32
Energy & Fuels 1987,1, 32-36
Iron-Catalyzed Gasification of Brown Coal at Low Temperatures Yasuo Ohtsuka,* Yasukatsu Tamai,+and Akira Tomita Chemical Research Institute of Non-Aqueous Solutions, Tohoku University, Katahira, Sendai 980, Japan Received September 4, 1986. Revised Manuscript Received October 8, 1986 Studies of brown coal gasification with H2 or H20 in the presence of iron have been carried out with a thermobalance. Iron markedly promoted the hydrogasification at as low a temperature as 873 K, and the coal conversion reached 76 wt % within 40 min. The rate enhancement by iron of the reaction with H 2 0 was very small at this temperature but became large at higher temperatures. The effectiveness of the iron catalysts depended on the precursor salts, and the activity sequence among these salts was the same with both gases. It is suggested from the XRD measurements that finely dispersed iron catalysts at the devolatilization stage exhibit high activity in the subsequent char gasification. The activity of iron was influenced by both the iron loading and the addition of foreign metals. The gasification proceeded in a single stage with H 2 0 but in two stages with H2. The main chemical form of iron during the reaction with H 2 0 was magnetite and with Hz was metallic iron. The presence of fine metallic particles seems to be necessary for the occurrence of the two-stage gasification. Introduction Catalytic coal gasification has attracted increasing attention because a lowering of the gasification temperature has several advantages. Thus, many studies have been made of the catalytic effectiveness of various compounds.' It is generally known that alkali-metal compounds like K2C03are the most effective catalysts for gasification in H20. Recently, it has been found that a nickel catalyst markedly promotes the steam gasification of brown coal at low temperatures, around 800 K.2-4 K2C03is inactive in this temperature region. The continuous gasification of nickel-loaded Yallourn brown coal using a fluidized bed reactor has shown that more than 80 w t % of the coal is converted to very clean gas containing neither tarry material nor H2S5and that methane-rich gas is directly produced under pressure.6 Realization of such a low temperature gasification with a cheaper catalyst than nickel should be a final target for the catalytic gasification of coal. In the present work, iron catalysis of brown coal gasification is attempted at low temperatures. The catalytic effectiveness of iron was first investigated in H2. It exhibited a high activity, comparable to that of nickel, at 873 K. Factors that influence the catalytic activity were examined in detail. Second, the gasification was carried out in H20/N2or H20/H2. Experimental Section Coal and Catalyst. Yallourn brown coal from Victoria, Australia, was used. I t was received in a briquette form. Proximate analysis (wt %): moisture, 14.3; volatile matter, 47.3; fixed carbon, 37.6; ash, 0.8. Ultimate analysis (wt %): C, 67.1; H, 4.8; N, 0.8; S, 0.3; 0 (diff), 27.0 (daf). Fe(N03)3was usually employed as the precursor salt for the iron catalyst. Three other types of iron compounds, (NH,),Fe(c204)3, FeCl,, and Fe2(S04),, were also used in order to check the effect of the anion. For reference Ni(N03)2and CO(NO,)~ were used. Coal was impregnated with catalyst precursors by kneading the coal with aqueous solutions of the above salts.
* To whom correspondence should be addressed. 'Present address: Department of Industrial Chemistry, Faculty of Engineering, Science University of Tokyo, Kagurazaka, Shinjuku, Tokyo 162, Japan. 0887-0624/87/2501-0032$01.50/0
Catalyst loading was 10 w t % as metal, unless otherwise stated. T o examine whether or not a small amount of foreign additive influences the iron-catalyzed gasification, Fe(N03)3and KNO, or Fe(N0J3 and Ca(N03)2were simultaneously impregnated on coal as above. The loading of these additives was 1wt% as metal. Gasification Procedure. The gasification experiments were carried out with a thermobalance (Shinku Riko, TGD-5000), which can heat the sample (20 mg) a t a rate of about 300 K/min with an infrared lamp. All runs were performed a t a constant temperature under atmospheric pressure. Pure H2 was used for the hydrogasification a t a flow rate of 120 cm3/min (STP). For the steam gasification, an H 2 0 (66 kPa)/N2 mixture was used a t a total flow rate of 48 cm3/min (STP). The reaction consisted of the devolatilization step and the subsequent char gasification step. Coal conversion is expressed as wt% on a dry ash-free, catalyst-free basis. Characterization of Catalyst. X-ray diffraction analysis (XRD) was conducted by using Fe K a radiation to characterize the catalyst a t the devolatilization and gasification stages. The samples for XRD were prepared in a thermobalance in the same manner as the gasification runs. Coals with different iron salts were devolatilized or gasified in H2 and/or H20. After a predetermined reaction time (1 min for devolatilization), the gas stream was switched to pure N2 in order to purge the residual reactant gas. This purge was essential to avoid the reaction of iron catalyst with reactant gas during the subsequent step. The catalyst-bearing chars were then quenched to room temperature for XRD measurements. The average crystallite size of iron species was determined by the Debye-Scherrer method.
Results Hydrogasification. (a) Activity of Iron-Group Metals. Figure 1 illustrates the gasification reactivity of Yallourn coal with iron, cobalt, and nickel at 873 K. The rapid weight loss within a few minutes corresponds to a devolatilization step. Weight loss in this step was rather small in the presence of the iron catalyst. The reactivity of the resultant char was very low without catalyst. On (1)McKee, D.W. Chem. Phys. Carbon 1981, 16, 1-118. (2)Tomita, A.;Ohtsuka, Y.; Tamai, Y. Fuel 1983, 62, 150-154. (3) Higashiyama, K.; Tomita, A.; Tamai, Y. Fuel 1985,64, 1157-1162. (4) Ohtsuka, Y.;Tomita, A.; Tamai, Y. Appl. Catal., in press. (5)Tomita, A.;Watanabe, Y.; Takarada, T.; Ohtsuka, Y.; Tamai, Y. Fuel 1985, 64, 795-800. (6) Takarada, T.; Sasaki, J.; Ohtsuka, Y.; Tamai, Y.; Tomita, A. Ind. Eng. Chem. Res., in press.
0 1987 American Chemical Society
Iron-Catalyzed Gasification of Brown Coal 1001
Energy &Fuels, Vol. I, No. 1, 1987 33
1
Table I. Activities of Iron Compounds in H2and Their Characteristics at the Devolatilization Stage av cryst size of activity chem form iron metal, iron compds at 873 K at 873 K nm a-Fe, Fe3C 29 Fe(NOd3 0 27 a-Fe, Fe3C (NH4)3Fe(C204)3 0 FeC1, X a-Fe >100 a-Fe, FeS >100 Fe2(SO4I3 X
E
E None
20}
-
30
0
*Key: 0,high activity;
90
60
metals.
-,--I 1073
40
-.-.
+< ,_,_._._.-.-.
2ol 01
./'
/'
K
'0 0
30
O 60
90
1L 2 0
Time.min
Figure 3.
I
I
I
30
60
90
I
metals.
Steam gasification at 923 K catalyzed by iron-group
120
Time, min
peratures.
- - -1
Hydrogasification at 873 K catalyzed by iron-group 100
Figure 2.
no activity.
loo(
Time, min
Figure 1.
X,
Iron-catalyzed hydrogasification at different tem-
the other hand, the char was rapidly gasified in the presence of iron-group metals. With iron catalyst the coal conversion reached 76 w t % within 40 min. However, further gasification did not occur at this temperature. The catalytic activities of cobalt and nickel were somewhat higher than that of iron; conversions of 85-90 w t % were attained within 30 min, but the reactivity of the remaining char was extremely low as in the iron-catalyzed gasification. (b) Temperature Dependence. Figure 2 illustrates the gasification profile at different temperatures. The iron catalyst derived from Fe(N03)3promoted the gasification, even at as low a temperature as 773 K, and the coal conversion was about 70 wt% at 120 min. The reaction at 873 K proceeded more rapidly, but the conversion leveled off a t about 75 wt% as stated above. At 1073 K, the gasification of char took place in two separate stages. When the gasification profile at 1073 K was compared with that at 873 K, the amount of char gasified at the first stage was larger at 873 K, whereas the reaction rate at the second stage was slightly higher at 1073 K. On increasing the temperature to 1273 K the first-stage gasification disappeared and the reaction proceeded in a single stage. This reaction corresponds to the second-stage reaction, and the rate was higher than at 1073 K. (c) Catalyst Loading. The effect of iron loading was determined at 873 K, where only the first-stage gasification was observed and the conversion leveled off at around 30 min, as seen in Figure 2. The amount of coal gasified in the first stage increased with increasing iron loading; the conversion at 40 min was 53, 55, 76, and 83 wt% for loadings of 0, 6, 10, and 16 w t % , respectively. The reactivity enhancement by iron was not so significant at a low loading of 6 wt%. The coal conversion with 16 w t % iron was high and comparable to that with 10 w t % nickel. (a) Precursor Salt. The activities of four iron compounds were compared in Table I. (NH4),Fe(C2O4I3exhibited a catalytic effectiveness similar to Fe(N03)3;the
coal conversion at 40 min was 78 w t % with (NH4),Fe( c 2 0 4 ) 3 . The temperature dependence of gasification was determined with this salt, and it was found to be almost identical with the results mentioned above for Fe(N03),-loaded samples. The reactivity of coals with FeC1, and Fe2(S04)3was almost the same as that without catalyst. Steam Gasification. (a) Gasification Profile. Figure 3 illustrates the reactivity of Yallourn coal with iron-group metals at 923 K. As was observed in H2 (Figure l ) , the weight losses on devolatilization were rather small in the presence of catalyst. The loss with the iron catalyst, 35 wt%, was much lower than that without catalyst. Iron catalyst promoted the steam gasification of char, but the coal conversion before 30 min was lower than that without catalyst because of a lower weight loss in the devolatilization step. Conversions at 120 min were 88 and 60 w t % with and without iron, respectively. At a lower temperature, 873 K, the reaction rate was low and the coal conversion at 120 min was only 68 wt% . This low activity is in contrast with the rapid gasification rate in Hzat the same temperature. The gasification of iron-loaded char proceeded in a single stage. On the other hand, two-stage gasification was observed in the presence of cobalt and nickel (Figure 3). The first-stage reaction was complete within 5 min, and about 80 w t % of coal was converted in this stage. However, the reaction rate for the remaining 20 wt% was so low that the conversion at 120 min was only a little higher than that with iron. More details on 'the two-stage gasification catalyzed by nickel are described e l s e ~ h e r e . ~ ? ~ - ~ (b) Catalyst Loading. With the iron catalyst, the coal conversion at 923 K increased with increasing loading; the conversion at 120 min was 60, 7 7 , 81, 88, and 89 wt% at loadings of 0,2,6,10, and 16 wt%, respectively. The rate considerably increased with a small amount of catalyst, in contrast with the case of hydrogasification. The reactivity enhancement leveled off beyond a loading of 10 wt%. (c) Precursor Salt. Fe(N03), and (NH4)3Fe(C204)3 exhibited a similar catalytic effectiveness, the coal con-
34 Energy & Fuels, Vol. 1, No. 1, 1987
Ohtsuka et al.
Table 11. Activities of Iron Compounds in H 2 0 and Their Characteristics at the Devolatilization Stage av cryst size of activitp chem form iron compds at 923 K at 923 K magnetite, nm 10 Fe(N03)3 0 Fe304,FeO (NH4)3Fe(C204)3 0 FeaO4 29 FeCl, X Fed34 >100 X Fe304,FeS >IO0 Fe2(S04)3
Table 111. Chemical Form of the Iron Catalyst during the Gasification coal conv, chemical av cryst gasification condn wt% form size. nm 65 a-Fe 44 Hz,873 K, 10 min H2, 873 K, 40 min 76 a-Fe 54 HzO, 923 K, 30 min 56 Fe304 32 H2/H20,923 K, 30 min 46 a-Fe >100 M: magnetha W: wilstite
Key: 0,high activity; X, no activity.
Fe
*Or
0'
I
I
I
1
30
60 Time. min
90
120
M
M
Figure 4. Effect of addition of potassium or calcium on the iron-catalyzed steam gasification at 923 K.
versions at 120 min being 88 and 85 wt%, respectively. On the other hand, the chloride and the sulfate showed little activity at 923 K. The activity sequence among these salta (Table 11) is the same as observed in Hz (Table I). (d) Foreign Additives. Figure 4 illustrates the influence of potassium or calcium with the iron catalyst. Although the rate enhancement by potassium alone (1 wt%) was small, the presence of both potassium and iron resulted in a very high reaction rate and the coal was completely gasified within 60 min. It took about 150 min with the iron catalyst alone for the complete gasification. The catalytic activity of calcium in the steam gasification of Yallourn coal was examined,'~~ and it was found that the activity was fairly large compared with that of iron alone (Figure 4), even at a calcium loading of only 1 wt%. The reaction rate with both calcium and iron present was higher than that with calcium alone. However, the rate difference between Ca/Fe and Ca systems was not so large as observed in the case of added potassium. ( e ) Gasification with H2 and HzO. H2 gas was mixed with H 2 0 in the hope that it may keep the iron catalyst in the reduced state and maintain a high activity for steam gasification.1° Reactivity was examined in H2/H20with molar ratios ranging from 1 to 5 at 873 and 923 K. Contrary to expectation, the addition of Hz strongly inhibited the steam gasification in the whole concentration range studied. For example, at 923 K and a H2/H20ratio of 4.3, the coal conversion a t 30 min, 46 wt% ,was nearly equal to the weight loss on devolatilization, 42 wt%. Catalyst State. Tables I and I1 show the chemical form and dispersion state of iron catalysts prepared from different precursor salts immediately after devolatilization in H2 and H20, respectively. Fe(N03), and (NH4),Fe( c 2 0 4 ) 3 were reduced to metallic iron (cy-Fe) in H2, the average size of iron crystallites being 29 and 27 nm, respectively. XRD peaks of Fe3C were also observed with these salts. FeCl, and Fe2(S04),were reduced to metallic iron, but the crystallite size was too large to determine by (7) Nabatame, T.; Ohtsuka, Y.; Takarada, T.; Tomita, A. J.Fuel SOC. Jpn. 1986,65,53-58. (8)Ohtsuka, Y.;Tomita, A. Fuel, in press.
I
30
I
40
50
J
60
28(Fe-Ka), deg.
Figure 5. XRD patterns of chars gasified in H20 at 923 K. Catalysts are Fe, Fe/K, and Fe/Ca.
the line-broadening method. FeZ(SO4),was partly transformed to FeS. The chemical forms of the iron catalysts formed during devolatilization in H 2 0 were different from that formed in H2. Fe(N03)3and (NH4)3Fe(Cz04)3 were transformed to magnetite (Fe304)(average size 10 and 29 nm, respectively). With Fe(N03)3,f i e particles of wiistite (FeO) were also formed. FeC& and FeZ(SO4),were converted to magnetite with a very large size. Weak diffraction peaks of FeS were also observed with Fez(S04)3. Table I11 shows the state of the iron catalyst derived from Fe(N03)3in several gasification environments. Fe304 was the predominant species after steam gasification for 30 min. a-Fe was the main chemical form in H2 and in H2/Hz0 with a molar ratio of 4.3. It is noteworthy that the crystallite size of metallic iron in H2/Hz0was much larger than that observed in Hz alone. Figure 5 illustrates XRD patterns for the chars after steam gasification with added potassium or calcium. Coal conversion was 54-56 w t % for all catalyst systems. Only magnetite (Fe304)was observed with Fe(N03), alone. On the other hand, magnetite and wiistite were detected for the mixed-catalyst systems. No diffraction peaks derived from the additives themselves were detected because of their small quantities and the high degree of dispersion. Discussion Catalyst Effectiveness in Hz. The catalytic activity of iron in the hydrogasification of carbons and coal chars at low temperatures (750-950 K) has been investigated,%l3 and it has been reported that iron shows little activity in (9)Tomita, A.; Tamai, Y. J. Catal. 1972,27,293-300. (10)McKee, D.W. Carbon 1974,12,453-464. (11)Tamai, Y.;Watanabe, H.; Tomita, A. Carbon 1977,15,103-106. (12)Tanaka, K.; Okuhara, T.;Miyahara,K.;Aomura, K. J . Chem. SOC. Jpn. 1980,945-950. (13)Tarki, H.T.; Kiennemann,A.; Chornet, E. Fuel 1984,63,30-34.
Iron-Catalyzed Gasification of Brown Coal this temperature region. In the present work, however, iron promoted the gasification even at 773 K. Such a high activity can be explained by the state of the iron catalyst on the char substrate. Fe(N03), and (NH4),Fe(C204),, which exhibited a high activity in the hydrogasification, were reduced to metallic iron with a fine size on devolatilization, whereas FeC1, and Fe2(S04)3were reduced to very large iron crystallites, which were inactive (Table I). Highly-dispersed iron metal at the devolatilization stage seems to be essential for high catalytic activity in the subsequent hydrogasification. Fe,C as well as iron metal was formed from two iron compounds, showing a large catalytic effect. The formation of carbide in active catalysts suggest that the reaction may proceed via dissolution of carbon in the meta1.14J5 The detailed mechanism should be clarified by further study. The effectiveness of the iron catalyst depended on iron loading, and a high loading, more than 10 wt% , was necessary for low-temperature gasification. Poisoning of iron by H2S evolved from coal may be one reason for the above observation. At low temperatures of around 850 K, most of the iron surface may be covered with sulfur even in an H2Sconcentration of about 10 ppm.16 Although the sulfur content of Yallourn coal is only 0.3 wt% ,the evolution of such a low concentration of H2S would be quite probable during the hydrogasification. When a North Dakota lignite (South Beulah coal) with a high sulfur content (2.9 wt% S) was used in place of Yallourn coal, no char gasification took place at 873 K even in the presence of 16 wt% iron. The fact that the catalyst prepared from Fe2(S04),was inactive at 873 K (Table I) was explained in the preceding section by the growth of iron particles, but sulfur poisoning may also contribute to catalyst deactivation. Thus, a coal with a high sulfur content was not suitable for the lowtemperature hydrogasification by iron catalysts. However, a brown coal with a low sulfur content, for example Rhein brown coal, was gasified in a manner similar to Yallourn coal. Catalyst Effectiveness i n H 2 0 . Iron catalysts have been reported to be ineffective for the steam gasification of coal chars."-21 In the present study, however, iron catalysts were found to promote the gasification of Yallourn coal with H 2 0 as well as with H2. As is shown in Table 11, Fe(N03), and (NH4)3Fe(C204)3,which were transformed to fine particles of iron oxides on devolatilization, were effective for the steam gasification. On the other hand, the chloride and the sulfate, which were converted to magnetite with a large particle size, were not effective. As for the hydrogasification, the high degree of dispersion on devolatilization is a key factor for a large catalytic effect. The chemical form of the iron catalyst during the reaction was magnetite (Table 111). Magnetite has been considered to be inactive in gasification with H 2 0 and C02.19,22 However, an in situ XRD study for the ironcatalyzed C02gasification of carbon revealed a high catalytic activity of magnetite: the gasification was catalytically accelerated in the region where the only iron com(14)Keep, C. W.; Terry, S.; Wells, M. J. Catal. 1980,66,451-462. (15)Holstein, W. L.;Boudart, M. J. Catal. 1981,72,328-337. (16)McCarty, J. G.;Wise, H. J. Chem. Phys. 1982, 76, 1162-1167. (17)Kayembe, N.;Pulsifer, A. H. Fuel 1976,55, 211-216. (18)Hippo, E. J.; Jenkins, R. G.; Walker, P. L., Jr. Fuel 1979,58, 338-344. (19)Kasaoka, S.;Sakata, Y.; Yamashita, H.; Nishino, T. J. Fuel SOC. Jpn. 1979,58,373-386.;Int. Chem. Eng. 1981,21,419-434. (20)Tomita, A.;Takarada, T.; Tamai, Y. Fuel 1983,62,62-68. (21)Huttinger, K. J. Fuel 1983,62,166-169. (22)Walker, P.L.,Jr.; Rusinko, F., Jr.; Austin, L. G. Chem. Phys. Carbon 1968,4,287-383.
Energy di Fuels, Vol. 1, No. 1 , 1987 35 Table IV. Gasification Profile of Yallourn Coal with Nickel and Iron
precursor salts Ni(N03h Fe(N03h
gas
HZ H20 HZ H20
gasification profile two stages two stages two stages single stage
chem form Ni Ni a-Fe Fe304
pound present was magnetiteVz3Therefore, it is possible that magnetite would catalyze the steam gasification of brown coal. The presence of foreign compounds, especially potassium, considerably increased the activity of iron catalysts (Figure 4). Some wiistite was detected in Fe(NO,),-loaded coal immediately after the devolatilization (Table 11),and it disappeared after some extent of gasification (Figure 5). The above additives may function to keep wiistite as such or to reduce magnetite to wiistite. Since wiistite exhibits a higher activity than magnetite,23the higher activity of iron catalysts with these additives can be ascribed to the presence of wiistite. It has been reported that ironsodium binary catalysts like Na[HFe(C0)4]and Na2C03/Fe(N03), are more active than Na2C03and Fe(NO,), in the steam gasification of coal.24 It was suggested that the active species may be the iron compound, which is maintained in a lower oxidation state by the action of the sodium component. It has also been reported that iron enhances the potassium-catalyzed gasification of graphite with steam.25 Iron showed little activity in a mixture of H2/H20. Generally, the addition of H, in the uncatalyzed steam gasification reduces the gasification rate due to the occupation of active sites by H2. On the other hand, reactivity in the iron-catalyzed steam gasification is increased by H2°,19,21 because the iron is kept in the reduced state, which is considered to be catalytically active. In the present work Fe(NO,), was reduced to metallic iron in a H2/H20 gas mixture (Table 111) in accordance with the above general observations, but this iron was almost inactive. Since iron was active in both constituent gases, this result was unexpected. The reason for inactivity may be the rapid sintering of the iron. Iron metal agglomerated readily in spite of a small extent of gasification and the average iron particle size became very large (Table 111). The activation of iron catalysts by adding H2 is usually observed at more which is much higher than the present than 1100 K,10,19,21 gasification temperatures. The catalyst dispersion may not be such an important factor at high temperature, but it is closely correlated with the catalytic activity at low temperature. The different dependencies of reactivity on iron loading observed with H 2 0 and with H2 can be explained by the form of the iron species. The reaction of H2S with Fe304 in H20 is more difficult than with metallic iron in H,. Therefore, the steam gasification suffered from sulfur poisoning less seriously than did the hydrogasification. Thus a low loading of 2 wt% Fe was enough to be catalytically effective. Gasification Profile. The reaction profile of Yallourn coal is summarized in Table IV. The profile varied with catalyst species and reactant gas. In H,, the gasification proceeded in two stages, irrespective of the kind of catalyst. (23)Ohtauka, Y.;Kuroda, Y.; Tamai, Y.; Tomita, A. Fuel 1986,65, 1476-1478. (24)Suzuki.. T.:. Mishima.. M.:. Takahashi. T.: Watanabe. Y.Fuel 1985. 64,661-665. (25)Carrazza, J.; Tysoe, W. T.; Heinemann, H.; Somorjai, G. A. J. Catal. 1985,96,234-241.
36
Energy & Fuels 1987,1, 36-44
On the other hand, in HzO, the reaction profiles for both catalysts were different: two stages with nickel and a single stage with iron. This may be explained by the difference in the chemical form of the catalyst during the reaction. The nickel catalyst existed in a form of metallic nickel, whereas the chemical form of the iron catalyst was magnetite in H20. The minimum H2/H20ratios required to convert the lowest metallic oxide to the metal at 923 K are approximately 3 for Fe and 0.005 for Ni. Thus, only nickel can be in the metallic state in the presence of small amounts of reducing gases such as volatile matter and/or gasification products. The first-stage gasification in H2 terminated at a coal conversion around 75 w t % with the iron catalyst and 85 wt% with the nickel catalyst, and the rate became very small thereafter (Figure 1). As the reaction proceeded, the particle size of iron metal increased from 29 nm on devolatilization to 54 nm at the ultimate conversion of 76 w t % (Table 111). The size of the nickel particles also increased from 8 nm at the initial stage to 32 nm at the termination point. This sintering is due to the consumption of char around the metal particles. The termination of the
first-stage gasification may be related to the deactivation of the catalyst owing to sintering. The disappearance of the first stage at a high temperature of 1273 K (Figure 2) may also be due to the sintering of iron catalysts. Similar results were obtained for the nickel-catalyzed hydrogasification. At 1273 K nickel particles of about 0.1 pm in size were observed even at the initial stage.26 It is emphasized again that the presence of fine metallic particles is necessary for the occurrence of the two-stage gasification. Acknowledgment. Y. Ohuchi and E. Sat0 are thanked for their assistance in carrying out experiments. This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Japan, Special Project for Energy (No. 59040033). Registry No. Fe(N03)3, 10421-48-4;(NH.J3Fe(C20J3, 14221-47-7;FeC13, 7705-08-0;Fe2(S04)3,10028-22-5;KNOB, 7757-79-1; Ca(N03)2, 10124-37-5; Fe, 7439-89-6; Fe304,1309-38-2; Ni, 7440-02-0. (26)Higashiyama, K.;Tomita, A.; Tamai,Y.Fuel 1985,64,1525-1530.
Characterization of the Binding Sites of Vanadium Compounds in Heavy Crude Petroleum Extracts by Electron Paramagnetic Resonance Spectroscopy John G. Reynolds*+ and Emilio J. Gallegos Chevron Research Company, Richmond, California 94802
Richard H. Fish* and John J. Komlenic Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720 Received March 27, 1986. Revised Manuscript Received October 16, 1986 The high-performance liquid chromatographic (HPLC) separated fractions of pyridine/water extracts of selected crude petroleums were analyzed by electron paramagnetic resonance (EPR) spectroscopy to determine the first coordination sphere around the vanadium. The extracts were separated by polarity on an octadecylsilane column (ODS) into three fractions-low, moderate, and high polarity. As determined by EPR, the Boscan moderate-polar and Prudhoe Bay moderate- and low-polar fractions exhibited NzS2coordination. Cerro Negro and Wilmington moderate-polar fractions showed S4 coordination, and the Boscan low-polar fraction showed N4 coordination. The coordination of the Cerro Negro low-polar fraction had distinctly different parameters, showing a NOS2coordination. These results are important in the identification of non-porphyrin metal-containing compounds in heavy crude petroleums and residua. Introduction We recently reported on the molecular size and polarity of the vanadium and nickel compounds found in selected heavy crude petroleums, Boscan, Cerro Negro, Wilmington, and Prudhoe Bay, and their We examined the metal-containing compounds by size-exclusion chromatography in conjunction with graphite furnace atomic absorption selective metal detection (SEC-HPLC-GFAA), and found the metal distribution to be unique for each petroleum, while the histogrammic metal profiles may have utility for fingerprinting the heavy crude petroleums. For t Present address: Lawrence Livermore National Laboratory, University of California, Livermore, CA 94550.
0887-0624/87/2501-0036$01.50/0
vanadium, the majority of the metal-containing compounds fall into the 2000-9000-Da molecular mass (MW) range, while 3-7% was found in the MW range of >go00 Da. The low molecular mass range was calibrated by vanadyl and nickel model compounds, with 23 to 30% having MW in the
