Table I. ~~
Concentration in equilibrating s o l u t i o q Sulfate, Phosphate, m 11 J!l 0 000
01
0 000 0 360 0 720 1 440 1 430 2 160 2 880 4 320 4 320
0 0 0 0
5 760
0 01
01 01 01
0 01 0 01 0 01
Sulfate Analyses Results
Thiosulfate used,a i d . 0 58 i 0 O4* 0 60 i 0 04 1 66 i 0 05 2 81 i 0 05 5 49 f 0 06 5 47 f 0 06 8 03 i 0 06 10 35 i 0 06 15 14 i 0 07 15 15 i 0 07 20 10 i 0 07
Sulfate, mmole Taken Found 0 0 0 0 0 0 0 0 0
0090 0180 0360 0360 0540
720 1080 1080 1440
0 0 0 0 0 0 0 0 0 0 0
Recovery,
%
0040
0041 0115 0195 0380 0381 0556 0717 1049 1051 1393
127 70 108 33 105 55 105 83 102 96 99 59 97 13 97 32 96 74
a Thiosulfate used for 20 00-nil aliquot taken out of 25 00-ml volume of the equilibrating solution The reported values of milliliters are the average of five determinations Sormality of thiosulfate is 0 06654 * Std dev for five determinations
less than 1%. Calibration of the method against the known sulfate concentrations reduces errors caused by equilibration and handling procedures. Interferences. Chloride, bromide, perchlorate, and nitrate in concentrations of 0.351 or less do not interfere. Phosphate, if present in higher concentrations than 0.0231, interferes and yields somewhat higher values t h a n those theoretically predicted Cations, which form insoluble iodates or which can oxidize iodide to iodine, must be eliminated. This can be done by passing the solution through a cation exchange resin in a hydrogen cycle and the resulting solution containing sulfate and phosphate can be analyzed successfully. LITERATURE CITED
(1) Andrew, L. JT’
Evaluation of Results. Evaluation of results is based o n the analyses of five replicate samples a t w r i o u s concentrations of sulfate and phosphate in 40yc acetone-water solutions. T h e results for the determination of sulfate are summarized in Table I. Overall recovery of sulfate varies with concentration in the equilibrating solution. However, the volume of thiosulfate used in the titration of iodate
that is liberated is directly proportional to the sulfate concentration, and thus the unknown sulfate concentration can be determined from the calibration curve. By this method, if temperature is controlled to 0.5” C., amounts of sulfate as low as 0.01 mmole (0.32 mg. of sulfur) per 25 ml. of equilibrating solution can be determined within a relative standard deviation of 2%) and at higher concentrations than 0.02 mmole, within
J . A m . Chrm. 11, 567 (1890). ( 2 ) Erdey, L., Banyai, Eva, Z . ilnal. Chem. 161, 16 (1958). (3) Jentoft. R. E., Robinson. R. J.. ASAL. CHEM.26. 1156 11954). ( 4 ) lfacdonald, A,’ M. G., Ind. Chemist 36, 345 (1960). ( 5 ) Sojbelman, B. I., Zh. Analit. Khim. 3 , 258 (19483. ~
RECEIVED for revie)? Alarch 20, 1964. Accepted June 12, 1964. Q’ork supported by a Frederick Gardner Cottrell grant in aid from the Research Corp
Densimetric Method for Characterizing Asphalt 1. W. CORBETT Esso Research and Engineering Co., linden, N. J .
b A relatively rapid and simple method for characterizing asphalt i s described. It i s accomplished b y first separating asphalt into asphaltenes and petrolenes, then applying densimetric techniques to the latter fraction. This characterizes petrolenes, the component or fraction grossly responsible for an asphalt’s physical and chemical properties. The results are expressed in terms of the fraction of carbon atoms in aromatic rings, the number of aromatic and naphthene rings per molecule, and a characterization index related to the degree of ring condensation. The densimetric technique was extended from published works b y Van Krevelen and b y Williams, and involves a calculation based upon the relationship between molar volume and atomic H/C ratio. It requires only the measurement of per cent carbon, per cent hydrogen, and the molecular weight of the petrolene fraction. This work demonstrates its repeatability and its applicability to straight reduced stocks from 15 crude
sources and to more detailed fractions obtained b y chromatography and molecular distillation of asphalts. Because of the simplicity of this method, it should prove useful in those laboratories wishing to follow changes in asphalt during manufacture, and service, and possibly for fingerprinting purposes.
&!t
.my IUETHOIIS have
been proposed for composition analysis of asphalt, but most of these are quite laborious and detailed. I n many instances laboratories are not equipped or cannot devote the time necessary for lengthy procedures, and therefore composition analyses are not carried out even when they could be the solution to For these reasons, a a problem relatively simple method for characterizing asphalt has been worked out with the hoile that it will fill this need. =isphalt is a w r y complex mixture of high molecular weight hydrocarbons of variable qize and type together with
sulfur, oxygen, and nitrogen compounds. This complexity is generally reduced by first making soine kind of a major separation. At this point a decision must be made as to the time and effort that can be devoted to further sellarations. To keep it simple, the first and most logical step is to separate the asphalt into its two structiirally distinct components, asphaltenes and petrolenes. This can he accomplished by solvent precipitation (deasphaltening) using a solvent such as n-hexane. I t has been shown that the petrolenes ( I , 4, j), are more variable in character than asphaltenes and have a greater influence on the overall properties of an asphalt. Asphaltenes are the dispersed phase of the colloid ( 6 ) and are a minor proportion of the asphalt. Although both components are necessary for the makeU ] J of an asphalt, the characterization of the petrolenea contribute> a great deal more toward characterizing the nhole asphalt. This work s h o w that petrolenes may be characterized by applying an anal) VOL. 3 6 , NO. 10, SEPTEMBER 1964
1967
EXPERIMENTAL
Complexity of Asphalt Reduced by Deasphalting. The separation of asphaltenes from the petrolenes is a
I PRECIPITATE P I T H n-HEXANE & F I L T E R AT 100 10'1
PPEC.PITAIE
PETROLENES
TENES
CARBO+
DETERUINE: PERCcY'AGE
IHYDROGEN M O L E C U L A R WT.
DENSITY FRACTION AROMATlC (rill C O I D E N S A T I O N INDEX i C l l R I N G S AROMATIC IR,,l RlSGS V A P H T H E V I C rRn)
Figure 1.
Method of separation and
densimetric analysis that identifies the average or predominating structures present. This is done by modifying and adapting the original Van Krevelen ( 7 ) densimetric technique. I t involves a calculation based upon the relationship between molar volume and atomic H/C ratio and requires only a measurement of per cent carbon, per cent hydrogen, and molecular weight.
Table I. The Relative Meaning of Condensation Index Ring structures Poly-condensed Cata-condensed Peri-condensed
For of carbon in rings 100 0 33 0 50 1 00
50 0 17 0 25 0 50
25
0 08 0 13 0 25
Table 11. Calculation of Test Parameters by the Densimetric Method Example By Measurement: MW = hlolecular Weight %C = Wt. ciCarbon YcH = Wt. 9; Hydrogen By Calculation: d 20/4 = density = 1.4673 - 0.0431 (C/H) H/C = hydrogen/carbon ratio = 11.92 (C/H/7&) J f c l d = atomic molar volume = 1201/(d 20/4 %C) ( J t ~ / d )=~ molar volume
976 86 0 10 8 1 001 1 50
13 9
I "
ja= fraction aromatic = 0.09 ( . l f ~ / d ) c - 1.15 ( H / C )
+
0.77 (3.1. = concentration index = 2 - H/C - j a I C = av. number of car-
bon atoms MW)/1200
1t
=
(GC
0 28 0.22
logical one because of the big difference between the chemical structure of these fractions. This does much toward reducing the complexity of a n asphalt, thus making the petrolenes available for subsequent analysis and characterization. The schematic procedure for asphaltene/pe trolene separation and petrolene characterization is relatively siniple and is illustrated in Figure 1. Initially, it involves treating 5 grams of asphalt' with n-hexane in a 2011 ratio. After dispersion by refluxing, the asphaltenes are separated by filtering a t 100" F. through a Gooch crucible using a glass fiber filter paper (Huribut 934-AH, 3.2 cm., Reeve Angle R. Co.), washing, drying, and weighing. The hexane solubles (pet,rolenes) are recovered by stripping off the hexane in a 250" F. vacuum oven under a small stream of nit,rogen. These petrolenes, without further treatment, are then characterized by subsequent analysis. Development of the Densimetric
Method for Characterizing Hydrocarbon Mixtures. ;imethod of characterizing hydrocarbon mixtures, based on density and per cent, carbon and hydrogen was firat, developed by Van Krevelen (7-9) and termed the statistical-graphical method. This author found that ryhen the molar volume per carbon atom was plotted against atomic H,'C ratio for pure hydrocarbons, lines of constant aromatic ring carbon could be drawn. Aromatic ring carbon is herein identified by the term. fa, which is defined as the fraction of carbon atoms in aromatic rings, and for brevitjy ip: termed, fraction aromatic. These lines of constant' aromatic carbon were found to be parallel and approximately equally spwed for equal incremenh of fa, and were also api)rosimat'ely parallel t'o the lines for paraffins. Van Krevelen thus showed that fa can be det,ermined for an unknown hydrocarbon or hydrocarbon mixture by measurement of molar volume per carbon atom and the atomic H O Cratio. The original densimetric method was applied by Van Krevelen to the analysis of coal and \vas used later by Yen (11). The method of Van Krevelen was then modified by \\T'illiams (10) using data from M I project' 42. He constructed a better relat'ionship of molar volume t o atomic H / C as shown in Figure 2. The following equation was then cast by Williams using data from t,he figure.
.
total number of rings/ mole = [*C(C I )/2]
70
ja= 0.09
=
+ 1
number of carhon in aromatic rings = f,,
JC,
- 1.15
0.77
where
=
(*C)
R, = number
of aromatic ring/mole = (43, - 2)/4 Iln = number of naphthenic rmgs/niole = It - R a
1968
8 7
(7) (g) +
ANALYTICAL CHEMISTRY
19 8
4 4 4 3
carbon mass - molar volume per mass/volLime carbon atom
ATGh'lC H / C
Figure 2. Relationship of molar volume to atomic H/C ratio using data from API Project 42
H/'C
j a
=
C C
(11.92) . %H __ = %C atomic H/C ra,tio aromatic carbon total carbon fraction aromatic
Williams also shot\-ed that confidence can be placed in this equat,ion by linearly relating calculated values with known values of fa on repre>entative high molecular weight compoundi; made UJI of single rings, uncondensed niultiple rings, and condensed rings with and without, naphthene rings. In the Van Krevelen ivork a relationship between the fract,ion aromatic, HiC ratio, t,otal rings (R), and total weight per cent carbon (C) was also given :
2(R - 1) ___ C
=
2 - H/C
- fa
The first terin is known as the ring condensation index ('2.1.) which becomes slightly negative for paraffins. 0 for single rings, and positive for multirings. RESULTS
Table I serves as a guide for interpreting the ring index with respect to the various ring structures. These are the maximum values which will be obtained from infinite ring structure based on six-membered rings. The Williams formula and the Van Krevelen relationship were used as the basis for deriving equations for such test parameters as fraction aromatic, condensation index, number of aromatic rings, and number of naphthene rings as shown in Table 11. I3ecause of assumptions that must he made in the calculation. the values for. the number of rings is the weakest of all reported parameters.
Characterization of Petrolenes Accomplished by Applying the Densimetric Method. Segregation of the petrolene fraction provides an opportunity for appl ig the densimetric method of anal) ;inalyses for niolet metric method (Z)], per cent carbon, and gen can lie accomplished methods. The densiis then made by following the calculation step also shown in Table 11. On the basis of sis repeat tests, most of whirh were made o n different testing days;, Table 111 show!, that test results can be repeated i n an acceptable manner. The standard deviation of each measured 1)aranieter i s reasonably lowv.with coefficients of variation well under 10%. For emi)irically based test ~iaralneters,this is quite good. Densimetric Method Applicable to Characterization of Chromatographic Fractions. T h e ability of the method t o reflect large differences in composition are apparent from the analyses of four chromatographic fractions (3) separated from 1)etroleries and shown in Table IV. In this case an obtained by the use of nuclear 'c resonance ( S l I R ) can be coiii1)ared with that obtained by the tleii,~iiiietric~ method. Ihsically. the two methods are quite dissimilar. The depend^ upon a measureydrogen distribution together w i t h clenien1al analysis and calculation 10 arrive at the index of liranrhing, the chain lengtli: and the number of rings. 'The densimetric method laces the most rmphasiq on the fravtion of ciarbon in aromatic- ring3 derived f'loni a relationshill of molar. volume to H C ratio :is described abovc. 1 % coiiil)aring ~ thr ixiranieters between thp c~hroiiiatogral)hic. fractions, 1arg.r diffcrenccs are reflerteil by both iiiethotls. Sota1)le is the fraction aromatic which moat directly intlics,tc,.< the relative aromatic- rh:tracter of a given fraction. Further evidrnw oi the adal)tability of the method is shripvn in Table TT. Hew H com1)arision i,s drawn between a dciisimetric anal? ~)ctri~lcneh and a n.eighted summation of r w u l t s fi,oni four fractions separated froni the saiiw ~)etr(ilenesby chroins-
Characterization of Molecular Distillation Fractions. D a t a shown in T a 11 IC, V 1 i 11List r a t e t lit a 11pli 1-at ion of tlie tiensinirtrio nirthotl of molerular distillation fractionelxirat(+ on the hasi-. of 1)oilirig ljoint wliic~hrc.latr-: t o increasing molecular wvcighi. For this part i ('u1:rr sa ni 1) I P the ar o ma t i? char a('t cr inrre:iwq with hcreasing nli)Ie(~ul:+rsizc. 'The nuniber of total rings anti the ~
Table 111.
Repeat Analysis of a 91 Penetration Venezuelan Straight Reduced Asphalt
s o . of tests 6
'Z Asphaltenes On Pitrolenes hlolecular Weight
Ilensitv Fraclticin iiromatic Condensation Index Rings Aromatic Rings Saphthenic Carbon/Itydrogen Ratio
Table IV.
Coef.
Av. value
15 3 657
6 6
39 0 004 0 007
0 998 0 25 0 22
6 6 6 6
6
var., b(, 1 8
Std. dev. 0 28
6 0
0 4 2 8
...
, . .
2 4 3 6
0.17 0.17
4.7
7 8
0 07
0 9
7.1
Analyses of Four Chromatographic Fractions Separated from Petrolenes from a Venezuelan Straight Reduced Flux
Isphalt fraction S M R Analysis Branrhiness Index, B.I. CarbonslSide Chain, C/SC Ring Aronmticv, Ito
Parafins
+
~
~~
~
1
2
3
0.28
0 90 13.2 1.2
0 . .is
0.60
0 14 0.14
0 2;j
...
0 0
Ilensirrietric~Analysis Fraction Aromatic, Condensation Index, (2.1. Rings Aromatic, I < & Rings Saphtheriic, Rn
0.01 0.04 0.0 1.9
6.7 4.2
5 6 5 6
0 35
0.24 2.6 4.4
1.2 3.2
condensation index also increase, indicating more c~omplete latticae t y ) e structures in the higher molecular n-eight fractions. This exanil~ledemonstrate.; the applicability of the densimetric method to fraction\ where sei)aration is made on the ba-is of molecrilar .size rather than by tylje. Densimetric Method Used to Characterize Paving Binders. 'The need for composition anal! preising in t h e c a w of asphalt Iiaiing binder. (See also reference us treatment of viater-
EXPERIMENTAL
lcrtic acid na-. di.tilled three timer, the fraction Imling at 117-18" C.
being collected; aniline was distilled three timer, the fraction boiling at 153-4" C. being collected. .\bsolute methanol was treated with silver nitrate and distilled over potassium hydroxide through a fractionating column. Potentiometric titrations were made a t 25" C. with a "Labelled Beckman Glass Electrode-] 190-60," a saturated calomel electrode with a porous fiber junction, and a lleckman Model G pH meter. The electrode !vas standardized with aqueous phthalate (pH 4.01) and phosphate (1iH 6.86). -hiline in methanol-water solvents was converted to its hydrochloride by the addition of the requisite amount of hydrochloric acid. Solutions of acctic acid and anilinium hydrochloride, each al)lmximately 0.01 molal, were titrated with 0.1 inolal aqiicous sodium hydroxide with parallel addition of pure methanol to maintain the methanol-water composition constant, About 12 pH nieasurements were made during the course of each titration, hetween about 20 and SOYc neutralization. IVith the aid of these pH values, values of ])I
