GB2024246A

GB2024246A - Hydrocarbon synthesis

Info

Publication number: GB2024246A
Application number: GB7920635A
Authority: GB
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 1978-06-16
Filing date: 1979-06-13
Publication date: 1980-01-09
Also published as: ZA783466B; FR2434793B1; FR2434793A1; JPS5527173A; CA1112672A; DE2924139A1; GB2024246B

Abstract

This invention relates to hydrocarbon synthesis and particularly to the production of gasoline with a range of C5 to C12. In particular the invention relates to a process for synthesising hydrocarbons in the C5 - C12 range from a mixture of hydrogen and carbon monoxide gases, comprising contacting the said mixture with a supported ruthenium catalyst wherein the said mixture is at a temperature within the temperature range of (500 to 550) DEG K and wherein the outlet partial pressure of carbon monoxide is not less than 0.8 atmospheres in the temperature range (500 to 525) DEG K and not less than 3.0 in the temperature range (525-550) DEG K. <IMAGE>

Description

SPECIFICATION Hydrocarbon synthesis This invention retates to hydrocarbon synthesis.

So-called "synthesis" gas produced from coal has been used for the synthesis of hydrocarbons on a commercial scale in the Fischer-Tropsch process. In the currently used process the synthesis gas, composed of hydrogen and carbon monoxide, is passed over iron catalysts.

With presently used commercial catalysts it is not possible to limit hydrocarbon synthesisto a desirable product range, e.g. the hydrocarbons within the gasoline range. The products produced comprise the whole spectrum from methane to waxes.

Ruthenium is known as a catalyst in hydrogenation reactions, but has not been used commercially in the Fischer-Tropsch process because of its relatively high cost compared with iron catalysts.

The present invention is based on the discovery that with the use of ruthenium catalysts, it is possible to obtain a product mix which favours the gasoline range of hydrocarbons. From a practical point of view ruthenium also now is more attractive due to the development of new techniques for the preparation of relatively cheap supported catalysts which contain low concentrations of ruthenium, e.g. of the order df Q.5 per cent by mass.

By comparison with the promoted iron catalysts used commercially ruthenium would appear to be intrinsically more selective, for casoline range hydrocarbons. Thus Figure 1 shows a comparison of published data for the iron catalyst with that which we have obtained using a ruthenium catalyst. It is seen that for a given methane selectivity, the yield of gasoline (i.e. C5 - C12) is much higher and the maximum yield of gasoline possible is also mich higher. Curves in Figure 1 wihtout individually plotted points refer to promoted Fe catalyst as reported in the literature (M.E.Dry I and EC, Prod.Res. & Dev. vol 15 No.4 p 283 (1976)) According to this invention a process for synthesising hydrocarbons in the C5 to C12 range from a mixutre of hydrogen and carbon monoxide gases comprises contacting the said mixture with a supprted ruthenium catalyst such that the said mixture is at a temperature within the range 500 to 550"K and such that the outlet partial pressure of carbon monoxide is not less than 0.8 atmosphere (in the 500 to 525"K temperature range) and not less than 3.0 in the 525 to 550"K temperature range.

Controlling the reaction in this way has been found to give unexpectedly high yields of the gasoline fraction with minimum quantities of the less desirable dry gas and heavy wax fractions.

Preferably the weight hourly space velocity based on the mass of the supported catalyst is within the range 0.1 to 0.25 hr1. Space velocity is defined as mass flow rate of reactant gas per unit time per unit mass of the catalyst. The outlet partial pressure of carbon monoxide is the product of the total reactor pressure and the fraction by volume of carbon monixide remaining in the gaseous reaction products existing from the reactor.

The supported ruthenium catalyst preferably takes the form of 0.5% by weight ruthenium metal deposited upon the external surface of 3 x 3 mm cylindrical pellets of gamma alumina and to a depth of 200 - 300clam.

However in a fluidised bed reactor a powdered catalyst (100 - 200 B.S.mesh) is preferred and for this purpose the above described pellets may be crushed.

Description ofApparatus: Figure 2 is a schematic drawing of the apparatus used an of the flow diagram used to product hydrocarbons.

The reactor used was a stirred gas-solid reactor 10 driven by a motor 11 through a magnetic coupling. The reactor was housed in an oven 12. Gas enters the reactor above the catalyst 13 and is withdrawn from below so that there is a net downward flow of gas away from the bearing surfaces, thus preventing accumulation of fines and reaction products.

The catalyst used in these examples was 0.5% by weight ruthenium on gamma-alumina in the form of approximately 3 x 3 mm cylindrical pellets with the ruthenium impregnated only on the outer shell of each pellet. The main gas supply to the reactor is from cylinder 14 containing premixed synthesis gas. A cylinder 17 supplied hydrogen gas to feed through a de-oxo unit 15 and a drier 16. Athreeway valve 18 controls the gas feed to the reactor. A needle valve 19 controls the rate of gas flow into the reactor 10. A pressure regulator 20 is preset to produce the reactor operating pressure required. A thermocouple not shown embedded in the reactor wall is used to control the temperature of oven 12.

A system consisting of two separate gas chromatographs was devised of which one measures the complete product spectrum and the other measures only the CH4, CO and C2,s (which was noramllyvery low) after the removal of water and hydrocarbons above C2. These analyses, together with a measure of the flow rate of the final effluent stream (CH4, CO, C2 and H2) yield the flow rate of the total product stream directly from the reactor.

Each experiment utilised a fresh charge of catalyst taken from the same container obtained from the supplier. This charge was reduced for 12 hours with flowing hydrogen at a rate of 10 ml/min at a temperature of 673 K. After switching over to synthesis gas for reaction, samples of the product stream were analysed periodically in order to establish deactivation within the reactor. The selectivities of the hydrocarbons (considering the total hydrocarbon fraction only) was found to be practically the same over both the initial rapid deactivation period and a subsequent slow deactivation period. The product distributions and selectivities reported below were obained from analysis of samples taken at a time when the deactivation rate was very small.

Selectivity is defined as percentage weight of carbon in converted carbon monoxide found in the given product.

Example I Selectivities to Gasoline This example illustrates the fundamental essence of this discovery. From a large number of runs covering a temperature range 500to 600K, reactor pressure range 8 to 16 atmospheres and weight hourly space velocity 0.1 - 1.0 (hour)~ it was found that very high selectivities to gasoline (Cg - C12) were obtained if, for a given temperature, the minimum outlet CO partial pressure were greater than a specified value. These results are shown in Figure 3. These show that independent of total pressure and space velocity, high selectivities are obtained at 525 K if and only if the minimum (i.e. outlet( CO partial pressure is greater than 0.8 atmosphere.Relatively high selectivities are obtained at the higher temperature of 550K if, and only if, the minimum CO partial pressure is greater than 3 atmospheres. Conversely at 575K good selectivities could not be obtained.

Example 2 High conversion selectivities are not in themselves sufficient to ensure economically high yields. High conversions of carbon monoxide are also necessary and desirable in their own right The requirement set out above imposes severe limitations upon the preferred operating conditions. Figure 4 illustrates this point The conversion of carbon monoxide is related to the outlet CO partial pressure in the manner shown.

Normally it is desirable to have a CO conversion in excess of 50%. Shown in Figure 4 are the ranges according to the present invention defined by this 50% conversion limit and the minimum CO partial pressure discussed in example 1.

As is readily apparent a total pressure in excess of 6-atmospheres is required at a temperature of 500 - 525 K and a temperature of 525 - 550 K would imply a total pressure in excess of 20 atmosphers.

Also shown in Figure 4 are the weight hourly space velocities required at 525 K to obtain the indicated conversions at the different pressures. Typical conditions as a preferred embodiment can be deduced from this Figure. For example, at 525 K 8 atmospheres and a 3 : 1 H2/CO ratio, space velocities should be held within the range WHSV = 0.12 - 0.20 (hour)~ Examples 3-6 (Table 1) These illustrate actual examples falling within the preferred ranges given in Example 2. Table 1 shows typical run conditions and the product yield structure which results.

Examples 7-9 (Table 1J These illustrate examples following outside the present invention.

In Example 7 the outlet partial pressure is too low primarily because the WHSV is too low.

In Example 8 the outlet partial CO pressure of 1.63 atmospheres is too low (i.e. below 3) for the operating temperature of 545.

In Example 9 the outlet CO partial pressure of 1-84 atmospheres is too low for the operating temperature of 573 K.

TABLE 1 according to invention comparative examples Example No. 3 4 5 6 7 8 9 H2/CO 3 3 3 3 3 3 3 Totalpressureatm. 8 8 8 8 8 10 12 Temperature K 525 525 525 525 523 545 573 WHSVhr1 0.15 0.18 0.19 0.14 0.11 0.44 0.53 CO Conversion 54.5 55.4 57 69.5 77.4 52.1 54.0 Minimum CO Partial Press.Atms. 1.1 1.1 1.1 0.8 0.66 1.63 1.84 Selectivities O/ow of Hydrocarbon Products C1 29.1 24.2 24.3 26.9 33.7 38.9 71.7 C2 3.8 3.2 3.3 4.2 4.4 5.8 8.7 C3 6.9 7.3 7.9 7.3 6.8 7.6 4.4 C4 9.6 8.5 8.1 8.2 8.3 10.6 6.3 C5-C12 50.6 56.8 56.5 53.4 46.8 37.1 8.9

Claims

1. A process for synthesising hydrocarbons in the C5 - C12 range from a mixture of hydrogen and carbon monoxide gases comprising contacting the said mixture with a supported ruthenium catalyst wherein the said mixture is at a temperature within the temperature range of (500 to 550)"K and wherein the outlet partial pressure of carbon monoxide is not less than 0.8 atmospheres in the temperature range (500 to 525)"K and not less than 3.0 atmospheres in the temperature range (525-550)"K.

2. A process according to Claim 1 wherein the ruthenium is in the form of ruthenium metal.

3. A process according to Claim 2 wherein the ruthenium metal catalyst is carried on a particulate support.

4. A process according to Claim 3 wherein the particulate support is made from y alumina.

5. A process according to Claim 4 wherein the support is in the form of 3 x 3 mm clyindrical pellets.

6. A process according to Claim 4 wherein the support is in powder form having a powder size falling within the range 100 - 200 B.S. mesh.

7. A process according to any one of claims 2 to 6 wherein the ruthenium metal is deposited in an amount up to 0.5 wt % and to a depth of 200 - 300 um on the support.

8. A process according to any preceding claim wherein the reactant gas is synthesis gas.

9. A process according to claim 1 wherein the ratio of H2: CO in the reactant das is within the ratio of between 2:1 and4: 1.

10. A process according to Claim 9 wherein the said ratio of H2 : CO is 3:1.

11. A process according to Claim 1 wherein the space velocity of reactant gas considered as the mass flow rate of reactant gas per unit time, per unit mass of catalyst falls within the range of 0.10 to 0.25.

12. A process according to Claim 11 wherein the said space velocity is within the range 0.12 to 0.20.