GB2291818A - Process for the synthesis of hydrocarbons from synthesis gases in the presence of a cobalt-based catalyst - Google Patents

Abstract

A mixture of essentially linear and saturated hydrocarbons containing at least 80% by weight C5<+> hydrocarbons, relative to all the hydrocarbons formed, is produced from a mixture constituted by hydrogen and oxides of carbon, in the presence of a cobalt-containing catalyst, molybdenum and/or tungsten and at least one additional element N from group Ib and the platinum group in which the cobalt, the molybdenum and/or tungsten and the N element(s) are dispersed on a support. The catalyst may also comprise at least one additional element from groups Ia, IIa and the lanthanide-actinide groups.

Description

The present invention relates to a catalytic process for producing hydrocarbons frcm C-H2 or CO-CO2-H2 mixtures (synthesis gases).

It more particularly relates to the use of a catalytic formulation making it possible to carry out the conversion of the synthesis gas into a mixture of hydrocarbons essentially constituted by C5 hydrocarbons (i.e. having at least 5 carbon atans per molecule) and usable as a liquid fuel or fuel oil.

It is knows that synthesis gas can be converted into hydrocarbons in the presence of catalysts containing transition metals. This reaction, performed at high temperature and under pressure, is known as FISCHER-TROPSCH synthesis. This, metals of group VIII such as iron, ruthenium, cobalt and nickel catalyze the transformation of CO-CO2-H2 mixtures into liquid and/or gaseous hydrocarbons.

The products prepared by FISCHER-TROPSCH synthesis in the presence of these metal catalysts have a very wide molecular weight distribut ion. Thus. only a small proportion of the products obtained are in the range of middle distillates constituted by kerosene and gas oil fractions, the kerosene fraction or fractions being constituted by a mixture of hydrocarbons, whose boiling points are between 140 and 300 C and whose gas oil fraction or fractions are constituted by a mixture of hydrocarbons having boiling points between 180 and 370 C during an atmospheric distillation, such as is carried out by Expert on a petroleun crude.

Considerable efforts have been made since 1973 to improve the middle distillate yield of processes based on the conversion of synthesis gas. In particular cobalt, which is known as a consti- tuent of FISCHER-TROPSCH catalysts since the earliest works of SABATIER and SENDERENS (J. Soc. Chen. Ind., 21, 504, 1902) and Gernan patents 293 787 (1913) and 295 202 (1914) has again been more recently used.

This. US patent 4 522 939 claims a recess for the preparation of a catalyst for the synthesis of middle distillates from synthesis gas containing cobalt and at least one other metal chosen fran among zirssniun, titanium or chnnium, said metals being dispersed on a support chosen from within the group constituted by silica, alunina or silica-aluninas. Molybdenun and tungsten are not claimed as cobalt promotors in this patent.

US patent 4 632 941 relates to an inproved process for the conversion of the synthesis gas into hydrocarbons using a cobalt-based catalyst. with or without thorium and incorporating molybdenun and/or tungsten as a supplementary constituent. It is also stated in said patent that the presence of thorium in the thoria state is preferred whereby the thorium concentration can vary between 0.1 and 15% by weight based on the cobalt and is preferably 15% by weight.Said catalyst also preferably contains a support preferably chosen from within the molecular sieves such as zeolites, or APO. This catalyst is preferably prepared by impregnating the cobalt and promotors on said support followed by an activation in the presence of hydrogen, coprecipitation of the molybdenum or tungsten leading to a sufficiently stable catalyst.

The hydrocaron mixtures synthesized according to this process only contain 50 to 72% by weight of C5 hydrocarbons and have a very high oleo in content (40 to 508 by weight according to the hydrocarbon fractions).

European patents 209 980 and 261 870 describe the use of catalysts based on cobalt and optionally one or more other metals chosen from within the group constituted by chromium, nickel, iron, molybdenum, tungsten, zirconium, galliun, thorium, lanthanum, cerium, ruthenium, rhenium, palladium or platinum. However, these fonnulations necessarily contain either cerium (EP 209 980) or zinc (EP 261 870) the molybdenun or tungsten not constituting essential elements of the catalytic formulation.

A catalytic canposition has now been found, whose performance characteristics are sufficiently stable and which, after reduction preferably under hydrogen, leads to conversion by the catalyst of a mixture of carbon oxides (CO, CO2) 2 and hydrogen, also knawn as the synthesis gas, into a mixture of essentially linear and saturated hydrocarbons containing at least 80% by weight of C5 hydrocarbons, based on all the hydrocarbons formed.

The catalysts according to the invention contain cobalt, at least one additional element M (e.g. in metallic form or in the form of oxide) chosen from within the group constituted by molydenum and tungsten and at least one additional element N (e.g. in metallic form or in the form of oxide) chosen from the group constituted by elements of group Ib and the platinum group (such as e.g. copper, silver, ruthenium and palladium), all these elements being dispersed on a support.

The at least one element N is preferably chosen from ruthenium and copper.

Preferably, the catalyst further comprises at least one additional element from groups Ia and lla (such as e.g. sodium, potassium, magnesium and silver).

Preferably, the catalyst further comprises at least one additional element from the lanthanide-actinide groups (such as e.g. rare earth metals such as praseodymium and neodymium, and uranium).

More preferably, the catalyst further comprises at least one additional element from groups Ia, lia and the lanthanide-actinide groups.

Preferably, the catalyst further comprises at least one additional element chosen from sodium, potassium and uranium.

The support used is preferably constituted by at least one oxide of at least one element chosen from within the group formed by the following elements: Si, Al, Ti, Zr, Sn, Zn, Mg, Ln (in which Ln is a rare earth, i.e. an element having an atomic number between 57 and 71 inclusive).

The contents of elements of the catalyst after calcination, expressed by element weight based on the weight of the support are normally 1 to 60 and preferably S to 40% by weight cobalt, 0.1 to 60, preferably 1 to 30% by weight of element M, and 0.01 to 15 and preferably 0.05 to 5 % by weight of element N.

The cobalt and the additional elements, which are also referred to as cobalt modifying agents or elements, can be introduced by using any known method such as e.g. ion exchange, dry impregnation, coprecipitation, gelling, mechanical mixing or grafting of organanetallic canplexes. Among these methods, impregnation or gelling are preferred for the preparation of the catalyst, because they permit an intimate contact between the cobalt and the modifying elements M and N.

It has in fact been found that the use of the ilopregnation or gelling of Xlt and molybdenum and/or tungsten and at least one additional element N and optionally at least one element chosen from within the group fanned by the elements of the support makes it possible to obtain a catalyst for converting the synthesis gas into hydrocarbons, which is both stable, active and selective with respect to C5 hydrocarbons.

A preferred method for the preparation of the catalyst according to the invention e.g. consists of impregnating a support by means of at least one aqueous solution (or in at least one appropriate solvent) containing cobalt and optionally all or part of the additional element or elements M or N, e.g. in the form of a halide, nitrate, acetate, oxalate, sulphate, complex formed with oxalic acid and axalates, a complex formed with citric acid and citrates, a canplex formed with tartaric acid and tartrates, a carplex formed with another polyacid or acid alcohol and its salts, a complex formed with acetyl acetonates and any other inorganic or organanetallic derivative containing cobalt and optionally all or part of the additional element or elements M or N, the other optional part of the additional element or elements M or N being impregnated subsequently.

In order to incorporate the element M (Mo or W), it is also possible to use at least one molybdate or at least one annoniun tungstate, such as ammonium molybdate, tetrahydrated ammonium heptamolybdate or aimniun metatungstate in exemplified manner.

After each impregnation of the cobalt and optionally the additional element or elements M or N on the chosen support, the product obtained is thermally treated, i.e. dried, by any knawn method, e.g.

under a flow of nitrogen or air at a temperature between 80 and 200 C, follcwed by calcination e.g. under an air or nitrogen flow at a temperature between e.g. 200 and 800 C.

Another preferred preparation method according to the invention consists of preparing a gel containing the cobalt and elements M and N. This preparation by gelling takes place by any known method.

However, two gelling preparation methods are preferred according to the invention. One of the preferred gelling methods consists of preparing a gel containing the cobalts and the elements M and N according to the procedure described in US patent 3 846 341, substituting the iron salt as described therein by a cobalt salt.

Thus, the gel containing cobalt, the elements M and N and the support can be prepared in the following way.

An aqueous solution A of the molybdenun salt, preferably ammonium paramolybdate, having a concentration between 1 and 2.5 gram atan of molybdenum per litre is introduced into a reactor ard stirred at a temperature below 20 C. To said solution A is added an aqueous solution B containing a cobalt salt, preferably cobalt nitrate, at a concentration abave 1 gran atom Per litre. A colloidal suspension is then obtained. This suspension can optionally be hardened during a slow reheating under limited stirring (v < 1000 rpn).

Ageing carried out at a tenperature above 10'C leads to the obtaining of a homogeneous gel. If necessary, the gel can be dehydrated at a temperature between 40 and 150'C, preferably between 50 and 90*C. It is then dried by any kncwn pure, e.g. under a nitro gen or air flow, at a temperature between 80 and 200'C, thecal- cined, e.g. under a nitrogen or air flow at a temperature between e.g. 200 and 800'C. The support can be introduced at any stage of the preparation as described hereinbefore.It is preferably intro- duced into the solution A or into the solution B, preferably in a finely divided form, i.e. the grains preferably have a size below 250 n.

Another preferred gelling method will now be described. It con- sists of preparing a gel obtained by mixing a solution A containing an organometallic compound, preferably an alkoxide of the precursor element of the support, dissolved in an organic solvent, preferably alcohol, and an aqueous solution B containing a cobalt salt, at least one salt of element M and at least one salt of element N and also containing a mineral acid, which speeds up the gelling, such as e.g. nitric, hydrochloric, sulphuric or phosphoric acid.The said cobalt salts and the elements M and N are e.g. halides, nitrates, acetates, oxalates, sulphates, complexes forned with a polyacid or an acid alcohol and salts or complexes formed with acetyl acetates, or any other inorganic derivative soluble in aqueous solution. The mixture of the solutions A and B, accoopa- nied by stirring in the presence of said acid, leads to the obtaining of a gel formed in less than 10 min and at a temperature between 20 and 80 C. The thus formed gel is separated fran the residual solvents by any knawn method, e.g. by centrifuging ar filtering and is then dried, e.g. under a nitrogen or air flow at a temperature between 80 and 200'C and is finally calcined, e.g.

under an air or nitrogen flow at a temperature between 200 and 800 C.

It is also possible to prepare the catalyst according to the invention by means of the method described in detailed manner US patent 3 975 302 and which consists of preparing an impregnation solution fran an anorphais solid gel and alkanol amine, followed by inpregnating a support with said solution.

The catalyst cooled optionally be shaped by any known process, e.g.

extrusion, droplet coagulation, drageification or pelletizing.

Following said shaping stage, the catalyst will optionally undergo a final thermal activation under the aforementioned operating conditions.

The catalysts prepared according to the operating procedures described in the invention are particularly suitable for use in processes for producing a mixture of essentially linear and saturated hydrocarbons, containing at least 80% by weight of C5 + hydro carbons, based cn all the hydrocarbons formed, fran a synthesis gas. The present invention consequently also relates to a process for the synthesis of hydroarbons from synthesis gases in the presence of a catalyst prepared according to the invention.

The conditions for using the catalysts for producing the hydrocarbons are normally as folIos. The catalyst, introduced into a reactor, is firstly prereduced by contacting with a mixture of inert gas (e.g. nitrogen) and at least one reducing compound (e.g.

carbon monoxide or hydrogen), the molar ratio of the reducing can- pound to the inert gas being 0.001:1 to 1:1. Prereduction is per formed at between 150 and 600 C, preferably between 200 and 500'C, at between 0.1 and 10 MPa and an rly volume rate of 100 to 40,000 volumes of mixture per volume of catalyst and per hour.

This prereduction is preferably carried out in the liquid phase if, subsequently, the hydrocatbon synthesis reaction is performed in the liquid phase.

The conversion of the synthesis gas into hydrocarbons is then carried out under a total pressure normally between 0.5 and 15 MPa, preferably between 1 and 10 MPa, the temperature generally being between 150 and 350 C, preferably between 170 and 300'C.

The hourly volume rate is normally between 100 and 10,000 volumes of synthesis gas per volume of catalyst and per hour and preferably between 400 and 5,000 volumes of synthesis gas per volume of catalyst and per hour and the H2 :00 ratio in the synthesis gas is normally between 1:1 and 3:1 and preferably between 1.2:1 and 2.5:1.

The catalyst can be used as a calibrated fine powder (approx. 10 to 700 pm) or in the fonn of particles having an equivalent diem- eter between approximately 2 and 10 rtrn, in the presence of a gaseous phase, or a liquid phase (in the operating conditions) and a gaseous phase. The liquid phase can be (mstituted by one or more hydrocarbons having at least 5 cart atans, preferably at least 10 capon atoms per molecule.

The catalysts having the co"oosition described hereinbefore are particularly active and stable in the synthesis reaction of hydrocarbons fron synthesis gases. They make it possible to obtain essentially paraffinic hydrocarWs, whose fraction having the highest boiling point can be converted with a high yield into middle distillates (kerosene and gas oil fractions) by a hydooconversion process such as catalytic hydroisomerization and/or hydrocracking.

The following exanples illustrate the invention without limiting its scope.

EXAMPLE 1 (comparative): Catalyst A A silica support is impregnated (stage a)) by an aqueous cobalt nitrate solution having a volume equal to the pore volume of the support and containing the desired cobalt nitrate quantity, i.e.

5% by weight of Co based on the silica weight (table 1), the solution then being slowly evaporated to dryness at 80iC (stage b)).

The thus obtained impregnated silica is then dried for approximately 1 hour at 100 'C (stage c)) and for approximately 16 hours at 150'C (stage d)) and is then calcined for approximately 3 hours at 500iC (stage e)).

The desired element M content, i.e. 1.5% by weight of Mo based on the silica weight (table 1) is then deposited in accordance with the protocol described in stages a) to e), in which the cobalt nitrate is replaced by tetrahydrated annoniun heptanolybdate, and the pore volume of the support by the pore volune of the cobalt-impreg- nated support.

This is followed by the deposition of 3% by weight potassium (element N) based on the silica weight and in accordance with the protocol described in stages a) to e), in which the cobalt nitrate is replaced by potassium nitrate and the pore volume of the support by the pore volume of the support impregnated with cobalt and molybdenum (element M).

EXAMPLE 2 (comparative): Catalyst B The preparation of the catalyst B differs fran that described in example 1 in that successive deposition takes place on the silica described in table 1 of 10% by weight cobalt based on the silica weight, by inpregnating cobalt nitrate according to stages a) to e), 3% by weight molybdenum based on the silica weight, by inpregnating tetrahydrated ammonium heptanolybdate according to stages a) to e) and then 0.6% by weight potassium based on the silica weight and in accordance with the protocol of stages a) to e).

EXAMPLE 3 (comparative): Catalyst C The preparation of catalyst C differs fmm that described in example 1 in that there is a simultaneous deposition on the silica described in table 1 of 25% by weight cobalt and 2.6% by weight molybdenun based on the silica weight, by inpregnating with a solu tion containing both cobalt nitrate and tetrahydrated ammonium heptamolybdate, in accordance with stages a) to e), followed by 0.8% by weight of sodiun based on the silica weight and in accordance with stage a) to e).

EXA9LE 12: Catalyst L The preparation of catalyst L differs frtm that described in example 3 in that deposition initially takes place simultaneously on the silica described in table 1 of 30% by weight cobalt and 2.6% by weight molybdenum based on the silica weight, by impregnating with a solution containing both cobalt nitrate and tetrahydrated ammonium heptanolybdate, according to stages a) to e), and then 0.5% by weight copper based cn the silica weight, by inpreenating with a trihydrated copper nitrate solution, according to stages a) to e).

EXAMPLE 16 (comparative) : Catalyst R 450 g (5.70 moles) of anroniun hydrogen carbonate are dissolved in 3 litres of distilled water and vigorously stirred at ambient temperature. To this solution is added another solution containing 30 g of hexahydrated cobalt nitrate (0.10 moles), 5 g of ammonium heptanolybdate (4 mmoles) and 89.25 g of hexa}ydrated zinc nitrate (0.30 mole), dissolved in 750 ml of distilled water. The addition rate of said second solution is approximately 12 ml/min. The pH of the bicarbonate solution remains reasonably constant during this addition (pH = 7.5 to 8.0). The resulting fine precipitate remains suspended in the stirred solution for the entire addition period.The precipitate is then filtered and dried on a filter and then washed by suspending in 500 ml of distilled water and accompanied by vigorous stirring. This washing is carried out a second time before drying the precipitate in an oven at 150 C and for 16 hours. The dried precipitate is then treated under nitrogen by raising fran ambient temperature to 450 0C at a rate of 30 C/h, it spends 6 hours at 450"C, followed by cooling to 20 C. The catalyst R obtained contains 24.1% by weight cobalt and 11% by weight molybdenum based an the zinc oxide weight.

EXAMPLE 17 (comparative) : Catalyst S 18.75 g of cobalt acetyl acetonate (Co(acac)3; 52.5 mmoles) are dissolved in 750 ml of acetone. The solution is slowly added to a eup containing 60 g of CeO2, vigorous stirring being maintained and then the mixture is slowly evaporated in vacuo using the ROTAVAPOR until a paste is obtained. The paste is dried on the water bath, accompanied by stirring and the product is simultaneously ground until an inpregnated ceria powder is obtained. The powder is then dried in air in an oven at 150 C.The dried product is then calcined under nitrogen with a rise fron ambient temperature to 450iC at a speed of 0.5 C/min, it spends 6 hours at 450iC and is then cooled to ambient temperature at 10 C/min.

EXAMPLE 18 (comparative) : Catalyst T 12.5 g of hexahydrated oobalt nitrate are dissolved in acetone (53 mmoles) and added to a solution containing 25 g of hexahydrated lanthanum nitrate dissolved in acetone (57.7 mmoles). The solution is slowly added to 50 g of ceria (CeO2) accwpanied by stirring and with simultaneous grinding until a consistent paste is obtained.

This paste is then dried in air in an oven at 150 C. The dried product is then calcined under nitrogen with a temperature rise frcm ambient temperature to 450 C at a rate of 3iC/min, it spends 6 hours at 4500C and is then cooled to anbient temperature at 10 C/min.

The catalysts described in examples 1 to 3, 12 and 16 to 18 are tested in the gaseous phase in a pilot unit operating continuously and on 20 cm3 of catalyst.

Catalyst L (example 12 according to the invention and catalysts A to C (comparative examples 1 to 3 which are described in the parent application GB 9212921.2) are previously reduced in situ to 240 C by a mixture of hydrogen and nitrogen containing 6% hydrogen in nitrogen and then by pure hydrogen to 350 C. at atmospheric pressure.

Catalyst R (comparative example 16) is reduced under hydrogen under the following conditions: - rise from ambient temperature to 125 C at 2 C/min - 2 hours at 125 C - rise fran 125 to 225 C at 2'C/min - 2 hours at 225 C - rise from 225 to 320 C at 2 C/min - 2 hours at 320 C - cooling to ambient terperature.

Catalysts S and T (comparative examples 17 and 18) are reduced by hydrogen under the following conditions: - rise fran ambient temperature to 400 C at 3 'C/min - 6 hours at 400 C - cooling to anbient temperature at 10'C/min.

The testing conditions for catalysts A to C, L and R to T are as follows: - temperature between 200 and 240'C - pressure 2 MPa - hourly volume rate (H.V.R.) between 600 and 2000 h-1 - H2: = 2:1 The catalytic performance characteristics of these catalysts are given in tables 2 and 3. With regards to catalysts A to C and L following reduction in situ to 350 C, the temperature of the catalytic bed is reduced to 170iC and the hydrogen-nitrogen mixture is substituted by pure nitrogen. With regards to the catalysts R, S and T, the hydrogen flow is substituted by nitrogen and the temperature is raised fran ambient temperature to 170iC at a rate of 10 C/min.

The pressure is then bright to 2 MPa in the reactor and the synthesis gas (hydrogen-carbon monoxide mixture with a H2 :00 ratio = 2:1) is then progressively introduced so as to obtain the desired HVR (table 2, HVR = 600 to 2000 h-l).

The nitrogen flow is then progressively eliminated and the temperature adjusted to the desired value (table 2, T=200 to 240 C) with a temperature rise rate of 6iC/min. The performances obtained after 400 hours stabilization under synthesis gas are indicated in table 2. Table 3 shows the distribution of the essentially linear, saturated hydracarbons synthesized under these conditions.

Table 2 shows that the catalysts according to the invention make it possible to achieve high carbon monoxide (CO) conversions and high hydrocaooon productivity rates. Moreover, table 3 also indicates that 80% by weight of the hydrocarbon formed with the catalysts according to the invention are hydrocarbons having at least 5 carbon atans per molecule (C5+ hydrocarbons). A large proportion of the hydscaSs formed consequently fall within the range of mediun distillates (kerosene, gas oil) or paraffins which are solid at anbient tenperature (waxes).The distribution of the hydrocarbons obtained is therefore very suitable for the preparation of middle distillates, the hydro fraction having the highest boiling points being convertable, with a high yield, into middle distillates by a hydroconversion process such as catalytic hydroisomerization and/or hydrocaracking.

The comparative examples of tables 2 and 3 also indicate that catalysts R, S and T, whose compositions are given in table 1, essentially lead to C5-C12 hydrocarbons, so that the proportion of + Cs hydrwXs forned is below 80% by weight. Moreover, the productivity levels are lower than with the catalysts according to the invention, particularly in the case of catalysts S and T. TABLE 1 : CATALYSTS PREPARED BY IMPREGNATION EXAMPLE Catalyst % Co M % M N % N support SB.E.T.

(m2/g) 1 (compa- A 5 Mo 1.5 K 3 SiO2 65 rative) 2 (compa- B 10 Mo 3 K 0.6 SiO2 55 rative) 3 (compa- C 25 Mo 2.6 Na 0.8 SiO2 38 rative) 12 L 30 Mo 2.6 Cu 0.5 SiO2 55 17 (comparative) S 5.2 - - - - CeO2 75 18 (comparative) T 5.1 - - La 15.9 CeO2 75 TABLE 2 : CONVERSION OF THE SYNIHESIS GAS INTO HYDROCARBONS Catalyst Temperature HVR CO.CONV. Productivity * ( C) (h-1) (vol. %) (kg/(m3 cat.h)) A (comp- 240 600 45 56 rative) B (compa- 230 800 62 100 rative) C (compa- 220 2000 55 220 rative) L 210 2000 74 296 R (comparative) 220 2000 45 175 S (comparative) 240 600 25 31 T (comparative) 240 600 18 22 3 * Total hydrocarbon productivity in kg/m of catalyst and per hour. TABLE 3 : DISTRIBUTION OF THE REACTION PRODUCTS CATALYST HYDROCARBONS PRODUCED (% BY WEIGHT) C4- C5-C12 C13-C19 C20+ C5+ A 15 35 20 30 85 B 13 33 21 33 87 C 12 27 25 36 88 L 13 23 26 38 87 R (comparative) 30 49 14 7 70 S (comparative) 22 44 19 15 78 T (comparative 24 42 16 12 76

Claims (14)

1. CLAIMS 1. A process for producing a mixture of essentially linear and saturated hydrocarbons containing at least 80% by weight C5+ hydrocarbons based on all the hydrocarbons formed, from a synthesis gas that is a mixture constituted by hydrogen and oxides of carbon (CO and CO2) in the presence of a catalyst prepared by gelling, ion exchange, dry impregnation, coprecipitation, mechanical mixing or grafting of organometallic complexes and containing cobalt, at least one additional element M chosen from molybdenum and tungsten, and at least one additional element N from elements of group Ib and the platinum group in which the cobalt and the elements M and N are dispersed on a support, the product obtained is thermally treated, followed by calcination, the contents of elements of the catalyst after calcination, expressed as weight of element based on weight of support, are 1.0 to 60% for cobalt, 0.1 to 60% for Mo and/or W and 0.01 to 60% for element N.
2. 2. A process according to claim 1 wherein the catalyst further comprises at least one additional element from the element of groups Ia and lla.
3. 3. A process according to claim I or claim 2 wherein the catalyst further comprises at least one additional element from the lanthanide-actinide groups.
4. 4. A process according to any one of claims 1 to 3, in which the support is at least one oxide of at least one of the following elements: Si, Al, Zr, Sn, Zn, Mg, and Ln, in which Ln is a rare-earth metal.
5. 5. A process according to any one of the preceding claims, in which the contents of elements of the catalyst after calcination, expressed by weight of oxide based on the weight of the calcined catalyst, are 5 to 40% cobalt, 1 to 30% Mo and/or W, and 0.05 to 5% element N.
6. 6. A process according to any one of the preceding claims, in which, before use the catalyst is prereduced by contacting with a mixture of inert gas and at least one reducing compound in a molar ratio of reducing compound to inert gas of 0.001:1 to 1:1, the reducing compound being hydrogen and/or carbon monoxide, the prereduction being carried out at 150 to 600"C, 0.1 to 10 MPa and a rate of 100 to 40,000 volumes of mixture per volume of catalyst per hour.
7. 7. A process according to claim 6, in which the prereduction is performed at 200 to 500"C.
8. 8. A process according to any one of claims 1 to 7 in which working takes place under a pressure of 0.5 to 15 MPa, a temperature of 150 to 350"C, a rate of 100 to 10,000 volumes of synthesis gas per volume of catalyst per hour, and a H2:CO molar ratio of 1:1 to 3:1.
9. 9. A process according to claim 8, in which working takes place under a pressure of 1 to lOMPa, a temperature of 170 and 300"C, a rate of 400 to 5,000 volumes of synthesis gas per volume of catalyst per hour and a H2:CO molar ratio of 1.2:1 to 2.5:1.
10. 10. A process according to any one of claims 1 to 9, in which the production of the essentially linear and saturated hydrocarbons from a synthesis gas is performed in the presence of a liquid phase incorporating one or more hydrocarbons having at least 5 carbon atoms per molecule.
11. 11. A process according to any one of claims 1 to 10, in which the prereduction of the catalyst takes place in the presence of a liquid phase incorporating a hydrocarbon having at least 5 carbon atoms per molecule.
12. 12. A process according to claim 10 or claim 11, in which the liquid phase comprises at least one hydrocarbon having at least 10 carbon atoms per molecule.
13. 13. A process according to claim 1, in which the catalyst is substantially as hereinbefore described in Example 12.
14. 14. A process according to claim 1, substantially as hereinbefore described.