GB2291819A - Process for the synthesis of hydrocarbons from synthesis gases in the presence of a cobalt-based catalyst - Google Patents

Description

2291819 The present invention relates to a catalytic process for producing

hydrocad:)ons from C-H2 or CO-W2-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 C 5 + hydrocarbons (i. e. having at least 5 carbon atoms per molecule) and usable as a liquid fuel or fuel oil.

It is known that synthesis gas can be converted into hydrocarbons in the presence of catalysts containing transition metals. This reaction, performed at high teTperature and under pressure, is known as F=ERTROPSCH synthesis. Thus, metals of groW VIII such as iron, ruthenium, cobalt and nickel catalyze the transformation of CO-CO 2 -H 2 mixtures into liquid and/or gaseous hydrocarbons.

The products prepared by FISCRER-TWPSCH synthesis in the presence of these metal catalysts have a very wide molecular weight distribution. 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 30CC and whose gas on fraction or fractions are constituted by a mixture of hyd-rocarbons having boiling points between 180 and 370T during an atmospheric distillation, such as is carried out by Fxpert an a petroleum crude.

Considerable effor-ts 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 ccnstituent of FISCRER-TROPSCH catalysts since the earliest works of SABATIER and SENDEFEM (J. Soc. Chem. Ind., 21, 504, 1902) and German patents 293 787 (1913) and 295 202 (1914) has again been more recently used.

Thus, US patent 4 522 939 claim a process for the prqp=tion of a catalyst for the synthesis of middle distillates fran synthesis gas containing cobalt and at least one other metal chosen fran among zirconium, titanium or chramium, said metals being dispersed on a support chosen fran within the group constituted by silica, alumina or silica-aluminas. Molybdenum and tungsten are not claimed as cobalt pranotors in this patent.

US patent 4 632 941 relates to an improved process for the ccnversicn of the synthesis gas into hydrocarbons using a cobalt-based catalyst, with or without thorium and incorporating molybdenum and/or tungsten as a supplementary constituent. It is also stated in said patent that the presence of thoriu-n in the thoria state is preferred, whereby the thoriLrn 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 suppor-t preferably chosen from within the molecular sieves such as zeolites, or -' 3 - c APO. This catalyst is preferably prepared by inpregnating the cobalt and pramotors on said support followed by an activation in the presence of hydrogen, =precipitation of the molybdenum or tungsten leading to a sufficiently stable catalyst.

The hydrocarbon mixtures synthesized according to this process only contain 50 to 72% by weight of CS+ hydrocarbons and have a very high olefin content (40 to 50% by weight according to the hydrocarbon fractions).

Eurcpean patents 209 980 and 261 870 describe the use of catalysts based on ct and cptionaUy one or more other metals chosen from within the group constituted by chromium, nickeJL, iren, molybdenum, tungsten, zirconiu-n, gallium, thorium, lanthanum, cerium, ruthenium, rhenium, palladiun or platinun. However. these formulations necessarily contain either cerium (EP 209 980) or zinc (EP 261 870) the molybdenum or tungsten not constituting essential elements of the catalytic fonulation.

A catalytic caTyposition 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 mL%ture of carbon oxides (CO, OD 2) and hydrogen, also kncwn 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 forned.

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 the lanthanideactinide groups (such as e.g. rare earth metals such as praseodymium, and neodymium, and uranium), all these elements being dispersed on a support.

The additional element N is preferably uranium.

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

Preferably, the catalyst further comprises at least one additional element from group Ib and the platinum group (such as e.g. copper, silver, ruthenium and palladium).

More preferably, the catalyst further comprises at least one additional element from groups la, Ha, 1b and the platinum group.

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

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, AI, 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 5 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 h organametallic carplexes. Among these methods. irrpregnation or gelling a 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 iripregnation or gelling of cobalt and molybdenum and/or tungsten and at least one additional element N and optionally at least one element chosen from within the group formed 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 inpregnating 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, ccnplex formed with oxalic acid and oxalates, a carplex formed with citric acid and citrates, a complex formed with tartaric acid and tartrates, a ccnplex formed with another polyacid or acid alcohol and its salts, a ccniplex formed with acetyl acetanates and any other inorganic or organametallic derivative containing cobalt and optionally all or part of the additional element or elements M or N, the other optional part of the additional elErnent or elements M or N being inpregnated subsequently.

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

1 25 After each impregnation of the cobalt and optionally the additional element or elements M or N an the chosen support, the product obtained is thermally treated, i.e. dried. by any known method, e.g. under a flow of nitrogen or air at a temperature between 80 and 200T, followed by calcination e.g. under an air or nitrogen flow at a temperature between e. g. 200 and 8OCC.

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 molybdenum salt, preferably anrionitin paranolybdate, having a concentration between 1 and 2.5 gran atcrn of molybdenum per litre is introduced into a reactor and stirred at a terperature below 20 C. To said solution A is added an aqueous solution B containing a cobalt salt, preferably cobalt nitrate, at a concentration above 1 gran atom per litre. A colloidal suspension is then obtained. This suspension can optionally be hardened during a slow reheating urxler limited stirring (v < 1000 rpn). Ageing carried out at a erature above 10T leads to the obtaining of a hanogeneous gel. If necessary, the gel can be dehydrated at a tenture between 40 and 150C, preferably between 50 and 90T. It is then dried ly any known procedure, e.g. under a nitrogen or air flow, at a temture between 80 and 200% thg,'calcined, e.g. under a nitrogen or air flow at a tenture between e.g. 200 and 8OCC. The support can be introduced at any stage of the preparation as described hereinbefore. It is preferably intrc),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 pm.

Another preferred gelling method will now be described. It cansists of preparing a gel obtained by mixing a solution A containing an organanetallic coy, 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 elenent 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 eletnents M and N are e. g. halides, nitrates, acetates, oxalates, sulphates, lexes formed with a 411 polyacid or an acid alcohol and salts or omplexes fomied with acetyl acetanates, or any other inorganic derivative soluble in aqueous solution. The mixture of the solutions A and B, accaTpanied by stirring in the presence of said acid, leads to the obtaining of a gel formed in less than 10 min and at a toTperature between 20 and 800C. The thus formed gel is separated frtm the residual solvents by any known method, e.g. by centrifuging or filtering and is then dried, e.g. under a nitrogen or air f1c;w at a terperature between 80 and 2009C and is finally calcined, e.g. under an air or nitrogen f1cw at a teTperature between 200 and 800C.

It is also possible to prepare the catalyst according to the invention by means of the method described in detailed manner in us patent 3 975 302 and which cmsists of preparing an inpregnation Solution fran an amorphous Solid gel and alkanol amine, followed by AMPregnating a support with said solution.

The catalyst could cptionally 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 cperating conditions. The catalysts prepared according to the cperating 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 C,+ hydro- to carbons, based on all the hydrocarbons fozmed, from a synthesis gas. The present invention consequently also relates to a process for the synthesis of hydrocarbons frrm synthesis gases in the presence of a catalyst prepared according to the invention.

The conditions far using the catalysts for producing the hydrocarbons are normally as follows. 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 cxz (e.g. carbon monoxide or hydrogen), the molar ratio of the reducing canpound to the inert gas being 0.001:1 to bl. Prereduction is performed at between 150 and 600 C, preferably between 200 and. 500 at between 0.1 and 10 MPa and an hourly volume rate of 100 to 40,000 volumes of mixture per volume of catalyst and per ha=. This prereductum is preferably carried out in the liquid phase if, subsequently, the hydrocarbon synthesis reaction is performed in the liquid phase.

The conversion of the synthesis gas into hydrocarbons is then carried out under a total pressure nonnall:y between 0.5 and 15 MPa, preferably between 1 and 10 MPa, the toupwature generally being between 150 and 3500C, preferably between 170 and 3000C.

The hourly volume rate is nonwilly 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 - it nonuUy between 1:1 and 3 2.5:1.

1 :1 and preferably between 1.2:1 and The catalyst can be used as a calibrated fine er (approx. 10 to 700 pm) or in the fonn of particles having an equivalent diameter between approximately 2 and 10 mn, in the presence of a gaseous phase, or a liquid phase (in the operating conditions) and a gaseous phase. The liquid phase can be constituted by one or more lyd=a having at least 5 carbon atoms, preferably at least 10 carbon atoms per molecule.

The catalysts having the caTposition described hereinbefore are particularly active and stable in the synthesis reaction of hydrocaxbons frcm synthesis gases. They make it Possible to obtain essentially paraffinic hydrocarbons, whose fraction having the highest boiling point can be converted with a high yield into middle distillates (kerosene aned gas oi.1 fractions) by a hydroconversion process such as catalytic hydraiscmerization and/or hydrocracking.

The following examples illustrate the invention without limiting its scope.

EXAMPLE 1 (comparative): Catalyst A A silica support is iffpregnated (stage M) 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 k 2_ A solution then being slowly evaporated to dryness at 800C (stage b)). The thus obtained impregnated silica is then dried for approximately 1 how at 100T (stage c)) and for approxkwtely 16 hours at 150C (staged)) and is then calcined for approximately 3 hours at 500T (stage e)).

The desired element M content, i.e. 1.5% by weight of mo based an 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 amnonium heptaimolybdate, and the pore volume of the support by the pore volume of the ccbalt-xTpregnated support.

This is followed by the deposition of 3% by weight potassium (element N) based an 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 s=port 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 frcm that described in example 1 in that successive deposition takes place an the silica described in table 1 of 10% by weight cobalt based on the silica weight, by impregnating cobalt nitrate according to stages a) to e), 3% by weight molybdenum based an the silica weight, by impregnating tetrahydrated annoniur heptamolybdate according to stages a) to e) kS and then 0.6% by weight potassium based on the silica weight and in accoi:dance with the protocol of stages a) to e).

EXAMPLE 3 (Comparative):

Catalyst C The preparation of catalyst C differs from that described in exanple 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 molybdenum based an the silica weight, by inpregnating with a solutim containing both cobalt nitrate and tetrahydrated amnonium heptanolybdate, in accordance with stages a) to e), followed by 0.8% by weight of sodium based on the silica weight and in accordance with stage a) to e).

A IL( EXAMPLE 13: Catalyst 0 The preparation of catalyst 0 differs frem that described in exarTple 3 in that deposition initially takes place simultaneously m the si 1 i ca descr in table 1 of 25% by weight cobalt and 2% by weight molybdenum based on the silica weight, by iffpregnating with a solution containing both cobalt nitrate and tetrahydrated amicnium heptanolybdate, according to stages a) to e) and then 1% by weight uraniun based an the silica weight, by impregnating with a hexahydrated uranyl nitrate solution and according to stages a) to e) c; ELE 16 (carparative): Catalyst R 450 9 (5.70 moles) of ammonium hydrogen carbonate are dissolved in 3 litres of distilled water and vigorously stirred at ambient tEillperature. To this solution is added another solution containing 30 g of hexahydrated cobalt nitrate (0.10 moles), 5 g of annonim hepta.nolybdate (4 mmoles) and 89.25 9 of hexahydrated 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 renains reasonably constant during this addition (pH = 7.5 to 8.0). The resulting fine precipitate renains 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 M1 of distilled water and accompanied by vigorous stirring. This washing is carried out a second time before drying the precipitate in an oven at 150T and for 16 hours. The dried precipitate is then treated under nitrogen by raising from ambient teimperature to 450T at a rate of 30T/h, it spends 6 hours at 450C, followed by cooling to 20T. The catalyst R obtained contains 24.1% by weight cobalt and 11% by weight molybdenum based on the zinc oxide weight.

t k is EXAMPLE 17 (comarative): CatalYst S 18.75 9 of ct acetyl acetonate (Co(acac)3; 52.5 mmoles) are dissolved in 750 ml of acetone. The solution is slowly added to a cup containing 60 9 of CeO 2' vigorous stirring being maintained and then the mixture is slowly evaporated in vacuo using the RirrAVAPOR until a paste is obtained. The paste is dried on the water bath, accompanied by stirring and the product is simultaneously ground until an impregnated ce-Fia er is obtained. The er is then dried in air in an oven at 150 C. The dried product is then calcined under nitrogen with a rise from ambient teTperature to 450 C at a speed of 0.5C/min, it spends 6 ha= at 4504C and is then cooled to ambient tEniperature at 10'C/min.

EXAMPLE 18 (carrparative): Catalyst T 12.5 9 of hexahydrated cobalt nitrate are dissolved in acetone (53 mmoles) and added to a solution containing 25 9 of hexahydrated lanthanum nitrate dissolved in acetone (57.7 mmoles). The solution is slowly added to 50 9 of ceria (Ce02) accarpanied by stirring and with simultaneous grinding until a consistent paste is obtained. This paste is then dried in air in an oven at 15CC. The dried product is then calcined under nitrogen with a temperature rise from ambient temperature to 450C at a rate of 3C/min, it spends 6 hours at 4500C and is then cooled to ambient temperature at 10C/min.

The catalysts described in examples 1 to 3, 13 and 16 to 18 are tested in the gas- 3 eous phase in a pilot unit cperating continuously and an 20 cm of catalyst.

% I Catalyst 0 (example 13 according to the invention) and catalysts A to C (comparative examples I 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 350C, at atmospheric pressure.

Catalyst R (canparative exmple 16) is reduced under hydrogen under the following conditions: - rise fran arnbient terrture to 12ST at 2C/min 2 hours at 12ST rise fran 125 to 225T at 2C/min 2 hours at 22ST rise from 225 to 320 C at 2 C/min 2 hours at 320T cooling to anbient temperature.

Catalysts S and T (comparative exanples 17 and 18) are reduced by hydrogen under the following conditions: - rise fran anbient tenperature to 400T at 3C/min - 6 hours at 4006C - cooling to anbient te-rperature at 10C/min.

The testing conditions for catalysts A to C, 0 and R to T are as follows: temperature between 200 and 2400C pressure 2 MPa - hourly volune rate (H. V.R.) between 600 and 2000 h-1 - H2:C0 - 2:1 i.9 The catalytic performance characteristics Of these catalysts are given in tables 2 and 3. With regards to catalysts A to C and 0 following reduction in situ to 350C, the teffperature of the catalytic bad is reduced to 170C 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 tayperature is raised fran ambient teqDerature to 170C at a rate of 10C/min.

The pressure is then brought to 2 MPa in the reactor and the synthesis gas (hydrogen-carban mancxIde mixture with a H 2:CD ratio - 2:1) is then progressively introduced so as to obtain the desired HVR (table 2, HVR 600 to 2000 h-1).

The nitrogen flow is then progressively eliminated and the tmperature adjusted to the desired value (table 2, T--200 to 240C) with a toperature rise rate of 6C/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, -ions.

saturated hydrocarbons synthesized under these condit Table 2 shows that the catalysts according to the invention make it possible to achieve high carbon monoxide (C0) conversions and high hydrocarbon productivity rates. Moreover, table 3 also indicates that 80% by weight of the hydrocarbon fo with the catalysts according to the invention are hydrocarbons having at least 5 carbon atoms per molecule (C5+ hydrocarbons). A L--rue proportion of the hydrocarbons formed consequently fall within the range of medlirn distillates (kerosene, gas oil) or paraffins which are solid at anbient temperab= (waxes). The distribution of the hyd=carbons obtained is therefore very suitable for the preparation of middle distillates, the hydrocarbon fraction having the highest boiling Points being convertable, with a high yield, into middle distillates by a hydroconversian process such as catalytic hydroisanerization and/or hydrocracking.

The ccgq:>,tive exmples of tables 2 and 3 also indicate that catalysts R, S and T, whose canpoS:iticxls arc given in table 1, essentially lead to CS-CI2 hydrocarbons. so that the praportim of CS + hydrwaxtms formed Is below 80% by t. Moreover, the productivity levels are looex than with the catalysts according to the Invention, particularly In the case of catalysts S and T.

TABLE 1: CATALYM PREPARED BY IMPRE12WRN EXMPLE Catalyst % CO m % m N % N 0rt S B 2 E.T.

(m 19) 1 (compa- A 5 MO 1.5 K 3 65 rative) S102 2 (compa- B 10 No 3 K 0.6 Sio 2 55 rative 3 (compa- c 25 W) 2.6 Na 0.8 a io 38 rar- i ve) 2 13 0 25 MO u I SID 2 55 17 (c rative) S - - Ceo 2 75 La 15.9 Ce02 75 18 (ompa rative) T 5.1 1 A -?- k TABLE 2: CMVERSIX OF IM SYNTHESIS GAS INM HYDR=BCW Catalyst Tenture MR CD.COW. Productivity CC) (h-l) (vol. %) (kg/(m 3 cat.h)) A (compa- 240 600 45 56 rative) B (compa- 230 800 62 100 rative) C (compa- 220 2000 55 220 rative) 0 220 2000 81 324 R (CUTP= ative) 220 2000 45 175 S (carpar ative) 240 600 2i 31 T (ccnpar ative) 240 600 18 22 Total hYdrOcarbM Productivity in "og/In 3 of catalyst and per ha=.

TABLE 3: DISTRIBIMM OF THE REWrION PRODUCTS CATAUT HYDROIC.A PRODUCED (b BY WEIGHT) C4 C5-C12 c 13 -IC 19 C 20 + C5+ A (ccxtive) 15 35 20 30 85 B (comtive) 13 33 21 33 87 c (comparative) 12 27 25 36 88 23 28 40 91 0 9 R (compa- 49 14 7 70 rative) 30 S (compa- 44 19 is 78 rative) 22 T (compa48 16 12 76 rative) 24 t3

Claims (14)

1. A process for producing a mixture of essentially linear and saturated hydrocarbons containing at least 80% by weight C,' hydrocarbons based on all the hydrocarbons formed, from a synthesis gas that is a mixture constituted by hydrogen and oxides of carbon (CO andC02) 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 the lanthanide-actinide groups 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. 0 1 to 60 % for element N.

2. A process according to claim 1 wherein the catalyst further comprises at least one additional element from the element of groups la and Ha.

3. A process according to claim 1 or claim 2 wherein the catalyst further comprises at least one additional element from the group lb and the platinum group.

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, AI, Zr, Sn, Zn, Mg, and Ln, in which Ln is a rare-earth metal.

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. 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. A process according to claim 6, in which the prereduction is performed at 200 to SOTC.

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 3STC, 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. A process according to claim 8, in which working takes place under a pressure of 1 to IOMPa, a temperature of 170 and 30WC, 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. 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.

1:),

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. 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. A process according to claim 1, in which the catalyst is substantially as hereinbefore described in Example 13.

14. A process according to claim described.

1, substantially as hereinbefore