields (g/Nm3)* CH4 11.5 14.2 9.7 11.3 14.6 C2H6 3.2 3.8 3.1 3.1 3.5 C2H4 13.6 14.6 10.9 12.1 13.1 03H8 1.9 1.9 1.6 1.7 1.9 C3He 22.5 23.5 20.9 21.4 22.0 isoC4H10 C4Hxo n-C4Hlo 1.7 0.2 1.6 1.6 1.8 1-C4H8 18.3 17.9 18.9 19.6 20.5 iso C4H8 1.0 0.9 1.3 1.1 1.1 cis C4H8 1.2 1.0 1.4 1.4 1.4 C2-C4 paraffins 6.8 5.9 6.3 6.4 7.2 C2-C4 olefins 56.6 57.9 53.4 55.5 58.1 C1-C5 hydrocarbons 90.7 94.7 88.5 93.8 101.3 * g/Nm3 means grams per cubic metres at normal pressure (760 mm Hg) and 000.

The manufacture of the polycrystalline iron whiskers is preferably carried out by thermal decomposition of gaseous iron pentacarbonyl in a magnetic field of at least 5000 Gauss, a primarily preferred growth occurring in the direction of the magnetic field. When using the catalyst in the liquid phase reactor it is recommended that the whiskers are previously sieved and that a particular sieve fraction is chosen which must be suited to the sedimentation behaviour in the reactor under the diverse influence, for example gas bubbles, pressure, temperature, viscosity of the dispersion medium. A sieve fraction of 0.5-0.06 mm has proved particularly favourable.The catalyst may be sieved either before or after incorporation, for example, by impregnation, of a substance which acts as a promoter or which yields on heating to a suitable temperature a substance acting as a promoter; if desired, a mixture of two or more of such substances may be used. It has proved advantageous, however, to carry out the sieving process after the incorporation of the promoter or promoters.

When using the catalyst in the fixed-bed reactor it should first of all be formed into pieces or pellets. A process for this consists, for example, of sieving the whiskers after they have been produced and sintering together a sieve fraction of 0.5-0.06 mm long whiskers in a graphite compression mould at a pressure of from 10 kp/cm2 to 2000 kp/cm2 and at a temperature of from 400 to 900"C in a hydrogen or nitrogen atmosphere. Mouldings are obtained of which the porosity depends on the pressure applied but is preferably 90 %.

In addition, any other suitable pelletisation process may be used, for example, admixing the iron whiskers with an aqueous methyl cellulose solution with subsequent granulation, drying, and, to increase the mechanical stability, sintering at 400 to 900"C in a hydrogen or nitrogen current.

Finally, a catalyst according to the invention may be produced in such a manner that the fine iron whiskers produced during the manufacture, after treatment with an aqueous solution of a nitrate yielding a promoter, are bonded with a ceramic adhesive (for example, one based on aluminium silicate). After hardening, the catalyst is comminuted to the desired grain size and, as described above, converted into a state suitable for use in the Fischer-Tropsch synthesis.

The incorporation of the above-mentioned promoters may be effected, for example, by impregnating the catalyst with an aqueous solution of a salt of an appropriate metal, preferably with a solution of a metal nitrate or chloride. In addition, the use of wetting agents (for example, methanol) provides uniform wetting of the iron whisker surface. Subsequently, the water and the methanol are evaporated off and the nitrate or chloride is decomposed at approximately 300 to 500"C, so that the corresponding oxide remains on the polycrystalline surface.In the case of catalysts containing sulphur, the sulphur may be added, before or after decomposition of the metal nitrate or chloride, in the form of a sulphide (for example sodium sulphide, potassium sulphide, ammonium sulphide etc.), in the form of an organic sulphur compound (for example thioacetamide, thiophene, thiourea etc.) or in the form of hydrogen sulphide.

Furthermore, the metals acting as promoters may be incorporated by thermal decomposition of the corresponding gaseous carbonyl compounds during or after the manufacture of the iron whiskers. Finally, as described above, the catalyst may be formed into pellets and impregnated with a substance yielding potassium and/or sulphur promoter.

The catalysts can then be converted into the active state by treatment with hydrogen at 300 to 400"C, especially at 350"C, and under superatmospheric pressure, for example, 2 atmospheres, at a space velocity of approximately 500 litres of hydrogen per litre of catalyst per hour over a period of 1 to 24 hours. This additional activation is not, however, absolutely necessary (see Examples 5 and 6).

The long-term behaviour of the iron whisker catalysts according to the invention is shown in Figure 1 with a pelletised iron whisker catalyst containing 0.3 % by weight of K2O,0.5 by weight of Co and 0.1 % by weight of S. On continuous operation in the fixed-bed reactor its activity accordingly did not exhibit any time dependence.

CO+H2 conversion (V%) Temperature ( C) operating time (days) Figure 1 Long-term behaviour of a pelletised iron whisker catalyst in a fixed-bed laboratory reactor.

There are not even any substantial changes in the selectivity of the catalyst towards the end of the three-month long-term test. Table 2, Example 7, shows a typical distribution of the product spectrum (gas phase) during continuous operation.

The following Examples illustrate the invention: Example 1 Polycrystalline iron whiskers of 1-0.06 mm length that had been tempered in a hydrogen current at 900"C and at a pressure of 1 bar were used as catalyst. The whiskers were impregnated with an aqueous potassium carbonate solution so that 1 % by weight of K2O (calculated on iron) was formed on the catalyst. The excess water was evaporated at 400C in a drying chamber. 5 ml were mixed with 40 ml of silicon carbide (grain size approximately 1-2 mm Zi) as filler and for the purpose of better heat transfer, and the mixture was introduced into a laboratory reactor. The reactor consisted of a refined steel tube of 17 mm internal diameter and 450 mm length.Activation in a current of hydrogen was effected at 3500C, under a hydrogen pressure of 2 atmospheres and a space velocity of approximately 500 litres of hydrogen per litre of catalyst per hour over a period of two hours. The temperature was then reduced to 24000. A carbon monoxide/hydrogen/nitrogen mixture (47.5 % by volume : 47.5 % by volume : 5 % by volume) was then introduced and the synthesis was commenced. The temperature was increased in stages, by 20"C each time, and the synthesis properties ascertained. Table 2 shows the yield of gaseous hydrocarbons at 320"C and an 87.9 % CO conversion in column 1.

Example 2 Polycrystalline iron whiskers that had previously been sintered together in a hydrogen current at 900"C under a low pressure of 10 kp/cm2 were used as catalyst. This sintered metal disc was comminuted and a grain fraction of 1-2 mm was removed by sieving. 6 Grams of this product were impregnated with a solution of 0.06 grams of Co(NO3)2.6 H2O + 0.88 grams of KNO3 and then dried. The nitrates were decomposed by heating to 300"C. The catalyst was mixed with 40 ccs of silicon carbide, introduced into the reactor and reduced and acted upon by synthesis gas as described in Example 1. Atypical yield of hydrocarbons is given in column 2 of Table 2.

Example 3 Polycrystalline iron whiskers that had previously been activated with 2 % of Mn, calculated on iron (used in the form of Mn(NO3)2.4 H2O), and 10 % of K2O, calculated on iron (used in the form of KNO3) were used as catalyst. The catalyst was mixed with 40 ccs of silicon carbide and introduced into the reactor. The reduction conditions were the same as those in the previous Examples. Typical yields at 3200C and a CO conversion of 97.9 % are given in column 3 of Table 2.

Example 4 Polycrystalline iron whiskers were used as catalyst. A sieve fraction of whiskers of a length of 1.0 - 0.06 mm was compressed in a compression mould at a pressure of 50 kp/cm2 and 500"C in nitrogen to form pellets of 3 mm length and 2 mm diameter.

40 grams of these pellets were impregnated with a solution of Co(NO3)2 and KNO3, so that 2 % by weight of Co and 1 % by weight of potassium were present in the catalyst. After drying at 800C and heating to 300"C the mixture was cooled again, and 0.1 % of sulphur was added in the form of a potassium sulphide solution and the mixture dried again. Typical yields are given in column 4 of Table 2.

Example 5 Cylindrical pellets, 2 mm in diameter and 3 mm in length, were used as catalyst. These pellets were moulded from polycrystalline iron whiskers (sieve fraction 1.0 - 0.06 mm) and tempered at 500 C (cf.

Example 4). 2 grams of pellets were impregnated with 0.5 % of K. To do this the corresponding amount of potassium acetate (CH3COOK) was dissolved in methanol and the pellets were impregnated with this solution. The pellets were then dried for 2 days in a dessiccator. The results of the test are listed in Table 2, column 5.

This Table shows conditions and product yields using a catalyst of the invention in a Fischer-Tropsch synthesis.

TABLE 2 Example 1 2 3 4 5 7 Synthesis conditions: CO:H2 ratio 1:1 1:1 1:1 10:9 10:9 10:9 Pressure (bars) 15 15.1 15 10 10 12 Temperature ( C) 320 320 320 280 360 280 CO conversion (%) 87.9 90 97.9 94.4 96.1 94.7 Space velocity (h-1) 380 850 410 900 150 140 Product Yield.

(g/Nm of H2 + CO used) methane 11.2 10.8 16.2 8.8 13.6 13.5 ethane 3.7 2.3 3.7 1.5 3.3 5.5 ethylene 12.4 10.5 12.8 29.9 18.0 14.3 propane 2.0 1.6 2.3 1.1 2.1 2.8 propylene 22.7 16.4 20.4 18.9 25.6 26.4 n-butane 1.7 2.2 1.7 1.0 2.0 2.3 but-1-ene 14.8 14.0 13.4 14.8 19.5 20.7 isobutene 2.4 1.4 1.6 0.7 1.0 1.4 cis-butene 1.5 2.1 1.2 1.1 1.4 pentane 1.3 1.4 1.7 2.4 1.5 1.2 pent-1-ene 13.6 15.2 14.8 8.9 10.2 8.8 CO2 396.6 400.4 236.6 416.0 434.0 434.0 C4-C4 olefins 53.8 44.4 49.4 48.2 65.2 64.1 C1-C4 paraffins 18.6 16.9 23.9 12.4 21.0 24.1 Olefin content of the C1-C4 fraction (% by wt.) 74.3 72.4 67.4 79.5 75.6 72.7 Example 6 To produce the catalyst the polycrystalline iron whiskers (sieve fraction 1 - 0.06 mm) were pressed into pellets as described in Example 4.These pellets were then impregnated with an aqueous/methanolic solution (1:1) of potassium nitrate and tetrachloroauric acid (HAuC14.4H20), so that 2 % by weight of gold and 1% by weight of potassium were incorporated in the catalyst. After evaporating the water and the methanol an aqueous potassium sulphide solution was added so that the catalyst contained 0.1 % of sulphur. 20 grams of this catalyst were used in the laboratory reactor. Synthesis conditions and product yields, as well as the percentage by weight distribution, are given in the following Table.

Table to Example 6 Synthesis conditions CO : H2 ratio 1: 2 CO conversion (%) 96.9 CO + H2 conversion (%) 67.9 Temperature ("C) 360 pressure (bars) 10 space velocity (VNh) 280 Yield g/Nm3 % by weight calc.

(used CO + H2) on C1+ methane 22.43 16.4 ethane 3.44 2.5 ethylene 15.91 11.7 propane 1.91 1.4 propylene 20.45 15.0 n-butane 1.53 1.1 but-1 -ene 14.79 10.8 isobutene 0.44 0.3 cis-butene 1.07 0.8 C5+ and O-compounds 54.45 39.9 C2-C4 paraffins 6.88 5.0 C2-C4 olefins 52.66 38.6 Total yield C,+ 136.42 Distribution of C2-C3-C4 olefins (mole %) 43:37:20 % of CO that reacted to form: CO2 30.8 C1-C5 46.0 C6+ 23.2

Claims

1. A catalyst suitable for use in the manufacture of olefins by the hydrogenation of carbon oxides with hydrogen, which comprises polycrystalline iron whiskers (as hereinbefore defined).

2. A catalyst as claimed in claim 1, wherein the polycrystalline iron whiskers are obtained by the thermal decomposition of gaseous iron pentacarbonyl in a magnetic field.

3. A catalyst as claimed in claim 1 or claim 2, wherein the polycrystalline iron whiskers have been thermally pre-treated at a temperature in the range of from 200 to 900 C, in hydrogen or nitrogen atmosphere.

4. A catalyst as claimed in claim 3, wherein the polycrystalline iron whiskers have been thermally pretreated at a temperature in the range of from 300 to 500 C.

5. A catalyst as claimed in claim 4, wherein the thermal pre-treatment is carried out under superatmospheric pressure.

6. A catalyst as claimed in any one of claims 1 to 5, wherein the polycrystalline iron whiskers are in the form of pellets that are obtained from sieved whiskers of a sieve fraction of 1.0 - 0.06 mm using a compression mould and at a pressure of from 10 to 2000 kg/cm2.

7. A catalyst as claimed in claim 6, wherein a pressure of from 30 to 100 kp/cm2 is used.

8. A catalyst as claimed in any one of claims 1 to 7, which contains a titanium, vanadium, chromium, manganese, cobalt, nickel, copper, gold, potassium or sulphur promoter or any two or more of such promoters.

9. A catalyst as claimed in claim 8, wherein the promoter or promoters is or are in the form of a metal oxide.

10. A catalyst as claimed in any of claims 1 to 8, wherein, calculated on the wieght of iron, it contains from 0.05 to 10 % by weight of potassium oxide and 0.01 to 0.5% by weight of sulphur.

11. A catalyst as claimed in claim 10, which contains from 0.5 to 5 % by weight of potassium oxide.

12. A catalyst as claimed in claim 10 or claim 11, which also contains 0.1 to 10 % by weight of gold, calculated on the weight of iron.

13. A catalyst as claimed in any one of claims 10 to 12, which also contains 0.1 to 10 % by weight of cobalt, calculated on the weight of iron.

14. A catalyst as claimed in any one of claims 1 to 8, wherein, calculated on the weight of iron, it contains from 1 to 10 % by weight of manganese, 0.1 to 10 % by weight of cobalt, 0.5 to 5 % by weight of potassium oxide, 0.5 to 5 % by weight of gold and 0.1 to 0.2 % by weight of sulphur.

15. A catalyst as claimed in any one of claims 1 to 14, which also contains a carrier.

16. A catalyst as claimed in any one of claims 2 to 15, wherein the magnetic field has a strength of at least 5000 Gauss.

17. A process for the manufacture of a catalyst as claimed in any one of claims 1 to 16, substantially as described herein.

18. A catalyst whenever obtained by the process claimed in claim 17.

19. A catalyst as claimed in claim 1, substantially as described in any one of the Examples herein.

20. A process for the manufacture of olefins by the catalyst hydrogenation of carbon oxides with hydrogen at a raised temperature, wherein the hydrogenation is carried out in the presence of a catalyst as claimed in any one of claims 1 to 18.

21. A process as claimed in claim 20, which is carried out at a temperature of from 200 to 400"C.

22. A process as claimed in claim 21, which is carried out at a temperature of from 220 to 360 C.

23. A process as claimed in any one of claims 20 to 22, which is carried out at a pressure of from 2 to 50 bars.

24. A process as claimed in claim 23, which is carried out at a pressure of from 4 to 15 bars.

25. A process as claimed in claim 20, conducted substantially as described in any one of the Examples herein.

26. A process as claimed in any one of claims 20 to 25, wherein the carbon oxide is carbon monoxide.

27. An olefin or olefin mixture whenever obtained by a process as claimed in any one of claims 20 to 26.