DE3789668T2 - Process for reducing methane production and increasing the yield of liquid products in Fischer-Tropsch reactions. - Google Patents

Description

The present invention relates to a process for reducing methane yield and increasing liquid yields in Fischer-Tropsch reactions US-A-4 547 525 discloses a process for reducing methane production in Fischer-Tropsch processes in which hydrocarbons are synthesized from feedstocks comprising mixtures of CO and H2 by adding at least one olefin to the feedstock. According to a preferred embodiment, the olefin or olefins comprise one or more C2 to C10 alpha-olefins having a molar ratio of olefin to CO of about 1:10 to 3:4 and the catalyst comprises at least one Group VIII metal supported on an inorganic refractory oxide support.

The present invention provides a method for reducing methane formation and increasing C5+ liquid yields in a Fischer-Tropsch process for synthesizing hydrocarbons from CO and H2, in which at least one olefin is added to a catalyst-containing reactor bed, characterized in that a gas mixture containing CO and H2 is introduced at the inlet end of the reactor bed and the olefin is separately introduced directly into the bed at a location more than 10% of the length of the bed from the inlet end of the bed and more than 10% of the length of the bed from the outlet end of the bed.

The amount of olefin added to the reactor bed may be based on a molar ratio of olefin to CO in the range of 1:100 to 5:1 (e.g. in the range of 1:20 to 5:1).

The olefin(s) may be an alpha-olefin of the type R-CH=CH₂, where R is hydrogen or an alkyl group having 1 to 17 carbon atoms. The olefin may comprise a C₂ to C₁₀ alpha-olefin.

The catalyst may comprise one or more Group VIII catalytic metals. The catalytic metal may be selected from iron, cobalt and ruthenium.

The process can be carried out at a temperature of at least 100ºC, preferably in the range of 100ºC to 500ºC.

Water may be added to the reactor bed at a location more than 10% of the bed length from the inlet end of the bed and more than 10% of the bed length from the outlet end of the bed.

The molar ratio of water to CO can be in the range of 0.1:1 to 5.0:1. The molar ratio of water to olefin can be in the range of 0.1:1 to 50:1 (e.g. in the range of 0.2:1 to 10:1).

The present invention is based on the discovery that liquid yields (C5+ ) and methane production in Fischer-Tropsch hydrocarbon synthesis reactions are respectively increased and decreased by adding one or more olefins directly to the reactor bed or by adding water and one or more olefins directly to the reactor bed at a range of positions in the bed in accordance with the invention as described herein. Thus, the present invention relates to a method for reducing methane production in Fischer-Tropsch processes in which hydrocarbons are synthesized from feedstocks comprising mixtures of CO and H2 and by adding at least one olefin or water and one or more olefins to the reactor bed, wherein the olefin may be obtained by separation from the product stream and recycled to the reactor bed, or may be obtained from an independent source such as by processing the paraffinic product of the Fischer-Tropsch reaction through a dehydrogenation reactor to convert the paraffins to olefins. According to a preferred embodiment, the olefin or olefins comprise one or more C₂ to C₂₀ α-olefins, wherein the molar ratio of olefin to CO in the reactor is from 1/20 to 5/1, especially 1/10 to 2/1 and even more preferably about 1/5 to 1/1. The molar ratio of water to olefin may be from 0.1 to 50, especially 0.2 to 10 and most preferably 0.5 to 10. The catalyst comprises at least one Group VIII metal, which is supported on an inorganic refractory oxide support. Alternatively, a cobalt or iron catalyst can be used.

According to a particularly preferred embodiment, the catalyst comprises ruthenium supported on titanium dioxide.

Detailed description of the invention

It has been found that methane production in Fischer-Tropsch hydrocarbon synthesis reactions is reduced by adding one or more olefins directly to the reactor bed or by adding water and one or more olefins directly to the reactor bed at a position or positions more than 10% of the length of the bed from the inlet end of the bed and more than 10% of the length of the bed from the outlet end of the bed. Thus, the present invention relates to a process for reducing methane production in Fischer-Tropsch processes in which hydrocarbons are synthesized from feedstocks comprising mixtures of CO and H₂. wherein at least one olefin and/or water and one or more olefins are added to the reactor bed, wherein the olefin may be obtained by separation from the product stream and recycled to the reactor bed, or may be obtained from an independent source. According to a preferred embodiment, the olefin or olefins comprise one or more C2 to C20 alpha olefins, wherein the molar ratio of olefin to CO in the reactor is 1/20 to 5/1, particularly 1/10 to 2/1, and most preferably 1/5 to 1/1. The molar ratio of water to olefin is 0.1 to 50, particularly 0.2 to 10, and most preferably 0.5 to 10. The catalyst comprises at least one Group VIII metal supported on an inorganic refractory oxide support. According to a particularly preferred embodiment, the catalyst comprises ruthenium supported on titanium dioxide. In addition, cobalt or iron catalyst can simply be used.

Preferred olefins useful in the process of the invention include alpha-olefins of the type R-CH=CH2 in which R is hydrogen or an alkyl group having 1 to 17 carbon atoms, more preferably the alkyl group has 1 to 11 carbon atoms and most preferably the alkyl group has 1 to 8 carbon atoms. Particularly preferred are C2 to C10 alpha-olefins. The amount of alpha-olefin recycled to the reactor bed is sufficient to maintain a molar ratio of olefin to CO of 1/100 to 5/1, more preferably 1/20 to 5/1 and most preferably 1/10 to 2/1. Internal olefins, where the unsaturation is located some distance from the terminal carbon atom, can also be advantageously added to the CO/H2 feedstock.

Although the process of the invention can be carried out in the presence of a suitable Fischer-Tropsch catalyst, in a preferred embodiment it is carried out in the presence of a catalyst comprising one or more Group VIII metals supported on an inorganic refractory oxide support, preferably ruthenium or cobalt supported on such a support. Thus, suitable supports include oxides of titanium (e.g., titania), niobium (e.g., niobium oxide), vanadium, tantalum, silicon (e.g., silica), aluminum (e.g., alumina), manganese, and mixtures thereof. Preferably, the catalyst support is selected from the group consisting of titania, zirconium titanate, mixtures of titania and alumina, mixtures of titania and silica, alkaline earth titanates, alkali titanates, rare earth titanates, and mixtures of any of the foregoing with supports selected from the group consisting of vanadium oxide, niobium oxide, tantalum oxide, alumina, silica, and mixtures thereof. Thus, according to a particularly preferred embodiment of this invention, the process is carried out in the presence of a catalyst comprising ruthenium supported on a titania support. Alternatively, the catalyst may comprise cobalt or iron supported on any of the foregoing inorganic refractory oxides.

Generally, the amount of catalytic metal cobalt present is 1 to 50 wt.% of the total catalyst composition, preferably 10.0 to 25 wt.%.

Iron catalysts containing 10 to 60 wt.% iron, especially 20 to 60 wt.% iron, and most preferably 30 to 50 wt.% iron are not supported but are promoted by refractory metal oxide (SiO2, Al2O3, etc.), alkali metal (K, Na, Rb), and Group Ib metal (Cu, Ag). These catalysts are usually calcined but usually not reduced, instead they are heated to reaction temperature directly in the CO/H2 feed.

Generally, the amount of ruthenium catalytic metal present is from 0.01 to 50 weight percent of the total catalyst composition, more preferably from 0.1 to 5.0 weight percent, and most preferably from about 0.5 to about 5 weight percent.

In general, in the process of the invention the temperature in the Fischer-Tropsch reactor is usually in the range of 100 to 500°C, in particular 150 to 300°C and most preferably about 200°C to 270°C at a pressure of 100 to 10,000 kPa, in particular 300 to 5,000 kPa and most preferably 500 to 3,000 kPa. The volume flow rate (V₁) of the feed gas (H₂ + CO) is in the range of 10 to 10,000 standard cm³/h/(cm³ catalyst), in particular 100 to 4,000 and most preferably 200 to 2,000. The volume flow rate (V₂) of the α-olefin is in the range of 0.1 to about 20,000 standard cm³/h/(cm³ catalyst), in particular 3 to 4,000 and most preferably 10 to 1,000. Thus, the volume ratio of V₁/V₂ is 0.005 to 10,000, more preferably 0.02 to 1,000, and most preferably 0.5 to 200. The molar ratio of hydrogen to carbon monoxide in the feed gas, H₂/CO, is in the range of 0.5 to 10, and preferably 1 to 3.

When the α-olefin is used without water addition, the α-olefin is injected through an inlet port in the side wall or the center of the reactor, the port being located below a point more than 10% of the length of the bed from the top of the reactor bed to the bottom of the reactor bed. and is located above a point more than 10% of the length of the bed from the bottom of the reactor bed to the top of the reactor bed.

Water can be injected into the top of the reactor through inlet ports in the side wall of the reactor or through inlet ports located anywhere in the reactor below a point that is more than 10% of the distance from the top of the reactor bed to the bottom of the reactor bed and above a point that is more than 10% of the distance from the bottom of the reactor bed to the top of the reactor bed. The ports for the water and the ports for the α-olefin can be located at different points in the reactor.

The reactor bed may comprise a single reactor bed with a catalyst system or two catalyst beds with different Fischer-Tropsch synthesis catalysts separated by an inert pre-separation zone located between the stages. The water and/or α-olefin may also be injected through an inlet opening arranged at the pre-separation zone located between the stages. Alternatively, the reactor bed may comprise several tubular reactors connected to one another as serially communicating tubes, the α-olefin being injected into the reactor bed according to the invention either in the first tubular reactor or after the first tubular reactor with or without a pre-separation zone located between the stages.

Description of the preferred embodiments

The invention will be more easily understood with reference to the following examples.

Fischer-Tropsch hydrocarbon synthesis Experimental procedure

An amount of between about 5 and 40 g of the catalyst was placed in a stainless steel reactor with an inner diameter of 0.78 cm, with a thermocouple placed in the catalyst bed to measure the temperature. The reactor was purged with He at a flow rate of 500 cm3/min and then pressurized (with helium) to 30 atm to ensure the integrity of the plant. The He in the reactor was then brought back to 1 atm and replaced with H2 at room temperature at a volume rate of between 200 and 600 V/V/h. The temperature was brought to a final reduction temperature of between 400ºC and 500ºC in approximately 2 to 3 hours and maintained at this temperature overnight.

After reduction, each catalyst was put into operation in one of two ways, which were found to be essentially equivalent. In one method, the reduced catalyst was treated at 1 atm 2H2/CO at 200°C for 15 to 50 hours (the volume rate of H2/CO used was varied from 200 to 1000 cm3 H2 + CO/h (cm3 catalyst)). The conditions in the reactor were then adjusted to the desired temperature, pressure and volume rate. In the other process, the atmospheric treatment in H₂/CO was not carried out and the catalysts were started up at the desired test pressure in H₂/CO, but at an initially lower temperature of 150 to 170ºC, which was then slowly increased (in 1 to 5 hours) to the desired test temperature.

Examples

In all of the examples, the determination of Fischer-Tropsch synthesis activity to the various products was measured by using an on-line gas chromatograph using a stainless steel isothermal fixed bed tractor (0.78 cm inner diameter) loaded with about 5 to 40 g of catalyst. A thermocouple was placed in the catalyst bed to measure the reaction temperature.

example 1 Preparation of the Ru catalyst

Titanium dioxide supports were prepared by pressing Degussa P-25 powder (20 to 70% rutile) into wafers using a hydraulic press at a pressure of about 20,000 lb/in2. The wafers were then crushed in a mortar to a coarse powder and sieved to obtain the 80 to 140 mesh (US standard) fraction for all TiO2 supported catalysts. The titanium dioxide support samples thus formed were calcined in flowing air (about 1 liter per minute) overnight at a temperature of 550°C to 600°C. The calcined samples were then reduced in hydrogen flowing at a rate of 1 liter per minute by heating from room temperature to 450ºC for 4 hours, after which the sample was cooled in flowing H₂, purged with helium and removed. These reduced samples had the characteristic blue-gray color of surface-reduced TiO₂.

Catalysts were prepared by impregnating the support material with a ruthenium nitrate/acetone mixture. The nitrate was obtained from Engelhardt as 10 wt% ruthenium metal in nitric acid.

The nitrate-impregnated TiO2 was reduced in flowing hydrogen (1 L/min) as follows: (a) heated from room temperature to 100°C and held for 0.5 hours, (b) heated from 100°C to 450°C at 3°C/min and held for 4 hours, (c) cooled to room temperature in H2 overnight, and (d) purged in the reduction cell with He or Ar (1 L/min) for 1 hour. Each reduced catalyst sample was then passivated by introducing 1% O2 into the He stream and then increasing the O2 content to 100% over a period of about 2 to 3 hours.

Example 2 Preparation of the cobalt catalyst

Degussa P-25 TiO2 was treated with acetone, dried at 90ºC and triturated with 9.6 wt.% Sterotex (vegetable stearin). The material was tabletted to a size of 3/8 inch using a pilling pressure that produced a material with a pore volume of 0.35 to 0.40 ml/g. The 3/8 inch pills were broken and screened to 42 to 80 mesh and calcined in flowing air at 500ºC for 4 hours to burn out the Sterotex. Portions of these were then again calcined in flowing air at 650ºC for 16 hours to obtain a high rutile content and screened to 90 to 150 mesh. The support composite used to prepare this catalyst was 97% rutile, 13.6 m²/g, 0.173 ml/g.

Impregnation process

10.8 g of cobalt nitrate (Co(NO3)2·H2O) and 16 mL of aqueous perrhenic acid solution (52 mg Re/mL) were then dissolved in about 300 mL of acetone in a 1 liter round bottom flask. 160 g of TiO2 (YAX-0487) were added and the mixture was placed on a rotary evaporator until dry. The catalyst was dried in a vacuum oven at 140°C for 18 hours and calcined in flowing air at 250°C for 3 hours. The calcined catalyst was sieved again to remove the small amount of particulate matter that had been generated during preparation.

Cobalt catalyst production

The analytical tests of the catalyst are given below:

Cobalt, wt.% 11.3

Rhenium, wt.% 0.42

Sodium, ppm 369

% Rutile (ASTM D 3720-78) 97

Surface m²/g 14.6

Pore volume, ml/g 0.122

Bulk density, g/ml 1.41

In addition to the quantitative indication of the rutile content, the X-ray diffraction spectrum shows the presence of Co₃O₄.

Example 3 (This is not an example according to the invention) Effect of ethylene feed cobalt catalysts

The general procedure described for Fischer-Tropsch hydrocarbon synthesis was modified as follows in Examples 3 and 4.

The catalyst was started in H2/CO at a volume rate required to achieve 25% to 45% CO conversion at 1700 to 2500 kPa. An ethylene/argon mixture was mixed with H2/CO feed and then added to the reactor at the inlet with an amount of ethylene to give 2.5% and 6.2% ethylene in the feed on the Co and Ru catalysts, respectively. The total reactor pressure was then increased to a level necessary to raise the H2 + CO partial pressure in the reactor to the level found prior to ethylene addition. The reactor was run at these conditions for 4 to 24 hours. Ethylene/argon feed was then passed so that it entered the reactor undiluted by H2. + CO, entered the reactor at a point 1/3 L (L = reactor length) downstream from the inlet, while H₂ + CO volumetric velocity and partial pressure were left at their previous value. The reactor was run at these conditions for 4 to 24 hours. The ethylene/argon feed was turned off and the reactor conditions returned to initial conditions to exclude irreversible deleterious effects of ethylene addition on synthesis activity and selectivity. Experiment % Ethylene in Feed Addition Site None Inlet Ethylene % Ethylene Converted Selectivity (%)* to Yield Selectivity * % ethylene converted that appears as these products. ** % ethylene added that appears as these products. *** Selectivity is defined as the percentage of CO converted that appears as a given product (it is almost identical to wt%). However, when ethylene is added, some of the C atoms come from it and the sum of the selectivities is greater than 100%.

11.7% Co/0.5 Re/TiO2, 200ºC, 2 050 kPa, H2 + CO, H₂/CO = 2.1/1

25 to 27% CO conversion.

The addition of ethylene (C2-) at the reactor inlet decreases the CH4 selectivity and increases the C5+ selectivity. Most of the ethylene (at 2.5% concentration) is converted, but only 13.5% of the converted ethylene appears as desirable C3+ products, the remainder (86.5%) is hydrogenated to ethane, which is unreactive toward chain growth to C3+ at Fischer-Tropsch synthesis conditions and therefore cannot be recycled without converting it to ethylene in a dehydrogenation reactor. Example 4 (This is not an inventive example) Effect of Ethylene Feed Ruthenium Catalyst Experiment % Ethylene in Feed Addition Site None Inlet Ethylene % Ethylene Converted Selectivity (%) (Ethane) Yield Selectivity * % ethylene converted that appears as these products. ** % ethylene added that appears as these products. *** Selectivity is defined as the percentage of CO converted that appears as a given product (it is almost identical to wt.%) However, when ethylene is added, some of the C atoms come from it and the sum of the selectivities is greater than 100%.

1.2% Ru/TiO2, 200ºC, 1700 kPa, H2/CO = 2.1/1, 35 to 45% CO conversion.

Addition of ethylene to H₂/CO feed at the reactor inlet (at a level of 6.2%) reduces the CH₄ selectivity from 5.5 to 4.3, while increasing the C₅⁺ selectivity from 87.5 to 105.6%. Most of the added ethylene (97%) is converted, of which only 18% appears as desired C₃⁺ products, the rest (82%) is hydrogenated to ethane, which is unreactive towards chain growth to C₃⁺ under Fischer-Tropsch synthesis conditions. and therefore cannot be recycled without converting it into ethylene in a dehydrogenation reactor.

Example 5 Feeding at the upper inlet opposite the lower inlet Ethylene-Ru

There is a clear advantage to bypassing the reactor inlet by introducing C2- below the inlet at the same concentration. C4 selectivity continues to decrease (from 4.3% to 3.9%), C5+ selectivity increases (from 105.6% to 117.0%), and the activity of the catalyst is not affected by the presence of the ethylene either at the inlet or below the inlet of the reactor. The obvious reason for this improved product selectivity is an increase in the yield of C3+ from ethylene (the percentage of the ethylene feed that is converted to C3+) from 17% to 26% despite the lower ethylene conversion when the addition is made below the inlet. The addition below the inlet dramatically decreases the hydrogenation selectivity (from 82% to 44%) while increasing the C3+ selectivity (from 18% to 56%). Therefore, it dramatically increases the efficiency of ethylene utilization while avoiding the formation of species such as ethane, which cannot be further polymerized under Fischer-Tropsch conditions. Experiment % Ethylene in Feed Addition Location Below the Top Third of the Reactor Top Ethylene Converted Selectivity Ethane Yield Selectivity * % ethylene converted that appears as these products. ** % ethylene added that appears as these products. *** Selectivity is defined as the percentage of CO converted that appears as a given product (it is almost identical to wt%). However, when ethylene is added, some of the C atoms come from it and the sum of the selectivities is greater than 100%.

1.2% Ru/TiO2, 200ºC, 1700 kPa, H2/CO = 2.1/1, 35 to 45% CO conversion.

Example 6 Feeding at the upper opposite the lower inlet Ethylene-Co

There is a clear advantage to bypass the reactor inlet by introducing C₂⁻ below the inlet at the same concentration. The CH₄ selectivity further decreases (from 8.3% to 7.2%), the C₅⁺ selectivity increases (from 92.9% to 99.3%) and the activity of the catalyst is enhanced by the presence of of ethylene, either at the inlet or below the inlet of the reactor. The obvious reason for this improved product selectivity is an increase in the yield of C3+ from ethylene (the percentage of the ethylene feed that is converted to C3+) (from 13% to 27.3%) despite the lower ethylene conversion when the addition is made below the inlet. The below the inlet addition dramatically decreases the hydrogenation selectivity (from 86.5% to 69.5%) while increasing the C3+ selectivity (from 13.5% to 30.5%). Therefore, it dramatically increases the efficiency of ethylene utilization while avoiding the formation of species such as ethane, which cannot be further polymerized under Fischer-Tropsch conditions. Experiment % Ethylene in Feed Addition Location Below Top Third Inlet Ethylene % Ethylene Converted Selectivity Yield Selectivity * % ethylene converted that appears as these products. ** % ethylene added that appears as these products. *** Selectivity is defined as the percentage of CO converted that appears as a given product (it is almost identical to wt.%) However, when ethylene is added, some of the C atoms come from it and the sum of the selectivities is greater than 100%.

11.7% CO/0.5 Re/TiO₂₁ 200ºC, 2 050 kPa, H₂+CO, H₂/CO = 2.1/1, 25 to 27% CO conversion.

Example 7 (This is not an example according to the invention) Experimental procedure for ethylene addition

The catalyst was started in H₂/CO at a volume rate required to achieve 15% to 30% CO conversion and at 2000 to 2100 kPa. Conditions were maintained for at least 48 hours. An ethylene/argon mixture was mixed with H₂/CO feed and then added to the reactor at the inlet with an ethylene concentration of 2 to 7 vol%. The total reactor pressure was then increased to a level necessary to raise the H₂ + CO partial pressure in the reactor to the level found before ethylene addition. The reactor was run at these conditions for at least 24 hours. Effect of Ethylene Addition Ruthenium Catalyst Experiment % Ethylene in Feed % Ethylene Converted Selectivity Ethane Yield Rate of Ethylene Conversion Rate of CO Conversion (mol CO/g-atom Ru h) Selectivity 1.2% RufriO₂, 191 to 192ºC, 2100 kPa, H2* +CO, -CO = 2.1/1, 18 to 22% CO Conversion * % ethylene converted that appears as these products. ** % ethylene added that appears as these products. *** Selectivity is defined as the percentage of CO converted that appears as a given product (it is almost identical to wt.%). However, when ethylene is added, some of the C atoms come from it and the sum of the "selectivities" is greater than 100%.

The addition of ethylene (C₂⊃min;) to H₂/CO feed at the reactor inlet reduces the CH₄ selectivity and increases the C₅⊃min; Selectivity with the Ru/TiO2 catalyst. A large fraction of the added ethylene (7% of the feed) is converted (73.4%), but only 49.5% of the converted C2 appears as desired C3+ products, the remainder (50.5%) is hydrogenated to ethane, which is unreactive to chain growth at Fischer-Tropsch synthesis conditions and therefore cannot be recycled without converting it to ethylene in a dehydrogenation reactor.

Example 8 (This is not an example according to the invention) Experimental procedure for ethylene addition and simultaneous addition of water

The catalyst was started in H2/CO at a volume rate required to achieve 15% to 30% CO conversion at 2000 to 2100 kPa. Conditions were maintained for a minimum of 48 hours. An ethylene/argon mixture was mixed with H2/CO feed and then added to the reactor at the inlet at an ethylene concentration of 2 to 7 vol.%. The total reactor pressure was then increased to a level necessary to increase the H2 + CO partial pressure in the reactor to the level found prior to ethylene co-addition. The reactor was run at these conditions for a minimum of 24 hours. Water vapor was then introduced at a concentration of 10 to 20 vol.% by blowing the H2 into a steam cylinder. + CO in bubbles through a saturator maintained at 120-145°C while the ethylene/argon flow was kept constant. The total reactor pressure was then increased to a level necessary to maintain the H₂ + CO partial pressure and the ethylene partial pressure in the reactor at the levels prior to water addition. In addition, the H₂/CO and ethylene/argon flow rates were increased so as to maintain the CO conversion at its previous value prior to water addition. The reactor was run at these conditions for at least 24 hours. Effect of Ethylene/Water Addition Ruthenium Catalyst Experiment % Ethylene in Feed % Water in Feed % Ethylene Converted Selectivity Yield Rate of Ethylene Conversion to (moles C2/g-atom Ru hr) Rate of CO Conversion Selectivity 1.2% Ru/TiO2, 191 to 192ºC, 2100 kPa, H2 + CO, H2/CO = 2.1/1, 18 to 22% CO Conversion * % ethylene converted that appears as these products. ** % ethylene added that appears as these products. *** Selectivity is defined as the percentage of CO converted that appears as a given product (it is almost identical to wt%). However, when ethylene is added, some of the C atoms come from it and the sum of the selectivities is greater than 100%.

The table shows that there is a clear advantage in feeding steam together with the ethylene and with the H₂/CO feed. While ethylene conversion decreases from 73.5% to 38.2% with the addition of 18% H₂O, the yield decreases only slightly (36.3% to 33.8%). Most importantly, however,

- the selectivity to the desired C₃⁺ products increases from 49.5% to 88.5%,

- the rate of ethylene conversion to C₃⁺ products and CO conversion increases approximately threefold, in other words, the activity of the catalyst for both reactions, C₂H₄ incorporation and Fischer-Tropsch synthesis, increases threefold, and

- the rate of ethylene conversion to ethane (i.e. hydrogenation rate) actually drops to about one-third upon addition of 18% steam to the H₂/CO/C₂⊃min; feed.

Associated beneficial effects are a decrease in CH4 selectivity (3.0% to 0.9%) and an increase in effective C5+ selectivity from 138.5% to 199.5%.

These results suggest that the effect of water is to increase the re-incorporation and chain growth of added ethylene while strongly inhibiting its hydrogenation to the undesirable ethane product.

Remarks

- Mass expressed in pounds (lbs) is converted to the equivalent kg by multiplying by 0.4536.

- Length expressed in inches is converted to cm by multiplying by 2.54.

Claims (13)

1. A process for reducing methane formation and increasing C5+ liquid yields in a Fischer-Tropsch process for synthesizing hydrocarbons from CO and H2, in which at least one olefin is added to a catalyst-containing reactor bed, characterized in that a gas mixture containing CO and H2 is introduced at the inlet end of the reactor bed and the olefin is separately introduced directly into the bed at a location more than 10% of the length of the bed from the inlet end of the bed and more than 10% of the length of the bed from the outlet end of the bed. 2. The process of claim 1 wherein the amount of olefin added to the reactor bed is based on a molar ratio of olefin to CO in the range of 1:100 to 5:1. 3. The process of claim 2 wherein the olefin: CO molar ratio is in the range of 1:20 to 5:1. 4. Process according to one of claims 1 to 3, in which the olefin or olefins is or are α-olefin of the type R-CH=CH₂, where R is hydrogen or an alkyl group having 1 to 17 carbon atoms. 5. A process according to any one of claims 1 to 4, wherein the olefin comprises a C2 to C10 alpha-olefin. 6. A process according to any one of claims 1 to 5, wherein the catalyst comprises one or more catalytic Group VIII metals. 7. The process of claim 6, wherein the catalytic metal is selected from iron, cobalt and ruthenium. 8. A process according to any one of claims 1 to 6, which is carried out at a temperature of at least 100°C. 9. A process according to claim 8, which is carried out at a temperature in the range of 100ºC to 500ºC. 10. A process according to any one of claims 1 to 9, wherein water is added to the reactor bed at a location more than 10% of the length of the bed from the inlet end of the bed and more than 10% of the length of the bed from the outlet end of the bed. 11. The process of claim 10, wherein the molar ratio of water to CO is in the range of 0.1:1 to 5.0:1. 12. A process according to claim 10 or claim 11, wherein the molar ratio of water to olefin is in the range of 0.1:1 to 50:1. 13. The process of claim 12 wherein the molar ratio of water to olefin is in the range of 0.2:1 to 10:1.