Phosphorus Pentoxide as a Refining Agent for Gasoline BORIS W. MALISHEV Shell Development Company, Berkeley, Calif.
Phosphorus pentoxide exercises a refining action on vapor-phase cracked distillates which not only results in a refined gasoline of high quality but yields a fuel with a more or l e s s pronounced increase in the octane nurnber.
N EARLIER article (4) gave the results of an investigation of phosphorus pentoxide as a refining agent for gasoline. Since these results appeared promising, the investigation was continued with the object of studying the chemistry of the phosphorus pentoxide refining action and improving the process to such a stage that further development on a large scale would be warranted. Two methods described in this paper were developed for refining gasoline. One method consisted in treating gasoline with dispersions of phosphorus pentoxide in heavy mineral oils, such as viscous lubricating oils. The other method consisted in treating gasoline with phosphorus pentoxide deposited on porous solid material.
ence of phosphorus pentoxide have already been published (3) With the aid of this reaction, benzene and ethylene, benzene and isobutylene, toluene and propylene, naphthalene and ethylene, and anthracene and ethylene were condensed in the presence of lampblack-phosphorus pentoxide dispersions with cresol as a peptizing agent. In the ethylation of benzene the reaction was carried out a t 250" C. and 27 atmospheres pressure. At this temperature and pressure metaphosphoric acid was found inactive when ethylating benzene, although there is a possibility that the reaction takes place a t higher temperatures. The metaphosphoric acid used for this purpose was ground under a layer of benzene to a fine powder in a ball mill. The toluene-propylene condensation proceeded a t temperatures as low as 150" C. It has been said that the polymerization reaction does not proceed as readily as the condensation reaction because, when aromatic hydrocarbons are present, the polymerization reaction is retarded. In fact it has been observed that diisobutylene in benzene solution is depolymerized since the main reaction product is isobutylbenzene. With an exress of olefins polymerization takes place. Pure olefins polymerize t o a gasoline-like product. For example, a mixture of a-,p-, and y-butylenes was heated at 250" C. with phosphorus pentoxide. A gasoline-like product was obtained, 80 per cent of which boiled within a range of 27" to 174" C. It was found that under these conditions a- and &butylenes are polymerized relatively much more slowly than the y-butylene. The polymerization of y-butylene was observed a t room temperature. T h a t the effect of phosphorus pentoxide is exceptional and different from metaphosphoric acid is shown by the fact that even ethylene was polymerized with phosphorus pentoxide a t 50 atmospheres pressure and 250" C. to a gasoline-like product. The polymerization product was a mixture of olefin, naphthene, paraffin, and aromatic hydrocarbons. The polymerization of ethylene starts a t a n appreciable rate a t 110" c. That the refining action of phosphorus pentoxide is due primarily to condensation and not to polymerization reactions
Chemistry of the Refining Process A study of the refining action on gasoline of phosphorus pentoxide showed that it catalyzes the direct alkylation of aromatic hydrocarbons with olefins, the conversion of olefins to naphthenes, and their partial polymerization. Because of the presence of aromatic hydrocarbons in the cracked distillate, the alkylation reaction proceeds more readily than the reactions of polymerization and isomerization of the olefins. The objectionable chain and cyclic diolefins and part of the sulfur compounds are removed, but the mechanism of these reactions has not been established. An appreciable increase in the octane number observed when treating some cracked distillates could find its explanation in this alkylation reaction. That the catalytic effect of phosphorus pentoxide in hydrocarbon reactions has not been observed previously is due to the insolubility of this compound in hydrocarbons and the difficulty of maintaining a large surface of contact. Commercial phosphorus pentoxide is in a state of colloidal subdivision, but its simple colloidal dispersions in hydrocarbons are not stable and they coagulate readily to hard infusible or sticky masses. Consequently, in the course of this investigation the need for maintaining phosphorus pentoxide in its colloidal state was recognized, and suitable dispersions were developed through the use of stabilizing colloids and peptizing agents. The best stabilizing colloid for the purpose of this investigation was found to be lampblack. Brown and Berry ( I ) obtained colloidal dispersions of phosphorus pentoxide in nitrobenzene by peptization with alcohols, phenols, or organic acids. The cracked distillates contained certain amounts of phenolic compounds and organic acids. When their content was found insufficient, naphthenic acids or phenols were added. Asphalt and wood-tar pitch were also found to promote the dispersion of phosphorus pentoxide in oils. The results of the investigation of the direct alkylation of aromatic hydrocarbons with olefins under the catalytic influ190
FEBRUARY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
is supported by the fact that the lubricating oils formed from the gasoline fraction as a result of the refining have a high index of refraction (about n D = 1.56) characteristic of aromatic hydrocarbons. The absence of resinous polymers is another factor supporting this viewpoint. It was reasonable to assume from these hydrocarbon reactions that, in refining cracked distillates, phosphorus pentoxide behaves not as a reagent but as a true catalyst, different from and more active than metaphosphoric acid. Its decline in activity is probably due to the formation of metaphosphoric acid from organic oxy-compounds present in the cracked distillate, which are necessary for peptization, to absorption of polymerizable products and asphaltic bodies on the surface of the contact, to agglomeration, and perhaps to transition of phosphorus pentoxide a t higher temperatures to a less active modification. The amount of phosphorus pentoxide required for refining various cracked gasolines was shown in the previous article (4) to be between 0.5 and 2 per cent by weight of the untreated gasoline. It was evident that this amount was not totally consumed but was rendered partly inactive by coagulation. When it was learned how to develop and to maintain stable dispersions of phosphorus pentoxide in oils and to apply them for refining light cracked distillate, 0.1 to 0.25 per cent and less of the phosphorus pentoxide was sufficient to obtain a gasoline of excellent qualities.
Refining w i t h Dispersions of Phosphorus Pentoxide in Heavy Oils The treatment was performed in a simple manner. The gasoline was vaporized by injecting it into a heated and stirred volume of heavy mineral oil with phosphorus pentoxide in suspension. A cylindrical still of about one gallon capacity was used for this purpose with an injection tube introduced through the cover or through the bottom. The gasoline vapors thus refined were dephlegmated, condensed, sodawashed, and doctor-treated. The best treating temperature was between 250" and 285" C. Any mineral oil which is not volatile a t these temperatures is suitable as a dispersing medium. The amount of phosphorus pentoxide which can be held in dispersion depends upon the type of mineral oil, its viscosity, the temperature, and a number of other factors not all of which are known. The amount of phosphorus pentoxide in suspension lies between 1 and 2 per cent. An excessover this amount settles upon standing and finally coagulates. It was found that unrefined lubricating oils were better dispersing media than refined because of the peptizing action of impurities. When injecting the unrefined gasoline into the treating oil, the phosphorus pentoxide dispersion settled out continuously and was drawn off in order to prevent its coagulation. The amount of stabilized phosphorus pentoxide, which has to be added continuously to keep the concentration of the dispersed phosphorus pentoxide in the treating oil constant and to maintain the same degree of refining, lies, as mentioned above, between 0.1 and 0.25 per cent by weight of the injected gasoline. The spent phosphorus pentoxide catalyst drawn off with the oil from the bottom separates on cooling as a soft asphaltic mass. The amount of oil so drawn off is continuously replaced by a heavy oil formed from gasoline as a result of the hydrocarbon reactions. The amount of the heavy oil formed constitutes the actual gasoline loss in refining. A vapor-phase cracked distillate, which was high in unsaturated hydrocarbons and could not he refined with sulfuric acid owing to heavy losses and depreciation of its antiknock value, was readily refined with phosphorus pentoxide suspensions. For this purpose a cylindrical vessel 43/a inches (11.1cm.) in inside diameter and 24 inches (61 cm.) in height, which was provided with a stirring device and electrical heating, was
191
TABLE I. PROPERTIES OF 238" C . END-POINT GASOLINE Untreated Dist.
A. 8. T. M. distn., Initial b. p. 10% 20 50
C.:
45 79 98 118 139
Dist. Treated with 0.25% PgOs 50
102
188 200 2 14 225 239 242 98.1 Yellow
80 104 121 141 102 181 199 211 222 229 238 98.0 30
Recovered % Color Saybolt Color drou after 1-day to . exuosure . sunlight ..... 3-5 Color Saybolt after 2-mpnth storage (in dark) i n tin container ,.... 30 Gum, rng.&OO 00.: Glass dish standard ..... 2-10 Glass dish standard after dark storagein tin container for 2 mo. ..... 20 Copper strip a t 50' C. Negative Doctor test . ... . Slightly positive ..... None Cloudiness after exposure to sunlight Octane No.: Research method 78 a t 239' C. end point 86 Motor method (A. S. T. M.) 08 a t 239' C. end point 80 84 a t 239' C. end point 60 Bromine No. Sulfur, % 0.15 a t 232' C. 0.09 a t 225' C. end point end point Fractionation in Badger column: 70.5 70.6 At 205' C At 225' C" 93.0 94.4 Yield of 205;' end-point gasoline 100.0 95.4 1 Yield of 225O C. end-point gasoline: 100.0 90.0 1 .
.
.
I
+
.
3
+ +
charged with 2500 grams of an untreated lubricating oil of medium viscosity (California Spray Oil of 0.93 specific gravity). Then 25 grams of phosphorus pentoxide were thoroughly mixed in a beaker with 26 grams of dried lampblack, and the mix was stirred into a small amount of oil to form a paste which was introduced into the oil in the treating vessel. The oil was heated to 275" C. and kept at this temperature, and 10,000 cc. of vapor-phase cracked distillate of 242' C. end point, dehydrated by filtering through salt, were injected; 9,535 cc. of refined gasoline of 238" C . end point were obtained from this operation. The refining action was maintained with 0.25 per cent phosphorus pentoxide introduced as before in the form of a paste. No oxy-compounds for peptization were found necessary in this case. The rate of injection of the untreated distillate was 10 cc. per minute and the speed of rotation of the stirring paddle was 600 revolutions per minute. This vapor-phase cracked distillate, before being treated with phosphorus pentoxide, was washed with 30 per cent sulfuric acid, neutralized with caustic soda wash, and finally dehydrated by filtering through salt. The properties of the vapor-phase cracked distillate which was refined in this manner are shown in Table I. The yields of gasoline were determined by fractional distillation of the untreated and the treated distillate using a Badger column and calculated as follows: The 205" C. endpoint gasoline yield is: 9,535 X 76.6 X 100 = 95m4% 10,000 X 76.5
The 225" C. end-point gasoline yield is: 9,535 x 94.4 x 100 = 96.070 10,000 x 93.8
This yield must be raised by 1per cent because of mechanical losses. Of the fifteen samples tested, the increase of the octane number determined by the research method over the untreated gasoline of the same boiling range amounted to:
INDUSTRIAL AND ENGINEERING CHEMISTRY
192 Increase
l: 8 7 5-6
No. of Cases 2 1
2
1 2 5 1
0-1
2
Per Cent PzOa Used i n Refining 5 and 10 R and 10
0.25and 10 1 and 0.25 0.25,0.5, 1 , and 5
1 an'd 2.5
The increase of the octane number determined by the motor method (A. S. T. M.) amounted to: Increase 16 12 7 2
No. of Cases 1 2 4 1
Per Cent PzOa Used i n Refining 10 0.25and 0.25 0.25.0.25. 1. and 1 2.5
Together with the increase in the octane number of the phosphorus-pentoxide-treated gasoline, a decrease in the bromine number invariably occurs on refining. The treatment with phosphorus pentoxide suspension in oil can also be carried out a t high pressure in order to give an adequate refining to the light ends or gasoline if necessary, and in a continuous manner by circulating the oil suspension in a pipe still while injecting the cracked distillate. A small laboratory pipe still was constructed: It consisted of 18 feet of a a/*-inch (0.95-cm.) coil heated with gas. The ratio of the circulating volume of the treating oil which carried the phosphorus pentoxide suspension to the injected cracked distillate was 10 to 1. The rate of the injection of the vapor-phase cracked gasoline into the coil was 30 CC. per minute. The pressure of the oil in the coil was 60 pounds per square inch (4.2 kg. per sq. om.) and its temperature 275' C. The circulated oil and gasoline vapors were discharged at atmospheric pressure (through a pressure-reducing valve) into a flash chamber. The treated gasoline vapors left through the top of the flash chamber, passed through a fractionating column, and were then condensed. The amount of phosphorus pentoxide added was 0.10 per cent on the injected gasoline. The spent phosphorus pentoxide, which coagulated to a liquid tarry mass and settled at the bottom of the flash chamber, was periodically drained. The vapor-phase treated gasoline, before being injected into the coil, was dehydrated by filtering through salt. The finished refined gasoline had a slightly positive doctor test and showed the following properties: Initial b. p O C. Final b. D.."" C. Color Saj.6olt Air-jet gum (g!asa), mg. 100 cc. Induction period (accei/erated oxygen test) Air-jet gum after induction, mg /lo0 cc. Octane No. (motor method) Bromine No.
Untreated Dist. 39 234 Yellow
.....
30 min.
.....
67.0 81
Dist. Treated with 0.1% P206 40 225 30 0.2
+
4 hr.+ 4.4 73.0 54.0
Treatment of Gasolines with Phosphorus Pent oxide Deposited o n Porous Materials
-
The deposition of catalysts on porous materials, such as pumice stone, is a convenient method extensively applied in chemical processes, especially in vapor-phase treatments. By passing vapors of cracked distillate at atmospheric pressure over phosphorus pentoxide deposited on pumice stone, a completely refined gasoline could not be obtained; but when a pressure of 200 to 260 pounds per square inch (14.1 to 17.6 kg. per sq. cm.) was applied to insure a liquid-phase contact, the results were good even without renewing the charged phosphorus pentoxide. Since phosphorus pentoxide attacks the silicates, another nonsiliceous porous material was sought. Coke was found to be such a material; it is inert to phosphorus pentoxide and also cheap. The following is a description of a laboratory installation for refining light cracked distillates by this method; the results obtained in the refining of a pressure distillate are also described :
VOL. 28, NO. 2
The distillate to be refined was taken from a measuring tank by an adjustable three-plunger pump, with a maximum feed of 90 cc. per minute, and pumped a t 200 to 250 pounds pressure per s uare inch throu h a heated 18-foot (5.5-meter) length of pipe inch (0.95 cmf in diameter. Leaving the pipe with a temperature ranging from 250" to 300' C. and under the same pressure, the distillate entered the bottom of a vertical cylindrical reaction chamber 3 inches (7.6 om.) in inside diameter and 5 feet (1.5 meters) in height, which was charged with the catalyst and heated electrically to maintain the distillate at 250' to 300' C. At the top of the reaction chamber the treated distillate passed a pressure-reducing valve and entered an atmospheric pressure reboiler heated by a flame and connected to a dephlegmator. Steam was introduced into the reboiler to prevent any possible cracking of the refined distillate. In many cases the phosphoruspentoxide-treated distillate was quite stable to direct fire heating and was distilled without using steam. The reaction chamber was charged with 300 grams of phosphorus pentoxide deposited on 3000 grams of an 8-mesh dried metallurgical coke. To cause the phosphorus pentoxide to adhere t o the surface of the coke, the latter was moistened with a viscous mineral oil before being placed into the reaction chamber, and was mixed mechanically with the required amount of phosphorus pentoxide before its admission into the chamber. As an illustration, Table I1 gives the properties of a gasoline fraction obtained from a pressure distillate at a feed rate of 90 cc. per minute, an average treating temperature of 285' C., and a pressure of 250 pounds per square inch. This pressure distillate, before being pumped into the treater, was washed with sulfuric acid of 30 per cent strength, then neutralized with a caustic soda wash, and finally dried by filtering through salt. After 16 gallons (60.5 liters) of distillate were passed through the treater, the refined qualities of the gasoline began to decrease. At this point the amount of phosphorus pentoxide required for the above degree of refining was 0.65 per cent on the charged distillate. The losses were somewhat high because of leakage. This California pressure distillate was high in nitrogen bases. When the bulk of nitrogen bases was removed with a sulfuric acid of 30 per cent strength, their presence in the distillate was still indicated by the very sensitive silicotungstic acid test. An acid of 50 per cent concentration removed more nitrogen bases as indicated by the test. How a complete removal of nitrogen bases and acid oils would affect the amount of phosphorus pentoxide required for refining has not been determined.
Manufacture of Phosphorus Pentoxide The phosphorus pentoxide process of refining petroleum distillates will have a chance to become a commercial process mainly because of t,he recent achievements made in the phosTABLE11. PROPERTIES OF GASOLINE FRACTION OBTAINEDBY TREATMENT WITH PHOSPHORUS PENTOXIDE DEPOSITED ON COKE
Index
A. 9..T. M. distn., Initial b. p. 10%
' C.:
Blank through Treater without PzOs (206' C. End-Point Dist.)
Dist. Treated with 0.65% ppd-g?On; c. Gasoline Doctor-Treated)
%%
40 71 88 100 116 127
60%
139
138
154
148 166 184 196 200 97 55.9 30
% ;:
2G6% % %%I b. p. Amount distilled, % ' Gravity Color Savbolt Gum, mg./!00 cc.: Copper-dish Air-jet (glass) Induction period accelerated oxygen oxidation test Air-jet gum (glass) after induction tests Sulfur % Brom&e No. Treating and mechanical loss, % '
-1 fiR --
184 198 206
98 54.4 Yellow 674 15.4 60 min.
. .0. ..5.9 62
.....
37 68
85 100 114 127
+
28
0.8
4 hr. 1.6 0.42 54 6.0
+
FEBRUARY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
phate industry. These developments relate to the concentration of low-grade phosphate ores by flotation and to the manufacture of phosphorus in the blast furnace. The production capacity of a blast furnace by the so-called one-step method of phosphoric acid manufacture by the Victor Chemical Works at Nashville, Ala. (2), is approximately 125 tons phosphorus pentoxide per day, but the furnace is designed to produce orthophosphoric acid. Some phosphorus pentoxide is obtained in this furnace in the dust-collecting equipment. One experimental blast furnace in Florida produced elementary phosphorus. As far as is known, no further development work has been done on this method of manufacture of phosphorus, arid the plant is closed. Since there is no special call for phosphorus pentoxide for technical applications, the price is still on a high level of about $400 per ton. As with all pioneering and epoch-making industrial developments, it will take some time for the market prices to decrease.
193
Even with this high price of phosphorus pentoxide the cost of refining some gasolines is very low because of the small amount required. This amount is 0.1 per cent of phosphorus and would be equivalent to 0.25 pound per barrel and a cost of 5 or 6 cents per barrel. The cost of coke (which can be recovered) is not large. Additional operating costs would then be the normal cost of redistilling gasoline which depends on the cost of fuel, running from 4 to 5 cents per barrel. The direct cost of the total treatment would be somewhere around 10 cents per barrel, excluding general overhead.
Literature Cited
’ (1) Brown and Berry, J.Phys. Chem., 29, 1312 (1925). (2) Easterwood, H. W., Trans. Am. I m t . Chem. Engrs., 29, 1-20 (1933). (3) Malishev, B . W., J . Am. Chem. SOC., 57, 883 (1935). (4) Malishev, B. W., Petroleum Z . , 28, S o . 17, 7-10 (1932). RECEIVED August 20, 1935.
Studies in the Drying Oils XIX. Oxidation of Linseed Oil’
ROBERT S. TAYLOR AND JUDSON G. SMULL Lehigh University, Bethlehem, Pa.
HE nature Of the process by which linseed oil molecules, under the influence of oxygen, are built up to colloidal dimensions has been the subiect of several theories. Scheifele advanced the theory t h i t film f a m a t i o n Was entirely the result of the condensation of the oil molecules containing Conjugated double-bond systems (IO). That this is not a complete explanation of the film-forming Process Was Pointed out by Scheiber (7) who subsequently developed this theory more fully (9). His theory states that the Preliminary tion of all the drying oils-with the exception of tung and related oils-results in the formation of conjugated doublebond systems throughout the oil, and it is about these centers of activity that condensation and polymerization occur. The mechanism proposed for this reaction is: -CHdHCH24H=CH---t
-CH=CH-C-CH=CH-
a
This theory has been extended by Scheiber and athers to account for the changes which occur in the formation of “stand oils” (3, 6, 8). Kappelmeier believes that the condensation which results from the conjugation may be ascribed to the “diene synthesis” (5) of Diels and Alder. ‘ Conjugate systems, in general, show the following characteristic properties: 1. A conjugated system has a higher refractive index than that of a nonconjugated isomer. 2. A conjugated system has a lower heat of combustion than that of a nonconjugated isomer. The first seven articles of this series appeared as unnumbered papers in IND. ENQ.CBEM. as f O l l O W S : 17, 138, 905 (1925); 18, 1245, 1282 (1926); 1 9 , 6 2 , 9 0 1 , 9 0 3 (1927). Parts VI11 t o X V I I I appeared in Volumes 20 t o 26 (1928 t o 19341, inclusive.
3. A conjugated system reacts with halogenating agents relatively s ~ o w ~( 1y) . 4. A conjugated system reacts readily with maleic anhydride, and. so far as is known. the nonconjugated system does not react. . -
Data under the first three headings are submitted in so far as they help to confirm the important results under the fourth heading. Complete data under the first three headings are not obtainable because it is practically impossible to prepare the nonconjugated oxidized isomers for comparison. Under the fourth heading, however, chemical reaction is shown when examination of the constantsis carefully made. The curves show perhaps clearly the decided changes that have taken place. These changes are explained later in detail. This study followed the changes in refractive index, heat of combustion, and iodine number resulting from the oxidation of linseed oil. In addition, the reaction of Diels and Alder
3
j E.
1.480
LOO
a ::
I 8
160
u
e
120
1
2
BO
1
7IEZ OF PXIMTIDH (DAYS1
FIGURE 1.
14
16
REFRACTIVE INDEX, OXYGENABIODIXEVALUEWITH TIME
CHANGE IN
SORBED, ASD
e
