GB2088407A

GB2088407A - Preparation of Hydrocarbons from Syngas

Info

Publication number: GB2088407A
Application number: GB8135705A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1980-11-28
Filing date: 1981-11-26
Publication date: 1982-06-09
Also published as: JPS57118524A; IT8125301A0; NZ199086A; FR2495134B1; BE890996A; IT1140495B; NL8006484A; FR2495134A1; DE3146927C2; BR8107699A; ZA818222B; AU7789881A; DE3146927A1; AU542034B2; GB2088407B; CA1171432A; IN157810B

Abstract

Two stage process for the preparation of hydrocarbons from syngas with a H2/CO mol. ratio between 1.0 and 2.0 in which the syngas is contacted in a first stage with a Fe-comprising catalyst composition having Fischer-Tropsch as well as CO-shift activity followed by contacting at least the H2 and CO separated from the first stage product in a second stage with a mono- or bifunctional catalyst comprising a Ni, Co or Ru Fischer-Tropsch function.

Description

SPECIFICATION A Process for the Preparation of Hydrocarbons The invention relates to a process for the preparation of a hydrocarbon mixture from a mixture of carbon monoxide and hydrogen with an H2/CO molar ratio of less than 2.0, using an iron-containing bifunctional catalyst or catalyst combination which, in addition to having activity for the conversion of an H2/CO mixture into substantially hydrocarbons, has activity for the conversion of an H20/CO mixture into an H2/CO2 mixture.

An investigation by the Applicant concerning this process has shown that the use of high space velocities has certain drawbacks. When the process is used for the conversion of H2/CO mixtures with an H2/CO molar ratio of less than 1.0, the stability of the bifunctional catalyst or catalyst combination is poor. When the process is used for the conversion of H2/CO mixtures with an H2/CO molar ratio between 1.0 and 2.0, a low conversion is obtained.Further investigation by the Applicant concerning this process has shown that these drawbacks can be overcome by contacting carbon monoxide and hydrogen present in the reaction product, if desired together with other components from the reaction product, in a second step with a nickel, cobalt or ruthenium-containing monofunctional catalyst, which has activity for the conversion of an H2/CO mixture into substantially hydrocarbons, on the understanding that if the feed for the second step has an H2/CO molar ratio of less than 1.5, water is added to this feed, and that in the second step a nickel, cobalt or ruthenium-containing bifunctional catalyst or catalyst combination is used which, in addition to having activity for the conversion of an H2/CO mixture into substantially hydrocarbons, has activity for the conversion of an H20/CO mixture into an H2/CO2 mixture.

The present invention therefore relates to a process for the preparation of a hydrocarbon mixture, in which process a mixture of carbon monoxide and hydrogen with an H2/CO molar ratio of less than 2.0 is contacted in a first step with an iron-containing bifunctional catalyst or catalyst combination as defined above, and in which process carbon monoxide and hydrogen present in the reaction product from the first step if desired, together with other components of this reaction product, are contacted in a second step with a nickel, cobalt or ruthenium-containing monofunctional catalyst as defined above, on the understanding that if the feed for the second step has an H2/CO molar ratio of less than 1.5, water is added to this feed, and that in the second step use is made of a nickel, cobalt or rutheniumcontaining bifunctional catalyst or catalyst combination as defined above.

The Dutch patent application No. 800321 5, filed on 3 June 1980, relates to a process for the preparation of a hydrocarbon mixture, in which process a mixture of carbon monoxide and hydrogen with an H2/CO molar ratio of less than 1.0 is contacted in a first step with an iron-containing bifunctional catalyst or catalyst combination as defined above, and in which process carbon monoxide and hydrogen present in the reaction product from the first step, if desired together with other components of this reaction product, are contacted in a second step with a cobalt or rutheniumcontaining monofunctional catalyst as defined above, on the understanding that if the feed for the second step has an H2/CO molar ratio of less than 1.5, water is added to this feed, and that in the second step a cobalt or ruthenium-containing bifunctional catalyst or catalyst combination as defined above is used.

The present patent application therefore relates to a process for the preparation of a hydrocarbon mixture, in which process a mixture of carbon monoxide and hydrogen with an H2/CO molar ratio of 1.0-2.0 is contacted in a first step with an iron-containing bifunctional catalyst or catalyst combination as defined above, and in which process carbon monoxide and hydrogen present in the reaction product from the first step, if desired together with other components of this reaction product, are contacted in a second step with a nickel, cobalt or ruthenium-containing monofunctional catalyst as defined above, on the understanding that, if the feed for the second step has an H2/CO molar ratio of less than 1.5, water is added to this feed, and that in the second step use is made of a nickel, cobalt or ruthenium-containing bifunctional catalyst or catalyst combination as defined above.

In the process according to the invention the starting material is an H2/CO mixture with an H2/CO molar ratio of less than 2.0. Such H2/CO mixtures can very suitably be prepared by steam gasification of a carbon-containing material. Examples of such materials are brown coal, anthracite, coke, crude mineral oil and fractions thereof and oils produced from tar sand and bituminous shale. The steam gasification is preferably carried out at a temperature of 900-1 5000C and a pressure of 10-100 bar. In the process accordinig to the invention the preferred starting material is an H2/CO mixture with an H2/CO molar ratio of more than 0.25.

The iron-containing bifunctional catalysts or catalyst combinations that are suitable for use in the first step in the process according to the invention should in addition to having activity for the conversion of an HdCO mixture into substantially hydrocarbons, have activity for the conversion of an H20CO mixture into an H2/CO2 mixture. It is preferred to use in the first step of the process a bifunctional catalyst prepared by impregnation and containing iron on a carrier.Examples of such catalysts are: (a) Catalysts which contain 30-75 pbw iron and 5-40 pbw magnesium per 100 pbw alumina and which have been prepared by impregnating an alumina carrier with one or more aqueous solutions of salts of iron and magnesium, followed by drying the composite, calcining at a temperature of 700 12000C and reducing. Particularly preferred catalysts are those containing in addition to 40-60 pbw iron and 7.5-30 pbw magnesium, 0.5-5 pbw copper as reduction promotor and 1-5 pbw potassium as selectivity promotor per 100 pbw alumina, and which have been calcined at 7508500C and reduced at 250--3500C.

(b) Catalysts which contain 1 0-40 pbw iron and 0.25-10 pbw chromium per 100 pbw silica and which have been prepared by impregnating a silica carrier with one or more aqueous solutions of salts of iron and chromium, followed by drying the composite, calcining and reducing at a temperature of 350-7500C. Particularly preferred catalysts are those which contain in addition to 20-35 pbw iron and 0.5-5 pbw chromium, 1-5 pbw potassium as selectivity promotor per 100 pbw silica, and which have been calcined at 350-7000C and reduced at 350-5000C.

The first step of the process according to the invention can very suitably be carried out by conducting the feed in upward or downward direction through a vertically mounted reactor in which a fixed or a moving bed of the iron-containing bifunctional catalyst or catalyst combination is present.

The first step may, for instance, be carried out in fixed-bed operation, bunkerflow operation, ebullientbed operation or fluidized-bed operation. The first step of the process is preferably carried out under the following conditions: a temperature of 200-3500C and in particular of 250-3500C, a pressure of 10--70 bar and in particular of 20-50 bar and a space velocity of 500-5000 and in particular of 500-2500 NI gas/l catalyst/h.

In the process according to the invention carbon monoxide and hydrogen present in the reaction product from the first step are used as the feed for the second step. In addition to carbon monoxide and hydrogen, the feed for the second step may contain other components of the reaction product from the first step. For instance, it is possible to use as the feed for the second step the C2 fraction or C4 fraction of the reaction product from the first step, and it is even possible to use the total reaction product from the first step as the feed for the second step.In the second step of the process according to the invention the intention is to convert as much as possible of the carbon monoxide present in the feed for the second step into substantially hydrocarbons over a monofunctional nickel, cobalt or ruthenium-containing catalyst with activity for this reaction. To this end the H2/CO molar ratio in the feed for the second step should be at least 1.5 and preferably 1.75-2.25. When an H2/CO mixture with a high H2/CO molar ratio is used as the feed for the first step, the process according to the invention can yield a reaction product from the first step that has an H2/CO molar ratio of at least 1.5 and that is suitable as such for conversion over the said catalyst in the second step.

If in the process according to the invention the first step yields a reaction product with an H2/CO molar ratio of less than 1.5, water should be added to the feed for the second step, and in the second step a nickel, cobalt or ruthenium-containing bifunctional catalyst or catalyst combination should be used which, in addition to having activity for the conversion of an H2/CO mixture into substantially hydrocarbons, has activity for the conversion of an H2O/CO mixture into an H2/CO2 mixture.

If in the process according to the invention the feed for the second step has an H2/CO molar ratio of less than 1.5, it is preferred to use in the second step a bifunctional catalyst combination composed of two separate catalysts, which, for the sake of convenience, will be designated catalyst A and catalyst B. Catalyst A is the nickel, cobalt or ruthenium-containing catalyst with activity for the conversion of an H2/CO mixture into substantially hydrocarbons, and catalyst B is the catalyst with activity for the conversion of an H2O/CO mixture into an H2/CO2 mixture.Both when using a monofunctional catalyst and when using a bifunctional catalyst combination in the second step of the process according to the invention, preference is given to a cobalt catalyst and in particular to a catalyst prepared by impregnation containing cobalt on a carrier, as catalyst A. Very suitable for the present purpose are catalysts which contain 1 40 pbw cobalt and 0.255 pbw zirconium, titanium or chromium, and which have been prepared by impregnating a silica carrier with one or more aqueous solutions of salts of cobalt and zirconium, titanium or chromium, followed by drying the composite, calcining at 350 7000 C and reducing at 200-3500C. Suitable B-catalysts are pre-eminently catalysts which contain copper and zinc and in which the Cu/Zn atomic ratio lies between 0.25 and 4.0. In the nickel, cobalt or ruthenium-containing bifunctional catalyst combinations catalysts A and B may be present as a physical mixture. When the second step of the process is carried out using a fixed catalyst bed, this bed is preferably built up of two or more alternating layers of particles of catalyst B and catalyst A successively.The addition of water to the feed for the second step together with the use of a bifunctional catalyst combination in the second step can, in the process according to the invention, be effected both in cases where the reaction product from the first step has an H2/CO molar ratio of less than 1.5, and in cases where the reaction product from the first step already has an H2/CO molar ratio of at least 1.5, but where it is desirable that the feed which is contacted in the second step with catalyst A should have a higher H2/CO molar ratio. If in the process according to the invention an embodiment is chosen in which water is added to the feed for the second step and a bifunctional catalyst combination is used in the second step, the required amount of water is determined substantially by the H2/CO molar ratio of the feed for the second step, the activity of the catalyst combination for the conversion of an H2O/CO mixture into an H2/CO2 mixture and the desired H2/CO molar ratio of the product that is contacted with catalyst A.

The second step of the process according to the invention can very suitably be carried out by conducting the feed in upward or downward direction through a vertically mounted reactor in which a fixed bed of the monofunctional catalyst or of the bifunctional catalyst or catalyst combination is present. The second step of the process can also be carried out using a suspension of the catalyst or catalyst combination in a hydrocarbon oil. The second step of the process is preferably carried out under the following conditions: a temperature of 1 25 0--3 500C and in particular of 1 750-2750C and a pressure of 1-150 bar and in particular of 5-100 bar.

The two-step process according to the invention can very suitably be employed as part of a threestep process for the preparation of, inter alia, middle distillates from an H2/CO mixture. In this case at least the part of the reaction product of the second step whose initial boiling point lies above the final boiling point of the heaviest middle distillate desired as the end product, is subjected in a third step to a catalytic hydrotreatment.

The invention will now be explained with reference to the following example.

Example In the investigation use was made of the following catalysts: Catalyst 1 A Co/Zr/SiO2 catalyst containing 25 pbw cobalt and 1.8 pbw zirconium per 100 pbw silica and prepared by impregnating a silica carrier with an aqueous solution containing a cobalt salt and a zirconium salt, followed by drying the composite, calcining at 5000C and reducing at 2800 C.

Catalyst 2 An Fe/Mg/Cu/K/AI203 catalyst containing 50 pbw iron, 20 pbw magnesium, 2.5 pbw copper and 4 pbw potassium per 100 pbw alumina and prepared by impregnating an alumina carrier with an aqueous solution containing an iron salt, a magnesium salt, a copper salt and a potassium salt, followed by drying the composite, calcining at 8000C and reducing at 3250C.

Catalyst 3 A Cu/Zn/AI2O3 catalyst with a Cu/Zn atomic ratio of 0.55.

Catalyst Mixture I Catalyst mixture I consisted of a layer of catalyst 3 and a layer of catalyst 1 in a volume ratio of 1:2.

Catalysts 1 and 2 and catalyst mixture I were tested for the preparation in one or two steps of a hydrocarbon mixture from an H2/CO mixture. The test was carried out in one or two reactors of 50 ml each in which a fixed catalyst bed was present. The test consisted of ten experiments. The experiments 1,3,6 and 9 were carried out in one step, the other experiments in two steps. In all experiments catalyst 2 was employed in the first step and the temperature was 2800C.In all experiments carried out in two steps the temperature in the second step was 2300 C. In all experiments the pressure was 30 bar and the space velocity based on the total catalyst system was 1000 Nl.l-1.h-'. In the experiments 2, 5, 7, 8 and 10 the total reaction product from the first step was used as the feed for the second step. In experiment 4 the C4- fraction of the product from the first step was used as the feed for the second step. The results of the experiments are listed in the table.

Table Experiment no. 1 2 3 4 5 6 7 8 9 10 Amount of catalyst in the first step, ml 10 5 10 5 7 10 5 2 10 3 H2/CO molar ratio of the feed for the first step 0.5 0.5 0.8 0.8 0.8 1.1 1.1 1.1 1.4 1.4 H2/CO molar ratio of the product from the first step at run hour 250 0.06 0.41 9 1.3 2.2 17 2.3 1.3 27 1.9 at run hour 3000 0.32 0.44 1.75 1.11 1.73 - - - - Catalyst or catalyst mixture in the second step, No. - | - | 1 - 1 | - 1 Amount of catalyst in the second step, ml - 5 - 5 3 - 5 8 - 7 Amount of water added to the feed for the second atep, ml (l catalyst in the second step)-1.h-1.

at run hour 250 - 241 - 66 - - - 90 - at run hour 3000 - 244 - 114 - - - - - Conversion of the synthesis gas, % at run hour 250 90 96 85 96 97 74 95 96 65 94 at run hour 3000 75 93 70 92 95 - - - - - Of the experiments listed in the table, only the two-step experiments 2, 4, 5, 7, 8 and 10 are experiments according to the invention. The one-step experiments 1, 3, 6 and 9 are outside the scope of the invention. They have been included in the patent application for comparison. Of the two-step experiments 2, 4, 5, 7, 8 and 10, only the experiments 7, 8 and 10 are experiments according to the present patent application. The two-step experiments 2, 4 and 5 are experiments according to Dutch patent application No. 8003215.

The advantages of the two-step process according to the invention as regards conversion of the H2/CO mixture and stability of the iron-containing bifunctional catalyst are evident when the results of the following experiments are compared: experiment 2 with experiment 1, experiments 4 and 5 with experiment 3, experiments 7 and 8 with experiment 6, and experiment 10 with experiment 9.

Claims

1. A process for the preparation of a hydrocarbon mixture, characterized in that a mixture of carbon monoxide and hydrogen with an H2/CO molar ratio of 1.0-2.0 is contacted in a first step with an iron-containing bifunctional catalyst or catalyst combination which, in addition to having activity for the conversion of an HdCO mixture into substantially hydrocarbons, has activity for the conversion of an H2O/CO mixture into an H2/CO2 mixture, and in that carbon monoxide and hydrogen present in the reaction product from the first step, if desired together with other components of this reaction product, are contacted in a second step with a nickel, cobalt or ruthenium-containing monofunctional catalyst which has activity for the conversion of an H2/CO mixture into substantially hydrocarbons, on the understanding that, if the feed for the second step has an H2/CO molar ratio of less than 1.5, water is added to this feed, and that in the second step use is made of a nickel, cobalt or ruthenium-containing bifunctional catalyst or catalyst combination which, in addition to having activity for the conversion of an H2/CO mixture into substantially hydrocarbons, has activity for the conversion of an H2O/CO mixture into an H2/CO2 mixture.

2. A process according to claim 1, characterized in that in the first step use is made of a bifunctional catalyst prepared by impregnation and containing iron on a carrier.

3. A process according to claim 1 or 2, characterized in that use is made of a catalyst containing 30-75 pbw iron and 5-40 pbw magnesium per 100 pbw alumina and which has been prepared by impregnating an alumina carrier with one or more aqueous solutions of salts of iron and magnesium, followed by drying the composite calcining at a temperature of 700-1 2000C and reducing.

4. A process according to claim 2, characterized in that use is made of a catalyst containing 1040 pbw iron and 0.2510 pbw chromium per 100 pbw silica and which has been prepared by impregnating a silica carrier with one or more aqueous solutions of salts of iron and chromium, followed by drying the composite, calcining and reducing at a temperature of 350--750"C.

5. A process according to any one of claims 1-4, characterized in that the first step is carried out at a temperature of 200--3 50"C, a pressure of 10-70 bar and a space velocity of 500-5000 NI gas/I catalyst/h.

6. A process according to any one of claims 1-5, characterized in that as the catalyst with activity for the conversion of an H2/CO mixture into substantially hydrocarbons, which catalyst is used in the second step of the process, a catalyst is employed which has been prepared by impregnation and contains cobalt on a carrier.

7. A process according to claim 6, characterized in that use is made of a catalyst which contains 10-40 pbw cobalt and 0.25-5 pbw zirconium, titanium or chromium per 100 pbw silica and which has been prepared by impregnating a silica carrier with one or more aqueous solutions of salts of cobalt and of zirconium, titanium or chromium, followed by drying the composite, calcining at 350-7000C and reducing at 200--3500C.

8. A process according to any one of claims 1-7, characterized in that water is added to the feed for the second step and in that in the second step a bifunctional catalyst combination is used which is composed of two separate catalysts A and B, of which catalyst A has activity for the conversion of an HdCO mixture into substantially hydrocarbons and catalyst B has activity for the conversion of an H2O/CO mixture into an H2/CO2 mixture.

9. A process according to claim 8, characterized in that in the second step use is made of a fixed catalyst bed built up of two or more alternating layers of particles of catalyst B and catalyst A successively.

10. A process according to any one of claims 1-9, characterized in that the second step is carried out at a temperature of 1 25-3500C and a pressure of 1-150 bar.