I n d . E n g . C h e m . Res. 1989, 28, 150-154
150
Effects of Vanadium and Zinc Promotion on the Olefin Selectivity of Iron Fischer-Tropsch Catalysts Mehmet Saglam Engineering Faculty, Department of Chemistry, Ege University, Bornova, Izmir, Turkey
The aim in most of the studies on Fischer-Tropsch synthesis has been the selective production of olefins, which are the raw materials of petrochemical industry. In this study, the effects of V and Zn addition, separately or together in the form of their oxides, to Fe catalysts obtained through precipitation on the olefin selectivity of the catalysts have been investigated. The experiments have been done in a fixed-bed reactor a t different temperatures and pressures with various ratios of H2/C0. The addition of V separately (catalyst 2) or together with Zn (catalyst 1)has greatly increased the olefin selectivity of Fe catalyst. So the amount of olefin in hydrocarbon fractions has reached over 80%. Besides, the cy-olefin parts in olefin fractions have gone over 90%. But the addition of Zn separately has been less effective on the olefin selectivity of the catalyst. Recently, production methods of chemical and energy sources depending on coal have again been important. The most important of these methods is the Fischer-Tropsch (F-T) synthesis. By use of this method, which was found in 1926, aliphatic hydrocarbons can be synthesized from the synthesis of gas (CO + H2). During WWII, by use of this method in the US and Germany, liquid fuels such as gasoline and motorine were produced from coal. Since 1955, the same production method has been carried out in the Republic of South Africa (Schulz and Cronje, 1978; Kolbel and Ralek, 1977; Hoogendoorn, 1982). However, today, as a result of changing economic and political conditions, by use of F-T synthesis, work has been aimed at producing small molecule olefins (such as ethylene, propylene, butenes-essential raw materials of petrochemical industry) and long-chain linear a-olefins such as C5-CI2 and C6-CI2 paraffins, which are materials of a cracking process (Kuhn and Elstner, 1977). For this purpose, extensive worked on the modification of known catalysts (such as Fe, Co, Ni, and Ru), which are effective in F-T synthesis, has been done, and these studies are still continuing. In most of the studies in the literature, work has been focused on studies with iron catalysts, having great industrial importance, and for the above-mentioned purposes, some transition metal oxides (such as Mn, Ti, Cr, V, Zn, and Zr) have been used to modify these catalysts (Gokgebay, 1982; Satterfield and Stenger, 1984; Kolbel and Tillmetz, 1976; Bussemeier et al., 1976; Gokgebay and Schulz, 1983; Saglam, 1983a,b; Bloss et al., 1986). It has been reported that the most effective metal oxides among those experimented was Mn (Gokgebay, 1982; Satterfield and Stenger, 1984; Kolbel and Tillmetz, 1976; Gokgebay and Schulz, 1983; Bloss et al., 1986), and the most suitable results were obtained with catalysts in which the ratio of Mn to Fe was 1011. On the other hand, it has been reported in one of our papers that considerably high olefin selectivity was reached in iron catalysts containing l.OFe, 2.4Mn, and 3.7Ti (Saglam, 1983a). There are not many precedents in the literature regarding the effect of the transition elements such as V and Zn on the selectivity of the iron catalyst. In a patented study, the catalyst was prepared by sinterization at 1050 "C by mixing Fe203,V206,ZnO, and KzC03containing 1.OFe + 0.7V + O.1ZnO + 0.04K20 by weight (Bussemeier et al., 1976). It was found in the synthesis products that the ratio of C1-C4 hydrocarbons was 84.3% and the ratio of C2-C4 olefins was 59.1%, and it was concluded that this catalyst was very suitable for the synthesis of lower molecular weight olefins.
Table I. Compositions of the Catalysts composition catalyst (by wt), g 1 lOOFe + 27Zn 68V 32K,O + 50Aerosil-200 + lOAl,O, 2 lOOFe + 66V l l K 2 0 50Aerosil-200 + 10A1203 3 lOOFe + 276Zn + 1.2K20 + 50Aerosil-200 + 10Al,03
+
+
+
+
'The amount of Fe in 1 g of catalyst. Zn in 1 g of catalyst.
aPP. gravity, M ~ ~ l M (l F ~ + M ~ , ~ g/cm3 mg mg 0.51 285 554 0.32
265
439
0.25
83
548
The amount of Fe
+V+
In another study, two catalysts were prepared by the precipitation of NH4V03and metal nitrates containing 1Fe + 2Zn + 6V or 1Fe + 6V, by weight (Gokgebay and Schulz, 1983). It was concluded that the first catalyst was more suitable for this purpose, and it carried out the synthesis of higher molecular weight a-olefins besides C&4 olefins. It was found that the amount of olefins in the Clo fraction obtained with catalyst was 81%,and 90% of these olefins was in the form of a-olefin. However, the amounts in the products obtained with catalyst 2, for the Cl0 fraction, were lower values, 45% and 4070, respectively. Since the chemical analyses of these catalysts prepared were not given, the comparison of the results with the first class of catalysts has not been possible. In the preparation of the catalyst by precipitation, it is not possible to obtain a Fe/V ratio of 1/6. In the published Ph.D. thesis of GokGebay (1982), it was mentioned that the composition of the catalyst was 1Fe + 0.64V instead of 1Fe + 6V as given in the above literature. This discrepancy is due to the conversion of metallic metavanadates which are less soluble metal hydroxides formed during the precipitation by K2C03solution around pH 7 and the entrance of the metavanadate ion to the solution. In this case, the catalyst-preparing conditions have a profound effect on the composition and the selectivity of catalyst. In this study, for the above-mentioned aim, the modification of Fe precipitator catalyst with V and Zn has been tested. The effects of the addition Zn and V, separately or together, on the olefin and cy-olefin selectivities-at different reaction conditions-of the catalyst have been investigated. Experimental Section The compositions of the catalysts prepared are given in Table I. The values given for Fe, Zn, V, and K 2 0 are obtained by chemical analysis. The values for AlZO3and
0888-5885/89/2628-0150$01.50/0 0 1989 American Chemical Society
Ind. Eng. Chem. Res., Vol. 28, No. 2, 1989 151 Table 11. Activities and Selectivities of Catalyst 1 for Varying Conditions of Reaction run 1 2 3 280 320 temp, "C 250 pressure, MPa 1 1 1 V
Hz/COratio cco--c,+, % CHz+CO~ %
r distribution of hydrocarbons in products of synthesis on C no., C %
C1 c2 c3 c4 c5 c6 c7 C8+
498 1.72 6.5 7.6 1.6
543 1.72 20.1 24.1 3.9
589 1.72 38.1 44.4 8.0
4 280 1 495 0.96 7.2 11.7 1.8
5 280 3 609 1.78 34.6 36.5 6.2
6 280 6 477 1.78 37.4 41.4 5.3
7 280 9 469 1.78 39.4 45.2 4.2
14.4 7.1 8.4 7.9 7.5 7.1 6.8 37.7
16.3 7.1 9.0 11.2 9.5 9.9 8.6 24.5
12.8 10.8 13.2 10.1 8.4 6.4 5.3 23.9
15.8 11.7 10.5 9.8 7.0 7.1 6.0 25.3
14.8 11.3 15.0 11.2 9.1 7.9 6.3 19.5
13.1 8.8 13.9 15.8 9.1 8.5 6.5 19.6
10.6 8.5 13.2 10.0 8.6 7.6 7.6 27.7
77.6 78.4 78.5 77.5 75.9 74.1 74.8 73.5 73.4 68.7 67.7 58.5 53.5
78.5 81.4 80.5 78.1 77.5 75.2 74.1 75.5 75.5 71.3 67.3 67.5 67.5
77.4 83.5 81.5 81.0 80.7 83.3 81.2 80.4 79.5 79.0 78.5 71.8 70.1
74.5 77.5 77.4 75.9 77.2 79.8 75.6 79.4 77.2 74.9 71.2 68.8 60.2
74.5 78.7 78.2 74.1 74.0 75.6 73.8 71.1 72.6 67.1 60.9 62.0 60.8
73.8 69.9 68.7 68.9 68.7 70.7 70.6 67.5 68.5 62.3 60.0 49.5 43.4
74.3 72.5 71.7 71.9 71.5 73.4 71.5 70.0 71.6 70.7 65.5 55.0 45.8
96.3 95.6 95.6 95.5 94.3 89.0 94.5 87.3 92.8 92.5 93.1 3.1 18.4 37.9
97.4 95.2 96.3 95.7 95.4 95.5 96.6 95.7 95.4 95.4 91.3 3.9 21.9 42.0
97.0 94.4 96.4 95.0 94.7 95.6 94.1 94.5 93.5 94.2 91.6 9.1 27.6 41.9
97.1 94.9 96.1 94.2 96.0 93.5 94.8 94.0 92.6 93.1 90.8 6.8 24.5 29.8
96.1 94.7 94.5 93.6 93.5 92.7 93.8 93.6 93.7 92.8 93.7 4.9 29.0 28.7
94.2 94.1 90.9 84.2 80.6 81.1 79.2 80.3 83.8 83.5 77.8 4.7 27.1 24.5
94.1 96.4 91.6 66.6 64.9 64.8 66.1 65.0 65.2 68.0 64.7 6.2 23.1 25.9
distribution of olefins in products of synthesis on C no., mol % c2 c3 c4
c5
c11
ClZ c13
c14
distribution of a-olefins in olefin fraction on C no., mol %
ClO c n 11 L12 c13 c14
alcohol selectivity, C % C2-Clolefins, C 70 linear a-olefins, C,+, C %
Aerosil-200 are taken during the preparation of catalysts. The catalysts in Table I are prepared as follows. The aqueous solutions of Fe(N03)3.9H20,A1(N03)3.9H20,Zn(N03)2-4H20, and NH4V03a t 70 "C are mixed with Aerosil-200 (Degussa). Precipitation is completed by adding 2 M K2C03to this solution until the pH is 7. After the precipitate is filtered out, the filtrate is washed with hot water until it contains no NO, ions. Then, the precipitate is dried at 110 "C. The experiments made with these catalysts are carried out in a laboratory-scale apparatus, operating with a fixed-bed reactor. The reactor having an interior diameter of 11mm, an outer diameter of 50 mm, and a height of 200 mm is made of stainless steel (GokGebay, 1982). The catalyst is located between the two quartz layers so as to be in the middle of the reactor. The reactor is placed within a ceramic tube and is heated by the resistance wires coiled around the tube. A three-way ventile heated to 200 "C follows the reactor. Then comes a hot separator heated a t 180 "C which allows the high molecular weight hydrocarbons to separate. The sample-collecting apparatus, which is developed by Schulz (1983),is heated to 160-170 "C, and the samples needed for gas chromatographic studies can be taken into the evacuated bulbs which are 5 cm long and 8 mm in diameter. After the sample is taken, the capillary end of the bulb is closed by melting. In the cooling trap which follows this apparatus, the con-
densing products a t 0 "C are collected. This is also followed by another sample-collecting apparatus for gas and a gasmeter. The catalyst having a particle size of 0.25-0.4 mm, after being located in the reactor, is activated at 370 "C by H2. After this operation, the reactor temperature is lowered to the operating temperature, and the synthesis is then ready to start by synthesis gas. The synthesis gas, before it is fed to the reactor, is purified by passing over zeolite and BTS (BASF product) catalysts. With the catalysts in Table I at various reaction temperatures, pressures, and synthesis gas compositions, the change in the olefin selectivity is studied. The compositions of the products which are formed in the syntheses at all these different conditions are determined by studying the samples, which are taken into the bulbs, using capillary gas chromatography. For the compositions of the samples in the bulbs, there might be Hz, N2, CO, COz, HzO, saturated and unsaturated hydroand low molecular weight alcohols carbons from C1to C20, up to hexanol. Studies have been made in a Perkin-Elmer F-22 model gas chromatography possessing a FID detector. The separation is accomplished in the methylsilicon-quartz capillary column of 50 m length and 0.2 mm interior diameter. In order to achieve a good separation, the operation is started at a coloumn temperature of -70 "C, and the tem-
152 Ind. Eng. Chem. Res., Vol. 28, No. 2, 1989 Table 111. Activities and Selectivities of Catalyst 2 for Varying Conditions of Reaction run 1 2 3 temp, "C 250 220 280 pressure, MPa 1 1 1 U 550 532 673 H,/CO ratio 2.07 2.07 2.07 1.7 10.4 44.9 CCO-C1+P 770 2.2 12.8 55.2 CHz+CO~ % r 1.7 10.8 55.6 distribution of hydrocarbons in products of synthesis on C no., C % 14.4 12.7 27.7 Cl 12.7 10.6 14.2 c2 15.6 12.9 17.0 c3 10.4 11.5 11.5 c4 7.2 10.9 8.5 c5 6.4 7.2 6.4 c6 5.6 5.7 3.8 C7 19.2 23.3 9.6 C8+ distribution of olefins in products of synthesis on C no., mol % 69.9 86.3 65.2 76.9 86.5 71.0 73.2 85.3 70.4 70.8 85.0 69.6 66.5 84.2 68.6 70.3 85.5 67.5 68.3 84.4 66.2 62.8 83.7 63.3 62.4 83.8 58.2 CIO 55.1 77.6 51.0 c11 51.0 75.2 45.3 Cl2 45.2 66.4 39.3 Cl3 43.0 54.5 35.8 c14 distribution of a-olefins in olefin fraction on C no., mol % 94.9 93.5 85.8 96.2 91.3 80.6 94.7 90.8 82.2 92.4 90.6 78.1 88.6 70.7 90.0 89.3 81.3 65.8 88.1 84.0 60.0 87.5 78.8 56.0 74.8 88.6 50.0 69.2 85.5 48.6 c13 70.4 86.9 45.3 C14 alcohol selectivity, C % 5.2 8.5 1.3 28.5 C2-C4 olefins, C % 30.4 29.4 linear a-olefins, C,+, C % 20.5 32.4 14.0
perature is increased to 200 "C regularly. The bulb containing the synthesis products is broken in a bulb breaker; then its contents are carried to a cooling trap which is cooled by liquid air and are kept here at -196 "C by condensing. After a definite period, the products are fed to the capillary column by immersing the trap in an oil bath at 150 "C. Studying the chromatogram obtained, the peak areas of products are determined by an electronic integrator. Only the CHI amount is determined by gas analysis. The gas evolving from the synthesis apparatus contains Hz, CO, Nz, and CHI determined by a Janac gas analyzer; the COz amount is determined by an Orsat apparatus.
Results and Discussion The total results relating to the effects of reaction pressure and temperature and the synthesis gas composition upon the activity and selectivity of catalysts are shown in Table I1 for catalyst 1, in Table I11 for catalyst 2, and in Table IV for catalyst 3. Elevating the reaction pressure from 1 MPa to 3,6, or 9 MPa increased the total yield of products. For catalyst 2, for example, when the reaction pressure was elevated from 1 to 9 MPa, the conversion of the products (CH,+CO) rose from 12.8% to 43.8%. The conversion of CO to organic substances ( Cco-cl+) also showed an increase.
4 250
9.7
5 250 3 581 2.07 22.7 24.5 18.4
6 250 6 559 2.07 36.2 38.7 28.9
7 250 9 534 2.07 42.2 43.8 31.7
15.7 12.1 12.9 12.2 8.3 7.4 5.9 8.1
15.6 9.3 13.9 12.3 7.2 6.4 5.2 24.6
17.7 11.5 14.9 11.5 8.4 6.6 5.6 17.0
16.1 13.5 13.0 11.0 7.9 5.9 4.7 17.2
80.5 88.7 86.4 85.9 85.9 84.8 83.7 84.3 79.0 72.0 65.0 59.6 58.5
72.2 78.6 78.5 76.8 78.5 80.1 78.4 78.2 75.4 75.9 72.1 63.8 59.9
46.4 60.0 60.4 59.5 58.6 60.5 62.1 60.9 58.4 53.0 51.2 43.7 38.5
42.1 57.0 56.3 56.8 55.1 59.0 59.2 57.7 55.2 51.0 46.6 40.6 33.2
95.8 94.1 94.2 93.7 91.5 90.8 88.5 87.0 86.9 86.5 87.1 7.4 31.7 27.9
94.6 93.3 92.7 88.4 88.3 88.5 87.8 90.0 91.6 86.8 85.9 5.5 27.3 28.6
89.5 88.5 81.2 85.5 83.2 80.3 80.2 82.4 77.3 80.9 77.2 6.8 21.2 17.2
88.6 88.0 87.6 83.5 80.6 78.0 76.7 78.5 14.7 71.4 74.0 10.7 19.3 15.4
1
512 1.02 7.0 11.1
The elevation of the reaction temperature also increased the activities of the catalysts. The increase of the CO amount in the synthesis gas lowered the activities of the catalysts. The hydrocarbons that are formed in the F-T syntheses have a characteristic distribution, according to the carbon number in the molecule (Schulz, 1977). As for CHI, generally when the carbon number in the hydrocarbon molecule increases, a regular lowering is expected in the formation of the hydrocarbon. However, after a noticable typical lowering in the Cz fraction, an important increase is observed in the C3 fraction. This situation may be a result of the capability of forming higher molecules of CzH4 in the C2 fraction, by undergoing the secondary hydrogenation reaction under the synthesis conditions (Schulz, 1977). After the increases observed in C3, C4,and C5,there is a regular decrease in the amount of higher molecular weight hydrocarbons. This characteristic distribution is observed under all the synthesis conditions. Also the distributions of olefins and a-olefins are shown in Tables 11-IV. It is known that olefins have also shown a characteristic distribution according to the carbon number in the molecule F-T syntheses. The olefin content, here, after it reached a minimum amount in the C2 fraction and a maximum in the C3 and C4 fractions has lowered in higher molecules. This distribution form is originated from the
Ind. Eng. Chem. Res., Vol. 28, No. 2, 1989 153 Table IV. Activities and Selectivities of Catalyst 3 for Varying Conditions of Reaction run 1 2 3 220 temp, O C 280 250 pressure, MPa 1 1 1 0
H d C O ratio CCo-Cl+, % CHa+CO, %
r distribution of hydrocarbons in products of synthesis on C no., C % C1
CZ c3 c4 c6
c6
c7 C8+
distribution of olefins in products of synthesis on C no., mol % C2 c3 c 4
c5 c6 CI
C* C, ClO c11 * L12 c13 c14
59 1 1.79 9.5 11.6 7.3
570 1.79 24.4 28.7 14.2
555 1.79 32.4 37.9 27.5
4 250 3 557 1.79 26.0 30.8 17.4
5 250 6 529 1.79 29.5 34.2 20.3
6 250 1 557 0.96 7.6 13.8 8.0
7" 254 1 594 2.09 27.8 39.8 3.16
13.8 11.7 13.9 11.4 10.4 7.7 4.9 16.5
15.4 11.9 15.8 13.5 10.4 7.1 4.9 14.3
17.7 12.8 16.4 13.8 11.4 6.5 4.9 10.7
20.1 12.6 16.6 11.0 10.4 5.6 4.3 9.8
19.7 12.0 17.4 12.0 8.5 5.4 3.9 9.4
24.2 14.5 15.6 10.8 5.8 4.3 3.1 10.0
21.2 12.5 17.5 12.3
28.8 61.3 72.5 72.5 54.7 48.9 38.7 38.9 35.0 27.8 24.3 18.8 22.4
18.1 54.5 63.8 66.5 60.4 54.1 47.9 43.9 41.8 34.5 28.9 23.9 19.9
15.3 53.4 52.5 52.2 48.4 43.0 38.0 35.0 33.8 30.5 26.4 21.2 18.1
16.7 48.3 56.2 55.4 48.5 45.9 39.9 37.8 33.7 24.0 23.5 17.7 17.7
12.9 42.0 49.1 52.2 46.0 41.1 34.3 28.9 26.1 22.3 18.8 13.8 15.7
17.0 49.3 66.9 66.3 55.7 50.4 44.0 40.9 38.0 33.6 28.1 25.1 25.7
6.7 37.6 53.4
55.0 61.9 41.5 33.7 31.6 29.6 24.6 14.3 23.5 22.5 18.4 9.7 20.8 8.5
41.0 31.4 24.0 22.6 15.5 17.6 17.6 15.7 21.5 16.5 17.0 6.7 19.4 4.7
40.0 30.8 22.2 20.1 18.6 17.2 16.5 16.4 16.3 16.0 15.3 5.8 18.0 3.6
44.2 49.8 38.3 31.8 21.7 16.0 21.1 17.1 21.9 18.2 21.1 9.6 16.3 5.1
44.7 54.3 39.9 36.0 25.2 18.9 21.6 16.5 15.6 19.8 20.8 11.7 14.8 4.5
50.8 44.1 35.8 25.4 20.5 20.0 25.6 16.7 15.8 21.3 21.3 11.7 17.4 3.2
27.6
44.6
15.5
16.1
distribution of a-olefins in olefin fraction on C no., mol % c4
c5 c6
C,
ClO Cll
ClZ c13 c14
alcohol selectivity, C % C2-C4 olefins, C % linear a-olefins, C,+, C % a
13.6
9.5
9.0 2.8 14.0
Gokqebay, 1982.
olefins formed by primary reactions undergoing secondary hydrogenation reactions (GokCebay, 1982). As a matter of fact, it is observed that the secondary hydrogenation is high in ethylene, but it is low in the C3 and C4olefins (Parsche, 1978). The occurrence of this secondary hydrogenation reaction is increased in the higher molecular weight olefines. From the results in Tables 11-IV, it is clearly seen that the primary olefin selectivity of catalysts 1and 2 was very high, and the secondary hydrogenation reactions of the above-mentioned olefins were decreased significantly. It is assumed that there were two kinds of active centers on the unmodified catalyst surface used in the F-T synthesis. While the synthesis reactions take place in one of these centers, the hydrogenation of olefins and the isomerization of double bonds occur in the other center (GokGebay, 1982). At this point, with the addition of V and Zn, separately or together, in the form of their oxides, it has been possible to decrease of the secondary reactions observed after the synthesis reactions. The results relating to an unmodified Fe precipitator catalyst (100Fe + 50Aerosil-200 + 10Al,03 + 0.3KzO), which is mentioned in the literature and which was obtained according to the production process applied in this study, are given in Table IV for the purpose of comparison (GokGebay, 1982).
Although the olefin selectivity is very low in the Fe catalyst not being modified with transition metal oxides, it is remarkably increased by adding V, alone or together with Zn, to the catalyst. The addition of Zn alone has created less effectiveness (Table IV). Up to the Clo fraction, the amounts of the olefin in catalysts 1 and 2 are unchanged, and the olefins do not undergo secondary reactions. For example, if the olefin amounts in the Cz fraction are 78.5% for catalyst 1 and 86.3% for catalyst 2, they are decreased to the values 75.5% and 83.8%, respectively, in the Clo fraction. The olefin selectivities obtained with these two catalysts are on the same level with those obtained with Mn, which is said in the literature to be the most effective transition metal for increasing the olefin selectivity (Gokgebay, 1982; Kolbel and Tillmetz, 1976; Bussemeier et al., 1976; GokCebay and Schulz, 1983). The increase of reaction temperature and the amount of CO in the composition of the synthesis gas makes no significant change in the olefin selectivity; however, the increase in the reaction pressure remarkably makes the olefin selectivity lower. Otherwise, most what is formed of the olefins which are formed with catalysts 1 and 2 at the reaction temperature of 250 "C, at the reaction pressure of 1 MPa, and a t the composition of synthesis gas possessing a Hz/CO ratio of nearly 2 is a double bond at the position of hydrocarbon chain (Tables I1 and 111). At this
154
Ind. Eng. Chem. Res., Vol. 28, No. 2, 1989
point, the addition of V, alone or together with Zn, has inhibited the secondary hydrogenation of double bonds, as well as the isomerization of the double bond which is formed at the a position. However, it was determined that over 87% of the formed olefins was in the form of a-olefins. In catalyst 3, the amount of a-olefin, which is found to be 40% a-olefins, decreased more than 20% with increasing number of carbon. This partition of a-olefin is higher than the a-olefin partition given by the unmodified Fe catalyst. While the increase in the reaction pressure reduced selectivities of a-olefins with catalysts 1 and 2, it did not make an important (or considerable) change with catalyst 3. The increase of the reaction temperature did not change the selectivity of a-olefins with catalyst 1. At the different temperatures experimented, a-olefin selectivity to C14 was over 90%. With catalysts 2 and 3, this selectivity decreased to some extent with increasing temperature; on the other hand, an increasing amount of CO in the synthesis gas increased the a-olefin selectivity in the catalysts. The composition of the catalyst which was mentioned in the introduction, obtained by sinterization (Biissemeier et al., 1976),is similar to that of catalyst 1 in terms of the ratio of Fe and V. There is an important difference in Zn and K 2 0 contents. These differences of composition and preparation technique have increased the selectivity of the higher molecular weight a-olefins to C14, whereas the lower molecular weight olefin selectivity of catalyst 1 has not changed. It was seen that catalyst 1has similar olefin and a-olefin selectivities with the catalyst that was prepared by precipitation (GokCebay and Schulz, 1983). This case shows that these two catalysts are similar to each other in terms of chemical composition and other properties. On the other hand, the catalyst prepared (1Fe + 0.12Zn + 0.71V + 0.38K20 ratio) by saturation of K2C03of the precipitate, which was precipitated and washed as metavanadates from Fe3+and Zn2+,showed again a high ratio of selectivity of olefin and a-olefin (Saglam, 1983b). Catalyst 2 is similar to the catalyst mentioned in the literature in terms of the chemical composition and preparation techniques (GokCebay, 1982). But it has been found that olefin and a-olefin selectivities of catalyst 2 were much better than with catalyst 1. We can say that this case is due to the differences in precipitation conditions and K 2 0 content. There is no example in the literature about the modification of this kind of Fe catalyst with only Zn. But it was observed that the olefin and a-olefin selectivities of the catalyst were better than that of the unmodified Fe catalyst. However, it is not possible to conclude that this result-obtained with catalyst 3-is satisfactory. As a result, the addition of V and Zn to Fe catalyst considerably increased olefin and a-olefin selectivities. It is possible to say that these results, obtained with catalysts 1 and 2, indicate that we can approach the recent aim of the F-T synthesis.
Acknowledgment The author thanks DAAD for a scholarship and Prof. Dr. H. Schulz for his help during this study at the Institute of Engler Bunte of Karlsruhe University of West Germany. Nomenclature flowing rate of gas, L/(L of catalyst-h) = conversion of CO to C,+, % CH2+C0 = conversion of (H2 + CO) to total product r = specific reaction rate, r,,,, mL of Fe/(g.min) u =
Cco-cl+
Registry No. Fe, 7439-89-6; V, 7440-62-2; Zn, 7440-66-6; K20, 7440-09-7; CO, 630-08-0.
Literature Cited Bloss, E.; Gross, B.; Hubert, H. J.; Schulz, H.; Tillmetz, K. D. Untersuchungen uber Katalysatoren, Selektivitaten und Reaktoren bei der Fischer-Tropsch-Synthese.Erdol Kohle, Erdgas, Petrochem. 1986,39, 425. Bussemeier, B.; Frohring, C. D.; Horn, G.; Kluy, W. Verfahren zur Herstellung ungesattigter Kohlenwasserstoffe. DE 25 18 964 B 2, 1976. GokGebay, H:, SelectivitAtslenkungbei der Fischer-Tropsch Synthese mit eisen Ubergangsmetaloxid-katalysatorenFortschr. Ber. VDIZ. Reihe Verfahrenstechnik, Reihe 3, Vol. 65, 1982. Gokcebay, H.; Schulz, H. Katalysator und Verfahren zur Herstellung von Olefinen-insbesondere linearen a-olefinen aus Synthesegas. DE 31 30 988 Al, 1983. Hoogendoorn, J. C. Producing automotive fuels from coal in South Africa. Hydrocarbon Process. 1982, 5, 34-E. Kolbel, H.; Ralek, M. Grundlagen der Fischer-Tropsch Synthese. In Chemierohstoffe aus Kohle; Falbe,. J.,. Ed.;. Geore-Thieme Verlag: Stuttgart, 1977. Kolbel. H.: Tillmetz. K. D. Verfahren zur Herstellune von Kohlenwasserstoffen und sauerstoffhaltigen Verbindungen. DT 25 07 647 Al, 1976. Kuhn, R.; Elstner, M. Petrochemische Grundprodukte aus Kohle. Erdol Kohle, Erdgas, Petrochem. 1977, 30, 117-122. Parsche, G. Selektivitatsuntersuchungen bei der Fischer-Tropsch Kohlenoxid-Hydrierung. Master Theses, The University of Karlsruhe, West Germany, 1978. Saglam, M. Fischer-Tropsch Sentezleri ile Temel Petrokimyasal Hammadelerin Eldesi. Doia Bilim Derg. Ser. B 1983a, Cilt: 7(Sayi: 3), 235-243. Saglam, M. Sentez Gazindan Petrokimyasal Hammaddelerin modifiye edilmig bir demir katalizoru ile Uretimi. Yildiz Universitesi Dergisi, 1983b, Vol. 2, 15-22. Satterfield, C. N.; Stenger, H. G. Fischer-Tropsch Synthesis on a Precipitated Mn/Fe Catalyst in a Well-Mixed Slurry Reactor. Ind. Engng. Chem. Process Des. Deu. 1984,23, 26-29. Schulz, H. Molekulaufbau bei der FT-Synthese. Erdol Kohle, Erdgas, Petrochem. 1977,30, 123-131. Schulz, H. Kapillar-GC-Gesamtprobentechnik. Erdol Kohle, Erdgas, Petrochem. ,1983, 36, 279. Schulz, H.; Cronje, J. Fischer-Tropsch-Synthese. I n Rohstoff Kohle, Eigenschaften, Gewinnung, Veredelung; Verlag Chemie: Weinheim, New York, 1978.
Received for review April 13, 1988 Accepted October 27, 1988
