Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 2, 1978
165
Studies on Kuwait Crudes. 1. Composition Analysis of Some Asphalts and Their Sulfurized Products Yusuf A. AI-Farkh,' Nizar R. El-Rayyes,' and Khairya A. AI-Zaid Petroleum & Petrochemicals Division, Kuwait Institute for Scientific Research, Kuwait
The differences in the chemical composition of five asphalts and one air-blown bitumen, obtained from Kuwait crudes, were studied using the densimetric technique. Two asphalts were then reacted with different weight percent of sulfur at 220 O C , and the effect of sulfur was followed by studying the composition analysis of the products. The results obtained revealed that the reaction with sulfur leads to an increase in the percent of asphaltene, which contains most of the bonded sulfur. It was also found that the above reaction increases the average number of carbon atoms per molecule as well as the aromaticity. The addition of up to 5 wt % of sulfur led to no significant increase in the sulfur content of the products.
Introduction T h e need for composition analysis is most pressing in the case of asphalt paving binders. This is due to the fact that over 70% of total asphalt sales are used for paving purposes. These asphalts have differences in their physical properties due to their crude source. These differences can be explained most logically by studying their composition. T h e composition of asphalt and other heavy residue fractions was the subject of several investigations over the years, because the obtained data will provide a great deal of help in the handling of problems related to the usage of asphalt. Many methods have been proposed for composition analysis of asphalt, but most of these are quite laborious and detailed. A few of the more commonly cited literature sources are those of Marcusson (1916), Grant e t al. (1940), Rostler et al. (1949), Traxler et al. (1953), Jewel1 et al. (1974), and Haley (1975). In the present investigation a relatively rapid and simple method for characterizing asphalt was used. This was described by Corbett (1964) and is known as the densimetric method for characterizing asphalt. I t can be accomplished by first separating asphalts into asphaltenes and petrolenes, then applying densimetric techniques to the latter fractions, whereby they can be characterized. Further information about the composition of the petrolene fraction can be obtained using the method suggested by Corbett (1969), which involves solvent deasphaltening for recovery of asphaltenes, followed by elution-adsorption chromatography to yield saturates, naphthene-aromatics, and polar-aromatics. The densimetric method was then applied to define the average chemical structures present. Further insight concerning the chemical composition of asphalts can be obtained from the evaluation of the C/H ratio, or chemical constant, of the heavy residues, and their fractions. Another objective of the present study was to investigate the reaction of sulfur with some heavy residues and to follow up the changes in their chemical composition. For this purpose the above-mentioned techniques of composition analysis were applied. I t is intuitively obvious t h a t this sort of information will be of prime importance in understanding the physical and rheological properties of the modified asphalts. Experimental Section Materials. The three atmospheric bottoms (A, B, C), the two vacuum bottoms (D, E) and the air blown bitumen (F) were kindly provided by the refineries of the Kuwait Oil Co. D e p a r t m e n t of Chemistry, University of Kuwait, Kuwait.
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(KOC), Kuwait National Petroleum Co. (KNPC), and Amin Oil Co. The elemental sulfur was obtained from KNPC. Commercially available Analar or reagent grade solvents were used (n-heptane, benzene, methanol, and trichloroethylene). The alumina used in chromatography was Brockmann Grade 1.The column was prepared from a piece of 3 X 100-cm borosilicate tubing with a quick fit joint a t the top, to fit the dropping funnel. Procedure. The reactions were carried out with molten sulfur a t atmospheric pressure without using any catalyst in a four-neck flask fitted with a stirrer, a thermometer, a reflux condenser, and gas outlet. Asphalt was treated with different w t % sulfur at 220 f 5 "C. The course of the reaction was followed by determining the generation of hydrogen sulfide by the use of lead acetate solution. The elemental analysis and average molecular weight determination (osmometry) were performed by A. Bernhardt Microanalytical Laboratory, West Germany. Fractionation. This was performed by treating 10 g of asphalt or the sulfur treated product with 200 mL of n-heptane. After dispersion by refluxing, the asphaltenes are separated by filtering a t 38 "C in a Buchner funnel having a fine porosity filter disk. The precipitate was washed with 100 mL of n-heptane in several portions. The solid consisted of asphaltenes. The fraction soluble in n-heptane was recovered by evaporating the solvent under vacuum. The heavy oil obtained was the petrolene. Densimetric Analysis. This requires only the estimation of percent carbon, percent hydrogen, and the molecular weight of the petrolene. I t involves a calculation based upon the relationship between molar volume and atomic H/C ratio (Corbett, 1964, 1969). The calculations are carried out according to Table I. Results and Discussion T h e present investigation intends to characterize three straight-run and two vacuum bottoms in addition to an airblown 60/70 penetration asphalt binder. All the investigated materials originate from Kuwait crudes and are supplied by different Kuwait refineries. Table I1 illustrates the physical properties of the tested materials. T h e composition analysis of the petrolenes of these materials was studied using the densimetric technique. The results are summarized in Table I11 in terms of element analysis, molecular weight, fraction of carbon atoms in aromatic rings, average number of carbon atoms per molecule, and the number of aromatic and naphthenic rings per molecule. Since the fraction of carbon in aromatic rings and the number of (C 1978 American Chemical Society
166
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 2, 1978
Table I. Calculation of Test Parameters by the Densimetric Method
0
By Measurement = Molecular weight = Wt % carbon = W t % hydrogen
MW %C %H
Asphaltene Petrolene
C
1
By Calculation = Density = 1.4673 - 0.0431 (% H) = Hydrogedcarbon ratio = 11.92 (% H/% C) = Atomic molar volume = 1201 (de% C ) = Molar volume corrected for heteroatoms = Mc/d - 6.0( 100 - % C - % H)/% C = Fraction aromatic = O.OS(Mc/d), - 1.15(H/C)
+
0.77 = Condensation index = 2 - H/C - f a = Average number of carbon atoms = (% C.MW)/ 1200 = Total number of ringdmol = (#C(C.I.)/2) + 1 = Number of carbon in aromatic rings = f a ( # C ) = Number of aromatic ringdmol = (#Ca - 2)/4 = Number of naphthenic rings/mol = R - R ,
C.I. #C
R
Figure 1. Asphaltene/petroleneratio of untreated and treated asphalt (D).
Asphaltene
0 Petrolene
Table 11. Physical Properties of the Asphalts
AsDhalts"
Characteristics
1
Values
A
Specific gravity (60/60 OF) 0.9786 Kin. viscosity 122 OF, cSt 938 4.24 Sulfur, % wt 0.968 B Specific gravity (60/60 O F ) Kin. viscosity 210 O F , cSt 40 4.4 Sulfur, % wt 1.010 D Specific gravity (60/60 OF) 725 Kin. viscosity 210 OF, cSt 5.3 Sulfur, % wt E Specific gravity (25 O C ) 1.010 Kin. viscosity 210 OF, cSt 750 5.06 Sulfur, % wt " A = atmospheric bottom; B = atmospheric bottom; D = vacuum bottom; E = vacuum bottom.
rings per molecule are indicative of the degree of aromaticity, it can be envisaged that the vacuum bottoms (D) and (E) as well as the air-blown bitumen (F) have more aromatic character than the atmospheric bottoms (A, B, C). Also, the fact that the condensation index has a positive value indicates that the rings in the molecules are of the multiple type. Other differences in the chemical composition of the atmospheric bottoms (A-C) on one hand and the vacuum bottoms (D, E) on the other hand can be noticed. It is noteworthy to mention in this respect that the air-blown bitumen (F) and its percursor (E) show no major differences in their composition analysis. T h e reaction of different weight percent of molten sulfur with the two vacuum bottoms (D and E) a t 220 "C was also investigated, and the composition analysis of the petrolene obtained from the products was studied using the densimetric
Figure 2. Asphaltene/petroleneratio of untreated and treated asphalt (E).
technique. Figures 1 and 2 illustrate the effect of sulfur reaction on the asphaltene content of the feeds (D, E) and their products. This illustrates the direct relationship between the amount of sulfur added and the asphaltene content. Table IV summarizes the densimetric analysis of the petrolene fractions obtained after reaction with sulfur. It can be disclosed that the above-mentioned reaction leads to a general increase in both the average number of carbon atoms in the molecules as well as in the degree of aromaticity. The latter is indicated by the increase in the fraction of carbon in aromatic rings and the number of rings per molecule. This increase in the degree of aromaticity is of importance when the resins are being adsorbed by the asphaltene particles; thus higher aromaticity of petrolene leads to better solvency for the asphaltenes. Also the increase of rings leads t o high solvency. This solvent power of the petrolenes is one of the most important considerations in understanding the physicochemical behavior of the asphalt colloid system. The amounts of bonded sulfur in the feeds and products as
Table 111. Densimetric Analysis of Asphalts and the Air-Blown Bitumen % As-
ASphalt"
%C
%H
%S
%N + O MW d20/4 H/C Mcld ( M c l d ) ,
fa
C.I.
0.2 0.2 A 84.49 11.27 4.04 0.2 387 0.98 1.6 14.48 14.18 0.2 0.19 B 84.35 11.85 4.13 0.34 313 0.98 1.59 14.44 14.12 0.19 14.23 0.2 C 84.23 11.3 4.22 0.25 361 0.98 1.6 14.5 0.23 0.21 D 83.6 10.85 4.93 0.62 692 0.99 1.55 14.37 13.98 E 84.5 10.96 4.32 0.22 599 0.99 1.55 14.35 14.03 0.25 0.2 13.8 0.25 0.21 F 84.35 10.84 4.44 0.37 556 1.10 1.50 14.2 " A, B, C = atmospheric bottoms; D, E = vacuum bottoms; F = air-blown bitumen.
#C
R
#Ca
R,
27.24 3.72 5.4 0.85 22 3.17 4.66 0.66 5.06 0.76 25.3 3.4 48.2 5.8 11.47 2.3 42.17 5.21 10.54 1.62 9.7 1.9 39 5.1
R,
phaltene
2.9 4.66 4.5 2.5 2.63 8.6 3.45 8.19 3.59 6.4 3.19 22.5
Ind. Eng. Chem. Prod. Res. Dev.,Vol. 17, No. 2, 1978
167
Table IV. Densimetric Analysis of Asphalt (D) and (E). Untreated and Treated with Different Weight Percent Sulfur
%S Feed
added
D
0 1
3 5 8 9 10
E
0 1
3 5 8 9 10 15
%C
%S
%H
83.6 10.85 4.93 83.51 10.58 5.1 82.69 10.88 4.70 83.03 10.21 6.21 82.83 10.66 5.74 82.89 10.69 5.86 81.45 9.67 8.42 84.5 10.96 4.32 83.66 10.68 4.87 83.28 10.46 5.46 83.1 10.35 5.97 81.96 10.91 5.06 82.57 10.9 5.48 82.34 10.07 7.14 79.33 9.66 10.47
M W d20/4
H/C
Mc/d ( M c l d ) ,
692 0.99 656 1.01 861 0.999 728 1.02 755 1.01 748 1.01 826 1.05 599 0.99 664 1.007 811 1.017 667 1.02 715 0.997 818 0.997 788 1.03 705 1.05
1.55 1.50 1.568 1.47 1.53 1.53 1.42 1.55 1.52 1.497 1.49 1.586 1.573 1.46 1.463
14.37 14.24 14.54 14.08 14.40 14.48 14.04 14.35 14.35 14.27 14.13 14.65 14.58 14.16 14.41
Product RAsphaltene OPetrolene
I
13.98 13.82 14.07 13.59 13.92 14.02 13.39 14.03 13.95 13.83 13.66 14.12 14.11 13.6 13.58
:
:
.
.
.
’
:
-
0.23 0.29 0.236 0.29 0.259 0.26 0.34 0.25 0.28 0.29 0.299 0.22 0.24 0.303 0.31
(2.1.
0.205 48.2 0.21 45.65 0.20 59.33 0.23 50.37 0.207 52.11 0.20 51.66 0.23 56.06 0.20 42.17 0.20 46.29 0.213 56.28 0.21 42.08 0.19 48.83 0.187 56.28 0.23 54.06 0.277 46.6
:
‘
MW
R 5.8 5.79 6.93 6.86 6.39 6.16 7.55 5.21 5.62 6.99 5.41 5.63 6.26 7.2 6.28
#C,
R,
R,
11.47 13.23 14.0 14.6 13.49 13.58 19.06 10.54 12.96 16.32 12.58 10.74 13.5 16.38 14.44
2.3 2.8 3.0 3.15 2.8 2.89 4.26 1.62 2.74 3.58 2.64 2.18 2.87 3.59 3.11
3.45 2.99 3.933 3.718 3.59 3.27 3.29 3.59 2.88 3.41 2.76 3.45 3.38 3.62 3.17
General formula C/H (atomic)
:
1
0
#C
Table V. General and Series Formulas of Untreated Asphalts and their Fractions
Asphalt
:Iz
fa
1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 % 5 added ( T of reaction 220 .C :)
X
0.63 0.63 0.63 0.67 0.66 0.67
16.64 19.5 16.2 32.3 25.1 26.0
0.62 0.62 0.62 0.64 0.64 0.64
11.88 9.0 9.8 21.3 18.7 17.9
Figure 3. The relationship between bonded and added sulfur in the asphalt product (D) and its fractions.
0.91 0.89 0.87 0.92 0.92 0.91
.
Product Asphaltene 0 Pet rolene
12
hydrogen sulfide. Addition of more sulfur to the reacting feeds leads to an increase of the sulfur content of the products, as well as their fractions. Thus by higher sulfur ratios (above 5 wt %) the sulfur probably acts as dehydrogenating and condensing agent. It can be noticed from Figures 3 and 4 that the two feeds differ slightly in their consumption of the added sulfur. This is obvious from the higher sulfur content of the products of feed (D). Other distinctive characteristics of the materials under investigation are forthcoming from their atomic carbon-tohydrogen ratio as well as their deficiency of hydrogen ( x ) according to formula CnHPn - x. Table V illustrated the C/H atom ratio, and the general series formulas of the different crudes and the air-blown bitumen, as well as their petrolenes and asphaltenes. The latter have a pronounced heterostructure and show a decided hydrogen deficiency and a relatively high C/H atom ratio, which reflect their aromatic character. The hydrogen content increases in petrolenes and hence their C/H atom ratio decreases, which supports the idea t h a t they are composed mainly of cyclic rings, mostly naphthenic, and branched hydrocarbon chains. The reaction of different weight percent of sulfur with the two asphalts (D) and (E) affected the chemical composition
:tL 1
0
1 2 3 4 5 6 7 8 9 101112 */. 5 added ( T of reaction 22O.C:)
Figure 4. The relationship between bonded and added sulfur of the asphalt product (E) and its fractions.
well as their petrolene and asphaltene fractions of vacuum bottoms (D) and (E) are illustrated in Figures 3 and 4. It can be envisaged that for any of the feeds or products the sulfur content of the asphaltene fractions is considerably higher than that of the petrolene fractions. Furthermore, the addition of up to 5 wt % sulfur to the two feeds does not show a significant increase in the amount of bonded sulfur in the products or their fractions. This indicates t h a t most of the added sulfur has acted as a dehydrogenating agent leading to evolution of
211.9 247.5 204.4 409.7 175.1 173.8
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 2, 1978
Table VI. General and Series Formulas of Sulfurized Asphalt (D) and Its Fractions
%S Type Products
added MW
General formula
3 5 8 9 10
Petrolenes
1
3 5 8 9 10 Asphaltenes
1
3 5 8 9 10
X
0.67 0.65 0.64 0.70 0.88
30.03 29.78 17.6 32.7 34.0 18.16 21.9 24.99 26.44 23.74 23.36 32.25 313
0.88 0.86 0.87 0.87
315.9 304.6 191.8 228.9 279.5
Type Products
X
1
0.68 0.67 0.63 0.70 0.69 0.64 0.63 0.65 0.66 0.67 0.62 0.63 0.68 0.68 0.88
26.8 25.9 19.1 31.4 32.36 16.5 15.56 21.68 27.73 21.36 19.66 23.4 28.79 25.1 288.66
3 5 8 9 10 15
0.92 0.88 0.87 0.86 0.87 0.87
324.8 180.85 200 180.8 239.5 238
3 5 8 9 10 15 Petrolenes
1
3 5 8 9 10 15 Asphaltenes
of their petrolenes and asphaltenes. Thus, in petrolenes it led to a general increase of the average number of carbon atoms per molecule and the deficiency in hydrogen ( x ) . These changes are reflected in their general formulas. Consequently, there is a slight increase in the C/H atom ratio (cf. Tables V, VI, and VII). The asphaltenes derived from the feed (E) showed similar behavior to the above petrolenes upon treatment with sulfur. However, the asphaltene of the sulfurized asphalt (D) showed different behavior. Upon treatment with sulfur this showed a decrease in the number of carbon atoms, the C/H atom ratio, and the hydrogen deficiency, as compared to the untreated asphaltene. This anomalous behavior can be interpreted by taking into consideration the particular reactivity of sulfur with the resins found in petrolene. These resins, under the catalytical effect of sulfur, undergo dehydrogenation and condensation toward higher molecular-weight material of low
R-CH-R
+ HSX
(1) (2)
.sx
R-CH-R
-, R, CH-SX-CH-R,
+ R-CH-R 1
.sx
2R-CH-R 2R-CH-R
-
(3)
(41
R,-CH-CH-R, R,CH-S,xCH-R,
(5)
.AX
HSX
HS. + SX - 1
--t
+ HS.
R-CH,-R
-,
R-CH-R
+ H,S
(6)
Scheme I1
+
C/H (atomic)
1
General formula
-
R-~H-R+.SX+ R-CH-R I
Table VII. General and Series Formulas of Sulfurized Asphalt (E)and Its Fractions %S added MW
+ .si
R-CH,-R
C/H (atomic) 0.68 0.69 0.62 0.69 0.69 0.63 0.65
1
Scheme I
HSx
-
+
HSxH
I -+
\
+
aromatization
\
HSxH
-+
H,S
+
*Sx-1
hydrogen content or asphaltene. It seems that the asphaltenes thus formed have lower molecular weight, with more aliphatic chains or longer chains on the ring, than the original asphaltene of the untreated feed. I t can also be deduced from the data in Tables V-VI1 that the C/H atom ratios of the petrolenes and the corresponding asphaltenes of the sulfurized asphalts approach each other more closely than those of the untreated feeds. This result may lead to better dispersion of the fractions. According to Hughes and Hardman (1951), incomplete dispersion results when asphaltenes differ too greatly in C/H atom ratio from petrolenes. A study of the literature concerning the mechanism of the sulfurization of asphalt reveals that a chemical reaction takes place between sulfur and the different hydrocarbon constituents of asphalt, by temperatures over 200 "C. This reaction proceeds by a free radical mechanism, initiated by the formation of the sulfur free radicals by the effect of high temperature. Accordingly, three major types of bonding may occur, namely, the sulfur-hydrogen bonds leading to hydrogen sulfide formation, the sulfur-carbon bonds, and the carboncarbon bonds. It can be assumed that the added sulfur will act both as a dehydrogenating and a linking agent (Petrossi et al., 1972; Tucker et al., 1965). Scheme I illustrates the proposed mechanism for the formation of the different types of bonds (cf. Tsurugi, 1958). In the light of the above free radical mechanism (Scheme I), the increase in the aromatic fraction, as a result of sulfurization, can be interpreted by assuming that the naphthene aromatics of resins will be aromatized according to Scheme 11. Several types of products can be also formed during the reaction of sulfur, among which are the sulfurized aromatics
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17,No. 2, 1978
(Silverwood e t al., 1962) and the substituted thiophenes (Rasmussen e t al., 1946). The types of sulfur products will be the subject of another investigation. Acknowledgment The authors wish to record their appreciation to the Kuwait National Petroleum Company (KNPC) and the Kuwait Oil Company (KOC) for providing the asphalts and sulfur. Literature Cited Corbett, L. W., Anal. Chem., 36, 1967 (1964). Corbett, L. W., Anal. Chem., 41, 576 (1969). Grant, F. R., Hoiberg. A. J., Proc. Assoc. Asphalt Paving Technol., 12, 87 (1940). Haley, A. G., Anal. Chem., 47, 2432 (1975)
169
Hughes, E. C.. Hardman, H., Proc. Assoc. Asphalt Paving Technol., 20, 1 (1951). Jewell, D. M., Albough, E. W., Davis, B. E., Ruberto, R. G., lnd. Eng. Chem. Fundam., 13, 278 (1974). Marcusson, J., Z.Angew. Chem., 29, 21 (1916). Petrossi. U., Bocca, P.L., Pacor, P., lnd. Eng. Chem. Prod. Res. Dev., 11, 214 (1972). Rasmussen, H. E., Hansford, R. C., Sachanen, A . N., lnd. Eng. Chem., 38,376 (1946). Rostler, F. S.,Sternberg, H. W., lnd. Eng. Chem., 41, 598 (1949). Silverwood, H. A,, Orchin, M., J. Org. Chem., 27, 3401 (1962). Traxler, R. N., Schweyer, H. E., OllGasJ., 52, (19), 158 (1953). Tsurgi, J., Rubber Chern. Technol., 31, 762 (1958). Tucker, J. R., Schweyer. H. E., Ind. Eng. Chem. Prod. Res. Dev.. 4, 51 (1965).
Received f o r review September 6, 1977 Accepted January 23,1978
Symposium on Interfacial Phenomena in Corrosion Protection A Review of Electrochemical Corrosion Fundamentals Thaddeus M. Muzyczko The Richardson Company, Research and Development Division, Melrose Park, lllinois 60 160
Of the many types of corrosion, those brought about by electrochemical reactions are a cause for major concern and study. For this type of corrosion to occur a corrosion cell consisting of an electrolyte, a cathode, an anode, and a flow of electrons between these electrodes is needed. The basic thermodynamics and kinetics are reviewed using “ideal models”. Limitations of these models and practical extensions for real cases are discussed. A summary of what we do know and do not know about electrochemical corrosion is presented.
Introduction T h e corrosion of metals is a multibillion dollar worldwide problem that results in losses of materials, energy and even lives (Znd. Week, 1975). If you own a car and drive in a metropolitan area, corrosion is a readily visible, annoying phenomenon. Pitted chrome trim, rotting rocker panels, and frozen bolts are loud testaments to the fact t h a t we have not yet licked the corrosion problem. T o be perfectly fair, the solution to corrosion problems requires many considerations these days: effectiveness, ecology, environment, effluent, emissions, energy, economy, and exasperation (Mazia, 1977). Often post-treatments and/or periodic retreatments of surfaces are the only current answers. Corrosion in general may be classified by its appearance, uniform or nonuniform, which may be microscopic or macroscopic (Henthorne, 1971a). The nature of the corrodant (wet or dry) is also a means of classification (see Figure 1). The two major mechanisms of corrosion are by direct chemical and electrochemical reactions. Most corrosion reactions, particularly of iron, are electrochemical in nature. Electrochemical corrosion is here defined as the unwanted and usually destructive oxidation of metals. I t is the main topic of this paper. Major considerations are surfaces and interfacial phenomena. For electrochemical corrosion to occur, a corro-
0019-7890/78/1217-0169$0.100/0
sion whole cell is needed, Le., an electrolyte, electrodes (anode-cathode), and an electron flow between the anode and cathode. Attempts to stifle these factors are the basis of current attacks on corrosion. Ideal Models The concept of a so-called “ideal model” will be used as a convenient basis to introduce the well-studied corrosion reactions. The more complicated and unfortunately more common “nonideal models” will be introduced later. An ideal model is a well-behaved, uniformly, freely corroding metal in contact with an ideal electrolyte and having no inhibiting or accelerating side reactions. A representation of such a surface is shown in Figure 2. For corrosion to occur as with any chemical reaction, two major questions arise: (1)will a metal corrode in a given environment to a calculable equilibrium point? and (2) how fast? The first question is answered by thermodynamics; the second by kinetics. Thermodynamics Why do some metals corrode in given environments? Can their tendencies to corrode be predicted? Thermodynamics can answer these questions. Practical observations indicate that most commercial metals are more stable as oxides or compounds rather than in their free metallic forms. Iron is
0 1978 American Chemical Society
