Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 615-621
615
Storage Stability of Synfuels from Oil Shale. 2. Effects of Nitrogen Compound Type and the Influence of Other Nonhydrocarbons on Sediment Formation in Model Fuel Systems John W. Frankenfeld" and Wllllam F. Taylor Exxon Research and Englneering Company, Products Research Division, Linden, New Jersey 07036
Dennls W. Brlnkman Bartlesville Energy Technology Center, U.S. Department of Energy, Bartlesville, Oklahoma 74003
The tendency of various nitrogen compounds to form sediment during storage was studied with pure compounds and model fuel systems. The activity of the various compounds depends greatly upon their detailed structural features. Nonbasic nitrogen heterocyclics with alkyl groups on ring carbons adjacent to nitrogen were highly reactive. In contrast, many other nitrogen compounds were found to be essentially nonreactive even after storage for periods in excess of 100 days at 43.3 O C . Thus, an accurate prediction of the storage stability of a shale-derived fuel cannot be made on the basis of total nitrogen content. The effects of adding sulfur and oxygen compounds to the base fuels, either separately or mixed with nitrogen compounds, was investigated. I n general, none of the sulfur or oxygen compounds produced sediment during storage at ambient or near ambient conditions when tested by themselves. Important interactions were discovered between pairs of nitrogen compounds and between nitrogen and sulfur or oxygen compounds. Both accelerating and inhibiting interactions occurred.
Introduction Synfuels from an alternate source such as oil shale often exhibit poor stability characteristics. This instability, which manifests itself in the formation of sediments or gums during storage at ambient conditions, is a feature of both crude and refined liquids. Only when such liquids have been upgraded by severe hydrotreating or other refining methods can fuels of acceptable quality be obtained. A major cause of sediment formation is the high nitrogen content of synfuels as compared with comparable fuels derived from petroleum (Frankenfeld and Taylor, 1981; Dineen and Bickel, 1951). In part 1 of this series (Frankenfeld et al., 1983a) the general features of nitrogeneous sediment formation were discussed. These included the effects of nitrogen level, solvent, moisture, temperature, light, and oxygen. This paper describes the effects of the structure of the nitrogen compound and the interactive effects between nitrogen compounds and between nitrogen and sulfur and oxygen compounds which have significant but varying influences on the rate of sediment formation. Experimental Section Test Fuels. Three petroleum-derived test fuels were employed as solvents. These were purified n-decane (Frankenfeld and Taylor, 1977), a jet fuel from the Bayway, NJ, refinery, and a no. 2 diesel fuel from the Baytown, TX, refinery. Both commercial fuels were free of additives. Inspections on the jet and diesel fuels are given in part 1 of this series (Frankenfeld et al., 1983a). Test Compounds. Test nitrogen compounds were purchased from commercial sources. Where necessary, these were purified by distillation or crystallization. Test compounds were added as ppm N (wt/vol); Le., 150 ppm of any nitrogen compound means 150 mg N/1000 cm3 of test fuel. Storage tests were conducted in an atmosphere containing excess oxygen (Frankenfeld et al., 1983a). 0196-4321/83/1222-0615$01.50/0
Accelerated Storage Stability Test. This test measures sediment formation during storage at 43.3 "C (110 O F ) . The method used is described in part 1 (Frankenfeld et al., 1983a). Results are presented as mg of sediment/100 cm3of test fuel. Blank corrections, obtained by applying the same test to the test fuels in the absence of added nitrogen compounds, were subtracted. Thirteen weeks at 43.3 "C are considered to be roughly equivalent to one year's storage at ambient temperature (White, 1973). Results As shown in previous studies (Frankenfeld et al., 1983a; Frankenfeld and Taylor, 1981) the structure of the nitrogen compound being tested has a large effect on the amount of sediment produced under accelerated storage conditions. Some compounds react nearly quantitatively in 4-6 months while others show little or no tendency to form sediment even after prolonged storage at elevated temperatures. These observations are consistent with earlier reports by Nixon (1962), Thompson et al. (1951), and Mapstone (1949), among others, all of whom showed that certain nitrogen heterocycles such as some pyrroles and indoles were especially prone to form sediment while other compounds were much less reactive. However, no concerted attempt has been made to correlate the chemical structure and reactivity toward sediment formation under fuel storage conditions. In this study, the effects of structure were investigated by using model nitrogen compounds whose structures varied in consistent ways to determine whether correlations between such chemical structures and reactivity could be drawn. A variety of nitrogen compounds were investigated. Those chosen for study were representative of compound types known or suspected to be present in shale-derived fuels. Pyrroles and Indoles. The results of accelerated storage tests with pyrrole and indole derivatives in the three fuel systems of increasing complexity are summarized 0 '1983American
Chemical Society
616
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
Table I. Sediment Formation with Various Pyrroles and Indoles after Storage at 43.3 “ C in Various Test Fuelsa level total sediment,b mg/100 cm3 added. N compd ppm N C 7 days 14 days 28 days 56 days 8 0 days 112 days __-
2,5-dimethylpyrrole (DMP) pyrrole carbazole
750 1500 1500
DMP
1500 750 150 7 50 150 1500 7 50 150
1,2,5-trimethylpyrrole (TMP) 2-methylindole
n-Decane 44.1 0 0 0 0 Jet Fuel 109 61.0 0.8 33.3 7.7 trace 0.4 0
102 0 0
0 0
314 141 21.2 104 13.5 14.9 11.4 trace
586 261 41.2 219.0 20.7 25.9 14.9 0.5
4.0 1.1 0.1
1.0 0.9 1.0
0.3 0.9 0.5
No. 2 Diesel 193 24.7 85.6 23.4 82.6
399 228 40.9
7 96 362 75.3
16.0 19.8 0.7
117 28.4 26.3 3.0
0
0 0
0 0
trace 0
328
n-Decane 3-methylindole
1500 750 150
DMP
1500 750 150 1500 750 150 1500 1500 1500 1500
TMP 2,4-dimethyl-3-ethyl-pyrrole pyrrole 1-phenylpyrrole 1-methylpyrrole 2-methylindole 3-methylindole indole 1,2-dimethylindole 2,3-dimethylindole 2,5-dimethylindole carbazole
1500 750 150 1500 750 150 1500 1500 1500 1500 1500
n-Decane trace 0.4 2.0 0.7 0.2 0 trace 0 0 0 0
13.0 9.8 5.0 0.5 0.2 0.1 1.0 0 trace trace 0
423 89.5
58.0 1.0 0 0.7
d
26.4 15.0 3.2 4.5 1.7 1.1 0.1 0 6.4 3.2 0
2.9 22.0 8.6
Sum of insoluble and adherent sediments; corrected for blanks. a Dark storage; average of 2 or more replicates. Based on nitrogen (wt/volume basis, i.e., 1 5 0 ppm is 1 5 0 mg N/1000 cm3 of diluent). Affords about 9 mg/100 cm3 on 1 2 0 days’ storage.
in Table I. The various compounds showed large differences in tendencies toward sediment formation. By far the most active compounds were the alkylated pyrroles. Compounds without alkyl side chains produced little or no sediment under the conditions of the test. The positioning of the alkyl groups on the heterocyclic ring is also important. Alkylation on carbon adjacent to the nitrogen atom activates the compound much more than on positions more remote while N-alkylation appears to retard sediment formation. Fusing an aromatic ring to the ring (indoles vs. pyrroles) also tends to reduce reactivity. These results were extended to other types of nitrogen compounds with results given in Table 11. Similar structural effects were observed although the overall level of sediment formation was much lower with all these compounds except pyrazoles than in the case of pyrroles and indoles. In all studies, the most reactive compounds were unsaturated nitrogen heterocycles with multiple alkyl groups, at least one of which is located on the carbon atom adjacent to nitrogen. Sulfur and Oxygen Compounds. A variety of sulfur and oxygen compounds are known to be present in shale liquids (Frankenfeld and Taylor, 1981). Some of these, especially the sulfur compounds, have been shown to be
unstable in thermal stability studies (Taylor, 1976; Taylor and Wallace, 1968). Several representatives of the most prevalent types were tested to determine whether they could either produce sediment by themselves or interact in some way to influence sediment formation by reactive nitrogen compounds. A summary of the results of accelerated storage tests with sulfur and oxygen compounds, tested by themselves, is given in Table 111. None of the oxygen compounds showed any tendency to form sediment in these studies. Of the sulfur compounds studied only p-thiocresol and p-toluenesulfonic acid afforded measurable sediments when tested by themselves and then only on fairly long-term storage. The former gave a small amount of sediment after five months at 43.3 “C but none at shorter storage periods. The p-toluenesulfonic acid afforded copious amounts of black tar after 56 days’ storage. The effects of other known reactive species such as hydroperoxides and peroxides were not studied. Interactive Effects. Although many nitrogen compounds, especially those that are basic in nature, fail to produce sediment themselves, they may “interact” with active nitrogen compounds to influence their sediment forming tendencies. Such interactions may be “positive”
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
617
Table 11. Tendencies of Various Nitrogen Compounds to Form Sediment on Storageu total sediment,b mg/100 cm3 after N compdC pyrazoles 3-methyl 4-methyl 3,5-dimethyl pyrazines 2-methyle 2,3-dimethyl 2,5-dimethyl 2,g-dimethyl pyrrolidines N-methyle 2,5-dimethyl piperazines N-methyl N.N-dimethyl 2-meth yl 2,5-dimethyl 2,6-dimethyl isoquinoline quinolines 2-methyl (quinaldine) 2,6-dimethyl 1,2-dihydro-2,2,4-trimethyl piperidines 2-methyl 3-methyl 2,5-dimethyl 2,g-dimethyl misc. heterocycles 7-azaindole 2-meth ylbenzoxazole 2-methylbenzothiazole 3-methylpyridazine 2,4,6-trimethylpyridine nonheterocyclic N compounds n-undecylcyanide tripropylamine trioctylamine m-tolylnitrile n-hexylamine e methylcyclohexylamine e 2,6-dimeth~laniline~ n-caproamide
fuel system
28 days
56 days
1 1 2 days
diesel diesel diesel
trace 0 0
1.0 0 trace
1.0 0.2 95.0
diesel diesel diesel diesel
0 0 0 0
1.0 trace trace trace
0.7 2.0 0.6
diesel diesel
0 0
0 trace
30.0 11.5
diesel diesel diesel diesel diesel diesel
0 0 4.0 0 0
0 0 7.0 trace trace
5.1 1.2
0
0
diesel diesel diesel
1.8 0 trace
4.0 trace 16.0
5.0 5.7
diesel diesel diesel diesel
trace trace 0 0
trace trace
13.2 15.7 2.1 3.8
diesel diesel diesel diesel n-decane
0.3 0 0 4.2 0
8.7 trace trace 4.0 0
diesel diesel diesel diesel n-decane n-decane n -decane n-decane
0 0 0 0 0 0
0 0 0
0 0
0 0
0 0 0 trace 0
17.9 24.3
trace trace
0 trace 0 0 trace 0 0 trace 0
Storage at 43.3 "C (110 O F ) for diesel blends, 22.2 "C (72 O F ) for decane samples. Sum of insoluble plus adherent sediment; corrected for blank; average of 3 replicates unless otherwise noted. Added at 1500 ppm N level (wtlvol). Six replicates. e Two replicates.
(i.e., accelerating) or "negative" (inhibiting) in nature. Thus, in a "positive" interaction, a mixture of nitrogen compounds will afford more sediment than the sum of the two interactants acting independently. "Negative" interactions have the opposite effect. Such interactive effects were demonstrated previously in thermal stability studies (Taylor and Frankenfeld, 1978). In the present study, a large number of interactions were discovered. The occurrence of an interaction was identified by means of a 2x2 factorial experiment (Brinkman, et al., 1981; Bennett and Franklin, 1954) and their significance was verified by use of Student's test (Davies, 1958). A summary of some of the more important interactions between pairs of nitrogen compounds is given in Table IV. The sediment levels actually obtained are contrasted with that which could have been expected from each component acting independently. A strong "positive" interaction was encountered between 2,5-dimethylpyrrole (DMP) and 1,2,5-trimethylpyrrole (TMP). In addition, both trioctylamine and isoquinoline, compounds which produce no sediment by
themselves, tended to promote sediment formation with both DMP and TMP. It appears, therefore, that some apparently innocous compounds can influence sediment formation when mixed with "active" materials. A number of %egative" interactions were also uncovered, only two of which are given in Table IV. All the examples in Table IV were carried out in no. 2 diesel fuel. However, the diluent had no effect on whether or not an interaction would occur. Important interactions were encountered between nitrogen and sulfur or oxygen compounds. Several of these interactions were "negative" (Le., stabilizing). Results of experiments with DMP and several 0 and S compounds are given in Table V. Aromatic thiols gave significant "negative" interactions with DMP at storage times in excess of 14 days. Such interactions were observed in earlier work when storage was conducted in sunlight, but the effect was reversed on long-term storage (Frankenfeld and Taylor, 1977). It has been suggested that this reversal was due to oxidation of the thiols to sulfonic acids, the former
618
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
Table 111. Accelerated Storage Tests with Sulfur and Oxygen Compounds" total sediment,c m g / l 0 0 c m 3 , in fuel no. 2 diesel
jet fuel
___-_______
compoundb benzylphenyl sulfide benzyl disulfide tert-butyl sulfide 1-dodecanethiol 2,5-dimethylthiophene p-thiocresol p-toluenesulfonic acid 2,5-dimethylfuran dibenzofuran 2-decanone n-decanoic acid 2,4,6-trimethylphenol
28 days
56 days
____
160 days
28 66 days days
0
0
0
0
0
0
0
0 0
0 0
0 0
.1
__-_
0
/ -
1 ' Z?
0 0
0 0
5 13
0 15.5
0 1609.6
D-T~ICCRESOL 8COOO
PLUS
pp"
30 13
2c 25
20.7
5:
.
75
100
I-ORACE TIME DAYS
20.0
0
0
0
0 0 0
0 0 0
0 0 0
0
0
0
0
0
Figure 1. "Negative" interaction between 2,5-dimethylpyrrole and aromatic thiols in no. 2 diesel fuel. (Storage at 43.3 "C in the dark.) ______
90
85 80 75
0
70
OMP 1750PPM NI ALONE
-
65
A 0
a Storage at 43.3 ' C in darkness. Present at 3000 pm S or 100 ppm 0 level (wtivol). Sum of insoluble and adherent deposits; average of 3 replicates.
,
2
, ,, /
/
being inhibitors and the latter accelerators. This phenomenon does not appear to occur under dark storage conditions. This "negative" interaction between aromatic thiols and some nitrogen compounds is illustrated, using DMP, in Figures 1 and 2. In the dark, this inhibition continues for at least 100 days at 43.3 "C.As little as 100 ppm of thiophenol (S basis) is sufficient for a significant negative interaction. The magnitude of the effect is con-
24
27
30
33
36
STORAGE TIME IDAVSI
Figure 2. Effects of thiophenol concentration on sediment formation with 2,5-dimethylpyrrole. (Storage at 43.3 "C in the dark.)
Table IV. Interactions Between Pairs of Nitrogen Compounds"
___.____.. ____-.
compd A 2,5-dimethylpyrrole (DMP) 2,5-dimethylpyrrole (DMP) 2,5-dimethylpyrrole (DMP) 2,5-dimethylpyrrole (DMP) 2,5-dimethylpyrrole (DMP) 1,2,5-trimethylpyrrole(TMP)
N, PPm 150 150 150 150 150 150
compd B 1,2,5-trimethylpyrrole (TMP) isoquinoline trioctylamine pyrrole 2-methylindole isoquinoline
N, ppm
type of
sediment. mg/lOO c&3
interaction expectedC
found
150
POS
133
164
1350 1350 1350 750 1350
POS POS neg neg posd
75.3 75.3 76.3 117 45.1
128 116 57.2 83.3 67.8
a All interactions shown are significant o r "highly significant" according t o Student's test (Davies, 1958). After 56 days storage a t 43.3 "C in no. 2 diesel fuel unless otherwise noted. Expected from sum of interactants tested by themselves. After 7 3 days at 43.3 "C.
Table V. Summary of Interactions between Nitrogen Compounds and Sulfur and Oxygen Compoundsa N compd
S or 0 compdC
2,5-dimethylpyrrole (DMP)
thiophenol
2,5-dimethylpyrrole (DMP)
p-thiocresol
2,5-dimethylpyrrole (DMP) 2,5-dimethylpyrrole (DMP) 2,5-dimethylpyrrole (DMP)
dodecanethiol benzylphenyl sulfide decanoic acid
2,5-dimethylpyrrole (DMP)
2,6-di-tert-butylphenol
2-methylindole
decanoic acid
" Storage a t 110 "F for 1 4 or 28 days. Present a t 750 ppm N (wt/vol). All significant by Student's test (Davies, 1958). (wtivol).
fuel diesel jet diesel jet diesel diesel diesel jet decane diesel decane diesel
type of interaction neg
Present a t 100 ppm 0 or 3000 ppm S
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
Table VI. Effects of n-Decanoic Acid o n Sediment Formation with 2,5-Dimethylpyrrole
fuel diesel
storage temp, "C ( O F ) 22.2 (72) 43.3 (110)
jet
22.2 (72) 43.3 (110)
n-decane
22.2 (72) 43.3 (110)
PPm
"bf
DMP
7 50 750 7 50 7 50 750 7 50 7 50 750 7 50 7 50 7 50 7 50
PPm of, RC0,H 100
100 100 100 100 100
619
(DMP)in Various Fuel Systems total sediment.a mg/100 cm3, aiter
1 4 days
28 days
18.6 16.1 88.5 88.0 7.0 12.7 61.3 84.7 18.3 69.2 44.1 92.8
42.6 46.1 245.8 245.0 140.5 221.0 38.1 103.9 101.5 225.2
Sum of insoluble and adherent sediments adjusted for blanks. RC0,H = n-decanoic acid; Nitrogen basis (wt/vol). 100 ppm on oxygen basis (wtlvol). Purified over silica gel and activated alumina (Frankenfeld and Taylor, 1977).
centration dependent as shown in Figure 2. Surprisingly, no effects were observed with either decanoic acid or 2,6-di-tert-butylphenol when tested with DMP in no. 2 diesel fuel, although "positive" interactions were observed with decanoic acid in jet fuel and decane and a negative interaction with 2,6-di-tert-butylphenol in decane (Table V). In addition, previous work in purified decane had shown significant accelerating effects with most organic acids, including decanoic, while phenols were inhibitors (Frankenfeld and Taylor, 1977). Since no interaction was detected in no. 2 diesel, a separate study was undertaken to investigate these seemingly contradictory results. The results are summarized in Table VI. Previous work had shown that decanoic acid alone afforded no sediment or color change in hydrocarbon fuels (Frankenfeld and Taylor, 1977). These results in Table VI confirmed the previous observation that decanoic acid interacts strongly with DMP in decane to promote sediment formation. A significant positive interaction also exists in jet fuel. In diesel, however, no interaction occurs. A possible explanation for these results lies in the fact that the base no. 2 diesel has an appreciable acid titer while both the jet fuel and n-decane were acid free. This suggests that acids, present normally in diesel, may contribute to sediment formation in that fuel and provides a possible explanation for the enhanced rate of sediment formation in diesel fuel as compared to jet fuel or decane (Frankenfeld et al., 1983a). Discussion Sediment formation in the current studies was caused almost exclusively by nonbasic nitrogen heterocycles. This is illustrated by the results of accelerated storage tests given in Tables 1-111 and by the comparison of the sediment forming tendencies of some typical compounds in Figure 3. Thus, analogous N, 0, and S species such as 2,5-dimethylpyrrole (DMP), 2,bdimethylfuran, and 2,5dimethylthiophene varied greatly in their relative tendencies to produce sediment when stored in various model fuel systems. The oxygen and sulfur heterocycles gave no sediment after over 100 days under conditions in which the nitrogen analogue (DMP) reacted nearly quantitatively. These findings are in sharp contrast to the results of thermal stability studies (Taylor and Wallace, 1968) in which many sulfur and some oxygen compounds were quite deleterious to jet fuel stability. The formation of deposits under high-temperature conditions apparently proceeds by different pathways than in the case of ambient or near ambient storage. Basic nitrogen compounds, exemplified by the two amines shown in Figure 3, showed a tendency to produce some color under accelerated storage conditions
n
2,5-DIMEIHYLPYRROLE (DMPI 586 mg/100 m i in 56 doyr
2.5-DIMETHYLFURAN 0 mg/l00 m l in >IO0 days
2-MnHYLINDOLE 27 m g 4 0 0 m l in 56 days
PYRROLE 1 m o i l 0 0 ml i n 56 days
2,5-DIMETHYLTHIOPHENE =- 100 d o y i
0 mg/l00 m l
NH2 n-H EXY L A M I N € Om$IOOml1n>13Udoyi
2.6-DIMETHYLANILINE 0.1 mg/IOOml in >IO0 days
Figure 3. Relative reactivity of some heterocyclic compounds toward sediment formation. Sediment levels are in no. 2 diesel fuel.
(Frankenfeld and Taylor, 1977) but gave no measurable sediment in current tests. Structural Effects on Sediment Formation. The nonbasic nitrogen heterocycles varied to a large extent in their tendencies to produce sediment under fuel storage conditions. Some compounds, exemplified by 2,5-dimethylpyrrole, gave large quantities of sediment in a short period; others produced little or none under the same conditions. From the results shown in Tables I and I1 certain correlations between chemical structure and tendency toward sediment formation can be drawn. These are illustrated by the orders of reactivity shown in Figure 4. Reactivity decreases from left to right and from top to bottom (i.e., from series A to B to C) in this figure. From this analysis the following tentative generalization can be drawn concerning structural effects and sediment formation under fuel storage conditions: (a) Alkyl groups are essential for significant reactivity; unsubstituted nitrogen heterocycles invariably gave negligible amounts of sediment in these tests. (b) The positions adjacent to nitrogen are by far the most reactive. Compare 2,5-dimethylpyrrole to all other pyrroles and 2-methylindoleto 3-methylindole. ( c ) More than one alkyl group generally increases reactivity, especially if two or more are on carbons adjacent to nitrogen. (d) Substitution on the nitrogen decreases activity toward sediment formation; compare 2,5-dimethylpyrrole with 1,2,5-trimethylpyrrole,1-methylpyrrole with pyrrole itself and 1,2-dimethylindole with 2- or 2,3-
620
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 A . PYRROLES
cJ$-c Oc>
c
H 2,5-Dimethyl
l
C
>)
I
C
2,4-Dimethyl-3-Ethyl
B.
H
I
C
C
_>
H
2,5-Dimethyl
3-Methyl
m)@-q@ I
H
1 ,Z-Dimethyl
Indole
F
I
I
H
2,3-Dimethyl
4j2J-J
I
R 1 -Methyl or 1 -Phenyl
Pyrrole
INDOLES
H
2 -Methy I
0
>
HI
H
1 ,Z,j-Trimethyl
(J
H
Corbozole
C. Q U I N O L I N E S
H 1 ,Z-Dihydro-2,2,4-trimethyl
2,6-Dimethyl
2-Methyl
Quinoline
Figure 4. Influence of structure on reactivity of various nitrogen heterocycles toward sediment formation. Reactivity decreases from top of iist to bottom (group A > B > C) and from left to right.
dimethylindole. (e) Although pyrroles are significantly more reactive than the corresponding pyrrolidines, most symmetrical aromatic compounds appear less reactive than their hydrogenated or partially hydrogenated counterparts. Compare piperazines and piperidines and 1,2-dihydro2,2,4-trimethylquinolinewith alkylated quinolines. In addition, condensed aromatic structures (e.g., indoles) are much less active than noncondensed heterocyclics such as pyrroles and pyrazoles. (f) Many basic nitrogen compounds, especially open chain varieties, have a very low order of reactivity toward sediment formation. It should be emphasized that the above generalizations are strictly applicable only to cases in which individual nitrogen compounds are present in hydrocarbon solvents of the no. 2 diesel type (in this case a straight run diesel) in the presence of oxygen but in the absence of light and at moderate temperatures. The order of reactivity in the presence of light is somewhat different. The alkyl indoles, for example, are relatively more susceptible to light than are the alkyl pyrroles (Frankenfeld et al., 1983a; Frankenfeld and Taylor, 1977). However, it is quite clear that not all nitrogen compounds are deleterious to the storage stability of synfuels, at least so far as sediment formation is concerned, and, even among those groups that are deleterious, significant differences in reactivity obtain. Thus, an accurate prediction of the storage stability of shalederived fuels cannot be made solely on the basis of total nitrogen content. Significance of Interactive Effects. As pointed out above, interactive effects between different types of nitrogen compounds may play a significant role in fuel stability. It has been estimated that in unprocessed shale liquids more than 50% of the molecules present will contain one or more nitrogen atoms (Cook, 1965). Since representatives of nearly all types of organic nitrogen compounds have already been identified in such liquids, the possibilities for interactions are almost limitless. The limited data shown in Table IV illustrates the range of
interaction effects than can, and no doubt do, occur, especially in raw or only partly refined materials. Unfortunately, no pattern has so far emerged relating chemical structure and the type or magnitude of interactions which might be expected between pairs (or groups) of nitrogen compounds. It is clear, however, that some compounds which appear harmless by themselves are capable of influencing sediment formation with other, more active species. Significantly, no “positive”interactions have been uncovered between two or more “inactive” nitrogen compounds. I t appears that at least one reactive species is necessary for significant interactions to occur. Interactions between nitrogen compounds and certain sulfur and oxygen compounds are more clear cut. Particularly interesting is the “negative” interaction between aromatic thiols and DMP (Table V, Figure 1). This effect is quite large and may play an important role in determining the stability characteristics of actual shale liquid in which compounds of both types are present (Frankenfeld et al., 1983b). It is likely that the thiols are acting as antioxidants (Nixon, 1962; Kennedy and Paterson, 1955). The elemental analyses of sediments from DMP plus thiophenol are similar to those obtained in the absence of sulfur (Frankenfeld and Taylor, 1981). This indicates that the sulfur compounds are affecting only the rate of reaction and not the characteristics of the sediment. This appears to hold true at least for such active sediment formers as DMP and 1,2,5-trimethylpyrrole (TMP). In the case of less active nitrogen compounds (e.g., pyrrole, l-methylpyrrole, and certain other nitrogen heterocycles) a different reaction path may possibly obtain. This possibility is discussed further in part 3 of this series (Frankenfeld et al., 1983b). Decanoic acid shows no accelerating effect on sediment formation with DMP when the compounds are stored in diesel fuel (Table V). This is in contrast to results obtained in either jet fuel or decane where a strong positive interaction is observed. Frankenfeld and Taylor (1977) have
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22,
shown this interaction to be general for organic acids and DMP in all cases where decane is the diluent. It appears that in no. 2 diesel, a more complex fuel, some trace impurity exists which either negates or overcomes the influence of added decanoic acid. It was pointed out previously that the no. 2 diesel fuel used in these experiments had an appreciable acid titer while both the jet fuel and decane are acid free. The most reasonable explanation for the lack of an interaction in diesel, therefore, appears to be that the fuel already has acids present which exert an accelerating effect on sediment formation. A small amount of additional acid added to this system produces no noticeable effect. It has been noted (Frankenfeld et al., 1983a; Frankenfeld and Taylor, 1981) that DMP produces more than twice as much sediment in no. 2 diesel than in decane under the same storage conditions. The presence of acids in the former fuel may well account for this difference. It is clear from these studies that interactive effects can occur in model systems. The impact of this results on interpreting the storage stability in actual shale liquids discussed in part 3 of this series of papers (Frankenfeld et al., 1983b). Registry No. Decane, 124-18-5; 2,5-dimethylpyrrole, 625-84-3; pyrrole, 109-97-7; carbazole, 86-74-8; 1,2,5-trimethylpyrrole, 930-87-0; 2-methylindole, 95-20-5; 3-methylindole, 83-34-1; 2,4dimethyl-3-ethylpyrrole, 517-22-6; l-phenylpyrrole, 635-90-5; l-methylpyrrole, 96-54-8; 1,2-dimethylindole, 875-79-6; 2,3-dimethylindole, 91-55-4; 2,bdimethylindole, 1196-79-8;3-methylpyrazole, 1453-58-3; 4-methylpyrazole, 7554-65-6; 3,bdimethylpyrrazole, 67-51-6; 2-methylpyrazine, 109-08-0; 2,3-dimethylpyrazine, 5910-89-4; 2,5-dimethylpyrazine, 123-32-0; 2,6-dimethylpyrazine, 108-50-9; N-methylpyrrolidine, 120-94-5; 2,5dimethylpyrrolidine, 3378-71-0; N-methylpiperazine, 109-01-3; NJV-dimethylpiperazine, 106-58-1; 2-methylpiperazine, 109-07-9; 108-49-6; 2,5dimethylpiperazine, 106-55-8; 2,6-dimethylpiperazinene, isoquinoline, 119-65-3; 2-methylquinoline, 91-63-4; 2,6-dimethylquinoline, 877-43-0; 1,2-dihydro-2,2,4-trimethylquinoline, 147-47-7; 2-methylpiperidine, 109-05-7; 3-methylpiperidine, 626-56-2; 2,5-dimethylpiperidine, 34893-50-0; 2,6-dimethylpiperidine, 504-03-0; 7-azaindole, 271-63-6; 2-methylbenzoxazole, 95-21-6; 2-methylbenzothiazole, 120-75-2; 3-methylpyridazine,
No. 4, 1983 821
1632-76-4;2,4,6-trimethylpyridine,108-75-8; n-undecyl cyanide, 2437-25-4; tripropylamine, 102-69-2; trioctylamine, 1116-76-3; m-tolylnitrile, 620-22-4; n-hexylamine, 111-26-2; methylcyclohexylamine, 100-60-7; 2,&dimethylaniline, 87-62-7; n-caproamide, 62802-4; benzylphenyl sulfide, 831-91-4; benzyl disulfide, 150-60-7; tert-butyl sulfide, 107-47-1; l-dodecanethiol, 112-55-0; 2,5-dimethylthiophene, 638-02-8; p-thiocresol, 106-45-6; p-toluenesulfonic acid, 10415-4; 2,5-dimethylfuran, 625-86-5; dibenzofuran, 132-64-9;2-decanone, 693-54-9; n-decanoic acid, 334-48-5; 2,4,6trimethylphenol, 527-60-6.
Literature Cited Bennet, C. A.; Franklin, N. L. I n "Statlstical Analysis in Chemistry and the Chemical Industry"; Wiley: New York, 1954. Brinkman, D. W.; Bowden, J. N.; Frankenfeld, J.; Taylor, W. F. ACS Symp. Ser. 1981, No. 783,297. Cook, G. L. Am. Chem. Soc.Div. Pet. Chem. Prepr. 1965, No. C-35. Davies, 0. L. "Statistical Methods in Research and Development"; Hafner Publishing Co.; New York, 1958. Dlneen, G. U.; Bickel, W. D. I d . Eng. Chem. 1951, 4 3 , 1604. Frankenfeid, J. W.; Taylor, W. F. "Fundamental Synthetic Fuel Stability Study"; First Annual Report for U.S. Dept. of Energy Contract DE-AC1979BC10045, DOE/BC/ 10045-12, Feb 1981. Frankenfeld, J. W.; Taylor, W. F.; Brinkman, D. W. Ind. Eng. Chem. Prod. Res. D e v . lg83a, preceding article In this issue. Frankenfeld, J. W.; Taylor, W. F.; Brinkman. D. W. Ind. Eng. Chem. Prod. Res. D e v . 1983b,following article in this issue. FrankenfeM. J. W.; Taylor, W. F. "Alternate Fuels Nitrogen Chemistry"; Final Technical Report for U S . Dept. of the Navy Contract No. 0019-76-C0675, NOV1977. Kenneriy, G. W.; Patterson, W. C. Am. Chem. SOC.Div. Pet. Chem. Prepr. 1955, NO. 191. Mapstone, G. E. Pet. ReNner 1949, 28, 111. Nixon, A. C. "Autoxidation and Antloxidants of Petroleum" in "Autoxidation and Antioxidants", W. 0. Lundberg, Ed., Interscience: New York, 1962; Vol. 11, Chapter 17. Taylor, W. F.; Frankenfeu, J. W. Ind. Eng. Chem. Rod. Res. Dev. 1978, 77, 86. Taylor, W. F. I d . Eng. Chem. Prod. Res. Dev. 1976, 75, 84. Taylor, W. F.; Wallace, T. J. Ind. Eng. Chem. Prod. Res. D e v . 1968, 7, 198. Thompson, R. B.; Chenlcek, I. A.; Druge, L. W.; Simon, T. Ind. Eng. Chem. 1951, 43, 935. Whlte, E. W. American Soclety for Testing and Materials (ASTM) Special Publication No. 531 (1973).
Received for review August 23, 1982 Accepted February 22, 1983
This work was supported by the U.S.Department of Energy under Contract No. DE-AC19-79BC10045.
