Gum in Cracked Gasoline... Cracked gasoline from Pennsylvania,
West Texas, and California stocks was
Formation and Composition
allowed to become oxidized, both by subjecting to oxidation at elevated temperature and by storing in contact with air. Each sample was then distilled into two overhead cuts, and a gum residue and analysis were made of each fraction, including determination of peroxide, aldehyde, and acid. The oxidation products, particularly the peroxides, tended to concentrate in the residue although they were also present in considerable amount in the overhead cuts. Study was also made of the formation of peroxide, aldehyde, and acid during the determination of gum by copper and glass dish, and elementary analysis of gum was made. The results support the conclusion earlier drawn that peroxides are primarily concerned in the gum-forming process but do not preclude aldehydes and acids taking part in the process.
J. C. MORRELL, C. G. DRYER, C. D. LOWRY, JR., AND GUSTAV EGLOF'F' Universal Oil Products Company, Riverside, Ill.
three typical cracked gasolines from Pennsylvania, West Texas, and California were subjected to varied degrees of oxidation both by accelerated aging and by storage in contact with air. The properties of the oxidized gasolines were determined, and then each sample was distilled under vacuum, which separated it into two overhead fractions and a gum residue. The distribution of the oxidation products in each fraction was determined. The gasolines had not been refined except that the West Texas sample had been sweetened with sodium plumbite. The properties of the original gasolines are presented i n Table I. PROPERTIES OF GASOLINES TABLEI. INITIAL
HEN cracked gasoline is oxidized, it forms peroxides, aldehydes, acids, and gum from the unsaturated hydrocarbons present. "Therates of increase in the concentration of these substances during the storage of cracked gasolines was reported earlier; the conclusions were drawn that gum formation is primarily due to the peroxides, and that aldehydes and acids are secondary products probably formed from peroxidic substances. In the present study the distribution of these oxidation products between the volatile portion of deteriorated gasoline, the gum dissolved in it, and the insoluble gum precipitated from it, either after accelerated oxidation or several months of storage, was investigated. The formation of oxidation products during determination of gum by evaporation of gasoline in glass and copper dishes and the elementary composition of gum itself were also studied. The theory that peroxidic compounds are responsible for gum formation in cracked gasoline has been proposed by a number of workers, as was shown in an earlier paper (4),and they have also demonstrated the presence in old gasoline of .aldehydes, ketones, and acids. Some investigators have examined the gum. Smith and Cooke (6) made elementary analyses of gum and concluded that aldehydes formed by breakdown of peroxides were probably of more importance in gum formation than peroxides themselves. Wagner and Hyman (7) also analyzed gum and presented a mechanism of gum formation in which "peracids" formed from aldehydes were essential catalysts. Story, Provine, and Bennett (6) studied gum formed by evaporation of gasoline in the copper dish and concluded that it was largely composed of acids but also contained some unsaponifiable material resembling polymerized aldehydes, ketones, or oxides. To study the reactions occurring during gum formation,
Gr., O A. P . I. Sp. gr. Color, Saybolt Gum, mg./100 c c . : A. S. T.M. Copper-dish Induction period, min. Sulfur, %
Pa. Cracked 63.8 0.7245 16 6 108 70 0.03
C. A . S . T. M. 100-cc. distn.: Initial b. D . 41 % distd. over: 10 55 50 121 90 173 End point 184
' F.
W. Texas Reformed 60.2 0.7381 4
Calif. Cracked 54.0 0.7628 Yellow 5 124 296 0.50
10 63 45 0.03 C.
O F .
C.
O F .
105
41
104
53
127
131
64 108 174 210
145 226 346 393
81 134 178 207
178 273 352 404
25G
343 364
These gasolines were from the same stocks as those used in earlier work on peroxidation (3) and gum mechanism (4),and are almost identical in properties with the gasolines employed in the previous work. The Pennsylvania gasoline was obtained by cracking a blend of water-white distillate and gas oil, the California sample was derived from the cracking of fuel oil, and the West Texas gasoline was prepared by "reforming."
Outline of Procedure Samples of each gasoline were oxidized in the steel bombs described in an earlier publication ( 2 ) under the conditions used in the determination of induction period. Each bomb was filled at room temperature with oxygen at 100 pounds per square inch (7 kg. per sq. cm.). It was then heated t o 100" C., causing an increase of pressureto about 135 pounds (9.5 kg.). The oxidation was stopped at several stages, 10 minutes before the beginnin of rapid oxygen absorption, and after the pressure had droppe8 5, 10, 20, and 50 pounds per square inch (0.35, 0.7, 1.4, and 3.5 kg. 465
I
466
INDUSTRIAL AND ENGINEERING CHEMISTRY
per sq. cm.). At the end of each experiment the bombs were quickly cooled by running cold water into the surrounding bath. Analysis was made of a portion of each sample of oxidized gasoline. The gasoline was then evaporated under a vacuum of about 2 mm. with a maximum liquid temperature of 175’ F. (79’ C.). Tests made under other conditions indicated that this temperature was necessary to remove volatile material. The vapors of the gasoline passed through two traps; the first was cooled with ice, and the second was surrounded by acetone containing solid carbon dioxide. Three fractions were thus obtained, a residue, a heavy distillate from the ice trap, and a light distillate from the carbon dioxide trap. Determinations of peroxide, aldehyde, and acid were made on each sample. When the gasoline was allowed to absorb a considerable amount of oxygen, gum sometimes separated as a heavy viscous layer. This precipitated gum was taken up in acetone, the acetone distilled off under vacuum at a low temperature, and the residue analyzed. The data on precipitated gum are shown separately in the tables. Fifteen-gallon (57-liter) samples of the Pennsylvania and West, Texas gasolines were exposed t o air in partially filled drums. At intervals, samples were removed, analyzed, and distilled in the same manner as the samples exposed to accelerated oxidation. The methods used in this study have already been Published. Copper-dish gums were determined by the method of the Atlantic Refining Com any (f), and peroxides by the procedure of Yule and Wilson (87 which was used in earlier studies (3, 4) Aldehyde and acid numbers were determined as before (h. The concentration of aldehyde is given in millimoles per liter (as butyraldehyde), acid concentration in milliequivalents per liter, and peroxide as milliequivalents of active oxygen per liter using similar units to allow direct comparison of peroxide, aldehyde,
VOL. 28, NO. 4
and acid concentrations. It is recognized that these tests have some limitations; the peroxide test at times gives values somewhat lower than the entire peroxide content of gasoline, the aldehyde test will give misleading results if certain aldehydes of high molecular weight are present, and the acid test is not quantitative for some acids of very high molecular weight.
Pennsylvania Gasoline
The data from the accelerated oxidation of the Pennxylvania gasoline are presented in Table 11. Distillation ranges of the oxidized gasoline and of the distillate cuts from representative experiments are presented in Table III. As the extent Of oxidation was increased, at first the concentration of all oxidation products became greater at increasing rates. When sufficientoxygen had been absorbed to cause a 20-pound (1.4-kg.) drop in pressure, the formation of precipitated gum was noted. F’i-Om this Point on there was no large increase in peroxide number in the gasoline, and aldehyde concentration remained nearly constant, but acid continued to increase. With Some irregularities the amounts of both copper a,nd airjet gum increased as oxidation continued. When the samples of oxidized gasoline were distilled, the oxidation products tended to concentrate in the residue, indica,ting that the reactive groupings were mainly parts of large molecules. I n the “light” distillate fractions there were low concentrations of peroxide and somewhat higher concentrations of aldehyde; acid content was low in the fractions after only slight oxidation TABLE 11. OXIDATION OF PENNSYLVANIA CRACKED GASOLINE and increased with the extent of oxidation. Extent of oxidation: None 10 Min. T -o Drop i n Pressure, Peroxide was considerably higher in the before Kg./Sq. Cm. (Lb./Sq. In.): “heavy” distillate while the aldehyde concentraBreak 0.35(5) 0.7(10) 1.4(20) 3.5(50) 1.4(201” Time of oxidation, min.: 0 65 90 105 115 145 166 tion was about the same and acid somewhat lower here than in the lighter fraction. The Properties of Gasoline Gum, mg./lOO cc.: 63 123 180 154 heavy distillate formed considerable quantiA. S. T. M. 6 19 126 Copper-dish 108 195 764 898 960 1101 1048 ties of gum both by A. S. T. M. and copper-dish 91.6 89.8 90.0 91.5 0.40 3.20 70.9 Peroxide No. methods. That this overhead product formed 16.6 19.0 14.0 16.6 0.18 0.60 10.0 Aldehyde No. Acid No. 0 0.10 1.5 2.6 3.8 4.5 5.8 gum in the air-jet test should be particularlj7 Properties of Gasoline Cuts noted since it indicates that even during the Light dist.: % of gasoline 55.9 53.6 51.0 58.3 54.5 55.1 58 6 r a p i d e v a p o r a t i o n employed in this test Gum, mg./100 cc.: A. S.T. M. 1 1 5 3 2 4 4 some actual formation of gum occurs, probC oqp er -di ah 3 6 13 27 14 22 10 ably by d e c o m p o s i t i o n of peroxides. The Peroxide No. 0.10 0.10 4.50 4.10 4.80 4.00 3.10 Aldehyde No. .. 0.60 9.0 10.0 10.0 5.0 12.5 data on the sample containing an inhibitor Acid No. 0 0.03 1.4 1.6 3.8 8.2 5.3 show that the course of o x i d a t i o n was the Heavy dist.: % of gasoline 42.0 43.2 45.7 38.3 40.3 40.7 35.8 same here as in the uninhibited gasolines, the Gum mg /lo0 cc.: A. b. T: M. 2 3 28 41 87 52 20 inhibitor serving only to delay the onset of 312 399 144 244 Copper,dish 413 330 214 rapid change. 52.5 63.0 45.1 37.6 81.0 0.22 2.00 Peroxide No. 7.0 5.0 0.20 0.40 Aldehyde No. 8.3 6.3 16.6 Under “Distribution of Oxidation Products,” Acid No. 0.05 0.15 1.1 1.3 2.0 2.8 1.7 Table I1 shows the amounts of products of Residue: of gasoline Negligible 0.35 1.7 1.4 1.8 2.2 3.0 each type present in the different fractions in ,. 58.1 1460 1640 1580 1440 808 %eroxide ’ No. terms of “units.” A unit is here defined as the .. 180 300 250 200 40 Aldehyde No. Acid No. .. 5:0 60 120 110 160 70 amount of an oxidation product present in 10 cc. Distribution of Oxidation Produotsb of oil in which the concentration of the product Peroxide units: Entire gasoline 40 320 7090 9000 9150 9160 8980 referred to, measured a.s peroxide, aldehyde, Gasoline fractions: or acid number, is one. Thus 1000 cc. of the Light dist. 5.6 5 230 239 207 218 182 Heavy 9.3 86 1718 3102 2115 2564 1615 Pennsylvania gasoline having originally, as Residuedist. 20 2482 2300 2844 3096 2424 Total 111 4430 5641 5166 5778 4221 shown in Table 11, a peroxide number of 0.40 16:9 % ’ of original recovered 42 35 63 62 56 47 63 and an aldehyde number of 0.18, would contain Aldehyde units: Entire gasoline 18 60 1000 1400 1660 1660 1900 40 peroxide units and 18 aldehyde units. By Gasoline Light dist. fractions: 32 459 583 545 275 674 employing this concept of units, i t is possible Heavy i:4 320 191 334 254 594 to compare the amounts of these oxidation prodResiduedist.’ .. . 17 . 306 420 450 430 120 Total .. .. ., 1085 1194 1329 959 1388 ucts (in terms of their active groups) present % original recovered . . 109 so 58 73 85 in the various gasoline samples and fractions Acid units: Entire gasoline 0 10 150 260 375 450 580 produced by distillation. An exact compariGasoline fractions: 0 1.6 71 93 204 440 311 son of the amounts of the oxidation products Light dist. 81 112 Heavy 2.1 6.5 50 50 61 present would be possible only if their molecular Residuediat. .. 1.7 102 168 198 344 210 Tota! .. 9.8 224 311 483 896 582 weights were known. 98 149 120 129 199 100 % original recovered . . The data by units show that not only are a Sample contained 0.025.7 wood tar, distillate inhibitor. peroxides present in the gum residues from b Based on 1000 cc. of oxicfized gasoline. distillation in higher concentration than in the
APRIL, 1936
INDUSTRIAL AXD ENGIKEERING CHEMISTRY
467
OF GASOLINE FRACTIONS TABLE 111. DISTILLATION
Gravity, ' A. P. I. Specific gravity
Entire gasoline 60.5 0.7370 OC.
A. S. T. M. 100-cc. distn.: Initial b. p. % distilled over: 10 50 90 End point
O F .
[After oxidation t o 50-pound (3.5-kg.) pressure drop1 .. Pennsylvania West Texas Light Heavy Entire Light Heavy dist. dist. gasoline dist. dist. 72.5 48.8 57.6 68.4 46.6 0.6936 0.7848 0.7483 0.7079 0.7972 "C. O F . "C. O F . OC. O F . O C . O F . 'C. O F .
7
California ____ Light Heavy dist. dist. 65.2 46.5 0.7194 0.7949
7
Enttre gasoline 52.8 0.7678
'C.
O F .
aC.
O F ,
OC.
O F .
35
95
32
90
117
242
36
96
35
95
121
250
56
132
48
118
128
261
57 119 167 178
135 247 333 352
44 80 126 150
112 176 258 302
136 150 172 183
277 302 342 361
58 109 169 192
136 229 337 378
51
123 178 243 300
130 151 182 194
266 304 360 382
84 135 181 196
184 275 358 384
63 90 127 164
146 194 260 328
140 157 183 201
284 315 361 393
81
117 149
overhead fractions but that in most cases, despite its small amount, the gum actually contains more peroxide than do the distillates, particularly if the oxidation has been severe. Aldehyde and acid, however, tend to be as high in the overhead fractions as in the residue, or even higher than in the residue. If we compare the sum of the units of oxidation products in the distillation products with the amounts initially present in the oxidized gasolines, the peroxide totals for the fractions are about 60 per cent of the original values, the aldehyde totals are not greatly different from the original, but the amounts of acid present have considerably increased, leading to the belief that during the evaporation, decomposition of peroxides occur, in spite of the low temperature used.
Storage of Pennsylvania Gasoline
Table IV gives data on the storage of Pennsylvania gasoline a t ordinary temperature. Comparison of these figures with those in Table I1 shows that the concentration of oxidation products increased as oxidation proceeded in much the same way in storage as in accelerated aging. I n storage, however, there was a much slower formation of aldehyde and acid. The oxidation products concentrated in the distillation residue to an even greater extent in the stored gasoline than in that subjected to more rapid oxidation. This point is brought out if we consider the figures for units of oxidation products, which show not only higher concentrations but also larger amounts of peroxide, aldehyde, and acid in the residue than in the overhead f r a c t i o n s Apparently the milder oxidation during storage a t room temperature IN STORED PENNSYLVANIA GASOLIXE TABLE IV. OXIDATIONPRODUCTS 93 107 produced peroxidation and polymerization, and 37 48 73 86 89 Time of storage, days: further oxidation to aldehydes and acids went Properties of Oxidieed Gasoline on to a lesser extent than when conditions are Gum, mg./100 cc.: 124 164 168 148 128 26 88 A. S. T. M. more severe. 1262 1524 259 632 983 1065 231 Copper-dish Peroxide No. Aldehyde No. -4cid No.
Light dist.: of gasoline urn, mg./100 cc.: A. S. T. M. Copper-dish Peroxide No. Aldehyde No. Acid No. Heavy dist.: of gasoline um mg /lo0 00.: A. 's. T: M. Copper-dish Peroxide No. Aldehyde No. Acid No. Residue: % ' of gasoline Peroxide No. Aldehyde No. Acid No.
z 8
33 71 7.2 13.5 10.0 16.6 0.9 4.7 0.05 0.10 0.40 1.00 Properties of Gasoline Cuts
88 16 6 1.20
52.2
58.8
52.0
52.0
54.0
57.5
1 4 0.25 0.3 0.05
0
0
0
0
3 2.54 4.50 0.75
0
0.75 1.7 0.20
4 2 1.60 1.11 0.20
4 3.45 5.0 0.90
3.78 3.50 1.00
4.20 6.25 1.70
45.6
40.3
46.0
46.0
42.5
39
60
2 324 3.3 0.2 0.10
2 169 6.6 1.9 0.10
26 174 16.0 2.62 0.30
12 209 31.0 5.0 0.55
12 205 37.5 7.1 0.50
20 356 52.5 5.0 0.80
135 62.7 10.0 1.60
0.02 0.45 1.4 1.7 588 790 1560 1880 160 222 400 30 50 20 30 Distribution of Oxidation Products"
1.9 1926 400 35
2.4 1960 250 40
3.1 1786 332
1
..
Peroxide units: 720 1350 Entire gasoline Gasoline fractions: 13 44 Light diet. 150 266 Heavy dist. 356 Residue 118 281 1210 Total 39 90 % of original recovered Aldehyde units: Entire gasoline 90 470 Gasoline fractions: 15 100 Light dist. 7 77 Hea,vy dist. 32 Residue 54 Total 60 % original recovered Acid units: Entire gasoline 5 10 Gasoline fractions: 3 12 Light dist. 5 4 Heavy dist. 6 23 Residue 39 14 Total 390 % original recovered 280 a Based on 1000 cc. of oxidized gasoline.
. .. ...
97 14.3 1.70
144 25 2.20
47.5 2
6
50
3250
7100
8800
9650
14360
83 736 2184 3003 93
132 1395 3196 4723 67
186 1693 3659 5438 62
217 2047 4707 6968 72
199 3041 5537 8777 61
1000
1660
1660
1430
2500
58 120 311 591 59
234 225 680 1139 79
270 302 760 1331
80
201 195 600 996 70
297 485 1029 1811 72
40
100
120
170
220
10 14 28 53 133
39 25 51 115 115
49 21 67 137 114
57 31 96 184 108
81 78 155 314 143
West Texas Reformed Gasoline Samples of this gasoline which had been exposed to accelerated oxidation were studied in the same way as those of Pennsylvania gasoline. I n addition, analysis was made of the precipitated gum which settled out of the gasoline after severe oxidation. The resulting data are presented in Tables I11 and V. The distribution of oxidation products is similar to that reported for the Pennsylvania gasoline; oxidation products of all the types studied tended to concentrate in the residue. The same degree of oxidation as measured by peroxide n u m b e r g a v e a h i g h e r c o n t e n t of g u m (A. S. T. M.) and gum residue in the West Texas than in the Pennsylvania gasoline. It was also noticeable that the residue from this gasoline was considerably higher in acidic substances. The distribution of oxidation products by units is also shown in Table V. The bulk of the peroxidic compounds are in the residue. Aldehyde is fairly uniformly distributed in all the three fractions while acid is particularly evident in the light distillate. The precipitated gum is notably different from the g u m , obtained as a residue on evaporation by reason of its higher content of acidic substances. The results of storage of this gasoline are shown in Table VI. The West Texas gasoline deteriorated a t a considerably slower rate than that from Pennsvlvania. but the conclusions drawn from the Pknnsylvania samples hold true
INDUSTRIAL AND ENGINEERING CHEMISTRY
468
TABLEV.
OXIDATIONOF WEST TEXASREFORMED GASOLINE
Extent of Oxidation:
None
10 Min.
before Break Time of oxidation, min. : Gum, mg./100 cc.: A. S. T. M. Copper-dish Peroxide No. Aldehyde No. Acid No.
50
Properties of Gasoline
10 174 170 218 278 444 63 407 808 935 979 1080 0.45 11.7 60.9 84.2 90.0 9 0 . 1 0.14 2.50 12.5 12.5 13.3 18.1 0 0.15 2.20 5.3 6.7 8.0 Properties of Gasoline Cuts
Light dist.: % of gasoline Gum, mg./100 cc. A. 8. T. I$. Copper-dish Peroxide No. Aldehyde No. .4cid No. Heavy dist.: of gasoline um mg /lo0 cc.: A. 'S. T'. M. Copper-dish Peroxide No. dldehyde No. Acid No. Residue: % of gasoline Peroxide No. Aldehyde No. Acid No. Insoluble gum: % of gasoline Peroxide No. Aldehyde No. Acid No. Distribution Peroxide units: Entire gasoline Gasoline frrtct,ions: Light dist. Heavy dist. Residue Total % original recovered Insoluble KUm Aldehyde units: Entire gasoline Gasoline fractions: Light dist. Heavy dist. Residue Total % original recovered Insduble gum Acid units: Entire gasoline Gasoline fractions: Light dist. Heavy dist. Residue Total, % original recovered Insoluble gum
z
5
To Drop in Pressure, Kg./Sq.0.70 Cm. (Lb./Sq. In.) 0.35 1.4 3.5 (5) (10) (20) (50) 70 80 90 150
64.2
62.0
60.5 67.2 64.0
1 5 0.10 0.80 0.05
8 25 0.80 1.20 0.05
11 1 2 1 20 8 7 7 2.64 4.70 4.40 4.62 2.50 5.0 7.0 14.2 1.20 4.30 5.4 8.3
58.6
33.3
34.5
35.5 28.7 30.5 36.3
2 245 0.30 0 16 0.20
83 523 6.3 1.60 0.10
141 116 13 29 524 365 262 199 27.4 62.9 54.3 58.1 8.0 5.0 10.0 20.0 0.80 2.70 2.80 2.80
0 17 16 6 4.5 0 50
2.4 278 50 4.50
2.4 2.6 2.9 3.6 1340 1620 1394 1162 125 200 166 222 44 56 60 50
..
.. .. ..
.. .. .. ..
0.13 0.10 0.31 162 121 2030 90 80 166 1050 600 640 of Oxidation Products5
.. .. ..
..
45
1170
6095 8420 9000 9010
6 10 28 44 98
50 218 669 936 80
..
160 318 282 271 972 1805 1656 2109 3216 4312 4043 4183 4176 6335 5981 6563 69 75 67 73 20 12 e30
14
250
1250 1250 1330 1810
..
51 5
..
64 450
74 55 120 250 100
0
15
220
530
670
800
3
3 4 11 17 113
73 28 105 205 93
291 77 146 514 97 131
342 85 174 601 90 60
486 102 180 768 96 199
8
..
7 1 11
.
..
..
151 339 448 ~~. 832 284 144 305 726 480 325 482 800 915 1133 1235 2358 73 89 93 150 11 12 52
..
..
Based on 1000 cc. oxidized gasolire.
here. The reactions in storage are peroxidation and polymerization, rather than aldehyde and acid formation. Moreover, all the oxidation products tend to concentrate in the distillation residue to an even greater extent in storage than during rapid oxidation.
California Gasoline The data from accelerated oxidation of the California gasoline are presented in Table VII. Compared to the other two gasolines, after oxidation to a given pressure drop this gasoline had a considerably lower peroxide number. As in the samples of the Pennsylvania and West Texas gasolines, the oxidation products, particularly the peroxides, concentrated in the residue left on evaporation. Considering the total amounts of oxidation products present (expressed in units), the peroxide in the residue greatly exceeded that in the fractions, but aldehydes and acid were present in greatest amounts in the light distillate. The precipitated gum was exceedingly high in acidic substances.
TABLEVI.
VOL. 28, NO. 4
OXIDATION PRODUCTS IN STORED WEST
TEXAS
GASOLINE Time of storage, days: Gum, mg./100 cc.: A. S. T. M. Copper-dish Peroxide No. A41dehydeNo. ricid No.
79 102 Properties of Oxidized Gasoline
109
134
108 136 245 639 11.75 26.7 2.00 3.57 0.15 0.50 Properties of Gasoline Cuts
292 785 41.5 7.15 0.55
310 1028 56 8 1.2
60
62
0 1 1.50 1.25 0.40
1 2.16 1.75 0.80
Light dist.: Yo of gasoline 65 59.5 Gum, mg./*lOO cc.: A. S. T. M. 10 0 Copper-dish 1 2 Peroxide No. 1.04 0.78 Aldehyde No. 0.80 1.00 Acid No. 0.10 0.50 Heavy dist.: 0 of gasoline 31.5 37 um mg./100 cc.: A . 8 . T M. 78 3 Copper-dish 165 149 Peroxide No. 15 8 Aldehyde No. 1.43 2.00 Acid No. 0.40 0.10 Residue : o of gasoline 1.2 2.5 eroxide No. 462 535 Aldehyde No. 71 71 Acid No. 10 10 Distribution of Oxidation Prod 1uctsa Peroxide units: Entire gasoline 1175 2675 Gasoline fractions: Light dist. 51 62 Heavy dist. 253 555 Residue 554 1337 Total 958 1954 % original recovered 82 73 Aldehyde units: Entire gasoline 200 357 Gasoline fractions: Light dist. 52 60 Heavy dist. 45 74 Residue 85 177 Total 182 311 9% original recovered 91 87 Acid units: Entire gasoline 15 50 Gasoline fractions: Light dist. 7 30 Hea,vy dist. 3 15 Residue 12 25 Total % original recovered 147 22 140 70 a Based on 1000 cc. of oxidized gasoline.
8
% '
0
36
33.5
4 130 39 3.00 0.30
14 185 32.5 2.5 0.70
2.5 930 166 10
2.3 1380 166 35
4150
5600
90 1402 2325 3819 93
134 1089 3174 4397 78
715
800
75 72 415 562 79
109 84 382 575 72
50
120
24 11 60 26
50 23 153 80
120
128
Analysis of G u m Elementary analysis and molecular weight determinations were made ol the samples of gasoline which had been oxidized until a 20-pound (1.4-kg.) pressure drop occurred and of the fractions of these samples. The molecular weights were determined by the freezing point method using benzene. The results appear in Table VIII. The data show oxygen present in low percentages in the oxidized gasoline and the fractions from it and in high percentage in the gum residue. The gum residues are similar in composition to the gum samples which have been analyzed by other investigators (6, 6, 7). The molecular weights of the gum residues increased with their content of oxygen. In Table IX are presented analyses of the fractions and gum formed during storage of the Pennsylvania and West Texas gasolines. The figures show the gum formed in storage to be nearly identical in composition with that formed on accelerated oxidation.
Oxidation of Gasoline during G u m Tests Further information regarding the steps in gum formation was obtained by evaporating 100-cc. samples of the Pennsylvania gasoline on a steam bath in glass and copper dishes and determining the concentration of oxidation products a t intervals during the evaporation. The data shown in Table X indicate that, as evaporation proceeds, the concentration of
INDUSTRIAL AND ENGIPTEERING CHEMISTRY
APRIL, 1936
TABLE VII. OXIDATIOW OF CALIFORNIA CRACKED GASOLINE Extent of oxidation: None Drop i n Pressure after Break, Kg./Sq. Cm. (Lh./Sq. In.) 0.35(5) 0.70(10) 1.4(20) 3.5(50) Time of oxidation, min.: 90 150 315 435 Properties of Gasoline Gum, mg./100 cc.: A. 9. T. M. 5 30 53 270 500 Copper-dish 124 253 335 824 1183 49.6 13.0 32.2 7.10 0.10 Peroxide No. 10.0 16.6 1.80 2.0 Aldehyde No. 0.18 10 1.00 5.3 0.60 0.25 Acid No. Properties of Gasoline Cuts Light dist.: 4rp of gasoline 49.1 41.3 42.5 45.5 44.5 Gum mg /lo0 cc.: A. 's. T.' 2 1 1 3 1 Copper -dis h 21 3 6 16 2 1 . 2 5 2 . 2 0 0 . 5 5 0 . 6 1 Peroxide No. 0.10 16.6 1.80 5.5 0.62 1.40 Aldehyde No. 5.9 13.7 1.30 0.15 0.70 Acid No. Heavy dist.: 50.3 56.6 56.0 50.7 52.4 % of gasoline Gum, mg./100 cc. 6 3 2 2 2 A. S. T. M. 613 490 262 363 439 Copper-dish 17.5 5.5 10.9 0.20 2.94 Peroxide No. 2.0 3.5 1.20 1.60 0.20 Aldehyde No. 1.80 0.55 1.80 0.40 0.60 Acid No. Residue: 3.25 1.6 2.65 0.6 1.9 % of gasoline 630 950 150 3.0 92 Peroxide No. 125 16 55 18 25 Aldehyde No. 20 50 75 10 12 Acid No.
v.
.. .. ..
Aldehyde No. Acid No.
..
... . .. ..
..
.. .. ..
0.07 569 200 1530
0.35 335 200 1460
Dist,ribution of Oxidation Productsa
Peroxide units: Entire gasoline Gasoline fractions: Light dist. Heavy dist. Residue Total % original recovered Insoluble gum Aldehyde units: Entire gasoline Gasoline fractions: Light dist. Heavy dist. Residue Total yooriginal recovered Insoluble gum Acid units: Entire gasoline Gasoline fractions: Light dist. Heavy dist. Residue Total % original recovered Insoluble g u m a Based on 1000 cc. of oxidized
10
710
1300
3220
4960
4.9 10.1 1.8 16.8 168
25 167 175 359 255
24 308 150 572 75
..
57 553 1660 2270 70 40
917 3088 4103 83 117
18,
180
200
1000
1660
30.5 10.1 10.8 51.4 350
58 68 48 174 96
76 90 26 192 96
..
250 102 147 499 50 14
739 184 406 1319 79 70
..
..
..
*.
__
25
60
100
530
1000
29 34 23 86 143
55
268 91 132 49 1 93 107
610 95 244 949 95 510
..
..
31
32 118 118
..
ELEMESTARY ANALYSIS OF CUTS OF OXIDIZED GASOLINE
TABLEVIII.
Carbon Hydrogen
%
gasoline.
oxidation products! particularly peroxide and aldehyde, increases in the gasoline, and notably faster in the copper than in the glass dish. The total amount of oxidation products present, as shown by the data in peroxide, aldehyde, and acid units, also increases for a time. However, when 99 per cent of the gasoline has been evaporated, it begins to decrease either because of volatilization or decomposition of the oxidation products; and when the sample is evaporated to dryness in the copper dish, the peroxide is greatly reduced, in some cases to zero, while in the glass dish no such marked change occurs: The concentration of aldehyde and acid is very high in the gum remaining after evaporation.
%
Sulfur
%
Pennsvlvania Cracked Gasoline 0.03 Entire oxidized gasoline 84.4 13.4 0.02 Light distillate 85.4 14.7 0.02 Heavy distillate 86.4 13.5 Residue 69.6 9.2 0.42 West Texas Reformed Gasoline Entire oxidized gasoline 86.4 14.0 0.03 Light distillate 85.5 14.3 0.04 Heavy distillate 86.2 13.2 0.03 Residue 74.9 9.4 0.44 California Cracked Gasoline Residue 76.2 10.58 2.91 a By difference.
Mol. Oxygen5 Weight
% 2.2
..
0: 1 20.8
342
..
..
..
ij:2 0.6 15.3
236
10.31
210
TABLEIX. ELEMENTARY ANALYSISOF STORED GASOLINES Carbon Hydrogen Sulfur Pennsylvania cracked gasoline: Entire oxidized gasoline Light distillate Heavv distillate Residue West Texas reformed gasoline residue a By difference.
TABLE X.
Mol. Oxygena Weight
%
%
%
%
85.1 86.1 86.5 69.8
13.9 14.0 13.5 8.7
0.06 0.02 0.02 0.40
0.9 0 0 21.1
346
73.6
9.6
0.4
16.4
294
..
..
FORMATION OF OXIDATION PRODUCTS DURING EVAPORATION OF GASOLINE
R8
7.4 20.2 6.0 28.0 112
469
-
Extent of Evaporation None 50% 75% 99% Dryness Pennsylvania Cracked Gasoline (0.060 g. gum) 1.50 4.90 27.5 167 0.40 2.5 10.0 150 1.00 0.18 0 0.05 0 7.5 83 4.0 7.5 12.3 2.8 1.0 1.8 5.0 6.3 1.0 0.9 0 0.3 0 0.8 0.5 (0.107 g.) 0.40 7.8 41.7 187 23.4 0.85 20.0 75 0.18 1.40 0 0.65 7.5 140 0.05 4.0 39.0 104 18.7 0.30 0.8 2.1 2.0 1.8 7.0 0 0.3 1.6 0.8 1.5 West Texas Reformed Gasoline 7
Glass dish: Peroxide No. Aldehyde N o . Acid No. Peroxide units Aldehyde units Acid units Copper dish: Peroxide No. Aldehyde No. Acid No. Peroxide units Aldehyde units Acid units Glass dish: Peroxide No. Aldehyde No. Acid No. Peroxide units Aldehyde units Acid units Copper dish: Peroxide No. Aldehyde No. Acid No. Peroxide units Aldehyde units Acid units Glass dish: Peroxide No. Aldehyde No. Acid No. Peroxide units Aldehyde units Acid units Co per dish: feroxide No. Aldehyde No. Acid No. Peroxide units Aldehyde units Acid units
0.45 0.14 0 4.5 1.4
0
1.70 1.10 0.05 8.5 5.5 0.3
5.0 1.00 0.10 12.5 2.5 0.3
105 45 5.0 10.5 4.5 0.05
2.6 14.2 140 1.30 5.5 50 0.10 0.30 20 0 35.5 14 13 4.5 13.8 5 1.4 6.5 2 0.8 0.5 0 California Cracked Gasoline 0.45 0.14
0.10 0.18 0.25 1.0 1.8 2.5
1.80 0.70 0.50 9.0 3.5 2.5
1.50 0.70 0.50 3.8 1.8 1.3
7.5 10.0 5.0 0.75 1.0 0.5
0.10 0.18 0.25 1.0 1.8 2.5
0.60 1.4 0.60 3.0 7.0 3.0
0.50 1.4 0.90 1.3 3.5 2.3
1.0 9.0 5.0 0.1 0.9 0.50
.. .. .. .. ..
..
(0.076 9.) 825 395
0
6.3 3.0
.. .. ..
.. .. .. (0.152 9.) 0 82 66
0
1.3 1.0
Conclusions 1. Three cracked gasolines were oxidized in the oxygen bomb and two of the original gasolines stored in the presence of air. At intervals during the accelerated oxidation and storage, samples of each gasoline were vacuum-distilled into a light and heavy fraction and a residue. 2. The residue remaining after vacuum distillation of oxidized gasoline contains peroxides, aldehydes, and acids
in high concentration. Regardless of the extent of oxidation of the gasoline, the gum contained these components in not greatly different concentrations. Gum precipitated from gasoline during oxidation is different in composition from the dissolved gum, being higher in acid. 3. In gasoline subjected to accelerated oxidation, the amounts of peroxides (in terms of their active groups) are
