November, 1929
INDUSTRIAL AND ENGINEERING CHEiVfISTRY
1079
Chemistry of Gum Formation b y Cracked Gasoline’ LeRoy G. Story, Robert W. Provine, and H. T. Bennett MID-COXTIXEXT PETROLEUM
CORPORATION, T U L S A , OBLA.
ANY cracked gasolines, especially those unrefined, resdily. The similarity of these reactions to those occurring deposit under certain conditions a thick resinous in gum formation are worthy of passing observation. material common!y known as gum. For eyample, Gum Formation by Evaporation in Dishes on long standing in the dark or diffused light, it is common to There is a t present no standard for determining gum. note a serni-fluid material graduslly accumu1:ite as a brown, sticky mass a t the bottom of the oil. In sunlight the reaction Each refiner has his own methods and specifications for conis much quicker, the gum is more fluid, and often pale yel!ow, trol of his product. Ncvcrthelcss, there are a few common resembling honey. By evaporation also of a cracked gTsoline methods of detcrniining gum in cracked gasoline which will in a copper dish, a dark brown gum, hsrd and resinous, is often bc pointed out a t this time. I’cl~hapsthe most gencral method is evaporation in a copper left as a residue. Whilc it is evident that the word “gum” as applied to the above formation may be somcnhnt confusing, dish. This was first described by Dean (3) primarily as a yet it has a uell-known meaning to those faiiiiliar with the test for aviation g:isoline. It consists briefly of evaporating on a steam bTth 100 cc. of the gssoline in a wcighed hemispheripetroleum industry. The name “gum” mas probably first applied to the deposits cal copper dish, about 3.5 inches (9 cm.) in diameter, and detcrmining the weight of from cracked gasoline begum deposited. cause of the similarity to Sniith and Cooke ( 6 ) , in natural gums in appearance A detailed study has been made of gum formation by t h e i r s t u d y of the gumand consistency; neverthecracked gasoline. The dish test is described and the forming c o n s t i t u e n t s in less it is obvious that the factors influencing the test discussed. The changes gasoline, adopted a method gums frorn g a s o l i n e a r e taking place in cracked gasoline during evaporation of evaporating on a steam chemically different f r o m and the composition of the gum deposited are given. bath 20 cc. of gasoline in a those uf natural sources. The absorption of oxygen and formation of gum when 30-cc. glass dish. They also The prescnt itivcstigation gasolines are esposed to sunlight has been investigated. gave results of tests made was undertaken in order to A theory of gum formation is offered, involving priwith copper, porcelain, and study the gencral types of marily autoxidation. silica dishes. r e a c t i o n which take place More recently, Cooke (2) and the nature of the comdeveloped a method consistp o u n d s produced in gum formation. I n workingwith gasoline, like all petroleum prod- ing of evaporating, in a specially designed steam oven, 20 cc. ucts, we are confronted with a complcx mixture of hydro- of gasoline in a 30-cc. glsss dish. The purpose of the steam carbons. For that reason, a t the outset, little hope was oven as pointed out by Cooke was to exclude the air and reentertained of identifying the specific products composing the place it with an inert atmosphere, whereby greater precision gum; but from the types of rcactions and the composition can be obtained. of the gum it was hoped to make some generalizations as to Factors Influencing Gum Test the chemistry of gum formation by cracked gasoline. KINDOF ATMOSPHERE-Perhaps the most important factor Literature in the gum test is the atmosphere in contact with the oil during evaporation. The following results were obtained by T h e subject of gum formation has probably been quite evaporation of a sample of cracked gssoline in different atgenerally studied in all refineries in order to control and im- mospheres: oxygen 526, air 394, steam 34, and natural gas prove the quality of the products manufactured. However 27 mg. per 100 cc. It is evident that the quantity of oxygen general this study has been, few detailed and extensive investi- in the atmosphere is a determining factor in the amount of gations have been published, and while some attempts have gum produced. This explains the difficulty in obtaining been made to explain the composition and formation of these consistent results by the copper dish method when the air gums, it is evident that the subject is not fully understood. coming in contact with oil is subject to variation due to air Smith and Cooke (6) made a n investigation of the gum currents over the dish. formed by evaporating several samples of gasoline in various It has been the writers’ experience that by the method of kinds of dishes and pointed out the similarity to Backeland’s Cooke, whereby the evaporation is conducted in an atmossynthetic resins. They were unable, however, to detect phere of stcam, low results are consistently obtained. The phenols in the gasoline gums and concluded that the resinous gum obtained by the steam oven method gives only gum deposits are polymerized aldehydes formed b y the oxidation which is already produced in solution in the oil before evaporaof olefins. tion, and givcs no indication of the potential gum forming The fluid resin, or gums that are formed from cracked gaso- ability. line on exposure to air, was studied by Brooks ( I ) and reported TYPEOF DISH-Glass, porcelain, and silica dishes consistas a mixture of organic peroxides, aldehydes, ketones, and ently give smaller amounts of gum than the copper dish. acids. H e concludes t h a t the gum is a result of oxidation in This is probably due to the presence of copper oxide which which peroxide formation is the initial step. More recent hastens the gum formation. T o test this, gum determinawork by Mardles (I)on slow combustion and autoxidation of tions were made in copper and glass dishes to which were gasoline in the liquid phase points toward peroxide formation added small amounts of copper oxide and the gum content was as the initial step in oxidation, whereby the olefins react most greatly increased, in one case approximately tenfold. 1 Received May 16, 1929. SPEEDOF EvAPORATION-while the temperature should
M
Vol. 21, No. 11
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1080
Developed during Gum Test of Gasoline
Table I-Acidity
GUMTEST
30%
50%
M g . KOH Evaporation of 100 cc. untreated cracked gasoline in copper dish Evaporation of 100 cc. untreated cracked gasoline in glass dish Evaporation of 100 cc. acid-treated cracked gasoline in copper dish
GUMRESIDUE
TOTAL ACIDITYOF OIL AT VARIOUS AMOUNTS EVAPORATED 70%
90%
d i g . KOH
Wt'
Mg.
Total acidity
Free acids
Saponifica- Neutralization tion equivalent0 equivalent0
Mg. KOH
7.8
14.0
19.3
25.2
243
71.6
18.6
181
730
Trace
Trace
2.1
2.8
10
3.5
1.8
160
312
Trace
1.3
1.7
2.0
24
8.4
2.1
160
641
remain approximately constant on an actively boiling steam bath, the circulation of air over the dishes and the boiling point of the gasoline mill affect the evaporation time. A slow evaporation gives morc timc for the reactions producing the gum to take place and consequently a larger quantity of gum residue a t the end of the test. Changes in Gasoline during Gum Test
Starting with the assumption that the principsl reaction in gum formation is oxidation, a morc detailed study was begun of the changes taking place in the gasoline during evaporation in copper and glass dishes. Preliminary tests of the gasoline during evaporation showed positive reactions for peroxide, oxygen, aldehydes, and acids. Quantitative estimations of the amounts of thesc compounds indicated that the peroxides and aldehydes were probably intermediate and the acids end products: consequently, acidity determinations were made a t various stages of the evaporation in the dishes. Table I shows results obtained from an untreated cracked gasoline in copper and glass dishes, also the same gasoline evaporated in a copper dish after treatment with sulfuric acid and rcdistilling. It ~villbe noted that the acidity in the copper dish is much higher than that in the glass, emphasizing again the effect of the kind of dish on the gum test. Thc acid treatment causcs a very pronounced decrease in the acidity, showing t h a t some constituents active in the development of acidity have been removed. The corresponding small weight of gum residue from the acid-treated sample and also from the untreated sample in the glass dish is very marked. It may also be mentioned that no aldehyde or peroxide could be detected in the acid-treated sample during evaporation. The rapid increase in acidity during the latter part of the evaporation in the copper dish is probably due to oxidation of thc less volatile material. The absence of this effect in the glass dish indicates some catalytic effect of the copper. The gum residues resulting from these evaporations were dricd a t 99" C. (210" F.) in a n air oven to constant weight. The weights, total acidity, and free acid are shown in Table I. The difference between the saponification, obtained b y saponifying the alcoholic solution of the gum for 3 hours on a steam bath, and the neutralization equivalent, determined by titrating thc cold alcoholic solution of the gum, suggests that the acidic compounds in the gum may exist largely as anhydrides. lactones, or some similar condensed form. The relation of the weight of gum residue to the amount of acid developed during these evaporations shows that the acids in some form are predominating constituents of the gum. Examination of Gum
In order to examine the gum more extensively, it was necessary to collect a sufficient quantity of the material. Owing t o the extremely small amount formed in glass, i t was decided to work only on that from copper dishes. ,Evaporations were made of an untreated cracked gasoline (gasoline used throughout this work was derived from liquid phase
cracking of midcontinent gas oil), having about 38" C. (100" F.) initial boiling point, 205" C. (401" F.) end point, and a Babcock bottle test of 20 per cent absorbed by 66" BB. sulfuric acid, until approximately 10 grams of the gum were collected. All evaporations were made in a similar mannernamely, by evaporating 100 cc. of the gasoline in a copper dish on a steam bath until a soft gum remained and then placing the dish in an air oven a t 99' C. (210" F.) and drying the gum to a constant weight. The dried gum was then scraped from the dish, ground to a fine powder, and wc!l mixed. The gum thus collected was brown, insoluble in water, and almost completely soluble in acetone, alcohol, and chloroform, dissolving in the last two very readily. It had no sharp melting point, but began to soften a t 98" C. (198' F.) and entirely melted a t 105" C. (221 ' F.). It boiled with decomposition a t 164-169' C. (237-304' F.). Since the gum appeared to be composed of material largely saponifiable, the plan of separation adopted was to saponify, steam-distil. filter, acidify, steam-distil again, filter, evaporate, and take u p the residue by solvents. In this way a separation was contemplated of (1) volatile unsaponifiable material, ( 2 ) non-volatile unsaponifiahle, (3) volatile acids, (4) insoluble nonvolatile acids, and (5) water-soluble, non-volatile acids. and Characteristics of Gum from Copper Dish UNSAPONIINORIGINAL FIABLE SOLUBLE SOLUBLE GUM MATTER ACIDS ACIDS Per cent 100 00 13.00 55 00 30 50 P e r cent P e r cenl Per cent Per c e n l 64 20 73 22 66 70 70 7 3 Carbon 6 81 7 20 Hydrogen 6 95 6 32 19 51 13 81 18 5 8 24 23 Oxygen Trace A-il Nil 0 13 Nitrogen 1 07 0 29 0 41 Sulfur 0 68 2 00 15 38 0 98 0 80 Asha Hanus iodine value 73 89 84 200 ... 119 Molecular weight 181 0 104 94 Saponification equivalent 732 0 460 24 1 Neutralization equivalent Physical nature Dark Dark Light Brown brown, brown, viscous brqwn, resinous solid solid liquid Melting point, a C. 98-105 , 192-195 ... Composed largely of dust accumulated during evaporations of oil in dishes. Table 11-Composition
...
...
..
(I
The gum is only slightly saponifiable b y aqueous potassium hydroxide, b u t saponifies readily in alcoholic potassium hydroxide. Approximately 2 grams of the dried material were saponified for 3 hours with alcoholic potassium hydroxide; the saponification value was found to be 191, as shown in Table I. The alkaline saponified solution was diluted with water and steam-distilled, but no products from the gum could be detected in the distillate. The solution was then filtered to remove the unsaponifiable non-volatile material. A solid dark brown mass was obtained which was dried a t 99" C. (210" F.) to constant weight. The dark brown filtrate was then acidified with dilute sulfuric acid and a flocculent precipitate appeared. The mixture was again steam-distilled, but no volatile material was obtained, showing absence of volatile acids. The mixture, after diluting to about 2
November, 1929
INDUSTRIAL ,411'D ENGILYEERISG CHEMISTRY
liters, was filtered t o separate insoluble non-volatile acids. A large brown precipitate was obtained, which was washed well with warm water and dried to constant weight. The remaining filtrate was bright yellow. This was evaporated almost to dryness and the oily residue was taken u p with ether and acetone. After removing the solvents the remaining semi-solid brown oil had an odor of organic acids. T h e above separation thus resulted in a division into unsaponifiable, water-insoluble, and water-soluble acids; no volatile material was detected. The analyses and tests of the original gum and the three products into Tvhich it was separated are shown in Table 11. The molecular weights were determined by the freezing point method using acetic acid as solvent. KO molecular weights are given for the unsaponifiable and soluble acids because of difficulty in finding a suitable solvent. Gum Formation in Sunlight
It has been mentioned that cracked gasolines form a certain type of gum when exposed to sunlight and air. Preliminary experiments had shown that sunlight, access to air, and temperature were factors inducing the formation of this type of gum. I n order to study the problem more thoroughly, a 10gallon plsin-glass gasoline pump bowl, the bottom of which was sealed with a glass plate and the top covered with a loose-fitting tin cap. allowing free access of air, was filled with cracked gasoline similar to that used in the fore part of this
Hours Exposure
Figure 1-Acidity
a n d Gum Developed on Exposure of Cracked G a s o l i n e to A t m o s p h e r e
work. The experiment was conducted during July and August when the average temperature was around 27.2" C. (81 " F.). Tests were made a t intervals on the oil for peroxide oxygen, acidity. and copper dish gum. The peroxide oxygen was determined by washing the gasoline with water and estimating the amount of iodine liberated b y the water solution from potassium iodide in acetic acid solution and the acidity by titration of the gasoline with 0.1 N potassium hydroxide. The results are shown in Table 111, and part of them are plotted in Figure 1. KO definite relationship could be ascertained between time of exposure and the peroxide oxygen, indicating that it is a n intermediate product. It was noted in this and other tests, however, that the peroxide oxygen accumulated during sunlight and decreased in the dark or on cloudy days. The curves in Figure 1 show a gradual accumulation of acidity and gum and indicate a relationship between the two. After the gasoline had been exposed about 200 hours, i t became cloudy and a n almost colorless liquid gum began to collect on the sides and bottom of the bowl. A t the end of the experiment approximately 40 grams of gum were collected. It may be mentioned a t this time that in other bowls exposed for longer periods larger amounts of gum were collected and in some cases as high as 300 grams were found after 4 months.
1081
The gum was a viscous, sticky liquid which gradually turned brown. It had a specific gravity of 1.0932 (20"/20" C.), which gave no test for peroxides and only faint tests for aldehydes and ketones. An attempt to vacuum-distil the gum was unsatisfactory, since only 35 per cent could be distilled a t 10 to 15 mm. pressure accompanied by liberation of water and much decomposition. of Acidity a n d Gum by Exposure of Cracked Gasoline to S u n l i g h t PEROXIDE OXYGEN ACIDITY TOTAL (IODINE PER (KOH PER GUM EXPOSURE SUNLIGHT 100 cc. OIL) LITEROIL) (COPPER DISH)
T a b l e 111-Formation
Hours 0 24 72 128 152 170 240 296 344 400 432 500 572 672
Houvs 0 12 2s 46 58 62 94 106 110 134 140 176 20s 224
ME. 0 15 0 53 0 24 0 50 0 44 0 63 0 54 0 54 0 60 0 54 0 140 0 158 0 148.0
Mg. 0 0 0.8 2.5
4.5 7.0 9.8 18.0 24.0 27.0 31.0 49.0 54.0 67.0
Mg. 400 400 430 500 550 600 6.50 730 9.50 1100 1370 1600 1800 2050
Examination of Gum Formed in Sunlight
The method of analysis of the gum formed in the sunlight was siniilar to that used on the gum formed by the copper dish test, The data on the various products are given in Table IV. The dried gum is the product obtained by drying the original soft gum to constant weight in a glass dish on the water bath. It resembled very much that formed b y the copper dish test. A sample of the soft gum was treated with approximately 0.25 S potassium hydroxide for 10 hours on the steam bath, using a reflux condenser. The saponified mixture was then steam-distilled to remove unsaponifiable steam volatile products. A yellow oil was obtained with a n aromatic odor and specific gravity of 0,8998. It was very soluble in alcohol, acetic acid, and acetone. Tests for ketones were positive. The non-volatile unsaponifiable material was obtained as a dark brown, solid mass b y cooling and filtering the alkaline solution, the analysis of which is shown in the table. The alkaline solution was dark brown, and resembled a soap solution by foaming easily on agitation. It was next acidified with dilute sulfuric acid and a brown gelatinous precipitate was formed. The mixture was then steam-distilled and the steam volatile acids extracted from the distillate by salting out and extracting with ether. The insoluble acids were filtered from the remaining solution. These insoluble acids were dark brown and resinouc, resembling the insoluble acids obtained from the copper dish gum. The remaining solution containing water-soluble acids mas a bright yellow color. It was evaporated almost to dryness and extracted with ether. Since only part of the sirupy acids were soluble in ether, the remainder was taken u p with acetone. These products, after the solvents were evaporated off , were reddish, viscous liquids, the analyses of which are shown in the last column of Table IV. The gasoline from which the gum was separated was mashed with 5 per cent aqueous sodium hydroxide. A dark brown soapy solution was obtained resembling the alkaline solution previously obtained b y saponifying the gum ahich separated from the oil. The alkaline solution was steamdistilled to remove hydrocarbons and then cooled and made almost neutral with dilute sulfuric acid. The acids were then liberated by four successive additions of 1 N sulfuric acid, the mixture being steam-distilled after each addition of acid. The first two additions caused the liberation of a large quantity of non-volatile insoluble acids, which solidified on cooling
INDUSTRIAL .4ND ENGINEERING CHEMISTRY
1082
and were filtered off. The third addition liberated a black oil, which was volatile in steam and found to be chiefly phenols similar to those isolated from cracked gasoline by Story and Snow (8). The find solution was reddish and, on being made slightly acid by the last portion of sulfuric acid, had an odor of organic acid. A distillate obtained from it by stexm distillation was strongly acid and had the odor of acetic acid. The distillate was saturated with calcium chloride and the acids were extracted with ether. The ether extract was fractionally distilled, but much polymerization occurred. The fractions were highly unsaturated. Acetic and acrylic acids mere identified in the lower boiling ruts and the remainder appeared to be higher unsaturated acids. The Table IV-Composition
ment with water, the pressure being maintained by a constant water head. The tube for introducing the oxygen extended nearly to the bottom of the flask of gasoline, which helped to keep the gasoline mixed as the oxygen bubbled through. Samples were drawn out a t the sampling tube, the volume of oxygen Rbsorbed, and acidity and gun1 content of the gasoline determined. The data are shown in Figure 3. The relation between oxygen absorption, acidity, and gum is evident from the curves. The time of exposure is given in total hours. It was fonnd the absorption of oxygen continued during periods when the sun was not shining, indicating that periodic exposures of direct sunlight and diffused daylight are sufficient to promote the reaction. It has been observed, however,
a n d Characteristics of C u m F o r m e d in S u n l i g h t
UNSAPONIPIABLE ORIGINALGUM
100.00 Per cent 64.97 Carbon 8.56 Hydrogen 26.08 Oxygen 0.22 Sulfur 0.17 Ash Hanus iodine value 47 Saponification equivalent 289 Ke itralization equivalent 625 Mol w l a r weight 172 Melting point. C. Physical nature Dark brown viscous liquid, sp. gr. 1.0932 200/200 c.
NON-VOLATII.E ACIDS
STEAM-
VOLATILE
DRIEDGUM Steam-volatile
Per cent
Vol. 21, N o . 11
54.40 P e r cent 71.95 7.99 19,48 0.33 0.25 95 144 651 338 68-71 Brown resinous solid
Non-volatile
8.93 Per cent 73.12 8.95 17.36 0.29 0.28 65 0
1?,20 Per cenl 77.64 11.06 11.14 0.16 0.00 68
0
0
*'IDs
6.20 P e r cent 70.87 9.34 19.27 0.52 0.00 142 215
0 156
334
466 117
Yellow liquid, sp. gr. 0.8998 200/200 c.
Brown semisolid
Yellow liquid
specific gravity and odor indicated absence of the saturated acids, and hence the unsaturated acids probably were derived from oxidation of hydrocarbons containing more than one double bond if the oxidation took place a t an unsaturated linkage. The water solution remaining contained the nonvolatile acids. It was bright yellow and on evaporation deposited some brown sirupy acids similar to those previously obtained from the gums. The insoluble acids extracted from the gasoline previously mentioned were washed well with water and dried. The product was yellowish brown, its melting point was 120-125' C. (248-257' F,); molecular weight, 301, and saponification equivalent, 180. Analysis showed 74.10 per cent carbon, 7.90 per cent hydrogen, and 18.00 per cent oxygen. It was slightly soluble in hot water and readily dissolved in dilute caustic forming a bright yellow solution. Absorption of Oxygen by Cracked Gasoline
The fact that cracked gasoline absorbs oxygen is very easily demonstrated by exposing a sample to sunlight and connecting it to a supply of oxygen. After a certain induction period the oxygen is rapidly taken u p by the oil. Experiments were conducted with straight-run gasoline, b u t only slight absorption was noted after extremely long periods at atmospheric temperatures. The absorption of oxygen is accompanied by the production of peroxide oxygen. That sunlight is an important factor in this phenomenon is shown in Table V.
.
Note-Since the completion of this work Voorhees and Eisinger presented a paper, "The Importance and Significance of Gum in Gasoline,'' before the American Petroleum Institute. on December 3 to 6, 1928, in which results are given of the absorption of oxygen by gasolines at 212' F.
An apparatus similar to that shown in Figure 2 was arranged whereby the volume of oxygen absorbed could be measured as well as the changes taking place in the gasoline. T h e volume of oxygen absorbed was measured b y displace-
WATER-SOLUBLE
Waterinsoluble 38.24 P e r cent 71.98 7.72 19.57 0.23 0.50 106 264 592 235 103-107 Brown solid
Ethersolul.le
Acetonesoluble
20.08 Per crnl 59.94 8.04 31.61 0.28 0.13 70 138 330 163
13.10 Per ccnl 52.49 7.96 36.83 0.40 2.32
Brown viscous liquid
110 198 358
Brown viscous
liquid
that oxidation proceeds in the dark once the induction period is passed, but only very slowly a t low temperatures. After approximately 40 hours' exposure the oil became cloudy and a yellowish gum began collecting in the bottom of the container and continued to increase. When approximately 200 hours had elapsed, gas began to be evolved a t the gas vent, which €ime corresponds with the steeper part of the curve in Figure 3. This gas contained approximately 10 per cent carbon dioxide, the remainder consisting chiefly of light gasoline vapors and oxygen. At the end of the experiment 54 grams of gum were collected in the flask from 5 liters of gasoline charged. Since the gum collected here resembled very much that obtained from the oxidation by air, described previously, no analysis was made of this material. Table V-Peroxide F o r m a t i o n b y Cracked G a s o l l n e (Mg. iodine per 100 cc.) SUNLIGHT SUNLIGHT SUNLIGHT DARK AND
EXPOSURE OXYGEN Hours Mg. 0 2 4 10 14 36
0 22.0 44.0 102.0 232.0 548.0
AND
WITHOUT
AIR
OXYGEN
Mg.
Ms.
0 12.0 24.0 36.0 60.0 300.0
0 4.0 4.0 4.0 8.0 8.0
WITH
OXYGEN ME. 0 Trace Trace Trace Trace Trace
Discussion of Results
The study of gum formation by evaporation in dishes has shown that oxidation is a primary factor in the process. This is proved by the initial peroxide formation and the gradual development of acidity as the evaporation proceeds. The copper dish accelerates the reaction, as is shown by Table I. These results also show that the oxidation is more rapid a t the end of the test, which is probably due to the better contact with air of the higher boiling hydrocarbons during the slow evaporation a t the end. Another feature is the decrease in gum formation of a gasoline after treatment with sulfuric acid. This suggests that the more active hydrocarbons, which are
November, 1929
INDUSTRIAL A N D ENGINEERING CHEMISTRY
pol-merized and removed by sulfuric acid, are the principal gum formers. The analysis of the gum from the copper dish shown in Table I1 is difficult to interpret. A close similarity has been noted in the composition of the gums analyzed in this investigation and those of Smith and Cooke ( 6 ) which indicate that a certain type of hydrocarbons is the source of the gum. Since thme products are complicated mixtures, any formula would be niorc or less conjectural. However, the ratio of carbon to hydrogen content shows that n e are dealing with highly unsaturated compounds or polymers of the same. The low iodine number reveals no high degree of unsaturation; therefore they are probably polymers or lactoncis. The low molecular weight and low iodine value of the inqoluble acids aboi-e can only be explained as some kind of lactone formation or a fissure of the condensed or polymerized molwule in solution. The unsaturated character of the gum and the highly colored solutions of the acids indicate they contain conjugated double bonds. The gum formation in sunlight is likewise an oxidation reaction. There appears to be a relationship between the time of exposure, acidity, and gum. The reaction proceeds in the absence of sunlight, and it appears only necessary to have occasional activation of sunlight to keep the reaction rapidly progressing a t low temperatureq. The examination of the gum formed in the sunlight differs from that from the dish evaporations by being more highly polymerized or condensed and also more extensively oxidized. T h e original gum here was a thick brown liquid having a varnish-like odor. The dried gum is thc result of drying this soft gum to constant weight. The higher molecular weight after drying shows thnt lightcr materials are driven off and condensntion or polymerization has taken place. The unsaponifiabk steam-volatile material probably consiits largely of high molecular weight ketones or aldehydes and some hydrocarbons. The unsaponifivble non-volatile material is similar t o the previous volatile material but more highly polymerized. The portion marked volatile acids, from the saponification equivalent, apparently contains considerable unsaponifiable material. The non-volatile water-soluble acids are more highly oxidized materials, probably hydroxy acids.
1083
which are closely related to the diolefins and usually undergo autoxidation. It is possible that these are among the hydrocarbons responsible for gum, The absorption of oxygen b y cracked gasoline proves most convincingly that gum formation is an autoxidation reaction. The sunlight apparently activates the more reactive unsaturated hydrocarbons, and the initial formation of peroxides indicates that oxygen is added in a molecular form. The reaction takes place rapidly and smoothly, the oxidation appearing to proceed with formation of acids and evolution of carbon dioxide and water. The continuation of the oxidation during periods when there is no sunlight, with a corresponding disappearance of the peroxide oxygen, shows that this peroxide is the source of the oxidizing power. ao
24
ct
21
-1
5
18
0
15
0
L
I2
?'
I)
i c
9
E6
0'
3
+c
80
IZO
160
zoo
2qo
Leo 320 360 +oo
Tlme o f Exposure ~n Hours
Figure 3-Relation b e t w e e n Oxygen Absorbed b y Cracked G a s o l i n e a n d t h e F o r m a t i o n of G u m a n d A c i d i t y
The gum formed as a result of direct absorption of oxygen appeared to be similar to the other gums, indicating the same general type of reaction. The peculiar nature of the acids present in all the gums indicates extensive polymerization of lower unsaturated acids or t h a t they are composed of higher unsaturated acids with which we are not familiar. The absence of saturated fatty acids clearly points out that saturated hydrocarbons do not extensively enter into the reactions in gum formation. Theory of Gum Formation
Figure 2-Oxygen
Absorption Apparatus
The acids extracted by caustic from the gasoline which had been esposed to sunlight indicate further t h a t oxidation of unsaturated hydrocarbons is responsible for the gum. The presence of acrylic acid and higher unsaturated acids is probably the result of oxidation of diolefins and similar hydrocarbons. The absence of appreciable quantities of saturated fatty acids seems to point toward Oxidation of an unsaturated bond in the alpha position which results in an unsaturated acid, carbon dioxide, and water; otherwise saturated acids might be expected. The yellow color of the saponified solutions and the water solutions of the soluble acids is significant. This is characteristic of conjugated double bonds, especially of the fulvenes,
The formation of gum b y evaporation of a cracked gasoline is apparently a result of the oxidation of unsaturated hydrocarbons. These hydrocarbons are of a type relatively active, which are readily polymerized and removed by sulfuric acid. The products of the oxidation appear to be initially peroxides, with acids as the chief end products making up the gum. The gum also contains some unsaponifiable material resembling polymerized aldehydes, ketones, or oxides. The physical characteristics and composition of the acids point toward polymers of unsaturated acids. Therefore, the original hydrocarbons may h a w been compounds containing conjugated double bonds. Of this type are diolefins, triolefins, and similar higher olefins. The autoxidation of these unsaturated hydrocarbons, with initial formation of peroxide, may be represented as follows: R- H C = C H ~
+ o2+R - ~ C - C H ~ + (02)
I
0-0
Olefin
R-
H
CEO, R-C=O,
Aldehyde
Ketone
I
Peroxide
R-
H
C-CHz,
'd
Oxide
No
R-C-OH,
Acid
COI, HzO
,
INDUSTRIAL A X D ENGINEERING CHEMISTRY
1084
The absorption of oxygen and formation of gum in the sunlight is a n autoxidation reaction. The furction of the sunlight appears t o be to activate the oxygen absorbing compounds, as evidenced by a n induction period. The reaction then would be: A -+A ’ -+A 0 -+Polymerized acids and higher
Olefin
Activated (Autoxidation) Peroxides
aldehydes and ketones
This explanation of gum formation agrees with results of Moureu and Dufraisse (5) who studied the autoxidation of acrolein, which they found was activated b y exposure to light or b y oxygen so that i t undergoes condensation or autoxidation. I n the study of autoxidation of organic compounds, Staudinger ( 7 ) obtained compounds which he termed “moloxides,” or those compounds of unknown structure containing molecular addition of oxygen according to the Engler-Bach theory. H e also obtained known compounds termed “peroxides,” particularly of the asym-diphenylethylene, PhzC=Chz and certain ketenes, R-C=CO.
Vol. 21, No. 11
The similarity of work of the above authors and the present investigation is evident. Owing to the complexity of the composition of cracked gasoline. it is impracticable to identify the specific compounds producing the gum or undergoing autoxidation. The experimental results, however, obtained in this investigation point rather definitely that unsaturated hydrocarbons are responsible to a large degree for gum formation and t h a t those inducing the reaction through peroxide formation are probably olefins containing more than one ethenoid linkage. Literature Cited (1) Brooks, IND. ENG.CIIEM.,18, 1198 (1926). Cooke, Bur. Mines, Repis. Inseslrca!icns 2686. Dean, Bur. Mines, Tech. Paper 214. Mardles. J . Chem. S c c . , 1938,XiP. hIoureu and Dufraisse, Bu!L soc. chim., 56, 1564 (1924); C. A , , 19, 1125
(2) (31 (4) (5)
(1925). (6) Smith and Cooke, Bur. Mines, Repls. lnvesligations 2394 (September, 1922). (7) Staudinger, Ber., 58B,1075 (1025); C. A . , 19, 2658 (1923). (8) Story and Snow, IND.ISNO. CHEM.,20, 359 (1925).
Cracking of Tars from Cannel Coal’ J. C. Morrell and W. F. Faragher UNIVERSAL OIL PRODUCTS COMPANY, CEIICAGO, ILL.
ANNET, c o a l is a A crude cannel-coal tar has been cracked to give and 2.8 gallons of light oil high yields of gasoline excellently suitable for motor non-coking bitumi(recovered fronl the gas) per fuel. It is suggested that the processing of cannel ton. The yields from Lower nous coal sometimes coal can be made profitable by working UP the retort classed under oil shales. It and Upper Freeport cannel residues into solid fuels and cracking the tars into was orieinallv called “candle sh:iles were 37.5 and 38.2 coal” cecause i t c o u l d b e high yields of motor fuel. galloris of crude oil and apignited readily with a lighted prosimately 2.5 g a l l o n s of match, giving a bright flame. Cannel coal usually contains light oil recovered from the gas. substantial amounts of spores and seed coats which are beTable 11-Analyses of K e n t u c k y C a n n e l Coals from Various lieved t o yield on distillation waxes and resinous compounds. Counties VOLATILE F I X E D Before the establishment of thc petroleum industry, cannel COUNTY MATTER CARBON ASH SIiLPUR coal and shale were commercially distilled into oils and subsePer cent Per cent Per cent Per cent quently refined. JohnSon 49.130 41.920 7.150 0.802 Pike 43.400 8.3GO 0.689 46.300 The deposits of cannel coal are probably next in importance 44.160 Perry 6.000 0.766 49.400 Breathitt 66.280 3 640 0.830 29.730 to the oil shales as far as potential production is concerned, Rrea thi tt 53,800 5 540 0.722 4FJ.000 and are more important than the oil shales because they Morgan 50.060 8 400 1.650 40.140 give a larger yield of oil or t a r and a residue tJhat can be used Gentry ( 7 ) shows comparative yields of products from coal, as a solid fuel. lignite, and shale as indicated in Table 111. The cannel coal Previous Work on Analysis and Yields used in these tests was exceptionally rich in volatile matter. An analysis of a Kentucky cannel coal is shown in Table I Table 111-Yield of Products i n T e s t s of Tozer R e t o r t PRODUCT P E R BITUMINOUS CANNEL ( 2 ) , and analypes of Kentucky cannel coals from various COAL LIGNITE S H A L R COAL G H O STON S count,ies as made by the Geological Survey of Kentucky in Semi-coke, pounds 1200 Waste 1700 880.0 27.2 36.1 2 3 . 8 1 02.1 Table IT (4). Kentucky is the largest producer of cannel coal. Tar. gallons
C
Ammonium sulfate, pounds
Table I-Typical
Analysis of K e n t u c k y C a n n e l Coal Per ceiil
MoistGre., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3R Volatile m a t t e r . ,. . . . . . . . . . . . . . . . . . . . . . . . . 48.40 Fixed carbon. Ash... . . . . . . . . . . . . 10.49 Sulfur.. . . . . . . . . . . . 1.20 Hydrogen. . . . . . . . . . . . . . . . . . . . . . . . . Carbon (total). . . . . . . . . . . . . . . . . . . . . iiitrogen.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.16 .......................... 8.70 Oxyg 13,770 B. t. Heat‘
ti.
per lb.
The following yields of products are given by Fettke ( 6 ) : Cannel c o d (upper Kittanning) gave 50 gallons of crude oil I Received April 16, 1929. Presented before the Division of Petroleum Chemistry a t the 77th Meeting of the American Chemical Society, Columbus. Ohio, April 29 t o M a y 3, 1929.
12.1
22.0
18.5
19.1
According to Craig ( 3 ) ,cannel coal is one of the important British sources from which oil may be obtained by distillation, although the only source a t present Leirig utilized is oil shale, which is mined and retorted in Scotland. The cannel coals of Great Britain usually run high in ash-e. g., 10 t o 30 per cent-and the average yield of crude oil per ton over the whole country from the cannel coals and the torbanitic cannel coals is 34 gallons. In addition, an average yield of 30 to 40 pounds of ammonium sulfate per ton can be recovered. It is cstimated that an economic unit for cannel coal is approsimately 1000 to 2000 tons per day and that at least six such retortirig and refining works can be established witliout difficulty. These plants, according to Craig, would make approximately
