Changes in Chemical Composition of a Kuwait Short Residue during Air Blowing Graeme A. Haley' School of Highway Engineering, University of New South Wales, Box 1, P.O., Kensington, 2033, NSW, Australia
A Kuwait short residue was blown with air at temperatures of 200 and 245 O C to viscosities 1800-3000 poise and 100000 poise. The asphalts produced were then fractionated by gel permeation chromatography and the fractions obtained were examined by nuclear magnetic resonance and infrared spectrometry. Fraction mean molecular weight and elemental composition were also measured. Blowing the short residue at 200 rather than 245 O C increased the degree of polymerization (main chemical reaction) and reduced internal cross-linking, dehydrogenation, and decarboxylation. This results in better molecular flexibility. Average paraffinic chain length was also higher for the asphalts blown at the lower temperature. In ail asphalts, polymerization and the formation of high molecular weight material was not through ester linkages.
The treatment of petroleum residues by blowing with air is used extensively for the production of paving grade asphalts. The physical nature and behavior of these asphalts like all organic substances depend on the structure and molecular weight of the elements they contain. The effect of temperature in the air blowing process was first studied by Ichikawa ( I ) in 1936. He considered low blowing temperatures produced asphalts with what he called superior physical properties. Later studies, where asphalt quality was measured either by durability (2-4) or susceptibility to hardening ( 5 ) ,appear to confirm the deleterious effect of high temperature air blowing. Lower temperature operations, however, result in lower outputs and increased production costs and until recently were considered uneconomical. Improvements in reactor design and efficiency of air utilization (6, 7) are allowing re-examination of lower temperature operations. The chemical changes produced by air blowing have been only superficially examined. Knotnerus (8-10) accounted for all oxygen take up by asphalt during air blowing as hydroxyl, carbonyl, and ester groups. Esters were believed to be important not only because they contributed 60% to the retained oxygen balance but because they could link two molecules together to produce higher molecular weight material. Campbell and Wright (11) disputed the formation of esters and from Petersen and coworkers' extensive studies (12, 13) the most accepted groups formed now are carboxylic acids, ketones, probably alkyl aryl, and dicarboxylic anhydrides. This leads to a change away from ester formation as the principal condensation mechanism during air blowing. Other mechanisms have been offered from physical data studies. Smith and Schweyer ( I 4 , 1 5 ) ,measuring heat of reaction of the air blowing process for different temperatures and crudes, postulated dehydrogenation of naphthenic rings as the main reaction and with some formation of oxygen function groups which could undergo decarboxylation as temperatures increased. 'Present address, Castrol Australia Pty. Ltd., Box 100, P.O., Guildford 2161, NSW, Australia. 2432
Fractionation into discrete samples with homogeneous properties is usually the first step in any attempt to determine the chemical make up of organic mixtures. Gel permeation chromatography has a number of advantages when compared with other fractionation systems which have been applied to asphalt. I t separates the asphalt according to molecular size and returns good yields with little alteration to the properties of the material. Suitable calibration of each asphalt chromatogram can be made by molecular weight measurements. Further examination of the fractions provides an insight into their chemical and structural homogeneity or heterogeneity. I t is these properties which greatly influence the physical and chemical behavior of each asphalt, while a comparison of these properties enables the differences in asphalt performance due to different blowing conditions to be explained. A structural analysis system suitable for asphalt has been described previously ( 1 6 )and it is intended in this paper to apply this system to a number of asphalts produced under different air blowing conditions and to examine the changes produced.
EXPERIMENTAL Air Blowing Process. A small pilot plant blowing still was used to produce four air blown asphalts from a Kuwait short residue. The still consisted of an electrically heated stainless steel cylinder of inside diameter 10 cm and height 60 cm. Air at the rate of 5 lit e d m i n was introduced through a number of small holes a t the bottom of the still. The 3.3-kg charge was stirred by four flat paddles attached to a central spindle. Temperatures were monitored by a mercury-in-steel thermometer and cooling water was circulated through the still to maintain the temperature a t the required value. Two blowing temperatures, 200 and 245 "C were used. Trials were run a t each temperature t o measure the change in viscosity with time, as determined by a capillary vacuum viscometer. Runs were then made to produce blown asphalts of viscosities at 60 "C of 1800-3000 poise and 100000 poise. Fraction Preparation. The four blown samples and the short residue were fractionated by gel permeation chromatography on a 2-cm i.d. X 150-cm long column with two pore size polystyrene gels prepared by the method given by Altgelt ( 1 7 ) . The solvent, 90% benzene-10% methanol, was used with a flow rate of 2 ml/min. Duplicates were run for each sample (1g as a 20% solution). Fractions of 5.5 ml were collected and vacuum dried a t 45 "C before weighing. Instrumentation. GPC fraction molecular weights were determined using a 301A Mechrolab Thermoelectric Vapor Pressure Osmometer operating a t 37 "C with a 50/50 v/v dioxane-chloroform mixture as solvent. Resistance readings were taken after 5 min. NMR spectra were obtained from 10% fraction solutions dissolved in carbon tetrachloride run on a Varian HA-60 NMR Spectrometer operating at 60 MHz with tetramethylsilane as an internal reference. Spectra and integrals were recorded at a sweep width of 500 Hz and a scan speed of 500 sec. Infrared spectra were run on a Beckman Infrared Spectrophotometer Model IR-20 as 10% w/w solutions in methylene chloride using 0.ll-mm matched KBr cells. Gain, period, scan speed, and slit width settings were kept constant for all fractions examined. Structural Analysis Input Data. The structural analysis system (16) requires the following calculated values from experimental data for use in determining the asphalt fraction structural parameters. 1 C/H carbon to hydrogen r a t i o (elemental analysis) hydrogen o n carbon a t o m s alpha to a n aro2 Ha m a t i c ring ( N M R )
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
Short Residue
1800-3000poise
I
m----100000 poise
250
350
rnls
io
LOO
Elution Vdume Elution Volume
Figure 1. Kuwait short residue molecular size changes during blowing at 200 OC
Hp HY 5
H.4
6
CN MMHC
7
*
hydrogen on carbon atoms beta t o an aromatic ring (NMR) hydrogen on methyl carbon atoms gamma or further removed from an aromatic ring (NMR) aromatic hydrogen (NMR) per cent naphthenic carbon (NMR) methyl plus methylene hydrogen t o carbon ratio (1R)
Structural Analysis Output Data. A series of equations (16) allows the above input data to be processed to give the following structural parameters: 1 C A C H ~ aliphatic-CH alpha to an aromatic ring aliphatic-CH, alpha to an aromatic ring 2 CACH2 aliphatic--CH, alpha to an aromatic ring 3 CACH3 4 CANCH1 naphthenic-CH alpha to an aromatic ring naphthenic-CH, alpha to an aromatic ring 5 CANCH2 aliphatic-CH beta or further removed 6 CBCHI from an aromatic ring aliphatic-CH, beta or further removed 7 CBCH2 from an aromatic ring aliphatic-CH, beta t o an aromatic ring 8 CBCH3 naphthenic-CH beta or further removed 9 CBNCH 1 from an aromatic ring 10 CBNCH2 naphthenic--CH, beta or further removed from an aromatic ring aliphatic-CH, gamma or further removed 11 CGCH3 from an aromatic ring aromatic internal carbon each bonded t o 12 c R I three other aromatic carbon atoms aromatic peripheral carbon each bonded 13 CRPC t o two other aromatic carbon atoms and one other aliphatic or naphthenic carbon atom aromatic peripheral carbon each bonded 14 CRPH to two other aromatic carbon atoms and one hydrogen atom
R E S U L T S A N D DISCUSSION Fractionation a n d Calibration. GPC Molecular Size Distributions. The molecular size distributions of the blown asphalts are shown in Figures 1and 2. I t has been shown that asphalt GPC separations may be affected by the type of molecular material present. A bulky paraffinic group may have the same size and thus the same elution volume as a compact aromatic group of a higher molecular weight. Hendrickson and Moore (18) and Altgelt (19) ran a series of paraffinic and aromatic model compounds while Oelert and his associates (20, 21) included a separate series of kata- and peri-conden-ed aromatics. The effect appears to be in part responsible for the different calibration curves for different asphalts. This effect becomes modified and reduced as the molecular size increases
Figure 2. Kuwait short residue molecular size changes during blowing at 245 OC
and the molecules become composites containing both aromatic and paraffinic parts. Calibration of each chromatogram by the measurement of the molecular weights of representative fractions is necessary for accurate comparisons between chromatograms. General trends are however apparent. Features of the distributions are the increase in the large molecular size material and the decrease of the small molecular size material on blowing. The rate of increase in the large molecular size material with blowing time is not linear, as the rate decreases as the viscosity increases. Most of the small molecular size material disappears in blowing to 1800-3000 poise. Further blowing removes only a slight amount of small molecular size material and only a t the higher temperature. There is no indication that the smaller sizes are combining to give the larger sizes or if random combination of all sizes is involved. The two significant fractions which were examined by the structural analysis method No. 7/8 and No. 13/14 are shown in the figures with the narrowness of the fraction cut indicated. Molecular Weight Calibration of GPC Chromatograms. Molecular weight VPO measurements were used to calibrate the different asphalt molecular size distributions. The calibration curves changed from asphalt to asphalt so that a universal calibration curve could not be used. Table I gives the molecular weights of the whole asphalt samples and their oxygen contents. The general trend is for the 200 OC blown asphalts to have lower weights than the 245 "C blown asphalts. The molecular weights are expressed as number averages so that with higher volatilization of low molecular weight components a t the higher blowing temperature, the molecular weights will be higher a t 245 "C. The number average molecular weight is also disproportionally influenced by the lower molecular weight components. The molecular weights of the blown asphalts and their fractions are plotted in Figures 3 and 4 and confirm the increases in molecular weight with blowing shown by the Table I. Unfractioned Asphalt Molecular Weights and Oxygen Contents Sample
Mol. wt
Short residue 840 1 8 0 0 - 3 0 0 0 poise 2 0 0 "C 980 1 8 0 0 - 3 0 0 0 poise 2 4 5 "C 1050 100000 poise 200 "C 1270 100000 poise 2 4 5 "C 1280 a Neutron activation analysis.
Oxygen, wt
0.290 t 0.009 0.458 t 0.012 0 . 4 9 6 t 0.014 0.967 t 0 . 0 3 8 0.973 t 0.038
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
2433
5000-
)i
LOO0 -
-Short
Blown 100000 poise Blown 1800-3000poise Residue
X
Blown I00000 poise Blown 1800-3000 poise Short Residue
-I-
0
LWO
0
\,>\
I
.c
P2000 -
3
-" L
O
3
01 0
I
IO00
-
800
-
600 -
Loo-loo
250
300 mls.
3 9
Elution Volume
Elution Volume
Figure 3. Kuwait asphalts blown at 200 OC
Figure 4. Kuwait asphalts blown at 245 OC
whole asphalts. The whole asphalt molecular weights depend mainly on the molecular weights of the elution volume fractions beyond 300 ml. The molecular weights of the 245 OC asphalts in this region are higher than those of the 200 "C asphalts so their whole asphalt molecular weights are higher. The effect of air blowing reactions in the short residue, as opposed to volatilization, is shown in the changes in the 200- to 300-ml elution volume region. At the same elution volume, the asphalts blown a t 200 OC have higher molecular weights than asphalts blown a t 245 OC. The increase in molecular weight with increase in temperature can be accounted for by a polymerization mechanism.
Flory (22) states: "An increase in the temperature of polymerization nearly always lowers the molecular weight of the polymer produced regardless of whether the molecular chain length is controlled by chain transfer or chain termination." Chain length in asphalt is almost certainly chain transfer controlled because of the relatively low molecular weights of the asphalt fractions. This means that the material produced by polymerization a t the lower temperature would have a higher molecular weight than that produced a t the higher temperature. However, if only polymerization of like material is occurring a t both temperatures, different distri-
Table 11. Structural Analysis Input Data Fraction No.
Ha
HP
819 14 20 25 29 34
0.182 0,151 0.131 0.126 0.143 0.190 0.140
0.576 0.574 0.618 0.632 0.580 0.511 0.594
0.188 0.168 0.131 0.138 0.189 0.122
0.548 0.573 0.642 0.627 0.534 0.600
0.189 0.171 0.188 0.140
0.534 0.586 0.568 0.600
0.189 0.159 0.135 0.135 0.189 0.153
0.540 0.593 0.639 0.627 0.532 0.616
0.170 0.164 0.183 0.146
0.560 0.595 0.545 0.618
HY
HA
cN%
CIH
MMHC ratio
0.033 0,047 0.037 0.040 0.051 0.085 0.044
25.1 20.4 14.8 16.2 17.8 22.8 21.1
0.860 0.779 0.709 0.643 0.665 0.731 0.680
2.38 2.36 2.30 2.30 2.33 2.39 2.32
24.4 19.3 15.3 16.5 21.1 16.5
0.870 0.765 0.645 0.640 0.720 0.684
2.33 2.36 2.31 2.31 2.32 2.31
26.8 19.4 19.7 17.2
0.815 0.751 0.682 0.665
2.35 2.35 2.34 2.34
26.2 18.8 15.0 15.9 19.9 17.6
0.866 0.769 0.652 0.642 0.734 '0.684
2.37 2.35 2.35 2.34 2.35 2.33
25.4 19.4 20.4 17.5
0.866 0.778 0.674 0.687
2.36 2.37 2.35 2.35
Short residue
Whole sample
0.204 0.228 0.214 0.202 0.226 0.214 0.222
1800-3000 poise 2 0 0 C ' asphalt
718 13/14 20 25 32/33
Whole sample
0.224 0.205 0.191 0.190 0.198 0.203
0.040 0.054 0.036 0.045 0.079 0.048
100000 poise 200 OC asphalt
718 13/14 31/32
Whole sample
0.217 0.195 0.186 0.212
0.060 0.048 0.058 0.048
1800-3000 poise 2 4 5 C ' asphalt
718 13/14 20 25 32/33
Whole sample
0.233 0.210 0.191 0.193 0.195 0.188
0.038 0.038 0.035 0.045 0.074 0.043
100000 poise 2 4 5 OC asphalt
718 13/14 31/32
Whole sample 2434
0.241 0.202 0.197 0.195
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14. DECEMBER 1975
0.029 0.039 0.075 0.041
Table V. Carbon Types in 3000 Poise Asphalt Blown at 245 "C
Table 111. Carbon Types in Short Residue Fraction Carbon type
Whole sample
Fraction
819
14
20
29
34
1
0
0
1
0
0
Carbon type
2 2 5 CANCH1 5 CANCH2 2 CBCH1 15 CBCH2 7 CBCH3 9 CBNCH~ 1 CBNCH2 9 CGCH3 38 cRI 15 CRPC 5 CRPH 125 Total
1 1 4 4 2 19 4 9 0 8 20 10 6 90
4 1 4
2 0 3 1
1 1 2 2
0 1
3
0 2 3
1
CACHI
1
1
1
1
7 2 3 1 4 6 6 4 40
15 3 7
CACH~ CACH2 CACH3
25
1
1 21 3 3 2
6 14
19 4 4 4
6 6 7 3 60
10
4 76
14 3 5 2 5
3
6 6
4 52
2 2
2
6 8 8 4 62
Table IV. Carbon Types in 3000 Poise Asphalt Blown at 200 "C
CACH2 CACH3
CANCHI CANCH2 CBCH2 CBCH3
CACH1 CACH2 CACH3
CANCH1 CANCH2 CBCH1 CBCH2 CBCH3 CBNCH1 CBNCH2 CGCH3 cRI CRPC
CRPH Total
718
13/14
1 1 1 2 8 1 16 4 1 6 9 34 13 5 112
1 2 0
2 4 2 13 6 6 4 6 16 9 5 76
20
0 6 0 1 1 1
23 6 9
25
1 1
0 2 2 1 16 4 5
1 7 10 8
6
4 77
4 54
1
5 6
1
4
1 2
0
1 1
2 4 2 18
7 9 4 8 24
10
CBNCHI
10
CBNCH2 CGCH3 cRI CRPC
8 36 14 4
11
5. 99
111
3
0 3 0 3
1 1 1 1
1 1
1 1
3
16 4 2 4 5 8
5 2 3 3 -3 6 7 3 40
21 4
1 1 1
3 2 22 5 8 0
8 10
8 4 75
7
5 59
1 7 1
6 12 7 5 71
Table VI. Carbon Types in 100000 Poise Asphalts
Fraction Carbon type
1
Whole 32/33 sample
25
20
5 0 2 6 1 8 6
CBCH~
CRPH Total
13/14
718
Whole 32/33 sample
0
0
3 0
3
1
2
2 2
1
0
7 3 4 2 3 6 6 4 42
20 3
1
7 1
7 10 8 4 68
butions of molecular size should be produced with identical calibration curves. The different molecular weight calibration curves for each of the blown asphalts may depend on a number of factors. Polymerized aromatic material will elute a t a greater elution volume than paraffinic material. Structural analysis parameter values given later show that the higher blowing temperature asphalts contain slightly more aromatic material so that the calibration curves would be reversed if separation by type was a major factor in GPC separation of asphalts. A more likely explanation of the different calibration curves is that association may have taken place in the GPC solvent of benzene-methanol which was later broken up by the VPO solvent of dioxane chloroform in which molecular weight measurements were made. Structural Analysis Results. Input data for the structural analysis system are given in Table I1 and are converted by the system to the carbon types as given in Tables 111,IV, V, and VI. The carbon types represent the average molecule for each of the GPC fractions and the whole asphalts. The effect of blowing on the amounts of different carbon types is apparent mainly in the high molecular weight fractions. The low molecular weight fractions 32/33, 25, and 20 carbon types are very similar for all asphalts. With the two 1800-3000 poise asphalts, the 245 OC asphalt high molecular weight fractions contain more aromatic carbon and less methylene chain carbon than the 200 OC asphalt. The 100000 poise asphalts are difficult to compare because of their different unit sheet weights. The 245 OC asphalt still
Carbon type
Blown at 200 "C fraction
Blown at 245 OC fraction
Whole 7 / 8 13/14 31/32sample
718
CACH1 CACH2 CACH3
0 1
1 3
1 2
1 1
CANCHI CANCHZ CBCH1 CBCH2 CBCH3
2 6 1 9 3
1 2 2 7 3
1 3 2 19 4
CBNCH~
7
3 1 1 13 4 5
1
7
6
6
4 4 6 4 40
7
CBNCH2
CGCH~ CRI CRPC
CRPH Total
16 16 9 1 0 5 4 69 76
8 7 5 67
Whole 13/14 31/32sample
1
1
0
0
0 1 4
2 0 3 5
3 0 0 2
4 0 2 2
1 17
1
1 17
10 1
20 6 15 7 12 44 1 6 4 141
6 8 4 8
22 1 1 5 93
6 3 4 2 3 4 5 5 38
6 7
1 6 12 8
4 70
contains more aromatic carbon but the percentage of CBCHZis approximately the same for both asphalts. Blowing Reactions and Mechanisms. Condensation Reactions with Ester Formation. One of the first suggested air blowing reactions in asphalt was thought to be of the formation of esters. As indicated previously, esters appear to be present in much smaller amounts than originally postulated. Further evidence can be presented to show that even if they are present and are the major contributors to the infrared absorption spectrum at 1700 cm-l, they are not a major reaction mechanism in the air blowing of asphalt. Quantitative infrared measurements on a number of model ester compounds give an absorptivity of 6.0 1. g-l cm-' of the 1700 cm-l absorption. Table VI1 gives the absorbances for the different asphalt fractions and whole samples which can be converted to the number of ester groups per molecule by multiplying the absorbance by molecular weight and dividing by 392. The latter is a factor which is a composite of absorptivity, cell path length, and solution concentration. All fractions show less than one group per molecule. Although there are some differences in the absorbance amounts between the short residue and the blown asphalts, the similarity between the absorbances of the blown asphalt fractions, knowing the wide differences in their molecular weights, does not support formation of esters as a significant air blowing asphalt reaction responsible for these different molecular weights.
ANAL.YTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
2435
Table VII. Absorbance of Infrared Peak at 1700 cm-I for GPC Asphalt Fractions 1800-3000 Poise
100000 Poise
Fraction No.
Short residue
2OO0C
245'C
200'C
245'C
415
0.013 0.003 0.012 0.009 0.009 0.004
0.032 0.021 0.016 0.017 0.017 0.018
0.021 0.019 0.023 0.016 0.018 0.020
0.030 0.020 0.020 0.017 0.015 0.016
0.025 0.020 0.020 0.016 0.019 0.020
0.005
0.015
0.021
0.016
0.020
11
17 22 29 35/36 Whoie sample
~
~~~
Table VIII. NMR and Structural Analysis Unit Sheet Weights with Equivalent Molecular Weights Elution volume
Fraction No.
Unit sheet weights Mol. wt
NMR
Structural
1800-3000 poise asphalt blown 200 "C
718 13/14 20 25 32/33 Whole sample
235.0 267.8 303.8 331.3 371.8
...
4200 2420 1110 800 5 10 980
1630 990 800 615 515 970
1650 1110
1120 780 510 990
1800-3000 poise asphalt blown 245 "C
718 13/14 20 25 32/33 Whole sample
236.0 270.0 304.5 331.2 374.7
...
2690 1740 1080 795 530 1050
1660 1530 825 645 610 800
1650 1430 970 845 590 1030
10000 poise asphalt blown 200 "C
240.0 273.4 371.5
718 13/14 31/32 Whole sample
...
4500 2540 560 1270
1050 960 500 730
1050 1110 570 980
10000 poise asphalt blown 245 "C
718 13/14 31132 Whole sample
240.1 272.2 372.7
...
3000 2530 595
1280
2180 1330 405 880
2080 1350 550 1000
Polymerization Reactions. The comparison of molecular and unit sheet weights of the higher molecular weight fractions of the bitumens gave some insight into polymerization reactions which take place during air blowing. The
short residue has been shown to have only one unit sheet weight or one aromatic condensed system per molecule (23) so that polymerization is occurring when the molecular weight becomes a multiple of the unit sheet weight. The unit sheet weights measured by the NMR method and by the structural analysis method (16) for the asphalt fractions are given in Table VI11 together with their equivalent molecular weights. Molecular weights were taken from the calibration curves a t the points appropriate to the unit sheet weight samples. The two highest molecular weight fractions 118 and 13/14 as shown in Figures 1 and 2 are the fractions containing the majority of material produced by blowing. The other fractions have only small changes in their weight distributions and are unlikely t o have detectable differences for different processing conditions, as is apparent in Table VIII. The main difference between the asphalts is the degree of polymerization during blowing. With free radical reactions taking place during blowing, more free radicals will be formed at the higher temperature and more internal crosslinking will occur to give lower molecular weights and a more rigid chemical structure. In the two samples blown to 1800-3000 poise, the original material (unit sheet weight ca. 2000) still makes a considerable contribution. In the harder samples, the effect of this material is less and the size of the unit sheet is larger for the higher blowing temperature asphalt. The larger unit sheet weights may be due to different sized sheets being polymerized at different temperatures or, more likely, it may be due to dehydrogenation and aromatization of the naphthenic ring structure. Dehydrogenation and Other Reactions. Smith and Schweyer (14, 15) postulated that one of the main asphalt blowing reactions was dehydrogenation of naphthenic rings (AH= -55 kcal/mol). They measured the air blowing process heat of reaction and found it to be from -60 to -75 kcal/mol of 0 2 depending on the blowing temperature and the source of short residue. Table IX examines the changes in the amounts of naphthenic, aromatic, and paraffinic carbon as calculated by the structural analysis method for the asphalt fractions. It shows that the aromatic and naphthenic structures increase at the expense of the paraffinic structures during the air blowing process. There is more aromatic carbon and less paraffinic carbon in the fractions and whole asphalts blown at the higher temperature. Some dealkylation may also be occurring. Although dehydrogenation of naphthenic rings is impor-
Table IX. Percent Aromatic Naphthenic and Aromatic Carbon Type Fraction No. Asphalt
Short residue
1800-3000 poise Blown at 200 "C
Blown at 245 "C
Blown at 245 "C
2436
a
34
27
31
18
21
40 22
55
48
38
819
14
20
25
Aromatic Naphthenic Paraffinic
46 24 30
40 21
37 16 47
39
718
13/14
20
Aromatic Naphthenic Paraffinic Aromatic Naphthenic Paraffinic
46 24 30 49 25 26
40 20 40 40 20 40
28 16 56 29 16 55
Aromatic Naphthenic Paraffinic Aromatic Naphthenic Paraffinic
43 28 29 45 26 29
40 20 40 41 21
...
100000 poise
Blown at 200 "C
29
Carbon type
38
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
... ... ... ... ...
25 30
18
52 34 17 49
... ... ...
...
... ...
Whole sample
32 21 47
32/33
Whole sample
38 22 40 40 25 35
32 18 50 34 17 49
34 20 46 37 21 42
30 18 52 34 17 49
tant, it does not appear as the major air blowing reaction. Smith and Schweyer assumed a high value for the formation of direct carbon to carbon bonds of -94 kcal/mol and demoted their effect where these bonds may in fact vary from -60 to -100 kcal/mol. Weak C-C bonds are more likely to be formed as the free radical initiation reaction will begin with the rupture of the most reactive, Le., the weakest C-H bond with energies down to -70 kcal/mol. As the energy for the C-H bond rupture rises, the initiation reaction becomes more endothermic compensating for the higher C-C bond strengths. The slight decrease in the heat of reaction as the blowing temperature is increased, is accounted for by increased decarboxylation and a higher dehydrogenation rate. A i r Blowing R e a c i i o n M e c h a n i s m . The primary reaction a t low blowing temperatures appears to be polymerization through the paraffinic chain structure with some internal cross-linking and dehydrogenation occurring to increase the relative amounts of naphthenic and aromatic carbon from that of the short residue. The amount of dehydrogenation is small as is dealkylation. As the blowing temperature is increased, more dehydrogenation and dealkylation occur with polymerization lessening. The effect of aromatization of the naphthenic structure is shown by the formation of high unit sheet weights. Since the naphthenic structures appear to be less highly condensed than the aromatic structure, their dehydrogenation will produce unit sheet weights which will no longer conform with the peri-condensed aromatic model. This leads to high values of the unit sheet weight. Diels-Alder reactions where an aromatic ring undergoes a condensation reaction with a dehydrogenated naphthenic ring have a similar but more pronounced effect on the unit sheet weight.
I
ACKNOWLEDGMENT The author thanks D. F. Orchard, E. J. Dickinson, and N. W. West for their helpful criticism and assistance. LITERATURE CITED Y. Ichikawa, J. SOC.Chem. lnd., Jpn Suppl. Binding, 39, 405 (1936). A. M. Chelton, R . N. Traxler. and J. W. Romberg, lnd. Eng. Chem., 51,
1353 (1959). P. Zakar, R. Csikos, G. Mozes. and M. Kristof, Magy Kern. Lapja, 18 (4), 157 (1963). S.H. Greenfeld, hd. Eng. Chem., Prod. Res. Dew., 3, 158 (1964). E. J. Dickinson. Proc. Assoc. Asphalt Paving Techno/., 43, 132 (1974). H. Senolt, Bitumen, Teere, Asphalte, Peche, 20 (12),574 (1969). Osterrelchlsche Mineralolverwaltung A.G., Brit. Chem. Eng., 14 (1l), 9 (1969). J. M. Goppel and J. Knotnerus, 4th WorM Pet. Congr. Proc., Sec. W G , 399 (1955). J. Knotnerus, J. lnst. Pet. London, 42, 355 (1956). J. Knotnerus, ErdoelKohle, 23, 341 (1970). P. G. Campbell and J. R . Wright, J. Res. Natl. Bur. Stand., 68c, 115 (1964). S. M. Dorrence, F. A. Barbour, and J. C. Petersen, Anal. Chem., 46, 2242 (1974). J. C. Petersen, F. A. Barbour, and S. M. Dorrence, Anal. Chem., 47, 107 (1975). D. B. Smith and H. E. Schweyer. lnd. Eng. Chem.. Proc. Des. Dev., 2, 209 (1963). D. B. Smith and H. E. Schweyer. Hydrocarbon Process., 46, 167 (1967). G. A. Haley, Anal. Chem., 44, 580 (1972). K. H. Altgelt, Makromol. Chem., 88,75 (1965). J. G. Hendrickson and J. C. Moore, J. Polym. Sci., Part A, 1 (4),167 11966). (19) K . H. Altgelt, Bitumen, Teere, Asphahe, Peche,21 (11).475 (1970). (20)H. H. Oelert and J. H. Weber, ErdoelKohle, 23, 484 (1970). (21)H. H. Oelert. D. R . Latham, and W. E. Haines. Sep. Sci., 5,657 (1970). (22)P. J. Flory, "Principles of Polymer Chemistry', Cornell University Press, ithaca, N.Y., 1953,p 145. (23)G. A. Haley, Anal. Chem., 43, 371 (1971). >
RECEIVEDfor review April 25, 1975. Accepted August 25, 1975. This project was sponsored by the Australian Road Research Board.
NOTES
Separation of Long Chain Fatty Acids as Phenacyl Esters by High Pressure Liquid Chromatography Richard F. Borch Department of Chemistry, University of Minnesota, Minneapolis, Minn. 55455
The separation and analysis of long chain fatty acid mixtures has been applied extensively to obtain information from a number of biological systems. Analytical methods frequently used include gas chromatographic analysis of methyl ( I ) , benzyl ( Z ) , pentafluorobenzyl ( 3 ) , and p-bromophenacyl ( 4 ) esters. More recently, high pressure liquid chromatography (HPLC) has been employed for these separations ( 5 ) .The preparation of UV-absorbing derivatives has been essential to obtain the sensitivity required for samples in the nanogram range. These derivatives include the benzyl ( 6 ) , p-nitrobenzyl (7), and 2-naphthacyl (8) esters. We describe here the HPLC analysis of C12-C24 fatty acids as their phenacyl esters. The use of a 1 0 - particle ~ size reverse phase column packing provides a high degree of resolution for a number of difficult-to-separate fatty acids.
EXPERIMENTAL Reagents. Acetonitrile was purchased from Burdick & Jackson laboratories, Muskegon, Mich., and used without further purification. Water was distilled from a glass still. Phenacyl bromide was obtained from Aldrich Chemical Company and was recrystallized from pentane. Triethylamine was distilled before use. Stock solutions of phenacyl bromide (12 mg/ml) and triethylamine (10 mg/ ml) in acetone were prepared and stored a t 0 "C. Fatty acids were purchased from Sigma Chemical Company. Derivatization Procedure (9). Approximately 100 pg of fatty acid, 10 pl of phenacyl bromide solution, and 10 p1 of triethylamine solution were combined and allowed to stand overnight a t room temperature. Rate of conversion was as follows: 2 hr, 50%; 6 hr, 80%; 8 hr, >go%. Alternatively, complete conversion may be achieved by heating a t 50 O C for 2 hr. An aliquot of this solution was injected directly into the liquid chromatograph. Chromatographic Procedure. Analyses were carried out using a Waters Associates Model ALC-100 chromatograph equipped with a Waters Model 660 Solvent Programmer and a Waters UV
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
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