STABILITY OF JACQUE C. MORRELL, WAYNE L. BENEDICT, AND GUSTAV EGLOFF Universal Oil Products Company, Riverside, Ill.
GASOLINE
QT
HE stability of gasolines to light is an important consideration t o the refiner and marketer of gasoline. Whether dyed or water-white, gaso-
TO
line should be stable from the time of production until used. Large quantities of gasoline are dispensed through pumps having glass bowls in which the gasoline may be subjected to direct sunlight. Under these conditions some gasolines become hazy and discolored and deposit sediment in the bowls. Previous workers (1,9,3) have indicated t h a t color formation in gasoline may be due to oxidation reactions involving sulfur compounds or unsaturated hydrocarbons in the gasolines. It has been reported t h a t gum formation in light is a. function of oxygen absorption (7,8). It has also been stated that the effect of oxygen is secondary (6). I n an earlier publication the effects of mercaptans, alkyl disulfides, and sulfur were discussed (6). It was shown t h a t alkyl disulfides or sulfur were detrimental t o color stability of gasolines exposed to light, and that sulfur and disulfides present as a result of sodium plumbite sweetening were responsible for color and haze formation in the Midcontinent gasolines studied. The purpose of the present investigation was to study t h e factors involved in color, haze, and gum formation in gasolines due to photochemical changes.
LIGHT Photochemical Formation of Color, Haze, Gum, and Reaction Products
Apparatus, Materials, and Procedure The source of light was the carbon-arc lamp described in the previous paper (5). This source of light was selected because of its uniformity and reproducibility. Samples to be tested (95 cc.) were placed in tightly corked quartz cylinders. An inlet tube extended to the bottom of the cylinder, and an outlet tube extended through the cork above the surface of the liquid. A 25-cc. expansion chamber provided with a stopcock was attached to the outlet tube to release the pressure in the cylinder due to heating of the gasoline, and to collect gaseous reaction products in some cases. Air, oxygen, nitrogen, carbon dioxide, or hydrogen was bubbled a t a rate of 10 liters per hour through the gasoline for one hour prior to exposure to light. The gas was delivered through a. manifold equipped with flowmeters and a pressure-regulating device for maintaining a constant rate. The cylinders were tested for Ieaks by closing the outlet tube and permitting the system ta stand under the pressure of the gas. The gasoline samples thus prepared were exposed to the carbon-arc lamp for one hour. Examination for the appearance of haze was made a t 2.5-minute intervals. The outlet tube was. momentarily opened at intervals of about 5 minutes to release pressure. After exposure to the light the gasoline was allowed to cool: and the Saybolt color, peroxide number (Q),acid number ( I ) ,a n d air-jet gum (A. S. T. M. method D 381-34T) were determined. Qualitative tests were made for hydrogen sulfide, mercaptans, sulfuric acid, and sulfur. Lead acetate paper was used to test for hydrogen sulfide. Mercaptans were determined by shaking the gasoline which had been freed from hydrogen sulfide witb sodium plumbite solution and sulfur. Sulfates were determined by barium chloride solution added to the water extract of the gasoline. Metallic mercury was used to detect elementary sulfur. If peroxides are present, ct black precipitate may result with mercury even in the absence of sulfur (9). Peroxides may be removed with ferrous sulfate solution. The Midcontinent straight-run gasoline used in these tests was treated with 2 pounds per barrel of 66' BB. sulfuric acid, followed by water wash and caustic soda treatment to yield a 30° Baybolt color. The cracked gasoline was refined by acid. and vapor-phase clay treatment. The blend consisted of equal parts of straight-run and cracked gasoline. Elementary sulfur was removed by shaking the gasolines with metallic mercury.
The stability of gasolines to light is an important consideration to refiners and marketers of gasoline. Gasoline is sold in exposed glass bowls in which it may be subjected to sunlight. Under these conditions some gasolines become hazy and discolored and deposit sediment in the bowls. Straight-run, cracked, and blended gasolines on exposure to carbonarc light in the presence of air developed color, gum, peroxides, acid, and aldehydes. The straight-run and blended gasolines developed haze, the cracked gasoline did not. The effects were photochemical since there was substantially no change when all conditions were kept constant with the exception of exposure to the arc light. Color and gum formed in the presence of elementary sulfur even in the absence of air. Haze, peroxides, and acids formed only in the presence of air. Haze could be removed by filtration and the color was greatly improved, but gum content was unaffected. The haze particles were found to contain sulfur dioxide and trioxide.
+
122
JANUARY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
Mercaptans were removed by agitation with silver nitrate solution. The gasolines had the following properties: Midcontinent Gasoline Gravity, a A. P.I. Sp. gr. Initial b. p., ' C. Distilled over, O C . :
Color, Saybolt Sulfur, % Peroxide No Acid No. Air-jet gum. mg./100 cc Bromine No.
Straight-Run 56.6 0.7523 53
86 141 193 210 30 0.06
+
0.00
0.00 1 1
Cracked 57.4 0.7491 48
80 124 175 198 30+ 0.15 0.10 0.00 2 57
Blend 57.0 0.7507 51
85 132 185 204 "$9 0.054 0.00 2
...
The gasolines comprising straight-run, cracked, and blends of these two were exposed to the carbon-arc lamp continuously for 60 minutes in atmospheres of air, oxygen, nitrogen, carbon dioxide, and hydrogen. The samples used were (1) gasolines with no additions, (2) those to which 0.01 per cent elementary TABLE I. EFFECT OF
sulfur was added, (3) those to which n-propyl disulfide was added in an amount equivalent to 0.10 per cent sulfur, and (4)those to which both sulfur and n-propyl disulfide were added. n-Propyl disulfide was chosen as representative of disulfides likely to occur in gasoline or to be formed during sweetening. The results of these tests are shown in Table I. The data show: (a) All gasolines in atmospheres of air or oxygen showed color drops whether sulfur was added or not; (b) peroxides, acids, and gums formed in all gasolines; (c) oxygen caused greater deterioration of the gasolines than air; (d) in many of the tests haze formation occurred in the gasolines. With nitrogen, carbon dioxide, or hydrogen, and with no additions of sulfur or n-propyl disulfide, the straight-run gasoline dropped in color from 30°+ to 28" Saybolt only, and the cracked and blended gasolines were unaffected. There was no formation of acids or gums in any of these gasolines, and only very small amounts of peroxides.
FORMATION O F COLOR, MIDCONTINENT GASOLINES
S U L F U R AND n-PROPYL DISULFIDE ON THE
Compound Added
-4tmosphere
Color Saybolt Straight-Run Gasoline Air 17 hazy Oxygen 12 hazy Nitrogen 28 clear GO2 28 clear Hydrogen 28 clear Air 2 cloudy Oxygen -13 cloudy Nitrogen 13 clear c02 14 clear Hydrogen 13 clear Air 8 cloudy Oxygen -12 cloudy Nitrogen 29 clear coz 30 clear Hydrogen 30 clear Air 1 cloudy -10 opaque Oxygen 20 clear Nitrogen coz 20 clear Hydrogen 19 clear O
None
Elementary sulfura
a-Propyldisulfideb
Elementary sulfura
+ n-propyl disulfideb
Elementary sulfur&
n-Propyl disulfideb
Elementary sulfura
+ n-propyl disulfideb
None
n-Propyl disulfideb
a C
+ n-propyl disulfideb
0.01% added. b Equiyalent t o 0.10% sulfur. Misleading values obtained due t o dissolved carbon dioxide.
-
HAZE,
GUM,PEROXIDES,
AKD
ACIDSIN
Remained Clear Min.
Haze Appeared Min.
Peroxide No.
Acid No.
A.S.T.M. Gum Mg./lOO cc.
17.5 2.5 60.0 60.0 60.0 12.5 5.0 60.0 60.0 60.0 5.0 7.5 60.0 60.0 60.0 2.5 2.5 60.0 60.0 60.0
20.0 6.0
3.14 9.10 0.072 0,062 0.049 2.89 2.71 0.060 0.049 0.058 0.63 4.00 0.065 0.084 0.035 0.70 0.63 0.080 0.054 0.086
0.20 0.40 None
6 10 2 2 2 10 24 4 5 4 7 14 2 2 2 12 19 4 0
60.0 60.0 60.0 60.0 60.0 5.0 ~.~ 2.5 60.0 60.0 00.0 60 0 22.5 60.0 60.0 60.0 2.5 5.0 60.0 60.0 60.0
.. .. ..
Blend of Straight-Run and Cracked Gasolines Air 25 clear 60.0 Oxygen 21 hazy 32.5 Nitrogen 30+ clear 60.0 coz 30+ clear 60.0 Hydrogen 304- clear 60.0 Air 7 cloudy 5.0 Oxygen -16 cloudy 2.5 Nitrogen 19 clear 60.0 coz 19 clear 60.0 Hydrogen 19 clear 60.0 Air 23 hazy 5.0 Oxygen 9 cloudy 10.0 Nitrogen 30+ clear 60.0 c02 30+ clear 60.0 Hydrogen 30f clear 60.0 Air 4 cloudy 2.5 Oxygen -16 opaque 2.5 Nitrogen 28 clear 60.0 coz 26 clear 60.0 Hydrogen 26 clear 60.0
-
Elementary sulfura
Elementary sulfur"
Cracked Gasoline 27 clear 26 clear 30 clear 29 clear e02 30 clear Hydrogen Air 3 cloudy Oxygen -12 cloudy 20 clear Nitrogen 21 clear eo2 Hydrogen 19 clear Air 27 clear Oxygen 18 haay Nitrogen 30+ clear GO* 30+ clear Hydrogen 304- clear Air 3 cloudy Oxygen -14 cloudy Nitrogen 27 clear coz 25 clear Hydrogen 25 clear Air Oxygen Nitrogen
None
123
.. ..
..
15.0 7.5
.. .. *.
7.5 10.0
.. ..
.. 5.0 5.0
.. .. ..
..
7.5 5.0
.. .. ..
25:O
.. .. ..
5.0 7.5
.. .. ..
3k:O
.. .. ..
7.5 5.0
*.
.. .. 7.5 12.5
.... ..
5.0 5.0
.. ..
..
c
None 0.35 1.30 None E
None 0.40 1.80 None c
None 0.45 2.20 None c
None
0
4.04 22.70 0.298 0.232 0.245 2.08 8.60 0.386 0.341 0.354 4.55 19.80 0.252 0.310 0.331 2.53 5.85 0.252 0.312 0.204
0.15 0.30 N:ne
4 15 2 2 2 15 34 5 5 9 5 20 3 1 2 13 26
None
0
4.32 16.90 0.108 0.150 0.172 1.44 4.10 0.131 0.128 0.187 3.42 14.46 0.134 0.181 0.172 2.17 2.60 0.173 0.200 0.187
0.20 0.40 None
5 18 2 2 2 16 36 7 6 9 5 20
None 0.30 0.70 None 0
None 0.15 0.35 None c
None 0.25 0.90 None c
c
None 0.35 1.00 None 0
None 0.15 0.40 None c
None 0.35 1.20 None E
None
3
2
: 2
11 25 1 0 1
124
INDUSTRIAL AND ENGINEERING CHEMISTRY
From the results we may conclude that color, haze, and gum formation in the gasolines were due to photochemical oxidation.
Effect of Sulfur I n both oxidizing and nonoxidizing atmospheres sulfur had a deleterious effect upon the gasolines. There was a marked increase in the amount of color and gum formed with air or oxygen. The acidity of the gasolines containing sulfur was greater after light exposure than in gasolines to which no sulfur had been added. The peroxide numbers were lower and the acid numbers higher than in the absence of sulfur. I n nonoxidizing atmospheres, color depreciation and gum formation occurred but were less than with air or oxygen. No haze or acids and only small amounts of peroxides were developed. Oxygen is necessary for the formation of haze, acids, or peroxides but is not always necessary for formation of gum or color. This is contrary to some previous statements (8) that gum does not form except when oxygen is present.
Effect of n-Propyl Disulfide The addition of n-propyl disulfide decreased the color stabilities in light and air of the straight-run and blended gasolines. I n oxygen the color stabilities of these gasolines were decreased still further, and the cracked gasoline was also affected. The disulfide had no effect on gum formation of the gasolines exposed to air but caused a small increase when exposed to oxygen. The peroxide number of the straight-run gasoline was lower and the acid number was higher than in the original gasoline exposed in a similar manner, but this was not true of the cracked gasoline. No depreciation occurred in the gasolines when exposed in hydrogen, nitrogen, or carbon dioxide. This shows that the color, haze, and gum formation occurring in gasolines containing disulfide was due to photochemical oxidation and depended upon the presence of oxygen.
Effect of Sulfur and n-Propyl Disulfide Addition of both sulfur and n-propyl disulfide gave results which were similar to those obtained when each was added separately, with the exception that in oxidizing atmospheres gasolines containing both sulfur and disulfide tended to form haze more rapidly and to develop more color than gasolines containing either sulfur or disulfide alone.
Effect of Light on Gum Formation The effect of light on gum formation was studied after 60minute exposure to the carbon-arc lamp; the results are shown in Table 11.
VOL. 28, NO. 1
effect so that the gum content of the exposed gasoline containing both was less than when sulfur alone was present. The gum contents of the gasolines without addition of sulfur and those containing disulfide were the same when exposed to air. With oxygen the cracked and blended gasolines developed more gum than did the straight-run. Addition of sulfur caused a greater amount of gum formation in the cracked and blended gasolines than in the straight-run. When exposed to light in carbon dioxide or nitrogen, only the gasoline containing elementary sulfur formed gum. When both sulfur and disulfide were present, no gum formed.
Gum Formation i n Straight-Run Gasoline Straight-run gasolines are ordinarily considered to be stable as far as gum formation is concerned. However, it is important to note from Tables I and I1 that, upon exposure to light in the presence of air, oxygen, or sulfur, the straight-run gasoline developed considerable gum. I n order to show that the effects observed were not due to rise in temperature during exposure to the light, samples of the straight-run gasoline were subjected to approximately the same conditions of temperature and time as were experienced in the arc lamp but with light excluded. The temperature was increased from 28" to 88' C. over a period of one hour. The results of these tests are shown in Table 111. ~~~
~
~~
~~~
~~
~
~
TABLE111. EFFECTOF TEMPERATURE ON STRAIGHT-RUN
GASOLINE
Compound added: Atmosphere: Color O Saybolt Peroiide No. Acid No.
Sulfur Reaction of vapors
.oo 00.
-NoneOxygen 30 f 0.045 0.00
Nitrogen 30f 0.054 0.00
Negatjve Negative Negative Negative Negative Neutral
Negatjve Negative Negative Negative Negative Neutral
2
0
-Sulfur (0.0170)-Oxygen Nitrogen 30 f 0.046 3: %54 0.00 0.00 0 0 Negative Negative Negative ,Negative Negative Negative Positive Negative Negative Poaitive Neutral Neutral
The results in Table I11 show that none of the changes noted after exposure to the carbon arc lamp occurred when the straight-run gasoline was heated in the dark even in the presence of oxygen or sulfur or both. There was no change in the presence of nitrogen. The effects observed during light exposure were therefore due to photochemical changes.
Relationship of G u m to Peroxide and Acid Formation in Light It has been shown previously (4) that there is a definite
relationship between gum and peroxide and acid formation in bomb and dark storage tests. A study of some of the relationships between these factors upon exposure of the gasolines to light is shown in Table IV. TABLE11. EFFECTOF LIGHTON GUM FORMATION The results in Table IV show that in all cases (In milligrams per 100 oubio centimeters) peroxides and acids formed simultaneously with -Straight-Run--Cracked--Blended-gum when the gasolines are exposed to light under Oz COa Air Oz COz Compound Added Air 01 COz Air oxidizing atmospheres. Tests with the gasolines None 6 1 0 2 4 1 5 2 5 1 6 2 Sulfur (0.01%) 10 24 5 16 34 5 16 36 6 e x p o s e d to light and air for 60 minutes also n-Propyl dmulfidea 7 1 4 2 5 2 0 1 5 2 0 2 showed the development of aldehydes (4). The n-Propyldisulfidea + sulfur (0.01%) 12 19 0 13 26 2 11 26 0 straight-run gasoline had a n aldehyde number of a Equivalent to O.lOY0 sulfur. 0.2 and the cracked 1.2 after exposure. Increasing the rate of gum formation by exposing the gasolines to oxygen instead of air, simultaneously inThe results show that oxygen caused greater gum formation creased ( a ) the rate of acid formation in all cases and ( b ) the than air in all of the gasolines. With air, n-propyl disulfide rate of peroxide formation in all cases except in the straightdid not affect the amount of gum formed, but with oxygen it run gasoline when sulfur or sulfur and n-propyl disulfide increased i t slightly. Sulfur increased the gum content of were added. exposed samples with either oxygen or air. The disulfide The gasolines to which sulfur, n-propyl disulfide, or both, when present with sulfur tended to reduce its deteriorating
JANUARY, 1936
INDUSTRIAL AND ENGINEERING CHER'IISTRY
125
TABLE IV. RELATIOXSHIP OF GUMTO PEROXIDE AND ACID FORMATION IN MIDCONTINENT GASOLINES EXPOSED TO
--
Compound Added
Straight-Run Gasoline--Air-OxygenPeroxPeroxide Acid ide Acid Gum No. No. Gum No. No. MQ./ 100 cc
.
None Sulfur (O.O!%) n-Propyl disulfide5 Sulfur (0.01%) n-propyl disulfidea a Equivalent t o 0.10% sulfur.
+
6
3.14 10 2 . 8 9 7 0.63 12 0 . 7 6
10 24 14 19
MQ./
1+f!3.
9.10 0.40 2 . 7 1 1.30 4.00 1.80 0.63 2.20
had been added had lower peroxide numbers and higher acid numbers than the gasolines without addition of these substances upon similar exposure to light in oxidizing atmospheres. The cracked and blended gasolines formed more gum and peroxides and less acids than the straight-run when exposed to light and oxygen.
Color, Haze, and G u m Formation I n order to determine whether a relationship exists between color and gum formation in gasolines exposed to light and air, the straight-run and cracked gasolines were exposed for various intervals of time employing the same conditions and methods already described. Table V shows the results.
4 15 5 13
Acid No.
/
0.15 0.30 0.15 0.25
15 34 20 26
%i
100 cc.
CC.
4.04 2.08 4.55 2.53
LIQHT -Blended Gasoline-Air------OxygenPeroxPeroxide Acid ide Acid Gum No. No. Gum No. No.
MQ./
100
100 cc.
cc.
0.20 0.35 0.40 0.45
-Cracked Gasoline----A r-i --OxygenPeroxPeroxide Acid ide Gum No. No. Cum No.
22.70 8.60 19.80 5.85
0.30 0.70 0.35 0.90
cc.
5 4.32 16 1 . 4 4 5 3.42 11 2 . 1 7
0.20 0.35 0.16 0.35
16 36 20 25
16.90 4.10 14.46 2.60
0.40 1.00 0.40 1.20
and in a second portion which had been passed through filter paper until it was clear. The haze and gum formation were as follows: Gasoline Straight-run Straight-run -k 0.01% sulfur
Atmosphere Oxygen Air
Not Filtered After Filtration Color Gum Color Gum 12 -1
14
10
24 14
12 9
The results show that filtration of the gasolines through filter paper improved the color but had practically no effect on the gum content. This means that, while the haze in the gasoline was responsible for much of the color, it did not materially affect the gum content.
Reaction Products of Photochemical Changes in Midcontinent Gasolines
Qualitative tests for sulfur dioxide and trioxide, hydrogen COLORAND GUN FORMATION IN MIDCONTINENT sulfide, mercaptans, and elementary sulfur were made on the GASOLINES EXPOSED TO LIGHT gasolines exposed to the carbon-arc lamp for 60 minutes. Time A. S. T.M. The results of the tests are shown in Table VI. Gasoline Atmosphere Exposed Color Gum Exposure of the straight-run and blended gasolines to which Mg ./lo0 nothing had been added resulted in formation of sulfur diMin. Saybolt cc. oxide and trioxide. This was no doubt due to the oxidation Straight-run Air 1s 2 of disulfides originally present in the gasolines since the ele30 22 6 45 18 7 mentary sulfur and mercaptans had been removed. Sulfur 60 17 8 dioxide and trioxide were formed in all of the gasolines when Air Cracked 0 30f 2 sulfur, n-propyl disulfide, or both, were present during ex15 30+ 5 posure in oxygen or air. Little or none of the elementary 30 46 230+ 8 60 28 6 sulfur remained as such after exposure to light in oxidizing Straight-run + sulfur (0.01 atmospheres. The elementary sulfur oxidized to sulfur diCarbon dioxide 60 20 0 %) + n-propyl disulfide oxide and trioxide. The formation of sulfur dioxide and triCracked i- sulfur (0.01%) Carbon dioxide 60 25 2 + n-propyl disulfide oxide and of the corresponding acids upon later addition of water was readily shown by exposing a tube containing sulfur and oxygen to the arc lamp for one hour. The results in Table V shorn that the straight-run gasoline Hydrogen sulfide formed by reaction between hydrocarbons exposed to light and air developed color and gum simuland sulfur wuuld be oxidized to elementary sulfur on exposure taneously. Most of the gum formation occurred in the first to light in oxidizing atmospheres. This in turn is oxidized 30 minutes of exposure with very little forming thereafter. t o oxides of sulfur. This was proved by exposing to the light I n the cracked gasoline exposed in air, gum but no color a quartz tube containing oxygen and hydrogen sulfide. Depoformed in the fmt 30 minutes of exposure. During the next sition of elementary sulfur on the sides of the tube began 30 minutes the color dropped from 30"f to 28" Saybolt withimmediately upon exposure to the light. Water extract after out any further increase in gum. one-hour exposure contained unconverted hydrogen sulfide, Exposure to light and carbon dioxide for 60 minutes of the suspended sulfur, and sulfuric and sulfurous acids. straight-run or cracked gasolines which contained sulfur and Exposure to nitrogen, carbon dioxide, or hydrogen of n-propyl disulfide resulted in color formation but no gum straight-run or blended gasolines without addition of sulfur formation. or sulfur compounds, resulted in the formation of mercapThe data show (a) that gum and color formation occur tans. This was probably due, where no hydrogen was added, simultaneously, (b) that gum formation occurs without color to the reduction of disulfides originally present in the gasoformation, or ( c ) that color formation occurs without gum lines to mercaptans by the hydrocarbons of which the gasoformation. There seems to be no fixed relationship between lines were composed. Gasolines to which n-propyl disulfide color and gum formation in the gasolines tested. was added showed the formation of mercaptans after exI n order to ascertain whether the gum which formed in the posure to light in nonoxidizing atmospheres. The disulfide straight-run gasoline was composed of haze particles, the was reduced by the hydrogen or hydrocarbons to the meroriginal gasoline and a sample containing sulfur were exposed captan. to light in oxidizing atmospheres for one hour. After exThe addition of sulfur resulted in the formation of hydrogen posure the gums were determined, in one portion as exposed sulfide and traces of mercaptans upon exposure to nonoxidizTABLE V.
I:+
;
INDUSTRIAL AND ENGINEERING CHEMISTRY
126
ing atmospheres. When both sulfur and disulfides were present, mercaptans were formed together with hydrogen sulfide. Exposure of gasoline containing free sulfur to the arc light resulted in practically complete removal of this substance.
Thermal Effect Exposure of the gasolines to the carbon-arc lamp was always accompanied by rise in temperature. Consequently the effect of temperature on the gasolines in the absence of light was determined. This was carried out as previously discussed by heating several samples of cracked gasoline over a temperature range approximately the same as that of 28" to the gasoline when subjected to the arc-namely, 58" C.-over a period of one hour. The gasolines were heated in a water bath in glass bottles painted black. At the end of one hour the samples were cooled and tested in the same manner as those exposed to the arc lamp. The data are shown in Table VII.
*
VOL. 28, NO. 1
rectly or after having reacted with the hydrocarbons present. I n the absence of sulfur or disulfides, no haze formed in the gasolines. A sample of straight-run gasoline from which sulfur and disulfides had been removed dropped from 30"+ to 29" Saybolt with no haze forming after one-hour exposure to light and air. It was shown that sulfur in nonoxidizing atmospheres reacted with hydrocarbons yielding hydrogen sulfide and colored compounds. Little or none of the sulfur remained as such in the system after exposure to light. I n oxidizing atmospheres no hydrogen sulfide was found. Both color and haze formed. The haze particles, which were removed by settling or filtration, mere soluble in dilute caustic and yielded positive tests for sulfate. Removal of the haze by filtration of the straight-run gasoline resulted in a reduction in acid number from 0.45 to 0.15. Similar removal of haze from lightexposed straight-run gasoline containing sulfur resulted in reduction in acid number from 2.10 to 0.15,. This means that most of the acid formed in the gasoline was present in
PRODUCTS OF PHOTOCHEMICAL CHANGESIN MIDCONTINENT GASOLINES TABLIO VI. REACTION
--
-
-
, 7 Straight-Run-Cracked MerMerSO1 Sulfur Has captan SO8 Atmosphere HIS captan SO8 SO? Sulfur Air Neg. Trace Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg. Pos. Pb's. Neg. .. Neg. Neg. Trace Oxygen Neg. Neg. Trace Neg. Neg. Neg. Neg. Neg. Nitrogen Neg. Neg. Trace Neg. Neg. Neg. Neg. Neg. coz Trace Neg. Pos. Neg. Neg. Nee. Neg. Hydrogen Neg. Air Trace Neg. Neg. PO@. Trace Sulfur (0.01%) Neg. Pb'8. Po0,b Neg. Oxygen Trace Neg. Poa. Neg. Trace Neg. Pos. Nitrogen Pos. b Pos. Neg. Trace Neg. Trace Poa. Pos. b P O S . con Pos. Pas. b Pos. b Pos. POS. Neg. Hydrogen *. Air Neg Poi. Poi. Neg. Neg. Neg. Neg. Neg. n-Propyl disulfidea Oxygen Neg: Neg. Pos. Pos. Neg. Neg. Neg. Pos. Pos. Neg. Nitrogen Neg. Pos. Neg. Neg. Neg. Pos. Neg. . Neg. Neg. Trace Pos. Neg. . , Neg. CO? Trace Pos. Neg. Hydrogen Neg. Pos. Neg. Neg. Neg. Pos. Neg. Neg. Neg. Air Neg. Neg. Pos. P o d Neg. Pos. Pos. Sulfur (0.01g) Pbs. Trace Nsg. Neg. Pos. Trace Oxygen Neg. Neg. Pos. n-propyl isulfidea Nitrogen POS. Pos. Neg. P0s.b Pos. Pos. Neg. , Neg. COP Poa. Pos. Neg. , P0s.b Pos. POS. Neg. Trace Hydrogen Pos. PO& Neg. P0s.b Poa. Pos. Neg. Neg. 5 Equivalent to 0.01% sulfur. ;Muoh less than unexposed blank.
Compound Added None
.... ..
.. ......
....
+
.. .. .. ..
.. . ..
.. . .. .. . .. ....
Has Neg. Neg. Neg. Neg. Neg. Neg. Neg. POS. POS.
Pos. Neg. Neg. Neg. Trace Neg. Neg. Neg. Pos. Pos. Pos.
Mercaptan Neg. Nee. Tracre Trace
Poa.
Nee. Neg. Trace Trace
Poa.
Neg. Neg. Pos. Pos. Pos. Pos. Neg. Pos. Pos. Pos.
-Blend
90s Trace Pos. Neg. Neg. Neg. Pos. Pos. Neg. Nee. Neg. Pos. Pos. Neg. Neg. Neg. Pos. Pos. Neg. Neg. Neg.
-__
--
so2
Sulfur Neg. Neg. Neg. ., .. Neg. Neg. Trace Pba. Trace . * Trace Trace Trace Neg. Pbe. Neg. Neg. Neg. Neg. Neg. Trace Neg. Trace Neg.
.. .. ..
.. ..
... .
.. ..
.... ....
d
TABLEVTI. EFFECTOF TEMPERATURB ON MIDCONTINENT the haze particles. The haze particles also contained organic CRACKED GASOLINE material, Sulfur dioxide was found in the vapors above the Compound. ---None-----. --Sulfur (0.01%) --.0.01% Sulfur exposed gasoline. Possibly other unidentified acids of sulfur +D & f:;: were present also. Atmosphere: Air 0 Air Oa Na 0 2 It was shown that gasolines containing n-propyl disulfide Color 29 28 30 29 30 29 contained sulfur dioxide and trioxide after exposure to light in 0.92b 0.836 0 . 8 3 b 0.83b 1.16b Peroxide No. 0.92b Acid No. 0.0 0.0 0.0 0.0 0.0 0.0 oxidizing atmospheres. A.S.T.M. gum, mg./
100 cc. Has
1 1 1 1 3 0 Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg. Ne& Neg. Neg. Neg. Nee. Neg. so2 Neg. Neg. Neg. Neg. Neg. Neg. SO3 POS. POS. PO& Neg. Neg. Poa. Sulfur Reaction of vapors Neutral Neutral Neutral Neutral Neutral Neutral 5 Equivalent t o 0.10% sulfur. b Same a s before heating; higher than previous values because samples had stood for several weeks in contact with air.
Mercaptan
The results in Table VI1 show that heating the gasolines in the dark under the same conditions of temperature and time as in the arc test had no effect on their properties other than a 1" to 2" Saybolt drop in color in some cases. This means that the results obtained upon exposure to light could not have been due to the rise in temperature alone but resulted from photochemical effects. The thermal effect with straight-run gasoline has been shown in Table 111.
Nature of Haze Particles Haze formation in the gasolines tested was a result of the oxidation of sulfur or disulfide to oxides of sulfur, either di-
Effect of Light and Air on Pennsylvania Gasolines I n order to show that the effects of light observed in these tests were not peculiar to Midcontinent gasolines, some of the tests were repeated using Pennsylvania straight-run and cracked gasolines and blends of the two, The Pennsylvania cracked gasoline was refined by vapor-phase clay treatment. The straight-run gasoline was unrefined. Free sulfur and mercaptans were removed from the gasolines. The blend consisted of equal parts by volume of the straight-run and cracked gasolines. Sulfur and n-propyl disulfide were added in the percentages used in the previous experiments. The gasolines were exposed to the arc light in quartz bottles for one hour in an atmosphere of air. The results are shown in Table VIII. The data show that the original Pennsylvania gasolines dropped from 30"f to 27" Saybolt upon exposure to light and air, but no haze formed. Addition of elementary sulfur, alone or in combination with n-propyl disulfide, caused further decrease in color together with the formation of haze in
.
JANUARY, 1936
INDUSTRIAL AKD ENGINEERING CHEMISTRY
127
periments. The gasolines were exposed to carbonPENNSYLVANIA GASOLINES arc light in the presence of air for one hour. The ReHaze Peroxresults are shown in Table IX. mained Apide Acid A.S.T.M. The results in Table IX show that the original Gasoline Compound Addeda Color Clear peared No. No. Gum Mg.1100 gasolines, including the straight-run, developed cc . Saybolt Min. Min. color, peroxides, acids, and gum upon exposure Straight-run None 27 clear 60.0 5.05 0.15 2 Sulfur (0.01%) 2 cloudy 1 0 . 0 l2:5 2.20 0 . 3 5 7 to light in the presence of air. Only the straightn-Propyl disulfideb 10 hazy 7.5 10.0 0.70 0.25 4 run gasoline became hazy. Exposure of the Sulfur (0.01%) + nDroDvldisulfideb -4 cloudv 7.5 10.0 0.70 0.40 8 - -California cracked gasoline in carbon dioxide Cracked None 27 clear 60.0 4 . 8 5 None 5 caused no color depreciation. The straight-run Sulfur (0.01%) 3cloudy 5.0 7:5 4.50 0.10 19 n-Propyl disulfideb 23 clear 60.0 .. 6.07 0.10 9 gasoline dropped from 30" to 29" Saybolt under Sulfur (0.010/,) + npropyl disulfideb 4 cloudy 2.5 5.0 4.20 0.10 16 similar conditions. 6 The presence of sulfur caused color, haze, and 16 5 gum formation in all of the gasolines. Addition cracked) Sulfu of n-propyl disulfide alone caused color formation 15 propyl disulfidei in all of the gasolines, and caused haze formation The original color of the gasoline plus the compound was 30'4- Saybolt in each case. b Equivalent to 0.10% sulfur. in the straight-run and blended gasolines but not in the cracked. It also caused slightly . greater gum formation in the gasolines upon exposure to light and air. all of the gasolines. The straight-run and blended gasolines In the cracked gasoline containing n-propyl disulfide the containing n-propyl disulfide alone, developed color and haze, peroxide and acid numbers were higher than in the original but the cracked gasoline formed no haze while decreasing gasoline. In the other gasolines containing sulfur or n-propyl from 30"f to 23' Saybolt. The effects of light and air on disulfide or both, the peroxide numbers were lower and the color and haze formation in Pennsylvania gasoline were acid numbers higher than in the original gasolines exposed to similar to those observed in Midcontinent gasolines. light. Acid numbers increased to a greater extent in straightPeroxides and acids formed in all of the gasolines in the run than in cracked or blended gasolines. same manner as with the Midcontinent gasolines. Gum The results obtained upon exposure of California gasolines formed in the cracked and blended gasolines to which no to light and air were similar to those obtained with Midsulfur had been added but did not form in the straight-run continent and Pennsylvania gasolines. The California gasogasoline. However, a sample of the straight-run gasoline lines differed from the Midcontinent gasolines in that ndeveloped 10 mg. of gum when exposed to the light for one propyl disulfide when added alone tended to increase gum hour in the presence of oxygen. The color was 26" Saybolt formation. They differed from the Pennsylvania gasolines after exposure. The addition of sulfur or sulfur and n-propyl in that the straight-run developed gum upon exposure to disulfide increased the gum contents of the exposed gasolines. light and air. The presence of n-propyl disulfide increased the gum content of the cracked gasoline but had no effect on the blend. Summary and Conclusions With the exception that the original straight-run gasoline developed no gum in air and that the gum content of the MIDCONTINENT GASOLIKES.Refined straight-run gasoline cracked gasoline was increased by the addition of n-propyl exposed to the carbon-arc light in the presence of air or oxygen disulfide, the effects of light and air on the Pennsylvania developed color, gum, peroxides, acids, and aldehydes. The gasolines were no different from those observed on Midconsame effects were observed with cracked gasoline and blends. tinent gasolines. The straight-run and blended gasolines developed haze but the cracked gasoline did not. Effect of Light and Air on California Gasolines The formation of gum, peroxides, acids, aldehydes, and haze did not occur in either the straight-run or cracked gasoThe California straight-run gasoline used in these experiline in the dark even in the presence of oygen, sulfur, or both, ments was treated with 4 pounds of 66" B6. sulfuric acid per and a t the same temperature as the samples exposed to the barrel. The cracked gasoline was treated with 10 pounds arc light. The reactions are therefore photochemical. of sulfuric acid per barrel. Elementary sulfur and merWith oxygen and exposure to light the cracked and blended captans were removed before testing. Sulfur and n-propyl gasolines formed more gum than the straight-run gasoline. disulfide were added in the amounts used in the previous exElementary sulfur increased the formation of color, haze, and gum upon exposure of the gasolines to light in the presence of air or oxygen. TABLEIX. EFFECTOB LIGHTON CALIFORNIA GASOLINES Cracked and blended gasolines formed more gum OrigiReHaze Peroxwith sulfur present than the straight-run gasoline. nal mained Apide AoidA.5.T.M Compound Added Color Color Clear peared No. No. Gum Gasoline In the presence of air or oxygen, n-propyl disulMQ./ fide decreased the color stabilities in light of the Saybolt Saybolt Min. Min. 100 ce. gasolines, causing haze formation in the straightNone 30+ 16hazy 27.5 30.0 2.76 0.20 6 Straight-run Sulfur (0.01%) 30+ -9 cloudy 2.5 5 . 0 1.84 0.65 11 run and blended g a s o l i n e s . W i t h oxygen, n-Propyl disulfide" 3 0 + 0 cloudy 1 0 . 0 1 2 . 5 0 . 4 6 0 . 5 0 10 cracked gasolines also formed haze. With air, Sulfur (O.Ol%) + npropyldisulfide" 30+ -7 cloudy 2.5 5 . 0 0 . 5 1 0.60 11 the disulfide had no effect on the amount of gum Cracked None 26 23 clear 60 0 3.95 0.10 7 formation. 26 12 hasy 7 : 5 l0:O 3 . 1 5 0 . 2 0 12 Sulfur (0.01%) n-Propyl disulfidea 26 21 clear 60.0 . . 4.85 0.20 10 I n the presence of air or oxygen, gasolines to Sulfur (0.01%)+ npropyl disulfideQ 26 15 hazy 5.0 7 . 5 2.48 0.20 12 which elementary sulfur or n-propyl disulfide were None 28 23 clear Blend (50% 60.0 4 41 0 15 8 added formed sulfur dioxide and sulfur trioxide straight-run Sulfur (0.01%) 28 2 cloudy 5.0 2:39 0:20 14 n-Propyldisulfide5 28 18hazy 15.0 17.0 3.50 0.15 11 upon exposure to light. Acid formation was + 509 (0.01%) + nSulfur crrtcke3) higher in the straight-run than in the cracked or propyl disulfide 28 7 cloudy 5.0 7 . 5 2.11 0 . 2 0 15 blended gasolines. a Equivalent to 0.10% sulfur. Both in the presence and absence of added TABLEVIII.
EFFECTOF LIGHTAND AIR
O
ON
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sulfur compounds, oxygen caused more color, haze, acid, and gum formation upon exposure to light than air. Haze, peroxides, and acids formed in the gasolines when exposed to light only in the presence of oxygen or air. With nitrogen, carbon dioxide, or hydrogen, color and gum formed in the presence of sulfur. Hydrogen sulfide was evolved in all cases. No color, haze, peroxides, acids, or gums formed upon exposure to light in nonoxidizing atmospheres of the gasolines which contained no elementary sulfur or those containing n-propyl disulfide. When gasolines containing both sulfur and disulfide were exposed to light in atmospheres containing no oxygen, some color but no gum formed. No fixed relationship was found between color and gum formation. Color and gum can form simultaneously; gum can form with no color depreciation; or color can form with no increase in gum content. Haze particles contained sulfur dioxide and trioxide and/or corresponding acids and organic material. Most of the acid formed in the gasoline was found in the haze particles which could be removed by filtration through filter paper. Removal of haze by filtration improved the color but did not affect the gum content of the gasoline. Exposure to light and air of straight-run gasoline from which sulfur and disulfides had been removed resulted in no haze formation and only a slight drop in color. Upon exposure to light in nonoxidizing atmospheres, mercaptans were formed by the reduction of n-propyl disulfide either by hydrogen or hydrocarbons. Hydrogen sulfide and traces of mercaptans were formed upon exposure to light of gasolines containing elementary sulfur to light in the absence of oxygen. Exposure of gasolines containing sulfur to light, air, or both, in the presence and absence of oxygen, resulted in
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practically complete conversion and removal of the elementary sulfur as such from the exposed gasolines. When both sulfur and disulfides were added to the gasolines, exposure to light in the absence of oxygen resulted in the formation of mercaptans and hydrogen sulfide. With sulfur and n-propyl disulfide present, exposure to light in the absence of oxygen resulted in color formation but no gum formation. PENNSYLVANIA AXD CALIFORNIA GASOLINES.Exposure of these gasolines to light and air produced effects on color, haze, peroxide, acid, and gum formation similar to those observed when using Midcontinent gasolines with the following exceptions : (a) The Pennsylvania straight-run gasoline containing no added sulfur compounds did not form gum upon exposure to light and air although gum was formed in the presence of oxygen; and ( b ) the addition of n-propyl disulfide caused slight increases in gum formation in the Pennsylvania cracked gasoline and in all of the California gasolines. The results with inert atmospheres were also the same as with the Midcontinent gasoline.
Literature Cited (1) Brooks, IND. ENG.CHEM.,18, 1203 (1926). (2) Brooks and Parker, Petroleum, p. 42 (July, 1924). (3) Carpenter, J. Inst. Petroleum Tech., 12, 518 (1926). (4) Dryer, Lowry, Morrell, and Egloff, IND. ENG.CHEnc., 26, 885 (1934). ( 5 ) Egloff, Morrell, Benedict, and Wirth, Ihid., 27, 323 (1935). (6) Freund, Brennstof-Chem., 14,61-4 (1933); Proc. World Petroleum Congvess, 2, 108 (1933). (7) Story, Provine, and Bennett, IXD. ENC).CHEM.., 21, 1091 (1929). (8) Vellinger and Radulesco, Compt. rend., 196, 1495 (1933); Proc. World Petroleum Congress, 2, 103 (1933); Ann. combustibles Ziquides, 8,883 (1933). (9) Yule and Wilson, IND.ENG.CHEM.,23, 1254 (1931).
RECEIVEDMay 11, 1936 Presented before the Division of Petroleum Chemistry a t the 89th .Meeting of the American Chemioal Sooiety, New York, N. Y . , April 22 to 26, 1935.
Courtesy, Glenmore Distilleries C o .
BOILERROOMIN POWERPLANT
