CA1236126A - Manganese - spinel catalysts in co/h.sub.2 olefin synthesis - Google Patents

Abstract

OLEFIN SYNTHESIS

ABSTRACT OF THE DISCLOSURE

Single phase, unsupported, Group IA or IIA
metal salt promoted manganese-containing iron spinel catalysts, having Fe:Mn atomic ratios of 2:1 or above, have been found to be highly active for the selective conversion of CO/H2 to alpha olefins.

Description

~3~

1 BACKGROUND OF THE I~VENTION

2 1. Field of the Invention

3 This invention relates to a Fischer-Tropsch

4 process for selectivity producing low molecular wei~ht

5 alpha-olefins utilizing an unsupported single phase

6 Ee-Mn spinel catalyst promoted with Group IA or IIA

7 metal salt in which the atomic ratio of Fe:Mn is 2:1 or

8 above.

9 2. Brief Description of the Prior ~rt Fischer-Tropsch processes have long been 11 known to produce gaseous and liquid hydrocarbons con-12 taining C2-C4 olefins. Because of the importance of 13 C2-C4 olefins, particularly as feedstocks for the 14 chemical industry, modifications of the Fischer-Tropsch 15 process are constantly being pursued toward the goals 16 of maximizing C2-C4 olefin selectivity with the 17 particular objective of maintaining high catal~st 18 activity and stability under the reaction conditions.
19 The main thrust of the efforts in this area has been in 20 the area of cataIyst formulation.

21 Coprecipitated and/or supported iron-based 22 catalysts, including those containing manganese, ~re 23 known for producing C2-C4 olefins. Examples of 24 disclosures in the art directed to such iron-manganese 25 catalysts and/or alloys include: W.L. vanDijk, et al., 26 Appl. Catal., 2, 273 (1982); Eur. Pat. Appl. 4988~ to 27 ~uhrchemie (1981); H.J. Lehman, 73rd AIChe Meeting 1 Paper #103D; W.D. Deckwer, et al., Chem. In~. Tech., 53 2 (10), 818 (1981); V. Rao and R. Gormley, Hydrocarbon 3 Processing, l , November (1981); H. Kolbel and K.
4 Tillmetz, U.S. Pat. 4,177,203 (1970); EPO Patent Pub-5 lication 0,071,770; U.S. Patent 2,605,275; U.S. Patent 6 2,850,515; Prepr. Div. Pet. Chem. Am~ Chem. Soc. (1978) 7 23(2) pp 513-20; Intersoc. Energy Convers. Eng. Conf.
8 1978, 13(1) pp 482-6; U.S. Patent 4,186,112; EP 49,888;
g React. Kinet. Catal. Lett. 1982, 20(1-2) pp 175-~0;

10 U.S. Patent 2~778,845; Khim. (1) Tekhnol~ Topliv i

11 Masel (Russ.) 10(6) 5-10 (1965); UK Patent Appln.

12 2,050,859 A; German Patent Appln. DT 2919-921; Prace

13 Ustavu Vyzkum Paliv 8, p. 39-81 (1964) (Czech).
_

14 An iron-manganese spinel of the formula,

15 Fe2MnO4, is reported as a catalyst component formed

16 during Fischer-Tropsch synthesis in which a coprecip-

17 itated Fe/Mn oxide catalyst is initially employed in

18 Applied Catalysis 5 (1983) pp. 151-170. However, this

19 and the above cited references do not describe a

20 Fischer-Tropsch hydrocarbon process initially employing

21 an unsupported single phase Fe/Mn spinel catalyst

22 having an Fe:Mn atomic ratio of 2:1 or above and being

23 promoted with a Group IA or IIA metal salt promoter

24 agent.

What is particularly desired in fixed bed 26 Fischer-Tropsch processes are catalysts for selectively 27 producing high levels of C2-C4 olefins and low levels 28 Of methane under the desirable combined conditions of 29 high catalyst activity and stability.

- - ~ ~
~3~2~i 2 It has been found that unsupported single 3 phase iron-manganese spinels containing iron:manganese 4 atomic ratios of 2:1 or above and being preferably 5 promoted with a Group IA or IIA metal salt, preferably 6 being substantially deposited on the surface of said 7 spinel provide desirable catalyst properties in fixed 8 bed Fischer-Tropsch processes. The initial spinels g prior to reduction and carbiding exhibit an X-ray 10 diffraction pattern isostructural with Fe3O4.

11 The subject spinels are prepared in a high 12 temperature solid state sintering reaction in a tem-13 perature range of about 600 to 110nC between the 14 component metal oxides and/or metals and mixtures 15 thereof, in an inert oxygen-free atmosphere or under 16 vacuum. The spinels prepared in this manner can then 17 be treated by surface impregnation or deposition with 18 promoter agents, particularly Group IA and Group IIA
19 metal salts, and particularly, potassium carbonate and 20 potassium sulfate. The resulting iron/potassium atomic 21 ratio is desirably in the range of about 20:1 to 200:1.
22 The promoted catalyst can then be partially reduced by 23 contacting with a hydrogen containing gas and partially 24 carbided in a CO-containing atmosphere before use in

25 the Fischer-Tropsch process. By the terms "partially

26 reduced" and "partially carbided" is meant that the

27 iron "portion" of the spinel remains substantially as

28 the oxide.

1 In accordance with this invention there is 2 provided a hydrocarbon synthesis catalyst composition 3 comprising an unsupported Group IA or IIA metal salt 4 promoted iron-manganese single phase spinel, said 5 spinel having the initial empirical foemula:

6 FexMnyO4 7 wherein x and y are inte~er or decimal values, other 8 than zero, with the proviso that the s~m of x I y is 3 9 and the ratio of x/y is 2:1 or above, said spinel 10 exhibiting a powder X-ray diffraction pattern 11 substantially isostructural with Fe304 and said metal 12 salt being substantially deposited o~ the surface of 13 said spinelO

14 Preferred embodiments of the composition include the parti~.ily reduced and carbided form of the 16 spinel, which is an active Fischer-T~opsch catalyst in 17~fixed bed process for producing low molecular weight 18 olefins.

19 Furthermore, there is provided a process for producing the above-~escribed spinel portion of the 21 composition comprising heating a mixture of iron and 22 manganese as their oxides and/or free metals at 23 elevated temperature in an oxygen free or inert 24 atmosphere for a sufficient time until the resulting oxide mixture exhibits an X-ray diffraction pattern 26 isostructural with Fe3O4.

3~

S~ecifically, and in accordance wi~h ~his invention there i8 erovided a process for syn~hesizing a hydcocarbon mixture containing Cz-C6 olefin~ comp~i~ing the step of contacting a catalyst composition comprised of an unsupported iron-mangane~e spinel, fiaid spinel exhibiting a single spinel pha~e, being isostructural with FE304 as determined by X-ray diffractomet~y.
and pos6es~ing an iron:manganese atomic catio o~ 2:1 to 19:1, 6aid ~pinel being ~urface impregnated or deposited with a potas~ium salt, ehe atomic ~atio of iron:potassium bei~g about 20:1 to 200:1, with a mixture of C0/H2 unde~ proces6 condition6 of pres~ure, space ~elocity (SHSV) and elevated te~perature fo~
time su~f icient to produce said C2-C6 olef ins .

The subject unsupported alkali- or alkaline earth metal salt promoted iron-manganese single phase spinels are new compositions of matter which are iso-structural with Fe~04, as determined by x-ray diffractometry using copper K alpha radiation and exhibit,a single spinel phase. By the term "spinel" is meant a crystal structure whose general stoichiometry corresponds to AB204, where A and B can be the same or different cations. Included within this definition is the commonly found spinel, MgAl204, A and B can have the following cationic charge combinations: A=~2, B=+3, A=+4, s=+2, or A=+6, B=+l. Spinels contain an approx-imately cubic close-packed arrangement of oxygen atoms 1 with 1/8th of the available tetrahedral interstices and 2 1/2 of the octahedral interstices filled, and can 3 exhibit hundreds of different phases. Further descrip-4 tion of the spinel structure can be found in 5 "Struc-tural Inorganic Chemistry "by A. F. Wells, Third 6 Edition, Oxford Press, and the Article "Crystal 7 Chemistry and Some Magnetic Properties of Mixed Metal 8 Oxides with the Spinel Structure" by G. Blasse, 9 Phillips Research Review Supplement, Volume 3, pp 1-30, (1964). By the term "isostructural" is meant crystal-11 lizing in the same general structure type such that the 12 arrangement of the atoms remains very similar with only 13 minor change in unit cell constants, bond energies and 14 angles. By the term "single phase spinel", as used 15 herein, is meant one structural and compositional 16 formula, corresponding to a single spinel material into 17 which all of the metal components are incorporated, and 18 exhibiting one characteristic X-ray diffraction 19 pattern.

The subject iron-manganese spinels generally 21 possesses a BET surface area up to about 5 m2/g, as 22 determined by the well-known BET surface area measure-23 ment technique as described in the reference JACS 60, 24 p.309 (1938) by S. Brunauer, P.H. Emmett, and 25 G. Teller. Preferably, the spinel has a surface area 26 of about 0.1 to 5 m2/g. This range of surface area 27 generally corresponds to a particle size range of about 28 1 to 10 microns.

29 The spinel can be represented by the

30 formula: FexMnyO~, wherein x and y are decimal or

31 integer values, other than zero, and wherein the sum of

32 x plus y is 3, and the ratio of x to y is greater than

33 2:1 or above, and preferably being about 2:1 to 19:1

34 and particularly preferred is where the iron to 1 manganese atomic ratio is about 3:1 to 7:1. The com-2 position can further be comprised of a mixture of 3 single phase spinels, of different iron-manganese 4 atomic ratios.

Representative examples of the various 6 spinels corresponding to the Eormula are 7 Fe2.85Mn0.154r Fe~.625Mn0.3754, Fe2 25Mno 754 8 Fe2.g7MnQ.03O4-.

9 Physical properties in general of these10 subject spinels are similar to those of magnetite and 11 include melting point of above 1400C, and a color of 12 brownish-red.

13 The iron-manganese spinels are used in 14 unsupported form in H2/CO hydrocarbon synthesis.

A Group IA alkali metal or Group IIA
16 alkaline earth metal salt promoter agent is used in 17 the subject composition and can also be used to par-18 ticularly promote olefin formation in the subject 19 process. Representative examples of suitable classes 20 of promoter agents include carbonates, bicarbonates, 21 organic acid and inorganic acid salts e.g. acetates, 22 nitrates, halides, sulfates, and hydroxide salts of 23 Group IA and IIA metals including lithium, sodium, 24 potassium, cesium, rubidium, barium, strontium, mag-25 nesium and the like.

26 Representative examples of specific promoter 27 agents are potassium carbonate, potassium sulfate, 28 potassium bicarbonate, cesium chloride, rubidium 29 nitrate, lithium acetate, potassium hydroxide, and the 30 like. Preferred are the Group IA compounds and a par-31 ticularly preferred promoter agent is potassium ~3~6 1 carbonate. The promoter, if used, is generally prese~t 2 in about a 0.1 to 10 gram-atom ~ of the total gram-3 atoms of metals present. A preferred level of promoter 4 agent is in the range of 1 to 2 gram-atom % of the 5 total gram-atom metal present. In the empirical 6 formulas used herein, the amount of the promoter agent, 7 e.g., potassium, is expressed in terms of gram atom 8 percent based on the total gram-atoms of metals used.
9 Thus, "1 gram-atom percent of potassium signifies the 10 presence of 1 gram-atom of potassium per 100 total gram 11 atoms of combined gram atoms of Fe and Mn. Thus, the 12 symbol "/1% K" as used herein indicates 1 gram-atom 13 percent potassium based on each 100 gram atom of the 14 total gram atom of iron and manganese present.

A particularly preferred spinel compositi~n 16 of the subject invention is Fe2.2sMno 7sO4/1% K. The 17 catalyst spinel in the subject process may also be used 18 in conjunction with a diluent material, one which ai~s 19 in heat transfer and removal from the catalyst be~.
20 Suitable materials include powdered quartz, silicon 21 carbide, powdered borosilicate glass, kieselguhr, 22 zeolites, talc, clays, Group II-VII oxides and rare 23 earth oxides including TiO2, SiO2, A12O3, MgO, La2O3, 24 CeO2, Cr2O3, MnO2 and the like.

The diluent, if used, is generally used in a 26 1:4 to 9:1 diluent/spinel composition weight ratio to 27 the spinel. Preferred is a 1:1 weight ratio.

28 The utility of these spinels is their 29 ability upon subsequent reduction and carbiding to fo~m 30 active catalysts in a fixed bed Fisher-Tropsch process 31 for making C2-C6 olefins from CO/hydrogen.

1 The partially reduced and carbided forms of 2 the above-described spinel are also subjects of this 3 invention.

4 The subject spinel is prepared by a solid 5 state high temperature reaction between (1) the com-6 ponent oxides, iOe. Fe3O4 and Mn3O4l or (2) a mixture 7 of iron metal, manganese oxide and iron oxide, iOe. Fe, 8 Mn3O4 and Fe2O3 or (3) a mixture of manganese metal, 9 iron oxide and manganese oxide, i.e. Mn, Fe3O4, Fe2O3 10 and Mn3O4, or (4) a mixture of iron and manganese 11 metals, iron oxide and manganese oxide, i.e., Fe, Mn, 12 Fe2O3 and Mn3O4, in the empirical formula Eor the 13 composition formula as given above. Preferred is 14 reaction (2) described above. The reaction is con-15 ducted at temperatures in the range of about 600 to 16 1100C and preferably from about 800 to 1000C, in an 17 inert gas, oxygen-free atmosphere or vacuum environ-18 ment. Example of useful inert gases are heliu~, 19 nitrogen, argon, and the like. The solid state hi~h 20 temperature reaction "sintering" should be performed on 21 thoroughly mixed samples of the metal oxides and/or 22 metal and metal oxide mixtures. Preferred method of 23 forming the mixture is by intimate grinding. The 24 sintering reaction should be conducted until an X-ray 25 diffraction pattern indicates a single spinel phase is 26 formed which generally requires about an 8 to 24 hour 27 period and preferably about 12 to 18 hour period.
28 Generally, at the end of each reaction period material 29 is thoroughly ground and mixed and then resubjectea to 30 the high temperature conditions for an additional 1 to 31 5 cycles or until X-ray diffraction reveals the 32 presence of a single spinel phase.

1 Prior to the hydrocarbon synthesis run the 2 iron-manganese spinel is conditioned by treating in a 3 reducing atmosphere at elevated temperature, generally in a temperature range of about 200 to 500C and 5 preferably 350 to 450C. The treatment can be carried 6 out with various reducing gases including hydrogen, 7 hydrogen/CO and the like, and mixtures thereof.
8 Preferably, hydrogen gas, either by itself or in an g inert carrier medium such as helium neon, argon, or 10 nitrogen, is preferably used. The pressure of the 11 reducing gas in this procedure may be in the range of 12 1.5 to 1000 psig and preferably in the range of 15 to 13 150 psig. The reducing gas feed rate may be in the 14 ranqe of 1-10,000 V/V/hr and preferably in the range of 15 10-1000 V/V/hr. A preferred method of totally reducing 16 the Fe-Mn spinel is described in copending S~ (C-1544), 17 in which the spinel is heated with metallic calcium to 18 substantially form Fe Mn alloy after acid leaching.

19 The resulting partially reduced spinel is 20 useful in the subject Fischer-Tropsch process for 21 making C2 to C6 olefins as described herein, after 22 being treated in a suitable carbiding atmosphere.

23 Suitable carbiding atmospheres include CO, 24 CO/H2 and the like, and the atmosphere during CO/~2 25 hydrocarbon synthesis conditions described below. Also, 26 the reduction and carbiding steps can be conducted con-27 currently in CO/H2.

28 Also, a subject of the instant invention is 29 a ~ischer-Tropsch fixed bed process for producing C2-C6 30 olefins by utilizing the treated iron-manganese spinel, 31 described hereinabove ~3g~

1 Although a fixed bed Fischer-Tropsch process 2 is a preferred mode for operating the process, 3 utilizing the catalysts described herein, a slurry type 4 process wherein the catalyst is suspended in a liquid 5 hydrocarbon can also be utilized.

6 The subject fixed bed process utilizes the 7 above-described materials as catalyst, as iron-mang-8 anese spinel, isostructural with Fe3O4, and its reducea g and carbided forms. The reduced and carbided materials 10 are generally made in situ in the apparatus prior to, 11 and during the carrying out of the hydrocarbon syn-12 thesis process. ~ full discussion of the spinel and 13 reduced form materials, their properties and thei~
14 preparation are given hereinabove and need not be re-15 iterated.

16 Prior to the CO/hydrogen hydrocarbon 17 synthesis fixed bed run, the sintered iron-manganese 18 catalyst is generally conditioned in the apparatus by 19 purging with nitrogen to remove reactive oxygen con-20 taining gases and then the temperature is increased to 21 the reaction temperature range. Then the system is 22 generally subjected to a hydrogen treatment for several 23 hours. The pressure and space velocity during this 24 conditioning step are not critical and can be utilized 25 in the range which is actually used during actual 26 hydrocarbon synthesis.

27 Following the reduction step, th~
28 CO/hydrogen feedstream is introduced into the apparatu~
29 catalyst chamber and the pressure, space velocityJ
30 temperature, and hydrogen/CO molar ratio are then 31 adjusted as desired, for hydrocarbon synthesis con-32 ditions. Alternately, the reduction and carbiding 1 steps can be carried out concurrently by contacting the 2 promoted spinel with CO/H2 atmosphere at elevated 3 temperature or under hydrocarbon synthesis conditions.

4 In the process, the hydrogen and CO are used 5 in a molar ratio in the gaseous feedstream of prefer-6 ably about a 0.5 to 2.5 molar H2/CO ratio and prefe-7 rably 1:1 to 2:1 molar ratio. Higher and lower molar 8 ratios may also be used.

9 The temperature in the process is generally 10 in the region of about 200 to 350C and preferably 11 being 250 to 300C.

12 The pressure useful in the process is gen-13 erally conducted in the range of about 50 to 1000 psig 14 and preferably about 100 to 300 psig. Higher æressures 15 can also be used.

16 The space velocity (SHSV) used in the pro-17 cess is generally about 200 to 4000 volume oE gaseous 18 feedstream/per volume of dry catalyst/per hour and is 19 preferably in the range of about 400 to 1200 V/V/hr.
2~ Higher and lower space velocities can also be used.

21 The percent CO conversion obtainable in the 22 subject process while providing substantial quantities 23 of C2-C6 olefins, ranges from about 20 to 98% and 24 preferably above about 30%. Higher and lower ratio 25 percentages of CO conversion may also be utilized.

26 "Total hydrocarbons" produced in the process 27 is related to the selectivity of percent ro conversion 28 to hydrocarbons, being those hydrocarbons from Cl to ~6~6 1 about C~o inclusive, and is generally about 0 to 50 2 percent and higher of the total C0 converted, and the 3 remainder being converted to CO2.

4 The percent total C2-C6 hydrocar~ons of the 5 total hydrocarbons produced, including olefins and 6 paraffins is generally about 20 to 50 wt.% and pre-7 ferably about 40 to 50 wt.%. The weight percent of 8 C2-C6 olefins produced of the C2-C6 total hydrocarbons 9 produced is generally about 50 to 90 wto% and prefer-10 ably above 60 wt.% of the C2-C6 total hydrocarbons.
11 The olefins produced in the process are substantially 12 alpha-olefins.

13 The selectivity to methane based on the 14 amount of CO conversion is about 4 -to 10 weight percent 15 of total hydrocarbons produced. Preferably about 8 16 percent and lower methane is produced in the process.

17 ~s discussed above the percent selectivity 18 to CO2 formation in the process is about 40 to 50 19 percent of CO converted.

The reaction process variables are prefer-21 ably adjusted to minimize CO2 production, minimize 22 methane production, maximize percent CO conversion, and 23 maximize percent C2-C6 olefin selectivity, while 24 achieving activity maintenance in the catalyst syste~.

Generally, this format can be achie~ed i~ a 26 preferred mode of operating the process where the 27 empirical formula of the catalyst used is 28 Fe2~2sMno~75o4/l%K the pretreatment procedure is 29 conducted at 500C, 9:1 H2/N2, 5 5 hrs. 100 psig, 30 500-750 v/v/hr, the CO/hydrogen molar ratio is 1~ he 31 temperature is conducted in the range 270-320C, a~ a ~36~

1 pressure of 150-300 psig, and space velocity 800-1200 2 v/v/hr. By carrying out the above process in the 3 stated variable ranges eEficient activity maintenance ~ and production of C2-C6 olefins can be achieved.

The effluent gases in the process exiting 6 from the reactor may be recycled if desired to -the 7 reactor for further CO/hydrocarbon synthesis.

8 Methods for collecting the products in the g process are known in the art and include distillation, 10 fractional distillation, and the like. Methods for 11 analyzing the product liquid hydrocarbons and gaseous 12 streams are also known in the art and generally include 13 gas chromatography, liquid chromatography, high 14 pressure liquid chromatography and the like.

Apparatus useful in the preferred process is 16 any conventional fixed bed type reactor, being hori-17 zontal or vertical, moving bed, and the like. Other 18 apparatus not specifically described herein will be 19 obvious to one skilled in the art from a reading of 20 this disclosure 21 The following examples are illustration of 22 the best mode of carrying out the claimed invention as 23 contemplated by us and should not be construed as being 24 limiting on the scope and spirit of the i~stant 25 invention.

2 Catalyst Preparation 3 Solid solutions of the composition 4 Fe3_yMnyO4 (where y varies from 0.025 to 2.85 and x as 5 originally defined equals 3-y) were prepared by 6 carefully weighing and thoroughly mixing Mn3O4, Fe2O3 7 and Fe powder (reagent quality or better -Alfa 8 Chemicals Co.) according to the stoichiometry:

9 -3 Mn34 + (-3 - 9 ) Fe23 + (-3 - -9) Fe >Fe3_yMnyO4 The individual spinels were prepared from 11 the following mixtures of starting materials accordin~
12 to the value of "y" as given below in the Table:

14 Catalyst y Fe2O3(9 ) Fe(g.~ Mn3o4(g~) 15 Control 0 21.080 1.84000.00 16 A 0.15 21.853 1.91081.2360 17 B 0.375 20.146 1.76153.0927 18 C 0.75 17.293 1.51196.1946 19 D 1.0 15.3886 1.33798.2668 E 1.5 23.124 2.022124.849 21 F 2.85 1.0646 0.093121.737 22 Each solids mixture was placed into a quartz tube 23 (15 mm i.d., 18mm o.d.) evacuated to 10-3 torr, sealed 24 under vacuum and then heated to 800C for 24 hours. The 25 resulting solids were isolated, thoroughly reground~
26 pelletized and resubjected to the same high temperature ~6~6 l sintering process at 800-1000C for an additional 24 to 2 48 hours. Powder X-ray diffraction analysis was the~
3 conducted to ensure that the material was single phase 4 and isostructural with Fe3O4. The catalyst pellets 5 were then impregnated with aqueous solutions of K2CO3 6 or K2SO~ to achieve a potassium loading level of l-lO
7 gm atom percent K per gm atom of combined metal, and 8 then dried, pelletized crushed and sieved to 10-4 9 mesh.

The resulting measured BET nitrogen surface 11 area of each Fe-Mn spinel was measured and the results 12 given below.

14 Spinel Empirical Formula Surface Area ~m2/g) 15 Control Fe3O4/1% K 0.27 16 A Ee2.85MnO.15O4/1% K 0.36 17 B Fe2.625Mn0.3754/l% K 0.28 18 C Fe2,25Mno.75o4/l% K 0.21 19 D Fe2MnO4/1~ K 0.25 E Fel,5Mnl.5O4/1% K 0.19 21 F Fe,lsMn2.8sO4/l% K 0.28 22 It is pointed out that Spinels E and F are 23 comparative examples.

About 8.8 cc. of the above-prepared spinel C
2~ (where x=0.75) was placed into an upflow 304 SS stainl-27 less steel reactor (0.51 inch I.D.) and pretreated with 28 a gaseous stream of H2 and (helium, nitrogen) in a 1~3 29 volume ratio at lO0 psig at 500C and 600 v/v/hr.

~2:3~26 l (SHSV) for 5.5 hours. Then the pretreated catalyst was 2 contacted with a 1:1 H2:CO feedstream in helium at 300 3 psig, at 305C, and a space velocity of lO00 v/v/hr 4 (SHSC) for one or more hours and the products 5 collected and analyzed by gas chromotography versus 6 known standards. The results are listed below in Table 7 III. Unless otherwise indicated, the listed tempera-8 tures in the process are furnace temperatures.

9 A Comparative run was made under substan-lO tially the same conditions using a Fe3O4/1%K catalys-t ll as prepared by the procedure described above in Example 12 l).

~3~

2 Catalyst Fe84/1% KFe2.25Mn.75o4/l~ K

3 Bed Temp tC) 350 305 4 H2/CO feed 1.0 1.0 5 SHSV (v/v/hr) 1000 1000 6 Pressure (psig) 300 300 7 % CO Conversion 87 92 8 to C2 9 to HC's 38 48 10 Wt.% Selectivity (CO2-free basis) 11 CH4 19.0 9.6 12 C2 5.7 8.6 13 c3= 15.9 14.9 14 c4= 8.6 10.2 15 Cs= 6.0 16 C2-C5 15.4 7.0 17 C6=-C20 14.9 20.1 18 C6-C20 10.4 15.7 19 C21+ 5.1 7.9 As is seen from the data, the Mn-containing 21 spinel catalyst provides greater activity, lower meth-22 ane and higher C2-Cs alpha-olefin selectivity than the 23 all iron analg-Catalyst D, as prepared by the proceduLe 26 outlined in Example 1, where y = 1.0, was promoted with 27 1 gm.-atom ~ K as K2CO3 or K2SO4. Samples of 8.8 cc of 28 the catalysts were pretreated with H2 at 100 psig, 600 ;

1 v/v/hr and maintained at 500C for 5.5 hr. Then, CO
2 hydrogenation conditions were employed at: 300C, 1:1 3 H2/CO, SHSV of 1000 v/v/hr and 300 psig in the tubular 4 upflow 304 SS reactor described in Example 2. Results 5 are provided in Table IV.

7 Performance of ~e2MnO4/1~ K
8 As a Function of Potassium Promoter 9 Promoter K2CO3 K2SO4 10 ~ CO ConversiOn94.4 96.3 11 to CO2 42.0 41.0 12 to HC's 52.4 55.3 13 Wt.% Selectivity 14 CH4 6.6 C2=-C6 18.5 35.9 16 C2-C6 4.8 5.6 17 c7+ 6g.0 51.9 _ 18 Conditions: 300C, 1:1 H2:CO, 1000 v/v/hr., 300 psig 19 As seen in the above results, the use of 20 K2SO4 as a promoter leads to higher selectivity to 21 alpha-olefins. (See also W.L. Van Dijk et al., Applied 22 Catalysis, 2 (1982) pp. 273-288).

24 Catalysts prepared by the procedure outlined 25 in Example 1, where y = C.15, 0.75, 1.0 and 2.85, with 26 1~ wt. K as K2CO3 employed as a promoter were pretrea-27 ted according to the procedure described in Example 2 28 and then subjected to CO hydrogenation conditions:

- 2n -l 270C, 0.66:1 H2:CO, SHSV of lO00 v/v/hr and 300 psig 2 in the tubular 304 SS upflow reactor described in 3 Example 2 for 12 hours. Results are provided in Table 4 V.

TABLE V

6 Per~ormance of Fe3_yMnyO4/1% K
7 as a Function of Fe:Mn Ratio 8 Y= 0.15 0.75 1.0 2.85 9 Fe:Mn 19 3 2 0.05 lO % CO Conversion80.0 89.~ 38.9 <5.0 ll to CO2 32.0 35.0 18.9 NAa 12 to HC's 48.0 54.1 20.0 NA

13 Wt.% Select 14 CH4 6.5 4.3 5.0 NA
15 C2 -C6 22.8 19.2 32.2 NA
16 C2-C6~ 4.8 3~2 7.8 NA
17 C7+ 65.9 73.3 55.0 NA

18 Conditions: 270C, 0.66:1 H2:CO, 1000 v/v/hr, 300 19 psig.
aNot available 21 As seen in the above results, catalys-ts with 22 an Fe:Mn atomic ratio > 2.0 give good activity and 23 selectivity to alpha-olefin although catalysts with 24 Fe:Mn > 2.0 exhibit diminished activity relative to 25 more iron rich analogs.

Claims (15)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Specifically, and in accordance with this invention there is provided a process for synthesizing a hydrocarbon mixture containing C2-C6 olefins comprising the step of contacting a catalyst composition comprised of an unsupported iron-manganese spinel, said spinel exhibiting a single spinel phase, being isostructural with FE3O4 as determined by X-ray diffracometry, and possessing an iron:manganese atomic ratio of 2:1 to 19:1, said spinel being surface impregnated or deposited with a potassium salt, the atomic ratio of iron:potassium being about 20:1 to 200:1, with a mixture of CO/H2 under process conditions of pressure, space velocity (SHSV) and elevated temperature for a time sufficient to produce said C2-C6 olefins.

2. The process of claim 1 wherein said hydrogen and CO are present in a H2/CO ratio of about 0.5 to 2.5.

3. The process of claim 1 wherein said temperature is in a range of about 200 to 350°C.

4. The process of claim 1 wherein said pressure is in a range of about 50 to 1000 psig.

5. The process of claim 1 wherein said space velocity is in the range of about 200 to 4000 V/V/hr.

6. The process of claim 1 wherein said spinel is of the formula: FexMnyO4, wherein x and y are integer or decimal values other than zero, the sum of x+y is 3 and the ratio of x/y is 2:1-19:1.

7. The process of claim 6 wherein the ratio x/y is 3:1 to 7:1.

8. The process of claim 6 wherein said spinel is of the formula: Fe2.85Mn0.15O4, Fe2.625Mn0.375O4, Fe2.25Mn0.75O4, or FE2.97Mn0.03O4.

9. The process of claim 1 wherein said catalyst is further in admixture with a diluent.

10. The process of claim 9 wherein said diluent is selected from powdered quartz, porous silica. kieselguhr, talc, powered borosilicate glass, TiO2, SiO2. Al2O3, clays, zeolites, MgO, La2O3, Cr2O3, MnO2, and the like.

11. The process of claim 1 wherein said potassium salt is selected from potassium bicarbonate, potassium carbonate, potassium sulfate, and potassium hydroxide.

12. The process of claim 11 wherein said promoter agent is potassium carbonate or potassium sulfate.

13. The process of claim 1 wherein said spinel is partially reduced and carbided in situ in the process.

14. The process of claim 1 wherein said product hydrocarbon mixture contains 20 wt.% and above C2-C6 hydrocarbons of the total weight of hydrocarbons produced.

15. The process of claim 14 wherein said C2-C6 hydrocarbons contains C2-C6 olefins in above 50 wt.% of the total C2-C6 hydrocarbons.